Pumps – With condition responsive pumped fluid control – Fluid flow rate responsive
Patent
1986-04-03
1987-12-29
Freeh, William L.
Pumps
With condition responsive pumped fluid control
Fluid flow rate responsive
417310, F04B 4900
Patent
active
047157933
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a flow regulating arrangement for a rotary vane pump with regulation of pump output flow by means of a bypass flow regulating valve in which a metering throttle has been disposed.
The arrangment as heretofore been known in the German Pat. No. 24 02 017 (U.S. Pat. No. 3,989,414). A rotary vane pump having such a flow regulating arrangement has the disadvantage that in starting of the pump, especially at low temperature, undesirable noises develop.
The present invention has for its purpose, the avoidance of such starting noises with pumps of the kind described.
Such purpose is effected by utilization of a viscosity responsive metering throttle.
In the prior art of rotary vane pumps (German patent application No. P 34 23 812.3, U.S. Pat. No. 33 49 714), a variable metering throttle is used as a restricted orifice operable independently of viscosity. This means that the quantity of pressure agent, e.g., oil flowing to a consumer, i.e., a servosteering system is independent of the temperature of the oil for low and high temperatures, causing noise. The passage length of the throttling is made as short as possible in the prior art as compared with the present invention. The flow at reduced pressure for the regulation of pump flow thus takes place downstream of the variable throttle.
Accordingly when the discharge rate of the prior art pump amounts, for example, to 8 liters/min., 7 liters/min. are pumped to the consumer, and the bypass flow back to the suction side of the pump from the flow regulating valve amounts only to 1 liter/min. In order to pump 8 liters/min. it's necessary for the pump to maintain a flow of 7 liters/min. from the tank.
For low oil temperatures, injector action, i.e., the entraining effect on oil from the tank is not sufficient as effected by the bypass flow because of the viscosity of the oil to maintain a suction of the required 7 liters/min. The cavitation developing thereby leads to the undesirable noises.
In the present invention, a flow regulating valve with a metering throttle responsive to oil viscosity is used and in event of low temperature, the final regulation occurs sooner than would occur in the prior art and thus less oil need be conveyed to the consumer. Accordingly, a smaller quantity of oil goes to the consumer, while the main quantity pumped is bypassed to the suction side of the pump. In consequence only a very small quantity of oil needs to be replenished from the tank so that no heavy flow cavitation with accompanying noise will occur.
The viscosity responsiveness or viscosity dependence of the metering throttle member is achieved by a radial flow cross section of a metering throttle bore of small flow area in relation to the surface wetted by the flowing stream of oil therein. The wetted surface is determined by the periphery of the flow cross sectional area and the length of the metering throttle bore. Because a peripheral layer of oil is thicker for cold, i.e., viscous oil, the effect of the surface contact is greater than in the case of warm, i.e., thin bodied oil.
In order to effect precise regulation of the oil stream, it is advantageous to have a viscosity independent restrictor bore upstream of the viscosity responsive throttle. Thus, there is achieved as a result of the restrictor bore regulation, a close regulation while as a result of the viscosity responsive metering throttle, prevention of noise will be effected.
The purpose of the invention may be achieved simply by means of a metering throttle, viz, a tube with a bore having a cross section corresponding approximately to the cross section of the restrictor bore and the length of which is greater as compared to the length of the restrictor bore and as compared to the diameter of the viscosity responsive bore. This may be achieved particularly simply by a composite bore of constant cross section, whereby the upstream portion is a restrictor bore of a relatively short length and a second portion is angularly oriented to the first portion and has a relatively great length.
An advant
REFERENCES:
patent: 3314495 (1967-04-01), Clark et al.
patent: 3349714 (1967-10-01), Griener
patent: 3989414 (1976-11-01), Rieber
Gunther Seidl
Johann Merz
Freeh William L.
Zahnradfabrik Friedrichshafen AG.
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