GB1602246A

GB1602246A - Pressure fluid operated braking systems for vehicles

Info

Publication number: GB1602246A
Application number: GB1860978A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-06-14
Filing date: 1978-05-10
Publication date: 1981-11-11
Also published as: DE2751143A1; FR2409176B2; FR2409176A2

Description

(54) IMPROVEMENTS IN OR RELATING TO PRESSURE FLUID OPERATED BRAKING SYSTEMS FOR VEHICLES (71) We. ROBERT BOSCH GMBH, a German Company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to pressure fluid operated braking systems for vehicles, and more particularly to air over hydraulic braking systems.

Braking systems using compressed air as the transfer medium are very widespread. In these systems in the majority of cases a multi-circuit braking valve is actuated bv a braking pedal. The pressure which is proportional to the force applied to the pedal is fed to a so-called booster or pressurising cylinder. It is customary to use one pressurising cylinder per brake circuit or even per axle. Such an arrangement comprises for example two brake valves and two pressurising cylinders and can be combined into one device. In the case of a two circuit brake system the compressed-air actuated piston and a hydraulic piston are arranged one behind the other in a so-called tandem arrangement.

In these systems anti-locking devices for avoiding wheels being locked by the brakes while the vehicle is still travelling are also used. In systems having so-called loose design in which the brake valve and pressurising cylinder are not combined spatially, a pressurising cylinder is used for each control channel. An anti-lock adjusting member is inserted in the connection line to the brake valve and by way of this member which is triggered by an electronic unit the pressure in the pressurising cylinder is regulated. The corresponding pressure level in the hydraulic brake circuit corresponds to the pressure transmission.

Taking into account the additional expenditure on anti-locking, the solutions described represent a not inconsiderable expenditure with regard to the technology of the device. The pressurising cylinder combination must be of appropriately large dimensions so that even in the case of badly adjusted brakes an appropriate braking pressure is reached. These systems are disadvantageous if the relevant brake circuit is badly leaking. In this case on the majority of occasions the full braking pressure is not obtained. Without an additional warning device a driver is not necessarily aware of the impairment of the operation. Since the majority of braking actions take place in a region of partial braking, the faulty operation only becomes noticeable by reduced braking when full braking action is applied by the driver, and this often represents a dangerous situation.

According to the present invention a pressure fluid braking system for vehicles comprises at least one air over hydraulic brake pressure modulator for supplying hydraulic brake fluid in a hydraulic circuit to a group of hydraulic wheel brake cylinders a foot-actuable braking valve for admitting actuating compressed air in an air circuit into the pressure modulator, and an antiwheel locking system including at least one multi-way air valve in the air circuit and at least one hydraulic valve in the hydraulic circuit for establishing anti-lock brake pressure modulation.

A braking system embodying the present invention can by contrast have the advantage of being able to bring back into action immediately a brake circuit which is badly leaking or which has become inoperative due to vapour lock.

It is also an advantage that only a single modulator is necessary per vehicle axle or per brake group. for the system to In addition it is be operated as a high pressure air pump in order to be able to brake by means of increased air pressure should the hydraulic unit fail.

The invention will be further described by way of example with reference to Figs. 2 to 8 of the accompanying drawings in which Fig. 1 is a diagrammatic illustration of a pressure fluid operated braking system used hitherto, and in which Fig. 2 is a diagrammatic illustration of one embodiment of the invention and having a loose design, some components separate from one another Fig. 3 is a diagrammatic longitudinal sectional view of a pressure modulator used in the embodiment of Fig. 2 Fig. 4 is a longitudinal sectional view of two modulators combined with one another, Fig. 5 is a loose design having a multipositional valve, Fig. 6 illustrates a further combination possibility Fig. 7 is a diagrammatic illustration of a further embodiment, and Fig. 8 is a diagrammatic illustration of yet another embodiment.

An external force braking system illus- trated in Fig. 1, has a brake pedal 15 which can actuate an "air over hydraulic" booster 1 having an pneumatic cylinder 4 to which air is supplied from two reservoirs (not shown) through lines 2 and 3 respectively, and a hydraulic tandem master cylinder 5 to supply two brake circuits I and II. Two air lines 6, 7 pass from the air reservoir lines 2 3 to two pressure modulators 8, 9 respectively: one pressure modulator 8 is associated with the brake circuit I and the other pressure modulator 9 with the brake circuit II. In addition two hydraulic lines 10 and 11 lead from the tandem master cylinder 5 to the pressure modulators 8 and 9 respectively.

The two pressure modulators 8 and 9 are constructed differently respectively for a front axle brake and for a rear axle brake or for a plurality of brakes in the case of dual or multiple axles because, as a result of the arrangement of two sensors 13 and 14, one for each front wheel, each of the brake cylinders which are associated with the front axle can be supplied with a different pressure; since only one sensor 17 is associated with the rear axle 16 the two brake cylinders which are associated with the rear axle are supplied with the same pressure. In such case one speaks of a 2-channel control unit for the front axle and a 1-channel control unit for the rear axle. The rear axle brakes can however also be regulated individually as in the example of the front axle.

Fig. 2 shows now a similar design as Fig.

1, embodying a system according to the present invention in the form of a so-called loose brake system, that is to say a system in which the modulators used are separate from one another.

A pneumatic dual circuit foot operable braking valve 20 supplies two brake pressure modulators 21 and 22 with compressed air. Each modulator 21, 22 has respectively e.g. a three-port two-way solenoid valve 23, 24 for the compressed air and a hydraulic topping-up reservoir 25, 26. The modulator 21 has additionally two two-port two-way solenoid valves 27 and 28 as a 2channel control unit, and the modulator 22 has a two-port two-way solenoid valve 29 for a 1-channel control unit. The remaining reference numerals are the same as those in Fig.1.

The pressure modulator 21 for the front axle 2-channel control unit is shown in section in Fig. 3. It can be seen that the line 6 from the reservoir leads to the three-port two-way solenoid valve 23 which monitors the compressed air supply to a pressure chamber 30 in the modufator 21. The pres- sure chamber 30 is in part defined by a modulator piston 31 which closes off an outer air chamber 32 on its other side. In this chamber 32 a restoring spring 33 for the piston 31 is located and a limit switch 35 is disposed on an end wall 34.

A piston rod 36, connected to the modulator piston 31, is constructed in its front part 37 as a hydraulic piston which in part defines a hydraulic chamber 38. This chamber 38 is connected on the one hand to the topping-up reservoir 25 and on the other to two two-port two-way solenoid valves 39 and 40 which are disposed parallel and near to one another. The hydraulic chamber 38 has a small dead space when the piston 37 is in its brake-actuating end, i.e. to the left as seen in Fig. 3. The lines from the left hand end of the chamber 38 to the valves 39 and 40 are very short.

The hydraulic piston 37 is bored axially and accommodates a spring 41 and push rod 42 which carries at its other end a valve closure member 43 for a valve 43, 44 whose valve seat 44 is disposed at the opening of a line leading from the topping-up reservoir 25. The magnets of the solenoid valves 23 39 and 40 are connected electrically to the sensors 13 and 14 by way of an electronic control device 80. (Fig.2).

The arrangement illustrated in Figs. 2 and 3 operates as follows: When braking the three-port, two way solenoid valve 23 allows compressed air to pass from the braking valve 20 into the pressure chamber 30. The modulator piston 31 is moved against the force of the spring 33 the valve 43, 44 communicating with the topping-up reservoir 25 is closed and hydraulic fluid passes by way of the two twoport two-way solenoid valves 39 and 40 to the front axle brake cylinders.

If the front wheel brakes lock the front wheels the three solenoid valves 23, 39, 40 are switched over by the electronic switch ing device 80 to effect anti-wheel locking.

By means of the Channel control unit each brake cylinder of the front axle 12 can be regulated separately. In this manner only one pressure modulator 21 is required for the individual regulation of the wheels of the front axle 12.

Should vapour lock occur in the brake circuit I the modulator piston 31 moves up to the end wall 34 and actuates the limit switch 35. Actuation of the switch 35 causes illumination of a warning light. The switch 35 is also used in conjunction with the electronic switching device for the purpose of topping up a defective hydraulic brake circuit.

For this purpose the two solenoid valves 39 and 40 in the hydraulic circuit are switched to a holding condition (valves closed) and the three-port two-way solenoid valve 23 in the compressed air line is switched to a pressure relief condition. This results in the restoring spring 33 moving back the piston 31. After the rod 42 has opened the valve 43, 44 hydraulic fluid is drawn in from the reservoir 25. A renewed application of air pressure to the compressed air piston 31 results in the piston moving to the left as seen in Fig. 3 and hydraulic fluid being fed again into the brake circuit with the solenoid valves 39 and 40 in the hydraulic circuit opened again. In the limiting case, e.g. if there is no more hydraulic fluid in the reservoir, this arrangement can even operate as a high pressure compressed air pump due to the small dead volume.This pumping action is possible because during the return travel of the brake pedal the two-port two-way solenoid valves 39 and 40 have shut off the brake lines to the brake cylinders. The dead space between the main brake cylinder piston in the end position and the two-port two-way solenoid valves 39, 40 must thereby be small in order to reach a sufficiently high pressure level.

The modulator 22 of the rear axle 16 also operates in a similar manner and is likewise connected to the electronic control device 80.

Fig. 4 illustrates diagrammatically part of an embodiment in which two pressure modulators are combined with one another. In the arrangement of Fig. 4 a braking valve 50 is associated with two combined pressurising cylinders and brake pressure modulators 51 and 52 and anti-lock air valves 53 and 54, and hydraulic valves 55, 56 and 57 are combined spatially into one unit. In the case of the brake pressure modulator 51 pressure at the front side of the compressed air piston is switched by air valve 53 to the rear side of that piston in order to reduce the brake pressure. In the case of the other brake pressure modulator 52 compressed air at the front side of the compressed air piston is released by air valve 54 into the atmosphere in a conventional manner in order to reduce brake pressure.The two pressurising cylinders and brake pressure modulators 51 and 52 are each provided with a limit switch 58 or 59. The method of operation of this arrangement is similar to that already described in connection with Figs. 2 and 3.

Fig. 5 illustrates a further embodiment which is basically the same basic arrangement as that of the embodiment of Fig. 4 but in a so-called loose design in which certain components are separated spatially from one another. In the embodiment of Fig. 5 there is only one spatially combined unit which consists of a braking valve 60, pressurising cylinder and brake pressure modulator 61, anti-lock air valve 62 and antilock hydraulic valve 63. It will be apparent that this spatially combined unit supplies brake pressure fluid for the front axle brake cylinders, in contrast to the rear axle brake cylinders which are further away from the brake valve 60.If the distance is very great, which results in correspondingly great line lengths, the throttling resistances in the hydraulic line would be too great, which in the case of an anti-locking operation would result in a delayed pressure distribution.

These disadvantages from the point of view of control technology can be eliminated if a second combination having a pressurising cylinder and brake pressure modulator 61' is disposed in the vicinity of the rear axle.

Conceivably the anti-locking valves comprising a compressed air valve to regulate the compressed air on the primary side of the piston in the pressurising cylinder and dual or multi-positional valves in the hydraulic circuit can be combined into a single multi-position valve unit such as indicated by the reference numeral 64. In the case of this multi-position valve unit a longitudinal slide valve having a compressed air actuated adjusting piston, for example, is regulated into an appropriate position. To actuate it a three-port three-way valve 65 is switched by the electronic unit; a position feed-back signal as an aid to correct positioning is supplied by a position sensor 66.

Fig. 6 illustrates a further possible combination using two electro-magnetically actuated three position air or hydraulic valves 67 and 68 having together six ports and which represent servo valves controlling main valves 69 and 70 which may be equally well in the compressed air circuit or in the hydraulic circuit. In order to use the initially previously described switching arrangement for topping up a hydraulic circuit a double valve is required as the main valve 70; this valve responds when the two servo valves 67 and 68 are both in their third position in which they establish connections between the respective ports as illustrated in the right hand block of the valve 67 in Fig. 6. When the valves 67 and 68 are in their third positions the double main valve 69 is changed over.

A further embodiment is illustrated in Fig. 7 in which a pneumatic dual circuit foot operable braking valve 120 supplies com pressed air to a modulator 121 which has a three-port two-way solenoid valve 123 in the compressed air circuit, a hydraulic topping up reservoir 125, and two two-port two-way solenoid valves 139, 140 for a 2-channel control unit for the pressure in two wheel brake cylinders 113 and 114.

A line 106 leads from the braking valve 120 to the three-port two-way valve 123 which monitors the compressed air supply of a pressure chamber 130 in the modulator 121. The pressure chamber 130 is in part defined by one side of a modulator piston 131 whose other side closes a chamber 132 communicating with outside air. A restoring spring 133 for the piston 131 is located in this chamber 132 and a limit switch 135 is disposed on end wall 134.

A piston rod 136 connected to the modulator piston 131 is constructed in its front part 137 as a hydraulic piston which in part defines a hydraulic chamber 138. This chamber 138 is connected on the one hand to the topping-up reservoir 125 and on the other to two hydraulic two-port two-way solenoid valves 139 and 140 which are disposed parallel and near to one another. The hydraulic chamber 138 has a small dead volume in the brake-actuating end position of the piston 137. In addition the lines from there to the valves 139 and 140 are very short. It is also possible to use only one of the two solenoid valves 139 or 140 for pressure modulation. A residual pressure valve 100 is provided upstream of the solenoid valve or valves and is accommodated with the two solenoid valves 139 and 140 in a common housing 105. The housing 105 is disposed on the housing of the modulator 121.

The hydraulic piston 137 is bored open axially and accommodates a spring 141 and a push rod 142 which carries at its other end a valve closure member 143 for a valve 143, 144 whose valve seat 144 is disposed at the opening of a line leading from the toppingup reservoir 125. The solenoids of the valves 123, 139 and 140 are connected electrically to sensors 103 and 104 at the vehicle wheels through an electronic control device.

The system illustrated in Fig. 7 operates as follows: When the braking valve 120 is released the residual pressure valve 100 retains brake fluid in the brake cylinders 113, 114 under a reduced excess pressure; by this means brake fluid presses more tightly than otherwise against seal lips in the brake cylinders 11). 114 and air cannot pass into the system.

When braking the three-port two-way solenoid valve 123 allows compressed air to pass from the braking valve 120 into the pressure chamber 130. The modulator piston 131 is moved against the force of the spring 133, the valve 143, 144 to the topping-up reservoir 125 is closed and hydraulic pressure fluid passes through the residual pressure valve and the two two-port two-way solenoid valves 139 and 140 to the brake cylinders 113 and 114. Because of the previously existing pressure retained by the residual pressure valve 100 there is relatively little free travel in the brake cylinders 113 and 114 and a quick braking action results.

If the wheel brakes lock the wheels the three solenoid valves 123, 139 140 are switched over by the electronic switching device to effect anti-locking. By means of the 2-channel control unit each brake cylinder 113, 114 can be regulated separately. In this manner only one modulator 121 is required for the individual regulation of the wheels of one axle.

Fig. 8 illustrates a system including a design of modulator 151 which is assembled with a standard master cylinder 152. The standard master cylinder 152 has a piston 153 having a primary and a secondary seal 154 and 155. It accommodates in a spherical recess 156 the end of a piston rod 157 of a modulator piston 161.

In the case of this design a residual pressure valve 160 is located at the base 158 of the master cylinder 152. A brake line 159 leads to two hydraulic two-port two-way solenoid valves 162 and 163 which are disposed nearby to a three-port two-wav solenoid air valve 164 which corresponds to the valve 123 in Fig. 1. In this manner the electrical operation is simplified.

Lines leading to the wheel brake cylinders lead from the two two-port two-way solenoid valves 162 and 163. The method of operation of this system is the same as that of the system of Fig. 7.

WHAT WE CLAIM IS: 1. A pressure fluid braking system for vehicles, comprising at least one air over hydraulic brake pressure modulator for supplying hydraulic brake fluid in a hydraulic circuit to a group of hydraulic wheel brake cylinders, a foot-actuable braking valve for admitting actuating compressed air in an air circuit into the pressure modulator, and an anti-wheel locking system including at least one multi-way air valve in the air circuit and at least one hydraulic valve in the hydraulic circuit for establishing anti-lock brake pressure modulation.

2. A braking system as claimed in claim 1, in which the or each multi-way air valve is a three-port two-way electromagnetic valve, and the or each hydraulic valve is a two-port two-way electromagnetic valve.

3. A braking system as claimed in claim 1 or 2 in which one multi-way air valve and two hydraulic valves and the air over hydraulic modulator are combined into one unit

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pressed air to a modulator 121 which has a three-port two-way solenoid valve 123 in the compressed air circuit, a hydraulic topping up reservoir 125, and two two-port two-way solenoid valves 139, 140 for a 2-channel control unit for the pressure in two wheel brake cylinders 113 and 114. A line 106 leads from the braking valve 120 to the three-port two-way valve 123 which monitors the compressed air supply of a pressure chamber 130 in the modulator 121. The pressure chamber 130 is in part defined by one side of a modulator piston 131 whose other side closes a chamber 132 communicating with outside air. A restoring spring 133 for the piston 131 is located in this chamber 132 and a limit switch 135 is disposed on end wall 134. A piston rod 136 connected to the modulator piston 131 is constructed in its front part 137 as a hydraulic piston which in part defines a hydraulic chamber 138. This chamber 138 is connected on the one hand to the topping-up reservoir 125 and on the other to two hydraulic two-port two-way solenoid valves 139 and 140 which are disposed parallel and near to one another. The hydraulic chamber 138 has a small dead volume in the brake-actuating end position of the piston 137. In addition the lines from there to the valves 139 and 140 are very short. It is also possible to use only one of the two solenoid valves 139 or 140 for pressure modulation. A residual pressure valve 100 is provided upstream of the solenoid valve or valves and is accommodated with the two solenoid valves 139 and 140 in a common housing 105. The housing 105 is disposed on the housing of the modulator 121. The hydraulic piston 137 is bored open axially and accommodates a spring 141 and a push rod 142 which carries at its other end a valve closure member 143 for a valve 143, 144 whose valve seat 144 is disposed at the opening of a line leading from the toppingup reservoir 125. The solenoids of the valves 123, 139 and 140 are connected electrically to sensors 103 and 104 at the vehicle wheels through an electronic control device. The system illustrated in Fig. 7 operates as follows: When the braking valve 120 is released the residual pressure valve 100 retains brake fluid in the brake cylinders 113, 114 under a reduced excess pressure; by this means brake fluid presses more tightly than otherwise against seal lips in the brake cylinders 11). 114 and air cannot pass into the system. When braking the three-port two-way solenoid valve 123 allows compressed air to pass from the braking valve 120 into the pressure chamber 130. The modulator piston 131 is moved against the force of the spring 133, the valve 143, 144 to the topping-up reservoir 125 is closed and hydraulic pressure fluid passes through the residual pressure valve and the two two-port two-way solenoid valves 139 and 140 to the brake cylinders 113 and 114. Because of the previously existing pressure retained by the residual pressure valve 100 there is relatively little free travel in the brake cylinders 113 and 114 and a quick braking action results. If the wheel brakes lock the wheels the three solenoid valves 123, 139 140 are switched over by the electronic switching device to effect anti-locking. By means of the 2-channel control unit each brake cylinder 113, 114 can be regulated separately. In this manner only one modulator 121 is required for the individual regulation of the wheels of one axle. Fig. 8 illustrates a system including a design of modulator 151 which is assembled with a standard master cylinder 152. The standard master cylinder 152 has a piston 153 having a primary and a secondary seal 154 and 155. It accommodates in a spherical recess 156 the end of a piston rod 157 of a modulator piston 161. In the case of this design a residual pressure valve 160 is located at the base 158 of the master cylinder 152. A brake line 159 leads to two hydraulic two-port two-way solenoid valves 162 and 163 which are disposed nearby to a three-port two-wav solenoid air valve 164 which corresponds to the valve 123 in Fig. 1. In this manner the electrical operation is simplified. Lines leading to the wheel brake cylinders lead from the two two-port two-way solenoid valves 162 and 163. The method of operation of this system is the same as that of the system of Fig. 7. WHAT WE CLAIM IS:

1. A pressure fluid braking system for vehicles, comprising at least one air over hydraulic brake pressure modulator for supplying hydraulic brake fluid in a hydraulic circuit to a group of hydraulic wheel brake cylinders, a foot-actuable braking valve for admitting actuating compressed air in an air circuit into the pressure modulator, and an anti-wheel locking system including at least one multi-way air valve in the air circuit and at least one hydraulic valve in the hydraulic circuit for establishing anti-lock brake pressure modulation.

which is disposed separated from the braking valve.

4. A braking system as claimed in claim 1, 2 or 3, in which a hydraulic chamber in the pressure modulator has a small dead volume at the end of a brake actuation stroke.

5. A braking system as claimed in claim 4, in which the hydraulic valves are adjacent the hydraulic chamber.

6. A braking system as claimed in claim 1, 2 or 3, in which a residual pressure valve for pressure in wheel brake cylinders is provided downstream of the air over hydraulic brake pressure modulator and upstream of said at least one hydraulic valve in the hydraulic circuit whereby a residual-pressure can be retained on the wheel brake cylinder side of the modulator on release of the braking valve.

7. A braking system as claimed in claim 6, in which the residual pressure valve is disposed upstream of a line which branches to two such hydraulic valves.

8. A braking system as claimed in claim 7, in which the residual pressure valve is accommodated jointly with the hydraulic valves in a common housing which is seated on the housing of the air over hydraulic pressure modulator.

9. A braking system as claimed in claim 7 or 8, in which the residual pressure valve is inserted in a hydraulic main chamber of the pressure modulator.

10. A braking system as claimed in claim 1 or 2, in which a first brake pressure modulator for front axle wheel brake cylinders is combined into one unit with the braking valve, and a second brake pressure modulator for other axle wheel brake cylinders is disposed separately.

11. A braking system as claimed in claim 10, in which one multi-way air valve and one hydraulic valve are combined with the first brake pressure modulator and the braking valve into one unit.

12. A braking system as claimed in claim 11, in which said one multi-way air valve is a three-port two-way electromagnetic valve, and said one hydraulic valve is a three-port four-way electromagnetic valve.

13. A braking system as claimed in claim 10, 11 or 12, in which a second multi-way air valve and the second brake pressure modulator and hydraulic valves are combined into a second unit.

14. A braking system as claimed in claim 13, in which the air valve and hydraulic valves associated with the second brake pressure modulator are combined into a single multi-position valve unit.

15. A braking system as claimed in claim 1, in which a first multi-way air valve, a first brake pressure modulator, and a first hydraulic valve, and a second multi-way air valve, a second brake pressure modulator and two hydraulic valves, and the braking valve are combined into one unit.

16. A braking system as claimed in claim 15, in which the first multi-way air valve is a four-port two-way electromagnetic valve, the first hydraulic valve is a three-port three-way electromagnetic valve, the second multi-way air valve is a three-port two-way electromagnetic valve, and the two hydraulic valves are two two-port two-way electromagnetic valves.

17. A braking system as claimed in claim 1, in which said air and hydraulic valves include two electromagnetically operable servo-valves and two main valves responsive thereto.

8. A braking system as claimed in claim 17, in which one of the main valves is a double valve which responds when both of the servo-valves are in predetermined positions and controls two two-port two-way hydraulic valves.

19. A braking system as claimed in any preceding claim, in which a limit switch is disposed in a pressure modulator and is actuable by an air piston therein as it approaches its full braking position therein.

20. A braking system as claimed in claim 19, in which the limit switch is connected to said at least one hydraulic valve through an electronic control device, whereby to permit topping up of the hydraulic circuit.

21. A braking system as claimed in claim 19 or 20, in which the limit switch is connected to a warning light.

22. A pressure fluid braking system for vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 2 with any of Figs. 3, 4, 5 or 6 of the accompanying drawings.

23. A pressure fluid braking system for vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly with reference to and as illustrated in Fig. 7 or Fig. 8 of the accompanying drawings.