GB2268988A - Adjustable linkage for a load sensing valve - Google Patents

Abstract

A compression spring 14, an internally threaded member 12 having a spring seat, an externally screwthreaded lower member 7 screwed into the upper member 12, a first bearing element 4 rigid with the lower member 7, and a coaxial second bearing element 2, are arranged in series in a linkage between a load sensing valve mounted on a vehicle body and a wheel suspension member 1 whose vertical distance from the vehicle body is a function of the vertical load applied to the corresponding wheel by the vehicle. The upper member 12 is rotatable in order to adjust the height of the spring seat in relation to the suspension member 1 and is lockable by means of a clip 23. <IMAGE>

Description

Sensor Linkage The present invention relates to sensor linkages and in particular, but not exclusively to a linkage for coupling to a load sensing valve used in a vehicle braking system.

In the control of braking systems on vehicles, it is known to include a load sensing valve for sensing the load on a wheel, in order to allow the braking force to be controlled as a function of that load. In one known arrangement, a load sensing valve is fixed rigidly to the vehicle body and is linked to a rear wheel suspension member by a linkage. The valve is coupled into the hydraulic braking circuit of the vehicle via input and output ports provided in the valve housing.

Figure 1 of the accompanying drawings is an exploded isometric view of the linkage used in the known arrangement. The linkage includes a compression spring 14 and a seat member 112 having a seat for the lower end of the spring. The seat member 112 is fixed on a first bearing element 104 having a horizontal axis and coaxial with a second bearing element 102 which is mounted on the suspension member 1. The valve (not shown) has a lever 51 (Fig. 2) connected to a seat member 16 on the upper end of the spring 14. The lever 51 is held between the seat member 16 and a retaining element 17 having a recess which receives the upper end 18 of a rod 19 as a push fit.The lower end of the rod 19 is welded to the bearing element 1011. A rubber bush 106 is fitted between the bearing elements 102 and 1011.

The valve has a piston acting on the lever 51, under the action of the hydraulic pressure in the braking circuit, in reaction to the load of the spring 14. Movement of the suspension member 1 relative to the vehicle body (such as that arising from an increased load in the vehicle) changes the spring force acting on the piston, dynamically tuning the valve characteristics to the vehicle load. The valve therefore functions as a pressure-reducing valve, the hydraulic pressure applied to the input port being modulated by the spring force acting on the piston, so as to provide at the output port a hydraulic pressure which is a function of the vehicle load.

In modern vehicles having dual circuit braking systems, a load sensing valve is usually associated with each brake circuit to ensure that, for a given vehicle load, the front/rear braking distribution is substantially equal for both sides of the vehicle.

It is important therefore, to ensure that the operational characteristics of the valve in one brake circuit are substantially the same as those of the valve in the other circuit. As the characteristics of each valve are controlled dynamically by the forces exerted by the respective compression spring and associated linkage mechanisms it follows that the linkage mechanisms for both sides of the vehicles must be set and maintained to a relatively high degree of accuracy to ensure that vehicle braking efficiency is maximised for both braking circuits for various vehicle loads. If the required linkage tolerances cannot be achieved and maintained, differential braking of the vehicle from one side to the other can occur, causing the vehicle to swerve or vary from its desired course during braking operations.Hence, some adjustment is provided in the connection between the seat member 112 and the suspension member 1 in order to take account of dimensional variations in the relationship between the valve mounting location and the suspension member.

In the known arrangement this requirement is satisfied by connecting the second bearing element 102 to the suspension member 1 via a bracket 54 with two mounting holes 52,53, one of which (52) is for location and the other of which (53) is slotted to allow a restricted amount of movement of the bracket 54 relative to the suspension member 1. The bearing element 102 is welded to a longitudinal extension 56 of the bracket 54. To provide a mounting point on the suspension member 1, a sheet metal boss 57 is provided with two holes 58 in register with two nuts 59 which are welded to the boss 57 and to the suspension member 1. Two bolts 61 are threaded into the nuts 59 through the respective holes 52,53 and the holes 58.The bolts 61 are initially partially tightened with an air-powered tool; then the position of the bracket 54 relative to the suspension member 1 is adjusted by hand; and finally the bolts 61 are fully tightened with a torque-wrench. Thus, as well as a manual adjustment operation that is relatively difficult to achieve to the required accuracy, four separate tightening operations using two separate tools are required for each valve.

It would therefore be desirable to be able to provide an improved form of linkage mechanism which enables the adjustment to be made simply, and to a higher degree of accuracy than known mechanisms, without the use of substantial tools. The improved mechanism should also enable easy readjustment of the mechanism, if required, such as may arise from a change in valve operating characteristic caused through use, during periodic service of the vehicle.

The present inventidn provides a linkage between a sensor mounted on a vehicle body and a wheel suspension member whose vertical distance from the vehicle body is a function of the vertical load applied to the corresponding wheel by the vehicle, the linkage comprising, in series between the sensor and the suspension member, a compression spring, a pair of mutually coaxially engaged members constituted by an externally screwthreaded member screwed into an internally screwthreaded member, one of the said members having a seat for one end of the spring, a first bearing element rigid with the other of the said members, and a second bearing element rigid with the suspension member, the arrangement being such that the said members are rotatable relative to each other in order to adjust the position of the said seat in relation to the suspension member, the said members being lockable relative to each other once adjustment has been done.

Preferably, the sensor comprises a load sensing valve for a vehicle braking system.

Preferred features are set forth in claims 2 et seq.

The invention will be described further, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is an exploded isometric view of a linkage between a load sensing valve (not shown) and a wheel suspension member of a vehicle, according to the prior art; Figure 2 is a cut-away perspective view of the lever of a load sensing valve and its connection to a linkage such as is shown in Figure 1 and Figure 3; Figure 3 is an exploded isometric view of a linkage between a load sensing valve (not shown) and a wheel suspension member according to the present invention; Figure 4 is an exploded side view of the linkage of Figure 3, with certain parts omitted; Figure 5 is a side view of the linkage as shown in Figure 2; ; Figure 6 is a schematic cross-section through part of the linkage, showing how a clip connects two screwthreadedly-engaged members; Figure 7 is a fragmentary schematic perspective view of another embodiment of the outer of the two screwthreadedly-engaged members, showing the structure for receiving a modified form of clip; Figure 8 is a front elevation of the part shown in Figure 7; Figure 9 is a section on line IX-IX in Figure 4; Figure 10 is a fragmentary perspective view of a pin forming part of the modified clip; and Figure 11 is an axial section through the pin shown in Figure 10.

Figure 3 shows part of a suspension member 1 which is one of the parallel links of a rear wheel suspension and which moves up and down relative to the vehicle body (not shown), depending on the vertical load applied to the wheel by the vehicle; A bearing pin 2 is fitted through a hole 3 in the member 1 and fixed there by projection welding. A steel bearing ring 4 is coaxially mounted on the pin 2 by means of a moulded rubber bush 6.

An externally screwthreaded steel member 7, with longitudinal grooves 8 of V-shaped cross-section (Figure 11), has its lower end projection-welded to the periphery of the ring 4 and is aligned along a vertical axis 9 intersecting the horizontal axis 11 of the bearing (2/6). The member 7 is screwthreadedly engaged in an internally threaded upper member 12, preferably made of nylon or other resilient plastics material and produced by injection moulding. The member 12 has an integral collar 13 and provides a lower seat for a helical compression spring 14. An upper seat is provided by an injection moulded plastics seat member 16 which cooperates with the lever 51 (Figure 2) of a load sensing valve (not shown) mounted on the vehicle body, the lever beind held between the seat member 16 and a retaining element 17.The seat member 16 has integral segmentsl6a which are a snap fit in a hole in the lever 51.

The retaining element 17 has a recess which receives the upper end 18 of a metal rod 19, the end 18 being push-fitted (or screwed) into the recess. The lower end 21 of the rod 19 is push-fitted into a recess 22 in the upper member 12.

To adjust the linkage the upper member 12 is turned by hand; the collar 13 may have a rough (e.g. knurled or milled) periphery to facilitate this. The rotation of the upper member 12 causes relative axial movement of the upper member 12 and lower member 7, owing to their interengaging screwthreads. When the required adjustment has been made, a plastic or metal locking clip 23 (shown substantially in Figure 24) is inserted into a lateral aperture 24 in the upper member 12 to prevent relative rotation of the members 7,12. The clip 23 has a crosspiece 23a which enters the aperture 24 and has a projection 23b which engages in one of the grooves 8 in the lower member 7.The clip also has a pair of arms 23c for retaining the clip in the aperture 24, the arms being appropriately shaped and/or arranged to produce a slight clamping bias; in another embodiment, one or both of the arms may engage in the screwthread of the lower member 7 inside the upper member 12. One or more further lateral apertures 24 may be provided at different circumferential locations, to facilitate fitting of the clip 23.

Figures 7 to 9 show another embodiment of the member 12, provided on each side with a cut-out 41 for receiving the crosspiece of a clip. The cut-outs leave radial portions 42, each of which is provided with a hole 43 for receiving a corresponding resilient pin 2424 of the clip. To facilitate deformation the pin 44 has a longitudinal slot 46 dividing it into two fingers 47 each (or one) of which has a latching projection 248 in the form of a ramp (or some other convenient shape).When the pins 2424 are pushed through the holes 243, the projections 48 clear the far ends of the holes and the fingers 247 regain their natural spacing so that the projections 48 engage the radial portions 42 in order to resist removal of the clip.

Various modifications may be made within the scope of the invention. For instance, the helical spring may be replaced by another compression spring, such as a stack of spring-washers.

The lower end of the rod 19 may be screwed into the upper member 12, which may also be made of metal. The locking clip may be replaced by a set screw. Alternatively, the members 7 welded to the ring 4 may be an internally screwthreaded member and the upper member 12 may be an externally screwthreaded member.

Furthermore, although the invention has been described with reference to a linkage mechanism disposed about a vertical axis, other axes may equally be used with appropriate linkages to translate the relative movement of the suspension member with the vehicle body to the particular axis used.

Additionally, the sensor linkage mechanism has been described in relation to a load sensing valve by way of example.

However, it should be realised that other sensors may equally be used with the mechanism, such as pressure sensors or displacement sensors, as will be apparent to persons knowledgeable in this art.

Claims (17)

Claims:

1. A linkage between a sensor mounted on a vehicle body and a wheel suspension member whose vertical distance from the vehicle body is a function of the vertical load applied to the corresponding wheel by the vehicle, the linkage comprising, in series between the sensor and the suspension member, a compression spring, a pair of mutually coaxially engaged members constituted by an externally screwthreaded member screwed into an internally screwthreaded member, one of the said members having a seat for one end of the spring, a first bearing element rigid with the other of the said members, and a second bearing element rigid with the suspension member, the arrangement being such that the said members are rotatable relative to each other in order to adjust the position of the said seat in relation to the suspension member, the said members being lockable relative to each other once adjustment has been done.

2. A linkage as claimed in claim 1, in which the first bearing element is welded to the said other member.

3. A linkage as claimed in claim 1 or 2, in which the second bearing element is welded to the suspension member.

11. A linkage as claimed in any preceding claim, including a resilient bush interposed between the bearing elements.

5. A linkage as claimed in any preceding claim, in which the internally threaded member has at least one lateral aperture for receiving a locking member engageable with the externally threaded member.

6. A linkage as claimed in claim 5, in which the externally threaded member has longitudinal grooves for selective engagement by the locking member to prevent relative rotation of the members.

7. A linkage as claimed in claim 5 or 6, in which the lateral aperture communicates with at least one hole for receiving a pin on the locking member.

8. A linkage as claimed in claim 7, in which the pin has a latching projection for resisting withdrawal of the pin from the hole.

9. A linkage as claimed in claim 7 or 8, in which the pin is longitudinally slotted to facilitate insertion in the hole.

10. A linkage as claimed in claim 8 or 9, in which the locking member has at least one arm engageable in the screwthread of the externally threaded member inside the internally threaded member.

11. A linkage as claimed in any preceding claim, in which the internally threaded member is of plastics material.

12. A linkage as claimed in any preceding claim, further comprising a seat member having a seat for the other end of the spring.

13. A linkage as claimed in claim 12, including a rod extending coaxially through the spring and the seat member, one end of the rod being connected to the said one member and the other end of the rod being connected to a retaining member.

14. A linkage as claimed in claim 13, in which the said one end of the rod is a push fit in a corresponding recess in the said one member.

15. A linkage as claimed in claim 13 or 14, in which the said other end of the rod is a push fit in a corresponding recess in the retaining member.

16. A linkage as claimed in any preceding claim, in which the sensor comprises a load sensing valve.

17. A linkage between a sensor and a wheel suspension member, substantially as described with reference to, and as shown in, the accompanying drawings.