Brake release mechanism for vehicle towing

Spring-applied, pressure-released brakes are useful, for example, in construction vehicles or other vehicles that require an automatic braking in the event of an engine failure. In order to tow the vehicle for service, the brakes must be released. Most brake release systems require an alternate pump and associated valves on each vehicle with the fluid from the alternate pump being controlled by the brake valve on the vehicle. The alternate pump on each vehicle add cost to the vehicle and the spool of the brake valve is a known path for fluid leakage thus requiring an alternate pump of a larger capacity than is actually needed. The present brake release mechanism provides an isolating mechanism that is effective to isolate a work port of a brake valve from a valving element in a housing. The isolating mechanism is adapted to connect with an alternate source of pressurized fluid and adapted to direct the pressurized fluid to a brake for release thereof. The isolating mechanism and the alternate source of pressurized fluid are adaptable to several vehicles thus eliminating the need of the alternate pump and associated valves on each vehicle. Furthermore, the alternate source is smaller in capacity since the leakage in the brake valve during towing is eliminated.

TECHNICAL FIELD 
This invention relates generally to a brake release mechanism for towing a 
disabled vehicle having spring applied pressure released brakes and more 
particularly to a brake release mechanism that provides pressurized fluid 
to release the brakes during towing while bypassing the brake valve. 
BACKGROUND ART 
Brake release mechanisms are provided on vehicles having spring applied, 
pressure released brakes in order to release the brakes for towing in the 
event that the vehicle becomes disabled. Many of the well known brake 
release mechanisms are mounted directly on the vehicle, thus requiring 
various components for each vehicle. These components; such as, control 
valves, check valves, manual shutoff valves, auxiliary hand pumps and 
associated lines add complexity and extra cost to each vehicle. Other 
brake release mechanisms that are not mounted directly on the vehicle are 
normally coupled to the existing lines and uses the vehicle brake control 
valve to release the brakes. These mechanisms experience varying degrees 
of leakage due to the pressurized fluid from the auxiliary pump being 
directed through the brake control valve. Consequently, a larger source of 
pressurized auxiliary fluid is needed to maintain the brakes in the 
released condition while towing the vehicle. 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention, a brake release mechanism is 
provided for use in a vehicle having a spring applied, pressure released 
brake, a primary source of pressurized fluid, a reservoir and a brake 
valve. The brake valve has a housing defining a bore, an inlet port 
connected to the source, a work port connected to the brake and a drain 
port connected to the reservoir. Each of the ports intersect the bore at 
axially spaced locations. A valving element is located in the bore and 
selectively movable between first and second positions. In the first 
position of the valving element, the work port is in open communication 
with the inlet port while being blocked from the drain port. In the second 
position of the valving element, the work port is blocked from the inlet 
port and in open communication with the drain port. A means is provided 
for isolating the work port from the valving element and the drain port 
and is adapted to connect an alternate source of pressurized fluid to the 
brake so that the brake may be released on failure of the primary source. 
The present invention provides a mechanism that may be mounted on the brake 
valve which isolates the work port from the valving element and the drain 
port thus eliminating leakage of the alternate source of pressurized fluid 
by bypassing the valving element. Furthermore, this mechanism is adaptable 
to the brake valve of various vehicles thus not requiring an auxiliary 
pump and the various valves associated therewith be mounted on every 
vehicle.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, a brake release mechanism 10 is shown for 
use in a brake control system 12 of a vehicle (not shown) having spring 
applied pressure-released brakes 14,14'. As more specifically shown in 
FIGS. 1 and 2, the brake control system 12 includes a source of 
pressurized fluid, such as a pump 16, a reservoir 18, a brake control 
valve 20 and an operator input mechanism 22. The brake valve 20 is 
connected to the spring applied brakes 14,14' respectively by conduits 
24,26. A drain conduit 28 connects the reservoir 18 to the brake valve 20. 
The brake valve 20 includes a housing 30 having first and second bores 
32,34 defined therein. First, second and third chambers 36,38,40 
respectively surround the first bore 32 at axially spaced locations. Since 
the second bore 34 is identical to the first bore 32, prime numbers are 
used to identify corresponding chambers 36',38',40'. An inlet port 42 is 
defined in the housing 30 and intersects the first chamber 36,36' of each 
of the first and second bores 32,34. A drain port 44 is defined in the 
housing 30 and connects the third chamber 40,40' of each of the first and 
second bores 32,34 to the drain conduit 28. A first work port 46 is 
defined in the housing 30 and intersects the second chamber 38 of the 
first bore 32. The conduit 24 is connected to the first work port 46. A 
second work port 48 is defined in the housing 30 and intersects the second 
chamber 38' of the second bore 34. The conduit 26 is connected to the 
second work port 48. As shown in FIG. 1, the first and second work ports 
46,48 are oriented transversely to the respective first and second bores 
32,34 and are respectively laterally offset. It is recognized that the 
first and second work ports 46,48 could be at different angles with 
respect to the respective first and second bores 32,34 as long as they do 
not intersect either of the first and third chambers 36,36',40,40' of the 
first and second bores 32,34. 
First and second valving elements, such as first and second spools 50,52 
are respectively slideably disposed in the first and second bores 32,34. 
Each of the spools 50,52 is movable between first and second positions. A 
spring 54 biases the first spool 50 to the first position while spring 56 
biases the second spool 52 to its first position. As is well known in the 
art and clearly shown in FIG. 1, each of the spools 50,52 controls the 
fluid flow to and from the brakes 14,14'. 
As shown in FIG. 2, first and second plugs 58,60 are respectively disposed 
in the end of the respective work ports 46,48 opposite the connection of 
the conduits 24,26. 
A conduit 62 connects the pump 16 to the inlet port 42 of the brake valve 
20. As is well known in the art, a relief valve 64 is connected to the 
conduit 62 and adapted to control the maximum pressure level of the fluid 
from the pump 16. 
The operator input mechanism 22 includes first and second pedals 66,66' 
each respectively connected to the respective spools 50,52 by associated 
linkages 68,68'. 
The spring-applied, pressure-released brakes 14,14' each include an 
actuator 69 having a pressure chamber 70, a spring chamber 71, and a 
spring 72 located in the spring chamber 71. 
As shown in FIG. 3, the plugs 58,60 have been removed and replaced with 
first and second sleeve members 73,74. Each of the sleeve members 73,74 
has an axial passage 75 extending therethrough. The sleeve members 73,74 
are each sealingly disposed in the respective work port 46,48. Each of the 
sleeve members 73,74 has sufficient length to extend into and through the 
respective second chamber 38,38' to effectively isolate the work ports 
46,48 from the spools 50,52. 
An alternate source of pressurized fluid, such as a pump 76, draws fluid 
from a reservoir 78 and directs the pressurized fluid to the first and 
second sleeve members 73,74 through a conduit 80. The pump 76 may be a 
hand pump or driven by an electric motor (not shown) or any other suitable 
means. A relief valve 82 is connected to the conduit 80 and controls the 
maximum pressure level of the fluid from the pump 76 in a well known 
manner. 
The sleeve member 73/74 constitutes a means 84 for isolating the work port 
46/48 from the valving element 50/52 and the drain port 44 and for 
connecting the alternate source 76 to the brake 14/14'. 
It is recognized that a brake system having only one brake and one valving 
element would need only one sleeve member. Furthermore, the alternate 
source 73 of pressurized fluid could be connected to the brake conduit 
24/26 without being directed through the sleeve member 80/82. 
Consequently, the axial bore 75 of the sleeve member 80/82 would be 
plugged. 
INDUSTRIAL APPLICABILITY 
During normal operation of a vehicle having spring-applied, 
pressure-released brakes, pressurized fluid from the pump 16 is directed 
through the brake valve 20 to the pressure chambers 70,70' of the brakes 
14,14'. The force from the pressurized fluid acts against the bias of the 
respective springs 72,72' to release the brakes. To apply the brakes 
14,14', the operator depresses the pedals 66,66', either individually or 
simultaneously, thus moving the spools 50,52 from their first position, at 
which the work ports 46,48 communicate with the inlet port 42 and are 
blocked from the drain port 44, to the second position, at which the work 
ports 46,48 are blocked from the inlet port 42 and open to the drain port 
44. Between the first and second positions of the spools 50,52, the fluid 
flow to the brakes 14,14' is variable controlled. By venting the 
pressurized fluid from the pressure chambers 70,70' of the brakes 14,14', 
the force of the springs 72,72' applies the brakes 14,14'. 
Upon failure of the pump 16 or if the engine of the vehicle stops running, 
the pressurized fluid in the pressure chambers 70,70' drops thus applying 
the brakes 14,14'. In order to move the vehicle, the brakes must be 
released. The plugs 58,60 as shown in FIG. 2 are removed and the sleeve 
members 73,74 are inserted in the work ports 46,48 as shown in FIG. 3. The 
alternate source 76 of pressurized fluid is connected to the sleeve 
members 73,74 by the conduit 80. The sleeve members 73,74 effectively 
isolate the spools 50,52 from the alternate source 76 thus eliminating 
leakage across the spools 50,52. The pressurized fluid from the alternate 
source 76 is directed to the pressure chambers 70,70' thus releasing the 
brakes 14,14' for towing. Due to the small volume of fluid needed to 
release the brakes 14,14' without concern about leakage, the alternate 
source 76 is relatively small in size. 
Once the vehicle has been towed to its destination, the alternate source 76 
is shut off and the conduit 80 rexoved. The sleeve members 73,74 are then 
removed and replaced by the plugs 58,60. The brake system is now ready for 
normal operation once the problem is resolved. 
The brake release mechanism set forth above provides an arrangement that 
does not require that an extra pump and associated valving be supplied on 
every vehicle. The service technician would only need the two sleeve 
members 73,74, the conduit 80 and the alternate source 76 to tow several 
different vehicles without needing numerous special service items. 
Furthermore, since the work ports are isolated from the spools, the normal 
leakage is eliminated thus allowing the use of a small alternate source. 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and the appended claims.