GB2049076A - Handbrake lever operated braking system - Google Patents

Abstract

A handbrake lever operated braking system comprises a pivoted handbrake lever 1 connected through linkage 14, 15, 18 etc to brakes 23 the system including at least one energy storing device 5 comprising a compression spring 7 which is compressed during initial brake applying movement of the lever 1 and which expands to release its stored energy in a subsequent stage of brake applying movement to increase the applied effort. As shown there are three energy storing devices 13, 17 and 24, coupled to the handbrake lever and linkage. Each device is an over-centre device e.g. axis of device 5 moves from one side to the other side of line 13 between pivot points 2, 12 as spring effect alters from compression to expansion. <IMAGE>

Description

SPECIFICATION Braking systems This invention relates generaily to vehicle braking systems and more particularly to handbrake applying arrangements.

In such arrangements there is commonly provided a handbrake lever which actuates a cable and/or simple lever system to apply the brakes, which may be disc brakes or drum brakes. With known handbrakes a certain manual effort or load has first to be applied to the lever to take up free play in the system, until the brakes first engage and thereafter the braking load increases substantially proportionally to the manual effort applied to the handbrake lever until a maximum is attained. The maximum braking load is limited to the amount of manual effort considered acceptable. To meet legal requirements for maximum handbrake effort, the simple lever systems are suitable only for iight vehicles, i.e.

cars and small commercial vehicles. Manual handbrake effort is insufficient for larger vehicles and other parking brake applying arrangements have to be used. As an example, heavy trucks commonly use spring brake actuators so that the brakes are applied by a large spring when it is desired to the park vehicle. The spring force is applied simply by releasing air pressure, which normally hoids off the spring.

The aim of the present invention is to provide a handbrake operated braking system in which the maximum manual effort is reduced for a given braking load.

In accordance with the invention, there is provided a handbrake operated braking system in which energy of manual effort to initially move the handbrake lever is stored and used to assist such manual effort in the latter movement of the handbrake.

Preferably, the energy is stored in a resilient means, for example a coil compression spring.

In a preferred embodiment of the invention the energy is stored by an over-centre device, the device releasing stored energy after a predetermined movement of the handbrake lever.

A handbrake lever operated braking system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of the system, Figure 2 is an axial cross-section of an energy storing device of the system, Figure 3 is a side view of the energy storing device illustrating its mounting, and Figures 4A to 4D are graphs of handbrake lever load vs. handbrake lever travel for different handbrake lever operated braking systems.

Referring to Figure 1, the system comprises a handbrake lever 1 one end of which is pivotally connected at 2 to a fixed plate 3. Also pivotally connected at 4 to the handbrake lever 1 is an energy storing device 5.

As best seen in Figure 2, the energy storing device comprises a body 6 which houses a coil compression spring 7, the spring 7 seating at one end against an end wall 8 of the body 6 and at the other end on a plate 9 secured to a push rod 10 guided in the other end wall 11.

The body 6 of the device 5 is pivoted at a fixed point 12 and the push rod 10 is connected to the handbrake lever. The axis of the device 5 is disposed to one side of the line between pivot points 2 and 1 2 so as to act as an over-centre device as best illustrated in Figure 3. Initial rotation of the handbrake lever in a clockwise direction as seen in Figure 1 effects rotation of the device 5 and moves the rod inwardly to compress the spring which thus stores energy. When the axis of the device 5 is coincident with the neutral line 13 between pivot points 2 and 12 the spring compression is maximum and thereafter further rotation of the handbrake lever is assisted by the device, the spring expanding and releasing its stored energy.

The handbrake lever 1 is connected to a brake actuating linkage which comprises a rod 14 which is connected to a depending relay lever 1 5 pivoted at a fixed point 1 6 and which is connected to the rod of an energy storing device 1 7. To a point intermediate the ends of lever 1 5 is connected one end of another rod 18 the other end of which is connected to an arm of a load equalising lever 1 9 which is pivotally mounted at 20 to a pivoted plate 21 and which is rotatable to apply a load through linkages 22 to respective brakes 23.

Another energy storing device 24 is connected between the plate 21 and a point on the equalising lever 1 9.

Both devices 17, 24 are similar to the device 5 and provide the same effect of resisting handbrake lever movement in the initial stage of rotation and assisting movement in the latter stage when brake loads are increasing.

Although illustrated with three devices 5, 17, 24, the braking system will usually have only one such device; three have been shown simply to illustrate optional positions for the devices in the system.

Figures 4A to 4D illustrate the effect of the energy storing devices. Figure 4A is an illustration of the handbrake lever load vs. travel for a braking system using simple levers to transmit handbrake lever effort to the brakes. The handbrake load increases gradually to a maximum after some initial free play is taken up. In Figure 4B there is illustrated the load/stroke characteristics of an energy storing device 5, 17, 24. Figure 4C illustrates the effect of using a single device in a system comprising simple levers such as illustrated in Figure 1. It will be seen from Figure 4C that, as compared to Figure 4A, more work is required during initial handbrake lever movement but less is required towards the end of such movement, the peak effort being only about 65% of that of Figure 4A. Figure 4D shows the curve for a system incorporating the energy storing device in a linkage having ratio change levers, the lever ratio changing in a controlled manner during operation.

This provides a more even distribution of the handbrake lever effort through the stroke of the lever and a further reduction in the peak effort.

Claims (2)

1. A handbrake lever operated vehicle braking system comprising a pivotal handbrake lever connected to a brake actuating linkage and a plurality of energy storing devices one coupled to the handbrake lever and at least one more coupled to the linkage, each said device comprising a compression spring which is compressed during initial brake applying movement of the handbrake lever and whose stored energy is released in a subsequent stage of brake applying movement and applied to the linkage in a sense to increase the applied effort.

2. A handbrake lever operated braking system substantially as herein described with reference to the accompanying drawings.