GB1576052A

GB1576052A - Hydraulic servo steering unit for a motor vehicle

Info

Publication number: GB1576052A
Application number: GB1301877A
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: FR2346197B1; DE2630617A1; CS216700B2; IT1058692B; ES457133A1; FR2346197A1; HU175153B; SU727125A3; DE2630617C2

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 statement: This invention relates to a hydraulic servo steering unit for a motor vehicle, the steering unit having a steering screw for actuation by a steering wheel, a steering nut disposed in screw-threaded engagement with the steering screw, the steering nut and the portion of the steering screw extending through the nut being received in an axial cavity in a piston coaxial with the steering screw, said piston being slidable sealingly ina cylinder which the piston divides into two working chambers, the piston having a toothed portion forming a rack which co-operates with a toothed segment to convert the axial movements of the piston in one direction or the other into corresponding angular movements of the toothed segment, which segment is fixed to a steering shaft for coupling with a steering linkage the wheels of the vehicle, the unit including a hydraulic distributor for controlling the supply of fluid under pressure to, and the discharge of fluid from, said chambers, a moving actuating part of the distributor being connected to the steering nut via a mechanism such that when the steering screw moves angularly about the axis of the steering screw, the distributor is so operated that fluid under pressure is introduced into one or other of said chambers in the cylinder to move the piston axially in the appropriate direction.

To save space and limit the axial dimensions of such a servo steering unit, it has been suggested in our co-pending Application NO. 13017/77, Serial No. 1576051' that the distributor should be disposed in the piston in a cavity formed therein.

The distributor might be arranged trans- versely of the axis along which the piston moves, or parallel with said axis but located eccentrically in relation to that axis. In the case in which the hydraulic distributor is disposed in the body of the piston parallel with, but eccentric with respect to, the piston axis, as in the above noted co-pending application, an actuating rod connected with the moving actuating part of the distributor may extend in an extension of the recess in the piston which receives the steering nut.

In order to simplify the construction it is preferred that this recess be connected to one of the said two chambers of the servo steering unit cylinder. In the construction disclosed in the above noted co-pending application the connection between the actuating rod and the actuating mechanism operated by the steering nut is disposed in a passage which provides a connection between the distributor and one of said two chambers. The disposition of an actuating rod of this kind, for the moving part of the distributor, in a space connected to one of the cylinder chambers, which is alternately pressurised and depressurised, causes an axial thrust on the rod when the cylinder chamber is pressurised, such thrust acting on the moving part of the distributor, so that the hydraulic conditions of the distribution are changed.

Since the elimination of such a thrust would require the presence of complicated devices, it is an object of the invention not to prevent the occurrence of such a thrust, but to use it within the framework of the operation of the servo steering unit in such a way that it forms an advantage, not a disadvantage.

To this end, in a servo steering unit of the kind to which the invention relates, a resistance must be transmitted to the steering wheel which at least partially conveys the feeling of direct steering, so that according to the invention the aforementioned thrust is used by transmitting the steering sensitivity to the steering wheel.

However, since a thrust of this kind is operative only in one direction, a problem arises which is precisely the problem to which the invention relates, namely to cause to act on the moving part of the distributor a further thrust which is equal and opposite to the thrust which can be'transmitted to the steering wheel via the actuating rod of the moving part of the distributor; to produce steering sensitivity in the opposite steering direction also.

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 defining the axis of the cavity, the distributor having a control member movable axially with respect to said further cavity by means of a lever mechanism mounted in the piston, 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 mechanism, movement of the control member of the distributor such as to place the distributor in a condition to supply fluid under pressure to one of said chambers and to connect the other of said chambers to a discharge passage, and wherein said distributor comprises an outer tubular part coaxial with said further cavity and a movable part which is coaxial with said outer part and can move axially in relation to the outer part, said movable part having at opposite ends thereof respective extensions which extend through and beyond respective transverse sealing walls adjacent the ends of said outer part, these extensions having identical effective cross-sectional areas exposed to the fluid in respective said chambers, said control member of the distributor comprising an actuating rod attached to said movable part and extending coaxially from said movable part.

An embodiment of the invention will now be described in greater detail with reference to the accompanying drawings, wherein: Fig. 1 is a longitudinal section view of part of a hydraulic servo steering unit with a distributor according to the invention, Fig. 2 is a partial view, in cross-section, along the line II-II in Fig. 1, Fig. 3 is a longitudinal section view of the distributor, but to an enlarged scale in comparison with Fig. 1, Fig. 4 is a partial view of the distributor, in cross-section, along the line IV-IV in Fig. 3, and Fig. 5 is a partial view of the distributor, in cross-section, along the line V-V in Fig. 3, 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.

Hydraulic fluid is supplied under pressure to one or other of the chambers 9, 10 while the chamber not so supplied is vented to a fluid reservoir in dependence on the direction in which the steering screw is being rotated (or no such fluid is supplied to either chamber, if the steering screw is maintained at rest), by means of a hydraulic distributor 14 which is located in a longitudinal cavity 15 provided eccentrically in the body of the piston 3 and extending parallel with the axis of the piston 3. The hydraulic distributor 14 has a generally cylindrical outer tubular part 16 fitting into the cavity 15 which is in the form of a cylindrical bore parallel with the axis of the piston, the part 16 having at its inner end a screwthreaded portion 160 screwed into a correspondingly screwthreaded part of bore 15. The part 16 also has at its outer end, cutaway portions 161 by means of which it can be rotated, using a suitable tool, in the cavity 15 and thus screwed in or out for purposes of adjustment.

The part 16 can also have an externally grooved or knurled portion 162 at its outer end against which there bears a block 163 (Fig. 5) made of a soft material and pressurized by a clamping screw 164 extending through the body of the piston 3, this feature ensuring that the part 16 will retain any position to which it is adjusted. The part 16 of the distributor has an axial passage in which is located a longitudinally movable part 17 which controls the operation of the distributor. The part 17 extends from the inner end of the distributor part 16 into a part 15a of the cavity 15, and is fixed to an actuating rod 18 which extends through part 15a of cavity 15 and is connected via a ball and socket joint 19 to the central portion 20 of a U-shaped part of a lever 21 which is disposed straddling the steering nut 5 and is pivotally connected to the inside wall of the cavity 6 by two opposing pivot pins 22.

Rigidly connected to the end 23 of the Ushaped part of lever 21 is an arm 24 which is disposed at right angles to the plane of the U-shaped part of lever 21. The arm 24 extends parallel with the axis of the steering nut 5 in a longitudinal groove 25 in the exterior of nut.5. Fig. 1 shows that there is disposed between the piston 3 and the steering nut 5 a device for resiliently returning the steering nut 5 to a neutral position in relation to the cavity 6 of the piston and therefore in relation to the piston 3. The device for resilient return has a spring 26 disposed in a recess 27 in the periphery of the steering nut 5. The spring 26, which is located between the recess 27 and a cutaway portion (not shown) in the body of the piston 3, determines the centred position of the steering nut and therefore the actuation of the distributor 14. The part 16 of the distributor has a peripheral groove 28 in its zone midway between its ends and two further peripheral grooves 29, 30 disposed on either side of the groove 28. Fig. 2 shows that the peripheral groove 28 is connected to a duct 31 which extends transversely through the body of the piston 3 and discharges into a longitudinally extended groove 32 in the exterior of piston 3, which groove remains always connected to a duct 33 extending from a port in the wall of cylinder 4 during the axial displacement of the piston 3, the duct 33 being formed in the body of the cylinder 3 and communicating via a bore 35 into a conduit 34 for connection to a pressure medium source (not shown). The peripheral grooves 29, 30 are connected in a similar manner to respective ducts (one of which is indicated at 36 in Fig. 2) extending transversely through the body of the piston 3, the last mentioned ducts both terminating in an open axial groove 37 in the body of the piston 3. The groove 37 is connected via a port in the wall of cylinder 4 to a duct 38 extending through the body of the cylinder 4 and connected to a conduit 39 which is connected to an unpressurised pressure medium-receiving reservoir (not shown).

Figs. 1 and 3 also show how the groove 28 has a plurality of radial bores 40 which discharge into the axial inner cavity of the part 16, the grooves 29, 30 also having a corresponding number of radial bores 41, 42.

The cylindrical inner wall of the part 16 of the distributor is formed with circumferential grooves 43, and 44 disposed in axial positions respectively between the positions of bores 40 and bores 41 and between the positions of bores 40 and bores 42. The movable part 17 of the distributor is formed by a cylindrical member formed with two axial bores 45 and 46 which extend from respective ends of part 17 but are separated from each other by a solid central part 1 7a of the part 17 of the distributor. Radial bores 47 extend through the part 17 from adjacent the blind end of the bore 45, the bores 47 discharging into the circumferential groove 43 of the member 16.

Similarly, radial bores 48 extend through the part 17 from adjacent the blind end of the bore 46, the bores 48 discharging into the circumferential groove 44 of the casing 16.

Radial bores 49 also extend through an axial prolongation 17b of the part 17 of the distributor from the bore 46, this prolongation being the portion of part 17 which is connected to the actuating rod 18. The bores 49, during the operation of the distributor, always remain in communication with the part 15a of cavity 15 which part 15a is connected to the chamber 10 of the cylinder 4 via the clearance between the steering nut 5 and the cavity 6 of the piston 3. The bore 45 is always in communication, via its open end 50, with the chamber 9 of the cylinder 4 of the servo steering unit. The open end 50 is provided at the free end of a prolongation 17c of the part 17. The moving part 17 of the distributor has also peripheral grooves 51, 52 and 53 which are formed on its outer surface and which, in a central position of part 17 in part 16 are opposite the radial bores 41, 40 and 42 respectively of the fixed part 16 of the distributor.

Fig. 3 also shows that the distributor 14 is closed by end walls 54, 55 which are formed by conventional sealing members in sealing engagement with the part 16 and through which sealing members prolongations 17b, 17c of the moving part of the distributor extend sealingly.

The respective external diameters of the stem-shaped prolongations 17b, 17c are so calculated that for a given strength of axial thrust applied to the piston from the wheels being steered, identical axial thrusts are applied to the part 17 by the hydraulic fluid in the chamber 9 or 10, for either direction of application of such a thrust to the piston 3, and the thrusts applied to the part 17 are proportional to the thrusts applied to piston 3 by the wheels being steered. As will be explained, the arrangement adopted allows corresponding thrusts to be transmitted to the steering wheel so that there is 'feed back' from the road wheels to the steering wheel.

If these diameters of prolongations 17b, 1 7c are smaller or greater than the maximum diameter of the moving part 17 of the distributor, and thus of different diameter from the narrowest part of the axial bore through part 16, annular chambers 56, 57 are formed, which alter in volume with changes in the axial position of part 17. In order to prevent hydraulic locks being formed by these chambers 56, 57 these are permanently connected with grooves 53, 51 via milled-away portions or longitudinal grooves 58, 59, so that these chambers are always connected to the discharge.

The distributor according to the invention operates as follows. The angular movement of the steering screw 1, which is operated in one direction or the other from the steering wheel (not shown) via the steering nut 5, results in pivoting of the arm 24 which engages with the longitudinal groove in the steering nut 5, and therefore results in pivoting of the lever 21. The actuating rod 18 and part 17 of distributor 14 are therefore moyed, via the ball and socket joint 19, 20, rectilinearly in the axial direction in one sense or the other. These movements take place in one direction or the other in relation to a neutral position determined by the force of spring 26, which is disposed between the steering nut 5 and the inner wall of the cavity 6 of the piston 3. The pressure medium which is supplied to the conduit 34 enters the peripheral groove 28 in the fixed part 16 of the distributor 14, to which it passes via duct 33, axial groove 32 and duct 31.

If we assume a movement of the moving part 17 to the right in Figs. 1 or 3, the pressure medium passes from the groove 28 via the radial bores 40 into the groove 52 and from the latter into the groove 44, which is connected to the axial bore 46 via the radial bores 48.

The pressure medium then passes via the bores 49 to the recess 15a, from which it passes to chamber 10 of cylinder 4 of the servo steering unit. As viewed in the drawings, thereof a thrust to the left is transmitted to the piston 3, resulting in an angular movement of the tooth segment 12 and a relative movement of the steerable wheels. The presence of pressure medium in the recess 15a also produces an axial thrust on the actuating rod 18, this thrust counteracting the movement conferred on the rod 18 by the steering wheel. This thrust is therefore sensed at the steering wheel and gives the feeling of resist ance to the steering of the vehicle.

Under the aforedescribed conditions the chamber 9 of cylinder 4 is connected to the discharge via aperture 50, axial bore 45, radial bores 47, groove 43, groove 51, radial bores 41 and groove 29. As explained previously the groove 29 is connected to the discharge (not shown) via one of the ducts 36.

If on the other hand the steering wheel has been turned in a direction such as to cause a movement of the movable part 17 of the distributor towards the left in Fig. 1, chamber 10 of cylinder 4 is connected to discharge via apertures 49, axial bore 46, radial bores 48, peripheral grooves 44, 53, radial bores 42 and peripheral groove 30, which is also connected to axial groove 37, and thus to discharge, via the other duct 36 extending through the body of the piston 3.

In contrast, the pressure medium passes from the peripheral groove 28 into chamber 9 of cylinder 4 via the hydraulic connections formed by bore 45 and aperture 50. Under these operating conditions the pressure in chamber 9 exerts an axial thrust on the front part of the prolongation 17c of the moving part 17 of the distributor, which always extends into chamber 9.

This thrust acts in the direction opposite from the movement of the moving part of the distributor, and is transmitted via actuating rod 18 and the lever and also via the steering nut 5 to the steering screw 1 and from the latter to the steering wheel (not shown) which is rigidly connected to the steering screw 1. This thrust therefore produces at the steering wheel the sensation of a resistance to the steering of the vehicle wheels in the angular direction opposite from that in which the angular movement of the steering wheel took place. Since the effective crosssectional area of the part 17c which is exposed to the fluid pressure in chamber 9 is so designed that it is equivalent to the effective cross-sectional area of the part 17b which is exposed to the fluid pressure in chamber 10, the reactions at the steering wheel are identical in both directions of angular movement of the steering wheel, for uniform driving conditions.

As the foregoing shows, the invention affords the advantage that the resistances to steering are reproduced at the steering wheel, i.e. there is feed-back through the steering wheel to the driver, without having to use mechanical devices, such as springs, despite the thrust which inevitably occurs from one side of the distributor due to the functionally indispensable presence of the actuating rod of the moving part of the distributor.

The construction and operation of the nut, 5 lever 21, spring 26, and the other mechanical parts of the steering arrangement is explained in greater detail in our co-pending application No. 13017/77, Serial No. 1576051 to which reference should be had.

With regard to Figures 1 and 3 of the drawings accompanying the present specification, it will be appreciated that for clarity of illustration clearances have been shown between portions of part 17 and portions of part 16 at places where in practice such clearances will be negligible. Thus the relative axial dimensions of the grooves 43, 44 and the land on the interior of part 16 between these grooves and of the groove 52 and the lands on the exterior of part 17 on either side of groove 52 will in practice be such that the mode of operation described above can be performed with optimum effectiveness.

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 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 defining the axis of the cavity, the distributor having a control member movable axially with respect to said further cavity by means of a lever mechanism mounted in the piston, 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 mechanism, movement of the control member of the distributor such as to place the distributor in a condition to supply fluid under pressure to one of said chambers and to connect the other of said chambers to a discharge passage, and wherein said distributor comprises an outer tubular part coaxial with said further cavity and a movable part which is coaxial with said outer part and can move axially in relation to the outer part, said movable part having at opposite ends thereof respective extensions which extend through and beyond respective transverse sealing walls adjacent the ends of said outer part, these extensions having identical effective cross-sectional areas exposed to the fluid in respective said chambers, said control member of the distributor comprising an actuating rod attached to said movable part and extending coaxially from said movable part.

2. A hydraulic servo steering unit as set forth in claim 1, in which the extension of the movable part of the distributor at the end thereof opposite that to which the actuating rod is secured, has an axial duct which extends substantially from the central zone of the distributor, where the duct has a closed bottom, as far as the free end of the extension, where an aperture is provided discharging into the respective said chamber to the fluid in which the respective extension is exposed, said axial duct communicating with radial bores in said movable part through which radial bores the pressure medium can pass from and to said outer tubular part of the distributor, such bores being disposed adjacent the closed bottom of the duct, further ducts being provided to connect the said tubular part of the distributor to a passage for connection with a pressure medium source and to the discharge passage.

3. A hydraulic servo steering unit as set forth in claim 1 or claim 2 in which that extension of the movable part of the distributor which is connected to the actuating rod has an axial duct which extends substantially from the central zone of the distributor, where the last mentioned duct has a closed bottom, to beyond the respective transverse sealing wall of the distributor adjacent the end nearer the actuating rod, the last mentioned axial duct communicating with radial apertures formed in the respective extension and disposed in the zone which during the axial movements always remains outside the respective transverse sealing wall, radial bores, formed in the portion of said movable part which remains inside the distributor, being provided through which pressure medium can pass from and to said outer

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. No. 13017/77, Serial No. 1576051 to which reference should be had. With regard to Figures 1 and 3 of the drawings accompanying the present specification, it will be appreciated that for clarity of illustration clearances have been shown between portions of part 17 and portions of part 16 at places where in practice such clearances will be negligible. Thus the relative axial dimensions of the grooves 43, 44 and the land on the interior of part 16 between these grooves and of the groove 52 and the lands on the exterior of part 17 on either side of groove 52 will in practice be such that the mode of operation described above can be performed with optimum effectiveness. 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 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 defining the axis of the cavity, the distributor having a control member movable axially with respect to said further cavity by means of a lever mechanism mounted in the piston, 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 mechanism, movement of the control member of the distributor such as to place the distributor in a condition to supply fluid under pressure to one of said chambers and to connect the other of said chambers to a discharge passage, and wherein said distributor comprises an outer tubular part coaxial with said further cavity and a movable part which is coaxial with said outer part and can move axially in relation to the outer part, said movable part having at opposite ends thereof respective extensions which extend through and beyond respective transverse sealing walls adjacent the ends of said outer part, these extensions having identical effective cross-sectional areas exposed to the fluid in respective said chambers, said control member of the distributor comprising an actuating rod attached to said movable part and extending coaxially from said movable part.

tubular part of the distributor, and further ducts being provided to connect the outer tubular part of the distributor to a passage for connection with a pressure medium source and to the discharge passage.

1

4. A hydraulic servo steering unit as set forth in any of claims 1 to 3 in which the outer tubular part of the distributor engages with the inner wall of said further cavity, in Which the distributor is received, via at least one screwthreaded portion whereby rotation Qf the outer tubular part will produce an axial movement of said outer part in relation to said further cavity and the moving part of the distributor, to maintain the hydraulic centring, transverse screws being provided to lock said outer tubular part in a preselected position in said further cavity in which the distributor is received.