Motor vehicles – Having four wheels driven – Including pump and fluid motor – or generator and electric...
Reexamination Certificate
1998-10-22
2001-12-04
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Having four wheels driven
Including pump and fluid motor, or generator and electric...
C180S247000, C180S308000, C060S456000, C060S468000
Reexamination Certificate
active
06325170
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a hydraulic vehicle drive, particularly for mobile hoisting platforms, with a first pair of wheels drivable by means of first hydraulic motors in dependence of a first control valve.
Numerous vehicles are available in the market, with either two or four hydraulically driven wheels. The two-wheel drive is suited for simple ground with only small slopes and particularly for indoor use. The four-wheel drive is required for difficult ground with larger slopes or for building sites. Until now the application fields have been limited by the type of driving.
Valve modules with constant flow quantity (flow control) and with constant outlet pressure (pressure control) are known from U.S. Pat. No. 4,981,159, which valve modules have substantially the same design and only differ in a few details. In these valve modules, a compensation valve and a control valve enabling the driving of a motor in both directions are connected in series.
SUMMARY OF THE INVENTION
It is the purpose of the invention to provide a hydraulic vehicle drive of the kind described in the introduction, which permits the optional driving of one pair of wheels, for example the two front wheels, or two pairs of wheels, for example the front and the rear wheels.
According to the invention, this task is solved by means of a second pair of wheels provided with second hydraulic motors and with a switching arrangement, which short-circuits the second hydraulic motors in the driving-free state and, for the purpose of cooling, supplies them with a flushing flow, and in the driven state activates a second control valve in dependence of which the second hydraulic motors are drivable.
By means of the switching arrangement, one pair of wheels can be driven or a second pair of wheels can be connected optionally. In the resting state of the switching arrangement it is provided that the wheels of the second pair can turn freely and that a too strong heat development is prevented. In the connected state the second wheel pair also works, and for this purpose it can, like the first wheel pair, be controlled by, for example, a user.
Preferably, the switching arrangement connects the second control valve with the first control valve. This connection of the two control valves makes the driving of the second wheel pair adapt to that of the first wheel pair. The connection can be mechanical or hydraulic, however, preferably electrical, for example also in the form of a remote control.
Particularly advantageous is that the degree of connection between the first and the second control valve is adjustable. Thus, the user can select the contribution of the second motors to the driving output, if required even dynamically, that is adjustable during operation. The driving output can, for example, be adjusted between 0 and 100% of the output, which the second hydraulic motors would supply at a certain driving output of the first hydraulic motor. At the same time, a very simple steering can be achieved via the connection.
It is favourable that the first control valve is a first valve module with constant flow quantity. Thus, the first wheel pair is driven with a flow quantity, and thus also a speed, which depends on the position of the first control valve.
Further, it is expedient that the second control valve is a second valve module with constant outlet pressure. In the case of a dynamic connection, for example the outlet pressure can be set. When in the connected state the second valve module is active, the second wheel pair not only receives the required flow quantity, but a pressure for creation of a sufficient torque is maintained. The use of valve modules is also an advantage, because the usually available module block, which is provided for all functions (direction control, hoisting and lowering functions, front-wheel drive), merely has to be supplemented by the second valve module required for the four-wheel drive.
Advantageously, it is provided that the main slide of the first control valve is adjustable by means of an operating element and that in the driven state the main slide of the second control valve is adjustable proportional to the main slide of the first control valve. This is a particularly simple way of connecting the two control valves. With a rigid connection the proportionality factor can be fixed and with a dynamic connection the proportionality factor can be adjustable.
Further, it is advantageous that a lever serves as operating element, which lever is pivotal for the adjustment of the first control valve and has a trigger for the operation of the switching arrangement. This gives a very simple handling of the driving arrangement. The trigger can also be used for setting the size of the share of the driving output from the second hydraulic motor, that is, for example, the adjustment of the proportionality factors.
It is also recommended that the switching arrangement have a control valve connecting the two sides of the second hydraulic motors with each other in the driving-free state, however separating them in the driven state. This control valve enables the required short-circuiting of the hydraulic motors in the resting state.
Further, it is advantageous that the second hydraulic motors have a leakage channel and that in the driving-free state of the switching arrangement they are connected with a pump connection via a pressure dependent valve arrangement. Using the leakage channel offers a simple way of realising the flushing flow.
It is a substantial advantage that the second valve module has a compensation valve and a main slide, which has two annular slide slots with axial slots originating from those, and which is arranged in a bore with a central annular pump slot, annular motor slots arranged on both sides of said pump slot, as well as annular tank slots arranged outside said motor slots, the central axial slots having such a length that in the neutral position of the main slide they connect the annular motor slots with the annular pump slot, however separating one of these connections during a displacement. A minor extension of the central axial slot in a valve module for constant outlet pressure causes the annular motor slots to be connected with each other, which leads to the desired short-circuiting of the second hydraulic motors, additionally permitting a certain flushing flow through the second hydraulic motors in connection with the compensation valve.
Additionally, the valve module is a separate commercial unit, which is characterised by a housing with a pump connection, two motor connections and a tank connection as well as a main slide bore having a central annular pump slot connected with the pump connection via a compensation valve, two annular motor slots connected with motor connections being arranged on both sides of said pump slot, and two annular tank slots connected with the tank connection and arranged outside said motor slots, and by a main slide having two annular slide slots with axial slots originating from those, of which the two central axial slots have such a length that in the neutral position of the main slide they connect the annular motor slots with the annular pump slot, however separating one of these connections during a displacement.
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Christensen Jens S.
Thomsen Svend Erik
Danfoss Fluid Power A/S
DePumpo Daniel G.
Lee Mann Smith McWilliams Sweeney & Ohlson
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