Vehicle brake servo booster with traction control mode

A brake servo booster capable of operating in a traction control mode has a housing (100) containing a diaphragm assembly (500) which divides the housing into two chambers A and B. Supply of air to the diaphragm assembly is controlled by a valve mechanism which includes a reciprocable valve member (7) operatively connected to a force input member (5) actuated by a driver-operated control. The force input member includes two parts (11,12) connected respectively to the valve element and driver-operated control. The arrangement is such that operating force applied to the control is transmitted through both of the first and second input member parts (11,12) whilst a traction control operative mode is permitted by the second part (11) moving relative to the first part (12).

BACKGROUND OF THE INVENTION 
This invention relates to a brake servo booster, primarily for use in 
providing power assistance in the actuation of a brake master cylinder of 
a vehicle hydraulic braking system capable of operating in a traction 
control mode, the booster being of the general kind in which the supply of 
air to a servo piston, usually in the form of a diaphragm assembly, is 
controlled by a valve mechanism which includes a reciprocable valve 
element operatively connected to a force input member actuated by a 
driver-operated control. 
For the traction control mode, the booster is actuated automatically to 
apply the brakes without intervention by the driver and the connection 
between the force input member and the booster valve element must be such 
as to allow this to happen without significantly affecting the position of 
the brake pedal. An object of the invention is to provide a simple and 
convenient form of connection for this purpose. 
According to the invention, the force input member of a booster includes 
two parts of which a first one is connected, in use, to the 
driver-operated control, and the second one to the valve element, the 
arrangement being such that operating force applied to the control member 
is transmitted through both of said first and second parts of the input 
member to the valve element, whilst operation of the booster in the 
traction control mode is permitted by the second part of the force input 
member moving relative to the first part. 
In a preferred arrangement, the first and second parts of the force input 
member are telescoped together with one of the parts slidingly housed 
within a bore of the other part. 
Typically, the valve element is housed within a hub connected to the servo 
piston, and the hub carries abutment means which engages a housing part of 
the booster to set the retracted position of the first part of the input 
member and thereby of the control member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 of the drawings, there is illustrated therein part of a 
brake servo booster of the invention having a housing 100 composed of a 
pair of shells 200 and 300 joined together at 400 in fluid-tight manner. 
The interior of the housing is divided by a diaphragm assembly 500 into 
two chambers A and B, the diaphragm assembly being carried by a hub 600 
which would normally be urged by a return spring 700 to the right, as seen 
in the drawing. The hub 600 acts upon a force output rod 800 arranged to 
actuate a master cylinder (not shown) in conventional manner. The action 
of the rod is controlled by an arrangement of valves contained within a 
housing portion 900 of the booster and operated by a force input rod 5 
connected to a driver-operated pedal (not shown). 
As can be seen from FIGS. 2 and 3, the hub 600 contains a valve control 
piston 3 which is allowed limited axial movement within the hub and to 
which is crimped, or otherwise secured a ball end 4 of the force input 
rod. A reaction disc 6 is interposed between the left hand end of the 
piston 3 and the force output rod 800. The extreme right hand end portion 
of the piston 3 forms a valve seat 3A and the hub 2 forms a further valve 
seat 2A, both seats being arranged to cooperate with a popper valve 
assembly 7, in conventional manner. Part of the hub 2 is surrounded in 
spaced relationship by a relatively thin gauge sleeve 8 of which a closed 
end 9 lies beyond the right hand end of the hub 2 and is engaged by a 
flange 12B of the rod part 12. The opposite end of the sleeve is formed 
with a radially outwardly turned flange 10 which acts as an abutment to 
set the retracted position of the input rod, in the manner to be 
described. 
The force input rod 5 consists of two parts, of which a first part 11 
carries the ball end 4 and has a reduced diameter stem 11A extending 
within an axial bore 12A of the second rod part 12 which is provided with 
an eye 12C to receive a clevis or similar connecting device by means of 
which the rod part 12 is connected to an operating pedal. A radial flange 
13 on the rod part 11 abuts the inner end of the rod part 12 and forms an 
abutment also for a dish element 14 which surrounds the force input rod 
and extends therealong in a direction away from the rod part 11, the free 
end portion 15 thereof being turned outwardly to form an abutment for one 
end of a spring 16, of which the other end abuts a retainer 17 of the 
popper valve assembly 7 and urges the retainer into engagement with a 
shoulder 18 of the hub. A further spring 19 acts between the inner end of 
the dish 14 and the valve assembly 7 to urge the latter into engagement 
with the valve seats 2A and 3A. 
When the operating pedal is fully retracted and the booster inoperative, 
the flange 10 of the sleeve 8 abuts the housing 900 at location 1A and 
thereby sets the retracted position of the force input rod 5 and pedal. 
Operation of the booster for normal braking is effected by applying an 
input force to the part 12 of the force input rod 5, from which the force 
is transmitted to the flange 13 of the rod part 11, the latter acting on 
the control piston 3 in order to actuate the valves in conventional 
manner. Inward movement of the rod also moves the hub 600 inwardly and the 
abutment flange 10 of the hub becomes spaced from the housing 900, as can 
clearly be seen in FIG. 2. When the pedal is released, the hub and the 
various components return to the right until the flange 10 once more abuts 
the housing 900 to set the retracted position of the rod and pedal. 
When the booster operates in the traction control mode, the hub 600 moves 
forwardly without any movement of the operating pedal, or of the rod part 
12, the stem 11A of the rod part 11 sliding along the bore 12A of the rod 
part 12 to allow the rod part 11 to follow the hub. In this mode of 
operation, the hub 600 slides relative to the sleeve 8, leaving the latter 
with its flange 10 in abutment with the housing 900. At the cessation of 
the traction control mode, the hub returns to its innermost position 
within the sleeve under the action of the spring 700 (FIG. 1). 
It will be seen that the invention provides an extremely simple and 
effective means of allowing the booster to operate in a traction control 
mode independently of the foot pedal, allowing the booster/pedal 
arrangement to remain identical with boosters not intended for traction 
control. Since the input rod part 12 is located firmly relative to the 
sleeve 8, its retracted position is set by engagement of the sleeve flange 
10 against the booster housing 900 and there is no necessity, therefore, 
for an adjustable back stop to be provided on the pedal. It will be 
understood that the arrangement of the rod parts may be reversed, with the 
part 11A sliding over the part 12, if desired.