GB1576051A

GB1576051A - Hydraulic servo steering unit for a motor vehicle

Info

Publication number: GB1576051A
Application number: GB1301777A
Authority: GB
Original assignee: Riva Calzoni SpA
Current assignee: Riva Calzoni SpA
Priority date: 1976-03-29
Filing date: 1977-03-28
Publication date: 1980-10-01
Also published as: FR2346196A1; DE2630615C3; SU683610A3; CS216699B2; HU175025B; DE2630615A1; FR2346196B1; IT1058691B; ES457134A1; DE2630615B2

Description

(54) HYDRAULIC SERVO STEERING UNIT FOR A MOTOR VEHICLE (71) We, RIVA CALZONI S.p.A., an Italian joint stock company of 34, via Stendhal, Milan, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment :- This invention relates to a hydraulic servo steering unit for a motor vehicle, the unit comprising a steering screw for actuation from the vehicle steering wheel, and extending into a cavity in a piston slidable in sealing tight fashion in a cylinder coaxial with the steering screw, said piston dividing said cylinder into two chambers one on either side of the piston, said piston having on its 'exterior a toothed portion forming a rack in engagement with a toothed segment fixed to a steering shaft for coupling with a steering linkage for the vehicle wheels, whereby axial movement of said piston is converted into angular movement of said steering shaft, said steering screw being in screw threaded engagement with a steering nut also disposed in said cavity, and a hydraulic distributor operable by said steering nut to control the supply of fluid under pressure to and the discharge of fluid from said first and second chambers and thus to control axial movement of said piston.

A hydraulic servo steering unit of the kind specified is known.

The hydraulic distributor forms an important constructional element of the servo steering unit and is usually disposed on the longitudinal axis of the steering drive screw in such a way that the distributor adds to the axial length of the steering unit as a whole.

This arrangement of the distributor produces a structural form of the servo steering unit which is somewhat lengthened in the longitudinal direction, as compared with wholly manual steering units, the result being increased space requirement which is not always acceptable for modern vehicles, in which the various spaces must be precisely calculated and utilised to the maximum extent.

It is an object of the invention to provide an improved hydraulic servo steering unit including a hydraulic distributor and in which the distributor is so arranged in relation to the other working parts of the servo steering unit that the space required in the longitudinal direction of the unit is reduced to the minimum, without increasing the space required by the servo steering unit in other directions, as compared with known units, or having any adverse effect on the operation or reliability of the whole system.

According to the invention there is provided a hydraulic servo steering unit for a motor vehicle, comprising a steering screw for actuation from the vehicle steering wheel, the steering screw extending into a cavity in a piston slidable in sealing tight fashion in a cylinder coaxial with the steering screw, said piston dividing said cylinder into first and second chambers, said piston having on its exterior a toothed portion forming a rack in 'engagement with a toothed segment fixed to a steering shaft for coupling with a steering linkage for the vehicle wheels, whereby axial movement of said piston is converted into angular movement of said steering shaft, said steering screw being in screw threaded engagement with a steering nut also disposed in said cavity, said steering nut being mounted for movement, at least to a limited extent, relative to said piston, a hydraulic distributor operable to control the supply of fluid under pressure to and the discharge of fluid from said first and second chambers and thus to control axial movement of said piston, said hydraulic distributor being disposed in a further cavity in the piston, said further cavity being elongate in a direction parallel with the axis of the piston and being eccentric with respect to this axis, the distributor having a control member movable in directions parallel with the axis of the piston by means of a lever pivotally mounted in the piston and connected with said steering nut, the arrangement being such that rotation of said steering screw will cause movement of the steering nut relative to the piston and hence, via said lever, movement of said control member of the distributor, parallel with the axis of the piston in such a direction as to place the distributor in a condition to supply fluid under pressure to the appropriate said chamber to move the piston, axially in the cylinder in a direction the same as that direction of movement of the steering nut along the steering screw which is appropriate to said rotation of the screw having regard to the screw threaded engagement between the screw and the nut.

Preferably said steering nut is mounted for rotational movement about its axis, at least to a limited extent, relative to the piston, but is restrained against axial movement relative to the piston, and said lever is mounted within the cavity in the piston in which the steering nut is disposed, the lever comprising a generally U-shaped arcuate part extending circumferentially of the nut and straddling the nut and a further part extending from the end of one arm of the U in a direction parallel with the axis of the piston, the lever being pivotally mounted in the wall of the last mentioned cavity in the piston via the ends of the arms of the U for pivoting about an axis transverse to the longitudinal axis of the piston, said further part of the lever being accommodated in a groove on the exterior of the steering nut extending generally parallel with the axis of the same, the configuration of said further part and said groove being such that rotational movement of the nut, about its axis, relative to the piston will be accompanied by corresponding pivotal movement of the lever about its pivotal axis, the control member of the distributor being movable in a direction generally parallel with the axis of the piston and being coupled with that portion of the U-shaped part of the lever which is midway between the free ends of the arms of the U.

An embodiment of the invention is described below with reference to the accompanying drawings, wherein: Fig. 1 is a diagrammatic longitudinally sectioned view of a servo steering unit according to the invention; Fig. 2 is a section, taken along the line II- II in Fig. 1 and Fig. 3 is a section taken along the line III- 111 in Fig. 1.

As best shown in Fig. 1 a steering screw 1 of which only an end part is shown, has said end part passing screw threadedly through a steering nut 5. The screw 1 has a helical concave groove and the nut has a corresponding helical concave groove, these concave grooves forming tracks for a series of bearing balls which, as they emerge from one end of the nut during rotation of the screw in the nut, are led back via a guide to enter the tracks again at the other end of the nut. A screw threading arrangement utilizing bearing balls in this fashion, is known per se. The steering nut 5 is accommodated in an axial cavity 6 of a hydraulic piston 3 slidable in a cylinder 4 (shown only in part) forming the main element of the servo steering unit. The steering screw 1 extends through the nut 5 and into an axial cavity 2 in the piston 3, of lesser diameter than the cavity 6. The steering nut 5 can rotate to a limited extent relative to the piston 3, about the longitudinal axis of the steering screw 1, but cannot move in the axial direction in relation to the piston 3, since the steering nut 5 is retained against such axial movement in the cavity 6 by bearings 7, 8.

In conventional manner the piston 3 subdivides the cylinder 4 into two working chambers, one chamber being shown at 9 on the left of the piston in Fig. 1, and the other being shown at 10 on the right of the piston.

The piston 3 has a rack portion 11 engaging with a conventional toothed segment 12 keyed to a shaft, the axis of which is indicated at 13 and which steers the vehicle wheels.

A hydraulic distributor 14 is located in a cavity 15 provided in the body of the piston 3. The cavity 15 is elongate in a direction parallel with the axis of the piston 3 and is eccentric with respect to this axis.

In operation, in one position of the distributor 14, occupied when the steering screw is being rotated in one direction, the distributor connects chamber 9 with a supply of hydraulic fluid under pressure and vents the chamber 10 to a fluid reservoir, whilst in another position of the distributor 14, occupied when the steering screw is being rotated in the opposite direction the distributor connects chamber 10 with the supply of hydraulic fluid under pressure and vents chamber 9 to the fluid reservoir, whereas in a further position of distributor 14, occupied when the steering screw is maintained at rest, neither chamber is connected with the supply of hydraulic flud under pressure.

The hydraulic distributor 14 is secured in the cavity 15 in the required position, for instance, by means of a clamping screw 16.

A longitudinally movable part (not shown) of the distributor, which controls the operation thereof, is connected to an actuating rod 17 which extends from the distributor along cavity 15 and is connected via a ball and socket joint 18 to a lever 20 which is mounted in the piston for pivoting relative to the piston about an axis perpendicular to the longitudinal axis of the piston.

As will be apparent from Figures 1 and 2, the lever 20 includes an arcuate, generally U-shaped part, which as viewed along the axis of the screw 1, is approximately semicircular, the lever being pivotally mounted in the piston 3 by means of pivot pins 22, 21 carried by the wall of the piston 3 and extending from diametrically opposite posi tions in the wall of the piston 3, radially inwards into the cavity 6 and extending into complementary bearings formed in the Ushaped part of the lever 20, more specifically formed in the free ends 23, 24 of the arms of the Us It will be noted that the U-shaped part of lever 20 straddles the nut 5 and extends in the circumferential direction around the nut.

To save space in the radial direction the lever 20 is disposed in a semi-annular groove 25 formed in the outer surface of the steering nut 5.

The socket portion of the ball and socket joint 18 is formed in a central portion 19 of the U-shaped part of lever 20.

Extending from the end 23 of the U-shaped part of lever 20 is an arm 26 which is disposed at right angles to the plane of the U-shaped part of lever 20 and extends in a direction approximately parallel with the axis of the piston 3.

The arm 26 is received in a groove 27 extending longitudinally on the exterior of nut 5 parallel with the axis thereof.

As indicated above, the nut 5 is capable of only limited angular movement about its axis, relative to piston 3. This is because such angular movement is deliberately limited by a pin 28, screwed into the wall of the piston 3 and extending radially inwardly from the wall of cavity 6 into a recess 29 in the exterior of nut 5, the recess 29 receiving the pin 28 with clearance in the circumferential direction. Thus angular movement of nut 5 is limited by abutment of the pin 28 with walls 29a, 29b of the recess 29. The recess 29 may simply be a blind bore of greater diameter than pin 28.

As also shown in Fig. 3, there is disposed between the wall of the cavity 6 in piston 3 and the steering nut 5 a device for urging the nut 5 resiliently towards a predetermined neutral position in relation to the piston 3 regardless of the sense in which the nut 5 is displaced angularly from this position. This device is formed by a U-shaped spring 30 disposed in a recess 31 in the periphery of the steering nut 5. The spring 30 is borne between stops 32, 33 provided by the recess 31 and stops 34 and 35, provided by a slot 36 formed in the wall of the cavity 6.

The significant feature of the device mentioned is simply that whether the nut 5 is twisted clockwise or anti-clockwise from the neutral position shown in Fig. 3, the spring 30 is resiliently deformed and exerts counteracting bias tending to return the nut to this neutral position.

The servo steering unit operates as follows.

Rotation of the vehicle steering wheel (not shown) in known manner rotates the steering screw 1 in one direction or the other. The rotation of the steering screw 1 produces a partial angular displacement of the steering nut 5 mounted in the cavity 6 of the piston 3 The steering nut 5 is given an angular displacement against the resilient centring force exerted by the U-shaped spring 30 and the extent of this angular displacement is limited in one direction and the other by pin 28.

The angular displacement of the steering nut 5 causes a raising or lowering of the end of arm 26 which engages in the groove 27 in the steering nut, in dependence on the direction of angular displacement of the steering nut 5 and this causes a pivotal movement of the lever 20, in one sense or the other about the axis of pins 21, 22 and therefore causes an axial displacement of the actuating rod 17 of the movable part of the distributor 14.

The ball and socket joint 18 ensures that the rod 17 can move rectilinearity in directions parallel with the axis of cavity 15 and hence of piston 3 in response to pivotal movement of lever 20.

It will be noted that in order to permit such pivotal movement of the lever, only the free end portion of the arm 26 is a close fit, between the circumferentially spaced apart edges of the groove 27, the edges of the remainder of the arm being relieved to pro vide a substantial clearance with respect to said edges of groove 27. In order to permit limited angular movement of lever arm 26 in groove 27, a slight clearance may be provided at the end of arm 26 with respect to the edges of the groove 27, or the surfaces of the arm 26 at the free end, which engage the edges of the groove 27 may be arcuate in form.

The axial displacement of the movable part of the distributor 14, which is hydraulically connected to a pressure medium source and a discharge tank (both conventional and neither shown) determines whether hydraulic fluid under pressure is supplied to the chamber 9 or to the chamber 10, the chamber not so supplied being connected to the discharge tank.

This supply of hydraulic fluid results in an axial movement of the piston 3 in one direction or the other and therefore in an angular movement of the toothed segment 12 which guides the wheels of the vehicle in known manner.

The axial displacement of the piston 3 tends to rotate the nut 5 in the opposite sense from that in which the screw 1 was initially rotated and thus tends to return the distributor 14 to its neutral position.

The foregoing shows that the system according to the invention effectively affords the advantage of a hydraulic servo steering unit which has all the requisite operational features and whose axial space requirement is substantially reduced without adverse effect on the space requirement in the transverse or radial directions.

The construction and operation of the distributor 14 is described more fully in our co-pending application No. 13018/77 (Serial No. 1,576,052) to which reference should be had.

WHAT WE CLAIM IS: 1. A hydraulic servo steering unit for a motor vehicle, comprising a steering screw for actuation from the vehicle steering wheel, the steering screw extending into a cavity in a piston slidable in sealing tight fashion in a cylinder coaxial with the steering screw, said piston dividing said cylinder into first and second chambers, said piston having on its exterior a toothed portion forming a rack in engagement with a toothed segment fixed to a steering shaft for coupling with a steering linkage for the vehicle wheels, whereby axial movement of said piston is converted into angular movement of said steering shaft, said steering screw being in screw threaded engagement with a steering nut also disposed in said cavity, said steering nut being mounted for movement, at least to a limited extent, relative to said piston, a hydraulic distributor operable to control the supply of fluid under pressure to and the discharge of fluid from said first and second chambers and thus to control axial movement of said piston, said hydraulic distributor being disposed in a further cavity in the piston, said further cavity being elongate in a direction parallel with the axis of the piston and being eccentric with respect to this axis, the distributor having a control member movable in directions parallel with the axis of the piston by means of a lever pivotally mounted in the piston and connected with said steering nut, the arrangement being such that rotation of said steering screw will cause movement of the steering nut relative to the piston and hence, via said lever, movement of said control member of the distributor, parallel with the axis of the piston, in such a direction as to place the distributor in a condition to supply fluid under pressure to the appropriate said chamber to move the piston, axially in the cylinder in a direction the same as that direction of movement of the steering nut along the steering screw which is appropriate to said rotation of the screw having regard to the screw threaded engagement between the screw and the nut.

2. A hydraulic servo steering unit as claimed in Claim 1, wherein said steering nut is mounted for rotational movement about its axis, at least to a limited extent, relative to the piston, but is restrained against axial movement relative to the piston, and wherein said lever is mounted within the cavity in the piston in which the steering nut is disposed, the lever comprising a generally U-shaped arcuate part extending circumferentially of the nut and straddling the nut and a further part extending from the end of one arm of the U in a direction parallel with the axis of the piston, the lever being pivotally mounted in the wall of the last mentioned cavity in the piston via the ends of the arms of the U for pivoting about an axis transverse to the longitudinal axis of the piston, said further part of the lever being accommodated in a groove on the exterior of the steering nut extending generally parallel with the axis of the same, the configuration of said further part and said groove being such that rotational movement of the nut, about its axis, relative to the piston will be accompanied by corresponding pivotal movement of the lever about its pivotal axis, the control member of the distributor being movable in a direction generally parallel with the axis of the piston and being coupled with that portion of the U-shaped part of the lever which is midway between the free ends of the arms of the U.

3. A hydraulic servo steering unit as claimed in Claim 2 in which a resilient return device is disposed between the exterior of the steering nut and the wall of the cavity in the piston in which the nut is received, said resilient return device acting, when the nut is displaced angularly about its axis from a predetermined position relative to the piston, to urge the nut back to that predetermined position, said resilient return device comprising a U-shaped spring disposed in a recess in the steering nut and bearing against the side walls of a longitudinally extending groove formed in the wall of the cavity in the piston in which the steering nut is received.

4. A hydraulic servo steering unit as claimed in any of Claims 1 to 3 in which angular movement of the steering nut about its axis, relative to the piston is limited by a pin, fixed with respect to the piston and extending inwardly from the wall of the cavity in the piston which receives the steering nut, into a recess in the exterior of the steering nut, a clearance, in the circumferential direction, being provided between the pin and the last-mentioned recess.

5. A hydraulic servo steering unit for a motor vehicle, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. co-pending application No. 13018/77 (Serial No. 1,576,052) to which reference should be had. WHAT WE CLAIM IS:

1. A hydraulic servo steering unit for a motor vehicle, comprising a steering screw for actuation from the vehicle steering wheel, the steering screw extending into a cavity in a piston slidable in sealing tight fashion in a cylinder coaxial with the steering screw, said piston dividing said cylinder into first and second chambers, said piston having on its exterior a toothed portion forming a rack in engagement with a toothed segment fixed to a steering shaft for coupling with a steering linkage for the vehicle wheels, whereby axial movement of said piston is converted into angular movement of said steering shaft, said steering screw being in screw threaded engagement with a steering nut also disposed in said cavity, said steering nut being mounted for movement, at least to a limited extent, relative to said piston, a hydraulic distributor operable to control the supply of fluid under pressure to and the discharge of fluid from said first and second chambers and thus to control axial movement of said piston, said hydraulic distributor being disposed in a further cavity in the piston, said further cavity being elongate in a direction parallel with the axis of the piston and being eccentric with respect to this axis, the distributor having a control member movable in directions parallel with the axis of the piston by means of a lever pivotally mounted in the piston and connected with said steering nut, the arrangement being such that rotation of said steering screw will cause movement of the steering nut relative to the piston and hence, via said lever, movement of said control member of the distributor, parallel with the axis of the piston, in such a direction as to place the distributor in a condition to supply fluid under pressure to the appropriate said chamber to move the piston, axially in the cylinder in a direction the same as that direction of movement of the steering nut along the steering screw which is appropriate to said rotation of the screw having regard to the screw threaded engagement between the screw and the nut.