Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Patent
1990-10-26
1992-12-22
Smith, Leonard E.
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
F04B 4908
Patent
active
051730316
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is related to a device on an adjustable hydrostatic pump for regulating the delivery flow and, as necessary, also the delivery pressure of same. The demands on the control rate of such adjustable pumps have grown considerably. One of the limits for this control rate is determined by the pressure level of the control flow. This is generally ascertained from the inherent delivery flow of the pump; this is also why its pressure can reach, at most, the level of the initial pressure of the pump. At low operating pressure of the pump, this inevitably leads to limitations of the control rate. As remedies, solutions--e.g. according to FIG. 1 of the drawing--are known which connect the control system with an auxiliary pressure source in phases of low operating pressure. This can be an external pressure supply or a pressure storage system which is recharged from the pump's own circulation during the high-pressure phase in the work cycle. However, a disadvantage in these known devices consists in that a high pressure level now also occurs at low operating pressure at the control edge of the pump regulator. The high regulating accuracy of a conventional regulator-- particularly in the flow control at low operating pressure--is accordingly considerably reduced. This results from the fact that the pressure from which the control pressure is obtained no longer has a fixed relationship to the pressure required in the adjusting piston space. The regulating valve must therefore adjust the pressure divider ratio in the decisive position by means of small changes in position by means of its throttle cross section during every fluctuation in load pressure. In so doing, the effective control pressure differential changes, and the accuracy of the delivery flow deviates from the high standard which is in effect when the operating pressure is approximately equal to the control pressure.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a more accurate rapid control of the flow and, as needed, the delivery pressure of a hydrostatic pump, especially for low operating pressures.
This object and others will be made more apparent hereinafter is attained in a flow controlling device on an adjustable hydrostatic pump having an actuating element. The hydrostatic pump delivers a flow over a delivery line at a delivery flow rate and delivery pressure and the flow controlling device regulates the delivery flow and also, as needed, the delivery pressure. The actuating element is adjustable against a counterforce by at least one servo-piston which is acted upon by a control pressure. The control pressure is controlled in a regulating valve. Specifically, when an actual value of a delivery flow or delivery pressure is in approximate agreement with a reference value of the delivery flow or delivery pressure, respectively, the control pressure is controlled by means of a pressure divider which comprises the combination of a fixed throttle and a variable throttle in the regulating valve acted upon by the pressure differential across a measuring throttle arranged in the delivery line or the pressure differential across a throttle arranged in a line to a pilot valve, as well as a control spring which acts against the higher of the two pressures on the regulating valve. The flow controlling device also includes an auxiliary pressure source which can act on the servo-piston directly or indirectly via the regulating valve.
According to the invention the device for controlling flow and pressure of a hydrostatic pump further comprises means for obtaining the control pressure from a pressure of the delivered flow from the pump (switching position II of the regulating valve) via the pressure divider, when the actual value and reference value approximately agree, and, when they do not agree, means for obtaining the control pressure from a source of higher pressure for adjusting the pump (switching position III or IV), and wherein the servo-piston is relievable of pressure for
Bertsch Dieter
Nonnenmacher Gerhard
Robeller Walter
Tittmann Egon
Walter Heinz
Robert & Bosch GmbH
Smith Leonard E.
Striker Michael J.
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