Anti-lock brake devices

An anti-lock brake device comprises a cylinder adapted to be installed in a pipeline connecting a master cylinder with one or more wheel cylinders of a vehicle. A solenoid-actuated operating member is slidable in the cylinder and is positionable to prevent fluid flow through the device. The operating member is biased into a position in which fluid flow is permitted, energization of the solenoid causing the operating member to prevent fluid flow and, by volume displacement of at least part of the operating member to reduce the fluid pressure on the wheel cylinder side of the device.

The present invention relates to an anti-lock brake device for use in 
pneumatic or hydraulic brake systems. 
In the braking system of motor cars, it is usual to fit a pressure valve 
which limits the pressure which can be applied to the rear braking 
circuit. However, such a valve must clearly allow sufficient pressure to 
be applied to the rear brakes to allow rapid braking under ideal 
conditions. It follows that, under less than ideal conditions, such a 
valve will allow locking up of the rear wheels, or conversely insufficient 
braking effect from them. 
This problem is even greater for trucks, buses and semi-trailers, whether 
or not air brakes are used. 
According to the invention, there is provided an anti-lock brake device for 
use in a braking system of a vehicle, comprising a cylinder adapted to be 
installed in a pipeline connecting a master cylinder with one or more 
wheel cylinders, a solenoid-actuated operating member slidable in said 
cylinder and positionable to prevent fluid flow through the device, and 
means biasing said operating member to a position in which such fluid flow 
is permitted, energisation of the solenoid causing movement of the 
operating member against the biasing means so as to prevent said fluid 
flow and, as a result of volume displacement of the operating member or a 
part thereof, to cause the fluid pressure on the wheel cylinder side of 
the device to be reduced. 
In a preferred embodiment, the operating member allows fluid flow through 
the cylinder, and the operating member includes an elongate valve member 
which extends longitudinally of the cylinder, an apertured wall extends 
across the cylinder and is adapted to co-operate with said elongate valve 
member to prevent fluid flow through the cylinder, the arrangement being 
such that, when the solenoid is energised, the operating member is driven 
towards the apertured wall and the elongate valve member is driven through 
the aperture. 
The elongate valve member is preferably tapered at its leading end so as to 
facilitate its engagement with the apertured wall. The apertured wall may 
comprise an O-ring mounted in the cylinder. 
When the device is installed in a pipeline connecting the master cylinder 
with one or more wheel cylinders, with the operating member closer to the 
wheel cylinder end of the cylinder than the sealing member, and the 
solenoid coil is energised, the elongate valve member first contacts the 
sealing member, at which point further fluid flow through the cylinder is 
substantially prevented, and then continues to pass through the apertured 
wall, thus increasing the pressure in the fluid between the wall and the 
master cylinder and decreasing the fluid pressure between the wall and 
said one or more wheel cylinders, by valve member volume displacement. 
Thus, if the solenoid is actuated by an electrical signal when the wheel 
or one of the wheels associated with said device ceases to rotate, the 
reduction in pressure referred to above will cause the or each wheel 
cylinder to unlock the brake associated with that wheel. The solenoid will 
then of course, be de-activated, and the biasing means will force the 
operating member away from the sealing member and the elongate valve 
member out of engagement with the sealing member. It is possible during 
this de-activation operation that the pressure between the apertured wall 
and the wheel cylinder or cylinders will become greater than the pressure 
between the apertured wall and the master cylinder. In order to avoid 
this, it may be desirable to provide a check valve which allows 
equalisation in pressure by flow towards the master cylinder. Such a check 
valve could be provided within the cylinder, for example in a seal housing 
holding the apertured wall, or in a by-pass. 
The operating member is preferably provided with one or more grooves and/or 
one or more apertures extending the entire axial length thereof in order 
to allow the said fluid flow through the cylinder. 
In another preferred embodiment, the operating member comprises a piston 
which seals directly to the cylinder wall or has a sealing member mounted 
thereon, the sealing member being in contact with the cylinder so as to 
prevent fluid flow through the cylinder. By-pass means are provided so as 
to permit fluid flow past the piston when the solenoid is not actuated. 
In normal use of this embodiment, fluid flow through the cylinder is 
prevented by the piston and seal arrangement, and fluid flow towards and 
away from the wheel cylinders occurs through the by-pass means. 
However, when the solenoid is energised, the piston, with the seal thereon, 
moves along the cylinder, and when the seal passes the end of the by-pass 
means, further fluid flow through the device is prevented. Then, as the 
piston continues to move towards the master cylinder, pressure is steadily 
reduced until the brake is unlocked. The solenoid will then be 
de-activated, and the piston will be returned by the return spring to the 
position in which it is by-passed. If, of course, locking-up reoccurs, the 
device will be reactuated and the cycle described above will be repeated, 
until the conditions causing locking no longer exist. 
One or more seals can be mounted on the piston as desired. The sealing 
member preferably comprises an O-ring. The by-pass means preferably 
comprises a conduit, at least one end of which is connected to the 
cylinder. Alternatively, the by-pass means could take the form of one or 
more grooves in the wall of the cylinder. 
The anti-lock brake device is desirably arranged so that it operates as 
rapidly as possible when the solenoid is energised. However, it is also 
desirable to control the rate of return of the piston, so that the wheel 
cylinder or cylinders receive a steadily increasing pressure when the 
solenoid is deactivated. This can be achieved by selecting the strength of 
a return spring used as the biasing means, the fluid pressure resistance 
of the operating member, the diameter of the valve member and the pressure 
valve member. A multi-rate return spring could be used to give similar 
return characteristics, regardless of the line pressure. 
Although it is preferred to install an antilock brake device according to 
the invention in the pipeline leading to each wheel cylinder, a more 
economical, but somewhat less efficient, system could utilise a single 
device in the rear brake circuit or two devices, one in the front brake 
circuit and one in the rear brake circuit. 
The solenoid coil may be actuated by any known means for sensing that a 
wheel is stationary. Thus, for example, a speedometer drive cable driven 
by a wheel may be connected to a centifugal switch which is connected in a 
circuit with the solenoid coil. The switch is switched ON when the cable 
is stationary, thus completing the circuit and energising the solenoid. 
More complex sensing systems could alternatively be provided, for example 
those which compare vehicle speed and the rotational speed of a wheel. 
These are capable of producing a signal when wheel slippage, rather than 
wheel locking occurs. 
The device may be used in braking systems using a hydraulic brake fluid or 
in air braking systems.

The device shown in FIGS. 1 and 2 comprises a cylinder 1 having at one end 
thereof a threaded portion 2 adapted to be secured to a pipeline leading 
to one or more wheel cylinders of a braking system of a vehicle. A 
threaded portion 3 at the other end of the cylinder is adapted to be 
secured to a pipeline leading to a master cylinder of the braking system. 
A solenoid 4 surrounds the cylinder 1. An operating member 5 is movable 
axially in the cylinder and has a plurality of apertures 6 extending 
therethrough, so as to allow fluid flow through the cylinder. The 
operating member comprises a needle valve member 7 which extends axially 
along the cylinder. An apertured wall 8 is mounted in the cylinder and 
co-operates with the needle valve member 7 to prevent fluid flow through 
the cylinder when the solenoid 4 is energised, as shown in FIG. 2. A 
return spring 9 biases the operating member 5 away from the apertured wall 
8. 
The device operates as follows. When the braking system is operating 
normally, the operating member 5 remains in the position shown in FIG. 1, 
thus allowing brake fluid to flow in either direction through the cylinder 
1. When the solenoid 4 is energised in response to the wheel or one of the 
wheels with which the device is associated being locked, the operating 
member is moved leftwardly as shown in FIG. 2. 
After the tapered end portion of the needle member 7 has passed through the 
apertured wall 8, further fluid flow through the cylinder is prevented. 
Then, as the needle member 7 continues to move leftwardly, the pressure to 
the right hand side of the apertured wall 8 is reduced, thus reducing the 
force on the or each wheel cylinder, whereby the brake is unlocked and the 
wheel can once again rotate. The solenoid will then be de-energised, and 
the operating member 5 will commence to travel rightwardly (as seen in the 
drawings) at a rate determined by the various factors described above, 
whereby a steadily increasing fluid pressure is applied to the or each 
wheel cylinder. If the conditions which caused the brake to lock still 
persist, the solenoid will, of course, be re-activated, and the cycle 
described above will be repeated. During the period for which the needle 
member extends through the apertured wall, the fluid pressure between the 
apertured wall and the master cylinder will, of course, be increased, so 
that a greater braking pressure will be applied to the wheels with which 
the device is not associated, and the driver will detect a pedal response 
to a momentarily locked wheel. 
As shown in FIGS. 3 and 3A, a second embodiment of the invention also 
comprises a cylinder 1 having threaded portions 2, 3, the cylinder being 
surrounded by a solenoid coil 4. However, the operating member is in the 
form of a piston 10 which does not have any apertures therethrough and is 
sealed to the wall of the cylinder by an O-ring 11 fitted to the piston 10 
so as to prevent fluid flow through the cylinder 1. A by-pass 12 is 
provided to connect a point 13 intermediate the ends of the cylinder to a 
point 14 between the position occupied by the piston 10 when the solenoid 
is not actuated (shown in FIGS. 3 and 3A) and the wheel cylinder. A return 
spring 9 biases the piston into the illustrated position. 
The device operates as follows. In the position shown in the Figures in 
which the solenoid is not actuated, brake fluid can flow in either 
direction through the by-pass 12. The braking system can thus operate 
normally. When the solenoid 4 is energised, the piston 10, together with 
the seal 11 is moved leftwardly. As soon as the seal 11 has moved past the 
entrance 13 to the by-pass 12, further fluid flow through the device is 
prevented. Then, as the piston 10 continues to move leftwardly, the 
pressure on the right hand side of the piston is reduced, thus reducing 
the force applied to the or each wheel cylinder, whereby the brake is 
unlocked and the wheel can once again rotate. In other respects, the 
operation of this embodiment of the invention will be the same as that of 
the first embodiment. 
It will thus be seen that the invention, at least in its preferred 
embodiment, provides a device capable of preventing wheel locking under 
varying conditions of use which at the same time, is simple and hence 
inexpensive.