CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from German Application No. 10 2019 205 640.7 filed Apr. 17, 2019, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a proportional hydraulic valve with a valve housing, an actuating device and a valve piston axially movable in a piston chamber of the valve housing.

BACKGROUND OF THE INVENTION

In such valves, the valve housing has at least one pressure connection and at least one connection port. The valve piston blocks a flow path between the pressure connection and the connection port or proportionally releases this flow path by the valve piston moving between a closed position and an open position in the piston chamber in proportion to an actuating force generated by the actuating device. The connection port is often a tank port or return connection. Such a proportional hydraulic valve is known from DE 10 2005 022 693 A1, for example.

The proportional hydraulic valves known from the prior art regularly fulfil the intended function very well, for example as proportional pressure limiting valves. Pressure limiting valves have the task of limiting the system pressure to a certain nominal pressure. As soon as the nominal pressure is reached, the pressure limiting valve responds and the excess volume flow is directed from the pressure connection to the connection port or tank connection respectively. However, especially at high nominal pressures of, for example, more than 300 bar, an increased back pressure at the valve piston can occur. In this context, back pressure is the pressure difference between the pressure connection and the connection port or tank connection respectively.

To overcome this problem, the proportional hydraulic valves designed as poppet valves have smaller seats in order to obtain a smaller pressurized area. The disadvantage of this is that the volume flow also decreases, i.e. relatively little volume can flow in the open position of the valve.

SUMMARY OF THE INVENTION

Hence, it is the object of the present invention is to provide a proportional hydraulic valve at which a low back pressure can be achieved, especially at high nominal pressures, while at the same time a sufficient volume flow can flow between the pressure connection and the connection port or tank connection respectively.

The problem is solved with a proportional hydraulic valve as described herein. Preferable further embodiments are also described.

The proportional hydraulic valve according to the invention is characterized over the proportional hydraulic valves known from the state of the art in that the valve piston has a first spool area and a second spool area, and the valve piston has a circumferential recess after the first spool area and before the second spool area in the axial direction, and the recess together with the piston chamber forms a pressure chamber and the pressure connection opens into the pressure chamber. Furthermore, the proportional hydraulic valve according to the invention is characterized in that a first diameter of the first spool area is larger than a second diameter of the second spool area. The axial direction in the sense of the invention means the direction from the actuating device to the valve piston.

Due to the configuration of the valve piston as a spool-like valve piston in accordance with the invention, it can be achieved that the back pressure is relatively low, although a relatively large flow cross-section is available. This is because the effective or pressurized differential area is formed by the difference between the area of the first spool area as a function of the first diameter and the area of the second spool area as a function of the second diameter. Depending on the nominal pressure and the application for which the proportional hydraulic valve is to be used, a sufficiently large flow cross-section and a correspondingly small differential area can thus be selected so that overall a low back pressure is achieved despite a high maximum volume flow at particularly high nominal pressures.

Preferably the valve piston has a closing element in front of the first spool area in the axial direction and the valve housing preferably has a valve seat, whereby the closing element rests on the valve seat when the valve piston is in the closed position. The closing element may in particular be a valve cone. This provides particularly good sealing in the closed position and largely prevents leakage oil flow from the pressure connection to the connection port or tank connection respectively.

Preferably, the piston chamber has a first annular groove in front of the pressure connection in the axial direction, the connection port opening into the first annular groove and the valve seat being formed on a circumferential edge of the first annular groove, the first spool area positively covering the valve seat on a lift-off movement path. This increases operational reliability, since during a lifting movement of the valve piston from the valve seat from the closed position towards the open position, initially only a leakage oil flow from the pressure chamber to the first annular groove flows. Only when the valve piston has finished the lift-off movement distance a larger cross-section is released, so that a larger volume flow can flow from the pressure chamber to the first annular groove.

Preferably, the valve piston has at least one cut portion extending axially from the recess into the first spool area, the at least one cut portion being radially only partially circumferential. In other words, the at least one cut portion is not radially circumferential. Through the cut portion, the flow cross-section can be increased so that a larger volume flow can flow from the pressure connection to the connection port or tank connection respectively.

Preferably, the at least one cut portion has at least partially a cross-sectional area that increases in the axial direction. This allows the flow cross-section to increase gradually rather than abruptly. Overall, this results in a better response behaviour of the proportional hydraulic valve.

Preferably, the valve piston has two or more cut portions that are evenly distributed around the circumference. By providing two or more regularly arranged cut portions, it can be prevented that the valve piston is subjected to a force on one side and therefore runs eccentrically.

Preferably, the piston chamber has a damping chamber at one axial end, wherein the valve piston has a circumferential damping groove in fluid connection with the connection port and wherein a damping gap extends axially from the damping groove between the valve piston and the piston chamber, the damping gap being in fluid connection with the damping chamber. This dampens the movement of the valve piston in the piston chamber, which leads overall to a reduction or suppression of undesirable vibrations. The damping gap must be selected according to the desired damping.

Preferably, the second spool area is guided in a guide section of the piston chamber, the damping chamber being arranged in the axial direction after the guide section and the damping groove being formed on the second spool area so that the damping gap extends in the axial direction. This allows a particularly simple manufacture of the valve housing as well as a simplified assembly of the proportional hydraulic valve.

Preferably, the valve piston has an axial blind bore, a first bore passing radially through the valve piston and a second bore passing radially through the valve piston, the first bore being in fluid connection with the connection port and the second bore being in fluid connection with the damping groove. Consequently, the damping is arranged in the low-pressure area via the damping gap. When the valve piston moves from the closed position (or an intermediate position) in the direction of the open position, hydraulic oil is sucked into the damping chamber from the connection port or tank connection respectively via the first bore, the blind bore, the second bore and the damping gap. Accordingly, when moving from the open position (or an intermediate position) in the direction of the closed position, hydraulic oil is pressed from the damping chamber into the connection port or tank connection respectively via the first bore, the blind bore, the second bore and the damping gap. This allows a simple damping of the movement of the valve piston.

Preferably, at least one circumferential second annular groove is disposed on the second spool area. The annular groove suppresses a leakage oil flow from the pressure chamber via the second spool area. Of course, two or more second annular grooves can also be provided, whereby care must be taken that the axial length of the second annular grooves does not lead to eccentric displacement of the valve piston.

The proportional hydraulic valve is preferably a proportional pressure limiting valve. Depending on which actuating device is used, a proportional pressure limiting valve with a falling or rising characteristic curve can be realized. Alternatively, the proportional hydraulic valve can be a pilot-operated check valve.

The problem is also solved with a hydraulic system with a proportional hydraulic valve according to the invention. For example, the proportional hydraulic valve according to the invention can be used in a hydraulic system for pump control or for pressure limitation in a LS system.

