Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a method for
selective hydraulic driving of the wheels of a vehicle,
supplementary to the main driving wheels driven by an engine
through a torque converter or a gearbox, by automated control
of a closed hydraulic operating circuit, with wheel motors
fed from a variable capacity pump, and a variable capacity
pump and a control pump driven directly by the engine,
the flow and pressure of the working fluid being controlled
by the controllable control pump flow.
As is known, grader vehicles are used for heavy
earth moving operations. It is essential in this connection,
when releasing solid material, working uphill, or generally
working on subsoil offering little traction, for the entire
weight of the machine to be used as traction weight. The
front axle of a vehicle of this kind, namely a grader,
carries about one third of the total weight. Now if it
were possible to equip the vehicle with four wheel drive,
in addition to the rear main driving wheels, i.e. to cut
in the front axle, this would allow the thrust to be in-
creased by up to 50%. Due to special design requirements,
and this applies not only but more particularly, to graders,
the additional driving of further wheels has frequently
not been achievable. In the case of graders, the high
structural cost of mechanical types of drive, e.g. garden
shafts, may be the reason for this. The remaining operating
functions, such as blade operation, must be maintained
in full and care must also be taken to ensure adequate
front axle ground clearance and steering lock.
One recognizes that if it is possible to produce
a technical design which provides additional front wheel
drive, at an acceptable cost and without restricting any
of the usual functions of a grader, this should be welcome
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innovation in the industry.
However, matching the running speed of the main
driving wheels with that of the adapted to be selectively
"cut in", constitutes a problem.
Already known is a hydraulic drive for additional
driving wheels, adapted to be cut in at will for heavy
self propelled vehicles having their main driving wheels
driven through a multi speed gearbox, the said drive come
prosing a hydraulic pump and a control pump each driven
I proportionally to the rum of the main vehicle engine,
the said hydraulic pump making available the flow of working
fluid fed to the additional driving wheels, the control
pump, in the form of a fixed displacement pump, relieving
the pressure of its output through a choke, the flow of
working fluid for the additional wheels being controlled
by the pressure upstream of the said choke, the design
of the control device corresponding to the automated control,
known per so, of driving mechanisms, and the hydraulic
pump being in the form of a variable capacity pump which
is caused to produce larger displacement volumes by the
pressure upstream of the one or more chokes provided, and
to produce smaller displacement volumes by the working
pressure produced in the additional drive - seen for example
in German patent 30 35 522.
An arrangement of the latter kind requires manual
adjustment of the control pump flow with the aid of a ho-
draulic valve in order to control the drive to-the additional
wheels through the variable capacity pump. It is impossible
in this way to achieve a stable operating condition of
the additional drive wheels, especially over a wide range
of rum and with the main driving wheels in various gears.
It is an aim of the invention to provide a method
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and an apparatus for the implementation of the method for
operating selectively and hydraulically driven additional
wheels of a vehicle, the main driving wheels of which are
driven by an engine through a torque converter or a gearbox.
The rotational velocity of the additionally driven wheels
is to be matched as far as possible with that of the main
driving wheels.
In the case of the method described at the begin-
nine hereof, this purpose is perceived to be accomplished
in that, based upon an automated control, in superimposition
of the working fluid flow control, the working fluid pressure
is controlled by the pattern of a predetermined function
selectable in dependence upon the ratio between the output
rum of the engine and the output rum of the converter
stages or the gearbox. The pattern of the said function
may be in several stages like a staircase curve, alternatively
it may be linear or in conical sections. The pattern of
the function will preferably be like that of the converter
or gearbox output function.
Based upon the main driving wheels being driven
by an internal combustion engine through a torque converter
or a gearbox, and using an automated control for the flow
of working fluid to the selectively and hydraulically driven
additional wheels, a ratio former is provided, at the input
to which are formed, for each converter stage or each gear
speed of the main driving wheels, the output rum of
the engine and of the converter stages or gearbox, the
said ratio former releasing an output magnitude which cores-
ponds to the ratio between input magnitudes. Also provided
I is a function generator which, in dependence upon the output
magnitude from the ratio former, forms from the pattern
of a selectively predetermined function, a function value.
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Furthermore, the pressure, or the change in pressure, in
the working circuit is fed to the said function generator,
as a feedback, in order to complete the control circuit.
Proceeding now from a stationary operation of
the working circuit, known per so, to the additional driving
of other wheels, also with a known automated control, a
stationary pressure has also been formed in the said circuit,
for example at idling rum of the internal combustion
engine which also drives the variable capacity pump and
a control pump directly. In this connection, a specific
control angle of two adjusting elements, working against
each other with spring force, corresponds to the working
fluid flow volume delivered by the variable capacity pump.
Now if the main driving wheels move, the ratio of the rum
of the internal combustion engine, and of the torque con-
venter or gearbox output, is formed in the ratio former
and, in dependence upon this magnitude, a function value
is formed in the function generator, corresponding to the
selectively predetermined function. The value of the pros-
sure in the working circuit is compared with this function value in the function generator. A positive deviation
of the pressure in the working circuit, in relation to
the function value formed, causes the variable capacity
pump to alter the control angle to produce a smaller volume
of working fluid. Should no positive deviation appear,
the function generator will have no effect upon the variable
capacity pump. If it is assumed that, because of the in-
creased rum of the internal combustion engine, an in-
creased pressure, as compared with the idling rum con-
I diction, is fully formed, then a stable operating condition
is obtained. Here again, however, the control has no effect
upon the function generator until the pressure of the working
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circuit is transferred thereto, following the increase
in the rum of the internal combustion engine.
A further change in the output magnitude from
the ratio former, with the same selectively predetermined
function, then forms another function value in the function
generator and, after comparison with the actual pressure
in the working circuit, this leads, through a control de-
aviation, to adjustment of the control angle of the variable
capacity pump. Basically it is assumed, in this connection,
that the known automated control, in dependence upon the
rum of the internal combustion engine, will cause the
variable capacity pump to produce, in the working circuit,
a specific volume of fluid, thus establishing a corresponding
operating pressure, and that this will then be altered
in the sense of a speed regulation.
The selectively predetermined function, formed
by the function generator in dependency upon the output
magnitude from the ratio former, may utilize hydraulic
elements. Thus, for example, for the purpose of producing
a step-like function in the manner of a staircase curve,
to provide a plurality of parallel, individually controlled
limiting valves may be used, the respective excess pressure
flow from which causes the variable capacity pump to adjust
the control angle to produce a smaller flow of working
fluid, thus decreasing the pressure thereof.
In the case of a comparable design using electronic
elements know per so, the output magnitude from the ratio
former, which may also comprise an electronic signal and
which corresponds to the ratio of the measured rum
may be fed to an electronic function generator which depicts
a selected function and which compares the value f (p),
corresponding to the operating pressure of the working
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circuit, with the function value actually determined.
The electronic output signal from the function generator
may be fed, through hydraulic adjusting elements, to the
variable capacity pump, in order to alter the control angle
thereof.
A diagrammatical example of embodiment of the
invention is explained hereinafter in conjunction with the
drawing attached hereto, wherein:
Figure 1 shows the basic hydraulic circuitry
lo for operation of the method according to the invention
and the arrangements for the implementation thereof;
Figure 2 shows how a function generator may be
designed with hydraulic elements to provide a selectable
function.
Thus the embodiment is based upon a known pro-
pollution mechanism and a known automated control for selective
supplementary driving of addition wheels.
In Figure 1, engine 1, preferably an internal
combustion engine, drives the main driving wheels 4 of
a vehicle through a torque converter 2 and converter stages
3 thereof. Variable capacity pump 5 and control pump 6
are also driven directly by engine l, through a shaft.
These two elements of an automated control operate in a
closed hydraulic working circuit which feeds wheel motors
7, 8, thus causing additionally driven wheels 9, lo to
rotate. Hydraulic clutches are provided between the wheel
motors and the wheels. Pressure limiting valves 13, 14
; are provided for wheel motors 7 and 8.
The automated control also comprises, in its
control circuit for adjusting the control angle increasing
element 15 and decreasing element 16 of the variable capacity
pump, a fixed choke 17, a variable choke 18, a pressure
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limiting valve 19 and 4/3-way valve 20. The pressure relief
valve 21 limits the control pressure in the control circuit
to an adjustable fixed value. The same flow of fluid from
control pump 6 supplies the working circuit with fluid
through one-way valves 22 and 23. Clutches 11 and 12 can
be actuated by solenoid valve 24 only when the control
circuit is pressurized, and this also applies to the supple-
Monterey driving wheels.
Now this so far known arrangement is driven in
such a manner that, in superimposition of the working fluid
flow control, the working fluid pressure is controlled
by the pattern of a selectively predetermined function
in dependence upon the ratio between the output rum
of the engine and the output rum of the converter stages
or the gearbox.
To this end, a ratio former 25 is provided, to
the input 26, 27 of which are fed the engine and converter
output rum as measured at measuring points 28, 29, and
the output magnitude 30 of the said ratio former corresponds
to the ratio of the input magnitudes to each other. Also
provided is a function generator 31 which forms, from the
supplied output magnitude 30 of the ratio former 25, and
from the pattern of a selectively predetermined function,
a function value. Also fed to function generator 31, as
a feedback, through lines 32, 34, is a magnitude f (p)
corresponding to the pressure of the working circuit.
A positive deviation of the pressure in the working circuit,
in relation to the function value formed, is fed to variable
capacity pump 5, for the purpose of adjusting the control
angle thereof to produce a smaller volume of working fluid,
through output line 34, 4/3-way valve 20 and decreasing
element 16.
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In order to complete the picture, it is pointed
out that 4/3-way valve 20 performs the additional function
of determining the direction of travel according to its
position which is set magnetically. 4/2-way value 35, which
controls the pressure values fed to the function generator
from the working circuit, also cuts in dependence upon
the direction of travel.
Switch 36, which may be seen to form a unit with
function generator 31, provides the signal to actuate sol-
end valve 24.
Figure 2 illustrates an example of embodiment
for the representation of a function after the manner of
a staircase curve with the aid of hydraulic elements.
Corresponding technical arrangements bear the same reference
numerals.
A pressure, fed through line 32 from the working
circuit, is applied, with the 4/3-way hydraulic valve,
which is also controlled magnetically, in the setting shown,
to limiting valve 38 and, in the event of a positive pressure
deviation from the set pressure, is fed, in a control
deviation, through output line 34, to variable capacity
pump 5. The remaining settings of 4/3 hydraulic valve
37 carry the pressure in line 32 to further limiting valves
39 or 40, which are adjusted to other pressure values.
In this connection, the pressure stages of limiting valve
38 and additional limiting valves 39 and 40, will be set
progressively, e.g. 250, 150 and 100 bars. This produces,
at choke 41, a control pressure in excess of the feed pros-
sure hitherto obtained.
As already indicated herein before, selectable
functions may also be obtained by means of electronic
elements known per so. Moreover, a corresponding control
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deviation may be converted, as an electronic output signal,
through hydraulic adjusting elements, into the release
of a signal to the variable capacity pump.
