Vehicle brake systems

In a vehicle brake system a wedge is provided between the brake pedal and the pushrod which operates the master cylinder. Movement of the wedge is controlled by a control unit by means of a solenoid, when the control unit anticipates that the brakes may be operated by the driver, for example because the accelerator pedal has been released, the wedge is driven between the brake pedal and pushrod to move the brake pads into a pre-activated position in which they are just in contact with the brake pads. This reduces the pedal travel required to operate the brakes.

FIELD OF THE INVENTION 
The present invention relates to brake systems for vehicles, and in 
particular to the problem of reducing brake pedal travel. 
BACKGROUND OF THE INVENTION 
As crash safety becomes increasingly important in vehicles there is an 
increasing desire to eliminate, or at least reduce the size of, brake 
servos. However this creates a problem because higher lever ratios are 
then required in the brake pedal, which result in increased brake pedal 
travel and a reduced ability to take up slack in the brake actuation 
system. This leads to poor feel, and difficulty meeting legislative 
requirements for circuit failure. It also increases the risk of accidental 
acceleration where the driver presses the brake pedal but, because his 
foot is not properly place on the pedal, also catches the accelerator 
pedal. If there is a lot of free travel in the brake pedal, the two pedals 
can be depressed quite a long way without much resistance, increasing the 
speed of the vehicle considerably when the driver intends to apply the 
brakes. 
It is known, for example from U.S. Pat. No. 3,726,369 to provide a brake 
control system in which sudden release of the accelerator triggers a brief 
period of braking produced by a solenoid actuator in anticipation of 
driver braking. 
It is also known from GB 2 250 070 to provide a vehicle braking system in 
which, when driver braking is anticipated, for example due to release of 
the accelerator pedal, a low pressure is applied to the hydraulic braking 
circuit for a period of a few hundred milliseconds which is sufficient to 
take the slack out of the system, but not sufficient to apply the brakes. 
SUMMARY OF THE INVENTION 
Accordingly the present invention provides a vehicle brake system 
comprising a rotatable member arranged to rotate with a wheel of the 
vehicle, a braking member movable into engagement with the rotatable 
member to provide braking, a driver input member arranged to be operated 
by a driver of the vehicle to control movement of the braking member, and 
actuation means arranged to anticipate operation of the brakes by the 
driver and, when operation of the brakes is anticipated, to move the 
braking member into contact with the rotatable member and then to return 
it to a partially released position. 
The rotatable member may be a brake disk or a brake drum. 
Preferably the system further comprises force transmitting means arranged 
to transmit force from the driver input member to the braking member to 
provide normal braking, and the force transmitting means includes two 
parts which are arranged to be urged together when force is applied to the 
driver input member, and the actuating means is arranged to drive said 
parts apart to urge the braking member towards the wheel mounted member. 
Preferably the driving apart of said parts also urges the driver input 
member towards the driver, in a direction which would normally release the 
brakes. The advantage of this arrangement is that, in the event of a 
frontal impact, the free play in the input member, generally a brake 
pedal, is reduced, and its ability to support the part of the driver 
actuating it, generally his leg, is increased over the first part of its 
travel. This is beneficial because it has been found that controlled 
support of the driver's leg on frontal impact can reduce injury to the 
lower leg. 
Indeed the present invention further provides a vehicle brake actuation 
system comprising a hydraulic brake actuation circuit including a master 
cylinder, driver input means arranged to be operated by a driver of the 
vehicle to operate the master cylinder, and actuation means arranged to 
anticipate operation of the brakes by the driver and, when operation of 
the brakes is anticipated, to move two parts of the driver input means 
relative to each other to take up slack in the actuation system. 
For example the actuation means may include a wedge arranged to be driven 
between said parts to move the braking member towards the rotatable 
member. Alternatively it may comprise a cam which can be rotated to 
produce the same effect, or indeed any other suitable mechanical 
mechanism. One of said parts preferably comprises part of a brake pedal 
and the other of said parts preferably comprises a pushrod. 
The actuation means may be driven by a simple solenoid, or alternatively by 
a stepper motor, a linear motor, or a vacuum or pneumatic device. 
Preferably the actuation means includes sensing means for sensing an action 
by the driver and control means arranged to anticipate operation of the 
brakes by the sensing of said action. 
Preferably the control means is arranged to determine on the basis of said 
signals when such operation is no longer anticipated, and respond by 
releasing the partial actuation means. This enables the brakes to remain 
in the partially actuated condition for as long as conditions prevail in 
which the driver might use the brakes. 
The present invention further provides a brake system comprising driver 
input means to allow actuation of the brakes by a driver, partial 
actuation means operable to partially actuate the brake system, sensing 
means, and control means arranged to anticipate, on the basis of signals 
from the sensing means, operation of the driver input means and, when such 
operation is anticipated, to operate the partial actuation means to effect 
partial actuation of the system thereby to take up slack in the system, 
and to determine on the basis of said signals when such operation is no 
longer anticipated, and respond by releasing the partial actuation means. 
Preferably the sensing means comprises proximity sensing means arranged to 
sense the proximity of a part of a driver to the driver input member. 
The sensing means is preferably arranged to sense release of an accelerator 
of the vehicle. 
The control means is preferably arranged to monitor the operation of a 
power train of the vehicle and is arranged to anticipate operation of the 
brake from the operation of the power train, for example when it senses 
that the power train is in overrun applying a braking force to the 
vehicle. 
Preferred embodiments of the present invention will now be described by way 
of example only with reference to the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to FIG. 1, in a first embodiment of the invention, a braking 
system comprises a brake pedal 10 mounted on a pivot 12, a pushrod 14 
which operates the master cylinder 16 of a hydraulic brake actuation 
system, and a brake pad supported in a brake calliper 18 and movable by a 
hydraulic slave cylinder 22 into an actuated position in which it is in 
contact with a brake disk 20 to provide braking, from a released position 
in which it is clear of the disk 20. At the rear end of the pushrod 14 is 
a stirrup 24 having a base 26 attached to the main part of the pushrod 14 
and two side arms 28 between which fits the front edge 30 of the brake 
pedal 10. Each of the side arms 28 has a slot 32 through it, and, 
protruding from each side of the brake pedal 10 is a boss 34 which extends 
through a respective one of the slots. The pushrod 14 can therefore move a 
limited distance longitudinally relative to the brake pedal 10 by movement 
of the bosses 34 along the slots 32. 
A wedge 36 is supported between the arms 28 of the stirrup between the 
brake pedal 10 and the stirrup base 26. The wedge 36 is supported by means 
of a spring 38 which has one end attached to the top of the wedge and the 
other end attached to a support member 40 which is mounted on the base of 
the stirrup. The support member 40 and the front edge of the brake pedal 
10 have respective flat surfaces 42, 44 on them which form a tapered gap 
46 in which the wedge 36 is located. From the bottom of the wedge 36 
extends a rod 48 which extends into a solenoid 50 mounted on the rear edge 
of the brake pedal 10 beneath the stirrup 24. The solenoid can therefore 
be powered to urge the wedge 36 into the gap 46 against the return force 
of the spring 38 to move the pushrod 14 and brake pedal 10 apart, thereby 
urging the brake pads towards the brake disks, and urging the brake pedal 
towards the driver, i.e. towards its fully released position. Clearly 
application of a braking pressure to the brake pedal 10 will tend to urge 
the pedal 10 and pushrod 14 towards each other thereby tending to narrow 
the gap 46. 
The solenoid 50 is powered by a control unit 52 which receives inputs from 
various sensors including a brake pedal movement sensor 54, a sensor 56 
for sensing movement of the accelerator 58, and a proximity sensor 60 for 
sensing the presence of a drivers foot within a predetermined distance of 
the brake pedal 10, as well as from the engine management system 62 which 
monitors and controls the operation of the engine of the vehicle. The 
control unit 52 monitors the current through the solenoid 50 which is 
indicative of the load on the wedge 36. 
In operation, when the vehicle is being driven and the accelerator 58 is 
depressed, the brake pedal 10 and the wedge 36 stay in their rest position 
as shown in FIG. 1. If the accelerator 58 is released the control unit 52 
detects this using the accelerator sensor 56. Since release of the 
accelerator is an indication that the brakes are likely to be applied, the 
control unit 52 anticipates this by powering the solenoid 50 to drive the 
wedge 36 upwards between the brake pedal 10 and the pushrod 14. This 
pushes the pushrod 14 and the brake pedal apart. Initially this takes up 
the slack in the system pushing the brake pedal 10 towards the driver 
towards the limit of its rearward travel. Then as the force increases it 
moves the pushrod 14 forwards until the brake pads are just in contact 
with the brake disks 20. This contact increases the pressure in the 
hydraulic system and the electrical load in the solenoid, and the control 
unit detects this increasing load. The control unit 52 then controls the 
current through the solenoid to maintain a predetermined light contact 
pressure between the brake pads and the brake disk 22 for a predetermined 
period of, say 5 seconds, and then retracts the wedge 36 by a 
predetermined distance to an intermediate, partially released position. 
The initial contact is not sufficient to provide any significant braking 
effect, but serves to dry the brake disks 20 if they are wet and to warm 
them slightly, which improves the effectiveness of the brakes if they are 
applied. This partial release has the advantage that the system acts in a 
similar manner to a brake adjuster so that, in the pre-activated state, 
the position of the brake pads is substantially fixed and the amount of 
brake pedal travel required to operate the brakes is therefore also 
substantially fixed. 
The friction between the wedge 36 and the flat surfaces 42, 44 and the 
strength of the return spring 38 are arranged such that brakes can be held 
in this partially actuated or `pre-activated` state with only minimal 
force from the solenoid 50. The brakes are held in the pre-activated state 
until either the accelerator pedal is depressed again, in which case the 
power to the solenoid will be cut and the wedge will be pushed out of the 
gap 46 by the return spring 38 allowing the brake pads to move away from 
the disks 20 back to their normal rest position, or the brake pedal 10 is 
depressed to activate the brakes. If this is done, because prior to the 
driver's foot coming into contact with the brake pedal 10 the wedge 36 has 
already taken up much of the slack in the brake actuation system and the 
brake pads are already moved into contact with the disks 20, only a 
relatively small amount of pedal travel is required to fully activate the 
brakes. 
Furthermore, if the vehicle is in a frontal impact it is likely that, at 
the time of impact, the driver will have lifted his foot off the 
accelerator and at least placed it on the brake pedal. This means that, as 
the driver is moving forward as a result of the impact, the pedal will 
provide a significant resistance to that movement from the limit of its 
rearward travel, i.e. from the fully released position. This helps to 
absorb steadily the forces that the impact places on the driver's foot, 
and to reduce the chances of a sharp increase in those forces, and can 
therefore reduce the injury to the driver's leg. 
The control unit 52 also uses the signals from the brake pedal sensor 54, 
the proximity sensor 60, and the engine management system to anticipate 
when the brakes might be applied. The proximity sensor 60 sends a signal 
to the control unit 52 as soon as the drivers foot approaches the brake 
pedal. If the accelerator pedal 58 has not been released so the solenoid 
50 has not been activated, the control unit 52 responds to the movement of 
the driver's foot by activating the solenoid and moving the brake pads 
into the pre-activated position. This ensures that the brake pedal cannot 
be depressed without the brakes being partially activated, even when the 
accelerator pedal is still depressed. The brake pedal sensor sends a 
signal to the control unit 52 as soon as the brake pedal is moved out of 
its normal rest position. This can be used as a back-up to activate the 
system of the proximity sensor has not worked for any reason. 
The signals from the engine management control unit 62 indicate when the 
vehicle is in overrun and the engine is producing more than a 
predetermined amount of engine braking. In this case the control unit 52 
activates the solenoid 50 to move the brake pads into the partially 
activated position in anticipation of braking by the driver, regardless of 
the position of the brake and accelerator pedals 10, 58. 
Once the brakes have been `pre-activated` by the control unit 52 they will 
remain in that condition until all of the conditions for pre-activation 
have ceased, i.e. engine braking is below the predetermined level, the 
brake pedal has been released, the driver's foot has moved out of range of 
the proximity sensor 60, and the accelerator pedal has been depressed. 
There is then a short time delay before the brakes are fully released. 
This means that, under almost any circumstances in which the driver will 
apply the brakes, they will be partially actuated in preparation. 
It will be appreciated that, in the embodiment shown in FIG. 1, as the 
wedge 36 moves upwards and the pedal rotates clockwise about its pivot 12, 
the surface 44 on the pedal will become misaligned with the surface of the 
wedge 36. Therefore, as shown in FIG. 2, it is preferable to include a 
second stirrup 164 pivotably mounted on a pin 134 which extends through 
the pedal 110 and is rigidly fixed to it. The pin 134 also extends through 
slots 132 in the stirrup 124 to which the pushrod 114 is attached as in 
the first embodiment. This stirrup 164 has two arms, one on each side of 
the pedal 110 and fits between the side arms 128 of the first stirrup 124. 
The wedge 136 therefore acts on the base 166 of the second stirrup 164 
which acts on the pedal 110 via the pivot pin 134. As the wedge 136 moves 
upwards and the pedal 110 rotates, the second stirrup 164 rotates about 
the pin 134 so that its base 166 remains parallel to the face of the wedge 
136 which is acting on it. 
In a modification of the system described, the partial retraction can be 
achieved simply by providing a mechanical stop which prevents return of 
the wedge 36 past an intermediate position under the force of the return 
spring 38, but which can be overcome by applying current to the solenoid 
to positively withdraw the wedge 36. Alternatively it can be achieved by 
using an over-center spring as the non-return spring 38. This arrangement 
has the advantages that the solenoid does not have to be powered for all 
of the time that the brakes are in the pre-activated state, and that the 
brake pads are not be held in contact with the disks 20 for long periods 
of time which could cause excessive heating and wear. 
Referring to FIGS. 3a, 3b, 3c and 3d, in a further embodiment of the 
invention the wedge 36 and solenoid 48, 50 are replaced by a modified 
wedge 236 and a ball screw actuator 250. The wedge 236 acts between the 
pedal 210 and a reaction member 240 connected to the pushrod 214. The 
wedge 236 has a cavity 237 inside it with an opening in each of the 
operating faces 236a, 236b of the wedge, and which houses a pair of 
rollers 239 rotatably mounted on a carrier 241. The carrier 241 has a 
projection 241a on its front end, pointing towards the narrow end of the 
wedge 236, which is slidably received in a guide slot 236d in the wedge. 
The carrier also has stem 241b which extends out through the wide end of 
the wedge 236 and is connected to the shaft 250a of the actuator. The 
carrier 241 and rollers 239 can therefore be moved backwards and forwards 
relative to the wedge 236, with the limit of forward travel being the 
point at which the projection 241 on the carrier 241 contacts the end of 
the guide slot 236d, and the limit of backward travel being the point at 
which the rollers 239 contact the rear end of the cavity 237 in the wedge 
236. The rollers 239 are mounted side by side on the carrier so that they 
are in contact with each other and so that, with the carrier in its 
rearmost position, as shown in FIG. 3a, the surfaces of the rollers are 
just below the operating surfaces 236a, 236b of the wedge, and with the 
carrier in its forwardmost position, as shown in FIG. 3b, the rollers 
project above the operating surfaces 236a, 236b. 
The actuator 250 is controlled by a control unit similar to that of FIG. 1, 
and having the same sensor inputs. When the brakes are fully released and 
the system does not anticipate their operation, the wedge 236 in the 
position shown in FIG. 3a, fully retracted with its operating faces 236a, 
236b clear of the pedal 210 and the reaction member 240. When braking is 
anticipated, the actuator pushes the carrier 241 forward, firstly to the 
position shown in FIG. 3b wherein the rollers 239 project from the sides 
of the wedge and contact the surfaces on the pedal 210 and reaction member 
240. Then when the projection 241a on the carrier contacts the end of the 
guide slot 326d, as the actuator then continues to push the carrier 241 
forwards towards the position shown in FIG. 3c, the carrier 241 carries 
the wedge 236 with it. As the rollers 239 are pushed forwards they urge 
the reaction member 240 and pedal 210 apart, taking up slack in the 
braking system and bringing the brake pads into contact with the brake 
disks. As the rollers roll up the surfaces of the pedal 210 and reaction 
member 240 they remain in contact with each other and, because they turn 
in opposite directions, roll against each other. Therefore force is 
transmitted from the pedal 210 to the reaction member 240 directly through 
the rollers, and the forces on the carrier 241 are substantially less than 
those on the rollers 239. When the wedge 236 reaches the position shown in 
FIG. 3c, i.e. when the brake pads contact the brake discs, the pressure in 
the hydraulic brake circuit increases rapidly, and this is detected by 
changes in the current in the actuator. At this point the driving current 
to the actuator 250 is cut. The pressure in the braking system urges the 
reaction member 240 and pedal 210 together, which in turn urges the 
rollers 239 in the rearward direction, or downwards as shown on FIGS. 4a 
to 4d. The rollers 239 and carrier 241 therefore move relative to the 
wedge 236, which may be held in place by a weak spring, until the rollers 
239 are retracted below the operating surfaces 236a, 236b of the wedge. At 
this point, as shown in FIG. 3d, the pedal 210 and reaction member 240 
trap the wedge 236 between them and are prevented from moving together 
further by the wedge 236. The brakes are therefore partially released, the 
brake pads having moved away from the discs by an amount which is 
determined by the amount by which the rollers 239 project above the 
operating surfaces 236a, 236b of the wedge 236 when the carrier is in its 
forwardmost position. 
As with the first embodiment the brakes are held in the partially released 
intermediate position until all the possible indicators of intended 
braking are absent. However, the advantage of this embodiment is that no 
power is required of the actuator to hold the brakes in the intermediate 
position, since the wedge 236 does this by virtue of the friction between 
it and the pedal 210 and reaction member 240. When the brakes need to be 
returned to the fully released condition, the actuator 250 is operated in 
reverse to positively retract the carrier 241, and therefore the wedge 236 
to its initial position as shown in FIG. 3a. 
As an alternative to using the actuator current to detect when the brake 
pads contact the brake discs, a pressure sensor in the hydraulic circuit 
could be used. As a further alternative the actuator could be arranged so 
as to have a limited force just sufficient to bring the pads and discs 
into contact without producing significant braking. This would have the 
advantage of simplifying the control of the actuator, which could simply 
be turned on for a brief period, long enough to allow the pads to reach 
the discs, and then turned off again to allow the pads to return to the 
partially released position. 
The above embodiments are all systems in which the force applied by the 
driver to the brake pedal is transmitted to the brake, generally through a 
booster and hydraulic actuation system. However, the present invention 
also has application in so called `brake-by-wire` systems in which 
movement of the brake pedal is sensed by a control unit which operates the 
brakes solely by means of an electrical actuator. In this type of system a 
single actuator can be used both for normal actuation of the brakes and 
for pre-actuation as described above. If the actuator is a linear type 
actuator, which frequently takes the form of a ball screw actuator, 
pre-actuation can be achieved in a manner corresponding to the first 
embodiment described above, the brakes being applied up to a predetermined 
actuator force and then retracted by a predetermined distance to a 
partially released state. It is also known to use electrically driven 
wedge-type actuators in drive-by-wire systems, particularly with drum 
brakes, and the wedge and roller arrangement described above with 
reference to FIGS. 3a, 3b, 3c and 3d could clearly by used in such a 
system.