GB2235425A

GB2235425A - An axle drive for a four wheel drive motor vehicle

Info

Publication number: GB2235425A
Application number: GB9015974A
Authority: GB
Inventors: Joachim Horst
Original assignee: Viscodrive GmbH
Current assignee: GKN Viscodrive GmbH
Priority date: 1989-07-25
Filing date: 1990-07-20
Publication date: 1991-03-06
Anticipated expiration: 2010-07-20
Also published as: DE3924520A1; IT9020977A0; GB9015974D0; GB2235425B; FR2650228A1; DE3924520C2; JPH0361123A; IT1243671B; JP2614139B2; IT9020977A1; FR2650228B1; DD296455A5

Abstract

The axle drive comprises a propeller shaft (7), two viscous couplings (21), and switching devices (50, 51, 52, 53, 54, 55; 66, 67, 72, 73, 74, 75) operable to connect or disconnect the outputs of the couplings from roar wheels of the vehicle. During anti-lock braking control the outputs are disconnected to prevent the axles from influencing each other during braking. The switching devices are coupled together to ensure that both adopt the same condition and the unpowered rest condition of each switching device corresponds to the disconnected condition of the outputs from the wheels. <IMAGE>

Description

1 PD/89086GB1 AN AXLE DRIVE This invention is concerned with an axle drive

for a motor vehicle having four wheel drive.

It is known for the wheels of a front axle of a four wheel drive vehicle to be driven through a front axle differential and for the wheels of a rear axle thereof to be driven through a driveline comprising two fluid friction couplings instead of a rear axle differential. Fluid friction (or viscous) couplings are well known and comprise a housing in which a hub is rotatably mounted.

A space between the hub and the housing contains outer plates which are rotationally fast with the housing and inner plates which alternate with the outer plates and are rotationally fast with the hub. The space around the plates contains a viscous fluid which acts to transmit torque between the housing and the hub. The two fluid friction couplings of such a driveline are each arranged between a propeller shaft of the driveline and one of the wheels of the rear axle. The hubs are, normally, mounted for rotation relative to one another in a common housing which is driven by the propeller shaft. The driveline also comprises switching devices operable to connect the hubs to the associated wheels, so that the hubs act as an output of the driveline to transmit torque, or to disconnect the hubs therefrom when drive to the rear wheels is not required.

A prior art example of such an axle drive is described in European Patent Specification No. 0216749, which describes an axle drive in which the torque intended for the respective axle is passed on to the

1 2 associated wheels by two viscous couplings. The advantage of such drives is that the usual differential drive with the necessary bevel gears may be eliminated. Because the coupling hubs are rotatable relative to each other, differential movements on curves betwen the inner and outer wheel are compensated for.

A further development of such an axle drive is described in European Patent Specification No. 0330776 where a torque separating device is arranged in the differential collar. When the brake is actuated and when control of the anti-locking system commences, it is the object of the torque separating device to disconnect the axle driven through the torque splitter from the other axle(s) in respect of torque in order to prevent the axles from influencing each other during braking. The torque separating device described there has a disadvantage in that the two wheels of the associated axle are temporarily in torque connection. Especially in cases where the said axle was previously temporarily subjected to high loads and high torques had to be transmitted, there is a possibility that both viscous couplings representing the axle drive enter the so-called hump mode so that their behaviour is similar to that of a fully locked differential.

West German Patent Specification No. 3317247 also describes a torque splitter in which the two axle drive outputs leading to the wheels are provided with devices which may be connected and disconnected in respect of torque and by means of which the two associated wheels may be disconnected from the axle drive if this is necessary for maintaining the driving stability of the vehicle.

3 The drive variations described above have a disadvantage in that dangerous driving conditions may occur if, due to a technical error, one of the switching devices assumes a condition which differs from that of the other device. Such a condition may arise for example if one actuating means fails. In consequence, there occurs a yaw moment around the rear axle, which adversely affects the driving stability of the vehicle.

It is the object of the invention to provide an axle drive of the said type in which unstable driving conditions cannot occur when establishing a torque connection between the wheels associated with the axle and the drive.

The invention provides an axle drive for a motor vehicle having four wheel drive with the wheels of a front axle thereof driven through a front axle differential and the wheels of a rear axle thereof driven through a driveline comprising a propeller shaft, two fluid friction couplings each arranged between the propeller shaft and one of the wheels of the rear axle, the couplings each comprising a hub acting as an output of the driveline to transmit torque to the wheel associated with the coupling, the hubs being mounted for rotation relative to one another in a common housing, and switching devices operable to connect or disconnect the outputs of the driveline from the associated wheels, wherein the switching devices are coupled together to ensure that both switching devices adopt the same condition, and the unpowered rest condition of each switching device corresponds to the disconnected condition of the outputs from the wheels.

The advantage of the axle drive design in accordance 1 4 with the invention is that a unilateral moment adversely affecting the driving stability of the vehicle cannot occur at one of the wheels and that, if actuating means of a switching device is subject to interference, the axle drive assumes the disconnected condition so that the torque connection between the two associated wheels Is interrupted.

In an advantageous embodiment of the invention, the switching devices comprise a common mechanical switching member movable by an actuating means. The switching member may be a draw key, and the actuating means may be pneumatic, hydraulic or electromagnetic. This design ensures in a simple way that both wheels are disconnected simultaneously by pneumatic, hydraulic or magnetic actuating means.

According to a further embodiment of the invention, it is proposed that the switching devices should each comprise electromagnetic actuating means connected in series. This design ensures that a failure in the electric supply prevents connection of both hubs to their respective wheels.

In a further embodiment of the invention, the switching devices each comprise hydraulic or pneumatic actuating means and the two actuating means can be pressurised through a common pressure channel. This alternative design also ensures that pressure chambers of the actuating means are pressurised with a pressure agent simultaneously and simultaneously depressurised.

There now follows detailed descriptions, to be read with reference to the accompanying drawings, of two illustrative embodiments of the invention.

1 In the drawings:

Figure 1 is a diagram illustrating the drive concept of a motor vehicle incorporating an axle drive in accordance with the invention; Figure 2 is a cross-section through a first embodiment of the axle drive which has a common mechanical switching member; and Figure 3 is a cross-section through a second embodiment of the axle drive which has electromagnetic actuating means.

Figure 1 shows a four wheel drive motor vehicle 1 whose engine 2 is connected to the driven front wheels 6 through a manual gearbox 3 and a front axle differential 4 and front halfshafts 5. In addition, the drive for the rear axle branches off from the front axle differential 4 through a propeller shaft 7. The propeller shaft 7 serves to drive an axle drive 8 which, through two joints 9, 10 at the axle drive end and two wheel joints 11, 12, is in torque connection with the rear wheels 13 through driveshafts 14, 15. Two embodiments of the axle drive 8 are explained in more detail in connection with Figures 2 and 3.

The axle drives 8 illustrated in Figures 2 and 3 each comprise an axle drive housing 16 supporting a bevel gear 17 with a propeller shaft 7, which has established an operating connection with a crown gear 18, with the crown gear 18, by means of threaded bolts 19, being non-rotatingly connected to the common coupling housing 20 of two fluid friction couplings 21 which are each arranged between the propeller shaft 7 and one of the 6 wheels 13 of the rear axle. The couplings each comprise a coupling hub 22, 23. The hubs 22, 23 are rotatingly supported in the coupling housing 20, with the coupling housing 20 being non-rotatingly connected to sets of outer plates 24 and with the coupling hubs 22, 23 being associated with two sets of inner plates 25, 26 and with the outer plates 24 being arranged so as to alternate with the inner plates 25, 26. Viscous fluid is contained in the spaces occupied by the plates 24, 25, 26. The hubs 22, 23 each act as an output of the driveline to transmit torque to the wheel 13 associated with the coupling.

The coupling hubs 22, 23 are sealed against the coupling housing 20 by seals 27, 28. The coupling housing 20, in turn, is received in the axle drive housing 16 on roller bearings 29, 30. Furthermore, the coupling housing 20 rotatably supports two output shafts 31, 32 connecting through joints 9 and 10 respectively to the input shafts 14, 15 of the rear wheels 13. The joints 9, 10 each consist of an outer joint member 33, 34 and an inner joint member 35, 36 receiving a ball cage 37, 38 accommodating the joint balls 30, 40. The input shafts 14, 15 of the rear wheels, through teeth 41, 42 engage the corresponding teeth 43, 44 of the inner joint member 35, 36. The parts 34, 36, 38, 40, 42 and 44 are not visible in Figure 2 but appear in Figure 3. A boot 45, 46 on the input shafts 14, 15 seals the joint 9, 10 which is open at one end.

The upper half of Figure 2 shows the connected condition and the lower half the disconnected condition of the rear wheels 13. The axle drive 8 also comprises switching devices operable to connect or disconnect the hubs (outputs of the driveline) 22, 23 from the 1 t i 7 associated wheels 13. The ends 47, 48 of the output shafts 31, 32 engage the coupling hubs 22, 23 and are provided with recesses 49 receiving spherical supporting rings 51 axially connected to a draw key or actuating tappet 50 of the switching devices. In the region of the recesses 49, the output shafts 31, 32 are provided with radial through- bores 52 holding locking members 53. The actuating tappet 50 is guided in one of the output shafts (in this case, in output shaft 31) and at the outwardly pointing end of the output shaft 31 it is axially connected to a membrane 54. The membrane 54 and the seal 76 outwardly seal a pressure chamber 55 which may be pressurised through a filling sleeve 77. The actuating tappet 50 is provided with a spring 56 which loads the actuating tappet 50 with the spherical supporting rings 51 into a releasing position for the locking members 53 so that, in this spring- loaded condition, the locking members 53 may escape radially outwardly. Thus, the switching devices comprise a common mechanical switching member, in the form of the tappet 50, and hence are coupled together to ensure that both switching devices adopt the same condition. The tappet 50 is movable by an actuating means, provided by the membrane 54, which is in this case pneumatic. However, if desired, hydraulic actuating means may be used. Each switching device may alternatively have its own hydraulic or pneumatic actuating means and the two actuating means can be pressurised through a common pressure channel so that their simultaneous operation is ensured. The unpowered rest condition of the switching devices corresponds to the disconnected condition of the outputs from the wheels 13, i.e. when the chamber 55 is depressurised, the spring 56 ensures disconnection of the drive.

The through-bores 52 of the coupling hubs 22, 23 are 1 8 provided with axially extending grooves 57 which, with the assistance of the spherical rings 51, hold the locking members 53 in order to establish a torque connection between the coupling hub 22, 23 and the output shafts 31, 32.

In the axle drive 8 shown in Figure 3, the switching devices have electromagnetic actuating means which are connected in series. Operation of the switching devices connects and disconnects the output shafts 31, 32 relative to the joints 9, 10 of the input shafts 14, 15, with the ends 47, 48 of the output shafts 31, 32 engaging the coupling hubs 22, 23. As the actuating means are connected in series, simultaneous connection and disconnection of the input shafts 14, 15 is ensured. The is lower half of the figure shows the connected condition and the upper half the disconnected condition of the rear wheels 13. At their second ends 58, 59, the output shafts 31, 32 are provided with output discs 60, 61 with teeth 62, 63 and with a radially positioned bearing part 64, 65 on which adjusting discs 66, 67 are supported and axially movably arranged on several circumferentially distributed bearing pins 68, 69. The adjusting discs 66, 67, with corresponding teeth 70, 71, engage the teeth 62, 63 of the cylindrical output discs 60, 61 in the connected condition and transmit the input torques on to the input shafts 14, 15. In this case, the actuating means is provided by annular magnets 72, 73 firmly connected to the axle drive housing 16. The magnets 72, 73 are energised to pull the adjusting discs 66, 67 axially in the direction of the viscous coupling 21, so that secure engagement of the teeth 62, 63 and 70, 71 is ensured. When the voltage is switched off, or in the event of a power failure, the rear wheels 13 are returned into the disconnected condition by spring washers 74, 75 J 1 9 which, on the one hand, are attached to the adjusting discs 66, 67 and, on the other hand, to the outer joint members 33, 34. The bearing pins 68, 69 are secured in the outer joint member 33, 34.

1

Claims

1. An axle drive for a motor vehicle having four wheel drive with the wheels of a front axle thereof driven through a front axle differential and the wheels of a rear axle thereof driven through a driveline comprising a propeller shaft, two fluid friction couplings each arranged between the propeller shaft and one of the wheels of the rear axle, the couplings each comprising a hub acting as an output of the driveline to transmit torque to the wheel associated with the coupling, the hubs being mounted for rotation relative to one another in a common housing, and switching devices operable to connect or disconnect the outputs of the driveline from the associated wheels, wherein the switching devices are coupled together to ensure that both switching devices adopt the same condition, and the unpowered rest condition of each switching device corresponds to the disconnected condition of the outputs from the wheels.

2. An axle drive according to Claim 1, wherein the switching devices comprise a common mechanical switching member movable by actuating means.

3. An axle drive according to Claim 2, wherein the switching member is a draw key.

4. A axle- drive according to Claim 1, wherein the switching devices each comprise electromagnetic actuating means and the two electromagnetic actuating means are connected in series.

5. An axle drive according to any one of Claims 1 to 3, wherein the switching devices each comprise hydraulic or x 1 pneumatic actuating means and the two actuating means can be pressurised through a common pressure channel.

6. An axle drive substantially as hereinbefore described with reference to and as shown in Figure 2 or Figure 3 of the accompanying drawings.

Published 1991 at 17he Patent Office. State House. 66/71 High Holbom. LondonWC I R47P. Further copies Tray be obtained from Sales Branch, Unit 6, Nine Milc Point. Cwmfelinfach. Cross Keys, NcwporL NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent,