GB2033513A

GB2033513A - Vehicle load sensing arrangements

Info

Publication number: GB2033513A
Application number: GB7934645A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-10-20
Filing date: 1979-10-05
Publication date: 1980-05-21
Also published as: FR2439108A1; JPS5587853U; DE7929698U1

Abstract

A vehicle load sensing arrangement for a vehicle braking system comprises a mounting (12) for a leaf spring (13) the mounting being supported by a lever (5) on a vehicle frame (2). The lever (5) is engageable with a load sensing device (1) mounted on the frame (2) and is so arranged that deflection of the leaf spring due to changes in vehicle loading causes rotation of the lever (5) and actuation of the load sensing device (1). The lever is mounted for rotation about an axis (X) extending longitudinally of the vehicle. <IMAGE>

Description

SPECIFICATION Vehicle load sensing arrangements This invention relates generally to vehicle load sensing arrangements for use with vehicle braking systems.

Braking systems commonly have a fluid pressure source in the form of a pedal-operated master cylinder which supplies pressure directly to the front wheel brakes and through a brake pressure control valve to the rear wheel brakes. The control valve may be a pressure reducing valve which, when a predetermined "cut-in" pressure has been attained, limits the pressure supplied to the rear wheel brakes as compared to that supplied to the front wheel brakes to reduce the risk of rear wheel lock. The valve may optionally be a pressure limiting valve which prevents any increase in pressure at the rear wheel brakes after the cut-in pressure has been attained.

Usually, the control valve has a valve member which is movable to open and close the valve and which is subjected to a load, commonly called a "pre-load", which varies in dependence upon vehicle loading, the cut-in pressure being dependent upon the pre-load.

The pre-load is controlled by a vehicle load sensing arrangement which may be in the form of a mechanical linkage which is connected between the sprung and unsprung parts of the vehicle and senses the loading between the vehicle parts. The pre-load applied to the control valve member is dependent upon the sensed deflections.

On assembly of the vehicle, the control valve and linkage are set to provide a desired pre-load for a given vehicle load. Such valves and linkages have the disadvantage that during use the vehicle suspension settles which requires that the valve and the linkage has to be frequently reset to compensate for settling.

Furthermore, during extreme vehicle deflections there is the possibility of over-travel damage and excessive loading in the linkage system which require complex lost motion and over-travel mechanisms. Also the linkages have to be sufficiently robust to withstand transient suspension loads.

Proposals have been made to overcome the aforementioned problems by detecting movement of a vehicle leaf spring relative to the frame supported by the leaf spring. One such proposal is described in British Specification No. 929 598 in which the variation load of a leaf spring is sensed by varying the pressure of fluid in a pressure chamber of a hydraulic load sensor. In one embodiment described in that specification, the leaf spring directly engages a piston working in the pressure chamber. Such an arrangement is suitable only for pressure-sensitive or hydralic load sensors since the loads involved are so large that a mechanical arrangement would require extremely robust components.

In another embodiment described in the prior specification, there is shown a lever arrangement in which a long lever is pivotally mounted on the vehicle frame for rotation about a transverse axis and is coupled at opposed ends respectively to the leaf spring and to the hydraulic load sensor. Such an arrangement requires substantial space. A further disadvantage is that operation of the load sensing arrangement requires a substantial amount of vertical wheel movement which subtracts from the total amount of wheel deflection movement that would be available if the spring were solidly mounted on the vehicle frame.

The embodiments of the present invention, described in more detail below, aim to overcome one or more of the above-mentioned disadvantages.

In accordance with the present invention, there is provided a vehicle load sensing arrangement for a vehicle braking system, comprising a mounting for a leaf spring, said mounting being connected to a lever mechanism which is mounted on a vehicle frame for rotation about an axis extending longitudinally of the vehicle, and a load sensing device mounted on said frame and engaged by the lever mechanism, deflection of the leaf spring causing rotation of the lever and actuation of the load sensing device.

Preferably, the lever mechanism comprises a two-armed lever, one arm of which engages the load sensing device. The other arm of the lever is preferably engageable with a stop which limits rotation of the lever. The stop is preferably of resilient material and acts as a buffer.

Some forms of load sensing arrangement in accordance with the invention will now be described, by way of example, with reference to the accompaning drawings in which: Figure 1 is a part cross-sectional view of one form of load sensing arrangement, Figure 2 is a side view taken in the direction of arrow Z in Fig. 1, Figure 3 is a top plan view of the arrangement of Fig. 1, Figure 4 is a side view, partly in axial crosssection of another form of arrangement, Figure 5 is a view similar to that of Fig. 4 of yet another form of arrangement, and Figure 6 is a section taken along line VI-VI of Fig. 5.

The load sensing arrangement of Figs. 1 to 3 comprises a load sensing device 1 mounted on a frame member 2 of a vehicle chassis.

Attached to the frame member 2 is a bifurcated support bracket 3 (Fig. 2) between the arms 3A, 3B of which extends a pivot pin 4, the pin axis X extending substantially longitudinally of the vehicle. The pin 4 pivotally supports a rocker arm in the form of a Lshaped lever 5 having two arms one arm 6 engaging a plunger 7 of the load sensing device 1 and the other arm 8 being engagea ble with a resilient buffer stop 9 secured to the frame member 2.

Secured to the lever 5 by a pin 11 is a mounting in the form of a yolk or shackle 1 2 which supports one end of a leaf spring 1 3 in known manner. The shackle 1 2 is mounted on the pin for pivotal movement about the pin axis Y which extends substantially transversely of the vehicle.

In use of the vehicle changes in vertical loads on the shackle 12, due either to dynamic effects such as caused by braking or statically by actual loading of the vehicle, causes rotation of the lever 5 to alter the load on the plunger 7 of the load sensing device.

The changes in the load on the plunger are transmitted to a pressure control valve (not shown) incorporated in known manner in the vehicle braking system, usually in a pressure line to the rear wheel brakes, to alter the characteristics of the valve and the ratio of rear wheel to front wheel brake pressures. The plunger loading may be transmitted to the valve by any suitable means, for example hydraulically, mechanically, or electrically.

In the arrangement of Fig. 4, the load sensing device 1 5 is mounted on the frame member 1 6 of the vehicle chassis. One arm 1 7 of an L-shaped lever 1 98 engages a plunger 1 9 of the load sensing device 1 5 and the other, downwardly depending arm 20 is fast with one end of a shaft 21 which extends transversely of the vehicle through an aperture 22 in the frame member. Attached to the other end of the shaft 21 is a mounting 24 for one end of a leaf spring 25.

Intermediate the arm 20 and mounting 24 is a ball joint 27 comprising an insert 28 located in the aperture 22 of the frame member 16, the insert having a past-spherical recess 28A on its inner surface which receives a complementary shaped member 29 of rubber or plastics material acts as an interlining between the recess 28 and a part spherical portion 30 of a ball member 31 mounted on the shaft 21. A nut 32 holds the ball member 31 and the mounting 24 on the shaft 21. A resilient stop 33 may be located between the arm 20 and the load sensing device 1 5.

Operation of the arrangement is similar to that of Figs. 1 to 3. If there is a change in vehicle loading the mounting 24 moves relative to the frame member 16 and the shaft 21 rotates (clockwise when the load is reduced) about an axis A extending longitudinally of the vehicle. In this way the load applied to the plunger 1 9 by the aarm 1 7 is varied in dependence upon vehicle loading.

The above-described load sensing arrangements have the advantages that all the loads are fed to the chassis in a manner similar to conventional leaf spring support arrangements in which the mounting is secured directly to the frame member and not through the intermediary of the pins 4, 11 or shaft 21. Thus, no additional strengthening or outriggers are required. Furthermore, since the lever 5, 1 8 is mounted for rotation about a longitudinal axis and each load sensing device is mounted on the frame member, the load sensing arrangment occupies substantially the same space as a conventional leaf spring support arrangement. Because of the compactness, less material is required than in known load sensing arrangements connected to vehicle leaf springs and thus there is less weight.

The arrangement of Figs. 5 and 6 is similar to that of Fig. 4 and the same reference numerals are used to denote corresponding parts. In the arrangement of Figs. 5 and 6 the shaft 21 is mounted in the frame member 16 as previously described, but has a substantial length. Connected to the end of the shaft 21 remote from the leaf spring 25 is an arm 34 of a bell-crank lever 35 pivotally mounted on the frame member 1 6 for rotation about a longitudinal transverse axis B. The other arm 36 of the lever 35 is attached to the plunger 1 9 of the load sensing device 1 5. In this embodiment the arm 36 is biased towards the resilient stop 33 by a coil compression spring 37.

Operation of arrangement of Figs. 5 and 6 is similar to that of Fig. 4 in that movement of the leaf spring 25 relative to the frame member 1 6 causes rotation of the lever 21 and thus the bell crank lever 35 to alter the load on the plunger 1 9. In this embodiment, however, the length of shaft 21 provides a high lever ratio between the leaf spring 25 and the bell crank lever 35 thus making the arrangement more sensitive to vehicle load changes.

However, more space is clearly required.

It will be appreciated that in each of the above-described embodiments only a small amount of wheel movement is required to operate the arrangements and such small movement does not substantially affect the total available wheel deflection which would be available if the leaf spring were conventionally mounted on the frame member. In other words, the above-described arrangements do not substantially affect the normal operation of the vehicle suspension and permits substantially the same maximum wheel deflection as would be the case if the arrangements were not used.

It will be appreciated that the measurement of vehicle load using the above-described arrangement is independent of the height of the sprung part of the vehicle above the road.

Claims

1. A vehicle load sensing arrangement for a vehicle braking system, comprising a mounting for a leaf spring, said mounting being connected to a lever mechanism which is mounted on a vehicle frame for rotation about an axis extending longitudinally of the vehicle, and a load sensing device mounted on said frame and engaged by the lever mechanism, deflection of the leaf spring causing rotation of the lever mechanism and actuation of the load sensing device.

2. An arrangement according to claim 1, wherein said mounting is pivotally connected to the lever mechanism for rotation about an axis extending transversely of the vehicle.

3. An arrangement according to claim 1 or 2, wherein the lever mechanism comprises a two-armed lever member one arm of which is engageable with said load sensing device.

4. An arrangement according to claim 3, wherein the other arm of said lever member is engageable with a resilient stop which limits rotation of said lever member about said longitudinal axis.

5. An arrangement according to any of claims 1 to 4, wherein the lever mechanism is pivotally mounted on a pin attached to the frame and is secured to the mounting for movement therewith about said longitudinal axis.

6. An arrangement according to claim 5, wherein the mounting is a yolk which supports the leaf spring and which is pivotally secured to the lever mechanism for rotation about an axis extending transversely of the vehicle.

7. An arrangement according to any of claims 1 to 4, wherein the lever mechanism comprises a shaft attached at one end to the mounting and mounted in the frame for rotation about said longitudinal axis.

8. An arrangement according to claim 7, wherein the shaft has a ball and socket connection with said frame.

9. An arrangement according to claim 7 or 8, wherein elastomeric material is interposed between the shaft and the frame.

10. An arrangement according to any of claims 7 to 9 as appendant to claim 1 or 2, wherein the shaft is connected to one arm of a bell-crank lever the other arm of which is engageable with the load sensing device, said lever being pivotally mounted on said frame.

11. An arrangement according to claim 10, wherein said other arm is also engageable with a resilient stop which limits rotation of the lever.

1 2. A vehicle load sensing arrangement constructed and arranged substantially as herein described with reference to Figs. 1 to 3 of the accompanying drawings.

1 3. A vehicle load arrangement constructed and arranged substantially as herein described with reference to Fig. 4 or Figs. 5 and 6 of the accompanying drawings.