GB1602240A - Hydraulic steering boosters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO HYDRAULIC STEERING BOOSTERS (71) We, ROBERT BOSCH GMBH, a German company of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to hydraulic steering boosters.

In one known hydraulic steering booster having a spool-type control valve and a double-acting steering working cylinder, the adjusting force of a steering wheel is applied to a spring unit which can permit travel in both directions.

There is no reactive effect on the steering wheel in the known steering boosters of this type. and no follow-up control exists which would render the steering more sensitive.

According to the present invention there is provided a hydraulic steering booster for closed-centre or open-centre operation, in which the adjusting force of a steering wheel is applied to a spnng unit which can permit travel in both directions to be transmitted to a control valve connected to control a double-acting steering servo-cylinder, said booster including an adjusting member associated with the control valve for countering the transmission of the steering wheel travel to said control valve, the adjusting member being centered by centering spring means and having two working surfaces which are subjected in opposite directions to the pressure introduced by the control valve to the steering servo-cylinder.

One advantage of a hydraulic steering booster embodying the present invention resides in that, with given effective surfaces of the servo-cylinder and of the adjusting member, optional characteristics of force input to pressure output can be obtained on the adjusting member solely by varying the spring characteristics. In servo-steering systems, it is desirable that, above a specific manual force, a further increase in the output force or in the output pressure can be obtained merely by maintaining the manual force and not by increasing it. This can be made possible by providing stops to limit the movement of the adjusting member away from its centered position.

Finally, it is also advantageous that the forces between the actuating member and the valve remain very small up to the maximum actuating forces. This is of basic importance for a practical embodiment of servo-steering systems, since their dimensioning can be correspondingly compact.

The invention will be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a section through a steering booster according to a first embodiment of the invention; Fig. 2 is a section through a second embodiment of the steering booster of Fig.

1, and Fig. 3 shows a further simplification of a steefing booster.

A steering wheel 1 is connected to a steering shaft 2 whose pinion 3 drives a toothed rack 4 which is connected to steerable wheels (not illustrated) of a vehicle.

For the purpose of boosting the steering force, the pinion 3 is journalled on a rocker arm 6 which is pivotally mounted at 5 and whose free end 7 acts upon a travelpermitting spring unit. This spring unit has a fixed housing 9 in which are arranged two centering spnngs 10 and 11 which seek to maintain the free end 7 of the rocker arm 6 in a central position. A lever 8 is mounted on the free end 7 of the rocker arm 6 and is connected to a yoke 14 by way of a rod 13.

A spool 16 of a control valve is coupled to one end 15 of the yoke 14, and an adjusting member 18 is coupled to the other end 17 thereof.

The control valve spool 16 controls com- munication between a pump 19 and a return-flow reservoir 21 and a double-acting servo-cylinder 22 which is intended for steering the vehicle wheels by auxiliary force and which is coaxial with the toothed rack 4.

In the embodiment of Fig. 1, the adjusting member 18 is a follow-up piston 23 arranged parallel and adjacent to the con trol valve spool 16. The follow-up piston 23 has two working surfaces 24 and 25 of equal size which are subjected to the pressures in the opposite ends of the servo-cylinder 22.

The effective working surfaces 24 and 25 may be of differing sizes in order, for example, to compensate for differing sizes of effective surfaces of the servo-cylinder 22.

Centering spring assemblies 6 and 27 are arranged one at each end of the follow-up piston 23 and, in the illustrated embodiment, the two spring assemblies are identical and each othem is of two-stage construction. Their travel is limited by an end stop 28, 29 respectively. Each centering spring assembly 26 or 27 comprises two springs which, in the present embodiment, are in the form of helical springs. Alternatively, a combination of helical springs and cup springs can be used, or a rubber spring acting in stages.

Although an open-centre steering system is shown in Fig. 1, the arrangement can just as readily be constructed for a closed-centre steering system having a hydraulic accumulator 20, as is shown in Fig. 2.

Instead of the embodiments, illustrated in Figs. 1 to 3, having a rocker arm 6 and helical springs 10 and 11, any other optional arrangements can be used in which the forces exerted upon the steering wheel 1 are converted to travel by way of a spring unit (by way of, for example, a torsion rod).

The construction shown in Fig. 1 operates as follows: When in the starting position, the centering spring assemblies 26 and 27 maintain, by way of the yoke 14, the control valve spool 16 in its illustrated starting position in which working fluid flows through freely without a build-up of differential pressure. Upon turning the steering wheel 1, the rocker arm 6 pivots under the action of the reaction force.

Since the follow-up piston 23 is fixed by the centering spring assemblies 26 and 27, only the control valve spool 16 moves to the le or the right in the first instance after the force of one of the two springs 10 or 11 has been overcome. Thus, the centering force of the springs 10 and 11 determines the application of the servo-force.

Consequently, pressure medium is introduced into one end or the other of the servo-cylinder 22, and the steering force is servo-assisted. The pressure introduced by the control valve spool 16 also acts upon one of the two working surfaces 24 or 2of the follow-up piston 23 and, when the pressure is sufficiently high, the follow-up piston 23 leaves its central position and returns the control valve spool 16 to its starting position by way of the yoke 14. The greater the actuating force applied to the steering wheel 1, the greater is the deflection of the control valve spool 16 and of the follow-up piston 23. All the movable parts return to their starting positions when the actuating force ceases to be applied.

Fig. 2 shows a closed-centre steering system having a hydraulic accumulator 20. In this steering system, the follow-up piston adjusting member is formed by a sleeve 40 of a control valve. In this instance, the two identical working surfaces are designated 24' and 25'. The spring units for centering adjusting member are in the form of two rubber springs 42 and 43 which are of graduated construction and which, upon full actuation, are compressible such that they substantially fill their respective reception chambers 44 and 45. In this manner, a substitute for the stops 28 and 29 of the construction of Fig. 1 is obtained. In the present instance, a lever 8' corresponding to the lever 8 of Fig. 1 is directly coupled to the control valve spool 41. The same reference numerals have otherwise been used for the parts corresponding to the construction of Fig. 1.

The pressure introduced into the servo- cylinder 22 moves the sleeve 40, forming the adjusting member, in one or the other direction. In this manner, the control movement introduced by the lever 8' is countered by corresponding movement of the sleeve 40 until no further pump pressure is built up in one or other of the working chambers of the servo-cylinder 22. The control valve then remains at rest in its neutral state but displaced against one or other of the springs 42,43.

Fig. 3 shows a simplified construction in which a servo-cylinder 22' is used as an adjusting member having follow-up piston characteristics. It will thus be seen that, in the present instance, the servo-cylinder 22', applying the servo force to the wheels to be steered, acts directly as the adjusting member. For this purpose, the servocylinder 22' is centered by means of a centering spring unit 47. A housing 48 for a control valve spool 49 (not illustrated) is mounted on the servo-cylinder 22'. The springs 10 and 11 and the rod 13 correspond to those shown in Fig. 1.

The method of operation of this system is substantially the same as that already described, except that, in the present instance, the servo-cylinder 22' itself is the follow-up piston adjusting member. Thus, the present embodiment is rendered very compact and inexpensive.

A special advantage of the arrangement of Fig. 3 is that the servo-cylinder can be of any optional form with optional effective surfaces and into which the pressure can be alternately introduced in any optional manner, since only the force actually applied by the servo-cylinder is converted to travel by way of the spring unit 47 and is transmitted to the adjusting member. Large frictional forces in the servo-cylinder also do not impair the function in any way.

WHAT WE CLAIM IS: 1. A hydraulic steering booster for closed-centre or open-centre operation, in which the adjusting force of a steering wheel is applied to a spring unit which can permit travel in both directions to be transmitted to a control valve connected to control a double-acting steering servo-cylinder, said booster including an adjusting member associated with the control valve for countering the transmission of the steering wheel travel to said control valve, the adjusting member being centered by centering spring means and having two working surfaces which are subjected in opposite directions to the pressures introduced by the control valve to the steering servo-cylinder.

2. A steering booster as claimed in claim 1, in which the control valve and the adjusting member are arranged parallel and adjacent to one another and are connected to one another and to the travel-permitting spring unit by way of a yoke.

3. A steering booster as claimed in claim 1 or 2, in which the adjusting member is the steering servo-cylinder which is supported for movement in its axial direction and upon which the centering spring means act so as to yield to axial movement of the servo-cylinder.

4. A steering booster as claimed in claim 1 or 2, in which the adjusting member is a separate follow-up piston which is subjected to the pressures prevailing at both ends of the steering servo-cylinder.

5. A steering booster as claimed in claim 4, in which the centering spring means acting upon the follow-up piston comprise springs of two-stage construction, and the travel of each spring is limited by a respective end stop.

6. A steering booster as claimed in claim 4, in which the centering spring means acting upon the follow-up piston comprise rubber springs whose stiffness is increased upon compression.

7. A steering booster as claimed in claim 4 or 6, in which the control valve comprises a spool accommodated in a sleeve which forms the follow-up piston.

8. A hydraulic steering booster, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. to the adjusting member. Large frictional forces in the servo-cylinder also do not impair the function in any way. WHAT WE CLAIM IS:

1. A hydraulic steering booster for closed-centre or open-centre operation, in which the adjusting force of a steering wheel is applied to a spring unit which can permit travel in both directions to be transmitted to a control valve connected to control a double-acting steering servo-cylinder, said booster including an adjusting member associated with the control valve for countering the transmission of the steering wheel travel to said control valve, the adjusting member being centered by centering spring means and having two working surfaces which are subjected in opposite directions to the pressures introduced by the control valve to the steering servo-cylinder.

2. A steering booster as claimed in claim 1, in which the control valve and the adjusting member are arranged parallel and adjacent to one another and are connected to one another and to the travel-permitting spring unit by way of a yoke.

3. A steering booster as claimed in claim 1 or 2, in which the adjusting member is the steering servo-cylinder which is supported for movement in its axial direction and upon which the centering spring means act so as to yield to axial movement of the servo-cylinder.

4. A steering booster as claimed in claim 1 or 2, in which the adjusting member is a separate follow-up piston which is subjected to the pressures prevailing at both ends of the steering servo-cylinder.

5. A steering booster as claimed in claim 4, in which the centering spring means acting upon the follow-up piston comprise springs of two-stage construction, and the travel of each spring is limited by a respective end stop.

6. A steering booster as claimed in claim 4, in which the centering spring means acting upon the follow-up piston comprise rubber springs whose stiffness is increased upon compression.

7. A steering booster as claimed in claim 4 or 6, in which the control valve comprises a spool accommodated in a sleeve which forms the follow-up piston.

8. A hydraulic steering booster, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.