Power plants – Pressure fluid source and motor – Methods of operation
Patent
1994-05-13
1995-07-25
Look, Edward K.
Power plants
Pressure fluid source and motor
Methods of operation
60426, 91515, 91517, 91518, 91445, 91446, 91448, 137111, F16D 3100, F16D 3102, F15B 1108
Patent
active
054351324
DESCRIPTION:
BRIEF SUMMARY
The invention generally relates to hydrostatic transmissions and more specifically relates to a method and a flow control valve assembly for achieving mutual balancing of flows through consumers or working apparatuses in hydrostatic transmissions, of the kind indicated in the preambles of claims 1 and 5 respectively.
Hydrostatic transmissions of the kind indicated in the introduction are especially employed for propelling special vehicles, such as cross-country vehicles and other slow moving vehicles, whereby the drive motor, for instance a combustion engine or an electric motor, of the vehicle is employed for driving one or more hydraulic pumps which usually are of the kind having a variable displacement. The flow from the hydraulic pump/pumps drive hydraulic motors which directly or through a gear-box drives wheels or (caterpillar) tracks of the vehicle.
One problem that has to be solved in connection with such vehicles is that, on the one hand, the drive wheels or tracks of the vehicle must be permitted to rotate with different speeds, in order for the wheels or tracks to be able to cover distances of different lengths during the same time, and simultaneously must be able to transmit equal drive power, for instance when the vehicle is turning, and that, on the other hand, the drive wheels or tracks must not be allowed to slid due to a lower load or a lower coefficient of friction against the ground surface. Due to the varying nature of the ground or road surface a maximum tractive force is obtained which is equal to the number of wheels or tracks multiplied with the tractive force obtained from the wheel or track being able to transmit the lowest tractive force. By vehicles having gear-transmission this problem is solved by means of a differential gear having a differential lock which may be engaged and disengaged. The hydrostatic transmission does not require any equivalent to the differential, but in order to obtain maximum tractive force for each separate wheel or track, a mutual controlling or balancing of the hydraulic flows of the motors at the respective wheels or tracks must achieved.
An obvious solution is to provide the vehicle with a hydraulic pump feeding each hydraulic motor, but this solution is employed very seldom today due to the coherent large requirement for space, high cost and obvious control problems.
An alternative, previously known solution is to supplement the hydraulic system of the vehicle with some kind of flow regulating hydraulic component such as a flow divider or flow combiner, i.e. provided upstream and/or downstream of the hydraulic motors, and presently there are a number of different kinds of such components on the market. However, said components have the common problem that they only operate satisfactorily within a relatively narrow range of flows. At flows below this range the operation is not satisfactory and at flows exceeding this range the pressure drop across the flow regulation or control becomes unacceptably high. This means that this kind of flow control, like the differential lock in a mechanical gear-transmission has to be engaged and disengaged depending upon the driving conditions. More specifically, the flow has to be bypassed the flow control when the volumes of flow are large. This means that such a flow control system additionally has to be supplemented with further valves which make the system relatively expensive and complicated without providing for any optimum operation.
A favourable operation may however be achieved by employing proportionally controlled valves which are provided one for each hydraulic motor and which are controlled by an advanced electronic control system employing sensors on each wheel/track. Such systems do however become very complicated and very expensive and may for that reason only be a possible choice in very specific cases on advanced vehicles where the increased cost may be accepted. Moreover, such a system becomes sensitive to interferences.
Accordingly, the basic object of the invention is to provide a method and a
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Lindholm Jan
Lindholm Thomas
Look Edward K.
Nguyen Hoang
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