Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF INVENTION
The present invention relates to braking systems in
general and, in particular, to a Eriction braking system or a
rubber tire transit vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference
may be had to the accompanying drawings in which:
Figure 1 is a elevational end view of a typical transit
vehicle.
Figure 2 is a cross-sectional elevational view of a
friction brake actuator showing the air-actuated service brake
containment portion in the actuated condition, and the spring-
activated emergency parking brake containment portion in a spring-
off position.
Figure 3 is a cross-sectional elevational view of the
friction brake actuator showing the spring in the parking or
emergency position with the service brake containment portion not
actuated by air.
Figure ~ is a schematic diagram of the prior art
friction braking system.
Figure 5 is a schematic diagram of the riction braking
system of the present invention.
Figure 6A is a graph showing the deceleration
characteristic utilizing the prior art friction braking system
upon application of the emergency brakes.
Figure 6B is a graph of the prior art system showing the
- deceleration characteristic upon the system experiencing a broken
spring in the emergency brakes.
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Figure 6C is a graph of the deceleration characteristic
of the present invention upon application of the emergency brakes
under normal operation.
Figure 6D is a graph of the deceleration characteristics
of the fric-tion brake system of -the present invention with a
spring failure.
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BACKGROUND OF THE INVENTION
Modern transit vehicles such as used in San Francisco's
Bart system and the Orlando and Atlanta airports utilize a
combination of dynamic or regenerative braking and friction
braking to bring the vehicles to a controlled stop. These modern
systems have been described in articles such as 'IAtlanta Airport
People Mover," by Thomas C. Selis, Manager, in the Conference
Record of the 28th IEEE Vehicular Technology Group in Denver,
Colorado, on March 22, 1978, and also in an article " Recent
Applications of Microprocessor Technology to People Mover
Systems," by Michael P. McDonald et al., in the Conference Record
of the 29th IEEE Vehicular Technology Group Conference in Chicago,
Illinois, March 28, 1979.
U.S. Patent No. 3,398,992 issued to Joseph C. Littmann,
dated August 27, 1968, discloses a brake control system for
hydraulic brakes on a trailer connected to a towing vehicle. The
Littmann patent teaches variation of the pressure o the fluid in
the hydraulic system to vary the degree of braking. U.S. Patent
~0 No., 4,384,330 issued to Matsuda et al., dated ~ay 17, 1983,
discloses a brake control system for an automotive vehicle for
controlliny application release of brake pressure in order to
prevent the vehicle from skidding. Another deceleration control
system is disclosed in UOS. Patent No. 3,751,116 issued to Thomas
H. Engle, dated ~ugust 7, 1983, which discloses a railway brake
controller which modulates the train line brake-controlling signal
as required to maintain balance between a command force indicative
of a desired rate of retardation and a feedback force developed by
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a liquid-filled column subjec-t to the actual rate o~ retardation.
Another brake control apparatus is disclosed in U.S. Patent No.
4,410,154 issued to Thomas C. Matty, dated October 18, 1983, and
assigned to the present assignee. The Matty reference discloses a
transit vehicle control apparatus which determines a safe brake
velocity for a vehicle in relation to a speed control relationship
including roadway system design deceleration, the deceleration of
the vehicle in relation to inertial space and the deceleration of
the vehicle in relation to the roadway. The Matty patent teaches
the use of microprocessor-based technology to accomplish braking
control.
The typical transit vehicle or "people mover" as part of
the braking system includes friction drum brakes of the same kype
that are used on tractor trailers and which are well known in the
art. The friction brakes are controlled by friction brake
actuators which are typically integral units having a fail-safe
design such that if the actuators suffers loss of air pressure, a
spring causes the friction brakes to engage. Referring to Fig.
6A, there is shown a typical deceleration curve upon the
application of the emergency brake spring-activated system. As
apparent from graph 6A, there is typically an initial spike or a
high deceleration rate which may produce an uncomfortable jerk for
passengers on the transit vehicle. This spike occurs as a result
of the service brakes which are air-activa-ted being fully applied
during an emergency stop having a faster response time than the
spring-activated system. An accelerometer which is typically
connected in circuit with the service brakes is typically too slow
to retard the onset of the service brakes even though sufficient
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deceleration is being supplied by the spring activated system~ A
typical prior art system producing this response is shown in Fig.
4.
S~MMARY OF_T~IE I~VENTION
The present invention is provided in combination with a
friction braking system ~or a transit vehicleO The typical
transit vehicle includes a car body, axles mounted -to the car
body~ Wheels are carried by the axles. A braking system is
provided, including friction drum brakes mounted on the axles.
Friction brake actuators are provided for actuating the friction
brakes to retard the rotation of the wheels. Friction brake
actuator controls are provided for controlling the friction brake
actuators.
The friction brake actuators typically comprise a rod
member means for connection ko the friction brakes, and an outer
chamber enclosing an air-actuated service brake containment
portion and also encIosing a spring-activated emergency-parking
brake containment portion. The air-actuated service brake
containment portion encloses service brake means for moving the
rod member means. The spring-activated emergency-parking brake
containment por-tion encloses emergency-parking brake means Eor
moving the rod member means.
The emergency-parking brake means for moving the rod
member means includes a springO The spring-activated emergency-
parking brake containment portion includes a first diaphragm
affixed to the outer chamber. The interior of the outer chamber
proximate the emergency-parking brake containment portion and the
first diaphragm define a first air chamber. The first diaphragm9
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upon air pressure being applied to the ~irst air chamber, causes
the spring to be in a compressed condition.
The service brake means for moving the rod member
includes a second diaphragm affixed to the outer chamber. The
interior o~ the outer chamber proximate the service brake portion
and the second diaphragm de~ine a second air chamber. The second
diaphragm, upon air pressure being applied to the second chamber,
causes the rod member means to operate the ric-tion brakes.
The friction brake actuator control includes a first
electro-mechanical air valve connected in fluid co~munication with
the first air chamber. An air source is provided for supplying
air to the first air valve. A second electro-mechanical air valve
is connected in 1uid communication with the second air chamber
and the air source. A power source is provided for energizing the
first and second air valves.
An emergency brake control switch is connected in
circuit between the power source and the first air valve. A
service brake control switch is connected in circuit between the
power source and the second air valve~ An accelerometer switch is
connected in circuit with a power source and the second electro~
mechanical air valveO
The improvement o the present invention comprises the
accelerometer switch being initially connected in circuit to the
power source through the emergency brake control switch~ A time-
delay switch means is included and is connected in circuit with
the accelerometer for switching the accelerometer from being in
circuit with the power source through the emergency brake control
switch to being in circuit with the power source after a
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predetermined delay, and by-passing the emergency brake con-trol
switch. The service brake con-trol switch prevents the initial
onset of the service brake means Eor moving the rod member means
until after the spring means Eor moving the rod membe:r thereby
preventing undesirable jerks of the vehicle during emergency
stopping.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to Fig. 4, there is shown a prior art
friction braking system 10 for a transit vehicle 12 such as shown
in Figure 1. The transit vehicle 12 includes a car body 14 and
the axle means 16 mounted to the car body. Wheel means 18 which
may be rubber tired are carried on the axle 16. The braking
system 10, such as shown in Fig. 4, includes friction drum brake
means 20 mounted on the axle 16 which is conventional and is not
shown. Friction brake actuator means 22 is provided for actuating
the friction brakes 20 to retard -the rotation of the wheels 18.
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Friction brake actuator control means 24 is
provided for controlling the friction brake actuator 22.
Referring to Figs. 2 and 3, the ricticn brake
actuator may be such as manufactured by Anchor Lok, Inc of
Culver City, California, Model No. 9-15. The friction
braka actuator 2~ comprisss a rod member means 26a, 26b for
connectiGn to ths friction drum brakes 20 shown schemat -
cally in Figs. 2 and 3. Friction brake actuator also
includes outer chamber means 28 enclosing an air-powered
service braka containment portion 30 and also enciosing a
spring-powered emergency-parking brake containment portion
32. The air-powered service brake containment portion 30
encloses service brake means 34 Ior moving the rod member
means 26. The rod member means 26 typically includes a
pair of push rods 27~, 27b. The s~ring-ac~ ate~
emergency-parking brake containment portion 32 encloses
emergency-parking brake means 36 for moving the rod member
means 26 including a spring 38. The spring-activated
emergency-par~ing brake containment portion 32 inc'udes a
first diaphragm 40 affixed to the outer chamber 28. The
inner surface 42 of the outer chamber means 28 proximate
the emergency-parking brake containment portion 32 and ths
irst diaphragm 40 defining a first air chamber 44. The
first diaphragm 40, upon air pressure being supplied to the
irst air chamber 44, causing the spring ~8 to be in a
compressed condition.
Service brake means 34 for moving the rGd member
26 includes a second diaphragm 46 affixed to the outsr
chamber 28. The i~ner surface a8 of the outer chamber 23
proximate the surface brake portion 30 defining a second
air chamber 50. The second diaphragm 46, upon air pressure
being applied to the second air chamber 50, causes the rod
member ?6, i.e., push rod ~7â~ to operate the frl-~ion
brakes 24. Typically, the service brake means for moving
the rod means 26 is used for service brakes where the
variation of air pressure in the first chamber controls the
amount of braking effort exerted by the friction brakes.
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.
Referrin~ to Fig. 4, the friction brake actuator
control means 24 includes a first electro-mechanical air
valve means 52 connected in fluid communication with the
first air chamber 44. An air source 54 is provided for
su?plying air to the first air valve 52. A second
electro-mQchanica~ air valve msans 56 is connscted in ~ id
communication with the sscond air chamber 50 and the air
source 54. A power source 58 is provided for energizing
the first air valve 52 and the second air valve 56.
Emergensy b~ake control switch means 60 is conne-ted in
circuit between the power source 58 and the first air valve
52. Service brake control sw1tch means 62 is connected in
circuit between tne power source 58 and the second air
valve 55. EmergQncy hrak~ control switch means 60 typical-
ly includes emerge~cy brake; control 5~ and emergcncy brakecontact relay 61. Service brake control switch means 62
typlcally includes service braXe control 63 and service
brake contact relay 65. The service brake control 63 and
emergency brake control 59 maybe microprocessor based
controls as disclosed i~ the aforesaid U.S. Patent No.
410,154 issued to Matty. Accelerometer switch means 64,
such as manufactursd by Ed Cliff Instruments, a subsidiary
of Systxon-Donner Corporation oI Monrovia, California,
Model No. 7-600, is desirably connected in circuit with the
power source 58 and the second electro-magnetic air valve
56. The Criction braking system described thus far is
gen2rally conventionzl.
The improvement o the present invention entails
initially connecting accelerometer ~witch 64 in circuit
with the power source 58 through the emergency brake
control switch 60 as shown in Fig. S. A time-delay switch
means 66, such as manufactured by Potter Bromfield, Model
CDC38-30G25, may be u~iiized. The Potter Bromfield Switch
is a slow-release relay. The time-deLay switch 66 is for
switching the accelerometer switch means from being in
circuit with the power source 58 through the emergency
brake control switch means 60 to being in circuit with the
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power source 58 after a predetermined delay and by~passing
the emergency brake switch means 60, whereby upon the
emergency brake switch 60 being ener~ized, the service
brake switch means 62 can only be activated ~fter a prede-
tsr~inG~ dela~, thereby ~reventing undesirabl~ jerks of thetransit vehicla 1' durlng em~rgency stopping.
With rQfsrence to the graph shown in Figs. 6A-6D,
it can be seen that utilizing the present invention, the
spike 67 which may be caused by the prior art initial air
servicQ braXe activation is eliminated by the time-delay of
the time-delay switch 66 which can be one second, for
example, which permits the spring-activated emergency brake
to take eLfect. If the spring brake is insu ficient, ~he
accelerometer switch 64 will permit the air service ~rake
por_ion 3~ to taXe effect after the time delay. Graphs 63
and 6D indicate that under spring 38 failure the
accelerometer switch will successfully close and then open
as braking is applied by the air system with an acceptable
one-second time deiay, as shown in Fig. 6D, occasioned by
the time-delay switch 66 of the present invention.
