GB2030531A - Steering systems for motor vehicles - Google Patents

Abstract

A motor vehicle steering system includes a hydraulic steering damper 7 which is also used as the fluid pressure motor of a power-assisted steering system. Power assistance is provided only in a low vehicle speed range so that the system serves as a parking aid. An adjusting device 23 of the power- assisted steering servo system and an electric or electronic control device 28 for the adjusting device can be part of an anti-lock regulating system for the vehicle braking system, and the adjusting device can be in the form of a multi-position valve. <IMAGE>

Description

SPECIFICATION Improvements in or relating to steering systems for motor vehicles The present invention relates to steering systems for motor vehicles.

Some steering systems for motor vehicles, generally in the lower middle class range of passenger cars incorporate a hydraulic steering damper. On the other hand, in order to assist the manual power required for steering, power-assisted steering systems are used in larger and heavier passenger vehicles and in commercial vehicles. Power-assisted steering systems use adjusting cylinders to transmit servo power to the steering linkage. Like all hydraulic steering dampers, these adjusting cylinders have frictional forces which adversely affect the restoring moment of the steering system, and the straight running of the vehicle can be impaired.

Thus, great importance has to be attached to low frictional forces in the construction of the steering mechanism and all of the transmission devices in the steering linkage.

According to the present invention a steering system for motor vehicles comprises a steering shaft, a steering mechanism, a rod which transmits its transverse movement initiated by the steering shaft and the steering mechanism to the vehicle wheels by way of linkages, a two-chamber cylinder and piston unit acting as a hydraulic steering damper, pressure fluid lines connecting the two chambers to an adjusting device of a servo system, and an electric or electronic control device controlled byway of a force sensorforfeeding control signals to the adjusting device.

A steering system embodying the present invention can have the advantage that a power-assisted steering system can be provided with a minimum of structural expense. The frictional forces are not additionally increased. In addition to this, brake fluid can be used as hydraulic medium for operating a parking power-assisted steering, particularly with media separation. Furthermore, it is advantageous that a conventional steering damper compensating chamber can be dispensed with by connecting the steering damper to a hydraulic circuit which has a reservoir. It is also advantageous that damper valves can be simplified and mounted outside the cylindrical chamber. Thus, it is a relatively simple matter to check and/or service the damper valves.

Finally, it is advantageous that, for special requirements, it is possible to separate the hydraulic fluid used in the steering damper circuit from that in an energy supply.

The invention will be further described by way of example with reference to the accompanying draw ings in which: Figure 1 is a diagram of an electro-hydraulic power-assisted steering system having a modified steering damper, according to one embodiment of the invention, Figure 2 shows a steering damper, according to a second embodiment of the invention, Figure 3 is a detail section through a throttle, and Figure 4 shows a system for separating one pressure medium from another.

A toothed rack 4 surrounded by a tube 3 is driven by a steering shaft 1 by way of a steering mechanism 2, and the two ends of the toothed rack extend out of the tube 3. The two locations at which the toothed rack extends out of the tube are protected against dust and dirt by means of bellows 5 and 6. The rack 4 is connected (in a manner not shown) to the steered wheels of a motor vehicle by way of various appropriate linkages.

A steering damper 7 is arranged parallel to the tube 3 and its housing 8 is secured to the tube 3 by way of a connecting bar 9. The steering damper 7 is a piston and cylinder unit having two chambers 10 and 11 which are separated by a piston 12. The piston 12 is carried buy a piston rod 13 whose end is connected to the toothed rack by way of a link 14.

The steering system described up to this point is a conventional mechanical steering system having a hydraulic steering damper and of the type used in many vehicles of the lower middle class.

In accordance with one embodiment of the present invention, the steering damper 7 is modified by providing in its housing 8 two opposing pairs of non-return valves 15, 16 and 17, 18 which are offset parallel to the axis of the cylindrical chamber, each pair of non-return valves being equipped with a throttle acting as a damper. Furthermore, two connections 19 and 20 for two hydraulic lines 21 and 22 are provided on the housing 8 of the steering damper and lead to an adjusting device 23. The adjusting device 23 is part of a servo system which also includes a pump 24, an accumulator 25 and a reservoir 26 for a pressure medium. The adjusting device 23 is connected by way of an electrical lead 27 to an electric or electronic control device 28 which is in turn connected by way of a lead to a torque sensor 29 which is mounted on the steering shaft 1.

By way of example, the vehicle is provided with an anti-lock regulating system (not illustrated) for the vehicle braking system and such regulating system is connected to the control device 28 by way of a lead 30 and whose switching signals are also processed in the control device 28. Thus, information relating to the velocity of the vehicle always exists in the control device 28.

The mechanism so far described operates as follows: The pump 24 is driven preferably intermittently, such that pressure medium is permanently available in the servo device.

The electric or electronic control device 28 evaluates the velocity information originating from the wheel rotational speed sensors or the like and fed by way of the lead 30, such that the control device actuates the adjusting member to enable the servo system only when the vehicle is travelling relatively slowly for example at not more than a speed of 5 km/h. Thus, in this range of speed, which is usually adhered to when parking, a signal produced in the torque sensor 29 upon turning the steering shaft 1 produces in the control device 28 a control pulse which is fed to the adjusting device 23 by way of the lead 27. Valves (not illustrated) in the adjusting device 23 are operated such that pressure medium flows from the accumulator 25 into one or the other of the two lines 21 and 22.The non-return valve 15 or 17, together with the throttle, then performs the function of a conventional throttle valve in a conventional steering damper, and the non-return valves 16 and 18 operate like a known steering damper bottom valve. The two non-return valves 16 and 18 then prevent a vacuum from developing during movement of the damper piston 12, so that the two chambers 10 and 11, located one at each side of the piston 12, are rapidly filled with fluid. It is only then that the steering damper can operate correctly.

If only low demands are made on the quality of the damping of the steering, the non-return valves 15 and 17 can be omitted, since their only function is to maintain a low initial pressure in the chambers 10 and 11.

The system acts as a parking aid in the manner described. It reduces the manual force to be applied to the steering shaft 1 by introducing the servo force into the modified steering damper 7. When the vehicle is travelling at a velocity in excess of 5 km/h, only small forces are required for swinging round the steering wheels, and the velocity signal fed to the control device 28 by way of the lead 30 renders the servo system inoperative, so that the steering damper 7 operates like a conventional damper.

Figure 2 shows a second embodiment of a steering damper 39 modified in accordance with the invention. Parts which correspond to those shown in Figure 1 carry the same reference numerals as in Figure 1. In the embodiment of Figure 2, two adjusting pistons 39 and 40 are additionally provided in a damper housing 38 and are provided with push rods 41 and 42. The push rods 41 and 42 serve to open the non-return valves 16 and 18.

In orderto render it possible to turn the steering wheel rapidly and to initiate the servo force rapidly during operation of the steering damper 37, the damper chamber 10 or 11, in each case located opposite the damper chamber which is increasing in volume, is connected to the pressure medium return line without throttling by opening the corresponding non-return valve 16 or 18 by means of the adjusting piston 39 or 40.

Figure 3 shows a temperature-compensated throttle 43 which can be fitted in the region of the non-return valves 15 and 17 instead of a conventional throttle. The purpose of this kind of throttle 43 is as follows: The viscosity/temperature characteristic of the fluids, which have hitherto been used as pressure media in steering dampers, differs at low temperatures from the corresponding viscosity of brake fluids. This difference is now decreased by virtue of the fact that the throttle 43 has a throttle screw 44 which has, opposite its housing 45, a stop 46 having a variable temperature coefficient. The quality of the variation of the throttling gap can be further improved by means of a two-stage or multi-stage throttle.

Finally, Figure 4 shows a device for using two different pressure media. A steering damper 47 is combined with two aneroid capsules 48 and 49 which are equipped with two diaphragms 50 and 51.

These diaphragms separate one pressure medium from the other.

The valve combination described with reference to Figure 1 and 2 is provided between the aneroid capsules 48 and 49 and the steering damper 47 and is illustrated only in a simplified manner in Figure 4.

A device of this type is intended for particularly high demands made on the steering damper 47.

In order to save space and to simplify the line system, it can be advantageous to combine the housing of the adjusting member 23 with the housing of the steering damper 7,37,47. Finally, it may be mentioned that, when the device is combined with an anti-lock brake regulating system, the adjusting member 23 can be in the form of a multi-position valve in order simultaneously to undertake functions of the anti-lock brake regulating system. The housing of the multi-position valve can then be assembled together with the housing of the steering damper.

Claims (14)

1. A steering system for motor vehicles, comprising shaft, a steering mechanism, a rod which transmits its transverse movement, initiated by the steering shaft and the steering mechanism to the vehicle wheels by way of linkages a two-chamber cylinder and piston unit acting as a hydraulic steering damper, pressure fluid lines connecting the two chambers to an adjusting device of a servo system and an electric or electronic control device controlled by way of a force for feeding control signals to the adjusting device.

2. A steering system as claimed in claim 1, in which valves of the steering damper are arranged externally of the damper chambers.

3. A steering system as claimed in claim 1 or 2, in which the servo system comprises, a pump, an accumulator, a reservoir for pressure medium and said adjusting device and variation of the volume of the steering damper is compensated by the reservoir.

4. A steering system as claimed in any of claims 1 to 3, in which the steering damper is provided with adjusting pistons for reducing the throttling action when the servo device is operative.

5. A steering system as claimed in any of claims 1 to 4, in which the steering damper includes a temperature compensating throttle.

6. A steering system as claimed in any of claims 1 to 5, in which pressure medium separators are fitted between the steering damper and the adjusting device for separating the pressure medium in the steering damper from the pressure medium in the servo system.

7. A steering system as claimed in any of claims 1 to 6, in which the housing of the adjusting device is combined with the housing of the steering damper.

8. A steering system as claimed in any of claims 1 to 7, in which the control device and preferably also the adjusting device are parts of an anti-lock regulating system for the vehicle braking.

9. A steering system as claimed in claim 8, in which the adjusting device is a multi-position valve of an anti-lock regulating system.

10. A steering system as claimed in claim 9, in which a housing of the multi-position valve is assembled with the housing of the steering damper.

11. A steering system as claimed in any preceding claim, in which the force sensor is a torque sensor associated with the steering shaft.

12. A steering system for motor vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.

13. A steering system as claimed in claim 12, including throttle means constructed and arranged and adapted to operate substantially as herein before particularly described with reference to and as illustrated in Figure 3 of the accompanying drawings.

14. A steering system as claimed in claim 12 or 13, including pressure media separators constructed and arranged substantially as hereinbefore particularly described with reference to and as illustrated in Figure 4 of the accompanying drawings.