DE4106310A1 - Power-assisted steering for vehicle - contains servo motor, and two work chambers are connected via work conduits to control valve - Google Patents

Abstract

Via the control valve (6), the servo motor (1) is alternately connectable to a servo pump (7) and a pressure medium container (8). In each of the two work conduits (4,5) a check valve (10) and a pressure restriction valve (12) are fitted in parallel, the check valve opening in the direction of the work chambers (2,3), and the pressure restriction valve towards the control valve. Parallel to the check and restriction valves is a throttle (11), and both the valves are spring-loaded, a single pressure spring being used to load their respective pistons. The two valves, together with the throttle, are located in a common housing, the throttle serving to damp vibrations. USE/ADVANTAGE - As power-assisted steering for an automotive vehicle, in which negative damping during travel is minimised.

Description

The invention relates to an auxiliary power steering system, especially for motor vehicles, with a servo motor, whose two work rooms are connected to one with work lines Control valve connected and via the control valve alternately with a servo pump and one Pressure medium containers are connectable, with each of the two working lines parallel to each other Check valve and a pressure relief valve such are arranged that the check valve in the direction of opens the work area and the pressure relief valve in Direction to the control valve opens.

Such power steering is known from the DE-C3 18 14 794. One check valve and one each Pressure relief valve together form one Preload valve. Through the bias valves Vibrations and pendulum movements caused by Uneven road surfaces or similar obstacles are prevented by simple means that in a certain, all pressure chambers of the servo motor maintain consistently high preload pressure becomes. In certain applications, such as commercial vehicle Steering systems is a constantly maintained Preload pressure is not desirable because it causes the Reset of the axis can be braked or decelerated could.

The invention is therefore based on the object To create power steering, in which the influence of a negative dynamic damping is reduced.  

This object is achieved by the in claims 1 and 2 respectively marked auxiliary steering released. By installation a throttle or a check valve that in Opening direction is spring-loaded, becomes almost undamped return flow from the two workrooms of the Servo motor reached during normal steering movements. First when jerky movements with higher oil emissions occur, either the effect of the throttle occurs, or the check valve is closed. In both cases the pressure relief valve becomes at a certain pressure to open. By dimensioning the Pressure relief valve can define the damping effect be that the driver bumps or vibrations only in weakened shape on the steering wheel. The effect of Impacts on the mechanical transmission parts decreased.

With a combination of the throttle and the Opening direction spring-loaded check valve can application-specific damping characteristics targeted can be achieved.

The pressure relief valve can advantageously be arranged within the check valve. It is it is also possible to put these two valves and the throttle in to accommodate a common housing.

The invention is not based on the combinations of features of claims limited. For the person skilled in the art further sensible combinations of requirements and individual claim characteristics from the task.

The invention is based on three in the Drawing illustrated embodiments closer explained. It shows  

Figure 1 shows the first embodiment of the power steering system according to the invention in a schematic representation.

FIGS. 2 and 3 each show a detail from FIG. 1 with a valve combination according to two further exemplary embodiments;

Fig. 4 shows a longitudinal section through a combination valve of the embodiment of FIG. 3;

5 shows the cross section through the valve combination according to the line VV in Fig. 4.

Fig. 6 shows a longitudinal section as in Fig. 4, but in a constructive variant.

The power steering system according to the invention contains a servo motor 1 , the working spaces 2 and 3 of which are connected to a control valve 6 via working lines 4 and 5, respectively. The control valve 6 can be adjusted via a steering handwheel (not shown) and controls the inlet from a servo pump 7 to the two working spaces 2 and 3 of the servo motor 1 and the return from the two working spaces 2 and 3 to a pressure medium container 8 .

The following components are arranged parallel to each other in each of the two working lines 4 and 5 :

• 1. A check valve 10 , which opens in the direction of the working space 2 or 3 of the servo motor 1 and prevents a return from this working space.
• 2. A throttle 11 , which throttles the return from the work space 2 or 3 and thereby dampens vibrations. The required damping effect of the throttle is set by the selection of the flow cross section of the throttle 11 .
• 3. A pressure relief valve 12 that opens in the direction of the control valve 6 . The pressure relief valve 12 limits the pressure in the working space 2 or 3 to a certain maximum value, for example 30 bar, and thereby prevents an excessive load on the mechanical steering parts.

FIG. 2 shows a valve combination in which the throttle 11 is omitted compared to the combination of FIG. 1. Instead of the simple check valve 10 , a check valve 13 is used, which is spring-loaded in the opening direction. It is thereby achieved that the check valve only closes when jerky movements of the piston 14 of the servo motor 1 cause higher oil ejection flows.

FIG. 3 shows a valve combination that corresponds to the combination from FIG. 2, but additionally contains the throttle 11 . This version is particularly suitable for steering systems in which the mechanical steering gear parts are heavily loaded by the steered vehicle wheels when driving over obstacles because the pressure builds up too slowly. Dynamic steering damping is avoided during normal steering movements.

In FIG. 4 is a longitudinal section through a constructive design of the valve combination of FIG. 3 is illustrated. A valve piston 16 of the check valve 13 is guided axially displaceably against the force of a compression spring 17 in a housing 15 . The valve piston 16 acts as a closing body of the check valve 13 with a valve seat 18 fixed to the housing. The compression piston 17 pushes the valve piston 16 away from the valve seat 18 .

In order to enable an unimpeded flow of the pressure medium in the opened state of the check valve 13 , lateral flattened portions 20 and radial bores 21 are provided on the valve piston 16 .

The pressure relief valve 12 is arranged inside the valve piston 16 of the check valve 13 . The pressure relief valve 12 has a valve piston 22 which is held in contact with a valve seat 24 by a compression spring 23 . The valve seat 24 is formed on the valve piston 16 of the check valve 13 . The compression spring 23 is supported on a stop ring 25 which is connected to the valve piston 16 . In the valve piston 16 further radial bores 26 are arranged, via which an annular piston surface 27 of the valve piston 22 is pressurized from the working space 2 or 3 . When the pressure relief valve 12 is open, the bores 26 enable a connection from the working space 2 or 3 to the control valve 6 .

The throttle 11 is formed in the valve piston 16 of the check valve 13 as a bore 28 .

If the compression spring 17 of the check valve 13 is omitted, the valve combination is obtained, which is shown schematically in FIG. 1.

FIG. 6 shows a design variant of the valve combination shown in FIG. 4. Parts that correspond to one another are provided with the same reference symbols in both figures. In this embodiment, the two compression springs of the pressure relief valve 12 and the check valve 13 are combined in a single compression spring 30 . The remaining structure corresponds to the structure in FIG. 4.

With this variant, the number of components can be reduced. The tuning of the opening pressures has to be done solely by the sizes of the effective piston areas, while in the embodiment according to FIG. 4 the two compression springs 17 and 23 can also be used for tuning.

The following is the function of the invention Power steering described:

If the control valve 6 is moved to the right in FIG. 1, the servo pump 7 delivers pressure medium via the working line 4 into the working space 2 of the servo motor 1 . The pressure medium opens the check valve 10 and also flows through the throttle 11 in the direction of the working space 2 . The pressure medium ejected from the working space 3 flows into the pressure medium container 8 via the throttle 11 of the working line 5 . The pressure relief valve 12 opens at pressures which occur during abrupt movements of the piston 14 and are above a predetermined maximum pressure.

In the embodiments according to FIGS. 2 and 3, the flowing out of the working chamber 3 virtually unimpeded pressure fluid flows through the open held by the compression spring 17 check valve 13 to the pressure fluid container 8. The check valve 13 does not close until a larger oil flow of, for example, 10 to 15 l / min, which can occur during abrupt movements. The damping is activated. Here too, the pressure relief valve 12 does not open until the correspondingly higher pressures have been set.

Reference numerals

1 servo motor
2 work rooms
3 work space
4 work management
5 work management
6 control valve
7 servo pump
8 pressure medium containers
9 -
10 check valve
11 throttle
12 pressure relief valve
13 check valve
14 pistons
15 housing
16 valve pistons
17 compression spring
18 valve seat
19 -
20 flattening
21 hole
22 valve pistons
23 compression spring
24 valve seat
25 stop ring
26 hole
27 ring piston surface
28 hole
29 -
30 compression spring

Claims (7)

1. Power steering, in particular for motor vehicles, with a servo motor ( 1 ), the two working spaces ( 2, 3 ) of which are connected to a control valve ( 6 ) via working lines ( 4, 5 ) and via the control valve ( 6 ) to a servo pump ( 7 ) and a pressure medium container ( 8 ) can be connected alternately, a nonreturn valve ( 10 ) and a pressure relief valve ( 12 ) being arranged in parallel in each of the two working lines ( 4, 5 ) in such a way that the nonreturn valve ( 10 ) towards the working space ( 2, 3 ) opens and the pressure relief valve ( 12 ) opens in the direction of the control valve ( 6 ), characterized in that a throttle ( 11 ) is arranged parallel to the check valve ( 10 ) and the pressure relief valve ( 12 ). 2. Power steering according to the preamble of claim 1, characterized in that the check valve ( 13 ) is spring-loaded in the opening direction. 3. Power steering system according to claim 1, characterized in that the check valve ( 13 ) is spring-loaded in the opening direction. 4. Power steering system according to one of claims 1 to 3, characterized in that the pressure relief valve ( 12 ) is arranged within the check valve ( 10, 13 ). 5. Power steering system according to claim 1 or 3, characterized in that the check valve ( 10, 13 ), the pressure relief valve ( 12 ) and the throttle ( 11 ) are arranged in a common housing ( 15 ). 6. Power steering system according to claim 2, characterized in that the check valve ( 13 ) and the pressure relief valve ( 12 ) are arranged in a common housing ( 15 ). 7. Power steering system according to claim 2 or 3, characterized in that the valve piston ( 16, 22 ) of the pressure relief valve ( 12 ) and the check valve ( 13 ) are loaded by a common compression spring ( 30 ).