SE540826C2 - An axle gear system, a driving axle system and a motor vehicle - Google Patents

Abstract

An axle gear system (8) for distribution of torque between a forward driving axle and a rear driving axle in a motor vehicle, comprising an input shaft (11), a forward output shaft (12) for transmitting torque from the input shaft to the forward driving axle, a rear output shaft (15) for transmitting torque from the input shaft to the rear driving axle, a connection wheel (16) connected for common rotation with the rear output shaft, a first tapered rolling bearing (19) supporting the connection wheel, a second tapered rolling bearing (20) supporting the input shaft in the connection wheel, further comprising a connection means (22) movable between an engaged position in which the connection wheel and the input shaft are connected for common rotation, and a disengaged position in which the connection wheel and the rear output shaft are disconnected.

Description

An axle gear system, a driving axle system and a motor vehicle TECHNICAL FIELD OF THE INVENTION The present invention relates to an axle gear system according to the preamble of claim 1, to a driving axle system comprising such an axle gear system, and to a motor vehicle. In particular, but not exclusively, the invention relates to an axle gear system for use in a driving axle system in the form of a tandem bogie or a tridem bogie, i.e. a bogie with two and three driving axles, respectively.

BACKGROUND AND PRIOR ART A conventional driving axle system in the form of e.g. a tandem or tridem bogie of a motor vehicle comprises two or more driving axles arranged to be driven by a single input shaft connected to a power source. In the case of a tandem bogie, the bogie comprises two driving axles which are often referred to as a forward-rear and a rear-rear driving axle. The forward-rear and rear-rear driving axle each include a pair of drive shafts on which one or more wheels of the motor vehicle are mounted. Each of the forward-rear and rear-rear driving axles further includes a differential gear set that allows the vehicle wheels on each driving axle to rotate at different speeds. Further, an axle gear system including means for distributing torque between the forward-rear and the rear-rear driving axles, such as an inter-axle differential, is usually provided. The inter-axle differential allows the wheels of the two driving axles to rotate with mutually different rotational speeds and thereby compensates for slippage, cornering, mismatched tires, etc.

EP2942224 discloses another configuration of a driving axle system and an axle gear system. According to this configuration, the forward-rear and the rear-rear driving axles are connected by a shaft, operatively coupled to a slip clutch. The amount of torque which is transmitted to the rear-rear driving axle can thereby be controlled by the degree of engagement of the slip clutch, thereby compensating for slippage etc.

A torque distribution system that compensates for slippage etc. is useful in many applications, but both of the above mentioned configurations are relatively complex and involve a plurality of costly components. In certain applications, such as for cargo carrying vehicles, e.g. long-haulage trucks, intended to transport cargo on relatively smooth roads, such complex torque distribution systems are superfluous. However, the total weight of such vehicles may vary considerably depending on the weight of the transported cargo, and on whether the vehicle is loaded or not. When the vehicle is heavily loaded, it is desirable to use both driving axles, while as when the vehicle carries no load, it may be desirable to elevate the rear-rear driving axle off the ground and drive the vehicle with only the forward-rear driving axle in order to reduce losses in the powertrain of the vehicle.

SUMMARY OF THE INVENTION It is a primary objective of the present invention to provide an in at least some aspect improved solution for distribution of torque between two driving axles of a motor vehicle. In particular, it is an objective to provide a robust solution for distribution of torque between two driving axles, which is less complex than the above described prior art solutions and which is suitable for heavy motor vehicles driven under load conditions that vary over time, such as cargo carrying vehicles travelling sometimes with and sometimes without cargo.

At least the primary objective is according to a first aspect of the invention achieved by means of the initially defined axle gear system, which further comprises a connection means movable between an engaged position in which the connection wheel and the input shaft are connected for common rotation, and a disengaged position in which the connection wheel and the rear output shaft are disconnected. Thus, in the engaged position, torque can be transmitted to both driving axles so that both driving axles obtain the same rotational speed, while as in the disengaged position, torque can only be transmitted to the forward driving axle and not to the rear driving axle. In other words, the input shaft and the rear output shaft are either connected via the connection wheel and the connection means and in that case rotate as a unit, or disconnected with no possibility to transfer torque to the rear output shaft. The connection means are configured for non-slip engagement, i.e. no intermediate positions between the engaged and the disengaged position are available.

The axle gear system according to the invention constitutes a robust driving unit for use in e.g. a bogie of a motor vehicle. It has fewer moving parts, and is thereby less complex and more robust than a conventional axle gear system comprising an inter-axle differential. It is also less space-consuming. It enables inactivation of a rear-rear driving axle of a driving axle system comprising the proposed axle gear system when the conditions are such that this is desirable. This may be the case e.g. when the motor vehicle is travelling without load and it is sufficient to use one driving axle. When the rear-rear driving axle is disconnected and thereby inactive in the driving of the motor vehicle, it is possible to either elevate the inactive rear-rear axle in order to reduce rolling resistance, or use it as a passive support axle, depending on the conditions. The non-slip configuration of the connection means offers a very reliable solution for connecting and disconnecting the rear driving axle using a small number of components.

The second tapered rolling bearing serves to transmit axial forces between the input shaft and the connection wheel, including preload forces and gear forces in both the engaged and the disengaged positions. Axial forces may be further transmitted via the first tapered rolling bearing to e.g. a housing of the axle gear system. The second tapered rolling bearing supports the input shaft stably and efficiently transfers axial forces using a small number of components and thereby contributes to the robustness of the axle gear system according to the invention.

According to the invention, said connection means comprises a sleeve arranged around the input shaft, said sleeve being movable along a longitudinal axis of the input shaft. The sleeve offers many possibilities for achieving a reliable selectable connection between the input shaft and the rear output shaft.

Said sleeve is provided with internal splines engaging with external splines provided on the input shaft, thus providing an efficient connection between the input shaft and the sleeve such that these rotate as a unit.

According to one embodiment, the internal splines of the sleeve are configured to, in the engaged position, engage on one hand with said external splines provided on the input shaft and on the other hand with external splines provided on the connection wheel. In the engaged position, the input shaft and the rear output shaft are thereby securely locked together and rotate as a unit.

According to another embodiment, the sleeve and the connection wheel have end faces provided with teeth configured to engage with each other when the connection means is in the engaged position. The sleeve thus functions as one clutch half and the connection wheel as another clutch half, together forming a nonslip clutch, such as a dog clutch. This is an alternative way of achieving a reliable non-slip connection between the input shaft and the rear output shaft.

According to one embodiment of the invention, the axle gear system further comprises a control device configured to move the connection means between the engaged position and the disengaged position upon receipt of a signal. Thus, a driver of the motor vehicle may easily provide a signal, e.g. by pushing a button or similar, that it is desired to disengage or engage the connection means.

According to one embodiment of the invention, the axle gear system further comprises a housing in which the connection wheel and the input shaft are supported and in which the connection means is located. The housing protects the components and thereby prolongs their service life.

According to one embodiment, the axle gear system further comprises a third bearing supporting the input shaft in the housing. The third bearing is suitably provided forward of the first and second bearings, where the input shaft enters into the housing. It is preferably in the form of a tapered rolling bearing. Together with the first and the second tapered rolling bearings, it is configured to transmit axial forces arising during torque transmission to the housing.

According to one embodiment of the invention, the forward output shaft extends in parallel with the input shaft. The forward output shaft is connected to the input shaft by means of e.g. transfer gear members which are always in engagement. A rotation of the input shaft will thus always lead to a rotation of the forward output shaft. Depending on whether the connection means is in an engaged or a disengaged position, either some or all of the input torque will be transmitted via the forward output shaft. The amount of torque transmitted via the forward output shaft will in the engaged position depend on axial pressure, friction, etc., but will usually be around 50 % of the total transmitted torque.

According to another aspect of the present invention, at least the above mentioned primary objective is achieved by means of a driving axle system comprising at least one proposed axle gear system, at least one forward driving axle driven by the forward output shaft, and at least one rear driving axle driven by the rear output shaft. Advantages and advantageous features of such a driving axle system appear from the above discussion in connection with the proposed axle gear system. Of course, it is possible to also have a foremost driving axle, located at a front of the motor vehicle, which does not form part of this driving axle system.

According to one embodiment, the driving axle system is a tandem drive system. Such a system has two driving axles coupled to a single axle gear system.

According to one embodiment, the driving axle system comprises at least two of said axle gear systems and at least three driving axles driven by said at least two axle gear systems. In this case, a forward axle gear system and a rear axle gear system may be provided together with a forward-rear, a middle-rear and a rearrear driving axle. When the connection means of the forward axle gear system is in the disengaged position, the middle-rear and the rear-rear driving axles will both be inactive, i.e. all torque will be transmitted from the input shaft to the forward-rear driving axle, regardless of the position of the rear axle system’s connection means. When the connection means of the forward axle gear systems is in the engaged position, torque will be distributed to either all of the driving axles or to the forward-rear and the middlerear diving axles, depending on the position of the rear axle gear system’s connection means. Thus, with this driving axle system, it is possible to alternate between one, two and three rear driving axles. Of course, it is also possible to connect one or more additional axle gear systems and driving axles.

The invention also relates to a motor vehicle comprising the proposed driving axle system, preferably wherein the motor vehicle is a heavy motor vehicle such as a bus or a truck, e.g. a long haulage truck adapted to transport cargo on a trailer, a military truck, a construction or distribution truck, a truck for use in forestry, mining, etc. The motor vehicle may be a motor vehicle powered by an internal combustion engine, or a motor vehicle entirely or partly powered by an electric power source, such as a hybrid vehicle.

Other advantageous features as well as advantages of the present invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will in the following be further described by means of example with reference to the appended drawings, wherein Fig. 1a schematically shows a motor vehicle having a driving axle system according to an embodiment of the invention, Fig. 1b schematically shows a motor vehicle having a driving axle system according to another embodiment of the invention, Figs. 2a-b show an axle gear system according to a first embodiment of the invention, and Figs. 3a-b show an axle gear system according to a second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION An exemplary motor vehicle 1 according to an embodiment of the invention is schematically shown in fig. 1a. The motor vehicle 1 comprises a front axle 2 configured to steer the vehicle and a pair of front wheels 3 mounted thereon. It further comprises a powertrain 4 including an engine 5, a transmission 6 and a driving axle system 7. The driving axle system 7 comprises an axle gear system 8, a forward driving axle 9 and a rear driving axle 10. To each driving axle, a wheel assembly including four wheels 3 is mounted, such that the motor vehicle 1 in total includes ten wheels 3 distributed between three axles 2, 9, 10.

Each driving axle 9, 10 may or may not include an axle differential enabling rotation of the left and right wheel assemblies at mutually different rotation speeds. Such configurations are well known in the art and will not be further discussed herein.

A motor vehicle 1 according to another embodiment of the invention is schematically shown in fig. 1b . The motor vehicle 1 according to this embodiment differs from the one shown in fig. 1a only in that it has a driving axle system 7 comprising a forward axle gear system 8 and a rear axle gear system 8, a forward driving axle 9, a rear driving axle 10, and a middle driving axle 31. As described above with reference to fig. 1, each driving axle 9, 10, 31 may or may not include an axle differential.

Axle gear systems 8 according to a first and a second embodiment of the invention are shown in figs. 2a-2b and figs. 3a-3b, respectively. In both embodiments, an input shaft 11 having a longitudinal axis of rotation C is provided for transmission of torque from the engine 5 to the driving axle system 7. A forward output shaft 12 in the form of a pinion is configured to transmit torque from the input shaft 11 to the forward driving axle 9. Torque is transmitted from the input shaft 11 to the forward output shaft 12 via a transfer gear having a first gear member 13 mounted for common rotation with the input shaft 11 and a second gear member 14 mounted for common rotation with the forward output shaft 12. A rear output shaft 15 is configured to selectively transmit torque from the input shaft 11 to the rear driving axle 10. The forward and the rear output shafts 12, 15 both extend in parallel with the input shaft 11, but the forward output shaft 12 is laterally displaced with respect to the input shaft 11, while the rear output shaft 15 shares the longitudinal axis of rotation C with the input shaft 11.

A connection wheel 16 is connected for common rotation with the rear output shaft 15 by means of mutually engaging splines 17. The connection wheel 16 is supported in a housing 18 surrounding the components of the axle gear system 8 by means of a first tapered rolling bearing 19, having cylinder shaped rolling elements 19a. Its inner ring 19b is resting against a shoulder provided in the connection wheel and its outer ring 19c is resting against the housing 18. The first tapered rolling bearing 19 is tapered from the connection wheel 16 toward the rear output shaft 15. The input shaft 11 is supported in the connection wheel 16 by means of a second tapered rolling bearing 20, which is smaller than the first rolling bearing 19 but otherwise similar. The second tapered rolling bearing 20 has cylinder shaped rolling elements 20 and its inner ring rests against a shoulder provided in the input shaft 11, while its outer ring rests against a shoulder provided in the connection wheel 16. The second tapered rolling bearing 20 is tapered from the input shaft 11 toward the rear output shaft 15. The input shaft 11 is further supported in the housing 18 by a third tapered rolling bearing 21, arranged in a front portion of the housing 18. The third tapered rolling bearing 21 is tapered from an inside of the housing 18 toward the input shaft 11.

A connection means in the form of a sleeve 22 having internal splines is arranged around an externally splined section 23 of the input shaft 11. The sleeve 22 and the input shaft 11 may thus rotate as a unit, due to the mutually engaging splines.

In the first embodiment, shown in figs. 2a and 2b, the sleeve 22 has an axial end face 24 directed toward an axial end face 25 of the connection wheel 16. Both end faces 24, 25 are provided with teeth 26, 27. The sleeve 22 is movable along the longitudinal axis C between a disengaged position, shown in fig. 2a, and an engaged position, shown in fig. 2b. In the engaged position, the end faces 24, 25 are in contact and the teeth 27 provided on the end face 25 of the connection wheel 16 interlock with the teeth 26 provided on the end face 24 of the sleeve 22, such that the connection wheel 16 and the input shaft 11 rotate as a unit. Thereby, also the input shaft 1 1 and the rear output shaft 15 rotate as a unit. In the disengaged position, the teeth 26, 27 on the end faces 24, 25 are not in mutual engagement. The connection wheel 16 and the input shaft 11 are thus not connected for common rotation, and no torque is thereby transferable to the rear output shaft 15.

In the second embodiment, shown in figs. 3a and 3b, the connection wheel 16 is designed with an externally splined section 28, having splines adapted to engage with the internal splines of the sleeve 22. The sleeve 22 is movable between a disengaged position, shown in fig. 3a, and an engaged position, shown in fig. 3b. In the disengaged position, the internal splines of the sleeve 22 are only in engagement with the external splines of the input shaft 11. In the engaged position, the sleeve 22 partially overlaps both of the externally splined section 23 of the input shaft 1 1 and the externally splined section 28 of the connection wheel 16. Thereby, the internal splines of the sleeve 22 engage with the splines provided on the input shaft 11 as well as with the splines provided on the connection wheel 16, and the input shaft 11, the connection wheel 16 and the rear output shaft 15 rotate as a unit.

The movement of the sleeve 22 between the engaged and the disengaged positions is in both shown embodiments effected by a control device 29 having an actuator fork 30 adapted to move the sleeve 22. The control device 29 is configured to receive an input signal from a driver of the motor vehicle 1, and based on this input signal control the actuator fork 30 such that it takes on one of two possible positions, thereby moving the sleeve 22 between the engaged and the disengaged positions. The input signal may cause a control system of the vehicle to send a signal to the control device 29. The signal may be an electric signal or a pneumatic or hydraulic pressure signal. In both embodiments, the sleeve 22 is moved toward the rear output shaft 15 in order to be brought into the engaged position, and in the other direction in order to be brought into the disengaged position.

During torque transmission between the input shaft 11 and the forward output shaft 12 and/or the rear output shaft 15, axial forces including e.g. preload forces and gear forces are transmitted from the input shaft 11 via the second tapered rolling bearing 20 to the connection wheel 16, reagardless of whether the sleeve 22 is in the engaged position or in the disengaged position. The axial forces are further transmitted to the housing 18 via the first and third tapered rolling bearings 19, 21. This is the case in both of the shown embodiments.

In the motor vehicle 1 shown in fig. 1a, the axle gear system 8 distributes torque between the forward driving axle 9 via the forward output shaft 12 and the rear driving axle 10 via the rear output shaft 15.

In the motor vehicle 1 shown in fig. 1b , the forward axle gear system 8, corresponding to any one of the axle gear systems 8 shown in figs. 2a-2b and 3a-3b, distributes torque between the forward driving axle 9 via its forward output shaft 12, and the middle and rear driving axles 31, 10 via its rear output shaft 15. The rear axle gear system 8, also corresponding to any one of the axle gear systems 8 shown in figs. 2a-2b and 3a-3b, distributes torque between the middle driving axle 31 via its forward output shaft 12 and the rear driving axle 10 via its rear output shaft 15. When the connection means of the forward axle gear system 8 is in its disengaged position, torque is only transferred to the forward driving axle 9. When the connection means of the forward axle gear system 8 is in its engaged position, torque is transferred to the rear axle gear system 8 via the rear output shaft 15, functioning as the input shaft 11 of the rear axle gear system 8. Depending on the position of the connection means of the rear axle gear system 8, torque is therefore transferred to both of the middle driving axle 31 and the rear driving axle 10, or only to the middle driving axle 31.

The front axle configured to steer the vehicle may also be configured as a driving axle, in which case the vehicle comprises at least three driving axles.

The invention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with skill in the art without departing from the scope of the invention as defined in the appended claims.

Claims (12)

1. An axle gear system (8) for distribution of torque between a forward driving axle (9) and a rear driving axle (10) in a motor vehicle (1) , comprising - an input shaft (1 1) , - a forward output shaft (12) configured to transmit torque from the input shaft (11) to the forward driving axle (9), - a rear output shaft (15) configured to transmit torque from the input shaft (11) to the rear driving axle (10), - a connection wheel (16) connected for common rotation with the rear output shaft (15), - a first tapered rolling bearing (19) supporting the connection wheel (16), - a second tapered rolling bearing (20) supporting the input shaft (11) in the connection wheel (16), - a connection means (22) movable between an engaged position in which the connection wheel (16) and the input shaft (11) are connected for common rotation, and a disengaged position in which the connection wheel (16) and the rear output shaft (15) are disconnected, characterised in that said connection means (22) comprises a sleeve (22) arranged around the input shaft (11) , said sleeve (22) being movable along a longitudinal axis (C) of the input shaft (1 1) , wherein said sleeve (22) is provided with internal splines engaging with external splines provided on the input shaft (11).

2. The axle gear system according to claim 1, wherein the internal splines of the sleeve (22) are configured to, in the engaged position, engage on one hand with said external splines provided on the input shaft (11) and on the other hand with external splines provided on the connection wheel (16).

3. The axle gear system according to claim 1 or 2, wherein the sleeve (22) and the connection wheel (16) have end faces (24, 25) provided with teeth (26, 27) configured to engage with each other when the connection means (22) is in the engaged position.

4. The axle gear system according to any one of the preceding claims, further comprising a control device (29) configured to move the connection means (22) between the engaged position and the disengaged position upon receipt of a signal.

5. The axle gear system according to any one of the preceding claims, further comprising a housing (18) in which the connection wheel (16) and the input shaft (11) are supported and in which the connection means (16) is located.

6. The axle gear system according to claim 5, further comprising a third bearing (21) supporting the input shaft (11) in the housing (18).

7. The axle gear system according to any one of the preceding claims, wherein the forward output shaft (12) extends in parallel with the input shaft (11).

8. A driving axle system (7) comprising at least one axle gear system (8) according to any one of the preceding claims, at least one forward driving axle (9) driven by the forward output shaft (12), and at least one rear driving axle (10) driven by the rear output shaft (15).

9. The driving axle system according to claim 8, wherein the driving axle system (7) is a tandem drive system.

10. The driving axle system according to claim 8, comprising at least two of said axle gear systems (8) and at least three driving axles (9, 10, 31) driven by said at least two axle gear systems (8).

11. A motor vehicle (1) comprising a driving axle system (7) according to any one of claims 8-10.

12. The motor vehicle according to claim 11, wherein the motor vehicle (1) is a heavy motor vehicle such as a bus or a truck.