GB2094730A

GB2094730A - Power-assisted steering device

Info

Publication number: GB2094730A
Application number: GB8206843A
Authority: GB
Original assignee: SWF Spezialfabrik fuer Autozubehoer Gustav Rau GmbH
Current assignee: SWF Auto Electric GmbH
Priority date: 1981-03-13
Filing date: 1982-03-09
Publication date: 1982-09-22
Also published as: FR2501610A1; IT1150651B; IT8220063A0; DE3109622A1

Abstract

A power-assisted steering device for a motor vehicle comprises an auxiliary drive (16) and two friction clutches, the input elements (70, 71) of which are driven by the auxiliary drive (16) in opposite directions. The friction clutches each have at least one output element (66) which may be coupled with one or other input element (70, 71). The two clutches are disk clutches so that the available friction surfaces (67, 72) are planar and their elements (66, 70, 71) are axially displaceable relative to each other. <IMAGE>

Description

SPECIFICATION Power-assisted steering device This invention refers to a power-assisted steering device for a motor vehicle of the kind comprising an auxiliary drive and two friction clutches the input elements of which are driven by the auxiliary drive in opposite directions and which friction clutches have at least one output element which may be coupled with one or other input element.

Currently, many motor vehicles are equipped with so-called power-assisted steering devices which intensify the torque manually initiated via the steering wheel to such a high value that, on the occasion of difficult steering manoeuvres such as parking, only a low manual power is necessary. The auxiliary power necessaryforthe amplfication is gained from different systems. There are, for example, hydraulic power-assisted steering devices which have to include a pump for the working medium. It is also a disadvantage of a hydraulic power-assisted steering device that the hydraulic system has to be absoiutely closed so that neither the oil can leak nor particles of dirt can penetrate into it. The system becomes expensive and complicated by the measures necessark for its sealing.

Power-assisted steering devices are also known in which an electric motor serves as an auxiliary drive.

The electric motor drives a bevel pinion mating with two bevel wheels which thus rotate in opposite directions. A clutch drum rotates with each bevel wheel. The steering shaft has an upper and a lower part connected by a torque rod and which parts can therefore be twisted relative to each other. On each part of the steering shaft a clutch support is arranged in a manner protected against twisting. Atotal of four clutch shoes is provided; each of these clutch shoes is supported on the one and also on the other clutch support. The bearing is designed in such a way that, when the upper part of the steering shaft is twisted relative to the lower part and thus the upper clutch support relative to the lower clutch support one pair of shoes is moved outwardly and pressed against the respective clutch drum.The direction of rotation of this drum corresponds to that in which the steering shaft has been rotated. Thus an additional power can be transmitted by the drum via the brake shoes and the lower clutch support to the lower part of the steering column.

An electric motor provides the auxiliary drive for the known power-assisted steering device. The input elements of the two friction clutches are formed by the bevel wheels or by the two clutch drums. The lower clutch support has to be regarded as the output element.

The power-assisted steering device briefly described involves the disadvantage that the curvature of the clutch shoes can only be inaccurately adapted to the curvature of the clutch drums. An adaptation of the curvatures will, indeed, be effected with increasing service life. However the friction surface will change continuously until the adaptation has been effected completely, so that also the amplification varies. In addition to the changing amplification of a device during its service life the amplification can also vary from one device to another, because the amplification magnitude will depend on how well the diameter of the clutch shoes has been adapted to the diameter of the clutch drums of the particular embodiment.

Starting from the prior art described, the invention is based on the problem of further developing a power-assisted steering device of the kind referred to in such a way that, during the service life of the device, the amplification remains as constant as possible and does not substantially differ from one device to another. In this connection it has also to be taken into consideration that the device has to be solid, reliable and space-saving.

According to the invention in its broadest aspect a power-assisted steering device of the kind referred to is characterised in that the two clutches are disk clutches, so that the available friction surfaces are planar and that the elements are axially displaceable relative to each other. The friction surfaces of a power-assisted steering device according to the invention resting against each other during a powerassisted steering manoeuvre are of planar configuration. Plane surfaces can be produced very accurately, so that the friction surfaces rest against each other their entire area from the very beginning. The elements can be displaced relative to each other relatively easily, so that also the design of the device becomes iess complicated and can be made solid, space-saving and reliable.

Advantageous developments of the invention will now be referred to. The output element can be axially displaced if both friction clutches have one output element in common, or if several output elements are used, and each output of the two clutches may be coupled with a drive member of the steering shaft via a screw joint and with a driven member of the steering shaft via a push joint, whereby drive member and driven member may be twisted relative to each other against the force of of a spring. Thereby the joints can advantageously be developed on two catch plates of which one may be connected with the drive member of the steering shaft in a manner protected against twisting and displacement and the other with the driven member.

An advantageous arrangement for the catch plates is to position them in an axial direction between the input elements of the two clutches.

The drive member and the driven member of the steering shaft may be twisted relative to each other against the force of a spring. This is advantageously achieved in that in the direction of rotation the clutch plates are coupled with each other via at least one spring element. Of course this coupling is effected in the one direction of rotation and also in the other direction of rotation of the driving catch plate. When a helical spring is arranged in such a way that it extends with its longitudinal direction perpendicularly to the axis of rotation and perpendicularly to the radius beam of the catch plates running through their centre, this has the effect that, with a relatively weak spring, a sufficiently great torque is necessary for twisting the two catch plates relative to each other.By the fact that the helical spring is positioned between the ribs of the catch plates, which ribs are provided on each catch plate and are directed towards the respective other catch plate, it is achieved in a very simple manner that each end of the helical spring may be acted upon by both catch plates. In an advantageous embodiment a cage is formed for each helical spring by an appropriate arrangement of the ribs of the one catch plate on it.

The helical springs can captively be placed into these cages, when they are mounted. Each cage has apertures or gaps through which the other catch plate with its ribs can act upon the ends of each helical spring.

In order to exclude the danger that, due to spring fracture or too great steering forces the two catch plates can be twisted relative to each other at too great an amount, firm stops are provided between the driven member and the drive member of the steering shaft which limit the angle by which the two members may be twisted relative to each other. As soon as the maximum permissible twisting angle has been reached the two members are firmly coupled and taken along. The stops between the driven member and the drive member of the steering shaft are suitably also arranged on the catch plates or on the ribs of the catch plates.

Each output element of the two clutches may be coupled with a drive member of the steering shaft via a screw joint and with a driven member via a push joint. The joints may be arranged between the catch plates and the output element or output elements of the clutches. For the joints, slots are provided on the catch plates, advantageously in the ribs of the catch plates. In order to design the joints as simply as possible two correlated slots each are axially positioned on the same level and radially one behind the other and an output element engages in both slots with a single pin. This single pin is part of both joints. If several pairs of slots are provided on the catch plates, the output element has, of course, also several pins. However only a single pin is necessary for one pair of slots.

Whereas in earlier embodiments a screw joint and a push joint are provided for the adjustment of an output element, in an advantageous embodiment each output element is adjustable via a lever mechanism. Therefore it is no longer necessary to form the steering shaft of two separate parts which are only linked with each other by springs. Now a self-resetting movement of the steering shaft per pendicuiarly to its longitudinal direction can instead be used as an initiating movement for the entire power-assisted steering device. Thereby the selfresettting is advantageously achieved in that the adjustment of the output element of the friction clutches is effected against the force of a spring element. Of course this spring element need not directly act upon the output element.It can act upon any part which has to be moved before a steering manoeuvre can be assisted by the power-assisted steering device.

A transverse movement can be advantageously achieved in that the steering shaft has two parts connected with each other by a cardan joint and that the part carrying the steering pinion may be moved perpendicularly to its longitudinal direction. It is true that the steering shaft of this embodiment consists of two parts similar to the ones including screw and push joints. But now the two parts are directly coupled with each other via the cardan joint in a manner protected against twisting relative to each other. However the cardan joint permits the two parts to swivel towards each other in such a way that they form an angle. Thereby the transversal movement can be very small, because only a small axial movement of an output element is necessary and because the transverse movement can be transmitted via the lever mechanism.Therefore it does not result either in a bad feeling of steering or in a too great steering play. The design might be even simpler, if the steering shaft is movable as a whole. It is thereby conceivable to displace the steering shaft transversely over its entire length orto swivel it round an axle which stands perpendicularly on the steering shaft anywhere between the steering wheel and the steering pinion. The transverse movement can for example be made possible by developing a rolling bearing.

A further advantageous version of a powerassisted steering device according to the invention is that it includes an adjusting plate which is coupled with the lever mechanism and the movement of the adjusting plate may be derived from the movement the steering shaft can carry out perpendicularly to its longitudinal direction. This version can be developed advantageously. Thus, the parts of the power-assisted steering device, which are to be adjusted during a steering manoeuvre, can be reset in a simple manner in that the adjuting plate is fixed in a central position by a locking device including a spring element. If the adjusting plate is moved from the central position to one or other side, the spring element is prestressed more and attempts to return the adjusting plate into its rest position.This can be effected during a steering manoeuvre, when no outside torque is transmitted to the steering shaft any more through the steering wheel. As it is a matter of routine the locking device can include another locking cam and a locking element, for example a locking ball or a locking pin. Because a steering manoeuvre has, above all, to be intensified by the power-assisted steering device, when, during a parking manoeuvre or other slow movements of the vehicle, a great power is necessary to turn the wheels, it can be provided that the adjusting plate is lockable upon a particular vehicle speed. Thus, beginning with this vehicle speed, a power-assisted steering is no longer possible.

A further advantageous development of the invention is that the lever mechanism is realised by a lever which is swivellably mounted on a firm axle and coupled with each output element. Thus the lever along effects the connection between the adjusting plate and the output elements or the output element.

When the lever is developed as an angle lever a perpendicular or substantially perpendicular movement of the adjusting plate relative to the steering shaft can in a particulary simple way be transformed in a movement carried out approximately in the longitudinal direction or parallel to the longitudinal direction of the steering shaft. The coupling between the lever and the output element is advantageously achieved in that the output element is provided with an annular groove which is positioned in a plane on which the axial direction of the output element stands perpendicularly and in which annular groove the lever coupled with the output element engages.

As is known from the prior art a turn of the input elements of the two friction clutches can be effected in that an angular pinion is caused to mate with the two input elements developed as bevel wheels. If, in such a drive of the two input elements, the output element were arranged between the two input elements, seen in the radial direction, the friction surfaces would be restricted to the remaining space within the gear teeth of the input elements. It is therefore of advantage, in particular when a drive including a bevel pinion is concerned, when the output element or the output elements are not positioned between the gear teeth of the two input elements, but in the axial direction beyond the two gear teeth. Thus the output element can be coupled with the input elements and the lever mechanism.

It may be provided that the two friction clutches of a power-assisted steering device with lever mechanism be seated on a solely rotatable member of the steering shaft. For example this is possible, when the steering shaft consists of at least two parts which are connected via a cardan joint. Then the two friction clutches can be arranged on the part which can solely carry out a rotation movement, whereas the lever mechanism is controlled by the other part which is swivellable, too.

The output element of the friction clutches can directly exert a torque onto the steering shaft. It is, however, also of advantage, when a separate assistance shaft may be driven by the output element of the friction clutches, which assistance shaft is inde pendentofthe steering shaft, and may be brought into gear with the rack of a steering gear. On this assistance shaft also the two friction clutches can be positioned. Then the steering shaft can be built up in one piece.

In order to achieve a design as space-saving as possible it may be provided that the additional motor serving as auxiliary drive, preferably an electric motor, be seated on the steering shaft. Then the motor speed is preferably reduced by a planetary gear. The output of the planetary gear can advantageously be coupled with the two input elements of the friction clutches in various ways.

Embodiments of the invention will now be de scribe by way of example with reference to the accompanying drawings, in which: Figure 1 shows a first embodiment in which the output element is connected with a drive member of the steering shaft via a screw joint and with a driven member of the steering shaft via a push joint, Figure 2 shows a view of the embodiment of Figure 1 in which several parts have been omitted and the coupling of the two catch plates on the drive member and on the driven member of the steering shaft can be seen especially clearly, Figure 3 shows a partial view of Figure 2 seen in the direction of arrow A, Figure 4shows a second embodiment in which the output element of the friction clutches is adjusted via a lever, Figure 5 shows a section taken on the line V - V of Figure 4, Figure 6 shows a section taken on the line VI - VI of Figure 4, Figure 7 shows a third embodiment which is built up similarly to that of Figures 1 to 3, in which the electric motor is, however, supported on the steering column, Figure 8 shows a further embodiment with the electric motor similarly arranged to that of Figure 7, however the output element being controlled via a lever and Figure 9 shows the arrangement of a powerassisted steering device according to the invention in a motor vehicle wherein the motor vehicle engine serves as an accessory drive for the power-assisted steering device.

In the embodiment of Figures 1 to 3 the motor shaft 15 of the electric motor 16 carries a worm 17 which mates with a worm wheel 18. This worm wheel 18 is mounted on a common shaft 20 together with a toothed wheel 19. Between the toothed wheel 19 and the worm wheel 18 an overrunning device is built in. As can be seen especially clearly from Figure 2 beside the shaft 20 a second shaft 22 is arranged in the housing 23 in which the piece parts of the power-assisted steering device are accommodated.

A second toothed wheel 24 is mounted on the shaft 22 at a different level from the toothed wheel 19. The toothed wheel 24 is driven by the toothed wheel 19.

Thus the toothed wheels 19 and 24 rotate in opposite directions.

The steering shaft 30 having an upper drive member 31 and a lower driven member 32 extends in the housing 23 in parallel to the shafts 20 and 22.

The drive member 31 is supported on a ball bearing 33 which is arranged on a cylindrical stud 34 of the cover 35 of the housing 23 which cylindrical stud projects to the inside and in an axial direction is secured by a spring lock washer 36. The bearing of the driven member 32 which, after a small interspace, directly follows the drive member 31 and is flush with it, is effected by a needle bearing 38 positioned between the walls of the housing pot 37 and the end of the driven member 32 projecting into the pot and a ball bearing 39 which is held in a stud 40 of the housing 23 in the same way as the ball bearing 33 is in the stud 34. Between the needle bearing 38 and the ball bearing 39 the driven member 32 is developed as steering pinion, which mates with the rack 42.The engagement between the steering pinion and the rack 42 is developed free from play by means of a suitable device 43.

A catch plate, 50 and 51 respectively, is secured in a manner protected against twisting and displacement on the end of the driven member 32 and the drive member 31 of the steering shaft facing the respective other member. For this purpose each catch plate is provided with a collar surrounding the respective member 31 or 32, which collar is provided with two opposite bores which are flush with a bore in the respective member 31 or 32. Through the bores being flush a pin 53 is inserted in each, which causes a firm connection between the catch plate and the driven member 32 or the drive member 31.

On the sides of the catch plates 50 and 51 facing each other ribs are formed the height of which is only slightly smaller than the spacing between the two platens. Thus the ribs 54 and 55 on the catch plate 50 and the rib 56 on the catch plate 51 overlap in the axial direction. In addition they are arranged on concentric circles. Thereby the rib 54 can be regarded as a ring formed on the circumference of the catch plate 50 which ring, at three points having the same angle distance from one another is interrupted by a slot 57 extending diagonally to the axial direction. Between the slots 57 the respective inner rim of the ring 54 is staggered backwards over a particular sector of dial. The thus created recess is limited by the steps 58 in the circumferential direction.The ribs 55 are the respective individual ring segments extending over a sector of dial which corresponds approximately to the sector of dial in which the inner rim of the angle 54 is staggered backwards. A stop 59 attached on each end of a rib 55 and pointing to the rim 54 has the same function as a step 58. The front faces of a cage 60 are namely formed by the stops 59 and the steps 58, whilst the ribs 55 and the ring 54 are the sides of this cage in which a helical spring 61 is inserted. There is an interspace between the stops 59 and the steps 58 into which engages a rib 56 of-the catch plate 51.

Thereby the length of the ribs 56 has been selected in such a way that, when the catch plates 50 and 51 are not twisted relative to each other, each end of a screw spring 61 acts upon a stop 59, a step 58 and a rib 56. Like the ring 54 the ribs 56 extending from cage to cage are in their centre interrupted by a slot 65. This slot extends, however, in the axial direction.

When the two catch plates 50 and 51 are not twisted relative to each other, the slots 57 and 65 are aligned with one another in such a way that, seen in the circumferential direction, the slot 57 has in both directions approximately the same distance from the slot 65.

The catch plates 50 and 51 are surrounded by a friction ring 66 which on its top side and underside is provided with a friction lining 67 in each case. In three points having the same angular distance from one another a pin 68 is attached on the friction ring, which pin points radially to the inside. This pin penetrates a slot 57 and a slot 65. Two ball bearings 69 are fastened on it of which one is located in the slot 57 and the other in the slot 65. Above and below the catch plates 50 and 51 and the friction ring 66 a toothed wheel 70 or 71 is provided which is concentrically arranged to the steering shaft 30 like the catch plates and the friction ring. These two toothed wheels form the input elements of two uric'ion clutches, whose output element is the friction ring 66.Due to the fact that in the present example the toothed wheels are made of plastics material, on each of them a metal ring 72 is fixed opposite to the friction linings of the friction ring 66. The upper toothed wheel 70 mates with the toothed wheel 24, the lower toothed wheel 71 with the toothed wheel 19. The housing 23 and its cover 35 respectively and each of the two toothed wheels 70 and 71 are designed in such a way that between the housing and the respective toothed wheel a kind of shoulder ball bearing with the balls 73 is created. Thereby the shoulder is located on the toothed wheel in question.

By this type of bearing each toothed wheel 70 and 71 is secured in a radial direction and in one axial direction. In the other axial direction they are secured by balls 74 which are in a cage 75 and, as in a deep-groove ball bearing, can run in grooves developed on the toothed wheels.

In order to seal the space well in which the friction linings 67 are accommodated, rubber gaskets 76 are provided.

When a particular steering power is exceeded the drive member 31 and the driven member 32 of the steering shaft of the embodiment described are twisted relative to each other and thus the two catch plates 50 and 51. The magnitude of the steering power at which this is caused is predetermined by the prestress of the helical springs 61. Together with the catch plate 50 also the slot 57 is twisted relative to the slot 65, so that depending on the direction of the steering turn the friction ring guided in the slots 57 and 65 is axially displaced to the top or to the bottom, pressed against the steering wheel 70 or 71 and frictionally connected with it by the friction forces.Thereby the power supplied by the electric motor 16 is transmitted via the toothed wheel 70 or 71 and the friction ring 66 with its pins 68 to the catch plate 51 and thus to the driven member 32 and the steering pinion 41. If now the catch plate 51 coupled with the steering pinion reaches the same angle of rotation as the catch plate 50 coupled with the drive member 31 of the steering shaft 30, the friction ring 66 is returned to the initial position, that is the central position between the two toothed wheels 70 and 71.

In this position the friction ring 66 is separated from the turning toothed wheels and thus the power supply from the electric motor 16 to the steering pinion 41 is interrupted.

In order to exclude the danger that the two catch plates 50 and 51 are twisted too much relative to each other, stops 77 are formed on the ribs 56 of the catch plate 51,which stops can meet the stops 59 on the ribs 55.

If the power-assisted steering device is only needed for driving at slow speed it is conceivable that the electric motor 16 is controlled by a speedometer, a wheel or a switch dependent on the vehicle speed. It is also possible to switch on the electric motor by the twisting of the two catch plates 50 and 51 that means, when great steering powers appear.

The two catch plates could also be firmly connected with each other from a particular speed onwards, for instance by an electromagnet.

In the example shown in Figures 4to 6 a bevel pinion 85 is driven by the motor shaft 15 with the insertion of an overrunning device 21. This bevel pinion mates with two bevel wheels 86 and 87, which thus rotate in opposite directions. The two bevel wheels are part of a respective input element of the two friction clutches. The bevel wheel 86 is mounted on a hub 88 in a manner protected against twisting which hub is rotatably mounted on an assistance shaft 90 via the needle bearing 89. A clutch disc 91 is formed like a flange on the upper end on the hub 88. The bevel wheel 87 located just below the clutch disk 91 has a hub 92 pointing to the bevel wheel 86, with which hub it is mounted on the hub 88 via a needle bearing 93.Seen in the radial direction towards the other side outside of the clutch disk 91 a ring 94 is formed on the circumference of the bevel wheel 87, on which ring a second clutch disk 95 is secured in a manner protected against twisting at a spacing to the clutch disk 91. In the axial direction the two bevel wheels 86 and 87 are secured by the four needle bearings.

Between the two clutch disks 91 and 95 there is arranged the friction disk 100 on whose respective upper and under side a friction lining 67 is glued.

This friction disk is mounted on the assistance shaft 90 in a manner protected against twisting, but axially displaceable, by means of a cylindrical stud 101.

With the cylindrical stud 101 it extends through a central opening 102 of the clutch disk 95. Outside of this disk the stud 101 is provided with an annular groove 103.

The assistance shaft 90 is elongated beyond the stud 101 of the friction disk 100 and formed as a pinion 104 there which mates with the rack 42. In addition to the pinion of the assistance shaft 90 the actual steering pinion 42 mates with the rack 42, which steering pinion is arranged at the lower end of the steering shaft 30. The steering shaft 30 is mounted in a deep-groove ball bearing 103, which is mounted in a recess 106 of the housing 23. In the one direction the diameter of this steering shaft corresponds to the diameter of the deep-groove ball bearing 105, whereas perpendicularly to it its extension is greater than the diameter of the deep-groove ball bearings. Such a development can be clearly seen in a comparison between Figures 4 and 5.In Figure 5 the outer ring of the ball bearing 105 rests against the housing, whereas in the section according to Figure 4 there is still a small interspace between the outer ring of the ball bearing and the housing. Thus it is possible to move the steering shaft transversely a small amount. Such a movement may be transferred to an adjusting plate 107, which is linearly displaceably in the housing 23 and coupled with the steering shaft 30 via a pivoting bearing 108, which is located at the bottom end of the steering shaft 30. This adjusting plate 107 has a bore 109, in which the pinion 41 of the steering shaft 30 is located and a lateral groove extending approximately perpendicularly to this bore, in which groove the rack 42 is located. There is a connection between the bore and the groove, so that the steering pinion 41 can mate with the rack 42.In order to reduce the friction during a displacement of the adjusting plate 107 so-called flat cages 110 are inserted between it and the housing 23.

On the side of the adjusting plate 107 not facing the toothed rack 42 a locking cam 111 is provided.

On this locking cam a locking ball 112 is pressed which is positioned in a fixing yoke 113. This fixing yoke is guided in a pot 115 of the housing 23 and is loaded by the pressure spring 114. The locking cam 111 is formed in such a way that the adjusting plate 107 can only occupy a stable central position. When the adjusting plate is moved from this central position the locking device tends to return it to the central position.

A coupling between the adjusting plate 107 and the friction disk 100 is made by a two-armed angle lever 120. The one arm 121 of this angle lever substantially extends in a slot of the adjusting plate 107 and at its end it is coupled with the adjusting plate 107 via an oblong hole 122 and a round pin 123.

The other arm 124 of the lever 120 is developed as a fork with two tines 125, which encompass half of the stud 101 of the friction disk 100. On the tines 125 pins 126 are attached which are opposite to one another and project into the groove of the stud 101. On them rolling bearings 127 are seated, so that when the friction disk 100 turns, there is only a little friction between it and the lever 120. The lever 120 is rotatably mounted in the housing 23 by means of two pins 128 which are approximately positioned in the centre of the arm 124.

In the embodiment shown in Figures 4 to 6 the adjusting plate is thus displaced to the one or other side, when a particular steering power or a particular steering torque is exceeded which is determined by the force with which the adjusting plate is locked.

Thereby the lever 120 is swivelled, so that the pins 126 projecting in the groove 103 of the friction disk 100 move upwards or downwards and thereby adjust the friction disk along the assistance shaft 90.

The assistance shaft is pressed against one of the clutch disks 91 or 95 and non-positively coupled with it. The clutch disks 91 and 95 rotate in opposite directions like the bevel wheels 86 and 87, sci that the friction disk 100 is rotated in the one or other direction in dependence on which one of the clutch disks it is pressed. The rotation of the friction disk 100 is transmitted to the assistance shaft 90 which with its pinion 104 initates an additional force onto the rack 42.

If the steering force or the counterforce on the wheels of the vehicle diminishes, the adjusting plate 107 is returned into the central position by means of the locking cam 111, the locking ball 112 and the pressure spring 114. Thereby also the lever 120 is reset and thus the friction disk 100 is separated from the clutch disk 91 or 95.

If the power-assisted steering device is intended to be effective only below a particular speed it can be provided that the adjusting plate is locked when this speed is exceeded.

Figure 7 shows a power-assisted steering device according to the invention which is very similar to the example of Figures 1 to 3. The two embodiments mainly differ by the arrangement of the electric motor 16, to which we solely refer here. The electric motor is not arranged anywhere beside the steering shaft 30, but is seated concentrically on it. Thereby the armature 135 is developed as a statorwhich is non-rotatably fixed on the steering shaft 30. The motor housing 136 and the magnet rack 137 rotate around the armature 135. Below the armature 135 an inwardly directed ring gear 138 is secured on the motor housing 136. This ring gear represents the driving sun gear of a planetary gear. This planetary gear includes several planet wheels of which two each, namely a wheel 139 and a wheel 140 form a pair of planet wheels.Each pair is arranged on a common shaft 141,which is mounted in a web 142 which can rotate round the steering shaft 30. The planet wheels 139 and 140 carry out a movement with the same angular velocity. Whereas the planet wheels 139 mate with the ring gear 13%, the planet wheels 140 co-operate with the hollow ring gear 143 of the second sun gear 144. This sun gear is rotatably mounted on the steering shaft 30 and, in addition to the hollow ring gear 143 is provided with external gear teeth 145, with which it mates with the toothed wheel 19. The transmission of the movement on the two input elements 70 and 71 is then effected in the same way as in the example according to Figures 1 to3.

The power supply for the electric motor 16 is effected via collector rings, not shown in detail, which can be secured on the rotating housing 136.

The embodiment according to Figure 8 is in some details of its design similar to the embodiment according to Figures 4 to 6. However in this embodiment nearly all parts are carried by the steering shaft 30. As in Figure 7 the electric motor 16 is seated on the steering shaft 30. Aiso its design with the armature 135, the motor housing 136 with magnet rack 137 and the ring gear 138 is the same as in Figure 7. Again the planet wheels 139 and 140 are part of the gearing, which planet wheels mate with a hollow sun gear. This sun gear is firmly connected with the bevel wheel 86, and in the present example it is connected undivldedly. The second bevel wheel 87 is driven by several bevel pinions 85, which are firmly supported on the housing.Apart from this the bevel wheels 86 and 87, the clutch disks 91 and 95 and the friction disk 100 with the friction linings 67, the cylindrical stud 101 and the groove 103 provided on it are substantially arranged in the same way as the corresponding parts of Figure 4to 6. Now however the parts mentioned are held on the steering shaft 30.

The steering shaft 30 includes a drive member 31 and a driven member 32 as in the version according to Figures 1 to 3. These two parts are connected by a cardan joint 150, so that they cannot be twisted relative to each other, but it is possible to swivel the driven member 32 co-operating with the rack 42 against the drive member 31. The adjusting plate 107 is coupled with the driven member 32. The motion of the adjusting plate is transformed in an axial displacement of the friction disk via a lever 120 and the annular groove 103 as in the embodiment of Figures 4to6.

During a steering manoeuvre the driven member 32 of the steering shaft 30 is somewhat swivelled to the side, when a particular steering resistance has been exceeded. The adjusting plate is thereby somewhat displaced, so that the friction disk 100 is also adjusted and in dependence on the steering direction is pressed against one or other of the two clutch disks 91 and 95. Due to the fact that the friction disk 100 is connected with the steering shaft 30 in a manner protected against twisting an additional force is therefore initiated on the steering shaft. As indicated by the parts shown in the drawing with broken lines the additional force can also be initiated to the rack 42 via a separate assistance shaft 90. For this purpose the rack 42 is equipped with a toothed wheel 151 which mates with gear teeth 152 provided on the stud 101 of the friction disk 100. In this embodiment the friction disk 100 would be rotatably mounted on the drive wheel 31 of the steering shaft 30.

it is a particular advantage of the two examples of Figures 7 and 8 that they can be built very compactly.

Thereby an installation space alongside the steering shaft 30 can be used.

Figure 9 shows a diagrammatic section through a motor vehicle with the motor vehicle engine 153.

This motor is coupled with the steering gear 155 via a connecting element 154 and forms the accessory driveforthe power-assisted steering device which is with this exception accommodated in the steering gear 155. A separate auxiliary motor used for the power-assisted steering device alone is not necessary. For example a V-belt, a toothed belt, a cardan shaft or another element for the transmission of motion known in the art could be used as a connecting element 154.

Claims

1. Power-assisted steering device for a motor vehicle of the kind comprising an auxiliary drive (16, 153) and comprising two friction clutches the input elements (70,71; 91,95) of which are driven by the auxiliary drive (16, 153) in opposite directions and which friction clutches have at least one output element (66; 100) which may be coupled with the one or other input element (70,71; 91,95), characterised in that the two clutches are disk clutches, so that the available friction surfaces (67; 72,91, 95) are planar and that the elements (66,70,71; 100) are axially displaceable relative to each other.

2. Power-assisted steering device according to claim 1, characterised in that the two clutches have an output element (66; 100) in common which may be coupled with one or other input element (70,71; 91,95) by an axial displacement in opposite directions.

3. Power-assisted steering device according to claim 1 or 2, characterised in that each output element (66) ofthetwo clutches is coupled with a drive member (31,50) of the steering shaft via a screw joint (57, 68) and with a driven member (32, 51) of the steering shaft (30) via a push joint, whereby the driven member (31,50) and the driven member (32, 51) may be twisted relative to each other against the force of a spring.

4. Power-assisted steering device according to claim 3, characterised in that two catch plates (50, 51) are provided, of which one is connectable to the drive member (31) and the other to the driven member (32) of the steering shaft (30) in a way protected against twisting and displacement, and that the two catch plates (50, 51) are articulated with each output element (66).

5. Power-assisted steering device according to claim 4, characterised in that in an axial direction the catch plates (50, 51) are positioned between the input elements (70,71) of the two clutches.

6. Power-assisted steering device according to claim 4 or 5, characterised in that each catch plate (50,51) is provided with ribs (54,55; 56) of which each is directed towards the respective other catch plate (50,51) and which preferably overlap in an axial direction.

7. Power-assisted steering device according to claim 4,5 or 6, characterised in that in the direction of rotation the catch plates (50, 51) are coupled with each other by at least one spring element (61).

8. Power-assisted steering device according to claim 7, characterised in that the spring element (61) is a helical spring which in its longitudinal direction extends perpendicularly to the axis of rotation and perpendicularly to a radius beam of the catch plates (50, 51) running through its centre, and that each end of the helical spring (61) may be acted upon by both catch plates (50, 51).

9. Power-assisted steering device according to claim 8, characterised in that the helical spring (61) is positioned between the ribs (54, 55; 56) of the catch plates (50, 51).

10. Power-assisted steering device according to claim 9, characterised in that the ribs (54,55) are positioned on concentric circles.

11. Power-assisted steering device according to claim 9 or 10, characterised in that a cage (60) for a helical spring (61) is formed on the one catch plate (50) by two ribs (54, 55), which have a different distance from the axis of rotation and which, at a particular angular distance, have studs (58,59) laterally projecting from each other and pointing to the respective other rib (54, 55) and that a rib (56) of the other catch plate (51) engages in the gap between two each of the opposite studs (58, 59) of the two ribs (54, 55).

12. Power-assisted steering device according to any one of claims 7 to 11, characterised in that between the driven member (32) and the drive member (31) of the steering shaft (30) firm stops (59, 77) are provided which limit the angle by which the two members (31,32) may be twisted relative to each other.

13. Power-assisted steering device according to any one of the preceding claims, characterised in that the two catch plates (50, 51) are provided with stops (59,77) which limit the twisting of the two catch plates (50, 51) relative to each other.

14. PoLver-assisted steering device according to claim 13, characterised in that the stops (59,77) are developed on the ribs (55, 56).

15. Power-assisted steering device according to any one of claims 4to 14, characterised in that the catch plate (50) connectable with the drive member (31) of the steering shaft (30) is provided with at least one slot (57) extending diagonally to the axial direction and the other catch plate (51) is provided with at least one slot (65) extending in the axial direction and that each output element (66) engages in the two slots (57, 65) with a radially extending pin (68).

16. Power-assisted steering device according to claim 15, characterised in that the slots (57, 65) are provided in the ribs (54,56) and that the ribs are interrupted by them.

17. Power-assisted steering device according to claims 15 or 16, characterised in that two of the correlated slots (57, 65) are positioned axially on the same level and radially one behind the other and that an output element (66) engages in the both slots (57,65) by means of a single pin (68).

18. Power-assisted steering device according to any one of the preceding claims, characterised in that the output element comprises a friction ring (66), which is arranged radially outside of the catch plates (50, 51) and axially between the input elements (70, 71) the diameter of which is greater than the diameter of the catch plates (50, 51).

19. Power-assisted steering device according to claim 1 or 2, characterised in that each output element (100) is adjustable via a lever mechanism (120).

20. Power-assisted steering device according to claim 19, characterised in that a self-resetting movement of the steering shaft (30) perpendicularly to its longitudinal direction may be used as an initiating movement.

21. Power-assisted steering device according to claim 20, characterised in that the output elements (100) are adjusted against the force of a spring element (114).

22. Power-assisted steering device according to claim 20 or 21, characterised in that the steering shaft (30) has two parts (31,32) connected with each other by a cardan joint (150) and that the part (32) carrying the steering pinion may be moved perpendicularlyto its longitudinal direction.

23. Power-assisted steering device according to claim 20 or 21, characterised in that the steering shaft (30) may be moved as a whole.

24. Power-assisted steering device according to claim 22 or 23, characterised in that the adjustable part (32) of the steering shaft (30) is supported in a rolling bearing (105) positioned in a receptacle (106) fixed on the housing, and that the diameter of the receptacle in the one direction corresponds to that of the rolling bearing, whereas its extension perpendicularthereto is greater than the diameterofthe rolling bearing (105).

25. Power-assisted steering device according to any one of claims 19 to 24, characterised in that it includes an adjusting plate (107) with which the lever mechanism (120) is coupled and the movement of said adjusting plate may be derived from the movement the steering shaft (30) may carry out perpendicularly to its longitudinal direction.

26. Power-assisted steering device according to claim 25, characterised in that the adjusting plate (107) includes a bearing (108, 148, 149) for the steering shaft (30).

27. Power-assisted steering device according to claim 25 or 26, characterised in that the adjusting plate (107) is linearly displaceable.

28. Power-assisted steering device according to claims 26 and 27, characterised in that the bearing (108) is a self-adjusting bearing.

29. Power-assisted steering device according to any one of claims 25 to 28, characterised in that the adjusting plate (107) is fixed in a central position buy a locking device including a spring element (114).

30. Power-assisted steering device according to any one of claims 25 to 29, characterised in that the adjusting plate (107) is lockable at a particular vehicle speed.

31. Power-assisted steering device according to any one of claims 19 to 30, characterised in that the lever mechanism is realised by a lever (120) which is swivellably mounted on a firm axle (128) and coupled with each output element (100).

32. Power-assisted steering device according to claim 31, characterised in that the lever (120) is a two-armed angle lever.

33. Power-assisted steering device according to any one of claims 19 to 32, characterised in that one output element (100) is provided with an angular groove (103) which is positioned in a plane on which the axial direction of the output element (100) stands perpendicularly and in which annular groove the lever coupled with the output element (100) engages.

34. Power-assisted steering device according to claim 33, characterised in that the arm (124) of the lever (120) engaging in the annular groove (103) is developed as a fork (125).

35. Power-assisted steering device according to claim 33 or 34, characterised in that the arm (124) of the lever (120) engaging in the annular groove (103) carries pins (126) radially projecting into the groove (103) on which pins rolling bearings are seated.

36. Power-assisted steering device according to any one of claims 19 to 35, characterised in that the input elements (86,87) of the two friction clutches (86,87, 100) are provided with a set of gear teeth and that in the axial direction the output element (100) is located beyond both sets of gearteeth.

37. Power-assisted steering device according to claim 36, characterised in that the first input element includes a first disk (86) carrying the gear teeth, a hub (88) by means of which it is rotatably mounted on a shaft (90) and a second disk (91) at the end of the hub (88), that the second input element includes a first disk (87) by means of which it is rotatably mounted between the first and the second disk (86, 91) of the first input element on the hub (88) of the first input element, a second disk (95) and a hollow cylindrical stud (94) holding the first and the second disk (87,95) at a spacing, the diameter of the stud being greater than the diameter of the second disk (91) of the first input element, and in that the output element (100) is positioned between the two second disks (91,95).

38. Power-assisted steering device according to claim 37, characterised in that the output element (100) extends through a central opening (102) in the second disk (95) of the second input element by means of a cylindrical stud (101) and the annular groove (103) for the lever (120) is developed outside of the second disk (95) on the cylindrical stud (101).

39. Power-assisted steering device according to any one of claims 19 to 38, characterised in that the two frictions clutches are seated on a solely rotatabie part (31) of the steering shaft (30) (Figure 8).

40. Power-assisted steering device according to any one of claims 1 to 39, characterised in that a separate assistance shaft (90), which is independent of the steering shaft, may be driven by the output element, which assistance shaft may be brought into gear with the rack (42) of a steering gear.

41. Power-assisted steering device according to claim 39 or 40, characterised in that the output element (100) and the assistance shaft (90) are coupled with each other by gear teeth (Figure 8).

42. Power-assisted steering device according to claim 40, characterised in that the two friction clutches (86,97, 100) are seated on the separate assistance shaft (90) (Figures 4 to 6.)

43. Power-assisted steering device, according to any one of the preceding claims, characterised in that the vehicle engine (153) is used as an auxiliary drive and that the actuation is effected via V-belt, toothed belt, cardan shaft or other power-on torque transmitting elements (154).

44. Power-assisted steering device, according to any one of claims 1 to 42, characterised in that an additional motor seated on the steering shaft (30), preferably an electric motor, serves as an auxiliary drive.

45. Power-assisted steering device according to claim 44, characterised in that the armature (135) is firmly arranged on the steering shaft (30) and that the motor housing (136) rotates around the armature (135).

46. Power-assisted steering device according to claim 44 or 45, characterised in that the motor speed is reduced buy a planetary gear(138, gear (138,139,140,144).

47. Power-assisted steering device according to claim 46, characterised in that the output (144) of the planetary gear is positioned on the same axle (30) as the input element (86) of the one friction clutch and is directly connected with it in a manner protected against twisting (Figure 8).

48. Power-assisted steering device according to any one of the preceding claims, characterised in that the input element (87) of the second friction clutch is driven by the input element (86) of the first friction clutch via at least one intermediate wheel (85).

49. Power-assisted steering device according to claim 46, characterised in that the two input elements (86,87) of the friction clutches are driven independently of each other by the output (144) of the planetary gear via at least two intermediate wheels (19,24) (Figure 7).

50. Power-assisted steering device for a motor vehicle substantially as described with reference to the accompanying drawings.