Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
1999-03-23
2001-12-04
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C417S213000
Reexamination Certificate
active
06324841
ABSTRACT:
The invention relates to an output- and/or torque-regulating device for at least two adjustable hydraulic pumps having in each case one hydraulic servo control unit per hydraulic pump for infinitely variable adjustment of the delivery rate.
An output- and/or torque-regulating device of the type described is known, for example, from EP 0149 787 B2. In the known output- and/or torque-regulating device, the delivery rate of each hydraulic pump is determined in dependence upon the delivery pressure of the respective hydraulic pump in a delivery pressure line associated with the hydraulic pump and upon the control pressures in control lines provided for each hydraulic pump. To said end, the servo control unit comprises a swing-out device setting a pump actuator in maximum delivery rate direction and a piston, which acts upon the pump actuator in the direction of a delivery rate reduction and the piston area of which is loadable with the delivery pressure or connectable to an outlet by means of a hydraulically operable control valve. Operation of the control valve is effected by the control pressure in the control line of the respective hydraulic pump. For each servo control unit there is provided a torque valve having a valve piston, which is movable in a valve sleeve and forms a sealing fit with the valve sleeve and the closing force of which is determined by a measuring spring arrangement, which is connected to the pump actuator and preloaded in dependence upon the set delivery rate. Said torque valve of the two hydraulic pumps connects the control line of the associated hydraulic pump in dependence upon the control pressure in said control line and upon the control pressure in the control line of the other hydraulic pump to the outlet with simultaneous preloading of the measuring spring arrangement.
The characteristic of said known output- and/or torque-regulating device is illustrated in
FIG. 2
as a function of the high pressure pHD prevailing in the delivery pressure line in dependence upon the delivery rate Q of the associated hydraulic pump. An ideal output characteristic curve of one of the two hydraulic pumps given a disconnected consumer in the pressure circuit of the other hydraulic pump is denoted by the reference character
1
. In the case of said hyperbolic ideal characteristic curve
1
with constant output, the product of delivery rate Q and pressure pHD in the high-pressure line is constant and the curve therefore has a hyperbolic shape. In the case of the regulating device known from EP 0149 787 B2, the ideal characteristic curve
1
is approximated by a real characteristic curve
1
′. The real characteristic curve
1
′ has two linear portions. In each of the linear portions, the closing force of the valve piston of the torque valve is determined by one of two individual springs provided in the measuring spring arrangement of the torque valve. In said manner, the hyperbolic shape of the ideal characteristic curve
1
may be approximated sufficiently for practical needs.
When a consumer, e.g. a digger controller, is then connected in the pressure circuit of the other hydraulic pump, in the case of the regulating device known from EP 0149 787 B2 the torque valve provided in the servo control unit of the first hydraulic pump is additionally acted upon by a control line connected to the second hydraulic pump. This occurs in the regulating device known from EP 0149 787 B2 in that the valve piston of the torque valve is additionally loaded in opening direction against the measuring spring arrangement. In the P-Q diagram illustrated in
FIG. 2
, this corresponds to a parallel displacement of the characteristic curve
1
′ in y direction, which is illustrated by the vector y. As a result of the connection of the consumer in the pressure circuit of the second hydraulic pump, the original characteristic curve
1
′ of the first hydraulic pump is transformed into the characteristic curve
2
′. In the region of a relatively low delivery rate Q and/or in the region of a relatively high pressure pHD in the delivery pressure line, this however leads to a considerable deviation from the corresponding ideal characteristic curve
2
with constant output (Q×p=constant). In said region an excessive torque arises, which is illustrated in
FIG. 2
by the hatched area. This may lead to an overloading of the first hydraulic pump and/or of the drive unit. A better approximation would result from the, in sections, linearized characteristic curve
2
″, which is however not achievable with the regulating device known from EP 0 149 787 B2.
The relatively large deviation from the ideal characteristic curve (Q×p=constant) which is illustrated in
FIG. 2
may admittedly be avoided in principle by the use of a very costly, so-called hyperbolic output regulator or by electronically operating, e.g. microprocessor-controlled output regulators. The constructional outlay for such solutions and the associated manufacturing costs are however considerable and out of all proportion to the relatively low outlay for an output and/or torque-regulating device of the type described, such as is known, for example, from EP 0149 787 B2.
The object of the present invention is therefore to develop an output- and/or torque-regulating device of the type described in such a way that a better approximation to the ideal regulating characteristic curve is achieved.
Said object is achieved by the characterizing features in conjunction with the generic features.
The invention is based on the discovery that a far better approximation to the ideal characteristic curve may be achieved when not only the valve piston but also the valve sleeve of the torque valve are acted upon in a suitable manner by the control pressure and/or control pressures derived from the delivery pressure of the second hydraulic pump and/or the delivery pressures of the further hydraulic pumps provided in any desired number.
The advantages of the present invention are achieved in the following way.
For each control line there can be provided on the valve piston of each torque valve an associated measuring surface, which can be loaded by, in each case, the control pressure of the associated control line in the direction of opening of the torque valve. There can be provided on the pump actuator a driver pin which acts in the valve sleeve of the associated torque valve to vary the preloading of the measuring spring arrangement.
The control pressure prevailing in each case in the control line of the other hydraulic pump can act upon a valve sleeve-positioning piston in such a way that the valve sleeve-positioning piston displaces the valve sleeve against a restoring spring. It is advantageous when the direction of motion of the valve sleeve-positioning piston is directed substantially at right angles to the direction of motion of the valve sleeve because this enables a particularly compact structural design of the torque valve. An intermediate element can be provided between the valve sleeve-positioning piston and the valve sleeve. The contact surface between the valve sleeve-positioning piston and the intermediate element can compensate the displacement of the valve sleeve at right angles to the direction of motion of the valve sleeve-positioning piston when the intermediate element is guided simultaneously with the valve sleeve.
The valve sleeve-positioning piston or the intermediate element can have an oblique surface, which acts upon a bolt element in engagement with the valve sleeve. By virtue of the oblique surface, a deflection of the direction of motion of the valve sleeve-positioning piston into the direction of motion of the valve sleeve is achieved. By suitably dimensioning the angle of the oblique surface, a reduction ratio can be achieved. The driver pin of the pump actuator can take the form of a hollow body, including a hollow cylinder, the valve sleeve-positioning piston or the intermediate element engaging displaceably into the driver pin of the pump actuator and being enclosed
Beutler Gerhard
Maier Hermann
Brueninghaus Hydromatik GmbH
Lopez F. Daniel
Scully Scott Murphy & Presser
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