GB1588593A - Powerassisted steering gear - Google Patents

Description

(54) A POWER-ASSISTED STEERING GEAR (71) We, CAM GEARS LIMITED, a British Company of 45 Wilbury Way, Hitchin, Hertfordshire SG4 OTU, 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: - The present invention relates to a power-assisted steering gear including a resilient coupling, in which a pressure fluid supply valve is employed. This supply valve is operated by torque applied in either rotational sense, the resilience in the coupling affording a measure of the torque and therefore of the opening or closing of the valve.

The invention is an improvement in or modification of the invention of our Patent No. 1,531,726 which relates to a powerassisted steering gear including a pressure fluid supply valve and a resilient coupling comprising a torque input member and a torque output member coupled to respective parts of the valve and torsionally connected to one and another by one or more arcuately extending springs which are located in a plane normal to the rotational axis of the torque input and output members, and are secured at their two ends to respective ones of said members wherein on relative rotation of said torque input and output members in either direction from a rest position the or each spring is acted on by one of said members and acts on the other of said members whereby the torque input and output members are returned to a rest position solely by the force exerted thereon by the or each spring.

According to the present invention there is provided a power-assisted steering including a pressure fluid supply valve and a resilient coupling comprising a torque input member and a torque output member coupled to respective parts of the valve and torsionally connected to one another by one or more arcuately extending springs which are located in a plane normal to the rotational axis of the torque input and output members, and are secured at their two ends to respective ones of said members wherein on relative rotation of said torque input and output members in either direction from a rest position the or each spring is acted on by one of said members and acts on the other of said members whereby the torque input and output members are returned to a rest position solely by the force exerted thereon by the or each spring, in which the pressure fluid supply valve comprises a valve spool and a valve body, and in which the torque input member is coupled to said supply valve to effect relative axial displacement of the valve spool and valve body on relative rotation of the torque input and output members.

Both arrangements are advantageous in reducing "stiction" i.e. the tendency of the frictional force resisting relative movement of the valve spool and valve body to be greater when spool and body are stationary than when either of the spool and body is moved.

Embodiments of the invention will now be described by way of example with reference to the accompanying illustrative drawings in which: FIGURE 1 is an axial section of a steering gear of the invention FIGURE 2 is a perspective view of one of the springs used in the steering gear of Figure 1; FIGURE 3 is a section, similar to FIG URE 1, of part of a steering gear constituting a second embodiment of the invention; FIGURE 4 is a radial section, along the the line A-A of the steering gear of FIG URE 3; and FIGURES 5 to 7 show in plan view various further examples of springs which can be used in further embodiments of the invention.

The steering gear has a fixed steering box structure 1, in which is borne by means of ball bearings 2, a pinion shaft 3, which engages a rack on the rack bar 4, in well known manner. The ends of the rack bar 4 are connected in known manner to roadwheel steering arms.

The pinion shaft 3 has a bore 5 through which passes a pull/push rod 6 for operation of a valve which controls supply of pressure fluid to each end of a servomotor cylinder which provides the power-assistance for steering, in known manner. One end 7 of the rod 6 is rigidly connected to an input member 8 which may be regarded as the bottom end of a steering column, the rest of the column not being illustrated.

A needle bearing 9 supports the input member 8 for low-friction relative rotation on the pinion shaft 3. The needle bearing 9 is surrounded by an enlarged diameter flange 10 of the input member 8. This flange 10 is housed freely within a hollow cylindrical extension 11 of a driven member 12 which is pinned by radial pins 13, 13a to the shaft 3. A closure member 14 fills the open end of the extension 11 and is retained by pins 15, 15a.

The flange l0-is drilled radially to receive a number of fixed pins such as 16. These pins 16 -protrude into and are- a close sliding fit in a similar number of helical slots 17 formed through the wall of the extension 11. Thus, when the input member 8 is rotated relative to the pinion shaft 3, axial movement of the input member 8 relative to the shaft 3 results from the action of the pins 16 riding in the helical slots 17, the bearing 9 being constituted so as to permit this axial movement.

To provide -a force tending 'to neutralise the input member 8 in rotation relative to the pinion shaft 3, and to provide an increasing resistance to their relative rotation in either sense of rotation, some resilient means must be introduced into the assem bw. Two centralising springs 18, 1 8a are used, of which the general shape is seen in Figure 2. They are of spring wire, coiled almost to a full circle, their ends being bent outwards (and therefore being an interrupted annulus i.e: out of the plane of the annulus) to provide two parallel and axially directed projections 19 and 20. On assembly these projections 19, 20 flt closely into blind bores drilled in the inside faces of the members '12 and 14 and the annular flanking faces of the flange TO,.respectively.

Thus -rotation of the input member 8 in either direction winds up one.spring 18 or 1 8a and opens out the other.

To retain lubricant and exclude foreign matter, a rubber boot B encloses the whole assembly.

As already mentioned, the pinion shaft 3 has bore 5 through which passes a pull/ push rod 6 for valve operation. This rod 6 passes coaxially and freely through the pinion shaft 3 down to a diametrical pin connection at 21, which rigidly connects it to an axially movable valve spool 22 so that the valve spool 22 cannot either rotate or move axially with respect to the end of the rod 6 to which it is connected. The valve body 23, in which slides the spool 22, has four connections, 24, 25, 26 and 27. Con nection 24 is for pressure fluid feed from the accumulator (not shown) which is the source; connection 25 is for return to the fluid supply reservoir which is also part of a servosystem; connection 26 is for con nection to one end of a servomotor cylin der (not shown); and connection 27 is for connection to the other end of the servo motor cylinder. The spool 22 has three operative grooves, the central one 28 of which is always open to the supply con nection 24 through a passage 29, and which, when the spool 22 is axially moved, opens also either to connection 26 or connection 27. The upper groove 30 and lower groove 31, when the spool 22 is so moved, con nect alternatively connection 26 and 27 to return connection 25.

It will be noted that, since the spool 22 is fixed to the rod 6, axial movement of the spool 22 occurs conjointly with a consider ably larger rotational movement of the spool 22. If desired, by making the initial portions of the slot 17 circular instead of belical, it -can be arranged that the axial movement of the spool is preceded by a rotation thereof.

The pitch of the helical slots or tracks determines the axial displacement which actuates the spool valve.

Airariant is shown in Figures 3 and 4.

This arrangement corresponds to that of Figure 1 except that only one spring fs used.

Corresponding parts have like references.

The pinion shaft 3 is pinned at 13 to the extension 11 which, through the helical slots 17 and pins 16 are axially and rotation ally connected, to the flange 10 which is fixed with the input 8.

In the Figure 3 variant only one spring 32 is provided. The axially directed ends 20 of this spring are (like those of spring 18 of Figure 1) engaged in blind bores in the elements 11 and 10. The single spring 32 is so to speak, "double acting". That is to say in repose, unstrained, the spring exerts no torque. But if strained in either sense of rotation, it exerts a corresponding resist ant torque. By using an adjustment screw 33, its unstrained (i.e. neutral) condition may easily be fixed.

In Figure 5, a substantially annular spring 33 is interrupted at 34, and its ends are bent radially at 35, 36, respectively outward and inward, to engage complementary radial bores in coupling members equiva lent to 11 - and 10 which are appropriately modified for the purpose.

In Figure 6, the- spring 40 is extended spirally beyond the form of an interrupted annulus, to about 5400 of spiral angle: its en,-ds,- 41, 42 may be bent as in the Figure I or 3 or 5 example. The spiral may of course be of any convenient angle but should always be such that within the design parameters it does not become coilbound.

Figure 7 illustrates a variant in which a number of coplanar springs are used, nested one within another. Three namely 51, 52, 53, are shown and their ends, generally indicateld at 54 are in this case bent axially out of their planes. The springs 51, 52, 53 are preferably coplanar and the gaps of their ends are preferably disposed symmetrically at about 1200 (in reference to their common axis): but they may lie in planes which are axially separated if other design considerations so indicate.

It will be evident that variants as indicated may be made with only trivial alterations to the other parts of the coupling, such as changing the number and disposition of the bores which are engaged by the spring ends.

Another type of spring which could be used is an annular spring connected to a torque input part and to a torque output part by means of shoes provided at the ends of the spring abutting respective pins provided in the torque input part and the torque output part.

Instead of having the rod 6 move the valve spool, the rod may be attached to the valve body so as to transmit rotation and axial movement thereto, the spool being fixed. The same result, namely, ensuring that movement of the spool relative to the valve body occurs conjointly with or following a rotational movement of the spool relative to the valve body may still be achieved.

WHAT WE CLAIM IS: - 1. A power-assisted steering gear including a pressure fluid supply valve and a resilient coupling comprising a torque input member and a torque output member coupled to respective parts of the valve and torsionally connected to one another by one or more arcuately extending springs which are located in a plane normal to the rotational axis of the torque input and output members, and are secured at their two ends to respective ones of said members wherein on relative rotation of said torque input and output members in either direction from a rest position the or each spring is acted on by one of said members and acts on the other of said members whereby the torque input and output members are returned to a rest position solely by the force exerted thereon by the or each spring, in which the pressure fluid supply valve comprises a valve spool and a valve body and in which the torque input member is coupled to said supply valve to effect relative axial displacement of the valve spool and valve body on relative rotation of the torque input and output members.

2. A steering gear as claimed in Claim l, in which the coupling of the torque input member to the supply valve effects relative rotational displacement of the valve spool and valve body.

3. A steering gear as claimed in Claim 1 or Claim 2, in which the relative displacement of the valve spool and valve body is controlled by a helical connection between the torque input and output members.

4. A steering gear as claimed in Claim 3, in which the helical connection comprises at least one pin connected to one of the torque members and located in a helical slot in the other torque member.

5. A power-assisted steering gear substantially as herein described and shown in the accompanying drawings.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. I or 3 or 5 example. The spiral may of course be of any convenient angle but should always be such that within the design parameters it does not become coilbound. Figure 7 illustrates a variant in which a number of coplanar springs are used, nested one within another. Three namely 51, 52, 53, are shown and their ends, generally indicateld at 54 are in this case bent axially out of their planes. The springs 51, 52, 53 are preferably coplanar and the gaps of their ends are preferably disposed symmetrically at about 1200 (in reference to their common axis): but they may lie in planes which are axially separated if other design considerations so indicate. It will be evident that variants as indicated may be made with only trivial alterations to the other parts of the coupling, such as changing the number and disposition of the bores which are engaged by the spring ends. Another type of spring which could be used is an annular spring connected to a torque input part and to a torque output part by means of shoes provided at the ends of the spring abutting respective pins provided in the torque input part and the torque output part. Instead of having the rod 6 move the valve spool, the rod may be attached to the valve body so as to transmit rotation and axial movement thereto, the spool being fixed. The same result, namely, ensuring that movement of the spool relative to the valve body occurs conjointly with or following a rotational movement of the spool relative to the valve body may still be achieved. WHAT WE CLAIM IS: -

1. A power-assisted steering gear including a pressure fluid supply valve and a resilient coupling comprising a torque input member and a torque output member coupled to respective parts of the valve and torsionally connected to one another by one or more arcuately extending springs which are located in a plane normal to the rotational axis of the torque input and output members, and are secured at their two ends to respective ones of said members wherein on relative rotation of said torque input and output members in either direction from a rest position the or each spring is acted on by one of said members and acts on the other of said members whereby the torque input and output members are returned to a rest position solely by the force exerted thereon by the or each spring, in which the pressure fluid supply valve comprises a valve spool and a valve body and in which the torque input member is coupled to said supply valve to effect relative axial displacement of the valve spool and valve body on relative rotation of the torque input and output members.

2. A steering gear as claimed in Claim l, in which the coupling of the torque input member to the supply valve effects relative rotational displacement of the valve spool and valve body.

3. A steering gear as claimed in Claim 1 or Claim 2, in which the relative displacement of the valve spool and valve body is controlled by a helical connection between the torque input and output members.

4. A steering gear as claimed in Claim 3, in which the helical connection comprises at least one pin connected to one of the torque members and located in a helical slot in the other torque member.

5. A power-assisted steering gear substantially as herein described and shown in the accompanying drawings.