DE19709958B4 - Hydrostatic drive system - Google Patents

Abstract

Hydrostatic drive system with a pump (1) and at least one consumer (8a; 8b), which by means of a directional control valve (5a; 5b) that can be actuated by control signals (17; 18; 19; 20) alternately with the pump (1) and a container ( 3) can be brought into connection in order to control the movement of a positive and a negative load on the consumer, a preload valve (12) being arranged in an outlet line (11) leading to the container (3), which constantly controls the outlet line (11) pressurizes and opens in the direction of the container (3) when a set pressure is exceeded, characterized in that the preload valve (12) in the presence of a control signal (18; 19) of the directional valve (5a; 5b) for controlling the movement of a negative load as a function of the control signal (18; 19) of the directional valve (5a; 5b) can be additionally biased.

Description

The invention relates to a hydrostatic drive system having a pump and at least one consumer, which is alternately engageable by means of a controllable by control valves directional valve with the pump and a container in order to control a positive or negative load on the consumer, in one of the Container leading outlet line a bias valve is arranged, which constantly sets the outlet line under pressure and opens towards the container when a set pressure is exceeded.

Such drive systems found in work machines, such as excavators, use. The directional control valves in response to a control signal to the respective consumer, the movement of a positive or negative loads. A positive load here means a load which counteracts the movement set by means of the directional control valve on the consumer. Accordingly, a negative load represents a load that supports the set by means of the directional control valve on the consumer movement. A hydraulic cylinder that, for example, vertically operates a load is thus subjected to a positive load when lifting the load. When lowering the load, the consumer is subjected to a negative load.

When a negative load is actuated, operating conditions can occur in which pressure fluid flows out of the outlet side of the consumer faster than is provided by the pump on the inlet side of the consumer. This creates a lack of filling on the inlet side, which can lead to cavitation. In order to avoid this lack of filling at the inlet side of the consumer, it is known to arrange a spring-loaded biasing valve in the leading to the container outlet line, with which the pressure in the drain line to a value set at the biasing valve, usually a value of about 3 to 4 bar, is dammed up. The pent-up pressure medium in the outlet line can be made available here to the inlet side of the consumer. For this purpose, it is known to connect the outlet with the connected to the inlet side of the consumer conveyor line by means of a bypass passage in which a direction of the inlet side of the consumer opening check valve is arranged. In a control of the directional control valve and an operating condition in which the load is subjected to a negative load, for example a load to be lowered by a hydraulic cylinder, the pressure fluid flowing from the outlet side of the cylinder into the outlet conduit is thus accumulated by the biasing valve and flows through the bypass passage and the open check valve in the inlet side of the consumer. By this flowing from the outlet side to the inlet side of the consumer Nachladestrom the proportion of the feed stream, which must be supplied by the pump can be reduced.

In a multi-consumer drive system, consumers may have different demand for recharge currents. In an excavator, for example, when lowering the boom, the energy consumption can be reduced if most of the inflowing into the inlet side of the pressure medium flow from the biased in the outlet line return amount is removed and only a portion of the inlet flow must be supplied by the pump. In order to overcome the line resistances in such large Nachladeströmen and to avoid a lack of filling at the inlet side, it is known to provide consumers with a large Nachladestrom more bias valves having a higher biasing amount and are connected in series with the already existing biasing valve.

From the DE 43 18 945 A1 is a hydrostatic drive system with a pump and consumers known, which are controllable by means of one of each control signals operable directional control valve. The directional control valves are actuated by hydraulic control pressures in the corresponding switching positions, which are generated by means of pilot valves n and pending on corresponding control surfaces of the corresponding directional control valve. In one of the directional control valves to a container led outlet line, a pressure compensation valve is arranged, which has a flow position and a throttle position. The pressure compensation valve is relieved at a direction of the flow position control surface to the container. A control surface of the pressure compensating valve acting in the direction of the throttle position is connected to a load pressure signaling line, which communicates with a load pressure port of the corresponding directional valve, at which the load pressure of the corresponding consumer is removed when the directional control valve is actuated.

The present invention is based on the object to provide a drive system available in which the bias of the outlet conduit is variable and which has a lower construction cost.

This object is achieved in that the biasing valve in the presence of a control signal of the directional control valve for the control of the movement of a negative load in response to the control signal of the directional control valve is additionally biased.

The outlet line is set by means of the biasing valve to a value corresponding to a normal bias of about 3 to 4 bar. In a control of the directional control valve by a control signal in which the directional control valve is subjected to a negative load, the bias of the biasing valve is increased. The bias valve can thus be switched in response to a control signal for a negative load to a higher bias voltage. Characterized the bias of the biasing valve is adapted to the respective Nachladestrom of the consumer. In the inlet side of the consumer is thus effectively prevented even in operating conditions in which a large Nachladestrom is required, the emergence of a filling shortage. By switching the biasing valve to a higher bias amount in the control of a consumer with a large Nachladestrom according to the invention, only a single bias valve is necessary, whereby the construction cost of the drive system can be reduced. By eliminating further bias valves can continue to reduce the volume and the manufacturing cost of the drive system.

In one embodiment of the invention, in the presence of a control signal for controlling the movement of a negative load acting in the closing direction of the biasing valve effective surface is additionally acted upon by a pressure. By the additional pressurization of the biasing valve with a pressure, the bias of the biasing valve can be easily increased and thus the outlet conduit can be biased to a higher value.

A further embodiment of the invention provides that in the presence of a control signal for controlling the movement of a negative load, the biasing valve in the closing direction can be acted upon by an additional force. In this way it is also possible to switch the preload valve to a higher bias pressure.

Advantageously, the control signal, which controls the movement of a negative load, acts on a force acting in the closing direction of the biasing force, mechanical component, in particular a piston. To increase the preload pressure, an additional force acting in the closing direction of the preload valve is generated by the piston as a function of the control signal.

It is further advantageous if the control signal is applied to a switching valve which connects in a first switching position with the force acting in the closing direction effective area of the biasing valve or the mechanical component in communication pressure medium line with a container and in a second switching position with a pump. To increase the biasing amount of the biasing valve in this case is acting in the closing direction effective area of the biasing valve or the piston, which generates a force acting in the closing direction of the biasing force, with a to the delivery line of a pump, such as the feed pump of the drive system, connected pressure medium line in combination. The additional loading of the biasing valve is thus controlled by a switching valve which is actuated by means of the control signal of the directional control valve for a negative load. By this pilot control of the biasing valve, the biasing amount of the biasing valve can be increased accordingly even with control signals with a small size.

Conveniently, the switching valve in the direction of the first switching position of the force of a spring and in the direction of the second switching position of the control signal can be acted upon. This easily allows the bias valve to be switched to an increased bias amount in the control of a negative load.

It is particularly useful if the switching valve is designed as a throttling in intermediate positions directional control valve. The pending in the pressure medium line pressure is thus dependent on the size of the control signal of the directional control valve. The bias amount of the bias valve is thus increased according to the size of the control signal of the directional control valve.

With particular advantage, the directional control valve by means of one in a control pressure line pending hydraulic control pressure can be actuated, wherein the control pressure line, in which a control pressure is present to control the movement of a negative load, with the acting in the closing direction effective surface of the biasing valve, the mechanical component or with the switching valve communicates. By the hydraulic control pressure, the biasing valve can be easily switched to a higher pilot pressure by the control pressure line directly acts on the acting in the closing direction effective area of the biasing valve. In addition, the control pressure can act directly on the piston to increase the bias. In addition, the pilot control by means of the switching valve is possible.

In a preferred embodiment of the invention, the biasing valve is designed as a non-return valve opening against a spring force. A check valve is a simple valve element that can be easily installed in the outlet line of the drive system.

With particular advantage, the check valve has a with the spring side in Actively connected piston, which communicates with the control pressure line or with the pressure medium line connected to the switching valve. A piston communicating with the spring side of the check valve provides an easy way to generate a force acting in the closing direction of the biasing valve. The loading of the check valve can be done directly by the hydraulic control pressure of the directional control valve. In addition, the pilot control of the biasing valve by means of the switching valve is possible.

A further preferred embodiment of the invention is that the preload valve is designed as a counter to a spring force in the direction of the container opening pressure relief valve. A pressure relief valve provides a simple and inexpensive valve element with which the outlet line of the drive system can be biased.

In this case, it is particularly advantageous if the effective area of the pressure-limiting valve acting in the closing direction is in communication with the control pressure line or the pressure-medium line connected to the switching valve. The pressure relief valve is thereby acted upon in the closing direction directly by the control pressure of the directional control valve or in a pilot control by means of the switching valve of the pending in the pressure medium line pump pressure.

It is furthermore advantageous if a throttle is arranged in the control pressure line or pressure medium line which is in connection with the effective surface of the pressure relief valve in the closing direction and a branch line connected downstream of the throttle with the outlet line downstream of the pressure relief valve is provided, wherein a further one in the branch line Throttle is arranged. The pressure acting in the closing direction of the pressure relief valve pressure can be adjusted by the throttles. By arranged in the branch throttle the upcoming pressure relief valve pressure in the control pressure line or the pressure medium line is reduced as soon as no control signal is applied to the directional control valve and thus no increased biasing amount of the pressure relief valve is required.

Of particular advantage in a drive system with a plurality of hydraulically actuated directional control valves, the control pressure lines with at least one shuttle valve in operative connection, the output of which is connected to the leading to the biasing valve or the control valve leading to the control pressure line. By the shuttle valves, it is easily possible to connect several control pressure lines to the leading to the reversing valve or the biasing valve control pressure line. The bias of the outlet conduit can thus be easily adapted to the various Nachladeströmen the consumer in a drive system with multiple consumers.

The invention and further details of the invention are explained below with reference to exemplary embodiments illustrated in the schematic figures. Hereby show:

1 a circuit diagram to a drive system according to the invention with a directly acted upon by control pressure bias valve,

2 another embodiment according to the 1 .

3 a drive system with a pilot operated preload valve and

4 another embodiment according to the 3 ,

The 1 shows the circuit diagram to a hydrostatic drive system according to the invention with one of a drive motor 2 driven pump 1 constant or adjustable delivery volume. The pump 1 sucks pressure medium from a container 3 and promotes in a promotion line 4 , From the support line 4 branch conveyor lines 4a and 4b from that to directional valves 5a and 5b to lead. The directional valves 5a and 5b each stand by two lines 6a and 7a respectively. 6b and 7b with a consumer designed in this embodiment as a cylinder 8a and 8b in connection. However, the invention is also applicable to rotary consumers. From the directional valves 8a and 8b each lead two outlet branch lines 9a and 10a respectively. 9b and 10b to an exhaust pipe 11 that with the container 3 communicates. In the outlet line 11 is as a check valve 25 trained preload valve 12 arranged, which is acted upon in the closing direction by the force of a spring and towards the container 3 opens.

The wires 6a and 7a of the directional valve 5a are each by means of a bypass line 13 . 14 to the outlet branch lines 9a and 10a connected. In the bypass lines 13 and 14 is each a check valve 13a . 14a located that towards the lead 7a and 6a opens. In the same way are at the directional control valve 5b the wires 6b and 7b by means of two bypass lines 15 . 16 and check valves 15b . 16b to the outlet branch lines 9b and 10b connected.

The directional valve 5a has two opposing control surfaces 17a . 18a on, to which control pressure lines 17b and 18b to lead. at a control pressure 17 . 18 in the control pressure lines 17b and 18b is the directional valve 5a can be actuated in the appropriate switching position and alternately connects the conveyor branch line 4a and the outlet branch line 9a respectively. 10a each with one of the lines 6a . 7a , The directional valve 5b is by means of control pressures 19 and 20 that are in control pressure lines 19b and 20b queue and control surfaces 19a and 20a apply, actuated. The control pressure lines 18b and 19b are on the input side to a shuttle valve 21 connected to the output of another control pressure line 22 connected. The control pressure line 22 stands with a piston 23 in operative connection, the at the check valve 25 an additional in the closing direction of the check valve 25 produces acting force.

When controlling the directional control valve 5b with one in the control pressure line 19b guided control pressure 19 the directional valve goes 5b in the switching position shown on the left in the figure. In this switching position, pressure medium flows from the delivery line 4 , the conveyor branch line 4b and the directional valve 5b into the pipe 7b and thus in the inlet side of the consumer 8b , The outlet side of the consumer 8b is over the line 6b , the directional valve 5b the outlet branch line 9b with the outlet pipe 11 in connection. The pressure in the outlet pipe 11 will be according to the spring preload of the check valve 25 elevated. That in the outlet pipe 11 and the outlet branch line 10b pent-up pressure fluid flows into the bypass line 15 and the check valve 15a into the pipe 7b and thus in the inlet side of the consumer 7b , If the consumer actuates a negative load, for example a load pulling on the piston rod of the cylinder, a filling deficiency and thus cavitation are prevented by the bias of the return flow at the inlet side of the consumer. As a result of the recharging current flowing from the outlet side to the inlet side, the proportion of the feed flow delivered by the pump can be reduced, which results in a lower energy requirement.

In order to prevent a lack of filling at the inlet side, even with large Nachladeströmen, is the check valve 25 by means of the piston 23 that is above the control pressure line 22 and the shuttle valve 21 from that in the control pressure line 19b pending tax pressure 19 applied, additionally preloaded. When controlling the directional control valve 5b through the control pressure 19 in the control pressure line 19b the piston generates 23 an additional in the closing direction of the biasing valve 12 Acting force. The check valve 25 is thus switched to a higher biasing pressure.

Likewise, the bias pressure of the check valve 12 increased when the directional control valve 5a by a control pressure 18 in the control pressure line 18b is operated in the switching position shown in the figure on the right and controls the movement of a negative load. Such a negative load is, for example, that of the consumer designed as a cylinder 8a operated outriggers of an excavator. In the described switching position of the directional control valve 5a , ie when lowering the boom, can by the additional bias of the outlet 11 a large recharging current from the outlet line 11 into the bypass 14 and the check valve 14a to the line 6a and thus to the inlet side of the consumer 8a stream. This can be done by the pump 1 supplied flow rate can be reduced.

In the 2 is the preload valve 12 as a spring-loaded in the closed position pressure relief valve 30 designed. The spring side of the pressure relief valve 30 is to the control pressure line 22 connected and thus of the control pressure in the control pressure line 22 additionally acted upon. In the control pressure line 22 is a throttle 31 arranged. Downstream of the throttle 31 is the control pressure line 22 by means of a branch line 32 and one in the branch line 32 arranged throttle 33 to the outlet pipe 11 downstream of the biasing valve 12 connected. When controlling the directional control valve 5a by a control pressure 18 in the control pressure line 18b or the directional control valve 5b by a control pressure 19 in the control pressure line 19b is the respective control pressure in the control pressure line 18b respectively. 19b over the shuttle valve 21 and the control pressure line 22 on the spring side of the pressure relief valve 30 at. The additional preload of the pressure relief valve 30 thus takes place by the control pressure of the controlled directional control valve 5a . 6a , The height of the control pressure and thus the additional bias of the pressure relief valve 30 can through the throttle 31 to be influenced. With a withdrawal of the control pressure 18 respectively. 19 is the control pressure in the control pressure line 22 over the throttle 33 and the branch line 32 degraded, so that the normal bias on the pressure relief valve 30 is set.

The 3 and 4 show a bias valve by means of the in the control pressure line 22 upcoming tax pressure 18 respectively. 19 is vorsteubar. That according to the 3 as a check valve 25 trained preload valve 12 has a piston 23 on, to a pressure medium line 40 connected. In the pressure medium line 40 is designed as a directional control valve switching valve 41 arranged, in a first switching position 41a the pressure medium line 40 with one to the container 3 leading line 42 combines. In a second switching position 41b is the pressure medium line 40 to the support line 43 a pump 44 , For example, the feed pump of the hydrostatic drive system, connectable. However, it is also possible the delivery line 43 to the support line 4 the pump 1 to join. The switching valve 41 is in the direction of the first switching position of a spring and in the direction of the second switching position of the in the control pressure line 22 pending tax pressure 18 respectively. 19 acted upon. When operating the directional control valves 5a . 5b by control pressure 17 . 20 in the control pressure lines 17b or 20b is the switching valve 41 in the switching position shown. The pressure in the drain line 11 will be according to the spring preload of the preload valve 12 elevated. Once a tax pressure 18 respectively. 19 in the control pressure lines 18b or 19b is present, the control pressure is planted via the shuttle valve 21 to the control pressure line 22 continues and acts on the switching valve 41 in the switching position 41b , The pressure medium line 40 is in this switching position to the delivery line 43 the pump 44 connected, causing the piston 23 the check valve 25 by the delivery pressure of the pump 44 is acted upon and one in the closing direction of the check valve 25 produces acting force.

In one embodiment of the biasing valve 12 as a pressure relief valve 30 according to the 4 is in the pressure medium line 40 a throttle 45 intended. Downstream of the throttle branches one with the drain line 11 related branch line 46 off, in which another throttle 47 is arranged. The in the second switching position 41b the changeover valve 41 at the acting in the closing direction spring side of the pressure relief valve 30 Pending delivery pressure of the pump 44 can through the chokes 45 and 46 be matched.

Claims (14)

Hydrostatic drive system with a pump ( 1 ) and at least one consumer ( 8a ; 8b ), which by means of one of control signals ( 17 ; 18 ; 19 ; 20 ) operable directional valve ( 5a ; 5b ) alternately with the pump ( 1 ) and a container ( 3 ) in order to control the movement of a positive and a negative load on the consumer, wherein in one to the container ( 3 ) leading outlet conduit ( 11 ) a bias valve ( 12 ) is arranged, which the outlet line ( 11 ) constantly pressurizes and towards the container ( 3 ) opens when a set pressure is exceeded, characterized in that the biasing valve ( 12 ) in the presence of a control signal ( 18 ; 19 ) of the directional valve ( 5a ; 5b ) for controlling the movement of a negative load as a function of the control signal ( 18 ; 19 ) of the directional valve ( 5a ; 5b ) is additionally prestressed. Hydrostatic drive system according to claim 1, characterized in that in the presence of a control signal ( 18 ; 19 ) for controlling the movement of a negative load in the closing direction of the biasing valve ( 12 ) acting effective surface is additionally acted upon by a pressure. Hydrostatic drive system according to claim 1, characterized in that in the presence of a control signal ( 18 ; 19 ) for controlling the movement of a negative load the preload valve ( 12 ) can be acted upon in the closing direction by an additional force. Hydrostatic drive system according to claim 3, characterized in that the control signal ( 18 ; 19 ), which controls the movement of a negative load, a in the closing direction of the biasing valve ( 12 ) acting force generating mechanical component ( 23 ). Hydrostatic drive system according to one of Claims 1 to 4, characterized in that the control signal ( 18 ; 19 ) at a switching valve ( 41 ) is present, which in a first switching position ( 41a ) one with the acting in the closing direction effective surface of the biasing valve ( 12 ) or the mechanical component ( 23 ) associated pressure medium line ( 40 ) with the container ( 3 ) and in a second switching position ( 41b ) connects to a pump. Hydrostatic drive system according to claim 5, characterized in that the switching valve ( 41 ) in the direction of the first switching position ( 41a ) of the force of a spring and in the direction of the second switching position ( 41b ) from the control signal ( 18 ; 19 ) can be acted upon. Hydrostatic drive system according to claim 5 or 6, characterized in that the switching valve ( 41 ) is designed as a throttling in intermediate positions switching valve. Hydrostatic drive system according to one of claims 1 to 7, characterized in that the directional control valve ( 5a ; 5b ) by means of one in each case in a control pressure line ( 17b . 18b ; 19b . 20b ) pending hydraulic control pressure ( 17 . 18 ; 19 . 20 ) is controllable, wherein the control pressure line ( 18b ; 19b ), in which a control pressure ( 18 ; 19 ) is present for controlling the movement of a negative load, with the acting in the closing direction effective area of the biasing valve ( 12 ), the mechanical component or with the switching valve ( 41 ). Hydrostatic drive system according to one of claims 1 to 8, characterized in that the biasing valve ( 12 ) as a non-spring opening check valve ( 25 ) is trained. Hydrostatic drive system according to claim 9, characterized in that the check valve ( 25 ) a piston operatively connected to the spring side ( 23 ) connected to the control pressure line ( 18b ; 19b ) of the directional valve or with the to the switching valve ( 41 ) connected pressure medium line ( 40 ). Hydrostatic drive system according to one of claims 1 to 8, characterized in that the biasing valve ( 12 ) as a counter to a spring force towards the container ( 3 ) opening pressure relief valve ( 30 ) is trained. Hydrostatic drive system according to claim 11, characterized in that the effective area of the pressure-limiting valve acting in the closing direction ( 30 ) with the control pressure line ( 18b ; 19b ) or to the changeover valve ( 41 ) connected pressure medium line ( 40 ). Hydrostatic drive system according to claim 11 or 12, characterized in that, in the effective area of the pressure-limiting valve acting in the closing direction ( 30 ) associated control pressure line ( 18b ; 19b ) or pressure medium line ( 40 ) a throttle ( 31 ; 45 ) and downstream of the throttle ( 31 ; 45 ) one with the outlet ( 11 ) downstream of the pressure relief valve ( 30 ) associated branch line ( 32 ; 46 ) is provided, wherein in the branch line ( 32 ; 36 ) another throttle ( 33 ; 47 ) is arranged. Hydrostatic drive system according to one of the preceding claims, wherein a plurality of hydraulically actuable directional control valves ( 5a ; 5b ) are provided, characterized in that the control pressure lines ( 18b ; 19b ) with at least one shuttle valve ( 21 ) are in operative connection, whose output is connected to a to the biasing valve ( 12 ) or to the reversing valve ( 40 ) leading control pressure line ( 22 ) connected.

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