Pressure follow-up control means for servo-steering systems, and the like

Abstract

Abstract The springs associated with the control valves of a servo steering system are prestressed at least in that position of the valves where associated connections are blocked. Further, the springs are arranged supporting themselves in the valve by ends of the springs being arranged facing an activating member common to the valve and permitting the entire spring force to be received by the activating member alone. At least one component of each spring is supported by the valve housing, whereby the bias on the one component increases, based on the activating force limit during a reduction of the activating force, and reaches a maximum when power-flow between the activating member and the associated regulating spring is interrupted. BACKGROUND OF THE INVENTION The instant invention concerns a pressure follow-up control system for servo-steering systems, and the like, having two control valves for the purposes of inter-changeably connecting the working chambers of a hydraulic servo-motor with either a pressure source or an outlet, or outflow, as well as with a mechanical restoring mechanism for return movement of the servo motor, and passing an indication of pressures which exist in the working chambers to the activating member via the reaction areas stressed by these pressures to the control members of the control valves, or reaction areas, and to the reaction members which are in operative connection with the control members, whereby the control valves are operated by means of a common activating member. By this arrangement, the control valves each from the pressure of the working chamber represent pressure regulating valves which are guided, against the force of a regulating spring, with the help of reaction areas, and are of such a type which, below a predetermined pressure, produce a connection from the pressure source to the working chamber, or, when this pressure exceedes the predetermined limit, said pressure-regulating valves will increasingly throttle this connection, and finally block the same, and will open a connection from the working chamber to the outflow when the pressure increases further, whereby the regulating spring supports itself on the common activating member, according to U.S. Pat. application Ser. No. 391,272, filed Aug. 24, 1973 now U.S. Pat. No. 3,927,602. Pressure follow-up control systems of this type serve the purpose of retaining a minimum of pressure in the working chambers of the servo motor without a substantial consumption of pressure. This means that the regulating springs are prestressed at least in the center position of the vehicle wheels. During operation, there will result a gradually-increasing reaction force as a result of a further stressing of a regulating spring, and there will result a pressure in the respective working chamber, which pressure is proportional to this stress. In this manner, there is obtained a certain amount of initial pressure in the working chambers, whereas "jerky" motions in the steering and associated noise-formation are avoided. It is, however, heretofore been impossible to fulfill certain requirements which are placed on modern servo steering systems. One of the most important requirements demands is a power-transmission from the driver of the vehicle to the steering wheels without servo support up to an operating force limit. One considers thereby that in certain operational conditions of a vehicle, for example during fast driving on super highways, or on icy roads, the operational forces, which are not great in any event, would be reduced even more during direct-operating servo-support, and the feeling of driving, which is considered as essential, would be lost. On the other hand, the servo support should start as smoothly as possible after overcoming the operating force limit, and the operating force should remain constant above a second force-limit in the sense of a steering power limitation, or at least should increase only very slightly. In common servo steering systems, in order to obtain these goals, prestressed mechanical transmitting elements are mounted in the powerflow between an activating member and the valve housing which contains the control valves. The relative movements between the activating member and valve housing which are necessary for activating the control valves are able to become effective only after overcoming the prestressing of the transmitting elements, which are conventionally constructed in the form of some type of springs. Up until this point, however, there takes place a purely mechanical power transmission from the driver of the vehicle to the steered wheels. The disadvantage of this arrangement is in that the transmitting elements require an additional mounting space and result in undesirable costs. Additionally, it has not been possible, up to this time, to provide for smooth functioning with acceptable costs, after having overcome the prestress. SUMMARY OF THE INVENTION It has now been found that the desired steering characteristics is obtainable in an unexpectedly simple manner with small additional expenditures and practically with an equal amount of mounting space required by means of a design of the pressure follow-up control system according to the present invention. The structure, or design, consists in that the regulating springs of the pressure-regulating valves are prestressed at least in that position which blocks the connections, whereby these springs, with their free ends, support themselves directly, or via spring plates, etc., above an operating force limit which affects the same, only at the activating member or a section which is fixedly connected therewith. In this manner, the entire spring force is accepted by the activating member alone, while below the operating force limit at least one part of the spring force is supported on the control valve housing, or a part fixedly connected therewith, in such a manner so that this part -- based on the operating power limitation -- increases when the operating power is reduced, and reaches a maximum when the power-flow between the activating member and the regulating spring is interrupted. As already mentioned above, the regulating springs were previously provided with a prestress, or initial stress, and are supported thereby basically on the activator member, so that this, in the center position of the control member, is accepted as movement of rotation, or power comparator, in the balance. A deflection from the center position was possible with a power output starting from zero. A relaxing of one regulator spring complies with the stressing of another, and vise versa. In accordance with the instant invention, the regulator springs are contained in the control valve housing. A control member can only be deflected via the activating member when the prestressing of the corresponding regulator spring has been overcome. The other regulator spring looses then any contact with the activating member and will no longer influence the first regulator spring. Up to the moment when the prestressing is overcome, the system regulator-spring/control-member fluid head under pressure in the reaction chamber is to be seen as a mechanical-hydraulic lever system which enables a direct power transmission from the activating member to the control-valve housing. It is therefore possible to move the servo motor, together with the steered wheels, without servo support. The amount of pressure which is to be either supplied or removed by means of the change in the working chamber is able to flow through the control valves, since the pressure differences which develop in the working chambers will suffice to move the control members, via the reaction areas, into the correct position. Additional advantages and characteristics of the instant invention may be seen from the disclosure and the dependent claims.

Inventors

• 👤 Gunther Strauff

Bibliographic Details