Note: Descriptions are shown in the official language in which they were submitted.
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B_IL V~XCLE
.~
This invention relates to an adhesion
drive rail vehicle, whether in ~he form of a
fixed axle locomotive or bogie mounted
locomotive, powered by prime mover (e g. a
diesel engine or electric motor with or
without an associated flywheel) 9 with a
hydrostatic transmission to the or each
driving wheel or axle. A constant problem is
the avoidance of wheel slip during
acceleration and retardation of the vehicle -
a problem which is controllable in battery
powered adhesion drive rail vehicles for
instance, for selection of the current
automatically selects the torque. Once
slippage has occurred during retardation for
example, it is virtually impossible for the
driver to accelerate the wheels to match the
speed of the vehicle. Furthermore, on
relatively long gradients, it is difficlllt or
impossible to dissipate the heat generated at
con~entional disc or shoe brakes.
According to the present invention
there is provided an adhesion drive rail
--2--
vehicle comprising a prime mover;
a hydrostatic transmission comprising
a transmission circuit to power at least one~
driven wheel or axle of the vehicle and a
control circuit to control the transmission
circuit;
the transmission circuit incorporating
ta) an hydraulic motor provided at the
or each driven wheel or axle,
(b) a variable output pump biased to a
drive condition, and
(c) at least one throttle valve, to
control vehicle braking, located in a fluid
transmission line of the transmission circuit
extending from the pump to the motor(s) and
being operable by a disproportional area
actuator;
the control circuit incorporating
control means f`or the variable output pump and
at least one driver operated speed control
device movable in a first mode to cause
acceleration of the vehicle by sending a
variable presure signal to the pump oontrol
means whereby the pump comes on stroke, while
~5 the driver operated speed control device is
movable in a second mode to cause retardation
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of the vehlcle to send a variable pressure
signal to the disproportional area actuator,
to adjust the throttle valve to induce back-
pressure in the return line from the motor(s),5 a feedback loop monitors the regenerated
pressure and permits the throttle valve to
continue to close as the flow through the
valve reduce~ under the influence of the
actuator9 at a driver selected braking
pressure, until the vehicle comes to rest.
The result is that acceleration at a
constant torque may be achieved by maintaining
a constant pressure, while slippage during
retardation is avoided or corrected by the
gradually closing throttle valve. If the
driver should select a control pressure which
leads to wheel slip during retar~ation - a
condition which is readily sensed by the
driver - then returning his control device to
a neutral position alters the pressure signal
._
to the actuator and consequently adjusts the
throttle valve which, with the forward bias of
the variable output pump, accelerates the
wheelts) to rail speed~ whereupon the driver
25 ` may revert to the braking mode~ If the driver
should select a control pressure which leads
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to wheel slip during acceleration, the driver
eases his speed control device to reduce the
pressure signal which permits the pump to~
stroke at a lesser rate.
The transmission circuit may
incorporate two throttle valves whereby,
during braking of the vehicle, in either
direction of travel, pressure fluid exhausted
from the motor(s) is passed through one or
other of the throttle valves, before reaching
the hydraulic pump.
The vehicle may take the form of a
fixed axle locomotive or bogie mounted
locomotive and normally at least two wheels,
or a~ least one axle would be driven. It
follows that in a four wheel bogie mode~ the
bogie may have all four wheels drivable.
A major advantage is attainable in ~he
braking mode of the vehicle if fluid is
~o extracted from the transmission circuit and
passed through a cooler, whereby filtered and
cooled fluid is available from tank.
If, as would normally be the case, the
vehicle is required to run optionally in, both
Z5 a forward direction and a reverse direction, a
selector valve needs to be incorporated in the
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control circuit to select the direction of
pump output and hence the direction of
wheel/axle motor(s) rotation The vehicle may:
be provided with a driver's cab at one end
only, or with a driver~s cab at both ends.
In the latter case each cab incorporates a
driver operable speed control device in the
form of an acceleration valve and a brake
valve, which may be lever operated. Indeed a
single lever may be employed to operate both
valves. Conveniently, the pump is of the
swash plate type or bent axis type. The prime
mover conveniently also drives a second pumpt
which constitutes a boost pump, to boost the
15 main transmission and also to power the
control circuit e.g. to provide fluid at 250
p.s.i. to the driver's control valves.
Conveniently, the boost pump is of the fixed
delivery type. It is also preferred for the
throttle valves to be rotary valves and the
,
actuators to be rotary or linear actuators.
The pump control means associated with the
pu~p are preferably a pressure control device,
e~g. a remote controlled relief valve, a
` 25 constant H.P. device fed by check valves, and
a hydraulic stroke controller7 the latter
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being operable by the "direction of travel"
selector valve, whlch in effect selects the
"live" cab if two cabs are provided. -
The invention will now be described in
greater detail, by way of example, with
reference to the accompanying drawings, in
which:
Figure 1 is a circuit diagram of a two
cab vehicle in accordance with the invention,
indicating the acceleration and constant
velocity condition; and
Figure 2 corresponds to Figure 1 but
shows the service braking condition.
In the drawings, a prime mover, e.g. a
5~ diesel engine, is indicated at 1, which drives
via shaft 20 a variable output hydraulic pump
21 and via shaft 22 a boost pump 12. The
variable output hydraulic pump 21 is of the
swash plate type or bent axis type and the
, 20 swash plate angle is adjusted by a stroke
controller 6 e.g. a spring loaded, - double-
ended piston, mounted on the pump 21. Also
- mounted on the pump 21 are a constant H.P.
device 5 - basically comprising a spring
- 25 loaded valve and a pressure control device 4
constituted by a remote controlled relief
3~
valve. A transmission circuit comprises
basically the pump 219 an output/return line
23 extending from the pump 21 to a first-
throttle valve 3A, e.g. of the rotary type,
which throttle valve 3A is infinitely
adjustable between closed and maximum open
positions by ~ disproportional area actuator
2A, connected to the valves 3A by any suitable
means, e.g~ a chain engaging a sprocket wheel
?0 of the throttle valve if the latter are rotary
valves. From the first throttle valve 3A
extends an output/return line 24, two
hydraulic motors 10, one drivably connected to
each of two flanged rail wheels(not shown) of
the vehiole~ From each motor 10 extends a
return/output line 25 to a second throttle
valve 3B also controlled by a disproportional
i;.. . :
~ area actuator 2B, the clrcuit being completed
by a return/output line 28 from the valve 3B
to the pump 21.
Control of the transmission circuit is
effected by a control circuit powered by the
boost pump 12 subject to driver operated
controls for acceleration, constant speed and
; 25 retardation, and the drawings illustrate a
cirauit for a vehicle with two cabs identified
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as cab A and cab B. Each cab incorporates an
acceleration valve 14 (0-200 p.s.i.) and a
brake valve 15 (0-200 p.s~i.) both man~ally
operable by the driver via control levers and
forming part of the control circuit. The
desired direction of trave1 of the vehicle
dictates which cab controls shall be live and
for this purpose a cab selector valve 16 and a
control pressure selector ~alve 17 are
incorporated in the control circuit.
It is arranged that, in a stationery
condition of the vehicleg the engine 1 is
running as is the pump 21 but no fluid
delivery is taking place because of the
.. . .
neutral position of its swash plate. The
boost pump 12 is also running and delivering
pressure flu1d at 250 p.s.i. to the control
clrcuit. -In practice, the engine is arranged
to produce approximately half its power so
that coupling, uncoupling operations etc., can
be easily effe ted. Hence, the boost pump 12
. . , .-
supplies pressure fluid alon~ line 50 via the
cab selector valve 16 to the acceleration and
brake valves 14 and 15 of cab B, but as both
valves 14 and 15 are in a neutnal position9 no
boost pressure is supplied to either the
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acceleration line 52 or the brake line 53 of
the control circuit. From line 50 extends a
first branch 5:1 by which filtered cooled
hydraulic fluid enters the system by a low
pressure selector 9 comprising two one way
valves and hence boost pressure is supplied
along lines 54 and 55 to lines 24 and 25 of
the transmission circuit, and hence the whole
of the latter is at boost pressure, including,
through directional valve 18, line 56 by which
hot, contaminated hydraulic fluid leaves the
system via relief valve 11 (250 p.s.i.) and
thereafter a cooler 13 for the hydraulic
fluid. A second branch 57 from line 50
.. " . . ........ .
conveys boost pressure to the stroke
controller 6, and a thircl branch 58~conveys
boost pressure to contro]L pressure selector
. ~ valve 17. Fr;om the transmission circuit and
via high pressure selector valve 8 (4000
p.s.i.) boost pressure passes along branch 59
to the pressure control device 4. However,
the pump 21 cannot stroke until acceleration
valve 14 is opened to supply a pressure signal
along line 52 through valve 17, along line 60
25 and along branch 61 to the control valve 4,
while a branch 26 extends to the engine fuel
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pump 19. The control valve 4 is thereby
displaced and the engine 1 accelerated.
Previously, a proportion of the
hydraulic fluid supplied by boost pump 12 had
been allowed to spill off across the valve of
the stroke controller 6, with the control
- valve 4 held in a balanced condition.
However, with a press~re signal supplied along
line 52 from the acceleration valve 14 to the
; 10 pressure control device 4, the latter is
displaced and the vehicle now accelerates for
pump 21 is allowed to come on stroke thus
supplying fluid at 0 - 4,000 p~s.i. to the
transmission circuit, with the principle
quanti~y of fluid passing along line 24
~ through motors 10 and along line 25 back to
` the pump 21. ~ A smaller quantity of fluid
passes from line 24 along branch 63, a pilot
line 6~ which displa~es the spool of
, , ~. .~
directional valve 18, whereby a proportion of
fluid~exhausted from the motors 10 may pass
. ., ~
along branch 56, to the oil cooler 13 and then
back to tank.
Acceleration continues until the
deslred speed has been attained whereupon the
driver adjusts the acceleration valve 14, it
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being arranged that the pump 21 is slightly
biased in the direction of travel in that it
will not destroke but drives, for example, at
2 H~P. at full engine revolutions, the aim ;
being to match rolling friction etc.
When it is desired to retard the
- vehicle, the driver opens brake valve 15,
thereby activating line 53, which provides
control pressure to the opposite side of the
actuator 2A associated with the return line 24.
The disproportional area actuator 2A may have a
ratio of 22.5 : 1. The valve 3B associated
with the line 25 is gradually closed by
movement o~ the actuator 2B, wlth a reduced
quantIty of fluid supplied to the pump 1 from
the valve 3B ~(0-4500 p.s.i.)
~ ,
~ or ease of understanding the mode of
operation, the various c:ircuits have been
dicated by differing line styles in the
20. Figure9. ~ Thus, in Figure 1 t the control
pressure circuit is shown in chain dotted
., , ~ :
.: ~ line, the boost :pressure circuit in long-
dotted line, and the transmission pressure
circuit in ùeavy line; while in Figure 2, the
control pressure circuit (0-200 p.s.i.) is
~` again shown in chain-dotted line, the boost
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pressure circuit (250 p.s.i.) is again shown
in long-dotted line, while the regenerative
braking pressure circuit (0-4000 p.s.i.) is
shown in short-dotted line. '-
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