WO1996017765A1

WO1996017765A1 - Control apparatus for a hydrostatic auxiliary power steering arrangement

Info

Publication number: WO1996017765A1
Application number: PCT/DK1995/000487
Authority: WO
Inventors: Niels Arbjerg
Original assignee: Danfoss A/S
Priority date: 1994-12-07
Filing date: 1995-12-05
Publication date: 1996-06-13
Also published as: DE4443468C2; DE4443468A1; AU4252996A

Abstract

A control apparatus for a hydrostatic auxiliary power steering arrangement, in particular for vehicles, has a metering motor (10) and two coaxial rotary slide valves (16, 17) forming between them a directional valve (14). The directional valve (14) is opened by rotating the inner rotary slide valve (17) by means of a steering element (57), so that fluid under pressure is allowed to pass through the metering motor (10) to a steering motor (8) and the metering motor (10) adjusts the outer rotary slide valve (16) in dependence on the amount of fluid flowing through the inner rotary slide valve (17). To avoid abrupt changes in the rotational speed of the inner rotary slide valve, and therefore to prevent acceleration forces that are too high being exerted on the steered item and possibly on the person controlling the steering, the inner rotary slide valve (17) is connected to a damping arrangement (70) counteracting its rotational movement.

Description

Control apparatus for a hydrostatic auxiliary power steering arrangement.

The invention relates to a control apparatus for a hydrostatic auxiliary power steering arrangement, in particular for vehicles, having a metering motor and two coaxial rotary slide valves forming between them a directional valve, wherein the directional valve is opened by rotating the inner rotary slide valve by means of a steering element and allows fluid under pressure to pass through the metering motor to a steering motor and the metering motor adjusts the outer rotary slide valve in dependence on the amount of fluid flowing through the inner rotary slide valve.

In a known control apparatus of that kind, (DE 35 04 993 C2) , which is used in a steering system for wheels of a motor vehicle, fluctuations in pressure may occur which cause relative rotary oscillations of the rotary slide valves so that both the steering wheel and the wheels are affected. When using the known control apparatus for a vehicle with centre pivot steering, if the steering wheel is operated too quickly considerable lateral accelerations can be exerted on the driver, who normally sits above this centre pivot joint connecting the two frame parts.

The invention is based on the problem of providing a control apparatus of the kind mentioned in the introduction which largely prevents steering vibrations and steering acceleration forces that are too high. According to the invention, this problem is solved by connecting the inner rotary slide valve to a damping arrangement.

In this construction, the damping arrangement counteracts a rotary movement of the rotary slide valve. Any change in the rotational speed of the rotary slide valve, and thus also of the steering element, is thereby damped, so that it is impossible to carry out steering movements that are too fast and lateral acceleration forces are consequently also kept low. Conversely, reactions of the steered parts on the steering element and possible vibrations of these parts are also damped.

Provision is preferably made for the damping of the damping arrangement to change in dependence on the angle of rotation of the inner rotary slide valve, in particular for it to increase as the angle of rotation increases. In that case, principally a steering movement during travel straight ahead is damped less than when cornering.

It is then advantageous for the damping arrangement to be arranged inside the inner rotary slide valve. The space inside the hollow-cylindrical inner rotary slide valve is unoccupied in the control apparatus according to the preamble, since the articulated shaft of the metering motor lies substantially outside that space. If, therefore, the damping arrangement is arranged in this space, the construction is compact and no extra space is required.

In particular, the control apparatus can be constructed such that displaceably mounted in the inner rotary slide valve there is a twin piston arrangement, the two pistons of which lie, sealed, against the inside of the inner rotary slide valve and with their end faces bound a respective one of two chambers which are hydraulically connected to a tank for the fluid and to one another by way of a through-channel passing through the twin piston arrangement, that between the pistons a sleeve that is fixed, sealed, to the inside of the inner rotary slide valve surrounds, forming a seal, a cylinder mechanically joining the pistons, which cylinder is axially displaceable inside the sleeve, that two annular channels bounded by the end faces of the sleeve and the pistons are hydraulically connected by a first throttle duct passing through the sleeve, that the one annular channel is hydraulically connected by a second throttle duct to a first bore of the sleeve and the other annular channel is hydraulically connected by a third throttle channel to a second bore of the sleeve, that the first bore of the sleeve is hydraulically connected by way of a first bore of the cylinder and the second bore of the sleeve is hydraulically connected by way of a second bore of the cylinder to the through-channel in dependence on the displacement of the cylinder in the sleeve, that the one chamber is hydraulically connected to the one annular channel by a non-return valve and the other chamber is hydraulically connected to the other annular channel by a non-return valve, and that the twin piston arrangement is mechanically connected and, at least axially, displaceably connected to the outer rotary slide valve and connected to the inner rotary slide valve by a drive mechanism converting the rotation thereof into an axial advancement movement of the twin piston arrangement.

The drive mechanism may be, for example, a screw connection between the twin piston arrangement and the inner rotary slide valve. It is equally possible for a pin to be secured radially to the twin piston arrangement, which pin projects through a slot in the inner rotary slide valve into a slot in the outer rotary slide valve, for one slot to extend axially and both slots to intersect at an acute angle and to guide the pin with their longitudinal edges. The construction of threads between the twin piston arrangement and the inner rotary slide valve is consequently unnecessary.

The invention and its developments are described in greater detail hereinafter with reference to the drawings of a preferred embodiment. In the drawings,

Fig. 1 is a simplified view of a longitudinal section through a control apparatus according to the invention, Fig. 2 is an enlarged view of parts of the control apparatus according to Fig. 1, and Fig. 3 is a simplified side view of the rotary slide valve arrangement according to Fig. 2.

The control apparatus according to Fig. 1 has a valve housing 1 with a connection P for a pump, a connection T for a tank and two diagrammatically indicated working connections R and L for a steering motor 8. The valve housing 1 is connected by screws 9 to a metering motor 10 which has a set of gears, comprising a stationary internally-toothed annular gear 11 and a rotating and gyratory externally-toothed gear 12. The gear 12 has one tooth less than the annular gear 11 so that displacement chambers 13 form between the teeth.

In the valve housing 1 there is a valve arrangement 14 which is formed by a housing bore 15, an outer rotary slide valve 16 and an inner rotary slide valve 17. In the bore there are four annular channels 18, 19, 20 and 21 which are connected to the pump connection P, the working connection R, the working connection L and the tank connection T respectively. In the supply line between the pump connection P and the annular channel 18 there is additionally provided a non-return valve 22. Between the annular channels 18 and 19 there are distribution openings 23, each of which is connected to a displacement chamber 13, the number of which corresponds to the number of teeth on the annular gear 11.

An articulated shaft 42 is connected with its first head 43 by way of a coupling pin 44 on the side facing the set of gearwheels with the outer rotary slide valve 16. The coupling pin 44 here engages in recesses 46 in the outer rotary slide valve 16 and passes at the same time through openings, not illustrated, in the inner rotary slide valve 17, the circumferential dimension of which openings allows a limited relative movement between the two rotary slide valves 16, 17. The second head 47 of the articulated shaft 42 is connected by way of a multi-spline coupling 48 to the gear 12 so that they rotate together. To that end the gear 12 has a toothing 49 for a limited part of its length whilst the remainder of the through passagework 50 in the gear 12 has a larger diameter than the base of the grooving of that toothing 49. The axial position of the articulated shaft 42 is secured by an insert 51 which is retained by a cover 53.

The head 43 of the articulated shaft 42 projects into a recess 54 of short axial length in the inner rotary slide valve 17. Passing through the inner rotary slide valve 17 is a bore 55 which is connected to the tank by way of apertures 56 in the inner rotary slide valve 17 and apertures 41 in the outer rotary slide valve 16 which serve to receive restoring leaf springs, not illustrated.

To simplify the illustration, the rotary slide valves 16 and 17 are here shown without their customary control channels, control openings and annular channels. They are, however, provided as in the control apparatus according to German patent specification 35 04 993. With regard to further details, the reader is therefore referred to that patent specification. The co-operation of the rotary slide valves 16, 17 and the metering motor 10 in dependence on a rotation of the inner rotary slide valve 17 through turning of a steering element 57, here a steering wheel, which is linked to a coupling part 58 of the inner rotary slide valve 17 projecting from the housing 1, would likewise be the same as in the known control apparatus according to German patent specification 34 09 993, had a damping arrangement 70 according to the invention not been provided in the bore 55. Only those details relating to the mode of operation of the known control apparatus will therefore be mentioned: through rotation of the inner rotary slide valve 17 by means of the steering element 57 the directional valve 14 formed between the two rotary slide valves 16, 17 is opened, the fluid flowing to the steering motor 8 is initially conducted through the metering motor 10 and the latter adjusts the outer rotary slide valve 16 in dependence on the amount flowing through the metering motor to the inner rotary slide valve 17 until the directional valve is blocked again and the flow through the metering motor is interrupted, the steering motor 8 then having the position corresponding to the new rotated angle of the steering element 57.

In the known control apparatus so far described, pressure fluctuations which can lead to relative rotary oscillations of the inner and outer rotary slide valves may occur; these affect both the steering element and the steered vehicle wheels operated by the steering motor 8. When the known control apparatus is also deployed in vehicles with centre pivot steering, it is possible for high lateral acceleration to occur if the steering element is operated too quickly, and this is uncomfortable for the driver of the vehicle.

To avoid this, the damping arrangement 70 is provided, the construction and mode of operation of which are described below.

The damping arrangement 70 contains a twin piston arrangement 71 mounted in the inner rotary slide valve 17 so as to be axially displaceable, the two pistons 72 and 73 of which (see in particular also Fig. 2) lie, sealed, against the inside of the inner rotary slide valve 17 and with their end faces bound a respective one of two chambers 74, 75, which are hydraulically connected to one another by way of a through-channel 76 passing through the twin piston arrangement 71 and to the tank. Between the pistons 72, 73, a sleeve 77 that is secured, sealed, to the inside of the inner rotary slide valve 17 surrounds, forming a seal, a cylinder 78 mechanically connecting the pistons 72, 73. The cylinder 78 is axially displaceable in the sleeve 77. Two annular channels 79, 80 bounded by the end faces of the sleeve 77 and the pistons 72, 73 are hydraulically connected by a first throttle channel 81 led axially through the sleeve 77. The annular channel 79 is hydraulically connected by a second axial throttle channel 82 in the sleeve 77 to a first radial bore 83 of the sleeve 77, and the annular channel 80 is hydraulically connected by a third axial throttle channel 84 in the sleeve 77 to a second radial bore 85 of the sleeve 77. The first bore 83 of the sleeve 77 is hydraulically connected by way of a first radial bore 86 of the cylinder 78 and the second bore 85 of the sleeve 77 is connected by way of a second radial bore 87 of the cylinder 78 to the through-channel 76 in dependence on the displacement of the cylinder 78 in the sleeve 77. One chamber 74 is hydraulically connected to the one annular channel 79 by a non-return valve 88, which opens towards the annular channel 79, and the other chamber 75 is hydraulically connected to the other annular channel 80 by a non-return valve 89 which opens towards the annular channel 80. Fastened radially to the twin piston arrangement 71 there is a pin 90 which, as shown in Fig. 3, projects through a slot 91 of the inner slide valve 17 into a slot 92 of the outer rotary slide valve 16. One slot 91 extends axially, and both slots 91, 92 intersect at an acute angle and guide the pin 90 with their longitudinal edges, the pin 90 being firmly seated in a radial bore 93 of the cylinder 78.

A bolt 94, which is seated in radial bores of the sleeve 77 and the inner rotary slide valve 17, joins the sleeve 77 to the inner rotary slide valve 17 so that they rotate together and so that the sleeve is not displaceable axially. The sleeve 77 is therefore able to rotate only together with the inner rotary slide valve 17.

The piston 73 is in the form of a ring which surrounds, forming a seal, the cylinder 78 and is connected to this by a further bolt 95 which engages in radial bores of the cylinder 78 and the piston 73.

The chamber 75 is tightly sealed with respect to the metering motor 10 by a plate 96.

When the inner rotary slide valve 17 is rotated by means of the steering element 57, this rotary movement is converted by the drive mechanism formed by the pin 70 and the slots 91, 92 into an axial advancing movement of the twin piston arrangement 71. Let us assume that the twin piston arrangement 71 in Figs 1 and 2 moves to the right from the illustrated neutral position for driving straight ahead. In that case, the fluid contained in the annular channel 79 is initially displaced not only through the throttle channel 81 into the annular channel 80 which is enlarging axially as a result of displacement of the twin piston arrangement 71, but is also conveyed through the throttle chamber 82, the bores 83, 86, the through-channel 76 and the chamber 74 to the tank. Initially, therefore, that is, from the neutral position onwards, a relatively rapid displacement of the twin piston arrangement 71, and thus a relatively rapid rotation of the inner rotary slide valve 17 and the steering element 57, is possible with comparatively little damping. Once the displacement of the twin piston arrangement 71 is sufficiently advanced for the bores 83 and 86 no longer to overlap each other, the fluid is displaced from the annular channel 79 into the annular channel 80 only through the throttle channel 81, that is, at a correspondingly slower rate. During further displacement of the twin piston arrangement 71 in the same direction (to the right in Fig. 2) , the damping is therefore greater than it was initially. This is advantageous because the driver generally finds rapid rotation of the steering element towards a larger steering lock, that is, towards travel having a relatively small radius of curvature, more uncomfortable on account of the increasing lateral acceleration force than rapid rotation of the steering element in the range around the neutral position when travelling straight ahead.

If the steering element is then rotated back again in the opposite direction, during which the twin piston arrangement 71 is displaced to the left in Figs 1 and 2, the non-return valve 89 closes, so that as long as the bores 85 and 87 are not overlapping, fluid initially flows back again out of the annular channel 80 only by way of the throttle channel 81 into the annular channel 79, and then, on further displacement of the twin piston arrangement 71, drains away to the tank through the third throttle channel 84, the bores 85 and 87 and also the through-channel 76 and the chamber 74.

The same applies to a displacement of the twin piston arrangement from the neutral position illustrated in the opposite direction, to the left in Figs 1 and 2, and back.

Depending on the displacement direction of the twin piston arrangement 71, the annular channels 79 and 80 can be refilled with fluid by way of the non-return valves 88 and 89.

When using the damping arrangement 70 illustrated, it is therefore not possible to operate the steering element 57 too quickly, that is, to rotate a steering wheel faster than fluid is able to be displaced through the throttle channels 81 and 82, and 81 and 84. This means that the angular speed between the inner and outer rotary slide valves is damped and, for example, in a vehicle with centre-pivot steering, troublesome lateral acceleration is also reduced. At the start of operation of the steering element, when both throttle channels 81 and 82 and 81 and 84 are effective, there is a slight damping. When thereafter only one throttle channel 81 is effective, damping becomes greater. By suitable choice of the throttle dimensions and the number of throttle channels, it is also possible to change the damping characteristic, in particular also to effect a different damping on rotation of a steering wheel to the right and to the left. On a personal basis, it could also be felt to be more comfortable not to increase the damping as the steering lock increases, but to reduce it.

Should a leak which is larger than the amount of fluid draining off by way of the through-channel 76 into the tank occur in the metering motor 10, without the plate 96 the fluid could exert a pressure on the twin piston arrangement 71 which would lead to a rotation of the steering element 57. The plate 96 prevents a leakage flow in the metering motor 10 from exerting a pressure on the twin piston arrangement 71. The fluid accumulating in the through passagework 50 is therefore drained off by way of a bore, not illustrated, to the tank.

Modifications can comprise, for example, increasing the number of successively effective throttle channels in the sleeve 77 and the number of radial bores in the sleeve 77 and the cylinder 78 associated therewith by suitable axial displacement of these bores. The drive mechanism formed by the pin 90 and the slots 91, 92 can be replaced by a different drive mechanism which converts the rotary movement of the inner rotary slide valve 17 into a corresponding axial movement of the twin piston arrangement 71, for example, by providing a thread between the inner rotary slide valve 17 and the twin piston arrangement 71 and continuing to connect the twin piston arrangement 71 to the outer rotary slide valve 15 mechanically so that there is no relative rotation but so that the twin piston arrangement is axially displaceable.

The entire damping arrangement can also be replaced by one which exerts on the inner rotary slide valve 17 a high braking force when there is a great change in its rotational speed and a low braking force when there is relatively little change in the rotational speed, rather like an eddy-current brake.

Claims

Patent Claims

1. A control apparatus for a hydrostatic auxiliary power steering arrangement, in particular for vehicles, having a metering motor (10) and two coaxial rotary slide valves (16, 17) forming between them a directional valve (14), wherein the directional valve (14) is opened by rotating the inner rotary slide valve (17) by means of a steering element (57) and allows fluid under pressure to pass through the metering motor (10) to a steering motor (8) and the metering motor (10) adjusts the outer rotary slide valve (16) in dependence on the amount of fluid flowing through the inner rotary slide valve (17) , characterized in that the inner rotary slide valve (17) is connected to a damping arrangement (70) .

2. A control apparatus according to claim 1, characterized in that the damping of the damping arrangement (70) changes in dependence on the angle of rotation of the inner rotary slide valve (17), in particular it increases as the angle of rotation increases.

3. A control apparatus according to claim 1 or 2, characterized in that the damping arrangement (70) is arranged inside the inner rotary slide valve (17) .

4. A control apparatus according to one of claims 1 to 3, characterized in that displaceably mounted in the inner rotary slide valve (17) there is a twin piston arrangement (71), the two pistons (72, 73) of which lie, sealed, against the inside of the inner rotary slide valve (17) and with their end faces bound a respective one of two chambers (74, 75) which are hydraulically connected to a tank for the fluid and to one another by way of a through-channel (76) passing through the twin piston arrangement (71) , that between the pistons (72, 73) a sleeve (77) that is fixed, sealed, to the inside of the inner rotary slide valve (17) surrounds, forming a seal, a cylinder (78) mechanically joining the pistons (72, 73), which cylinder is axially displaceable inside the sleeve (77), that two annular channels (79, 80) bounded by the end faces of the sleeve (77) and the pistons (72, 73) are hydraulically connected by a first throttle duct (81) passing through the sleeve (77) , that the one annular channel (79) is hydraulically connected by a second throttle duct (82) to a first bore (83) of the sleeve (77) and the other annular channel (80) is hydraulically connected by a third throttle channel (84) to a second bore (85) of the sleeve (77) , that the first bore (83) of the sleeve (77) is hydraulically connected by way of a first bore (86) of the cylinder (78) and the second bore (85) of the sleeve (77) is hydraulically connected by way of a second bore (87) of the cylinder (78) to the through-channel (76) in dependence on the displacement of the cylinder (78) in the sleeve (77) , that the one chamber (74) is hydraulically connected to the one annular channel (79) by a non-return valve (88) and the other chamber (75) is hydraulically connected to the other annular channel (80) by a non-return valve (89) , and that the twin piston arrangement (71) is mechanically connected and, at least axially, displaceably connected to the outer rotary slide valve (16) and connected to the inner rotary slide valve (17) by a drive mechanism (90, 91, 92) converting the rotation thereof into an axial advancement movement of the twin piston arrangement (71).

5. A control apparatus according to claim 4, characterized in that a pin (90) is secured radially to the twin piston arrangement (71) , which pin projects through a slot (91) in the inner rotary slide valve (17) into a slot (92) in the outer rotary slide valve (16), one slot (91) extends axially and both slots (91, 92) intersect at an acute angle and guide the pin (90) with their longitudinal edges.