Hydraulic handbrake control system

A hydraulic handbrake control system for vehicles has a hand operable reversible fluid pump and a shuttle valve operable to circulate fluid in one direction for applying vehicle handbrakes, and in another direction for releasing vehicle handbrakes by governing flow of fluid alternately in application and release directions over application and lock release passages connected to a plurality of hydraulic handbrake cylinders. An improved lock control mechanism is associated with each of the cylinders having a check valve permitting passage of fluid from the application passage to the associated brake cylinder, but preventing release of fluid when handbrakes are applied. A lock release cylinder is associated with each handbrake cylinder and connected to the lock release passage having a lock release plunger biased to normally open the check valve that is hydraulically operable in response to pressure in the application passage to permit closure of the check valve and in response to pressure in the lock release passage to open the check valve.

BACKGROUND OF THE INVENTION 
This invention relates to fluid handbrake control systems, and while the 
invention is subject to a wide range of applications, a preferred 
embodiment of the invention will be particularly described as applied to a 
hydraulic handbrake control system having an improved lock control 
mechanism. 
It is common practice in braking systems for railway vehicles to provide 
hydraulic brake actuators on a vehicle that can at times be responsive to 
service brake control apparatus, and at other times responsive to 
hydraulic handbrake control apparatus. Such systems can be of the type 
disclosed, for example, in the Engle U.S. Pat. Nos. 3,508,794, 3,622,207, 
3,707,309 and 3,910,641. The merging of the service and handbrake control 
systems, according to these patents, requires the use of special devices 
known as interceptor valves to jointly govern flow of hydraulic fluid to a 
brake cylinder common to both systems, in order to avoid undesirable 
characteristics as discussed in column 1 of the above U.S. Pat. No. 
3,622,207. Another Engle U.S. Pat. No. 3,910,641 discloses such a system 
for an articulated carrier wherein a handbrake control mechanism on one of 
the sections of the vehicle governs the application of handbrakes on a 
plurality of sections of the vehicle. All of these patents require the 
brake cylinders to be of the type having hydraulically operated locks for 
governing mechanical locking of brake actuating mechanisms. 
An object of the present invention is to provide a hydraulic handbrake 
control system which substantially obviates one or more of the limitations 
and disadvantages of the described prior art systems. 
Another object of the present invention is to simplify hydraulic handbrake 
control systems by eliminating the need for mechanical locking of brake 
actuating mechanisms while maintaining safe handbrake control. 
Another object of the present invention is to reduce the costs of hydraulic 
handbrake actuating mechanisms. 
Other objects, purposes and characteristic features of the present 
invention will be in part obvious from the accompanying drawings, and in 
part pointed out as the description of the invention progresses. 
SUMMARY OF THE INVENTION 
A hydraulic handbrake control system for vehicles is provided comprising a 
hand operable reversible fluid pump and shuttle valve system operable to 
circulate fluid in one direction for applying vehicle handbrakes and in 
another direction for releasing vehicle handbrakes. Application and 
release of handbrakes is obtained by governing flow of fluid alternately 
in application and release directions over application and lock control 
passages respectively, connecting the fluid pump to a lock control 
mechanism associated with each of several hydraulic handbrake cylinders. 
An improved lock control mechanism is provided comprising a check valve 
disposed in a connection of the application passage to each of the 
hydraulic handbrake cylinders independently for permitting passage of 
fluid from the application passage to the associated handbrake cylinder 
and for hydraulically locking the associated brake cylinder in a brake 
application position. The check valve is biased to permit flow of fluid 
from an application passage to the associated handbrake cylinder but to at 
times prevent flow of fluid from the handbrake cylinder to the application 
passage. 
The improved lock control mechanism comprises a lock release cylinder for 
each handbrake cylinder connected to the lock release passage and having a 
lock release plunger normally biasing the associated check valve to an 
open position and hydraulically operable to remove the bias during hand 
brake application and to open the check valve in response to operation of 
the fluid pump in a direction for releasing the handbrakes. This provides 
that leakage of fluid from one handbrake cylinder when the handbrakes are 
applied will not release fluid from another handbrake cylinder, thus 
assuring that adequate braking can be maintained by the handbrake control 
system over a period of time, although there may be material leakage in 
one or more, but not all of the handbrake cylinders. 
For a better understanding of the present invention, together with other 
and further objects thereof, reference is had to the following 
description, taken in connection with the accompanying drawings, while its 
scope will be pointed out in the appending claims.

With reference to FIG. 1, a handbrake and associated pump and shuttle valve 
apparatus is illustrated at 10 operable to circulate fluid in one 
direction for applying vehicle handbrakes and in another direction for 
releasing vehicle handbrakes by governing flow of fluid alternately in 
application and release directions over application and release passages 
11 and 12 respectively which have multiple passages connected to lock 
control mechanisms 13, which are in turn connected to associated hydraulic 
handbrake cylinders 14 by fluid passages 15. 
With reference to FIGS. 1 and 2, each lock control mechanism 13 is 
illustrated in the preferred embodiment of the invention as being secured 
on the left-hand end 14a of its associated hydraulic handbrake cylinder 14 
and connected thereto by a fluid passage 15. Each of the lock control 
mechanisms has a check valve 16 provided for permitting fluid flow between 
the handbrake pump 10 and the associated hydraulic handbrake cylinder 14 
through passage 15, but at times for restricting flow of fluid from the 
associated handbrake cylinder to the handbrake pump 10. Each of the lock 
control mechanisms also comprises a lock release cylinder 17 and 
associated lock release piston 18 and lock release plunger 18a for 
normally biasing the check valve 16 to an open position and hydraulically 
operable to remove the bias during handbrake application and to open the 
check valve 16 in response to operation of the fluid pump apparatus 10 in 
a direction for releasing the handbrakes by applying pressure to passage 
12. 
Application indicator and unloading valve apparatus 19 is preferably 
connected across the passages 11 and 12 for providing a visual indication 
that the brakes are applied, and for causing an operator to sense 
completion of operation of the handbrake by unloading fluid pressure 
selectively in the passages 11 and 12. 
Having thus considered the general organization of this system, further 
consideration will be given as to the more detail structure that can be 
provided. 
With reference to FIG. 2, each hydraulic handbrake cylinder 14 and its 
associated lock control mechanism 13 is illustrated in its normal 
positions in which the handbrakes are released, a brake operating piston 
20 having been operated to its left-hand position, thus causing its piston 
rod 21 to have released the associated brakes (not shown). Under these 
normal conditions, the hydraulic passages 11 and 12 are both at 
substantially atmospheric pressure as well as chamber 22 at the left of 
piston 20 in the hydraulic handbrake cylinder 14, and the check valve 16 
is maintained in its normally open position by reason of lock plunger 18a 
holding the check valve 16 in its open position. This is accomplished as a 
result of bias on check valve 16 of opposing coaxial springs 24 and 25 
having their relative forces chosen so that the force of the spring 25 
overcomes the force of the spring 24 normally to an extent for maintaining 
the check valve 16 normally open. This permits free movement of fluid 
through the check valve normally to insure that fluid in the associated 
hydraulic handbrake cylinder is normally substantially at atmospheric 
pressure, but permits the immediate closing of the check valve 16 upon 
application of the handbrakes, when input pressure in the application 
passage 11 acts, through a small passage 11a to compress a spring 25 and 
remove the bias holding check valve 16 open. Thus, for example, the spring 
25 can be an 8 pound spring as compared to the spring 24 being a 4 pound 
spring to normally hold check valve 16 open, the spring 25 being 
compressed when pressure is applied from passage 11a and application 
passage 11 to a release piston 27 in order to permit the closure of the 
check valve 16 by its spring 24. Therefore, upon initiation of application 
of the handbrake, the lock control mechanism becomes effective to prevent 
release of fluid from the associated handbrake cylinder 14. 
With reference to FIG. 1, the handbrake pump and shuttle valve 10 can be 
provided as is fully disclosed in FIG. 4 of the above Engle U.S. Pat. No. 
3,910,641. The application indicator and loading valves 19 of FIG. 1 can 
be provided, for example, as is disclosed at 17 in the above-mentioned 
Engle U.S. Pat. No. 3,508,794. 
To consider the mode of operation it will first be assumed that the system 
is in its normal condition in which the handbrake is released, as is 
illustrated in the drawings, and it will further be assumed that an 
operator actuates the handbrake 10 to drive an associated pump, which can 
be of the positive displacement type, in a direction to apply pressure to 
the application passage 11. This causes hydraulic fluid to flow over 
passage 11 through a chamber 26 in each lock control mechanism 13 to the 
chamber 22 to the left of piston 20 in the associated hydraulic handbrake 
cylinder 14. This actuates the piston rods 21 to the right to apply the 
brakes (not shown). When proper brake pressure has been built up in the 
handbrake cylinder chambers 22, a pressure relief unloading valve 19 is 
actuated to bypass application passage fluid to return passage 12, and 
thereby relieve pumping pressure that has been developed by the handbrake 
operator so that the operator senses the completion of operation of the 
brakes to their application positions. He can then stop actuation of the 
pump, and the pressure built up in chambers 22 of the hydraulic handbrake 
cylinders 14 causes the closing of the check valves 16 of the associated 
lock control mechanism 13. 
When it is desired to release the handbrake, the handbrake operator 
reverses the drive of the pump 10, which actuates the associated shuttle 
valve to apply pressure in the release passage 12, which is connected to 
release chambers 27 in the lock control mechanisms 13, for actuating the 
release pistons 18 and their associated release piston rods 18a against 
the associated check valves 16 to open the check valves 16 and release 
fluid in the hydraulic handbrake chambers 22 to atmospheric pressure via 
return passage 11. At a pressure slightly higher than the pressure in 
passage 12 that is required to open the check valves 16, a relief valve in 
the application indicator and unloading valves 10 become actuated, and an 
indicator piston (not shown) is restored to its normal position to uncover 
a passage for fluid from passage 12 to atmospheric pressure in passage 11, 
thus unloading the handbrake and causing the operator to sense that his 
release of the handbrake has been completed. This mode of operation, for 
example, is disclosed in detail in the above-mentioned Engle U.S. Pat. No. 
3,508,794. 
One use for a handbrake system such as is disclosed by the present 
invention, can be to provide handbrakes on an articulated carrier vehicle 
having several coupled sections, wherein a hydraulic handbrake cylinder 
can be provided for operation of vehicle brakes on each of several of the 
articulated sections, all controlled from a single hand operated pump 10 
on one of the sections. This system can thus be used in connection with a 
conventional fluid braking system that can be either pneumatic or 
hydraulic in accordance with the requirements of practice. The hydraulic 
handbrake cylinders 14 can be used to actuate the same brake beams, for 
example, that are actuated by a conventional fluid brake control system. 
Having thus described a hydraulic handbrake control system for a vehicle 
having improved lock control mechanisms associated with the respective 
handbrake cylinders, as a preferred embodiment of the present invention, 
it is to be understood that various modifications and alterations may be 
made to the specific embodiment shown without departing from the spirit or 
scope of the invention.