DE4422553C2 - Servo valve arrangement - Google Patents

Description

The invention relates to a servo valve arrangement with high pressure, low pressure and motor connection and one between High pressure and motor connection arranged, as a seat valve trained pressure control valve and one between engine and low pressure connection arranged return control valve, the pressure control valve being closed normally and the Return control valve is open normally and both valves axially displaceable and arranged coaxially with each other Control parts have a common operation organ, especially pestle, closing the return control valve and opening of the pressure control valve actuated are cash.

A corresponding servo valve is known from DE 37 28 920 A1 arrangement known in principle. According to this document the valve arrangement controls the servo support Vehicle brake. The print tax and the return tax Valve are according to DE 37 28 920 A1 each as seat valves formed, the closure body of the pressure control  tiles with a valve seat arranged on the housing side interacts while the pressure control valve geson derte closure body of the return control valve one attached to the closure body of the pressure control valve ordered seat interacts. When the brake is applied The closure body of the return control is pedals tiles in the direction of the closure body of the pressure control valves and then closes one Locking body of the pressure control valve penetrating Axial bore, which is usually a piston work space a brake actuator with a relatively depressurized Hydraulic reservoir connects. As soon as after closing the Return control valve of the closure body of the pressure control then lifts the valve from its seat Piston working space with a pressure source or a pressure memory connected.

In the hydraulic systems currently used in motor vehicles The associated servo valve arrangement becomes power steering practically constantly flows through hydraulic medium, namely even if - such as B. when driving straight ahead - no servo power is required. The servo valve In principle, order consists of two parallel chokes stretch that between a pressure port and a Low pressure connection are arranged and two each oppositely controlled chokes arranged in series grasp, between which branches a motor connection. Depending on the direction and size of one on the steering  Actuating torque to be applied to the handwheel is the input-side throttle of a throttle section increasingly opened and at the same time the output choke of this choke stretch increasingly throttled while throttling the whose throttle section in the opposite direction ge be controlled. This way, between the engine connections of the two throttle sections one by direction and size controllable pressure difference, so that a corresponding servo motor a controllable servo force in one direction or another. In operation stands where no servo power is required all throttles in a middle position so that both throttles are evenly flowed through and between the Motor connections are equal in pressure.

Because with these known power steering systems a constant Hydraulic flow must be maintained constantly Performance needed.

With a view to reducing the power requirement from motor vehicles it is basically known to servo to provide steering with a so-called closed center, d. H. as long as no servo power is needed, the servo has motor has no connection to the pressure source, rather it is the servo motor in this state only with the low pressure connection or hydraulic reservoir connected to a to allow passive movement of the servo motor.  

In this context, power steering has been tried using the servo valve arrangement specified at the beginning realizations. In essence, you must then between a pressure source and an accumulator and a hydraulic likreservoir two servo valve arrangements of the input specified type can be arranged parallel to each other. Depending on the Be to be applied to the steering wheel The moment of actuation becomes the pressure control valve of one or other servo valve arrangement more or less far opened so that the motor connection of one or another servo valve arrangement with controllable throttle resistor was connected to the pressure source or the pressure accumulator and at the same time shut off from the low pressure connection becomes. This creates the between the motor connections two servo valve arrangements connected servo one Servo power in one direction or another.

The object of the invention is now in a servo valve order of the type specified is a particularly good one To ensure control behavior with a simple construction.

This object is achieved in that the Control parts of pressure control valve and return control valve are arranged as parts of a common valve piston and the return control valve in the manner of a slide valve with interacting control edges is formed.

The invention ensures that the closed state  of the pressure control valve with an exactly reproducible Position of the associated control part is connected and an adjustment of the control section immediately with one controlled opening of the pressure control valve. Otherwise, seat-controlled valves are characterized by this that they close practically leak-free.

It is preferably provided that the return control valve with the pressure control valve closed, only one throttle rare connection between motor connection and low pressure in the end. On the one hand, this ensures that the return control valve when opening the pressure control valve closes quickly. On the other hand, the return control valve in the open state in the sense of a damping of Movements of the servomotor act.

The invention will be described in more detail below with the aid of the drawing explained on the basis of a particularly advantageous embodiment form is described.

The only figure shows an axial sectional view of a servo valve assembly according to the invention.

According to the drawing, an essentially cylindrical valve cartridge 1 has an axial bore 3 which is closed at one end by a screwed-in base part 2 and which is expanded and narrowed several times in the form of a ring step. Between two sections with an enlarged diameter, a section with a reduced diameter is formed to form two ring edges 4 and 5 , the section of which is smaller than the diameter of the area of the axial bore 3 adjoining the base part 2 . Radial bores 6 are arranged axially above the ring edge 4 in the valve cartridge 1 and communicate with a pressure connection P, not shown. Axial between the ring edges 4 and 5 are radial bores 7 , which communicate with a motor connection P1 or P2 (not shown). The axially below the ring edge 5 remaining area of the axial bore 3 communicates via the lower end opening of the valve cartridge 1 with a low pressure connection T.

A valve piston 8 is slidably guided within the axial bore 3 of the valve cartridge 1 and is pushed into the normal position shown, in which the valve piston 8 , by means of a helical compression spring 9 , which is clamped between the base part 2 and the upper end face of the valve piston 8 in the drawing with a cone section 10 formed thereon sits tightly on the ring edge 4 . With its upper section adjoining the conical section 10 , the valve piston 8 is provided with a sealing ring 11 in the upper part of the axial bore 3 above the radial bores 6 , so that the part of the axial bore 3 receiving the helical compression spring 9 is shut off from the radial bores 6 of the pressure port P. remains.

At the bottom, a tapered area of the valve piston 8 connects to the cone section 10 , so that an annular space remains in the area of the radial bores 7 of the motor connection P1 or P2 within the valve cartridge 1 , which is directed downward through an annular edge 12 formed on the valve piston 8 is limited, which cooperates with the ring edge 5 of the valve cartridge 1 , as shown below. The section of the valve piston 8 adjoining the ring edge 12 downwards is dimensioned such that it can be inserted into the section of the Axialboh 3 between the ring edges 4 and 5 . Accordingly, an annular space communicating with the low-pressure connection T remains between the valve piston 8 and the wall of the lower section of the axial bore 3 .

In addition, the valve piston 8 has an axial bore communicating with the low pressure connection T, so that the space between the valve piston 8 and the base part 2 is constantly at low pressure.

In the normal position of the valve piston 8 shown , a narrow annular gap remains between the ring edges 5 and 12 , via which the motor connection P1 or P2 constantly communicates with the low-pressure connection T. If the valve piston 8 is raised by pressure on its tappet-like lower end against the force of the helical compression spring 9 , the said annular gap is increasingly narrowed and subsequently closed as soon as the ring edge 12 of the valve piston 8 is moved in the upward direction over the ring edge 5 of the axial bore 3 . At the same time, the cone section 10 of the valve piston 8 rises from the ring edge 4 . The motor connection P1 or P2 is thus disconnected from the low pressure connection T on the one hand and connected to the pressure connection P on the other hand. Accordingly, pressure medium then flows to the servo motor, not shown. As soon as the valve piston 8 again passes into the normal position shown, the motor connection P1 or P2 is separated from the pressure connection P and in turn brought into connection with the low pressure connection T.

Corresponding to the stroke movements of the valve piston 8 , 8 hydraulic medium is introduced via an axial bore 13 of the valve piston 8 from the low-pressure connection T into the space between the base part 2 and the valve piston 8 or displaced from this space. If the axial bore 13 , as shown, is designed as a throttle bore with a small diameter, the hydraulic medium flowing through the axial bore 13 must overcome a certain throttle resistance, so that the stroke movements of the valve piston 8 are hydraulically damped.

In the case of power steering of a motor vehicle, two valve cartridges 1 are arranged parallel to one another, depending on the direction of the manually applied torque of the valve piston 8 of one or the other valve cartridge 1 is lifted out of its normal position, so that either the port P1 or the port P2 of the servo motor disconnected from the low pressure port T and connected to the pressure port P and the servo motor generates a servo force in one direction or the other.

The servo valve arrangement described is not suitable only for power steering of motor vehicles.

For example, it is also possible to use the one described Servo valve arrangement the pressure in a (single acting) Control displacer or piston-cylinder unit so that analogous to the actuation acting on the servo valve due to the displacement or piston-cylinder unit (comparatively high) force is generated.

The servo valve and the displacement or Piston-cylinder unit for a so-called linear ver be more summarized.

Otherwise, with the servo valve according to the invention regulation also controls the braking force of a vehicle brake if this is designed as an accumulator brake, in which the pressure of a pressure accumulator is controllable on as a displacement unit formed actuator Brake is conducted.

Claims (3)

1. servo valve arrangement with high-pressure, low-pressure and motor connection and a pressure control valve arranged between the high-pressure and motor connection, designed as a seat valve, and a return-control valve arranged between the motor and low-pressure connection, the pressure control valve being normally closed and the return valve being normally opened and Both valves have axially displaceable and axially displaceable control parts which can be actuated via a common actuating organ, in particular tappet, by closing the return control valve and opening the pressure control valve, characterized in that the control parts of the pressure control valve ( 4 , 10 ) and return flow control valve ( 5 , 12 ) are arranged as parts of a common valve piston ( 8 ) and the return control valve ( 5 , 12 ) is designed in the manner of a slide valve with interacting control edges ( 5 , 12 ). 2. Servo valve arrangement according to claim 1, characterized in that the return control valve ( 5 , 12 ) is throttled normally GE. 3. Servo valve arrangement according to claim 1 or 2, characterized in that the lifting movement of the valve piston ( 8 ) is hydraulically damped.