Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1998-02-26
2000-07-11
Ryznic, John E.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
92136, B62D 506
Patent
active
060856335
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for the reduction of servo pressure in steering gear, in accordance with the preamble of claim 1.
STATE OF THE ART
In connection with steering mechanisms for motor vehicles, servo mechanisms are often utilised in order to supply power to the steering mechanism when turning the steering wheel of the vehicle. A commonly occurring steering gear comprises an input shaft on which the steering wheel is arranged, whereby the shaft transfers the movements of the steering wheel to a pinion which in turn is connected to a rack. The movements of the rack are in turn transferred to the wheels of the vehicle. Such a known steering gear may be complemented by a servo mechanism which comprises a hydraulic cylinder with a piston which is arranged on the rack. The servo mechanism also comprises a servo pump and a valve assembly. When turning the steering wheel of the vehicle, hydraulic oil is fed to the cylinder by means of the valve assembly, whereby the piston and consequently also the rack is influenced in a direction corresponding to the turning direction of the steering wheel. In this manner, power is supplied to the rack when turning the steering wheel.
In the previously known device, the flow of hydraulic oil from the servo pump to the steering gear is always constant. When the servo function comes into force, the servo pressure increases since the flow through the steering gear is throttled by means of the above mentioned valve assembly. This is particularly disadvantageous when the steering gear reaches one of its end positions, e.g. when the steering wheel is turned to the left or the right end position and causes problems in the form of noise and vibrations. Furthermore, the engine of the vehicle is heavily loaded by the servo pump, which entails that the idling speed of the vehicle cannot always be kept constant. Finally, the hydraulic oil is heated up at an abnormal rate, which may cause damage to the servo pump.
A previously known device which aims at solving these problems is known from U.S. Pat. No. 4,354,422. The device comprises a pivoting cage which may be turned in relation to an input shaft which is connected to the steering wheel of the vehicle. The cage is connected to a valve which can be adjusted so that oil is supplied for the displacement of a rack when the input shaft is turned. When the rack reaches one of its end positions, the cage will be influenced by a cam member and be turned back to a neutral position, independent of the force on the input shaft. This entails that the valve returns to a neutral position so that a connection between an oil supply line and an oil tank is short-circuited. In this way, the power from the servo pump is reduced.
The construction of this previously known device is, however, rather complicated, which results in high manufacturing costs and may also cause problems. Furthermore, it cannot be utilised in connection with all types of conventional steering gears.
SUMMARY OF THE INVENTION
A main object of the present invention is to solve the above mentioned problems and to provide an improved device which reduces the load derived from a servo mechanism of a steering gear when the steering wheel has been turned to a predetermined position and which may be utilised in connection with conventional steering gear. This object is achieved by a device of the type mentioned in the introduction, the characterizing features of which are evident from the characterizing portion of claim 1.
Accordingly, the invention comprises a special valve member, abutting directly against the rack and extending through a connection channel between the supply and return lines for servo oil, and the rack is provided with a portion having a modified shape for interaction with the valve member, whereby the valve member in an effective way may be displaced so that the supply and the return lines are short-circuited when the rack is in a predetermined position. In this manner, a simple but yet effective valve construction is obtained
REFERENCES:
patent: 1056600 (1913-03-01), Spohrer
patent: 2532342 (1950-12-01), Sloane
patent: 3407598 (1968-10-01), Yokota
patent: 4354422 (1982-10-01), Nishikawa et al.
patent: 4770205 (1988-09-01), Jones et al.
patent: 5385218 (1995-01-01), Migliori
patent: 5839527 (1998-11-01), Elser et al.
AB Volvo
Ryznic John E.
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