Note: Descriptions are shown in the official language in which they were submitted.
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VEHICLE
This invention relates to vehicles.
It is known to propel a tractor by means of a
hydraulic traction arrangement in which each of the four
ground contacting wheels has its own individual hydraulic
motor which is actuated by a respective hydraulic pump
driven by a diesel engine on the tractor.
It is an o~ject of the present invention to
provide an improved form of tractor or other vehicle
having a hydraulic drive arrangement.
According to the present invention there is
provided a vehicle having a front pair of ground
contacting wheels, a rear pair of ground contacting
wheels, an internal combustion engine, hydraulic motors
for driving each said ground contacting wheel, and a
plurality of variable flow hydraulic pumps for driving the
hydraulic motors, wherein the internal combustion engine
is arranged to drive directly first and second variable
displacement pumps for driving the motors of the front
pair of wheels and the motors of the back pair of wheels
respectively and also to drive first and second boost
pumps, wherein a control valve is supplied with hydraulic
fluid from one of the boost pumps and is arranged to give
an output hydraulic pressure which is dependent on the
speed of the engine, and wherein a further valve is
positioned, under the control of the output hydraulic
pressure from the control valve, in the path of hydraulic
fluid from each of the boost pumps to a respective
operating piston and cylinder arrangement for adjusting
the displacement of the hydraulic pumps in dependence on
the speed of the engine.
In one arrangement a direction selection valve
under the driver's control is positioned on the output
side of the control valve between the control valve and
the further valves for controlling the direction of
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movement of the vehicle. A bleed line having a pressure
relief valve under the driver's control may be connected
on the output side of the control valve for braking the
vehicle.
It is preferred that the hydraulic motors are
three speed hydraulic motors. Selection of the speed of
the motors can be under the control of a respective valve
operable by the driver and actuated by a pilot pressure
provided at the output side of the other boost pump.
It is further preferred that a two position valve
is provided in the hydraulic circuit between each variable
displacement pump and its respective hydraulic motors to
permit the motors to be driven in synchronism in response
to a pressure signal from a control valve under the
driver's control.
Preferably the internal combustion engine is a
diesel engine, although a spark ignition engine can
alternatively be used.
In order that the invention may be clearly
understood and readily carried into effect, a preferred
embodiment thereof will now be described, by way of
example only, with reference to the accompanying drawings,
wherein:
Figure 1 is a side view of a tractor; and
Figure 2 is a hydraulic flow diagram
illustrating the drive arrangement for the tractor of
Figure 1.
Referring to the drawings, a tractor 1 has a
pair of ground contacting front wheels 2 and a pair of
ground contacting rear wheels 3, each fitted with a
respective hydraulic motor. Tractor 1 is articulated
about a vertical pivot (whose axis is indicated at 4 in
Figure 1) for steering purposes, control of the direction
of the tractor being achieved by means of steering rams 5.
The front portion of the tractor carries a diesel engine
61
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under bonnet 6 which drives a pair of variable
displacement hydraulic pumps. Each such pump supplies
hydraulic fluid under pressure to the hydraulic motors of
a respective pair of wheels 2 or 3.
Figure 2 is a hydraulic flow diagram of the
drive arrangement for tractor 1. The diesel engine 7 has
a drive shaft 8 which drives, by means of a gear train 9,
the drive shafts 10, 11 of a pair of variable displacement
hydraulic pumps 12, 13, each of the axial piston
swashplate design. A unit embodying a pair of such pumps
is available under the designation "Variable Double Pump
A5VG Series 11" from Mannesmann Rexroth GmbH, Jahnstrasse
3-5, D-8770 Lohr am Main, Federal Republic of Germany.
Each pump 12, 13 has associated therewith a respective
15 boost pump 14, 15 driven by the associated drive shaft 10,
11 .
Hydraulic fluid is drawn from a reservoir 16
through lines 17, 18 as needed by boost pumps 14, 15. The
output from boost pump 14 is fed by way of line 19,
20 throttle 20, and line 21 to a first control valve 22 which
has a spring-loaded spool mounted within a body, the spool
having a throttle washer through which fluid can return to
the reservoir (as indicated at 23). When the rate of flow
in line 21 exceeds a threshold value, the spool of valve
25 22 moves against its spring and allows fluid to flow in
line 24 and through throttle 25 to a flow direction
control valve 26 which is coupled to a gear selector lever
(forward-neutral-reverse) situated in the cab of tractor
1. A valve suitable for use as valve 22 is sold by
30 Mannesmann Rexroth GmbH under the designation "Control
Valve DA".
A bypass line 27 is connected to line 24 and has
a valve 28 mounted therein. Valve 28 is coupled to a
brake pedal in the cab of tractor 1 and, when open,
35 permits fluid to return to the reservoir (as indicated at
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29).
Assuming that the driver of the tractor 1 has
selected "forward", valve 26 permits fluid to pass in line
30 to a respective pilot pressure port 31, 32 of a further
control valve 33, 34 associated with pumps 12, 13. Each
of valves 33, 34 may be of the type sold under the
designation "Control Valve HD" by Mannesmann Rexroth GmbH.
Valve 33 is used to control the flow of fluid from boost
pump 14 to a cylinder 35, a piston 36 in which controls
the position of the swashplate of pump 12 and hence its
displacement. In a similar manner valve 34 is used to
control the flow of fluid from boost pump 15 to a cylinder
37, in which slides a piston 38 that controls the
swashplate, and hence the displacement, of pump 13.
Reference numeral 39 indicates a return line
connected to the other pilot pressure ports 40, 41 on
valves 33, 34 for return of hydraulic fluid supplied via
ports 31, 32 back through direction selector valve 26 to
reservoir 29.
In operation of the tractor 1, the speed of
diesel engine 7 is under the control of the driver by
means of a conventional accelerator pedal in the cab.
Depending upon the position of valve 26, either a zero
pilot pressure is present in lines 30 and 39, if "neutral"
is selected, or a positive pilot pressure is present in
either line 30 or line 39, depending whether the driver
has selected ~forward" or "reverse" by means of valve 26.
This pilot pressure is dependent upon the speed of diesel
engine 7 and opens valves 33, 34 to an extent dependent on
such engine speed.
Supply of fluid to valve 33 from boost pump 14
is by way of line 19, throttle 20, and line 42, whilst the
corresponding flow of fluid from boost pump 15 to valve 34
is by way of line 43. Precise feedbac~ control over the
position of the spool of valve 33 is achieved by means of
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a conventional mechanical linkage, indicated at 44, linked
to the piston 36. In a similar fashion precise feedback
control over the position of the spool of valve 34 is
achieved by means of a conventional mechanical linkage 45
coupled to piston 38.
Pump 12 supplies the three speed hydraulic
motors 46, 47 of the front wheels 2, whilst pump 13
supplies the three speed hydraulic motors 48, 49 of the
rear wheels 3. The rate and direction of rotation of
wheels 2, 3 depends upon the positions of the swashplates
of pumps 12 and 13, as determined by the selector valve 26
and the speed of diesel engine 7 in the manner described
above.
It will be seen that the speed of motors 46, 47,
48, 49 is controlled by valve 22 which produces a pilot
pressure dependent upon the speed of diesel engine 7 that
is applied, depending upon the position of selector valve
26, to the selected pilot ports 31, 32 or 40, 41 of
control valves 33, 34 which in turn provide control of the
pistons for the swashplates of pumps 12, 13~ Thus a
single control valve 22 controls both pumps 12, 13.
The hydraulic fluid supply and return lines for
hydraulic motors 46, 47 are indicated by reference
numerals 50, 51. A two position spring loaded valve 52 in
line 51 allows each of motors 46, 47 to t~ke fluid freely
from pump 12 when the spool of valve 52 is in the position
shown in Figure 2. In its other operating position the
spool of valve 52 provides a 50/50 split between motors 46
and 47 so as to obviate wheel slip. A similar valve 53 is
positioned in line 54 which forms one of the supply and
return lines 54, 55 for motors 48, 49. Operation of
valves 52, 53 is effected by applying a pilot pressure in
lines 56, 57 by means of a valve 58, which is coupled to a
switch under the driver's control in the cab of tractor 1.
This pilot pressure is drawn from the output of boost pump
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15 in line 59. By operating valve 58 the driver can
ensure synchronous drive of the motors 46, 47, 48, 49 to
avoid wheel spin.
Line 59 also provides a pilot pressure to the
valve 60 which is arranged to operate a parking brake for
the tractor. It also provides a pilot pressure for valves
61, 62 which are operable by the driver to select the
appropriate speed range (first, second or third gear) for
the hydraulic motors 46, 47, 48, 49. Dependin~ upon the
position of the spool in valves 61, 62 a corresponding
pilot pressure may or may not be present also in line 63
and/or line 64. In combination therefore valves 61, 62
permit a total of four signals to be sent to hydraulic
motors 46, 47, 48, 49; three of these possible four
combinations of pilot pressures in lines 63, 64 are used
to select a respective one of the three speed ranges ~e.g.
0 - 12 km/h or 0 - 18 km/h or 0 - 35 km/h) of the
hydraulic motors 46, 47, 48, 49.
Pressure relief valves 65, 66 are used to set
the maximum pilot pressure from the boost pumps 14, 15 at
some suitable value, e.g. about 30 bar. The minimum pilot
pressure, e.g. about 6 bar, is set by valve 22. Pressure
relief valves 65, 66 also act to provide a corresponding
minimum pressure in the respective suction lines for the
variable displacement pumps 12, 13. Pressure relief
valves 67, 68 are set at a suitable value, e.g. about 440
bar, to limit the maximum output pressure from pump 12,
whichever direction of flow in lines 50, 51 happens to
prevail at any given time. Similar pressure relief valves
69, iO are provided for pump 13.
A conventional cooling arrangement indicated at
71 can be used to control the temperature of the
circulating hydraulic fluid, whilst filter 72 ensures
dirt-free circulation thereof. The remainder of the
hydraulic circuit, including return lines and connections
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to the hydraulic fluid reservoir, is indicated in Figure 2
of the drawings and does not require further description.
If desired, a further variable displacement pump
(not shown) can be coupled in parallel with pumps 12, 13
or in line with one of them for the purpose of driving an
auxiliary item of equipment which must be operated at a
speed that is dependent upon the speed of diesel engine 7.
Such further pump may be used, for example, for driving
the wheels of a trailer or for operating a distributor for
a fertiliser, herbicide, pesticide, or the like. In such
auxiliary equipment it is important that the drive speed
should be matched to that of the drive wheels 2, 3 and
that of diesel engine 7. Such a further pump conveniently
has a boost pump (similar to boost pumps 14, 15) and its
swashplate is under the control of a valve similar to
valves 33, 34, which is in turn controlled by a pilot
pressure from valve 22.
Instead of driving pumps 12, 13 and their boost
pumps 14, 15 in parallel, diesel engine 7 can be arranged
to drive them in line.
The illustrated tractor has very simple driving
controls. Thus the only controls needed are an
accelerator to control diesel engine 7, a direction
selector lever to operate valve 26, a foot brake to
operate valve 28, and a speed range selector lever which
operates valves 61, 62. A parking brake control acts on
valve 60, whilst wheel slip can be obviated by operation
of valve 58 by a switch in the tractor cab.
