GB2028741A - Servo steering device - Google Patents

Abstract

A servo steering device which is insensitive to variations in fluid supply pressure has a steering input member 4, and an output member 3 connected to a piston 2 in a cylinder 1. The steering member 4 has two spaced stop faces 6, each of which cooperates with a face of an element 7 mounted in the piston 2. Hydraulic fluid under pressure is passed to the centre of element 7, and passes out through one or the other, or both of the gaps between the stop faces and corresponding element faces. Fluid outlet conduits 30, 31 communicate with the gaps and lead to pressure pins 25 for actuating a control valve 22 which controls admission of pressure fluid to the cylinder 1. Movement of the input member 4 results in displacement of the stop faces 6 relative to the faces of the element 7 to create unequal pressures in the conduits 30, 31 with consequent displacement of the control valve 22. In another embodiment a rotary input member is coupled to the piston by a screw-thread, and the stop faces on the input member co-operate with respective faces of a fixed reaction member. <IMAGE>

Description

SPECIFICATION Device for amplifying a steering force to a driving force and device for converting a rotary steering movement into a rectilinear driving movement.

The invention relates to a device for amplifying a steering force to a driving force with the aid of a hydraulic or pneumatic motor, said device comprising on the one hand a steering member and a driving member and on the other hand a piston and a cylinder.

Such devices are often used as servo-steering devices on vehicles and for controlling the cutters of benches. It has, however, been found that the known devices are fairly sensitive to pressure fluctuations of the hydraulic or pneumatic fluid, which results in an irregular amplification of the steering force to the driving force. It has furthermore been found that in the known devices the steering member has to perform a comparatively large axial displacement before amplification is obtained.

The invention has for its object to obviate the aforesaid disadvantages and provides a device which is distinguished in that the steering member is provided with two relatively spaced, parallel stop faces co-operating with stop faces of a counterelement, in which a fluid supply conduit opens out in a space left between the stop faces and each fluid outlet conduit communicates with a space on the side of each stop face remote from the supply conduit, said outlet conduits communicating oppo site one another with a valve controlling the cylinder.

Owing to this disposition the device is very sensitive, irrespective of the pressure fluctuations of the fluid, since only very small pressure and volume differences on the two stop faces are sufficient to determine the position of the control-valve to energize the driving cylinder. Thus the fluid pressure fluctuations are completely levelled out.

In a further embodiment of the invention the device serves to convert a rotary steering movement into a rectilinear driving movement through the intermediary of a hydraulic or pneumatic motor, said device comprising on the one hand the elements piston and cylinder and on the other hand a threaded spindle and a nut, one (preferably the cylinder) of the pair of first-mentioned elements being fixed in place and the other (preferably the piston) safeguarded against rotation being rectilinearly movable and being connected with one (preferably the nut) of the pair of last-mentioned elements, the other (preferably the threaded spindle) of said pair being rotatable and being limited in the axial direction of movement by stop means having two relatively spaced pressure faces, in which in accordance with the invention the fluid inlet conduit opens out in the space formed between the pressure faces and each outlet conduit communicates with a space on the side of each pressure face remote from the firstmentioned conduit, said outlet conduits communicating opposite one another with a valve controlling the cylinder.

The invention will be described more fully with reference to a few embodiments. The drawing shows in Figure 1 a longitudinal sectional view of a first embodiment, Figure 2 a cross-sectional view taken on the line Il-Il in Figure 1, Figure 3 an axial cross-sectional view of a second embodiment.

Referring to Figures 1 and 2, reference numeral 1 designates the housing of the cylinder, 2 the piston axially movable therein. The piston 2 is rigidly connected with a driving member 3 and a steering member 4 extends coaxially inwardly through the cylinder 1 as far as into a central bore 5 of the piston 2.

At the right-hand end located in the central bore the steering member 4 has two stop faces 6, which are spaced apart to an extent such that an annular counter-element 7 can be arranged with intimate fit.

The correct axial distance between the stop faces 6 can be adjusted by means of a pressure ring 8 having the right-hand stop face 6 and loaded by a nut 10 screwed on a thread 9 at the end of the steering member 4.

The ring 7 is freely slidable in the central bore of the cylinder 2 and stuffing means are arranged between the ring and the inner wall of the bore. The bore itself is closed on the left-hand side by a suitable seal 12. Finally a compression spring 13 is arranged between the bottom of the bore and the pressure ring 8.

The steering member 4 is formed in the embodiment shown by a cylinder 15, whose right-hand end is provided with the aforesaid stop faces 6. In this cylinder 15 a piston 16 is provided on the left-hand side with a control-rod 17.

Suitable stuffing means 18 are arranged between the outer wall of the cylinder 15 and the inner wall of the cylinder housing 1 and stuffing means 19 are provided between the connecting rod 3 and the cylinder housing 1.

At the side of the cylinder housing 1 a controlvalve 20 is arranged, which has a central bore 21, in which a valve body 22 is reciprocatorily slidable. The valve body 22 has a narrowed central portion so that a space 23 for the fluid is formed.

On both sides of the valve body 22 pressure pins 25 accommodated in closing members 24 are acting upon the valve body, which will be explained more fully hereinafter.

A fluid inlet channel 26 leads to the space 23 of the control valve 20 as well as to the space 27 between the stop faces 6 of the steering member 4. Channels 28 and 29 lead to the respective ends of the main cylinder 1 and open out each on one side of the piston 2. The channels 28 and 29 communicate with the central bore of the control-valve 20.

Finally two channels 30 and 31 lead from the central bore 9 in the piston 2, one on each side of the stop faces 6, towards the pressure spaces 32 and 33 respectively in the closing members 24 of the control-valve 20. The inlet channel 26 also communicates with the pressure space in the cylinder 15.

The device operates as follows.

In the position shown in Figure 1, in which both the control-rod and the connecting rod occupy the extreme right-hand position in the cylinder housing 1, a state of equilibrium prevails, when the steering member 4 is not loaded, since the pressure of the fluid in the channel 26 has equal "leakages" via the space 27 along the two stop faces 6 so that equal pressures will prevail in the central bore 5 of the piston 2 on both sides of the ring 7. This results in equal pressures on the pressure pins 25so that the valve body 22 will not shift in place. As soon as the steering member 4 is moved to the left, the leakage along the left-hand stop face 6 will be greater than that along the right-hand stop face 6, as a result of which the channel 30 receives fluid and the left-hand pin 25 causes the valve body 22 to move to the right.

Thus fluid will flow through the valve, that is to say, the space 23 into the channel 29 so that the piston 2 is subjected to a fluid force directed to the left, the connecting rod 3 thus also moving to the left.

As soon as the steering member 4 is moved to the right, a reverse state of pressure will occur so that the connecting rod 3 moves to the right. As soon as the steering member 4 is no longer loaded, a state of equilibrium will again establish.

When the pressure in the channel 26 falls out, pressure will occur in the space 15 of the steering cylinder so that the steering rod 4 can move freely with respect to the cylinder and a direct connection between the steering rod 4 and the connecting rod 3 is avoided, the safety of the device being thus safeguarded.

The device shown in Figure 3 comprises a housing 51 having four portions 51a, 51b, Sic and 51d. The housing accommodates the elements piston 52 and cylinder 53 on the one hand and the elements threaded spindle 54 and the nut co-operating herewith and being, in this embodiment, integral with the piston 52 on the other hand. The nut 55 has an axial length such that the left-hand end as seen in Figure 3 projects out of the housing 51a as well as the threaded spindle 54. With the nut 55 has to be coupled the body to be displaced, for example, the steering rod of a vehicle.

With the opposite end of the threaded spindle 54, which also emerges from the housing 51, may be coupled any driving mechanism, for example, the steering wheel in order to rotate the threaded spindle 54.

In the housing 51 the threaded spindle 54 is axially journalled by stop means 56 formed by shoulders 56 rigidly connected with the threaded spindle and being spaced apart, whilst the proximal sides thereof co-operate with the head faces of the housing compartment 51c. For this purpose the housing compartment 51e has a smaller bore than the housing compartments 51b and 51 d. The shoulders 56 together with the housing compartment Sic constitute the pressure faces 57 and 57', which are formed at a given distance from one another.

The spindle 54 is furthermore supported by radial bearings 58.in the housing compartments 51b and 51d so that a play-free rotation is ensured.

The housing compartment Sic furthermore comprises a control-valve 59 and in bores 60 coaxial with the control-valve 59 the housing compartments 51 b and 51d comprise steering pistons 61 for the steering slide 62 of the control-valve 59.

The housing compartment Sic has a central bore forming a fluid inlet conduit 63, which opens out centrally in the control-valve 59 and in the space 64 between the two pressure faces 57 and 57' of the threaded spindle 54.

The control-valve 59 has furthermore two outlet ports 65 communicating with a conduit leading to one side of the piston 52 in the cylinder 53 and a port 66 communicating with a conduit leading to the other side of the piston 52 in the cylinder 53.

The conduit from the port 65 communicates with a radial recess in the housing compartment ski a having furthermore longitudinal channels 67 outside the cylinder 53. The longitudinal channels 67 communicate with passages 68 in the cylinder wall 53. The conduit from the port 66 is directly connected with the bore around the threaded spindle 54 in the housing compartment 51 b.

The housing compariments 51b and 51d have bores forming conduits 69 and 70 respectively opening out on the other sides of the pressure faces 57 and 57', viewed from the space 64. These conduits 69 and 70 open out opposite one another at the pistons 61 for the steering slide 62 of the control-valve 59. Plugs 71 close the conduits 69 and 70 to the outside.

The control-valve 59 has furthermore an outlet port 72 for conducting away fluid from the controlvalve 59 towards a central outlet duct 73. This duct 73 also communicates with the space between the bearings 58 in the housing compartment 51b and with a bore 74 serving like the port 72 for conducting away fluid on the other side of the control-valve 59.

The device operates as follows.

The inlet conduit 63 is constantly fed with fluid from any suitable means, for example, a hydropump. The fluid thus enters the central part of the control-valve 59 and the space 64. Owing to the normal bearing clearance along the pressure faces 57 and 57' fluid will leak along the shoulders 56 and flow back through the conduits 69 and 70 to the left-hand and right-hand steering piston 61 respectively on either side of the steering slide 62. Owing to an appropriate clearance between the steering pistons 61 and the bores 60 the fluid flows along the pistons 61 through the return conduits 72 and 74 back towards the conduit 73. Therefore, in the absence of a turn of the spindle 54 a state of equilibrium will be established and the control slide 62 will occupy the position shown in Figure 3.

As soon as the spindle 54 is turned the size of the gap near the pressure faces 57 and 57' will vary so that the equilibrium is disturbed. It is assumed that the spindle 54 is turned to an extent such that the piston 52 has to move downwards as seen in Figure 3 so that as a resuit of reactive force the threaded spindle 54 tends to move upwards. The gap at the pressure face 57' will be enlarged by a fraction, whereas that at the pressure face 57will become smaller. Therefore, a larger amount of fluid will flow through the channel 70 towards the control-valve 59 and a minor amount will flow through the channel 69. Thus a pressure difference is produced on the control-slide 59, which will move downwards as seen in Figure 3 so that the port 69 is released and the fluid flows from the channel 63 through the channel 66 to the space above the piston 52.The pressure of the fluid will, therefore, enhance the displacement of the piston 52 or the nut 55 respectively in a downward direction, which corresponds to the tendency of the threaded spindle 54.

When the rotation of the spindle 54 is stopped, the aforesaid state of equlibrium will immediately reestablish so that the control-slide 62 returns to the position shown in Figure 3 and will close the conduit 66. Upon an opposite turn of the spindle 54 the gap at the pressure face 57 becomes larger than that at the pressure face 57' so that a higher amount of fluid will flow through the conduit 69 and a minor amount through the conduit 70. This results in a pressure discrepancy on the control slide 62, which will move upwards so that the port 65 is opened and the lower side of the piston 52 is loaded by the fluid.

For the sake of completeness it is noted that the return of fluid on the no-load side of the piston 52 takes place through the port 72, when the piston 52 is moved downwards, and through the port 74, when the piston 52 is moved upwards.

As a matter of course, the invention is not limited to the embodiments described above. For the sake of completeness it is noted that one of the shoulders 56 is axially displaceable along the spindle rather than being rigidly fixed. In this way a bias force on the pressure faces can be adjusted so that the device is suitable for use with high pressures of the fluid. The high pressure results in an enlargement of the spindle portion between the stop faces so that the desired gap size at each pressure face is obtained.

Claims (5)

1. A device for amplifying a steering force with the aid of a hydraulic or pneumatic motor, said device comprising a steering member and a driving member on the one hand and a piston and a cylinder on the other hand, characterized in that the steering member has two relatively spaced, parallel stop faces co-operating with stop faces of a counterelement, in which a fluid inlet conduit opens out in a space between the stop faces and each fluid outlet conduit communicates with a space on the side of each stop face remote from the inlet conduit, said outlet conduits communicating opposite one another with a valve controlling the cylinder.

2. A device as claimed in Claim 1 characterized in that the steering member is slidable in an axial bore of the piston, the counter-element being formed by a ring arranged between the stop faces.

3. A device as claimed in Claims 1 and 2 characterized in that the piston and the driving member are integral with one another and the steering member is formed by a single-action cylinder-piston system, in which the pressure space communicates with the fluid inlet conduit.

4. A device for converting a rotary steering movement into a rectilinear driving movement with the intermediary of a hydraulic or pneumatic motor, said device comprising on the one hand the elements piston and cylinder and on the other hand the elements threaded spindle and nut, one (preferably the cylinder) of the pairoffirst-mentioned elements being stationary and the other (preferably the piston) safeguarded against rotation being rectilinearly movable and being connected with one (preferably the nut) of the pair of last-mentiond elements, the other (preferably the threaded spindle) of said pair being rotatable and being limited in its axial movement by stop means having two relatively spaced pressure faces, characterized in that a fluid inlet conduit opens out in the space formed between the pressure faces and each outlet conduit communicates with a space on the side of each pressure face remote from said first conduit, said outlet conduits communicating opposite one another with a valve controlling the cylinder.

5. A device as claimed in any one of the preceding Claims characterized in that elements having the stop faces are axially adjustable with respect to the steering member and the threaded spindle respectively.