CS198177B2 - Device for the change of the controlling force on the steering wheel of the servosteering - Google Patents

Abstract

1518136 Power-assisted steering systems ZAHNRADFABRIK FRIEDRICHSHAFEN AG 13 Oct 1975 [23 Oct 1974] 41804/75 Heading B7H The power-assisted steering system, Fig. 1, of a motor vehicle comprises a control valve 1 in communication with a pump 2 which is driven by the vehicle engine and which has an output flow characteristic line (as shown in Fig. 4) which, beginning just above the idling speed of the engine, falls with increasing engine speed. The control valve 1 is operable to control fluid flow to a servo motor 3 and comprises a valve piston 5 axially movable by actuating means including a pin 28 connected to a torsion bar 27. The steering system of Fig. 1 is intended to provide increase servo assistance at low engine speeds, for example during parking manoeuvres. In a modification of the steering. system of Fig. 1, the control valve has a valve member constructed as a rotary valve sleeve (105), Fig. 6 (not shown). a rotary sleeve

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a device for changing the steering force on a steering wheel of a power steering system, in particular a motor vehicle, comprising a steering gear with one mechanical and one hydraulic member. wherein the steering gear has a control valve with at least one adjustable piston of the control valve by means of a resilient torsion rod, the adjustment path of which is proportional to the angle of rotation of the steering wheel. flexible torsion bars.

The purpose of such a device is to keep the power supplied from the driver to driving at a slight level.

Previously known power-assisted steering systems are designed so that the steering force increases more in the middle steering position than in the area of greater steering deflection. This increase in power serves to center the steering and is needed by the driver to provide sufficient driving sensitivity.

The same increase in power must be overcome for this steering - also when parked, that is, with increased steering movement at reduced driving speed. Strong surge in parking. however, it is not desirable.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steering system of the type described above in which, in the low-speed range with low engine speed, for example when parking, and - with increasing resistance - steering. at higher speeds - driving - with - high - revolutions, - engine - the power rises more strongly on the steering wheel with increasing steering resistance.

In one known steering, as the driving speed increases, an increasing proportion of the steering force is produced by means of a second pump whose flow pressure rises in accordance with the speed of the motor vehicle. As a result, only low manual effort is required at low travel speeds. Generally, however, the second pump entails - undesirable financial and - construction costs.

According to the invention, this object is achieved in that the piston of the control valve has control stages at the control edges and that the servo pump has a decreasing characteristic.

According to further preferred embodiments of the invention, the piston of the control valve is formed either as a displaceable piston or as a piston rotatable about its axis of rotation.

The advantages achieved by the present invention are that due to the combination of a plurality of dependent steering with a decreasing characteristic of the servo pump, such a steering device could be achieved, which allows manual force to be applied in dependence.

188177 na. speed of the vehicle or the engine speed.

The invention is explained in more detail below in an exemplary embodiment in conjunction with the enclosed drawings, wherein FIG. 1 shows the control according to the invention in a schematic representation of a first embodiment without the mechanical coupling parts which are not essential to the invention; Fig. 2 and Fig. 3 is a control device according to Fig. 1, but with the control valve adjusted, Fig. 4 shows a diagram of the characteristics of the servo pump, Fig. 5 is a diagram showing the dependence of the steering wheel force on the servo pressure; shows a control device with a second embodiment of a control valve.

The hydraulic part of the control device according to the invention consists essentially of a control valve 1, a servo pump 2, a servomotor 3, a pressure medium reservoir 4 and associated pipes. For the sake of simplicity, the control valve 1 is shown only with one control valve piston 2. However, a control valve with two divided pistons is also known. It is also possible to create a control valve with one rotary slide. An exemplary embodiment with such a control valve will be described below.

The control valve 1 has a housing. 6 shows two supply grooves 9 and 10 connected to the servo pump via the supply lines 7 and 8. 2, and two return grooves 13 and 14 connected via return pipes 11 and 12 to the pressure medium reservoir 4. The two control grooves 15 and 18 in the piston 5 of the control valve are connected to two pressure spaces 19 and 20, respectively, of the servomotor 3 by means of the pressure lines 17 and 18 between the control grooves 15 and 16 and the supply lines. Inlet grooves 21, 22 are formed by the grooves 9, 10. The return control slots 23, 24 are formed between the control grooves 15, 16 and the return grooves 13, 14. The inlet control slots 21, 22 are wider than the return control. The control valve piston 5 has at the control edges of the supply slots 21, 22 control stages 25, 26, which are formed, for example, with oblique edges. In the neutral position of the piston 5 of the control valve, both the inlet control slots 21, 22 and the like are provided. the return control slots 23, 24 are open, so that the pressure environment. it can flow from the servo pump 2 via said slots into a pressure medium reservoir 4.

The piston 5 of the control valve is adjustable by means of a pin 28 connected to the flexible torsion bar 27. The arrangement and connection of the flexible torsion bar 27 and the pin 28 is formed in a known embodiment.

The characteristic of the flexible torsion bar 27 starts at the neutral position. to zero and relatively steeply rising. The adjustment path of the control valve piston 5 is proportional to the angle of rotation of the flexible torsion bar. 27, so that with a greater adjustment path of the piston 5 of the control valve, the increasing steering wheel force which is generated by the rotation of the flexible torsion bar 27 can be perceived. to say that a small adjustment path of the piston 5 of the control valve corresponds to a small manual control force, while a large adjustment path is assigned a large force.

As the piston 5 of the control valve increases, for example in the direction of arrow 29, the supply control slot 21 closes more and more while the second supply control slot 22 opens more. The closing closing inlet opening 21 regulates in this connection the working pressure in the supply lines 7, 8 and in the control groove 16, which is already at a slight deflection. The piston 5 of the control valve separates from the return groove 14. The return slot 23 further opens.

In the case of greater control resistance that arises on. steering wheels, for example when parked, would have to be for ·. obtaining the required servo pressure at a constant pressure medium pressure piston 5 of the control valve · deflected more than at a slight steering resistance · during rapid travel. It follows, . that when you parked it would be on. steering wheel exerted more manual force · than when driving fast.

Driving in low speed. . however, higher steering effort is not desirable in order not to hinder the parking maneuver. A slight increase in force can be achieved by reducing the angle of rotation of the flexible torsion bar 27, and thereafter by reducing the adjustment path of the piston 5 of the control valve. However, in order to be able to obtain sufficient pressure in the servomotor 3 when the supply control slot 21 is further opened, an increase in the pressure environment is required. This increase in the pressure environment could be delivered by means of a high-performance pump. The disadvantage, however, would be that. there would be a high pressure environment at higher engine speeds · and higher driving speeds, which would mean · too strong a steering · and thus a small proportion of manual power in the steering resulting in insufficient sensitivity · while driving.

The solution according to the invention therefore proposes to use a servo pump 2 with a decreasing characteristic for this control. · This means that · the servo pump · 2 feeds at low engine speed · large, for steering maneuver with large steering deflection with large. - the quantity transported. This conveyed quantity decreases with increasing engine speed, so that in the upper speed range, i.e.. at high engine speeds, only a small amount of pressure environment is produced. Figure 4 shows the characteristics of this. .servočerpadla-. · 2 dependence of transported volume · Q · 'on engine speed n. Such a pump · 2. it is provided, for example, with a control valve.

FIG. 2 shows the control valve 1 in a shifted state. with the engine running slowly. At a high pressure environment, a slight control valve piston adjustment path 5 is sufficient to adjust the required working pressure at the relatively wide open control supply slot 21. The slight control valve piston adjustment path 5 corresponds to a relatively small angle and even to the torsion bar 27, resulting in a low manual power steering. This manual steering force increases only slowly in order to set a higher servo pressure which increases the hydraulic fraction of the steering force as the spring torsion bar 27 and thereby the narrowing width of the feed-in slot 21 increase.

Giant. 3 shows the control valve 1 in an advanced state with the engine running. Due to the low pressure environment, the piston 5 of the control valve has to be adjusted more so that it reaches the same pressure via the further closed control slot 21. The greater adjustment path of the piston 5 of the control valve is also associated with a greater angle α of rotation of the flexible torsion bar 27. However, the large angle α2 of rotation creates a great manual steering force.

If the steering resistance rises further when parked, the deflection of the piston 5 of the control valve shown in FIG. 2 is no longer sufficient to achieve the necessary servo pressure to overcome the steering resistance. The piston 5 of the control valve moves more and more in the direction of the arrow 29 until the supply control slot 21 is completely closed. The flexible torsion bar 27 is rotated to this position of the piston 5 of the control valve, then no further rotation is effected and there is no further increase in manual force. Further pressure increase depends only on the magnitude of the steering resistance,

FIG. 5 shows the relationship between steering wheel force F and servo pressure P. The servo pressure is proportional to the steering resistance. The upper curve shows the curve at low engine speed and the corresponding high pumping volume, while the lower curve shows the curve at high engine speed and the corresponding low pumping volume. The end of the deflection of the piston 5 of the control valve is seen at the points where the curves bend vertically upwards.

To illustrate the curves and the controller, two examples are shown in the diagram.

In the first example, a force of 10 N is sufficient to achieve a pressure of 1 MPa at low engine speed, while a force of 30 · N is required at high engine speed with low pumping current.

In the second example, a force of 30. N at a pumping current of 3 · 1 / min, i.e. at a high engine speed, can only achieve a pressure of 1 MPa, while at a pumping current of 7 1 / min at a low engine speed 5 · · MPa. Thus, when parked, about five times the height of the pressure can be achieved at the same force on the steering wheel compared to fast driving. By the same manual steering force, · it is · overcome its · five-fold · resistance.

In fast driving, the steering resistances are generally so low that the separation point at which the supply control slot 21 closes is not reached. This is a perceptible increase in the manual steering force on the steering wheel over the entire steering area, as shown in the lower curve of FIG. 5.

FIG. 6 shows an exemplary embodiment of a control device in which a control valve piston 105 rotatable about its axis of rotation is used in place of the axially displaceable piston 5 of the control valve. The corresponding parts of Fig. 1 and Fig. 6 are indicated in Fig. 6 by reference numbers increased by 100.

While at the control valve piston 5, the control grooves are annular grooves, the pressure environment at the control valve 101 in the form of a rotary slide valve is controlled by longitudinal grooves distributed around the circumference of the control valve piston 105 and the cylinder body 10S . The pressure environment penetrates from the servo pump 102 via the supply lines. 107 and 108 to the two inlet grooves · 109 and 109A. The supply grooves 109, 109A are connected to the return grooves 113, 114 and 113A, 114A, respectively, in the neutral position of the control valve piston 105 by means of two control grooves 115, 116 and 115A and 116A, respectively. At the control edges of the feed slots 121, 121A and 122, 122A, which are formed between the feed slots 109, 109A with the control slots 115, 116, they are arranged in a manner similar to the piston 5 of the control valve of the control stage. The resilient torsion bar 127 is mounted in the center of the control valve piston 105. Control valve 101 in the form of a rotary slide valve corresponds to control valve 1 by its action and the arrangement of the pressure lines.

Claims (4)

SUBJECT A device for changing the steering force on a power steering wheel, in particular for motor vehicles, comprising a steering gear with one mechanical and one hydraulic member, a servo pump driven by a vehicle engine. a pressure medium reservoir, the steering gear having a control valve. p. at least one adjustable piston of the control valve by means of a flexible torsion bar, its adjustment path being proportional to the angle of rotation INVENT THE STEERING ROTATED Elastic Torsion Bars, characterized by:. piston [5, 105) of the control valve. has control stages (25, 26) at the control edges and that the servo pump (2) has a decreasing characteristic. Device according to Claim 1, characterized in that the piston (5) of the control valve is designed as an axially displaceable piston. 3. -Equipment according to. point. 2, characterized in that the piston. (5) control valve: it is designed as a piston. . rotatable about its axis of rotation. 6 sheets of drawings