FR2862108A1 - Hydrostatic driving system for e.g. transport truck, has valve with reservoir outlet for each of two control pressure chambers of piston, where pressure signal opposed to control pressure for cutting-off pressure is generated in each outlet - Google Patents

Abstract

The system has an actuating piston (5) with two control pressure chambers (5a, 5b) connected by an actuating valve (6) to a control pressure source and evacuated towards a reservoir (18). The valve includes a reservoir outlet for each control pressure chamber. A pressure signal opposed to the control pressure for cutting-off the pressure is generated in each reservoir outlet.

Description

Field of the invention

  The present invention relates to a hydrostatic machine, in particular a variable-speed axial piston machine operating in a closed circuit, the flow being regulated by means of a control system comprising an actuating piston having a first pressure chamber of control and a second control pressure chamber, which can be connected by an actuating valve to a control pressure source or discharged to a reservoir, a pressure cutoff function being provided.

  STATE OF THE ART Such variable volume flow-rate hydrostatic machines operating in a closed circuit are used as pumps or motors, for example for driving mobile machines or driving rotation of cranes. During the acceleration phase, when the machine reaches a maximum pressure, the pressure cut-off function controls the discharge flow in the direction of a reduction to avoid an implementation of the overpressure safety of the closed circuit constituted for example by a pressure limiting valve. This prevents the hydraulic fluid under pressure from leaving the circuit to escape by the overpressure safety and thus produce a loss of power and an unnecessary temperature rise of the hydraulic fluid.

  In the case of machines of the state of the art functioning as pumps, a pilot actuating valve, for example an actuating valve controlled upstream by means of a sensor piston receiving an upstream pressure, provides in a known manner as a pressure cut-off function, a valve controlling the upstream pressure, for example a pressure limiting valve which receives the discharge pressure of the pump. When the pressure limiting valve is operated, the upstream control pressure of the upstream control valve is reduced so that the pump is adjusted in the direction of a reduction in its flow rate. Such a pressure cutoff function however only works in the acceleration phase but does not allow to limit the brake pressure applied to the machine during the braking phase. The installation of the pressure limiting valve to cut off the pressure in the upstream control circuit of the actuating piston and thus inside the control channel of the input signal to have the desired reaction of the installation the discharge volume controller, for example an inclined plate, of the pump, produced due to the disturbing quantities existing, for example the friction of the sensor piston, a tendency to an unstable embodiment. In addition, the mounting of the pressure cut-off function in the upstream control circuit results in significant dead times for the response of the pressure limiting valve to the desired reaction of the volume flow control system. when the pressure limiting valve is loaded, it must go through the signal path formed by the sensor piston and the actuating valve.

  Document DE 100 37 195 A1 corresponding to the type defined above describes a machine having a function of breaking the pressure. For this pressure cut-off function, the output of the actuating valve towards the reservoir generates a pressure by means of the pressure relief valve of the circuit and this pressure opposes the actuating pressure applied to the piston of the circuit. actuation. This allows, in the acceleration phase and braking phase, to ensure a pressure cut by appropriate control of the machine. But this assembly can generate vibrations resulting in unstable control behavior.

  OBJECT OF THE INVENTION The object of the present invention is to develop a machine having a pressure cutoff function having a greater stability of regulation during the acceleration phase and during the braking phase.

  DESCRIPTION AND ADVANTAGE OF THE INVENTION For this purpose, the invention relates to a hydrostatic machine of the type defined above, characterized in that for each control pressure chamber of the actuating piston, the actuating valve comprises an output of tank and in each tank outlet can be created a pressure signal opposing the actuating pressure to cut the pressure.

  Thus, according to the invention, the actuating valve comprises a separate tank outlet for each control pressure chamber of the actuating piston; this output allows each time to establish a pressure signal to cut the pressure. This signal opposes the actuating pressure applied against the actuating piston and moves the flow control device against the actuating pressure.

  For this pressure cutoff, the intervention of the signal of the pressure cutoff is made according to the shortest path for the pressure signal opposing the actuating pressure, which avoids disturbing quantities such as friction at the level of pressure. sensor piston and minimizes downtime with the short signal path.

  Due to the separate tank outlet for the actuating valve, it is possible to simply transmit the pressure signal from the pressure cutoff function to the actual tank side of the actuating piston. Thus, in the acceleration phase, it will realize a pressure cut and in braking phase limiting the maximum brake pressure by achieving a stable control behavior.

  According to a preferred embodiment of the invention, an upstream control valve provided respectively for creating the pressure signal receives as input the pressure applied to the machine and cooperates with a throttling element installed in the tank outlet. An upstream control valve makes it possible to simply protect the delivery pressure applied to the machine during the acceleration phase or the brake pressure applied to the machine during the braking phase, and when the upstream control valve is requested, it is possible to pick up a volume flow of the corresponding pressure line of the closed circuit so that at the throttling installation there will be a rise in pressure in the corresponding tank outlet of the actuating valve to urge the actuating piston in the opposite direction to the actuating pressure. Thus, with reduced manufacturing cost and simple components, the pressure signal is generated for the pressure cut-off function.

  An actuating valve with separate tank outlets for the actuating piston operating pressure chambers is readily operable in that the actuating valve has a first actuating pressure connection connected to the first chamber. operating pressure of the actuating piston, a second actuating pressure connection connected to the second operating piston control pressure chamber, a control pressure connection connected to a control pressure source and a first tank connection connected to a tank and a second tank connection connected to the tank, in a first switching position of the operating valve, the first operating pressure connection is connected to the control pressure connection and the second connection is connected to the control pressure connection. operating pressure is connected to the second tank connection, the first tank connection being hit and in a second switching position of the actuating valve, the second actuating pressure connection is connected to the first control pressure connection and the first actuating pressure connection is connected to the first reservoir connection. the second tank connection being cut.

  Advantageously, the actuating valve has a neutral position for which the actuating pressure connections, the reservoir connections and the control pressure connection communicate.

  According to another embodiment, the invention relates to a hydrostatic machine according to which for the actuating pressure prevailing in the first control pressure chamber, the machine delivers in a first hydraulic fluid line and for the operating pressure prevailing in the second control pressure chamber it discharges into a second hydraulic fluid line, characterized by a first bypass line provided with a first upstream control valve, this line connecting the first hydraulic fluid line to the second hydraulic reservoir branch. the actuating valve, while a second bypass line is provided with a second upstream control valve for connecting the second hydraulic fluid line to the first tank connection of the actuating valve.

  According to an advantageous embodiment of the invention, the corresponding tank outlet of the actuating valve makes it possible to form in a simple manner with the aid of a throttling element, a pressure opposing the pressure of actuation if the first bypass line is connected to a tank bypass line connecting the second tank connection to the tank and the second bypass line is connected to a tank line connecting the first tank branch to the tank with downstream connecting the bypass line to the tank bypass line, each time a throttle element installed in the tank line.

  According to another development of the invention, upstream of the upstream control valve, a throttling point is provided in the bypass line which makes it possible to regulate in a simple manner the volume flow taken from the hydraulic fluid line to for the pressure.

  According to a preferred embodiment of the invention, the upstream control valve is constituted by a pressure limiting valve. This pressure limiting valve can be used with a reduced construction means to cut the pressure and the discharge pressure to be protected corresponds to the acceleration phase or the maximum braking pressure in the braking phase to the value of adjustment of the pressure limiting valve and when the pressure limiting valve is loaded, it is possible to take a volume flow in the hydraulic fluid line associated with the pressure limiting valve to establish a pressure signal at the pressure limiting valve. the corresponding tank connection of the actuating valve via a throttling element, this pressure opposing the actuating pressure at the actuating piston.

  The pressure relief valves can be set to the same setting value. It is also possible to have different adjustment values on the pressure limiting valves so that there will be different pressure levels to cut the pressure during acceleration phase and braking phase.

  The actuating valve is advantageously a pilot valve and / or a controlled position.

  A control valve upstream regulated in position can be carried out in a simple manner if the actuating valve comprises a control slide sliding longitudinally in a housing, this drawer cooperating with an upstream control installation and the housing with the actuating piston.

  The upstream control system is advantageously constituted by a spring biased sensor piston having a first control pressure chamber biased by a first upstream control pressure and a second control pressure chamber biased by a second control pressure. upstream.

  The invention also relates to a hydrostatic machine according to which for the first upstream control pressure prevailing in the first control pressure chamber, the actuating valve is biased towards the first switching position and for the second upstream control pressure. applied to the second control pressure chamber, the actuating valve is biased towards the second switching position, characterized in that the sensor piston is urged by a first complementary piston acting against the first upstream control pressure and a second complementary piston acting against a second upstream control pressure, the first complementary piston being biased by the pressure in the first hydraulic fluid line and the second complementary piston is biased by the pressure in the second hydraulic fluid line. Solving the sensor piston with the additional piston with the pressure generated by the pump causes the pump discharge pressure and thus the torque supplied by the pump to depend on the level of the upstream control pressure.

  It is particularly advantageous to use the machine for driving in displacement of a working machine such as for example a transporter carriage. The machine produced as a pump according to the invention makes it possible to cut off pressure for the two directions of displacement during the acceleration phase and during the braking phase and thus during the acceleration phase, to limit the discharge pressure and in the phase of braking, to limit the maximum brake pressure of the pump, while having a stable control behavior.

  The use of a machine according to the invention functioning as a pump for driving in rotation of a working machine and in particular of a crane or excavator, allows, for both directions of rotation, in phase of acceleration , to cut the pressure and in the braking phase, to limit the brake pressure by having a stable control behavior.

  The implementation of the pressure relief valves of the circuit avoids with reduced constructive means and effectively the pressure cut and thus leads to a low loss drive system and better temperature management and a reduction of the pulsations of the low pressure side.

  Drawings The present invention will be described below in more detail with the aid of an exemplary embodiment shown in the accompanying drawings, in which: FIG. 1 is a diagram of a drive system of a machine according to the invention, FIG. 2 shows a detail on an enlarged scale of FIG.

  Description of an embodiment

  Figure 1 shows the diagram of a hydrostatic drive system in a closed circuit, for example the drive-ment drive of a working machine or more simply mobile machine or the rotational drive of a crane.

  An engine not shown in detail, for example an internal combustion engine or an electric motor drives a hydraulic pump 1. This pump forms a closed circuit with at least one hydraulic consumer 2, including a hydraulic motor. The circuit is formed by a first line of hydraulic fluid (or liquid under pressure) 2a and a second hydraulic fluid line 2b.

  Pump 1 is an adjustable pump with adjustable flow rate; it comprises a flow control device 3, for example a rocker-shaped bias plate cooperating with an actuating installation 4.

  The actuating device 4 comprises, as shown in FIG. 2, a spring-loaded actuating piston 5 co-operating with the volume-flow control device 3. The installation comprises a first control pressure chamber 5a and a second control pressure chamber 5b. Instead of an actuating piston with two opposing pressure control chambers it is also possible to provide two antagonistic actuating pistons each having its control pressure chamber.

  To control the actuation of the actuating piston 5 there is provided an actuating valve 6, regulated in position, designed as a pilot valve. The actuating valve 6 comprises a control pressure connection 7 connected to a control pressure supply line 8 of a control pressure source not shown, for example a pressure pump of ordered. The control valve 6 or slide valve further comprises a first operating pressure connection 9a connected to a first operating pressure line 10a and a first control pressure chamber 5a of the operating piston 5. A second operating pressure connection 9b of the operating valve 6 is connected by a second operating pressure line 10b to the second control pressure chamber 5b of the operating piston 5 and thus the installation of volume flow control 3 cooperates by a mechanical linkage 11 with the housing of the actuating valve or actuating distributor 6.

  The control valve of the actuating valve or actuating distributor 6 co-operates for the control with the aid of a mechanical linkage 12 with an upstream sensor piston control system 13. The sensor piston 13 is sliding longitudinally-ment in a sensor cylinder 14 and comprises a first control pressure chamber 15a receiving a first upstream control pressure Z and a second control pressure chamber 15b receiving a second upstream control pressure Y. The control pressure chambers 15a, 15b each house a spring for resiliently centering the sensor piston 13.

  The sensor piston 13 comprises a first complementary piston 25a opposing the upstream control pressure Z prevailing in the first control pressure chamber 15a, it is subjected to the pressure applied via a pipe 23a from the first hydraulic fluid line 2a. A second complementary piston 25b is biased by the pressure applied via a pipe 23b from the second hydraulic fluid pipe 2b, opposing the upstream control pressure Y prevailing in the second control pressure chamber. 15b.

  The upstream control pressure Z applied to the sensor piston 13 urges the actuating valve or actuating valve 6 to the right according to FIG. 2, in a first switching position 6a; in this position, the operating pressure line 10a communicates with the control pressure supply line 8 so that the actuating piston 5 is displaced by the operating pressure applied to the control pressure chamber 5a so that the pump 1 discharges into the first hydraulic fluid line 2a. In the case of an upstream control pressure Y applied to the sensor piston 13, the actuating valve 6 is biased towards a second left switching position 6b according to FIG. 2 in which the operating pressure line 10b is connected to the control pressure supply line 8; the actuating piston 5 is displaced by the operating pressure in the control pressure chamber 5b for the pump 1 to flow into the second transfer line 2b.

  According to the invention, the actuating valve 6 is provided with a first tank connection 16a and a second tank connection 16b; the second operating pressure connection 9b is connected to the second tank connection 16b and thus the operating pressure line 10b connects the second control pressure chamber 5b of the operating piston 5 to a reservoir 18 for the first switching position of the actuating valve 6; in this position the first control pressure chamber 5a of the operating piston 5 is connected by the operating pressure line 10a and the operating pressure connection 9a to the control pressure connection 7 by the first pressure line. actuator 10a connected to the first tank connection 16a, the first control pressure chamber 5a of the actuating piston 5 is connected to the reservoir 18 for the second switching position 6b of the actuating valve 6; in this position the second control pressure chamber 5b of the operating piston 5 is connected by the operating pressure line 10b and the operating pressure connection 9b to the control pressure connection 7.

  In the first position 6a, the first tank branch 16a is cut. Correspondingly, in the second switching position 6b, the second branch 16b is cut. In the neutral position 6c shown in the actuating distributor 6, the operating pressure connections 9a, 9b and the control pressure connection 7 are connected to the tank connections 16a, 16b.

  A first tank bypass 17a joins the tank 18 from the first tank branch 16a of the actuating distributor 6; this bypass line 17a is equipped with a throttle dis-positive 19a. Upstream of the throttling device 19a, the first tank bypass line 17a is connected to a second tank bypass line 20b; the latter is connected by the pipe 23b to the second hydraulic fluid line 2b. The bypass line 20b is provided with an upstream control valve 21b in the form of a pressure limiting valve. Upstream of the upstream control valve 21b, the bypass line 20b has a throttling point 22b.

  Correspondingly, in a second tank bypass line 17b connecting the second tank branch 16b of the actuating distributor 6 to the tank 18 there is a throttle installation 19b; upstream of the throttling facility 19b, the reservoir bypass line 17b is connected to a first branch line 20a; it is connected by the pipe 23a to the first hydraulic fluid pipe 2a. The bypass line 20a also carries an upstream control valve 2a in the form of a pressure limiting valve and downstream of the upstream control valve 21a, the bypass line 20a is equipped with a throttling point 22a.

  An overpressure installation 25 protects the circuit. This installation is fined with the combination of rebreathing valves and pressure limiting 25a, 25b. The rebreathing and pressure limiting valve 25a is connected to the pressurized liquid line 2a and the pressure limiting rebreathing valve 25b is connected to the hydraulic fluid line 2b. The pressure limiting rebreathing valves 25a, 25b are connected to the operating pressure supply line 8.

  When the sensor piston 13 is biased by the upstream control pressure Z, it acts via the linkage 12 on the control spool of the actuating distributor 6 in the direction of the switching position 6a; in this position, the operating pressure line 10a is connected to the control pressure supply line 8 and thus creates an operating pressure in the control pressure chamber 5a of the actuating piston 5; this pressure moves the actuating piston 5 to the right and the flow control system 3 of the pump 1 is controlled in the direction of an increase in flow. The pump 1 thus delivers into the hydraulic fluid line 2a. The control pressure chamber 5b of the operating piston 5 is connected by the operating pressure line 10b to the switching position 6a of the operating distributor 6 to the second tank branch 16b and thus to the second branch. 17b tank bypass. In the acceleration phase of the drive system, the discharge pressure of the pump 2 delivering in the pipe 2a is applied via the pipe 23a and the bypass pipe 20a to the upstream control valve 2a1a. If the discharge pressure of the pump 2 exceeds the preset maximum discharge pressure at the upstream control valve 21a, the upstream control valve 21a as a pressure limiting valve is biased to the open position. The throttle member 19b installed in the tank branch line 17b generates a pressure signal at the second tank branch 16b. This signal is applied by the control pressure line 10b to the control pressure chamber 5b of the actuating piston 5 and urges the actuating piston 5 in the direction opposite to the operating pressure in the pressure chamber. command 5a to cut the pressure in the direction of a reduction of the flow rate by the flow control installation 3.

  In the braking phase, the reduction which occurs in the upstream control pressure Z causes the actuating valve 6 to move to the switching position 6b in which the control pressure supply line 8 is connected to the pressure line 10b and thus to the control pressure chamber 5b of the actuating piston 5. The control pressure chamber 5a is connected by the operating pressure line 10a and the first reservoir branch 16a of the actuating valve 6 at the reservoir bypass 17a. The flow control installation 3 of the pump 1 is thus set in the braking phase in the direction of reducing the volume delivered. As in the braking phase there is a pressure change in the pressurized liquid lines 2a, 2b, the brake pressure prevailing in the hydraulic fluid line 2b and driving the pump 1 functioning as a motor, is applied by the pipe 23b and the bypass line 20b to the upstream control valve 21b. If the brake pressure exceeds the maximum brake pressure set on the upstream control valve 21b, this upstream control valve 21b as a pressure limiting valve opens. Thus, a pressure signal is obtained at the first tank connection 16a of the actuating distributor 6 via the actuating installation 19a; this pressure signal is applied by the operating pressure line 10a to the first control pressure chamber 5a and opposes the actuating pressure in the control pressure chamber 5b; thus the actuating piston 5 moves the flow control device 3 to limit the maximum brake pressure in the direction of an increase in the discharge rate.

  Correspondingly, for a control signal Y, the pump 1 delivering in the hydraulic fluid line 2b during the acceleration phase, makes it possible to obtain using the upstream control valve 21b and the throttling point 19a. , a pressure cut and in braking phase, the brake pressure causing the pump 1 prevailing in the hydraulic fluid line 2a, provides, thanks to the upstream control valve 2la and the throttling point 19b , a limitation of the maximum brake pressure.

  The pressure cutoff is effected by the establishment of a final pressure in the corresponding reservoir outlet of the actuating distributor 6; the pressure signal acts directly against the operating pressure of the actuating piston 5 and thus inversely the actuating torque of the flow control device 3 in the form of an oblique disk device. The disturbing quantities, such as for example the friction at the sensor piston 13, are thus excluded. In addition, for the breaking of the pressure, there will be a rapid passage of the signal with reduced dead time. The tilting of the flow rate regulator 3 of the pump 1 to reduce the pressure in the acceleration phase and in the braking phase is done independently of the adjustment torque resulting from the discharge pressure or the brake pressure at the pump. of the flow control installation 3. The realization of the upstream control valves 21a, 21b as pressure limiting valves and the use of throttling means such as throttling means 19a, 19b, provide a cut-off of pressure acting in the acceleration phase and in the braking phase with simple components and an economy of means for stable control behavior.

Claims (13)

  1) Hydrostatic machine, in particular a variable-speed axial piston machine operating in a closed circuit, the flow rate being regulated by means of an adjustment device comprising an actuating piston having a first control pressure chamber and a second chamber of control pressure, which can be connected by an actuating valve to a control pressure source or discharged to a reservoir, a pressure cutoff function being provided, characterized in that for each control pressure chamber (5a, 5b) of the actuating piston (5), the actuating valve (6) has a reservoir outlet and in each reservoir outlet a pressure signal opposing the actuating pressure can be created for cut off the pressure.   2) A hydrostatic machine according to claim 1, characterized in that an upstream control valve (2la, 21b) respectively provided to create the pressure signal, receives as input the pressure applied to the machine and cooperates with a pressure element. throttling (19a, 19b) installed in the tank outlet.   Hydrostatic machine according to Claim 1 or 2, characterized in that the actuating valve (6) has a first actuating pressure branch (9a) connected to the first control pressure chamber (5a) of the operating piston (5), a second operating pressure connection (9b) connected to the second control pressure chamber (5b) of the operating piston (5), a control pressure connection (7) connected a control pressure source and a first reservoir connection (16a) connected to a reservoir (18) and a second reservoir connection (16b) connected to the reservoir (18), in a first switching position (6a) of the actuating valve (6), the first operating pressure connection (9a) is connected to the control pressure connection (7) and the second operating pressure connection (9b) is connected to the second operating pressure connection (7). tank (16b), the first tank connection (16a) being shot and in a second switching position (6b) of the actuating valve (6), the second operating pressure connection (9b) is connected to the first control pressure connection (7) and the first pressure connection actuator (9a) is connected to the first tank branch (16a), the second tank branch (16b) being cut.   4) hydrostatic machine according to one of claims 1 to 3, characterized in that the actuating valve (6) has a neutral position (6c) for which the actuating pressure connections (9a, 9b), connections tank (16a, 16b) and the pressure connection (7) are connected.   5) hydrostatic machine according to one of claims 2 to 4, wherein for the actuating pressure in the first control pressure chamber (5a), the machine (1) flows in a first hydraulic fluid line (2a ) and for the operating pressure in the second control pressure chamber (5b) it flows into a second hydraulic fluid line (2b), characterized by a first branch line (20a) provided with a first upstream control valve (2la), this conduit connecting the first hydraulic fluid line (2a) to the second tank branch (16b) of the actuating valve (6), while a second branch line (20b) is provided with a second upstream control valve (21b) for connecting the second hydraulic fluid line (2b) to the first tank branch (16a) of the actuating valve (6).   Hydrostatic machine according to claim 5, characterized in that the first bypass line (20a) is connected to a tank bypass line (17b) connecting the second tank branch (6b) to a tank (18), and the second bypass line (20b) is connected to a tank bypass line (17a) connecting the first tank branch (16a) to a tank (18), and downstream of the branch line branch (20a). 20b), the tank bypass conduit (17a, 17b) is provided with a throttle (19a, 19b).   7) A hydrostatic machine according to claim 5 or 6, characterized in that upstream of the upstream control valve (2la, 2lb) the bypass line (20a, 20b) comprises a throttling point (22a, 22b).   8) hydrostatic machine according to one of claims 2 to 7, characterized in that the upstream control valve (21a, 21b) is a pressure limiting valve.   9) hydrostatic machine according to one of claims 1 to 8, characterized in that the actuating valve (6) is a pilot valve and / or position control.   10) hydrostatic machine according to claim 9, characterized in that the actuating valve (6) comprises a control slide longitudinally sliding in a housing, the control spool cooperating with an upstream control facility and the housing with the piston of actuation (5).   Hydrostatic machine according to claim 10, characterized in that the upstream control device is a spring-loaded sensor piston (13) having a first control pressure chamber (15a) receiving a first upstream control pressure (Z). and a second control pressure chamber (15b) receiving a second upstream control pressure (Z).   12) hydrostatic machine according to claim 11, wherein for the first upstream control pressure (Z) in the first control pressure chamber (15a), the actuating valve (6) is biased towards the first position for switching (6a) and for the second upstream control pressure (Y) applied to the second control pressure chamber (15b), the actuating valve (6) is biased towards the second switching position (6b) characterized in that the sensor piston (13) is biased by a first complementary piston (25a) acting against the first upstream control pressure (Z) and a second complementary piston (25b) acting against a second upstream control pressure (Y ), the first complementary piston (25a) being biased by the pressure prevailing in the first hydraulic fluid line (2a) and the second complementary piston (25b) is biased by the pressure prevailing in the conde hydraulic fluid line (2b).   13) hydrostatic machine according to one of claims 1 to 12, characterized in that it is applied as a drive of a working machine or as a rotational drive of a working machine, including a crane or excavator.