Pumps – Three or more cylinders arranged in parallel – radial – or... – Condition responsive fluid control
Patent
1988-05-06
1989-11-21
Freeh, William L.
Pumps
Three or more cylinders arranged in parallel, radial, or...
Condition responsive fluid control
F04B 114
Patent
active
048818771
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
A radial multi-piston pump (DE-OS No. 35 22 796, for example) of the kind used herein has a pressure limiting valve that is coaxial with the drive shaft and is accommodated in an intermediate cover. The pressure limiting valve protects the pump and a consuming device connected with it against overloading after a maximum pressure determined by a spring is reached. The upstream high-pressure side of the pressure limiting valve is exposed to a collecting chamber that receives the oil under pressure from all pistons. The outlet side of the pressure limiting valve is connected with a return chamber that is closed by the front surface of the drive shaft.
Impact noises develop when such a radial piston pump is cold started. If the driver turns an auxiliary power steering mechanism supplied by the pump to highest pressure to get out of a parking space, the permissible maximum pressure builds up and the pessure limiting valve opens. This lets the volume being delivered by the pump at the moment to flow back to the return chamber. A back pressure is developed in the return chamber by the still viscous oil that, because of necessary shaft axial play, suddenly moves the drive shaft against the pump casing. This is the cause of the impact noises. The possibility of letting the oil flow off to the suction side of the pump more quickly through several drilled holes, instead of only one, does exist. However, a resulting unfavorable cost of production results. Also, the oil mass that is present in the entire pump and in the suction line acts as retardant to flow. As a result, the pump can only suck in a small volume initially when the oil is cold.
The objects of the invention are to eliminate the impact noises caused by a cold start; improve the pump's suction efficiency, improve the bearing lubrication efficiency while the pump is warming up by warming the return oil; maintain a low manufacturing cost, all effected by the main feature of the invention, viz., to warm return oil on start up.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the main feature of the invention, a throttle means is installed downstream of the pressure limiting valve. In construction this throttle is a bore provided in a disc-like support which support is already present as a reaction support for the compression spring of the pressure limiting valve.
The throttle converts the kinetic energy of the oil into heat energy as the oil flows through the throttle to a return chamber so that the oil's viscosity decreases. The oil flows from the return chamber more easily, so that the back pressure no longer suffices to impact against the drive shaft. Furthermore, the pump cylinders reach full volume more quickly, since the pistons suck in the warmer oil more rapidly. The warmer oil also improves the bearing lubrication. The throttle provided in the spring support being merely a flow throttling bore provided therein has no significant expense.
A detailed description of the invention now follows in conjunction with the drawing in which:
FIG. 1 shows a radial piston pump in longitudinal section.
FIG. 2 shows an enlarged section of the pressure limiting valve and throttling bore.
The radial piston pump has a housing 1, an intermediate cover 2, and a dome 3 as a collecting chamber. A shaft 4 with an eccentric 5 operates several pump pistons such as pistons 6 circumferentially arranged radially to the axis of the shaft in the usual manner. The pistons reciprocate in drilled cylinders 7. Screw caps 8 with guide bolts 10 for pressure springs 11 close the cylinders 7. The pressure springs 11 hold the pistons 6 next to the surface of the circumference of the eccentric 5. An oil tank (not shown) connects to a suction chamber 14 via a suction inlet 12 and a ring channel 13. The suction chamber 14 surrounds all the piston bases facing the eccentric 5. Each conveyor piston 6 has feed inlets 15 that act together with the suction chamber 14 in a known manner when the shaft 4 is rotating. During the compression stroke, interior spaces
REFERENCES:
patent: 2298749 (1942-10-01), Buschmann
patent: 3289606 (1966-12-01), Bosch
patent: 3885893 (1975-05-01), Glock
patent: 4681514 (1987-07-01), Griese
Freeh William L.
Zahnradfabrik Friedrichshafen AG.
Zalkind Albert M.
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