Motor vehicles – Steering gear – With fluid power assist
Patent
1995-08-04
1996-06-25
Caby, Richard M.
Motor vehicles
Steering gear
With fluid power assist
180428, 180441, 180421, 1376275, B62D 522
Patent
active
055291376
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a servo steering unit, especially for motor vehicles. The servo steering unit includes a steering valve which has two inlet seat valves and two outlet seat valves, the closing members of which are movable by actuating tappets depending on a rotation of a steering spindle. The closing members of the inlet seat valve are here actuatable in a closing direction by the force of pressure springs, so that the inlet seat valves are closed in the neutral position of the steering valve. The outlet seat valves are open in the neutral position of the steering valves. The inlet seat valves do not open until the respective outlet seat valve closes.
BACKGROUND OF THE INVENTION
Such a servo steering unit has been disclosed in the older German patent application P 41 26 020.1. In said servo steering unit, the spring-loaded closing member of the inlet seat valve can be released by means of a stop disc. This prevents a stronger actuating force from being needed for opening the inlet seat valve than for opening the outlet seat valve.
To obtain the effect described, a very thorough coordination of two actuation spaces is required. A first space between an actuating tappet and the stop disc must here be smaller than a second space between the closing surface of a closing member of the outlet seat valve and a valve seat of the outlet seat valve situated on the closing member of the inlet seat valve. Since the actuation paths of the seat valves are in the range of a few tenths of a millimeter, the coordination is very difficult. In addition, in said servo steering unit only one centering spring is active at the beginning of the adjustment of the steering valve away from the neutral position. The pre-load force of the pressure spring acting upon the closing member of the inlet seat valve will increase only after overcoming the first space and the actuating tappet abuts on the stop disc. This result is contrary to the requirement generally existing in regard to steering valves of an increased stiffness of the steering in the central position.
SUMMARY OF THE INVENTION
The invention is based on the problem of improving a servo steering unit in the sense of preventing the above described disadvantages while maintaining the advantages. In particular, the coordination of the actuation sequence of the inlet and outlet seat valves is to be made easier. The intensification of the centering force as the adjustment of the steering valve increases is likewise to be prevented.
This problem is solved by the servo steering unit according to the present invention. The solution specially results from the fact that the pressure springs of both inlet seat valves rest on one side on the actuating tappets and on the other constantly on the closing members. Besides, the pressure springs must be designed in a manner such that, in the neutral position of the steering valve, they exert a closing force upon the closing members and, when the steering valve is adjusted away from its neutral position, only one pressure spring abuts without applying force on the closing member as soon as the associated outlet seat valve is closed.
Convenient and advantageous embodiments of the invention are indicated in the sub-claims. But the invention is not limited to the combination of features of the claims. Other logical possible combinations result for the expert from the claims and individual features of the claims depending on the existing problems.
For a specially good coordination it is advantageous to use pressure springs having very high spring ratios. This can be obtained in a specially favorable manner when the pressure springs are designed as plate springs. If the actuating tappet is made of two parts, then the part on which the plate spring abuts can be pressed into the other part until reaching the desired pre-load of the plate spring between the actuating tappet and the closing member of the inlet seat valve. The required tolerances can be easily obtained thereby.
BRIEF DESCRIPTION OF THE DRAWINGS
The i
REFERENCES:
patent: 3750836 (1973-08-01), Kristof
patent: 4607717 (1986-08-01), Nakayama
Caby Richard M.
Johnson Victor E.
ZF Friedrichshafen AG
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