SE546255C2

SE546255C2 - Parking brake system for a vehicle combination

Info

Publication number: SE546255C2
Application number: SE2251427A
Authority: SE
Inventors: Eder Mendonca; Marcelo Almeida; Marco Amorim; Sten Lundgren; Vanderlei Santos
Original assignee: Scania Cv Ab
Priority date: 2022-12-06
Filing date: 2022-12-06
Publication date: 2024-09-17
Also published as: SE2251427A1

Abstract

ABSTRACT Parking brake system (200) for a vehicle combination (100) comprising a tractor (110a)/ trailer (110b). The system comprises a parking brake control (210) in a cabin (101) of the tractor and a trailer parking brake; a trailer spring brake chamber (280a, 280b) of the trailer parking brake, arranged to either activate the trailer parking brake by spring force; or disable the trailer parking brake when supplied with pressurised air overcoming the spring force; a pressurised air supply source (230); and a trailer parking relay valve (270). The trailer parking relay valve is configured to supply pressurised air to the trailer spring brake chamber (280a, 280b) when the parking brake control is set in an inactive position (d), thereby disabling the trailer parking brake; or discontinue the supply of pressurised air when the parking brake control is set in an active position (ß), thereby activating the trailer parking brake.

Description

PARKING BRAKE SYSTEM FOR A VEHICLE COMBINATION TECHNICAL FIELD This document discloses a parking brake system for a vehicle combination according to the appended patent claims.

BACKGROUND ln vehicles in general, a parking brake solution is often applied when the vehicle is parked in a standstill position, for avoiding that the vehicle starts rolling during unattended parking, which may cause severe accidents. The importance of the parking brake solution is important in particular for heavier vehicles such as trucks, busses and vehicle combinations.

A vehicle combination comprises one traction vehicle/ truck/ tractor and one or more towed vehicles such as a trailer or semi-trailer. ln prior art solutions, the tractor in a vehicle combination has a hand brake system which could be driver-activated by a parking brake control in the cabin of the tractor, thereby acti- vating the tractor parking brake. When activating the parking brake control, air is evacuated from a spring brake chamber/ pneumatic brake circuit and springs acting on the brakes of the tractor exerts a load on the brakes and thereby preventing the wheels of the tractor from rolling.

When activating the trailer brake, air may be evacuated from a separate pneumatic air source and springs acting on the trailer brakes may exert a load on the brakes and thus preventing the trailer wheels from rolling.

The above-described parking brake procedure of vehicle combinations is associated with several disadvantages/ problems. Firstly, it is a tedious and time-consuming procedure for the driver before both the parking brake of the tractor and the separate parking brake of the trailer have been activated and the parked vehicle combination is safe. Depending on the area where the driver stops the vehicle combination, exiting the cabin may present a danger for the driver to be mugged and/ or the vehicle combination to be hijacked. lt is also a risk that the driver is distracted while exiting the tractor and searches for the trailer parking brake control, thereby extending the crucial time of unsafe parking with the trailer, before activating the trailer parking brake. There is even a risk that the driver forgets or dis- regards activation of the trailer parking brake, for example when making only a brief stop, which presents a potentially dangerous situation. ln case of a pandemic outbreak/ chemical pollution or similar conditions in the operational zone of the vehicle combination, the driver may not even be allowed to exit the cabin (de- pending on local restrictions); and/ or only be able to exit the cabin by exposing him/ herself for a personal health risk; alternatively, firstly putting on protective gear/ clothing (typically inconvenient and time-consuming thing to do). ln addition, in some legislations, there is a legal demand for a safe and reliable parking brake solution, at least for some cases of vehicle combinations. One example of the latter is Bra- zilian Government resolution nr 872/2021, requiring a safe and reliable parking brake solu- tion for vehicle combinations having a gross train weight between 74-91 tons. lt appears that further improvement may be made for improving parking safety of a tractor and an attached trailer forming a vehicle combination.

SUMMARY lt is therefore an object to solve at least some of the above problems and provide a safe parking brake solution for a vehicle combination comprising a tractor and a trailer.

According to a first aspect of the invention, this objective is achieved by a parking brake system for a vehicle combination comprising a tractor and an attached trailer. The system comprises a parking brake control, comprised in a cabin of the tractor and connected to a parking brake control line. The parking brake control is adjustable between an inactive posi- tion and an active position. When the parking brake control is set in the inactive position, all wheels of the tractor and/ or trailer are allowed to rotate freely without parking brake activa- tion. This is typical the case during propulsion/ operation of the tractor and the trailer of the vehicle combination.

When the parking brake control is set in the active position, at least some wheels of the trailer and/ or the tractor are immobilised. The parking brake is thereby activated, typically the case when the tractor and the trailer of the vehicle combination are stationary.

The parking brake control may also be referred to as a parking brake actuating device or parking brake application device. The parking brake control may comprise a manually oper- able actuating element for actuating the parking brake. According to examples, the parking brake control may comprise e.g. a button, a lever, a handle or other similar device.

The parking brake system also comprises a first trailer parking brake friction surface, com- prised in the trailer, and a second trailer parking brake friction surface, associated with and arranged to rotate together with wheels of the same wheel axis on the trailer.

The first trailer parking brake friction surface is configured to engage with the second trailer parking brake friction surface, thereby braking/ immobilising the wheels; or disengage from the second trailer parking brake friction surface, thereby allowing the wheels to rotate freely.

The parking brake system in addition comprises one or several trailer spring brake cham- ber/s physically connected to the first trailer parking brake friction surface. The trailer spring brake chamber is arranged to either engage the first trailer parking brake friction surface with the second trailer parking brake friction surface by spring force of a spring comprised in the trailer spring brake chamber when the trailer spring brake chamber is not supplied with pres- surised air; or disengage the first trailer parking brake friction surface from the second trailer parking brake friction surface when the trailer spring brake chamber is supplied with pres- surised air overcoming the spring force of the spring.

The parking brake system comprises a pressurised air supply source, comprised in the trac- tor, connected to a parking brake air line.

Also, the parking brake system comprises a trailer parking relay valve situated in the tractor. The trailer parking relay valve is connected to the parking brake control line, to the parking brake air line and to a trailer outlet air line, which in turn is connected to the trailer spring brake chamber.

The trailer parking relay valve is configured to supply pressurised air of the parking brake air line to the trailer spring brake chamber via the trailer outlet air line when the parking brake control is set in the inactive position, thereby disengaging the first trailer parking brake friction surface from the second trailer parking brake friction surface; or discontinue supply of pres- surised air to the trailer spring brake chamber when the parking brake control is set in the active position, thereby engaging the first trailer parking brake friction surface with the sec- ond trailer parking brake friction surface.

Thanks to the described aspects, the driver is enabled to activate the trailer parking brake of the vehicle combination by a convenient parking brake control in the cabin of the tractor. lt is thereby avoided that the driver has to exit the cabin for activating the trailer parking brake, as performed in prior art solution.

Hereby, a fast and convenient parking brake activation of the tractor/ trailer in the vehicle combination is achieved, which minimises the risk of the driver omitting/ ignoring and or for- getting to activate the parking brake for the trailer when parking the vehicle combination. The saved time during the parking brake procedure multiplies over time (depending on number of stops of the involved vehicles), in the end resulting in shorter transportation time and more efficient usage of the vehicles. The provided solution also reduces ergonomic stress on the driver, creating an improved working environment for the driver.

Yet an advantage of the provided solution is that the implementation of the parking brake system does not affect functionality of the ordinary service brake of the tractor and/ or the trailer.

The convenience and fastness of the trailer parking brake activation via the parking brake control enables usage of the parking brake system as an efficient, yet safe emergency brake of the vehicle combination.

Other advantages and additional novel features will become apparent from the subsequent detailed description.

FIGURES Embodiments of the invention will now be described in further detail with reference to the accompanying figures, in which: Figure 1A illustrates an embodiment of a vehicle combination, comprising a tractor and a trailer.

Figure 1B illustrates an embodiment of a vehicle combination, comprising a tractor and a semi-trailer.

Figure 2 illustrates a parking brake system for a vehicle combination, according to an embodiment.

Figure 3A illustrates a subset of a parking brake system in an embodiment wherein the trailer wheels are not affected by parking brakes, implemented as drum brakes.

Figure 3B illustrates a subset of a parking brake system in an embodiment wherein the trailer wheels have been immobilised by a parking brake functionality, imple- mented as drum brakes.

Figure 4A illustrates a subset of a parking brake system in an embodiment wherein the trailer wheels are not affected by parking brakes, implemented as disc brakes.

Figure 4B illustrates a subset of a parking brake system in an embodiment wherein the trailer wheels have been immobilised by a parking brake functionality, imple- mented as disc brakes.

DETAILED DESCRIPTION Embodiments of the invention described herein are defined as a parking brake system for a vehicle combination, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. lt is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless oth- en/vise indicated, they are merely intended to conceptually illustrate the structures and pro- cedures described herein. Like numbers refer to like elements throughout.

Figure 1A illustrates a vehicle combination 100 of a powered vehicle 110a such as a tractor, and a towed entity 110b.

The towed entity 110b may comprise e.g. a trailer as schematically illustrated in the Figure 1A, or a semi-trailer as schematically illustrated in Figure 1B. Other terminologies used for denominating the towed entity 110b may be e.g. dolly, wagon, recreational vehicle, travel trailer, etc.

For increased readability, the towed entity 110b is subsequently referred to as a trailer. lt may however alternatively comprise a semi-trailer.

The vehicle combination 100 may comprise one powered vehicle/ tractor 110a and one or several trailers 110b, such as e.g. 1, 2, 3, etc. The powered vehicle/ tractor 110a may alter- natively be referred to as a truck, a tractor, a bus, a car or similar vehicle arranged for trans- portation on a driving surface.

The tractor 110a comprises a cabin 101, in which a driver normally is situated during opera- tion of the tractor 1 10a. ln some alternative embodiments, the tractor 110a may be driverless, i.e. autonomously controlled. However, for enhanced clarity, the tractor 1 10a is subsequently described as having a driver.

The tractor 110a also comprises a propulsion unit such as an internal combustion engine or an electrical engine, or a combination thereof.

The tractor 110a and the trailer 110b when forming the vehicle combination 100 are con- nected to each other via a physical coupling arrangement, which may be referred to as a towing coupling/ towing eye/ king pin. The tractor 110a and the trailer 110b when forming the vehicle combination 100 may exchange information over a datalink, e.g. via a bus such as e.g. a Controller Area Network (CAN) bus, a l\/ledia Oriented Systems Transport (l\/IOST) bus, or similar.

The vehicle combination 100 comprises a parking brake system 200, schematically illus- trated in Figure 2. The parking brake system 200 is a mechanism to ascertain that both the tractor 110a and the trailer 110b are maintained motioniess vvhen parked, also vvhen the vehicle combination 100 has been parked for example in a slope or other uneven under- neath, where gravity otherwise may bring the parked vehicle combination 100 into undesired movements, by immobilising wheels of the tractor 110a and/ or the trailer 110b. The parking brake functionality is sometimes also referred to as a hand brake.

Both the tractor 110a and the trailer 1 10b may also comprise dedicated service brakes which may be used by the driver when he/ she desire to decrease speed during normal operation of the tractor 110a and the trailer 110b; such as for example air line front service brake 160 and air line rear service brake 170 of the tractor 110a. The parking brake system 200 is operable independently of the tractor service brakes 160, 170, although they all may be sup- plied with pressurised air from the same pressurised air supply source The parking brake system 200 comprises a parking brake control 210. The parking brake control 210 is physically situated in the cabin 101 of the tractor 110a at some appropriate position where the driver is able to reach it without excessive ergonomic inconvenience, preferably while seated in the driving seat. ln case of using the parking brake system 200 as an emergency brake in an emergency situation, it may be important to enable the driver to easily find and pull/ operate the parking brake control The parking brake control 210 may comprise a hand lever which may be positioned/ set in an inactive position oi while driving the vehicle combination 100, i.e. the parking brake is released allowing the wheels 260a, 260b, 290a, 290b to roll.

The parking brake control 210 may be set in an active position ß when it is desired to park the vehicle combination 100. The parking brake of the tractor 110a and/ or the trailer 110b are activated, immobilising vehicle wheels 260a, 260b, 290a, 290b.

The parking brake control 210 may comprise an inlet port 211 connected to the pressurised air supply source 230 via a 4-way valve 150 and a compressed air supply line The parking brake control 210 may also comprise an outlet port 212, connected to a parking brake control line/s 305a, 305b.

The parking brake control 210 may also comprise a drainage port 213, arranged for draining the air inside the parking brake control line/s 305a, 305b when the parking brake control 210 is set to the ß position, i.e. parking brake on.

Via the parking brake control line/s 305a, 305b, the parking brake control 210 may provide an explicit or implicit control signal for activating/ disabling the parking brake of the tractor 110a and/ or the trailer 110b. ln some embodiments, one single parking brake control 210 may activate both the parking brake of the tractor 110a and the parking brake of the trailer 110b, in parallel. Time to en- gagement of the parking brakes of the vehicle combination 100 is minimised or at least re- duced. Space in the cabin 101 is also saved in comparison with having two distinct parking brake controls 210, one dedicated for controlling the parking brake of the trailer 110b and the second one dedicated for controlling the parking brake of the tractor 110a. Also, material is saved.

However, in alternative embodiments, two distinct parking brake controls 210 may be used for the parking brake of the trailer 110b and the parking brake of the tractor 110a. lt may then for example be enabled to park the tractor 110a and the trailer 110b, engage the respective parking brakes, disconnect the trailer 110b from the tractor 110a, release the parking brake of only the tractor 110a and depart, while leaving the trailer 110b parked with the parking brake active, possibly without the driver having to exit the cabin The parking brake system 200 comprises a first trailer parking brake friction surface/s 440a, 440b, comprised in the trailer 110b and a second trailer parking brake friction surface/s 441 a, 441 b. ln some embodiments, the first trailer parking brake friction surface/s 440a, 440b may be represented by a brake lining on a braking shoe of a drum brake while the second trailer parking brake friction surface/s 441 a, 441 b may be represented by an interior friction surface of the drum of the drum brake. This situation is better illustrated in Figures 3A-3B, and fur- ther described in detail in the corresponding section of the description. ln some alternative embodiments, the first trailer parking brake friction surface/s 440a, 440b may be represented by a friction pad in a ca|iper of a disc brake while the second trailer parking brake friction surface/s 441 a, 441 b may be represented by the disc of the disc brake. This situation is illustrated in Figures 4A-4B, and further described in detail in the corre- sponding section of the description.

The tractor 110a and the trailer 110b may both have the same type of brakes, for example both may have disc brakes on all axles/ wheels in some embodiments; or alternatively drum brakes on all axles/ wheels. ln other embodiments, the tractor 110a may have disc brakes on all axles/ wheels while the trailer 110b may have drum brakes on all axles/ wheels. Alternatively, the tractor 110a may have drum brakes on all axles/ wheels while the trailer 110b may have disc brakes on all axles/ wheels.

The tractor 1 10a (and/ or possibly the trailer 110b) may have one type of brakes on the front axle/ wheels and another type of brakes on rear axles/s wheels; for example, disc brakes on the front axle/ wheels while drum brakes may be applied on rear axles/s wheels. lrrespective of implementation form, the second trailer parking brake friction surface/s 441 a, 441 b is associated with and arranged to rotate together with wheels 290a, 290b mounted on the same wheel axis 291 on the trailer 110b when the first trailer parking brake friction sur- face/s 440a, 440b is disengaged from the second trailer parking brake friction surface/s 441 a, 441 b. lt may be mentioned that both the first trailer parking brake friction surface/s 440a, 440b and the second trailer parking brake friction surface/s 441 a, 441b typically is used also by a ser- vice brake of the trailer 110b, why other nomenclature often may be used for them in other contexts.

The first trailer parking brake friction surface/s 440a, 440b, irrespectively of representation, is configured to engage with the second trailer parking brake friction surface/s 441 a, 441b, thereby immobilising the wheels 290a, 290b; or disengage from the second trailer parking brake friction surface/s 441 a, 441 b, thereby allowing the wheels 290a, 290b to rotate freely.

Additionally, the parking brake system 200 comprises a trailer spring brake chamber/s 280a, 280b, physically connected to the first trailer parking brake friction surface/s 440a, 440b in the trailer 110b.

The trailer spring brake chamber/s 280a, 280b is physically connected to the first trailer park- ing brake friction surface/s 440a, 440b, for example via a rod The trailer spring brake chamber/s 280a, 280b is arranged to either engage the first trailer parking brake friction surface/s 440a, 440b with the second trailer parking brake friction sur- face/s 441 a, 441 b by spring force of a spring 410 comprised in the trailer spring brake cham- ber/s 280a, 280b when the trailer spring brake chamber/s 280a, 280b is not supplied with pressurised air. This is the situation schematically illustrated in Figure 3B.

The trailer spring brake chamber/s 280a, 280b is also arranged to disengage the first trailer parking brake friction surface/s 440a, 440b from the second trailer parking brake friction sur- face/s 441a, 441b when/ while/ as long the trailer spring brake chamber/s 280a, 280b is supplied with pressurised air overcoming the spring force of the spring 410 and releasing the first trailer parking brake friction surface/s 440a, 440b. This is the situation schematically illustrated in Figure 3A.

The parking brake system 200 comprises a pressurised air supply source 230 as already briefly mentioned, comprised in the tractor 110a, connected to a parking brake air line/s 310a, 310b, and the compressed air supply line 300. The pressurised air supply source 230 may supply pressurised air for all functions on-board requiring pressurised air such as brake cir- cuits and/ or service brakes 160, 170 of the tractor 110a, for example.

Pressurised air from air supply source 230 may pass through the 4-way valve 150 that may be configured to distribute compressed air for all the brake circuits, comprising the parking brake air lines 310a, 310b and the compressed air supply line The same pressurised air supply source 230 may be used by the trailer parking relay valve 270 for supplying pressurised air to the trailer spring brake chamber/s 280a, 280b, and by a tractor parking relay valve 240, for supplying pressurised air to a tractor spring brake cham- ber/s 250a, 250b, in optional embodiments. Hereby total weight is reduced, and space is saved onboard the tractor 110a.

Furthermore, the parking brake system 200 comprises a trailer parking relay valve 270. The trailer parking relay valve 270 may be situated in the tractor 1 10a in some embodiments. The trailer parking relay valve 270 is connected to the parking brake control line 305b; to the parking brake air line 310b; and also to a trailer outlet air line 320. The trailer outlet air line 320 may in turn be connected to the trailer spring brake chamber/s 280a, 280b of the trailer 110b directly or over/ via other not illustrated valves.

The trailer parking relay valve 270 is configured to supply pressurised air of the parking brake air line 310b to the trailer spring brake chamber/s 280a, 280b via the trailer outlet air line 320 when the parking brake control 210 is set in the inactive position d, thereby disengaging the first trailer parking brake friction surface 440a, 440b from the second trailer parking brake friction surface 441a, 441 b.

The trailer parking relay valve 270 is also configured to discontinue supply of pressurised air to the trailer spring brake chamber 280a, 280b when the parking brake control 210 is set in the active position ß, thereby engaging the first trailer parking brake friction surface 440a, 440b with the second trailer parking brake friction surface 441a, 441b. The parking brake force may be gradually controllable as the parking brake control 210 is transferred from the inactive position oi to the active position ß.

The parking brake control 210 may generate and continuously provide a parking brake con- trol signal via the parking brake control line/s 305a, 305b when set in the inactive position oi, i.e. during propulsion of the vehicle combination The parking brake control 210 may also discontinue provision of the parking brake control signal when/ while set in the active position ß. Hereby, the operative state of the trailer park- ing relay valve 270, which is connected to the parking brake control line 305b, is controlled by the parking brake control signal, depending on the position of the parking brake control 210, i.e. whether the parking brake control 210 is set in the inactive position d, or the active position ß.

The parking brake control signal may preferably be embodied as a pneumatic parking brake control signal in some embodiments, provided via the parking brake control line 305b to the trailer parking relay valve 270. A pneumatic parking brake control signal is fast and reliable.

However, in alternative embodiments, the parking brake control signal may be embodied as an electronic signal or possibly a wireless radio signal.

The trailer parking relay valve 270, in embodiments comprising pneumatic parking brakecontrol signalling via the parking brake control line 305b, may comprise at least three ports 271, 272, 274. The three ports 271, 272, 274 may comprise an inlet port 271, an outlet port 272, and a control port 274. The trailer parking relay valve 270 may in addition comprise a drainage port The drainage port 273 may drain the air inside the trailer spring brake chamber 280 when the parking brake control 210 is set in the ß-position, thereby activating the parking brake.

The inlet port 271 may be connected to the parking brake air line 310b, which in turn is connected to the pressurised air supply source 230 in the tractor 110a, e.g. via the 4-way valve 150. The outlet port 272 may be connected to the trailer outlet air line 320, which in turn may be connected to the trailer spring brake chamber/s 280a, 280b via one or several relay valves or similar. The control port 274 may be connected to the parking brake control line 305b, which in turn is connected to the parking brake control The trailer parking relay valve 270 may be configured to supply air flow from the inlet port 271 to the outlet port 272, for example by setting the trailer parking relay valve 270 in a position allowing pressurised air to flow from the inlet port 271 to the outlet port 272 when/ while the control port 274 receives the parking brake control signal/ when/ while the parking brake control 210 is set in the inactive position oi.

When no parking brake control signal is received on the control port 274 via the parking brake control line 305b, the air supply flow from the inlet port 271 to the outlet port 272 may be discontinued, for example by setting the trailer parking relay valve 270 in a position disal- lowing pressurised air to flow from the inlet port 271 to the outlet port The parking brake system 200 may also comprise a first tractor parking brake friction sur- face/s 450a, 450b, comprised in the tractor 110a, and a second tractor parking brake friction surface/s 451 a, 451b. The second tractor parking brake friction surface/s 451a, 451b may be associated with and arranged to rotate together with wheels 260a, 260b of the same wheel axis 261 on the tractor 110a.

The first tractor parking brake friction surface/s 450a, 450b and the second tractor parking brake friction surface/s 451a, 451b may be commonly used both by the parking brake and by a service brake of the tractor 110a.

The general functionalities of the first tractor parking brake friction surface/s 450a, 450b and the second tractor parking brake friction surface/s 451a, 451b are very similar to or evenidentical with the already described corresponding functionalities of the first trailer parking brake friction surface/s 440a, 440b and the second trailer parking brake friction surface/s 441a, 441b and may be represented in a similar way as either brake lining/ interior friction surface of the drum in a drum brake implementation; or by friction pad /disc brake, respec- tively in a disc brake embodiment.

The first tractor parking brake friction surface 450a, 450b may be configured to engage with the second tractor parking brake friction surface 451 a, 451 b, thereby immobilising the wheels 260a, 260b. The first tractor parking brake friction surface 450a, 450b may also be configured to disengage from the second tractor parking brake friction surface 451 a, 451b, thereby al- lowing the wheels 260a, 260b to rotate freely.

The parking brake system 200 may comprise a tractor spring brake chamber/s 250a, 250b, physically connected to the first tractor parking brake friction surface 450a, 450b. The tractor spring brake chamber/s 250a, 250b may be arranged to either engage the first tractor parking brake friction surface 450a, 450b with the second tractor parking brake friction surface 451 a, 451 b by spring force of a spring comprised in the tractor spring brake chamber 250a, 250b when the tractor spring brake chamber 250a, 250b is not supplied with pressurised air. The tractor spring brake chamber/s 250a, 250b may also be arranged to disengage the first trac- tor parking brake friction surface 450a, 450b from the second tractor parking brake friction surface 451 a, 451 b when the tractor spring brake chamber 250a, 250b is supplied with pres- surised air overcoming the spring force of the spring.

The tractor parking relay valve 240 of the system 200 may be connected to the parking brake control line 305a, to the parking brake air line 310a and also to a tractor outlet air line 315a, 315b, which in turn is connected to the tractor spring brake chamber 250a, 250b.

The tractor parking relay valve 240 may be configured to supply pressurised air of the parking brake air line 310a to the tractor spring brake chamber 250a, 250b via the tractor outlet air line 315a, 315b when/ while the parking brake control 210 is set/ maintained in the inactive position oi, thereby disengaging the first tractor parking brake friction surface 450a, 450b from the second tractor parking brake friction surface 451a, 451b. Thereby, the associated wheels 260a, 260b are allowed to rotate freely. The parking brake control 210 may then also allow that compressed air coming from air supply line 300 pass to the parking brake control line 305a, 305b.

The tractor parking relay valve 240 may also be configured to discontinue supply of pressur- ised air to the tractor spring brake chamber 250a, 250b when the parking brake controlis set/ maintained in the active position ß, thereby engaging the first tractor parking brake friction surface 450a, 450b with the second tractor parking brake friction surface 451 a, 451 b, immobilising the associated wheels 260a, 260b.

When the compressed air coming through the parking brake control line 305a, 305b reaches the control port 244 of parking brake relay valve 240 for the tractor 110a and/ or the parking brake relay valve 270 for the trailer 110b, it allows that compressed air coming from the parking brake air line 310a connected to parking brake relay valve 240 of the tractor 110a pass to the tractor spring brake chamber 250 for the tractor 110a through the tractor outlet air line 315a, 315b.

The compressed air coming from the tractor outlet air line 315a, 315b may then fill the tractor spring brake chamber/s 250a, 250b, thereby compressing the internal spring and releasing the brake lining and consequently releasing the associated tractor wheels 260a, 260b.

Compressed air coming from the parking brake air line 310b may pass through the parking brake relay valve 270 of the trailer 110b, to the trailer spring brake chamber/s 280a, 280b for the trailer 110b through the trailer outlet air line/ spiral hose 320. The compressed air coming from the trailer outlet air line/ spiral hose 320 may fill the trailer spring brake chamber/s 280a, 280b, thereby compressing the internal spring releasing the brake lining and consequently releasing the associated trailer wheels 290a, 290b. ln embodiments wherein the parking brake system 200 comprises both the trailer parking relay valve 270 and the tractor parking relay valve 240, the parking brake control 210 may be communicatively connected to the trailer parking relay valve 270 via a dedicated parking brake control line 305b. The parking brake control 210 may also be communicatively con- nected to the tractor parking relay valve 240 via a dedicated parking brake control line 305a.

Thereby, the trailer parking relay valve 270 and the tractor parking relay valve 240 may be configured to both receive the parking brake control signal via the parking brake control line 305a, 305b, in parallel.

The parking control line 305a, 305b may comprise a tractor parking control line 305a ar- ranged between the parking brake control 210 and the tractor parking relay valve 240, and a trailer parking control line 305b arranged between the parking brake control 210 and the trailer parking relay valve 270. According to an example, the tractor parking control line 305a and the trailer parking brake control line 305b may be arranged in parallel.

The parking brake control line 305a, 305b and/ or the parking brake airline 310a, 310b and/or the trailer outlet air line 320 and/ or the tractor outlet air line 315a, 315b may be comprised in the parking brake system When the parking brake control 210 is set in the ß- position, it means that parking is applied by braking the wheels 260a, 260b, 290a, 290b. The parking brake control 210 may then cut off compressed air on the parking brake control lines 305a, 305b. The compressed air inside the parking brake control lines 305a, 305b may be drained to the atmosphere through the drainage port 213 on the parking brake control When the parking brake control lines 305a, 305b are empty, the parking brake relay valve 240 for the tractor 110a disallow passage of compressed air from the parking brake air line 310a to the tractor outlet air lines 315a, 315b.

The air inside the tractor outlet air lines 315a, 315b and inside the tractor spring brake cham- ber/s 250a, 250b mounted in association with the tractor wheels 260a, 260b may be drained to atmosphere through the drainage port 243 on the parking brake relay valve 240 of the tractor 110a. When there is no pressurised air inside the spring brake chamber 250, the internal spring inside the tractor spring brake chamber/s 250a, 250b extends, actuating and engaging the first tractor parking brake friction surface 450a, 450b, with the second tractor parking brake friction surface 451 a, 451b.

Similarly, the parking brake relay valve 270 of the trailer 110b may also disallow passage of compressed air from the air supply line 310b to the trailer outlet air line/ spiral hose The pressurised air inside the trailer outlet air line/ spiral hose 320 and inside the trailer spring brake chamber 280a, 280b of the trailer 110b may be drained to atmosphere through the drainage port 273 on the parking brake relay valve 270 of the trailer 110b. When no pressurised air remains inside the trailer spring brake chamber/s 280a, 280b, the internal spring inside the trailer spring brake chamber/s 280a, 280b extends, actuating and engaging the first trailer parking brake friction surface 440a, 440b, with the second trailer parking brake friction surface 441a, 441 b, and braking the trailer wheels 290a, 290b.

The latter measures may occur approximately simultaneously in some embodiments. The reason is that the first tractor parking brake friction surface 450a, 450b, or brake lining, of the tractor wheels 260a, 260b is pushed towards the second tractor parking brake friction surface 441 a, 441 b by mechanical actuation of the spring comprised in the tractor spring brake cham- ber/s 250a, 250b while at the same time, the first trailer parking brake friction surface 440a, 440b, or brake lining, of the trailer wheels 290a, 290b is pushed towards the second trailer parking brake friction surface 441a, 441b by mechanical actuation of the spring comprised in the tractor spring brake chamber/s 280a, 280b, because both the trailer parking relay valves 240 and tractor parking relay valve 270 may be connected in parallel. ln some embodiments, the activation time of the trailer parking brake, after the parking brake control 210 has been set into active position ß may be shorter than the activation time of the tractor parking brake.

This effect may be created for example by adjusting the relative sizes of the drainage port 243 on the parking brake relay valve 240 of the tractor 110a and the drainage port 273 on the parking brake relay valve 270 of the trailer 110b, so that the evacuation of air from the trailer spring brake chamber 280a through the drainage port 273 on the trailer parking brake relay valve 270 takes less time than the corresponding evacuation of air from the tractor spring brake chamber 280a through the drainage port 243 on the tractor parking brake relay valve Thus, the activation time of the first trailer parking brake friction surface 440a, 440b with the second trailer parking brake friction surface 441a, 441b after the parking brake control 210 has been set into active position ß may be shorter than the activation time of the first tractor parking brake friction surface 450a, 450b with the second tractor parking brake friction sur- face 451a, 451b. Thereby, the associated wheels 290a, 290b of the trailer 110b may be immobilised before immobilising the associated wheels 260a, 260b of the tractor 110a. The associated wheels 290a, 290b of the trailer 110b may be immobilised briefly before immobi- lising the associated wheels 260a, 260b of the tractor 110a.

The associated wheels 290a, 290b of the trailer 110b may be immobilised before immobilis- ing the associated wheels 260a, 260b of the tractor 110a when the parking brake control 210 is used as emergency brake, causing that it is avoided that the trailer 110b push on the rear part of the tractor 110a during the emergency brake, which may have a destabilising effect on the tractor 110a. Thus, safe emergency brake functionality of the parking brake system 200 is provided.

Figure 3A illustrates a subset of the parking brake system 200, comprising a parking brake control 210, a pressurised air supply source 230, a trailer parking relay valve 270, a trailer spring brake chamber 280a, a trailer wheel 290a, a first trailer parking brake friction surface 440a and a second trailer parking brake friction surface 441 a.

The parking brake control 210 is set into the inactive position d. The trailer parking relayvalve 270 is thereby set in a position allowing passage of pressurised air from the com- pressed air supply line 300, connected to the pressurised air supply source 230, to be output on a parking brake control line 305b. A control signal may thereby be formed, which is pro- vided to the trailer parking relay valve The trailer parking relay valve 270, upon reception of the control signal via a parking brake control line 305b, is set in a position which allows for air supply to the trailer spring brake chamber 280a by connecting the air supply from the pressurised air supply source 230 via the parking brake air line 310b with the trailer outlet air line 320a, which in turn allow pres- surised air to enter/ fill the trailer spring brake chamber 280a.

The trailer spring brake chamber 280a is thereby filled with pressurised air, which is exercis- ing a pressure on a spring 410 via an airtight seal 415 in the trailer spring brake chamber 280a. The pressurised air in the trailer spring brake chamber 280a is thereby overcoming the spring force of the spring 410, as long as supplied with pressurised air. A physical con- nection linkage 420 between the trailer spring brake chamber 280a and a control mechanism 430 of the first trailer parking brake friction surface 440a is thereby pulled, bringing the first trailer parking brake friction surface 440a to disengage from the second trailer parking brake friction surface 441a on the inside of the drum mounted on the trailer wheel 290a, thereby allowing the trailer wheel 290a to rotate freely without interaction.

Figure 3B illustrates the same subset of the parking brake system 200 as previously illus- trated in Figure 3A. However, in this scenario, the parking brake is engaged.

Thus, the parking brake control 210 is set into the active position ß. The trailer parking relay valve 270 is thereby set in a position, disallowing air supply to the trailer spring brake cham- ber 280a by disabling air supply from the pressurised air supply source 230 via the parking brake air line 310b and the trailer outlet air line When no pressurised air is supplied to the trailer spring brake chamber 280a, the spring force of the spring 410 is causing a pressing action on a control mechanism 430 of the first trailer parking brake friction surface 440a, thereby causing the first trailer parking brake fric- tion surface 440a to engage with the second trailer parking brake friction surface 441a on the inside of the drum mounted on the trailer wheel 290a, thereby disallowing rotational movement of the trailer wheel 290a.

The functionalities and operations of the tractor parking brake, the tractor spring brake cham- ber/s 250a and the tractor parking relay valve 240 may be quite similar or even identical withthe described and illustrated corresponding entities in the trailer 110b, illustrated in Figures 3A-3B, in some embodiments. ln some embodiments, the parking brake system 200 may be configured to engage the first trailer parking brake friction surface 440a, 440b with the second trailer parking brake friction surface 441a, 441b by spring force of the spring 410 comprised in the trailer spring brake chamber 280a, 280b; and/ or to engage the first tractor parking brake friction surface 450a, 450b with the second tractor parking brake friction surface 451 a, 451 b by spring force of the spring comprised in the tractor spring brake chamber 250a, 250b when air pressure of the pressurised air supply source 230 is lower than a threshold limit, independently of whether the parking brake control 210 is set in the inactive position oi or the active position ß.

Thereby, thanks to the functionality of the tractor spring brake chamber/s 250a, 250b and/ or the trailer spring brake chamber/s 280a, 280b, the parking brake automatically becomes activated and engaged when there is an air supply leakage or other anomaly in the air pres- sure, and/ or when the pressurised air supply source 230 has run out of pressurised air. A compressor may then be activated to refill the pressurised air supply source 230 with pres- surised air, before the parking brakes could be released.

The illustrations in Figures 3A-3B illustrate general principles of the parking brake system 200 implemented with a drum brake in the trailer 110b. The parking brake system 200 may be implemented with a drum brake, also or alternatively in the tractor 1 10a. The trailer spring brake chamber 280a in Figures 3A-3B then corresponds to a tractor spring brake chamber 250a; the trailer wheel 290a corresponds to a tractor wheel 260a; the first trailer parking brake friction surface 440a corresponds to a first tractor parking brake friction surface 450a; and the second trailer parking brake friction surface 441a corresponds to a second tractor parking brake friction surface 451 a.

Correspondingly, the illustrations in Figures 4A-4B illustrate general principles of the parking brake system 200 implemented with a disc brake in a tractor 1 10a. The parking brake system 200 may be implemented with a disc brake, also or alternatively in the trailer 110b. The tractor spring brake chamber 250a in Figures 4A-4B then corresponds to a trailer spring brake chamber 280a; the tractor wheel 260a corresponds to a trailer wheel 290a; the first tractor parking brake friction surface 450a corresponds to a first trailer parking brake friction surface 440a; and the second tractor parking brake friction surface 451a corresponds to a second trailer parking brake friction surface 441a.

Figure 4A illustrates a subset of the parking brake system 200, comprising a parking brakecontrol 210, a pressurised air supply source 230, a tractor parking relay valve 240, a tractor spring brake chamber 250a, a tractor wheel 260a, a first tractor parking brake friction surface 450a and a second tractor parking brake friction surface 451 a.

The parking brake control 210 is set into the inactive position oi. The tractor parking relay valve 240 is thereby set in a position allowing passage of pressurised air from the com- pressed air supply line 300, connected to the pressurised air supply source 230, to be output on a parking brake control line 305a. A control signal may thereby be formed, which is pro- vided to the tractor parking relay valve The tractor parking relay valve 240, upon reception of the control signal via a parking brake control line 305a, is set in a position which allows for air supply to the tractor spring brake chamber 250a by connecting the air supply from the pressurised air supply source 230 via the parking brake air line 310a with the tractor outlet air line 315a, which in turn allow pres- surised air to enter/ fill the tractor spring brake chamber 250a.

The tractor spring brake chamber 250a is thereby filled with pressurised air, which is exer- cising a pressure on a spring 510 via an airtight seal 515 in the tractor spring brake chamber 250a. The pressurised air in the tractor spring brake chamber 250a is thereby overcoming the spring force of the spring 510, as long as supplied with pressurised air. A physical con- nection linkage 520 between the tractor spring brake chamber 250a and the first tractor park- ing brake friction surface 450a, or brake pad, as it also may be referred to as, is thereby pulled, bringing the first tractor parking brake friction surface 450a to disengage from the second trailer parking brake friction surface 451a, or disc, as it also may be referred to as, thereby allowing the tractor wheel 260a to rotate freely without interaction.

Figure 4B illustrates the same subset of the parking brake system 200 as previously illus- trated in Figure 4A. However, in this scenario, the parking brake is engaged.

Thus, the parking brake control 210 is set into the active position ß. The passage of pressur- ised air from the compressed air supply line 300 may then be blocked, so that no pressurised air is provided out to the parking brake control line 305a. When the tractor parking relay valve 240 no longer receives pressurised air via the parking brake control line 305a, the tractor parking relay valve 240 is thereby set in a position, disallowing air supply to the tractor spring brake chamber 250a by disabling air supply from the pressurised air supply source 230 via the parking brake air line 310a and the tractor outlet air line 315a.

When no pressurised air is supplied to the tractor spring brake chamber 250a, the springforce of the spring 510 is causing a pressing action on the first tractor parking brake friction surface 450a, or brake pad, thereby causing the first tractor parking brake friction surface 450a to engage with the second tractor parking brake friction surface 441 a, or disc, mounted in association with the tractor wheel 260a/ axle 261, thereby disallowing rotational movement of the tractor wheel 260a.

The terminology used in the description of the embodiments as illustrated in the accompa- nying drawings is not intended to be Iimiting of the described parking brake system 200. Different features illustrated in different Figures and/ or described in different sections of the description may with certain advantage be combined with each other, in different embodi- mentS.

Various changes, substitutions and/ or alterations may be made, without departing from in- vention embodiments as defined by the appended claims.

As used herein, the term "and/ or" comprises any and all combinations of one or more of the associated listed items. The term "or" as used herein, is to be interpreted as a mathematical OR, i.e., as an inclusive disjunction; not as a mathematical exciusive OR (XOR), unless ex- pressly stated othen/vise. ln addition, the singular forms "a", "an" and "the" are to be inter- preted as "at least one", thus also possibly comprising a plurality of entities of the same kind, unless expressly stated othen/vise. lt will be further understood that the terms "includes", "comprises", "including" and/ or "comprising", specifies the presence of stated features, ac- tions, integers, steps, operations, elements, and/ or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, ele- ments, components, and/ or groups thereof. A single unit such as e.g. a processor may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/ distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware but may also be distributed in other forms such as via Internet or other wired or wireless communication system.

Claims

1. A parking brake system (200) for a vehicle combination (100) comprising a tractor (110a) and an attached trailer (110b); wherein the system (200) comprises: a parking brake control (210), comprised in a cabin (101) of the tractor (110a) and connected to a parking brake control line (305a, 305b); wherein the parking brake control (210) is adjustable between an inactive position (d) and an active position (ß); a first trailer parking brake friction surface (440a, 440b), comprised in the trailer (110b); a second trailer parking brake friction surface (441a, 441b), associated with and arranged to rotate together with wheels (290a, 290b) the same wheel axis (291) on the trailer (1 10b); wherein the first trailer parking brake friction surface (440a, 440b) is configured to engage With the second trailer parking brake friction surface (441a, 441b), thereby immobilising the wheels (290a, 290b); or disengage from the second trailer parking brake friction surface (441a, 441 b), thereby allowing the wheels (290a, 290b) to rotate freely; a trailer spring brake chamber (280a, 280b) physically connected to the first trailer parking brake friction surface (440a, 440b), wherein the trailer spring brake chamber (280a, 280b) is arranged to either engage the first trailer parking brake friction surface (440a, 440b) with the second trailer parking brake friction surface (441a, 441b) by spring force of a spring (410) comprised in the trailer spring brake chamber (280a, 280b) when the trailer spring brake chamber (280a, 280b) is not supplied with pressurised air; or disengage the first trailer parking brake friction surface (440a, 440b) from the second trailer parking brake friction surface (441 a, 441 b) when the trailer spring brake cham- ber (280a, 280b) is supplied with pressurised air overcoming the spring force of the spring (410); a pressurised air supply source (230), comprised in the tractor (1 10a), connected to a parking brake air line (310a, 310b); a trailer parking relay valve (270), situated in the tractor (110a), wherein the trailer parking relay valve (270) is connected to the parking brake control line (305b); the parking brake air line (310b); and a trailer outlet air line (320), which in turn is connected to the trailer spring brake chamber (280a, 280b); and wherein the trailer parking relay valve (270) is configured to supply pressurised air of the parking brake air line (310b) to the trailer spring brakeChamber (280a, 280b) via the trailer outlet air line (320) when the parking brake control (210) is set in the inactive position (oi), thereby disengaging the first trailer parking brake friction surface (440a, 440b) from the second trailer parking brake friction surface (441a, 441 b); or discontinue supply of pressurised air to the trailer spring brake chamber (280a, 280b) when the parking brake control (210) is set in the active position (ß), thereby engaging the first trailer parking brake friction surface (440a, 440b) With the second trailer parking brake friction surface (441a, 441b).

2.- Th a first tractor parking brake friction surface (450a, 450b), comprised in the tractor (110a); a second tractor parking brake friction surface (451a, 451b), associated with and system (200) according to claim 1, further comprising arranged to rotate together with wheels (260a, 260b) of the same wheel axis (261) on the tractor (110a); wherein the first tractor parking brake friction surface (450a, 450b) is config- ured to engage With the second tractor parking brake friction surface (451a, 451b), thereby immobilising the wheels (260a, 260b); or disengage from the second tractor parking brake friction surface (451 a, 451 b), thereby allowing the wheels (260a, 260b) to rotate freely; a tractor spring brake chamber (250a, 250b) physically connected to the first tractor parking brake friction surface (450a, 450b), wherein the tractor spring brake chamber (250a, 250b) is arranged to either engage the first tractor parking brake friction surface (450a, 450b) with the second tractor parking brake friction surface (451a, 451b) by spring force of a spring (510) comprised in the tractor spring brake chamber (250a, 250b) When the tractor spring brake chamber (250a, 250b) is not supplied with pressurised air; or disengage the first tractor parking brake friction surface (450a, 450b) from the second tractor parking brake friction surface (451a, 451b) when the tractor spring brake chamber (250a, 250b) is supplied with pressurised air overcoming the spring force of the spring (510); a tractor parking relay valve (240), situated in the tractor (1 10a), wherein the tractor parking relay valve (240) is connected to the parking brake control line (305a); the parking brake air line (310a); and a tractor outlet air line (315a, 315b), which in turn is connected to the tractor spring brake chamber (250a, 250b); and wherein the tractor parking relay valve (240) is configured to supply pressurised air of the parking brake air line (310a) to the tractor spring brakeChamber (250a, 250b) via the tractor outlet air line (315a, 315b) when the parking brake control (210) is set in the inactive position (oi), thereby disengaging the first tractor parking brake friction surface (450a, 450b) from the second tractor parking brake friction surface (451a, 451b); or discontinue supply of pressurised air to the tractor spring brake chamber (250a, 250b) when the parking brake control (210) is set in the active position (ß), thereby engaging the first tractor parking brake friction surface (450a, 450b) with the second tractor parking brake friction surface (451a, 451b).

3. Th wherein the parking brake control (210) is configured to generate and continuously provide system (200) according to any one of the preceding claims, a parking brake control signal via the parking brake control line (305a, 305b) When set in the inactive position (oi); and discontinue provision of the parking brake control signal when set in the active position (ß); and wherein the trailer parking relay valve (270) is configured to supply pressurised air of the parking brake air line (310b) to the trailer spring brake chamber (280a, 280b) via the trailer outlet air line (320) while receiving the parking brake control signal of the parking brake con- trol (210) via the parking brake control line (305a), and otherwise discontinue the supply of pressurised air to the trailer spring brake chamber (280a, 280b) when no parking brake con- trol signal is received; and/ or the tractor parking relay valve (240) is configured to supply pressurised air of the parking brake air line (310a) to the tractor spring brake chamber (250a, 250b) via the tractor outlet air line (315a, 315b) while receiving the parking brake control signal of the parking brake control (210) via the parking brake control line (305b), and otherwise discontinue the supply of pressurised air to the tractor spring brake chamber (250a, 250b).

4. The relay valve (270) and the tractor parking relay valve (240) are configured to both receive the system (200) according to claim 3, wherein the trailer parking parking brake control signal via the respective parking brake control line (305a, 305b), in parallel.

5. The ““ parking brake control signal is a pneumatic parking brake control signal, provided via the parking brake control line (305a, 305b). ” _š_\*_§§___system (200) according to any one of claims 3-4, wherein the

6. The trailer parking relay valve (270) comprises at least three ports (271, 272, 274), of which ëwsystem (200) according to any one of claims 1-5, wherein the an inlet port (271) is connected to the parking brake air line (310b), which in turn isconnected to the pressurised air supply source (230); an outlet port (272) is connected to a trailer outlet air line (320), which in turn is connected to the trailer spring brake chamber (280a, 280b); and a control port (274) is connected to the parking brake control line (305b), which in turn is connected to the parking brake control (210); and wherein the trailer parking relay valve (270) is configured to supply air flow from the inlet port (271) to the outlet port (272) while the control port (274) receives the parking brake control signal and othenNise discon- tinue the air supply flow from the inlet port (271) to the outlet port (272).

7. The same pressurised air supply source (230) is used by :Wsystem (200) according to any one of claims 2-6, wherein the the trailer parking relay valve (270) for supplying pressurised air to the trailer spring brake chamber (280a, 280b), and the tractor parking relay valve (240), for supplying pressurised air to the tractor spring brake chamber (250a, 250b).

8. Thegg; engage the first trailer parking brake friction surface (440a, 440b) with the second 'gjgxsystem (200) according to any one of claims 1-7, configured to trailer parking brake friction surface (441a, 441b) by spring force of the spring (410) com- prised in the trailer spring brake chamber (280a, 280b); and/ or engage the first tractor parking brake friction surface (450a, 450b) with the second tractor parking brake friction surface (451a, 451b) by spring force of the spring (510) com- prised in the tractor spring brake chamber (250a, 250b)(_ when air pressure of the pressurised air supply source (230) is lower than a threshold limit, independently of whether the parking brake control (210) is set in the inactive position (oi) or the active position (ß).

9. The activation time of the first trailer parking brake friction surface (440a, 440b) with the second ågigäusystem (200) according to any one of claims 2-8, wherein the trailer parking brake friction surface (441a, 441b) after the parking brake control (210) has been set into active position (ß) is shorter than the activation time of the first tractor parking brake friction surface (450a, 450b) with the second tractor parking brake friction surface (451a, 451b), thereby immobilising the associated wheels (290a, 290b) of the trailer (110b) before immobilising the associated wheels (260a, 260b) of the tractor (1 10a).

10. The parking brake control (210) comprises a hand lever which allowgg positioning in the inactive ggsystem (200) according to any one of claims 1-9, wherein the position (d), and/ or the active position (ß).11. first trailer parking brake friction surface (440a, 440b), comprised in the trailer (110b) is rep-

11.The agwsystem (200) according to any one of claims 1-10, wherein the resented by a brake lining on a braking shoe of a drum brake and the second trailer parking brake friction surface (441a, 441 b) is represented by an interior friction surface of a drum of the drum brake.

12. Themg; first trailer parking brake friction surface (440a, 440b), comprised in the trailer (110b) is rep- system (200) according to any one of claims 1-10, wherein the resented by a friction pad in a caliper of a disc brake and the second trailer parking brake friction surface (441a, 441b) is represented by a disc of the disc brake.

13. The çgwsystem (200) according to any one of claims 2-12, wherein the first tractor parking brake friction surface (450a, 450b), comprised in the tractor (110a) is represented by a brake lining on a braking shoe of a drum brake and the second tractor parking brake friction surface (451a, 451 b) is represented by an interior friction surface of a drum of the drum brake.

14. The first tractor parking brake friction surface (450a, 450b), comprised in the tractor (110a) is f sgwsystem (200) according to any one of claims 2-12, wherein the represented by a friction pad in a caliper of a disc brake and the second tractor parking brake friction surface (451a, 451b) is represented by a disc of the disc brake.