Note: Descriptions are shown in the official language in which they were submitted.
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This application is divided out of copending Canadian application
No. 225,012 filed April 18, 1975.
A common form of vehicle service brake systems employs a master
cylinder which may be operated to transmit a fluid pressure to individual
brakes at each of the vehicle wheels for the purpose of applying the brakes.
~leavy trucks, earthmoving vehicles and the like often have a pneumatic
circuit for actuating the master cylinder or cylinders in response to
manipulation of an operator's brake control. It is customary to supplement
the service brake system with an emergency brake system which may be
independent of or an integral part of the service brake system.
In many cases, the emergency brake is of the spring applied fluid
released type for braking the rear wheels only. Such emergency brakes are
generally automatically applied by the actuating springs upon loss of fluid
pressure in the service brakes. While this is fundamentally a valuable
safety measure it can also complicate the operator's task. If conditions
permit, the operator would generally prefer to bring the vehicle to a more
controlled emergency stop by modulated controllable braking rather than by
suddenly having the brakes locked on and out of manual control. Furthermore,
under certain conditions, it is desirable to be able simultaneously to
actuate the emergency brake on the rear wheels along with the front service
brakes for additional braking power. However, this has not heretofore been
possible since the front brakes are applied by an increase in fluid pressure
and the rear brakes are only applied by a loss of fluid pressure.
It is also desirable to be able to tow the vehicle without the
brakes applied and it is the particular object of the invention of this
divisional application to provide for that desirability.
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According to the invention there is provided a brake system
for a vehicle comprising a first source of pressurized fluid; a spring
applied fluid released brake which is automatically applied in the
absence of actuating fluid thereto, a fluid conduit connecting said
first source of pressurized fluid to said springapplied fluid released
brake; valve means disposed in said fluid conduit and having a position
for directing pressurized fluid to said spring applied fluid released
brake releasing said spring applied fluid released brake, said valve means
being selectively positionable to block fluid flow to said spring applied
fluid released brake; a second source of pressurized fluid; a fluid
applied brake; conduit means connecting said second source of pressurized
fluid to said fluid applied brake; valve means disposed in said conduit
means for controlling flow of pressurized fluid therethrough and selectively
positionable to direct pressurized fluid through said conduit means to
apply said fluid applied brake; and a towing valve disposed in said conduit
means having a first position for communicating said pressurized fluid
from said second source of pressurized fluid to said fluid applied brake
and selectively positionable to connect said conduit means to said fluid
conduit for communicating said pressurized fluid from said second source
of pressurized fluid to said spring applied fluid released brake for
releasing said spring applied fluid released brake to permit the vehicle
to be towed in the absence of pressurized fluid from said first source
of pressurized fluid.
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Brief Description of the Drawing
The sole figure is a schematic drawing of a brake system
embodying the principles of the present invention.
Description of the Preferred Embodiment
Referring more particularly to the drawing, a brake system
embodying the principles of the present invention is generally in-
dicated by the reference numeral 10 in association with a pair of
front wheels 11 of a vehicle, not shown, and a pair of rotatable
shafts 12 each of which is operatively associated with a rear wheel,
not shown, for such a vehicle. A pair of fluid applied front brake
mechanisms 13 are individually operatively associated with the front
wheels 11 for stopping rotation thereof in the usual manner. A pair
of rear brake mechanisms 14 are individually associated with the
rotatable shafts 12 for stopping rotation thereof when the brakes
are applied.
Each of the rear brake mechanisms 14 includes a nonrotatable
housing 16 having an end wall 17. A first annular piston 18 is dis-
posed within the housing and adapted to clamp a plurality of alter-
nately interleaved stationary and rotatable discs 19 against the end
wall 17 for stopping rotation of the shaft 12. An actuating chamber
21 is formed between the first piston and the housing and is adapted
to receive pressurized fluid to move the piston toward the end wall as
will hereinafter be described. A second annular piston 22 is disposed
within the housing and is resiliently urged into abutting engagement
with the first piston by a plurality of springs 23 such that the discs
are clamped against the end wall. An actuating chamber 24 is formed
by the second piston and the housing and is adapted to receive fluid
to move the second piston against the bias of the springs for freeing
the first piston, which is retracted by return springs, not shown.
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Actuation of the front and rear brake mechanisms 13 and 14
is controlled through a control system 26 having a service brake cir-
cuit 27, a retarder circuit 28, and an emergency brake and parking
circuit 29. An air tank 32 is common to both the service brake cir-
cuit and the retarder circuit and stores pressurized fluid directed
thereto through a check valve 33 from a compressor, not shown. The
service brake circuit includes a first air actuated relay valve 34
disposed within a line 36 connecting the air tank with a master cylin-
der 37 and is normally resiliently positioned for blocking air flow
through the line. A second air actuated relay valve 38 is disposed
withln a line 39 co~necting the air tank with a double check valve
42 and is normally resiliently positioned for blocking air flow through
the line. A manually controllable service brake valve 43 is disposed
within a line 44 connecting the air tank with one end of the first relay
valve 34 and is normally resiliently positioned for blocking flow of
actuating air to the first relay valve. A branch line 45 connects
the line 44 between valves 43 and 34 with one end of the second relay
valve 38. A manually actuatable on-off valve 46 is disposed within
the line 45 for controlling flow of actuating air to the second relay
valve.
The master cylinder 37 is of the usual type having an air
chamber 50 connected to the line 36 and a fluid chamber 51 separated
from the air chamber by a stepped actuator piston 52. A conduit 53
connects the fluid chamber with a double check valve 54 which in turn
is connected by a conduit 56 to the actuating chambers 21 of the rear
brake mechanisms 14. The fluid chamber is also connected to a makeup
tank 57 through a check valve 58.
A line 59 connects the check valve 42 with an air chamber 61
of a master cylinder 62. A fluid chamber 63 of the master cylinder is
separated from the air chamber by a stepped piston 64 and is connected
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to the front brake mechanisms 13 through a conduit 66. A fluid makeup
tank 67 is connected to the fluid chamber through a check valve 68.
The retarder circuit 28 includes an air actuated relay valve
69 disposed within a line 70 eonnecting the air tank 32 with an air
chamber 71 of a master cylinder 72. A manually positionable control
valve 73 is disposed within a line 74 connecting the air tank with one
end of the relay valve 69. A fluid chamber 76 is separated from the
air chamber by a stepped piston 77 and is connected to the double check
valve 54 by a conduit 78 which has a two-position manual towing valve
79 disposed therein. The towing valve is normally suitably retained
in the position shown to permit fluid flow through the conduit 78 to
the double check valve.
The emergency and parking brake circuit 29 includes an air
actuated modulating valve 82 disposed within a conduit 83 connecting
a pump 84 with the aetuating chambers 24 of the brake mechanisms 14.
The modulating valve is normally resiliently positioned to communicate
the actuating chambers with a tank 85. A check valve 86 is disposed
within the conduit 83 between the pump and the modulating valve. A
normally closed pressure switch 87 is in communication with the con-
duit 83 and controls an electrical circuit to a warning light 88. Amanual emergency valve 89 and a parking valve 91 are disposed in series
within a line 92 which is connected to and transmits actuating air
from an air tank 93 to one end of the modulating valve 82. The air
tank receives pressurized air from the compressor, not shown, through
a check valve 94. An air actuated inversion valve 96 is disposed
within a line 97 connecting the air tank 93 with the double check valve
42 and is normally resiliently positioned to permit air flow there-
through. A line 98 is connected to the line 92 between the manual
emergency valve and the parking brake valve and communicates actuating
air from the manual emergency valve to one end of the inversion valve.
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The relay valves 34, 38 and 69, the inversion valve 96, the
service brake valve 43, the retarder valve 73, and the emergency brake
valve 89 are of the type wherein air flow therethrough is selectively
modulatable. Likewise, the modulating valve 82 is constructed for
modulating fluid flow therethrough.
Operation
~ hile the operation of the present invention is believed
clearly apparent from the foregoing description, further amplifica-
tion will subsequently be made in the following brief summary of such
operation. The air compressor and the pump 84 are driven by the
vehicle engine in the usual manner such that the air tanks 32 and 93
are pressurized by the air compressor automatically after the engine
is started and fluid from the pump is directed to the modulating valve
82. The valves 89 and 91 are normally in the position shown so that
pressurized air is transmitted through line 92 to shift the modulating
valve to a position for communicating the pump 84 with the chambers 24
of the brake mechanisms 14 through the conduit 83. The fluid in these
chambers moves the second pistons 22 against the bias of the springs
23 and frees the first piston 18 for normal service brake operations.
Manually positioning the on-off valve 46 permits the operator
to choose between service braking with the rear brake mechanisms 14
only or the combination of both front and rear brake mechanisms 13
and 14. With the valve 46 in the position shown, cnly the brake
mechanisms 14 are employed for normal service braking which is init-
iated by manually positioning the service brake valve 43 for directing
pressurized air to the end of the first relay valve 34. The first
relay valve is in turn shifted to establish communieation through line
36 to the air chamber 50 of the master cylinder 37. The pressurized
air in the air chamber acts against the piston 52 which pressurizes
the fluid in the fluid chamber 51 and directs such fluid through
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conduit 53, check valve 54 and conduit 56 to the chambers 21 of the
rear brake mechanisms for moving the first pistons 18 toward the end
walls 17 of the housings 16. The first pistons clamp the discs 19
against the end walls stopping rotation of the shafts 12 and thus the
rear wheels. Releasing the service brake valve results in the air
chamber 50 being vented to the atmosphere and releases the rear brake
mechanisms.
Manually shifting the on-off valve 46 to establish communi-
cation through the line 45 results in the simultaneous shifting of
both the first and second relay valves 34 and 38, respectively, when
the service brake valve 43 is manually shifted. Shifting valve 34
causes the rear brake mechanisms 14 to be applied as previously
described while shifting the relay valve 38 directs pressurized air
through line 39, double check valve 42, and line 59 to the air chamber
61 of the master cylinder 62. This pressurizes the fluid in the fluid
chamber 63 with the fluid being directed to the front brake mechanisms
13 thereby stopping rotation of the wheels 11. Thus, with the on-off
valve shifted both brake mechanisms 13 and 14 are applied simultan-
eously.
Considering now the retarding mode of braking, the control
valve 73 is manually shifted to direct pressurized air to the end of
the relay valve 69 which in turn is shifted to communicate pressurized
air to the air chamber 71 of the master cylinder 72. The control
valve 73 is preferably frictionally retarded or detented so that it
can be positioned in predetermined increments for precisely controlling
the air flow directed to the relay valve and thus to the master
cylinder. The air pressure in the air chamber results in pressuri-
zation of the fluid in the fluid chamber 76 with the fluid being
directed through the conduit 78, the normally open towing valve 79, the
30 double check valve 54, conduit 56 and into the actuating chambers 21
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of the rear brake mechanisms 14. The fluid in the actuating chambers
moves the first pistons 18 against the discs 19 an amount proportional
to the air pressure in the air chamber 71 of the master cylinder.
Thus the rear brake mechanisms are applied for the purpose of con-
trolling vehicle speed while traveling down a slope. Returning the
control valve 73 to the position shown releases the brake mechanisms
to permit rotation of the shafts 12.
The manually controlled emergency braking mode of operation
is initiated by manually shifting the manual emergency valve 89 simul-
taneously to block flow of pressurized actuating air through lines92 and 98 permitting the modulating valve 82 and the inversion valve
96 to be resiliently shifted toward their normal position. Shifting
the modulating valve toward its normal position results in blocking
fluid flow from the pump 84 while modulating the exhausting of fluid
from the chambers 24 of the brake mechanisms 14. This permits the
, H~Lb& 23 to move the second pistons 22 against the first pistons 18
which clamp the discs 19 against the end plates 17 for stopping
rotation of the shafts 12. The shifting of the inversion valve 96
toward its normal position by reducing actuating air pressure thereto
results in pressurized air being modulatably directed through line
97, the double check valve 42, line 59, and into the air chamber 61
of the master cylinder 62. This causes pressurized fluid to be
directed through the conduit 66 to apply the front brake mechan-
isms 13 for stopping rotation of the front wheels 11. Thus, both
brake mechanisms 13 and 14 are applied simultaneously through the
shifting of the manual emergency valve 89.
The rear brake mechanisms 14 may be used as a parking brake
by manually shifting the parking brake valve 91. This vents the con-
duit 92 permitting the modulation valve 82 to shift to a position
blocking fluid flow from the pump 84 while exhausting the actuating
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chambers 24 through the conduit 83. This causes the springs 23 to move
the second pistons 22 against the first pistons 18 which in turn clamp
the discs 19 against the end plates 17 for preventing rotation of the
shafts 12.
Although the brake system 10 is arranged to minimize the
probability of the rear brake mechanisms 14 being suddenly applied and
out of control of the operator, the rear brake mechanisms are auto-
matically applied under certain conditions for safety reasons. For
example, a loss of pressurized fluid from conduit 83 results in auto-
matic application of the rear brake mechanisms. Likewise, a suddenloss of air pressure in the conduit 92 permits the modulating valve 82
to shift to block fluid flow from the pump while exhausting the fluid
from chambers 24 and conduit 83 permitting the springs 23 to apply
the rear brake mechanisms.
The towing valve 79 is included to provide an alternate
source of pressurized fluid for releasing the rear brake mechanisms
14 when fluid pressure is not available from the pump 84 such as when
the engine is inoperative. Of course, the towing mode of operation
is dependent upon having pressurized air in the air tanks 32 and 93.
In some cases sufficient air pressure may remain in the air tanks for
the towing operations while in other cases it may be necessary to
connect the air tanks to the air system of the towing vehicle. With
air pressure in tank 93, the modulating valve 82 is shifted to permit
fluid flow through conduit 83. The towing mode is initiated by shifting
the towing valve 79 to connect the conduit 78 to the conduit 83. The
control valve 73 of the retarder circuit 28 is then manually shifted to
direct actuating air to shift the relay valve 69 which in turn causes
pressurized air to be directed to the air chamber 71. This results
in pressurized fluid from the fluid chamber 76 being directed through
conduit 78, towing valve 79, conduit 83 and into the chambers 24. The
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pressurized fluid in tbe chambers moves the second pistons against the
bias of the springs 23 to release the clamping force on the discs 19.
While the vehicle is being towed, both brake mechanisms 13 and 14 can
be applied to stop the vehicle by actuation of the valve 89 as pre-
viously described.
In view of the foregoing it is readily apparent that the
structure of the present invention provides an improved brake system
which provides for the simultaneous application of a fluid applied
brake and a spring applied fluid released brake by the manual manipu-
lation of a single control valve. This is accomplished by providingan air actuated modulating valve for controlling fluid flow to the
spring applied fluid released brake and an air actuated inversion valve
for controlling fluid flow to the fluid applied brake. Reducing the
flow of actuation air to the modulating valve causes it to shift toward
a position for blocking fluid flow therethrough for-s ~ ~ the
spring applied~released brake while reducing the flow of actuating air
to the inversion valve causes it to shift toward a position for
directing pressurized fluid to apply the fluid applied brake. Thus,
by controlling the flow of actuating air to the modulating and in-
version valves by a single control valve, both brakes are actuatedsimultaneously. Also, the spring applied fluid released brake is
always available for automatic emergency braking when fluid pressure
is lost from the system. Furthermore, the spring applied fluid re-
leased brake may be independent of or an integral part of a service
brake mechanism with the spring applied fluid release brake providing
an emergency brake system to supplement the service brake system.
While the invention has been described and shown with par-
ticular reference to the preferred embodiment, it will be apparent
that variations might be possible that would fall within the scope of
the present invention which is not intended to be limited except as
defined in the following claims.
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