Motors: expansible chamber type – Working member position responsive motive fluid control – Venting expanding chamber
Patent
1999-05-06
2000-12-19
Ryznic, John E.
Motors: expansible chamber type
Working member position responsive motive fluid control
Venting expanding chamber
91422, F15B 1520
Patent
active
061614653
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a pneumatic or hydraulic control motor, in which a shutoff device is provided in the end positions of a working piston. In the present version, the invention pertains to a power-assisted steering system, in particular for motor vehicles with a compressed air pump, a steering valve, and a servomotor.
Such shutoff devices are intended to prevent the hard impact of the working piston against the limit stops, because such impacts cause noise. When the working piston meets the limit stops, the pump pressure rises impermissibly to a maximum value, so that the built-in overpressure valve responds. If the steering valve remains deflected for a relatively long time in this operating state, the pump can be damaged by thermal overload.
BACKGROUND OF THE INVENTION
A shutoff device for a power-assisted steering system is known for instance from German Patent Disclosure DE 42 21 459. Here, in an end position of the working piston, which is at high pressure, the pressurized pressure chamber communicates with the pressure chamber that is subject to return pressure. The hydraulic oil can therefore drop in pressure and flow out via the pressure connection of the inactive pressure side. This relief course in the end positions of the servomotor proceeds via a longitudinal groove in the inner wall of the servo cylinder that comes to communicate with the pressure connection. This communication in the end positions is established by having the working piston overtake the longitudinal groove. On steering back into the other direction, however, such a shutoff device is initially incapable of building up any pressure, since the working piston must first cover a short distance before it can close the longitudinal groove. During this time, no servo force is available, and the driver must bring all the steering force to bear manually.
From French Patent Disclosure FR-A 1 125 999, another control motor with a shutoff device for a working piston is known in which a movable ball and spring unit is inserted into the working piston. A ball seals off a bypass channel around whichever pressure chamber is relieved at the time at a sealing edge of the working piston. By contact with a protruding edge in the two end positions of the servo cylinder, a respective ball is forced away from the associated sealing edge, so that the two pressure chambers enter into communication. With this arrangement, however, only a bypass channel with a very small flow cross section can be opened. Another control motor with a shutoff device is known from U.S. Pat. No. 4,860,646, As disclosed a small control piston protruding to both sides is disposed in the working piston, and by means of the control piston, a relatively narrow bypass channel is opened when the working piston arrives at the end wall of the cylinder.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to adapt the shutoff device in such a way that at the very onset of steering back out of one end position, the servo force is available. The power-assisted steering system is intended to meet this demand with the least possible engineering effort and expense.
This object is attained by the power-assisted steering system discussed hereafter where at least one idler piston with limited displaceability is disposed on the working piston and with its face ends seals off a bypass channel from the respective relieved pressure chamber of the servomotor. There is also a bush with a recessed collar located in the two end positions of the servo cylinder; the collar presses the displaceable idler piston away from its one sealing edge while the other sealing edge is opened, so that the two pressure chambers are made to communicate. The idler piston is embodied annularly and as a result can open a relatively large annular flow cross section. If when steering back in the other direction the working pressure flows into the previously relieved pressure chamber, the idler piston moves toward the other sealing edge and seals off the new pressure chamber; th
REFERENCES:
patent: 2703558 (1955-03-01), Wilcox
patent: 2895455 (1959-07-01), Clowers
patent: 3568570 (1971-03-01), Winders
patent: 3654834 (1972-04-01), Sifri et al.
Ryznic John E.
ZF Friedrichshafen AG
LandOfFree
Pneumatic or hydraulic control motor with a shutoff device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pneumatic or hydraulic control motor with a shutoff device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pneumatic or hydraulic control motor with a shutoff device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-263012