Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1996-06-20
1997-12-23
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913693, 91376R, F15B 910
Patent
active
056997132
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a brake booster, primarily for use in a vehicle hydraulic braking system for the purpose of providing power assistance in the actuation of a brake master cylinder, and of the general kind in which the supply of working fluid to a fluid-actuated servo piston is controlled by a valve mechanism actuated under the influence of a driver-operated force input member which acts via a reaction element on an output member arranged to provide power assisted input to the master cylinder.
A conventional brake booster of the aforesaid general kind provides a constant boost ratio throughout its operating range so that the boost increases progressively and rapidly with increased driver input, typically to a brake foot pedal. Whilst this provides satisfactory results in general use, it has become recognised that some drivers fail to exert enough force on the brake pedal during emergency braking, with the result that the available maximum deceleration of which a vehicle is capable without skidding is not always achieved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a brake booster of the aforesaid general kind which provides improved braking performance when relatively high levels of vehicle deceleration are required.
According to the invention, a brake booster of the aforesaid general kind includes a force transmission assembly providing surfaces through which force is transmitted between the input and output members, and yieldable means arranged to yield under a predetermined force to permit relative movement between parts of the force transmission assembly such as to change the ratio of the operative surface areas and thereby increase the boost ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with reference to the accompanying drawings in which:
FIG. 1 is a longitudinal cross-section of one form of the brake servo booster of the invention;
FIG. 2 is an enlarged view, partly in cross-section, of the encircled area of FIG. 1;
FIGS. 3 and 4 are views similar to FIGS. 1 and 2, illustrating an alternative form of the booster of the invention;
FIGS. 5 and 6 are views similar to FIGS. 1 and 2 illustrating a further alternative form of the booster of the invention;
FIGS. 7 and 8 are views similar to FIGS. 1 and 2 illustrating a further alternative form of the booster of the invention;
FIGS. 9 and 10 are views similar to FIGS. 1 and 2 illustrating a further alternative embodiment of the booster of the invention;
FIG. 11 is a graph illustrating an operational function of the booster of FIGS. 9 and 10;
FIGS. 12 and 13 are views similar to FIGS. 1 and 2 illustrating a further alternative embodiment of the booster of the invention;
FIG. 14 is a graph illustrating an operational function of the booster of FIGS. 12 and 13, and
FIGS. 15 and 16 are respectively similar views of parts of two further alternative embodiments of the booster of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The servo booster illustrated in FIGS. 1 and 2 of the drawings has a housing 1 which includes front and rear shells 2 and 3 joined together around their outer peripheries at 4 to form a closed unit. The interior of the housing is divided into two chambers A, B by a diaphragm assembly 5 which includes a flexible diaphragm 6 and a relatively rigid diaphragm support plate 7, the diaphragm 6 being trapped around its outer periphery at the joint 4 between the housing shells 2 and 3. The backing plate 7 is supported in its central region on an axially reciprocable hub 8 which extends therethrough and which is urged to the right, as seen in the drawing, by a coil return spring 9 acting between the hub and an internal surface portion of the shell 2. A force output rod 10 is carried by the hub and intended for connection, in use, to a piston of a master cylinder 1A forming part of a vehicle hydraulic braking system. A plurality of tie rods 11 extend axially through the housing 1 and, in addition to providing
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patent: 4690034 (1987-09-01), Ando et al.
patent: 5012723 (1991-05-01), Gauthier
patent: 5146837 (1992-09-01), Inoue
patent: 5261313 (1993-11-01), Yared
patent: 5367942 (1994-11-01), Nell et al.
patent: 5425302 (1995-06-01), Leurai et al.
Lucas Industries PLC
Nguyen Hoang
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