A LIMITED SLIP CLUTCH ARRANGEMENT

Technical Field

The present invention relates to a limited slip clutch arrangement for a road vehicle, the arrangement having an ingoing shaft, an outgoing shaft, alternate clutch plates connected to the two shafts, and actuators for engaging the clutch plates.

Background of the Invention In a road vehicle it is advantageous to be able to freely distribute drive torque to different wheels m order to enhance the driving characteristics of the vehicle

Limited slip clutch arrangements of the kind defined above can be used to distribute power between front and rear axles of four wheel drive vehicles or between drive wheels on the same axle

If a drive axle or a drive wheel is to be provided with a positive torque in a certain situation, such a limited slip clutch arrangement can be supplemented with a mechanical gear device in order to gear-up or increase the outgoing rotation speed from the limited slip clutch arrangement by for example 10%.

Many examples of such mechanical gear devices are for example disclosed m EP-B-O 546 733 Problems with such mechanical gear devices are for example costs, space requirement, and weight.

The main object of the invention is accordingly to attain the desired gear-up or rotation speed increase m a limited slip clutch arrangement m a cheaper and more space- and weight-effective way The Invention

This lib according to the invention attained m that the two shafts are eccentric m relation to each other - but parallel - and m that the actuators are so positioned in relation to the clutch plates that a desired gear-up or

gear-down between the two shafts is obtained at clutch engagement by means of selected actuators.

In an arrangement according to the invention the two shafts are accordingly eccentric in relation to each other, and at engagement the clutch plates connected to the respective shafts are not evenly loaded, but are loaded m a more concentrated zone, so that they obtain different resulting friction radii.

If a fixed eccentricity is desired, the two shafts may be ]ournaled m a housing, also containing the actuators for selectively applying its respective force at different desired locations.

If on the other hand it is desired to have the possibility to vary the eccentricity, either stepwise or continuously, the ingoing shaft may be journaled m a housing and the outgoing shaft eccentrically journaled m a control drum, which may be journaled coaxially with the ingoing shaft, may be provided with the actuators and may be rotated for accomplishing a desired eccentricity between the two shafts.

An arrangement according to the invention may be used m different ways in a vehicle.

The arrangement may for examp] e be mounted between the front and rear axles m a front wheel drive vehicle without center differential Herein the eccentricity may be variable, for example to provide a gear up ratio of l/l.l or a gear ratio of 1/1. The gear ratio 1/1 may be used under normal driving conditions, whereas the gear-up ratio of 3/1.1 may be used m a driving situation where a guaranteed rear axle drive is preferred.

In another example, an arrangement according to the invention is mounted between a crown wheel and each drive axle or half -axle of a rear axle without differential. Hereby a torque distribution between the front and rear

axles as well as between right and left rear wheels will be obtained

In a further example, where a free torque distribution between the two wheels on a front or rear drive axle is desired, an arrangement according to the invention may be mounted between a differential case and a drive axle or half -axle of a driven front or rear axle. The vehicle can be with or without four wheel drive

In the vehicle, the drive axle has to be coaxial with the differential case m order to transmit the drive torque to the wheel This means that extra measures to remove the eccentricity, caused by the arrangement according to the invention, have to be taken

In a first alternative, a second clutch arrangement of the same kind as the arrangement according to the invention and connected thereto is used to make the drive axle coaxial with the differential case

In a second alternative, a cycloidal speed reducing gear arrangement connected to the arrangement according to the invention ±s used to make the drive axle coaxial with the differential case

Brief Description of the Drawings

The invention will be described ]n further detail below under reference to the accompanying drawings, ±n which

Fig l is a schemacical view of a hydraulic circuit for a four-wheel drive system according to the prior art,

Fig 2 is a schematical sectional view through a first embodiment of a limited slip clutch according to the invention,

Fig 3 is a section along Lhe line III-III m Fig 2, Fig 4 is a schematical sectional view through a second embodiment of a limited slip clutch according to the invention, Fig 5 is a section along the line V-V m Fig 4,

Fig 6 is a schematical sectional view through a third embodiment of a limited slip clutch according to the invention,

Fig 7 is a section along the line VII-VII in Fig 6, Fig 8 is a sectional view through a fourth embodiment of a limited slip clutch according to the invention, and Fig 9 is a section along the line IX-IX m Fig 8. Detailed Description of Different Embodiments A simple all -wheel drive system for a road vehicle is shown m Fig 1 as an example of the environment for a limited slip clutch arrangement according to the invention. In this system a limited slip clutch 1 is incorporated m a drive tram between different driven axles m the vehicle, preferably a front axle and a rear axle, both with two wheels. Alternatively, the clutch 1 may be incorporated m other portions of the vehicle drive tram, as will be further discussed below. The clutch 1 is very schematically depicted and is known per se. It is preferably a multi- plate clutch. The clutch 1 is controlled by pistons m hydraulic cylinders 2. The hydraulic system to which the cylinders 2 belong may have the following general layout. Oil is transferred from an oil reservoir 3 to a spring-biassed accumulator 4 by means of a pump 5 driven by an electric motor 6 controlled from an ECU 7. The pressurized oil from the accumulator 4 can reach the clutch cylinders 2 via a control valve 8, which sets the pressure of the oil under the control from the ECU 7. After operation, oil can be transferred from the cylinders 2 back to the oil reservoir 3

The design and function of the limited slip clutch 1 is conventional m the art and is not described m detail here,- for a further description reference may for example be made to WO-A-97/04245, where also a more complex hydraulic system is shown and described.

Under certain driving conditions for a vehicle equipped with one or more limited slip clutches, it may be desirable to be able to gear up (or m other words to increase the rotation speed of) the outgoing shaft from the limited slip clutch by for example about 10%. This is for example the case when it is imperative m certain situations to provide an axle or a wheel with a positive moment. It is known m the art to make use of a mechanical gear mechanism for this purpose. The present invention aims at providing this gear up (or down) m a simpler way than by means of a mechanical gear mechanism.

A first embodiment of a limited slip clutch according to the invention is very schematically shown in Figs 2 and 3. An ingoing shaft 11 is journaled for rotation in a housing 12. An outgoing shaft 13 is also journaled for rotation m the housing 12. However, its axis is eccentric m relation to that of the ingoing shaft 11 (but parallel therewith) . As appears from Figs 2 and 3, the eccentricity is m the plane of Fig 2.

The ingoing shaft 11 is provided with inner or inwardly directed clutch plates and the outgoing shaft 13 with alternate outer or outwardly directed clutch plates, the two sets of clutch plates together forming a multi- plate limited slip clutch 14.

The clutch 14 may be engaged by means of pistons 15 m hydraulic cylinders. The number of cylinders is four m the shown case, and they are evenly distributed around the clutch 14. Other numbers and distributions are possible within the scope of the appended claims. The piston 15 m its cylinder is defined as an actuator. The four actuators are marked A, B, C, and D m Fig 3. Only certain of the actuators are actuated (by pressurized oil) m order to obtain a desired result with regard to the engagement of the clutch 14.

The actuators are here hydraulic, but they can equally well be for example electromechanical or pneumatic

Due to the shown eccentricity between the ingoing shaft 11 and the outgoing shaft 13, an engagement of the clutch by means of the actuator A will mean that the rotation speed of the outgoing shaft 13 will be higher than the ingoing shaft 11 or geared-up due to the larger friction radius for the ingoing shaft than the outgoing shaft Correspondingly, a gear-down effect from the ingoing shaft 11 to the outgoing shaft 13 will result, if the clutch 14 is engaged by the actuator B.

The magnitude of the gear-up or gear-down effect depends on the eccentricity e m relation to the friction radius .

If the same rotation speed for the outgoing shaft 13 as for the ingoing shaft 11 is desired, one or both of actuators C and D may be used, whereby the same friction radius for both shafts is obtained. In the first embodiment according to Figs 2 and 3 the eccentricity is fixed, which means that only a predetermined gear-up or gear-down effect may be obtained If a variable gear-up or gear-down effect or m other words a variable eccentricity is desired, a second embodiment according to Figs 4 and 5 may be used

The following elements from the first embodiment are provided with the same reference numera] s m the second embodiment, even if they are not identical the ingoing shaft 11, the housing 12, the outgoing shaft 13, the multi- plate clutch 14, and the pjstons 15

In order to obtain a variable eccentricity between the two shafts 11 and 13, the pistons 15 may be arranged _ n a control drum or control eccentric 16, which is rotatably journaled m the housing 12 coaxially with the ingoing shaft 1] The outgoing shaft 13 is rotatably ]ournaled m

the control drum 16 with its axis eccentric in relation to the axis of the ingoing shaft 11. By means of a control actuator (not shown) the control drum 16 may be rotated, as is indicated by arrows 17 m Fig 5, to the desired extent for accomplishing a desired eccentricity between the axes of two shafts 11 and 13. This control actuator may for example be hydraulic, electromechanical, or pneumatic. The desired gear-up or gear-down effect is then accomplished m the same manner as has been described above for the first embodiment of Figs 2 and 3.

As the control eccentric 16 may be rotatable to such an extent that actuators A and B come to the positions shown m Fig 5 of actuators C and D, the latter actuators may possibly be omitted from the design. Even one of the actuators A and B may be omitted - without losing the ability for the device to obtain the desired gear-up or gear-down effect - provided that the control drum 16 may be rotated to the necessary extent.

There are many possibilities to use the limited slip clutch according to the invention m a road vehicle. It may for example be mounted between the front and rear axles m a front wheel drive vehicle without center differential The clutch with eccentricity can be of the variable kind with two positions, namely with a gear ratio of l/l or with a gear-up ratio of about l/l 1 The first position is used under the majority of driving conditions, whereas the second one is used when the driving situation requires a more guaranteed rear wheel drive.

Another possibility is to arrange two clutches according to the invention between the crown wheel in the rear axle without differential and the respective drive axles (half axles) . In this way a torque distribution between front and rear axles as well as between right and left rear wheels will be obtained

Further, a limited slip clutch according to the invention may be arranged between the differential and one drive shaft of a front or rear axle of a road vehicle, or more precisely between the differential case (connected to the ring gear of the differential) and one drive shaft. The purpose of such an arrangement, which may be applicable also m a vehicle without four-wheel drive, is to allow a free torque distribution between the left and right wheel on the axle. It is suggested to make use of a limited slip clutch with fixed eccentricity of the kind shown m Figs 2 and 3. However, as the drive shaft has to have the same centerlme as the differential housing, extra measures have to be taken. Two embodiments for obtaining this desired result are shown in Figs 6 and 7 and m Figs 8 and 9, respectively.

The first of these two embodiments is shown m Figs 6 and 7 A drive shaft 21, extending out of an ordinary differential 22, is rotatably journaled m a housing 20 A case sleeve 23, which is also rotatably journalled m the housing 20, is connected to a differential case m the differential 22 As is known for a person skilled m the art, the differential case is attached to a ring gear driven by a drive pinion on a cardan shaft and contains gear wheels, which accomplish the differential effect and are connected to the outgoing drive shafts, of which drive shaft 21 is one

There is further a transmission sleeve 24, which is eccentrically journaled for rotation m the housing 20. In the same manner as has been described above with reference to Figs 2 and 3, there is a first multi-plate limited slip clutch 25 arranged between the case sleeve 23 and the transmission sleeve 24. This first clutch 25 may be engaged by pistons 26, which in their cylinders form actuators, evenly distributed around the clutch 25 and called A, B, C, and D m Fig 7. In the same manner, there is a second

multi-plate limited slip clutch 27 between the transmission sleeve 24 and a flange arrangement 21' on the drive shaft 21. This second clutch 27 may be engaged by pistons 28, corresponding to the pistons 26. In operation, the two clutches are engaged by the respective pistons 26 and 28 m a similar way as has been described above. The result is a gear-up or gear-down of the drive shaft 21 m relation to the other drive shaft on the same axle but also that the outgoing drive shaft 21 is coaxial with the outgoing shaft from the differential 22.

The second of these embodiments is shown m Figs 8 and 9. In this embodiment, use is only made of one eccentric multi-plate limited slip clutch for obtaining the desired gear-up or gear-down, whereas a cycloidal speed reducing gear arrangement is utilized for removing the offset effect from the eccentric clutch

A drive shaft 30 to the right m Fig 8 is to be connected to a planetary gear m an ordinary vehicle differential, whereas a case sleeve 31 is to be connected to the differential case of the differential A transmission sleeve 32 is eccentric in relation to the drive shaft and is rotatably journaled m a housing 33, through which the drive shaft 30 extends. A rotary motion is imparted from the case sleeve 31 to the transmission sleeve 32 without any gear-up or gear-down by means of a cycloidal speed reducing gear arrangement 34, whose design is not further described but is understood from the drawing by a person well skilled m the art. There is a multi-plate limited slip clutch 35 between the drive shaft 30 and the eccentric transmission sleeve 32 There are actuators distributed around the clutch 35, as has been described above m relation to previous embodiments A full arrow 36 indicates where actuation may occur for accomplishing a gear-up and a dotted arrow 37 where actuation may occur for accomplishing a gear-down