GB2052691A

GB2052691A - Motor Vehicle Brake Pedal

Info

Publication number: GB2052691A
Application number: GB7934389A
Authority: GB
Original assignee: GONELLA P
Current assignee: GONELLA P
Priority date: 1979-06-26
Filing date: 1979-10-04
Publication date: 1981-01-28
Also published as: YU103280A; IT1119004B; DE2930752A1; ES483199A1; JPS565249A; FR2459744A1; IT7968352A0

Abstract

A motor vehicle brake pedal of the variable lever arm type including a pedal lever (10) pivotally mounted on a fixed part of the motor vehicle chassis so that it can be depressed by the foot of the driver against the action of a return spring, and a plunger (38) engaging the piston (42) of the master brake cylinder and with the other end secured to a bifurcated bracket (18) pivotally connected to the pedal lever (10). The bracket (18) includes a cam follower (34) riding on a cam surface (36) of the pedal lever (10) to keep the plunger (38) constantly in a substantially horizontal position and exert a maximum force thereon in all positions of the pedal lever (10). <IMAGE>

Description

SPECIFICATION Motor Vehicle Brake Pedal This invention relates to a motor vehicle brake pedal of the variable lever arm type.

Motor vehicle brake pedals are known in which the length of the secondary lever arm diminishes as the brake pedal rotates under the pressure exerted thereon by the driver's foot, to increase the gain of force during the second portion of the braking operation. In this manner the gain of force at the beginning of actuation of the brakes is relatively low because in this initial phase the reaction force exerted by the master brake cylinder is small as in this phase the resiliency of the brake pipes and other yieldings of the brake circuit have to be overcome.But when in a second phase during actuation of the brake pedal the reaction force of the actual braking action is encountered, which force is much greater than the initial reaction force although the distances traversed during its exertion are much smaller, the secondary lever arm of the brake pedal is reduced to increase the gain of force and permit the driver to brake efficiently without having to press with an excessive effort on the brake pedal. In other words, such brake pedals within variable lever arm permit to exert a substantially constant force on the brake pedal even though the reaction force encountered by the master brake cylinder increases. This among other items avoids the necessity of making the brake pedal too large with an excessive angle of rotation and permits to keep the force required for actuation of the brakes below a predetermined maximum value.Such brake pedals with variable lever arm in some cases permit to avoid the use of expensive brake boosters and nevertheless achieve a strong braking action.

However, generally the conventional brake pedals with variable lever arm have the disadvantage that the plunger connected to the brake pedal and acting upon the piston of the master cylinder assumes variously inclined positions as the position of the brake pedal varies, due to the action of the lever arm reducing mechanism. Consequently, the plunger does not extend coaxially to the master cylinder piston over the entire path of movement of the brake pedal and when the plunger acts obliquely on the piston it causes transverse stress between the piston and the piston guides with the resuit that the master cylinder piston gradually goes out-ofround and its operation is impaired.

Another disadvantage of conventional brake pedals is that they usually comprise a relatively great number of parts and thus are expensive and also difficult to assemble.

A further disadvantage of the conventional brake pedals consists in that according to a well established law the gain of force during rotation of the brake pedal varies in a substantially linear fashion and it is not quite easy to establish a different law.

It is therefore an object of the present invention to provide a brake pedal with variable lever arm wherein the plunger actuating the master cylinder piston of the brake system remains in a substantially coaxial piston relative to the master cylinder piston over the entire path of movement of the brake pedal and wherein it is possible to establish an arbitrary law of variation of the gain of force during rotation of the brake pedal. A further object of the invention is to achieve this by providing a brake pedal comprising a reduced number of parts so that it can be produced at low cost.

These and other objects and advantages of the invention, which will become apparent in the course of the following description, are achieved according to the invention by a motor vehicle brake pedal of the variable lever arm type including a pedal lever pivotally mounted on a fixed part of the motor vehicle chassis to be actuated by pressure exerted on its free end against the action of a return spring, and a plunger pivotally connected to the pedal lever for actuating a master brake cylinder by depression of said pedal lever, characterized in that said plunger comprises a bifurcated bracket having a pair of coextensive arms embracing said pedal lever, and a pivot traversing a slot in said pedal lever inserted between said pair of arms, and said pedal lever further comprises a cam surface on the side thereof facing said plunger, and a cam follower rotatably mounted between said pair of arms of said bifurcated bracket at the end thereof adjacent said plunger away from said pivot for cooperation with~said cam surface, said cam surface being so shaped that, as said pedal lever is rotated for actuation of the brakes, said cam follower will divert the direction of action of said plunger so as to shorten the distance separating it from the fulcrum of said pedal lever.

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawing in which Fig. 1 is a side view of a motor vehicle brake pedal with variable lever arm according to the invention, and Fig. 2 is a plan view, on a larger scale, of the brake pedal of Fig. 1.

Referring to Fig. 1, the brake pedal according to the invention comprises a brake actuating pedal lever 10 having a hole 12 at one end for pivotal connection to a fixed point of the motor vehicle chassis and a foot support plate 14 at the opposite end for engagement by the foot of the driver for depressing the pedal lever and thereby actuating the brakes. The pedal lever 10 may conveniently be made by punching it from a thick steel sheet in the arcuate shape as is common in the art of making motor vehicle brake pedals.

Secured to the pedal lever 10 is a lug 16 having a hole for the attachment of a return spring, not shown.

Pivotally connected to the pedal lever 10 is a bifurcated bracket 1 8 having a pair of coextensive arms supporting therebetween a retaining pivot 20 received in a slot 22 in the pedal lever 10. The retaining pivot 20 is preferably provided with a collar 24 of antifriction material such as polyamide resin as well as washers 26 of the same material. A circlip 28 keeps the retaining pivot 20 assembled on the bifurcated bracket 18.

Further mounted on the bifurcated bracket 18 is a second pivot 30 similar to the pivot 20 and also kept in place by a circlip 32. Pivotally mounted on the pivot 30 is, however, a roller bearing 34 serving as a cam follower adapted to engage and roll on a cam surface 36 provided by appropriately shaping the adjacent peripheral surface of the pedal lever 10.

At its end opposed to its end of pivotal connection to the pedal lever 10, the bifurcated bracket 18 carries a plunger 38 screwed into a threaded hole in the adjacent rear end of the bifurcated bracket 18 and locked by a lock nut 40 to permit adjustment of the length of the plunger.

As shown in Fig. 1, the plunger 38 is arranged to act on a piston 42 of a master brake cylinder, not shown.

It will thus be evident that by depressing the pedal lever 10 and rotating it counterclockwise according to the illustration of Fig. 1, the pedal lever will exert a thrust on the bifurcated bracket 18 and through this bracket on the plunger 38 and on the piston 42 of the master brake cylinder and the direction of this thrust changes at the point of engagement between the cam surface 36 and the cam follower 34. In fact, as the pedal lever 10 rotates counterclockwise, the cam follower 34 rolls on the cam surface 36 because the plunger 38 is kept in place by its engagement with the piston 42. However, the straight line of action of the plunger 38 will remain parallel to the position shown in Fig. 1 because the slot 22 permits a certain adjustment of the bifurcated bracket to maintain this parallelism. It is also evident that the movement of the cam follower 34 along the cam surface 36 will change the straight line of action of the plunger 38 relative to the axis of the fulcrum 12 and will move it closer to the fulcrum, with the result that the equivalent secondary lever arm is reduced. The law governing this variation can be arbitrarily adjusted by changing the shape of the cam surface 36, which can be done in a very simple manner and without extra cost. It is considered unnecessary to describe here the way in which the shape of the cam surface 36 is determined because this is well within the ability of one skilled in the art and can be done empirically or by a geometrical analysis of the brake pedal in its various positions.

Claims

1. A motor vehicle brake pedal of the variable lever arm type including a pedal lever pivotally mounted on a fixed part of the motor vehicle chassis to be actuated by pressure exerted on its free end against the action of a return spring, and a plunger pivotally connected to the pedal lever for actuating a master brake cylinder by depression of said pedal lever, characterized in that said plunger comprises a bifurcated bracket having a pair of coextensive arms embracing said pedal lever, and a pivot traversing a slot in said pedal lever inserted between said pair of arms, and said pedal lever further comprises a cam surface on the side thereof facing said plunger, and a cam follower rotatably mounted between said pair of arms of said bifurcated bracket at the end thereof adjacent said plunger away from said pivot for cooperation with said cam surface, said cam surface being so shaped that, as said pedal lever is rotated for actuation of the brakes, said cam follower will divert the direction of action of said plunger so as to shorten the distance separating it from the fulcrum of said pedal lever.

2. A motor vehicle brake pedal as claimed in claim 1, wherein said cam follower comprises a radial roller bearing.

3. A motor vehicle brake pedal as claimed in claim 1, wherein said slot in said pedal lever extends substantially transversely to a line connecting said fulcrum to said slot.

4. A motor vehicle brake pedal as claimed in claim 1, wherein said plunger is screwed into said bifurcated bracket and adjustable by screwing it more or less deeply into said bifurcated bracket and lockable in the adjusted position by means of a lock nut.

5. A motor vehicle brake pedal of the variable lever arm type substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.