GB2094245A - Steering linkage for motor vehicles - Google Patents

Abstract

The steering linkage has tie rods 18, 18' arranged to transmit steering effort from a steering gear 19 to steering arms 17 connected to respective wheel carriers 14 for the steerable wheels 11. The steering arms incorporate hydraulic cylinders which, by the action of a hydraulic control system (63,64) increase the effective length of the steering arms (17) with increasing angle of steering lock of the steerable wheels (11). <IMAGE>

Description

SPECIFICATION Steering linkages for motor vehicles This invention relates to steering linkages for motor vehicles, especially passenger cars.

in the usual form of steering linkage for a motor vehicle, steering movement is transmitted by way of tie rods from a steering part mounted on the vehicle body to steering arms connected to the wheel carriers for the steerable wheels.

Due to the geometric arrangement of the tie rods and the steering arms, and the fact that the effective lever length of the steering arms decreases witn increasing angle of steering lock, the steering ratio of the steering as a whole inevitably decreases with increasing angle of steering lock. This is particularly disadvantageous with steering arrangements without power assistance.

German specification DE-AS 2141205 discloses rack and pinion steering with oblique teeth wherein, by variation of the tooth shapes along the length of the rack, it is possible to obtain a steering ratio which varies with the steering lock angle. However, this involves demanding production techniques, and also the teeth are severely weakened in the region of high steering ratio. Where such steering gears are provided with power assitance, it is considered advantageous for the maximum steering ratio to be provided for the centred position, and for the steering ratio to decrease in both directions away from the centred position. Because the increase in steering resistance with increasing steering angles is in this case taken care of by the power assistance, the advantage of direct response of the steering in this region can be fully utilised.

U.S. patent specificaion 3,765,697 discloses a steering arrangement in which, by the action of a hydraulic device, the length of a tie rod (drag link) can be varied in dependence upon the steering angle of the steering arm. Thereby, a steering system is available which operates unobjectionably, from a kinematic point of view, especially since it is possible to achieve the maximum available steering angle for the wheel at the inside of a curve without prejudicing the kinematic requirements of the steerable wheels. This known arrangement does not however involve any variation in the steering ratio.

By the present invention there is provided a steering linkage for a motor vehicle, in which tie rods are arranged to transmit steering effort from a steering part mounted on the vehicle body to steering arms conncted to respective wheel carriers, and means are provided for selectively varying the length of the steering arms.

Such a steering linkage provides a basis for achieving a variation in the steering ratio in dependence upon the angle of steering lock of the steerable wheels. Thereby, in steering systems without power assistance, the reduction in the steering ratio which normally occurs with increasing angle of steering lock of the steerable wheels, due to the geometric arrangement of the steering elements, in particular the steering arms, can be compensated and even reversed in effect. In power-assisted steering systems, having a high steering ratio in the centred position, the steering ratio can be made to decrease (in other words, be made more direct) in both directions away from the centred position.

The variation in the length of the steering levers is preferably effected in dependence upon the angle of steering lock of the steerable wheels, for which purpose any element of the steering system which varies in position in accordance with the angle of steering lock can be used as a control element.

For steering systems operating without power assistance it is advantageous, as pointed out above, for the steering ratio to increase with increasing angle of steering lock, and to arrange that the reduction in the steering ratio which normally occurs as a result of the geometry of the steering linkage is compensated or even reversed in effect (in other words, over-compensated).

For this purpose, in such steering systems, according to a preferred feature of the invention, the lengths of the steering arms are a minimum when the steerable wheels are in a straight-ahead driving position, and the lengths of the steering arms increase with increasing angle of steering lock of the steerable wheels. The result is that, to a corresponding extent, the effective lengths of the steering arms providing the variation in steering lock angle of the steerable wheels are increased, so that a specific amount of displacement of the tie rods produces a smaller angle of steering lock of the steered wheels.

According to further preferred features of the invention, the increase in the effective length of the steering arms during operation of the steering system in one direction ot the other takes place either in dependence upon the angle of steering lock of the steerable wheels or of the steering arms, or in dependence upon the amount of displacement of a steering part mounted on the vehicle body, or of the tie rods or a part of a tie rod.

According to an important preferred feature of the invention, the variation in the effective length of the steering arms is effected by hydraulic means. A hydraulic control arrangement for this purpose may comprise hydraulic sender cylinders actuated by a steering part mounted on the vehicle body, or by the tie rods or parts thereof, and hydraulic reciever cylinders connected to the steering arms by a conduit system, this conduit system being so constructed that each sender cylinder can sup ply both receiver cylinders simultaneously.

Advantageously the hydraulic reciver cylinders are integrated, in spce-saving manner, in the steering arms, with a casing of the cylinder connected to the vaheei carrier and a piston rod extending to the exterior and connected to the respective tie rod.

According to a further preferred feature of the invention, two sender cylinders, corresponding to the respective directions of the steering, are installed in a mirror-image ar- rangement with respect to the centre position and to the displacement paths of the steering part mounted on the vehicle body or of one of the tie rods, and during steering lock deflections in either dire ion only the sender cylinder corresponding eo the relevant direction of steering movement is acutated, whilst the other sender cylinder remains ':'ithcut effect.

To this end, according to a further preferred feature of the invention, an actuator lever mounted on the veMiacee boby is provided for each sender cylinder. Steering movement of the steering part mounted on the vehicle body, or of the tie rode o; a part thereof, causes the lever to pivot and thereby operate the respective sender cylinder.

To ensure that, during steering in one or other direction, onl the appropriate sender cylinder is made effective, the other sender cylinder remaining ineffective, a selective coupling device is provided between the steering linkage and the actuator levers for tjae sender cylinders. Ech ectuot::r lever is connectible to the steering part mounted on the vehicle body, or to the tie rods or a part thereof, by means of a pin which is mounted and guided in an elongate aperture in the actuator lever.

Each elongate aperture has 3 lateral opening which faces the directian of movement of the actuator lever such that during steering movement in a direction opposite to the direction proper to that particular actuator lever, the pin passes out of engagement with that actuator lever.

In the drawings: Figure 1 is a fragmentary plan view of a motor vehicle steering arrangement incorporating one embodiment of a steering linkage in accordance with the present invention, somewhat simplified by omission o6F some wheel-guiding elements; Figure 2 is a fragmentary section, with parts in elevation, through a steering arm constructed as a hydraulic cylinder, in the steering arrangeme s'cwn in Fig. 1; Figure 3 schematically skows one embodi- ment of a hydraulic ccn-roE arrangement for operating the steering rn shown in Fig. 2; and Figure 4 shows the ama hydraulic control arrangement but with the steering elements positioned for negotiation of a right-hand curve.

In Fig. 1 of the drawings, a front wheel 11 of a motor vehicle is shown as having a wheel disc 12, a brake disc 1 3, and a wheel carrier 14. A hydraulic telescopic shock absorber (damper) 1 5, forming part of a suspension strut, is fixedly connected to the wheel carrier 14. For clarity Fig. 1 omits a coil-type wheel suspension spring which encloses the shock absorber 15 and is supported on the housing 16 of the shock absorber, as well as a support bearing for the shock absorber and for the suspension spring on the vehicle body.

In the main, the steering linkage for the front wheel 11 consists of a steering arm 17 secured to the shock absorber housing 16, a tie rod 1 8 universally connected to this steering arm 17, and a rack and pinion steering gear 19 which is arranged centrally of the vehicle and is fitted with a so-called centre drivs for the tie rod 1 8 and an oppositely extending tie rod 1 8', resulting in identical lengths for both tie rods. A steering shaft connection is designated 20.

For the purpose of length adjustment, the tie rods 1 8 and 18; each have an intermediate member 21 which is provided with oppositely threaded portions and is screwed into tubular connecting members 22 and 23. The screw connections are secured against loosening by means of respective clips 24 and 25.

At both ends, the rack and pinion gear 19 is secured to the vehicle body by means of bushes 26 and clips 27.

For the purpose of connecting the tie rods 18 and 18' to a dispiaceable toothed rack (not shown) of the rack and pinion gear 19, respective threaded pins 28 and 28' are screwed into the rack and are secured against loosening by means of a common locking plate. The tie rods 18 and 18' are mounted rotatably on the screw-threaded pins 28 and 28' by means of respective bosses 29 and 29', but are held axially by the heads of the threaded pins 28 and 28'.

Pivot pins 30 and 30' allow respective actuating levers 31 and 31' to be articulated to the respective threaded pins 28 and 28', as will be described in more detail subsequently.

Fig. 2 shows the steering arm 17 in greater detail, the one on the other side being similar.

The steering arm 17 is constituted by a single-acting hydraulic cylinder which has a cylinder housing 1 7a and has at one end a boss 32 by which the cylinder housing is secured to the shock absorber 15. A piston rod 33 for a piston 36 extends outwardly of the cylinder through a central aperture in a cover 35. At the free end of the piston rod 33 there is a boss 34 provided with a bore 37 accommodating the shank of a ball pin 38, secured by means of a crown nut 39 which is locked by a spring clamp (split pin) 4Q. A part-spherical head of the ball pin 38 is mounted in a ball housing 41 forming an end portion of the tie rod 1 8. This creates a ball-jointed connection between the piston rod 33 of the steering arm 17 and the tie rod 18.

Within the cylinder housing 1 7a, the piston rod 33 is sealed by means of a gasket unit 42 comprising annular seals 42a and 42b of rectangular and trapezoidal cross-section respectively. Extending between the cylinder housing 1 7a and the piston rod 33 there is a rubber sealing boot 43 giving protection against contamination, and held on its seating surfaces by spring elements such as 45. To provide satisfactory isolation of respective working chambers 46 and 47, the piston 36 carries a rectangular-section annular seal 48.

The face of the piston remote from the piston rod is provided with an extension 49 which serves as a stop for limiting piston movement.

Arranged around this extension 49 there is a pre-loaded compresssion spring 50 which is seated on a base portion 51 of the cylinder housing 1 7a, the pre-load of the spring being such that, even when fully extended, the spring 50 is not completely relieved of stress.

This ensures that, shoud the hydraulic operating system become ineffective, the hydraulic cylinder forming the steering arm is moved by spring force into its extended condition and maintained in this position with adequate force.

In the piston rod direction, piston movement is limted by the gasket unit 42.

For the delivery and discharge of a working fluid (preferably hydraulic oil), the cylinder housing 1 7a is provided with a pair of connections 52 and 53. The individual parts are identified by reference numerals for the connection 53 nearer the shock absorber, the other connection 52 being constructed similarly. The connection 53 is shown as having a bore 54 and an internal thread 55. A screw 56 with a longitudinal bore 57 and a connecting transverse bore 58 is screwed into the internal thread, and a boss-shaped end piece 60 of a connecting conduit is clamped between the connection 53 and a head 59 of the screw 56 with the interposition of a sealing ring 61.

The end piece 60 has an internal annular groove 62 establishing communication between the connecting conduit and the interconnected transverse and longitudinal bores 57 and 58 of the screw 56.

The cylinder housing 1 7a of the steering arm 1 7 forms a hydraulic reciever cylinder and forms part of a hydraulic operating system which will now be described with reference to Figs. 3 and 4.

The hydraulic operating system for selective longitudinal extension movement of the steering arm 1 7 consists in the main of two sender cylinders 63 and 64, two receiver cylinders 1 7 and 1 7', and a conduit system for the delivery and discharge of working fluid to and from the working chambers located on both sides of the pistons.

Each pair of cylinders 1 7/17' and 63/64 is arranged symmetrically.

For operation of the sender cylinders 63 and 64, respective actuator levers 68 and 69 are pivotally mounted on the vehicle body in pivot bearings 66 and 67 respectively.

At the free ends of these levers, the pivot pins 30 and 30' that are connected to the threaded pins 28 and 28' of the centre drive of the rack and pinion steering gear 1 9 engage in elongate apertures 70 and 71 of the respective actuator levers 68 and 69, and in an intermediate region of these levers piston rods 72 and 73 of the single-acting sender cylinders 63 and 64 are articulated by means of pins 76 and 77 guided in longitudinal grooves 74 and 75 of the respective levers.

The elongate apertures 70 and 71 co-operating with the pivot pins 30 and 30' are provided with respective openings 78 and 79 facing away from the respective sender cylinders 63 and 64, the openings being aligned with the positions of the respective pins 30 and 30' in the centred position of the rack and pinmion steering gear 1 9. This construction ensures that during displacement of the two pins 30 and 30' in one or other direction, corresponding to the intended direction of steer, only one actuator lever 68 or 69 is entrained, whiist the other actuator lever remains ineffective, due to the fact that the relevant pin 30 or 30' moves out of the particular elongate aperture 70 or 71 through one of the openings 78 or 79.

The conduit system 65 between the sender cylinders 63 and 64 and the receiver cylinders 1 7 and 1 7' is such tht each individual sender cylinder 63 or 64 when operative acts simultaneously on both receiver cylinders 1 7 and 1 7'. For this purpose the working chambers 80 and 81 at the cylinder ends of the two sender cylinders 63 and 64 are connected in parallel by conduit sections 82 and 83, and the working chambers 47 and 85 at the cylinder ends of the two receiver cylinders 1 7 and 1 7' are connected in parallel by conduit sections 86 and 87, with the connections thus created between the sender cylinders and the receiver cylinders being interconnected by a further conduit portion 88.

In a similar way, a conduit system for the working chambers at the piston rod ends of the sender cylinders 63 and 64 and the receiver cylinders 1 7 and 1 7' is built up from conduit sections 89, 90, 91 and 92 and conduit portion 93. In the centred position of the steering gear 1 9, the pistons 94 and 95 of the sender cylinders 63 and 64 are in their fully extended position, whereas the piston 36 and 96 of the receiver cylinders 1 7 and 17' are retracted into the cylinder housing to their maximum extent. At this moment, compression springs 97 and 98 in the sender cylinders 63 and 64 are at their maximum extension, whereas the compression springs 50 and 99 in the receiver cylinders 1 7 and 17' are at maximum compression.

The mode of operation of the hydraulic actuating system is explained below with reference to Fig. 4, in relation to steering action for a right-hand turn, corresponding to displacement of the pins 30 and 30' to the left.

With movement of the rack and pinion steering gear 1 9 for a right-hand turn, both pins 30 and 30' are jointly displaced towards the left. The threaded pin 30' can move out of the elongate aperture 71 of the actuator lever 69 through the opening 79, and therefore remains without effect, whereas the displacement of the other pin 30 causes the actuator lever 68 to pivot in a clockwise direction about its pivot bearing 66. Due to the connection of the piston rod 72 of the sender cylinder 63 to the actuator lever 68, the piston 94 is displaced towards the left, thereby displacing the fluid via the conduit section 82, the conduit portion 88 and the conduit sections 86 and 87 into the corresponding working chambers of the parallelconnected receiver cylinders 1 7 and 17'.Consequently, the pistons 36 and 96 of the receiver cylinders 1 7 and 1 7' will be moved outwardly, corresponding to the reduction in volume (then complete) in the sender cylinder 63, with the result that the effective length of the steering arms 1 7 for both front wheels 11 is increased. The increase in length of the steering arms is proportional to the working stroke of the particular sender cylinder.

There is flow back from the working chambers 46 and 100 at the piston rod ends of the receiver cylinders 1 7 and 1 7' towards the working chamber 101 at the piston rod end of the sender cylinder 63 which increases in accordance with the working stroke of this cylinder. This flow-back takes place via the conduit sections 91 and 92, the conduit portion 93 and the conduit section 89.

When steering takes place for a left-hand turn, the right-hand sender cylinder 64 func tions as the working cylinder, and the lefthand sender cylinder 63 remains ineffective.

The receiver cylinders 1 7 and 17' are supplied with fluid in a manner similar to that described for the right-hand turn.

For precise operation of the hydraulic actuating system, it is also important that in the central position of the rack and pinion steering gear 1 9 (thus in the position of the pistons 94 and 95' shown in Fig. 3) the conduit sections 89 and 90 discharging into the working chambers at the piston rod ends of the sender cylinders 63 and 64 will be closed. This ensures that the piston of the sender cylinder 63 or 64 ineffective during a turning manoeuvre is not displaced by the working fluid flowing back from the receiver cylinders 1 7 and 17'.

Claims (14)

1. A steering linkage for a motor vehicle, in which tie rods are arranged to transmit steering effort from a steering part mounted on the vehicle body to steering arms connected to respective wheel carriers, and means are provided for selectively varying the length of the steering arms.

2. A steering linkage according to claim 1, in which the steering arms are variable in length in dependence upon the angle of steering lock of the steerable wheels.

3. A steering linkage according to claim 1 or 2, in which the lengths of the steering arms are a minimum when the steerable wheels are in a straight ahead driving position, and the lengths of the steering arms increase with increasing angle of steering lock of the steerable wheels.

4. A steering linkage according to claim 3, in which the lengths of the steering arms increase in proportion to the amount of displacement of a steering part mounted on the vehicle body and extending in the transverse direction of the vehicle.

5. A steering linkage according to claim 3, in which the lengths of the steering arms increase in proporation to the amount of displacement of the tie rods or of a part of a tie rod.

6. A steering linkage according to any one of claims 1 to 5, in which the change in length of the steering arms is brought about by hydraulic means.

7. A steering linkage according to claim 6, in which the steering arms are variable in length by the action of a hydraulic control arrangement comprising hydraulic sender cylinders actuated by a steering part mounted on the vehicle body, or by the tie rods or parts thereof, and hydraulic receiver cylinders, connected to the steering arms by a conduit system, the conduit system being so constructed that each sender cylinder can supply both receiver cylinders simultaneously.

8. A steering linkage according to claim 7, in which the steering arms are formed as hydraulic receiver cylinders having a piston displaceable therein and a piston rod extending to the exterior.

9. A steering linkage according to claim 8, in which cylinder casings of the receiver cylinders are connected to respective wheel carriers or to parts firmly connected thereto, and the piston rods of the receiver cylinders are connected to the respective tie rods.

10. A steering linkage according to claim 9, in which at both sides of the pistons the receiver cylinders are provided with respective connections for the delivery and discharge of hydraulic fluid.

11. A steering linkage according to any one of claims 7 to 10, in which two sender cylinders as aforesaid are installed in a mirrorimage arrangement with respect to the centre position and the displacement paths of the steering part mounted on the vehicle body, or of one of the tie rods, and during steering lock deflections in either direction only the sender cylinder corresponding to the relevant direction of steering movement is actuated, whilst the other sender cylinder remains without effect.

1 2. A steering linkage according to claim 11, in which actuator levers are provided for actuating the respective sender cylinders, and are caused to pivot by steering movement of the steering part mounted on the vehicle body, or of the tie rods or a part thereof.

1 3. A steering linkage according to claim 12, in which the piston rods of the sender cylinders are connected to respective ones of the actuator levers.

14. A steering linkage according to claim 1 2 or 13, in which the actuator levers are connected to the steering part mounted on the vehicle body, or to the tie rods or a part thereof, by means of pins which are mounted and guided in elongate apertures in the respective actuator levers, each elongate aperture being provided with a lateral opening such that during steering movement in a direction opposite to that corresponding to that particular actuator lever, the pin moves out of engagement with that actuator lever.

1 5. A steering linkage according to any one of claims 7 to 14, in which compression springs are mounted on the base of the respective receiver cylinders and are effective to place the receiver cylinders in a condition of maximum extension in the event of loss of pressure of the hydraulic system.

1 6. A steering linkage for a motor vehicle, substantially as hereinbefore particularly described and as shown in the accompanying drawings.