WO1993024355A1 - Rotary-spool valve for power-assisted hydraulic steering systems for motor vehicles - Google Patents

Abstract

The invention concerns a power-assisted hydraulic steering system with a rotary-spool valve (5, 6) and in which the relationship between the hand steering force and the hydraulic assistance can be characterized by the valve characteristic curve. Generally, a tight tolerance interval is required for this characteristic curve. The aim of the invention is to provide a device for the adjustment of the valve characteristic curve. In addition to the slot zones (Z, Z1) for normal control of the servo motor (27), the invention calls for additional zones (S, S1) for redistributing the hydraulic-fluid flow. Fitted in the return channel of the additional slot zones (S, S1) is an adjustable shutter (32). By modifying the hydraulic-fluid flow emerging through these slot zones (S, S1), the valve characteristic curve can be corrected.

Description

 Rotary slide valve for hydraulic auxiliary steering of motor vehicles

The invention relates to a rotary slide valve for hydraulic power steering systems of motor vehicles with a valve bush mounted in a steering housing and enclosing a rotary slide valve. To distribute the pressure oil to a servomotor, several repeating groove fields with control edges are incorporated on the valve bushing and on the rotary valve. In the neutral position of the rotary slide valve, there is an almost unthrottled connection between an inlet connection and a return connection. In the deflected position, a controlled pressure build-up takes place in the respectively active pressure chamber of the servomotor by stimulating or de-energizing the supply current at the control edges.

In the case of hydraulic power steering with a rotary slide valve, the relationship between the manual force to be exerted on the steering handwheel and the hydraulic assistance can be characterized using the valve characteristic. The vehicle manufacturer prescribes a narrow tolerance band for the supplier for the characteristic curve. Series production therefore places high demands on the quality and dimensional accuracy of the valve components.

Such a rotary slide valve is such. B. is known from EP-PS-0 247 060. The course of the characteristic curve depends here on the tolerances of the control edge geometry of the rotary valve, on the grooves of the valve bushing and on the dimensions of a torsion bar extending through an inner bore of the rotary valve. The torsion bar in a return bore of the rotary valve has been omitted from the document mentioned for the sake of simplifying the drawing. It comes in series production again and again that the desired characteristic falls outside the tolerance band. This results in high rework costs. For example, the rotary slide valves have to be dismantled and re-drilled with a corrected torsion bar.

It is therefore an object of the invention to find a device with which it is possible to make the valve characteristic curve adjustable.

This object is solved by the features of claim 1. Advantageous further developments result from subclaims 2 to 5.

According to the main feature of the invention, in addition to the usually multiply existing groove fields for the usual actuation of the servomotor, at least one further groove field is provided for redistribution of the oil flow. The further groove field is connected to a controllable return line, in which an adjustable diaphragm sits. The valve characteristic curve can be adjusted by changing the controlled oil flow flowing through the additional grooved field. To correct a characteristic that falls outside the tolerance band, all you have to do is change the aperture setting.

According to claim 2, it is advantageous to use the adjustable aperture accessible from the outside in the steering housing.

In the embodiment according to claim 3, the groove fields for the control of the servomotor and the groove fields for the redistribution of the oil flow are present in the same number and arranged alternately to one another. As a result, the hydraulic forces on the rotary slide valve are balanced with one another, ie the rotary slide valve is not subject to any one-sided pressure force on the circumference. The rotary slide valve can be designed according to claim 3, but also with a total of only three groove fields, in 120 degrees, of which two groove fields serve to control the servomotor and the remaining groove field controls the redistribution. In this version, the rotary slide valve is also suitable for smaller diameters.

According to claim 4, instead of only one adjustable orifice, two orifices can also be inserted in the two return bores of the valve bushing for the backflow of the return oil or the redistribution. This version makes it possible to correct an asymmetrical valve characteristic in a certain range. These orifices arranged in the steering gear housing are set in a valve test device.

The invention is explained in more detail with reference to the drawing in several exemplary embodiments. Show it:

1 shows a simplified longitudinal section through the rotary slide valve.

Fig. 2 an enlarged compared to Fig. 1

Cross section with valve housing omitted;

Fig. 3 further versions of a rotary slide valve and 4 in cross section and

Fig. 5 shows the setting range of a steering valve characteristic.

In the longitudinal section according to FIG. 1, a steering spindle 2 mounted in a valve housing 1 is connected via a torsion bar 3 to an output shaft 4, which, for example, is an unillustrated pinion of a rack and pinion steering gear wearing. A section of the steering spindle 2 is designed as a rotary slide 5, which extends into a valve bushing 6 connected to the output shaft 4. The rotary valve 5 and the valve bushing 6 form a rotary valve in a known manner. Stops (not visible) are provided between the steering spindle 2 and the output shaft 4, which allow a limited backlash to control the rotary slide valve 5, 6.

As the somewhat enlarged cross section according to FIG. 2 shows, the rotary slide valve 5, 6 has four groove fields S, S1 and Z, ZI, of which only two groove fields Z and S are explained in more detail below for the sake of clarity. In the outer circumference of the rotary valve 5 axially extending inlet grooves 7 and 8 are incorporated. These inlet grooves 7 and 8 are connected via bores 10 and 11 to an annular groove 12 connected to a high-pressure pump P. All inlet grooves 7, 8 have on their control edges, for. B. 9, 9A, control chamfers 19 and 19A, which allow a gradual up and down of the oil flow. In addition, the rotary slide valve 5 has axial return grooves 13, 14 and 15, 16, respectively. The return grooves 13, 14 of the groove fields Z are connected to an interior 17 of the rotary valve 5, which is connected to a container T via a bore 18 and a space 20 (FIG. 1). The return grooves 15, 16 of the groove fields S are connected to bores 21 and 22 which also lead to the container T. Furthermore, the valve bushing 6 has intermediate grooves 23, 24 within the groove fields S, which can establish a connection from the inlet grooves 8 to the return grooves 15 and 16, respectively. In the groove fields Z, the valve bushing 6 also has axial grooves 28 and 29 connected to pressure chambers 25, 26 of a servomotor 27. According to the invention, only the groove fields Z and ZI are used to supply the servomotor 27. The groove fields S and Sl serve to redistribute the oil flow, as will be explained in more detail. The return bores 21 and 22 of the two groove fields S and Sl are connected to an annular groove 30 (FIG. 1) of the valve bushing 6. The annular groove 30 opens into a channel 31, the flow of which can be changed by an aperture 32 which can be adjusted from the outside. For this purpose, the diaphragm is designed as a displaceable cone 33, which forms a flow cross section 34. After flowing through the flow cross section 34, the oil passes through a bore 35 into the space 20 connected to the container T.

2 shows the rotary slide valve 5, 6 in the neutral position. The pressure oil can from the bores 10 connected to the pump P of the groove fields Z, ZI via the control edges 9 open on both sides with the control chamfers 19, the axial grooves 28, 29 and the return grooves 13 and 14 into the interior 17 and from there via the bore 18 and the space 20 (Fig. 1) flow to the container T. Likewise, the oil brought in by the pump P via the bores 11 can flow into the annular groove 30 via the control edges 9A opened on both sides and the associated control chamfers 19A, the intermediate grooves 23 and 24, the return grooves 15 and 16 and via the bores 21 and 22. From the annular groove 30, the oil flows past the orifice 32 through the bore 35 and the space 20 is also in the container T. As a result of the diaphragm 32 of the Ölrϊ ^'ckfluß in the neutral position via the trip rails S and 61 lower than about the trip rails Z and ZI.

If the steering spindle 2 is turned to the right during a steering movement, the rotary slide moves in the direction of the arrow (FIG. 2) relative to the valve bushing 6. The opening created by the inlet groove 7 opens Control edge 9 wide, while the rear control edge of the inlet groove 7 gradually closes in the direction of rotation. The pressure oil brought in via the inlet bore 10 can flow into the pressure chamber 25 of the servomotor 27 via the axial groove 29. The pressure oil pushed out simultaneously from the pressure chamber 26 flows via the axial groove 28 and the return groove 13 into the interior space 17. From there the oil reaches the container T via the bore 18 and the space 20 (FIG. 1) The control process takes place in the same way within the slot field ZI.

A small proportion of the flow into the container T can be derived through the groove field S or S1 as follows:

When the rotary slide valve 2 is rotated in the direction of the arrow as described above, the connection of the intermediate groove 24 to the axial return groove 16 is gradually closed. Less and less pressure oil can therefore flow from the inlet groove 8 connected to the pump P via the bore 22, the annular groove 30, the diaphragm 32, the bore 35 and via the space 20 into the container T. The same happens in the area of the control edge 9A to the left of a center line M on the inlet groove 8. The connection to the return from the inlet groove 8 via the intermediate groove 23, the axial return groove 15 and via the bore 21 is throttled more and more. However, as long as the wheels can still be moved in the steering direction, a relatively low cut-off current always flows out via the diaphragm 32 to the container T. This cut-off current, which is to a certain extent removed from the servomotor control via the slot fields Z, ZI (redistribution), is lower the greater the steering force on the steering handwheel increases.

Fig. 5 shows the steering valve characteristic curve with a so-called wide curve B and a so-called narrow curve C. When adjusting the rotary slide valve, care must be taken that the Characteristic lies within the setting range D. According to the invention, depending on the setting of the diaphragm 32, a change in the amount of oil flowing through the groove fields S and S1 can be carried out. The valve characteristic curve can be varied by this change in the oil tightness. Thus, when the diaphragm 32 is completely closed and the rotary slide valve 5, 6 is adjusted, no pressure oil flows over the groove fields S and Sl. All of the oil flows over the grooved areas Z and ZI and the tight curve shape C results. With the aperture 32 completely open, however, the return cross section is correspondingly larger and the wide curve shape D is obtained with the somewhat smaller increase in force.

Suppose you turn the rotary valve 5, 6 z. B. in a sudden steering movement so far that the control edges are completely closed, then no oil flows through the adjustable aperture 32. The total amount of oil is available for the steering speed in this case. Likewise, the leakage oil occurring in the valve can be measured when the rotary slide valve is closed, since, as with conventional steering valves without adjustable valve characteristic, there is no additional oil loss.

3 has a total of three groove fields. The slot fields Z and ZI serve to control the servomotor 36, while only one slot field S is provided for the redistribution. The mode of operation corresponds to FIGS. 1 and 2.

4 corresponds to FIG. 3, but with the difference that instead of one adjustable orifice in the valve housing, two adjustable orifices 37 and 38 are provided in the valve bushing 6. These diaphragms are firmly seated in bores 40 and 41. The bores 40 and 41 are connected to the annular groove 30 connected to the container T (FIG. 1). Such an adjustment option has the advantage that the two characteristic branches (Fig. 5) can be set separately in each steering direction. In addition, an asymmetrical characteristic can be set to the zero point.

The inner orifices 37 and 38 can be adjusted in a valve test device. In this device, the adjustment of the aperture adjustment screws can be carried out from the outside via a rotatable shaft which is sealed in the device and is axially displaceable.

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Claims

Expectations 1. Rotary slide valve for hydraulic power steering systems of motor vehicles with the following features: a valve bushing (6) mounted in a housing (1) surrounds a rotary slide valve (5); To distribute the pressure oil to a servomotor (27), several repeating groove fields (Z, ZI) with control edges are incorporated on the valve bushing (6) and on the rotary slide valve (5); in the neutral position of the rotary slide valve (5, 6) there is an almost unthrottled connection between an inlet connection and a return connection; In the deflected position, a controlled pressure build-up takes place in the respectively active pressure chamber of the servomotor by de-energizing part of the inlet flow at the control edges, characterized by the following features: in addition to the groove fields (Z, ZI) for controlling the servomotor (27) there is at least one further groove field (S or Sl) provided for a redistribution of the oil flow; a diaphragm (32) is seated in a return line (channel 31) connected to the additional groove field (S or Sl) for the redistribution, such that the valve characteristic can be adjusted by changing an oil flow flowing through the additional groove field. 2. Rotary slide valve according to claim 1, characterized in that an adjustable diaphragm (32) is accessible from the outside in the housing (1) (Fig. 1). 3. Rotary slide valve according to claim 1, characterized in that the groove fields (Z, ZI) for the control of the servomotor (27) and the groove fields (S, Sl) for the redistribution of the oil flow are present in equal numbers and in the circumferential direction of the rotary slide valve ( 5, 6) lie alternately to each other (Fig. 2). 4. Rotary slide valve according to claim 1, characterized gekennz ei chnet that a total of three groove fields are provided, of which two groove fields (Z and ZI) serve to control the servomotor (27) and the further groove field (S) controls the redistribution (Fig. 3rd ). 5. Rotary slide valve according to claim 4, characterized in that two adjustable orifices (37 and 38) in each return bore (40 and 41) of the valve bushing (6) of the groove field (S) are used for the redistribution (FIG. 4).