FR3025853B1 - HYDROSTATIC DRIVE SYSTEM - Google Patents

Abstract

System having: - a first pump (10) adjustable, - a hydraulic motor (11) connected to the pump (10) by a closed circuit (9), via a pipe (12) receives hydraulic fluid from the first pump (10) and a pipe (13) through which the liquid flows from the motor (11) into the pump (10), - an open hydraulic circuit having a second pump (70) for injecting into the pipe (12) and a switched valve device for transferring the hydraulic fluid from the line (13) into the reservoir when the second pump (70) is delivering into the line (12). The switched valve device includes a pressure limiting valve device (100) switched between two pressure settings.

Description

Field of the invention

The present invention relates to a hydrostatic drive system having: a first pump adjustable between a positive and negative flow through a neutral position, a hydraulic motor connected to the first pump by a closed hydraulic circuit through a first active conduit through which in an operating state, the hydraulic motor receives hydraulic fluid from the first pump and a second active conduit through which, in the same operating state, the hydraulic fluid flows from the hydraulic motor into the pump an open hydraulic circuit having a second pump provided with the suction connection for sucking hydraulic fluid from the reservoir and a high pressure connection through which the hydraulic fluid is injected into the first active conduit of the closed hydraulic circuit and a valve device switched by which while maintaining a minimum pressure in the second cond When the second pump is active, the hydraulic fluid is transferred from the second active line to the reservoir when the second pump delivers to the first active line.

In other words, the invention relates to a hydrostatic drive system comprising a first pump adjustable between a positive flow and a negative flow through a neutral position and a motor or several hydraulic motors. These motors are connected by a closed hydraulic circuit passing through the first pump, by a first active line which, for an operating state of the hydraulic motor, provides hydraulic fluid and a second active line by which, for the same operating state of the hydraulic motor, the liquid comes from the pump. The first pump and the hydraulic motor are usual components of a hydrostatic circulation drive system; one can have several hydraulic motors, for example a motor per wheel in the case of a mobile machine. The operating state is usually forward, because then you have to have a certain speed of movement. In a second state of operation which corresponds to the reverse, the first active and the second active conduct are reversed. The hydrostatic drive system includes a second pump in an open hydraulic circuit. This second pump has a suction connection for drawing hydraulic fluid from the tank and a high-pressure connection for supplying hydraulic fluid to the first active conduit of the closed circuit. One can also have an injection of hydraulic fluid in the second mode of operation. Thus, the hydraulic motors receive the sum of the hydraulic fluid flow rates of the first pump and the second pump, which allows to rotate the hydraulic motors at a higher speed and thus the mobile machine can flow at a higher speed. The main function of the second pump is usually to supply the active functions of hydraulic cylinders or hydraulic motors with hydraulic fluid. The hydrostatic drive system further includes a switched valve device that, while maintaining the minimum pressure in the second active conduit of the closed circuit, allows liquid to flow from the second active conduit into the reservoir when the second pump delivers. in the first active conduct.

State of the art

Such drive systems are known from a series of documents.

Thus, DE 1 298 005 B discloses a hydrostatic drive system whose switched valve device consists of a spool valve having a first branch connected to the second active line and a branch to the tank and a pre-stressed check valve at a pressure of approximately 4 bar. This non-return valve is located between the connection of the slide valve to the tank and the tank itself. The slide valve has two switch positions. In the rest position, the first connection and the tank connection are cut off from one another; in the second position, the first branch and the tank connection are connected so that in this second position, the hydraulic fluid can pass from the second active line in the tank through the check valve, prestressed.

The slide valve is used not only to discharge hydraulic fluid from the second active line, but also to pass hydraulic fluid discharged from the second pump into the first active line. The distributor further has a third connection connected to the pressure connection of the second pump and a fourth connection connected to a throttle member adjustable by the accelerator pedal. The third connection and the fourth connection are locked relative to each other when the slide valve is in the rest position and in the second position they are connected to each other so that in this second position the hydraulic fluid discharged from the second pump passing through the slide valve and the adjustable throttle member and also between the throttle member and the first active conduit to pass through an open stop valve to the first conduit active, to arrive in this first active conduct. The volume of hydraulic fluid supplied to the closed circuit can be influenced by the adjustment of the opening section of the adjustable throttle. If the second pump that is a constant flow pump delivers too much hydraulic fluid, it returns to the tank through the pressure relief valve.

Also known is a hydrostatic drive system of the type defined above by DE 21 12 237 A. In this hydrostatic drive system, the switched valve device consists of a spool valve and a valve Prestressed antiretour installed between the spool valve reservoir connection and the reservoir. The shut-off valve is set for supply pressure of the closed circuit supply pump or at a higher pressure. The slide valve has an average rest position and two switch positions for which the third and fourth connections are exchanged with the first and the tank connections. In the hydrostatic drive system known from DE 21 12 327 A, the hydraulic fluid supplied by the second pump can supply the two active lines. The volume of hydraulic fluid injected is equal to the flow rate of the second pump which is a fixed flow pump.

Also known hydrostatic drive system of the type defined above according to EP2 017 114B1. In this hydrostatic drive system, the switched valve device consists of a spool valve which can assume a rest position and a switched position; it comprises a first connection and an open tank connection in the switching position to the first connection and a flow control valve between the first connection of the spool valve and the second active conduit. When hydraulic fluid is injected from the second pump into the first active pipe, a certain amount of hydraulic fluid passes from the second active pipe through the flow control valve through the first active connection and the reservoir connection of the slide valve. to return to the tank.

The second pump is a regulated pump with load sensing and feeds the spool valve which also has a third and a fourth branch and a constant throttle to the first active line. Thus, at least if the second pump does not supply hydraulic fluid to any consumer whose load pressure is higher than that in the first active line, the injected hydraulic fluid flow rate is constant. The flow control valve is set to a certain flow rate of hydraulic fluid, slightly less than the flow rate injected. The residual amount is removed by the flushing circuit of the closed circuit. The hydrostatic displacement drive comprising a pump and a hydraulic motor in a closed hydraulic circuit is usually also used to brake the vehicle. In this case, the hydraulic motor operates as a pump and the brake pressure is established in the second active line. The pump becomes a motor which then drives the motor that usually drives the pump, for example a diesel engine. Excess hydraulic fluid flows from the second active line through the closed circuit pressure relief valve directly into the first active line.

The difficulty of the known hydrostatic drive systems is that, when changing from the engine state in which the second pump injects into the first active conduit to the braking state, there is no control of the prevailing pressure. in the second active conduct. Indeed, the pressure limiting valves which are usually part of a closed hydraulic circuit and are alternately between the two active pipes, are not designed for the flow of hydraulic fluid transferred at high speed by the hydraulic motors in the second active driving.

OBJECT OF THE INVENTION The object of the invention is to develop a hydrostatic drive system of the type defined above making it possible, with simple means, to have greater safety even in the braking mode using the circuit. closed hydraulics.

DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose, the subject of the present invention is a hydrostatic drive system of the type defined above, characterized in that the switched valve device comprises a pressure limiting valve device switched between two pressure settings.

In the hydrostatic drive system according to the invention, the pressure limiting valve device in the basic operating mode of the closed hydraulic circuit, when the hydraulic motors rotate at low rotational speed, is set to a high pressure. This is preferably slightly greater than the pressure at which the pressure limiting valves forming part of the closed circuit are set. The pressure limiting valve device does not influence operation. If in connection mode, the second pump delivers in the first active line to have higher rotational speeds of the hydraulic motors or to increase the flow drawn by the hydraulic motor and for the same speed of rotation, increase the torque supplied, for to improve the machine's revving capacity, the pressure limiting valve device is set to a low pressure level which is preferably in the range of the supply pressure, the pressure at which the feed pump part of the closed hydraulic circuit discharges into the active line which is not at high pressure. The flow of hydraulic fluid supplied by the second pump then passes through the pressure limiting valve device while maintaining the supply pressure in the second active conduit.

If in the range of high rotational speeds the hydraulic motors are to be braked, the pressure limiting valve device is set to a high pressure. Thus, the second active line will be at a high braking pressure to effectively brake with the closed hydraulic circuit. However, a part of the large amount of hydraulic fluid injected by the hydraulic motors which first rotate at a still high speed in the second active line, to be evacuated by the pressure limiting valve device. This ensures that the pressure in the second active line does not reach dangerous values in an uncontrolled manner.

In principle, it is possible to design the pressure relief valve device by two pressure relief valves set at fixed and parallel pressure values and with a 2/2-way spool valve connected in series on the pressure relief valve is set to the lowest pressure and switch it to the active and non-active position. However, it is simpler that the switched pressure relief valve device has a pre-controlled pressure limiting valve having a main stage and a pilot stage and a two position switching piston receiving the pressure of the pressure relief valve. command to set the driver stage. The pilot stage and thus the main stage are set in a first end position of the switching piston on a low pressure level and in its second end position, on a high pressure level.

Preferably, the pressure limiting valve device is set to a high pressure if the device is not controlled, so that in case of fault control, the closed hydraulic circuit continues to operate.

If a pre-ordered pressure relief valve is used and whose switching piston is actuated by the control pressure, this piston having two end positions, to have a guaranteed basic position, the switching piston will be moved. towards its second end position loaded by a spring and the second end position to the first end position being biased by the control pressure.

The closed hydraulic circuit usually includes a feed circuit having a feed pump and a feed pressure limiting valve to limit the supply pressure and that provides hydraulic fluid to the active line when the pressure in the line active falls below the supply pressure. The low pressure level of the pressure limiting valve device is then preferably maintained at a level high enough so that the pressure in the second pipe activates and thus the supply pressure does not fall below a pressure. necessary to control the various functions of the drive system, for example to adjust the first pump. The function can also be to switch the pressure limiting valve device, itself, from the high pressure level to the low pressure level. The low pressure level is set so that the pressure limiting valve device remains stable at this low pressure level.

In order to adjust the pressure limiting valve device, a control valve is preferably provided which, depending on its position, discharges the control chamber from the pressure limiting valve device to adjust the pressure level or apply the pressure. and the low pressure level of the pressure limiting valve device has a value such that the pressure in the second active line and thus that in the supply circuit does not fall below the pressure required for the adjustment. of the pressure limiting valve device.

Preferably, the low pressure level of the pressure limiting valve device is such that the pressure in the second active line is at least substantially limited to the set value of the supply pressure limiting valve. Thus, in basic function mode and in connection mode, the pressure of the second active conduct is substantially the same.

The control valve which supplies the supply pressure to the control chamber of the pressure limiting valve device is advantageously hydraulically actuated. The second pump supplies the hydraulic fluid via a shut-off valve to the first active conduit of the closed hydraulic circuit so that, in the basic operating mode of the closed circuit, the first active pipe is cut to the second pump and to the other circuits. The shut-off valve can be a simple shut-off valve. The control valve is then advantageously controlled by the pressure applied in the pipe between the second pump and the shut-off valve. For this purpose, the control valve comprises an actuating chamber connected to the pipe by a fluid connection. If the second pump delivers in the first active line of the closed hydraulic circuit, the pressure in this line corresponds to that in the first active line. The control valve then switches from its rest position to its switching position and remains in this position. When the second pump does not inject, the line is relieved of pressure.

For this purpose, preferably between the second pump and the shut-off valve, there is an active valve; in a first position, it connects the shut-off valve to the second pump and in a second position, it cuts the pipe segment between it and the shut-off valve to the second pump and discharges the pipe to the tank; the actuating chamber of the control valve is connected to the pipe segment between the active valve and the shut-off valve.

To avoid cavitation and to ensure the correct operation of the hydraulic motors, in braking mode at high rotational speeds of the hydraulic motors, a preferred embodiment of the hydrostatic drive system according to the invention provides downstream of the limiting valve device. pressure, on the one hand a prestressed valve which maintains the pressure downstream of the pressure limiting valve device to a level higher than the pressure of the reservoir and, on the other hand, a shut-off valve connected by its inlet to the connection fluidic relationship between the pressure limiting valve device and the prestressing valve, its outlet being connected to the first active conduit. Thus, from the second active line, the hydraulic liquid exiting through the pressure limiting valve device returns directly back into the first active line.

In the case of a prestressed valve, the low pressure level of the pressure limiting valve device is advantageously less than the pressure at which the supply pressure limiting valve is set. The pressure level at the inlet of the pressure limiting valve device and thus in the second active line then corresponds to the addition of the prestressing pressure and the low pressure set on the pressure limiting valve device. . Advantageously, the high pressure level is set taking into account the prestressing pressure, that is to say for example to adjust the prestressing pressure below the pressure adjustment of the high pressure limiting valve. closed circuit.

The second pump usually feeds hydraulic users with hydraulic fluid to enable them to perform the active functions of the mobile machine. For this, the second pump is set at a higher flow rate, that is to say the amount of hydraulic fluid that the pump delivers for a single rotation of its drive shaft. The adjustment of the second pump is advantageously used then to inject different volumes of hydraulic fluid in the first active conduit.

If the second pump is a load-sensing controlled pump and has a load-sensing control valve for this purpose, the first active conduit of the closed hydraulic circuit is injected in a simple manner by a dosing diaphragm between the high-pressure branch. pressure of the second pump and the first active driving. The diaphragm is preferably continuously adjusted to different opening sections, all different from zero, and in that the load sensing control valve is biased by the load pressure applied to the first active pipe.

A load-sensing control valve is biased in the direction of increasing the flow rate of a pump for the highest load pressure of all hydraulic users supplied by the pump and by an adjusting spring whose The pressure equivalent is in a range of 15-30 bar and in the sense of a reduction of the flow rate by the pressure of the pump. The control valve regulates the pump so that the pump pressure around the pressure equivalent of the control spring is above the highest load pressure. Thus, the pressure difference on the metering diaphragm remains constant insofar as no hydraulic user with a higher load pressure is active. Normally, this is not the case when injected in a closed circuit so that, by the only adjustment of the opening section of the dosing diaphragm can be defined the amount of hydraulic fluid injected.

drawings

The present invention will be described in more detail below with the aid of an exemplary hydrostatic drive system shown in the accompanying drawings, in which: FIG. 1 shows a diagram of the entire system having a hydraulic circuit closed, a second pump operating in an open hydraulic circuit and a pressure control valve, switched, Figure 2 shows the diagram of a primary hydrostatic module of the closed circuit, Figure 3 shows the diagram of the secondary hydrostatic module of the closed circuit, FIG. 4 shows the diagram of the second pump, and FIG. 5 is a longitudinal section of the switched pressure limiting valve of FIG.

DESCRIPTION OF AN EMBODIMENT The exemplary embodiment of the hydrostatic drive system according to the invention shown in the figures, has a closed hydraulic circuit 9 as a drive for moving a mobile machine, for example a harvester harvester or a tuber harvester. The hydraulic circuit 9 comprises a primary hydrostatic module 10, preferably in the form of a hydrostatic machine with axial pistons with an oscillating plate and thus functioning as both a pump and a hydraulic motor. In pump mode which is the main mode, the hydrostatic primary module 10 is usually driven by a heat engine, for example a diesel engine. As the hydrostatic primary module 10 operates primarily as a pump, it will be referred to hereinafter as "pump" for the primary hydrostatic module.

The hydraulic circuit 9 furthermore has a secondary hydrostatic module 11, preferably in the form of a hydrostatic axial piston swash plate machine which can function both as a pump and as a hydraulic motor. As the secondary hydrostatic module 10 operates primarily as a hydraulic motor, it will be referred to hereinafter as "hydraulic motor" of the secondary hydrostatic module.

A first active conduit 12 connects the connection A of the pump 10 to the connection A of the hydraulic motor 11; a second active line 13 connects the connection B of the pump 10 to the connection B of the hydraulic motor 11. The flow rate of the pump 10, that is to say the flow rate of liquid under pressure by the rotation of the shaft of pump drive varies from maximum positive flow through zero flow to maximum negative flow; it is assumed that for a positive flow, the pump 10 delivers into the active pipe 13 and that for a negative flow, it delivers into the active pipe 12. The flow of the hydraulic motor 11 is variable from a maximum flow rate up to a flow rate near or equal to 0. It is assumed that the mobile machine advances when the pump 10 delivers into the pipe 12 and that it recoils when the pump 10 delivers in the pipe 13.

The functional embodiment of the pump 10 appears more precisely in FIG. 2. The pump comprises an adjustment device that adjusts the inclined position of the swashplate 14, shown schematically by a simple arrow. ; the adjusting device comprises a double-acting adjustment piston 15 between two adjustment chambers 16, 17. The piston is subjected to two springs 18 which position it in a median position corresponding to a zero flow. The arrival and exit of hydraulic fluid in the control chambers 16, 17 is controlled by an adjustment valve 19 constituted by a 4/3 way distributor with negative overlap and maintained in the middle position by a spring device 20 In the middle position, the control liquid supply connection, the tank connection and the control connection of the control chamber 16 as well as the control connection of the control chamber 17 are connected to each other in a controlled manner. strangled.

The adjusting piston of the regulating valve 19 is displaced by a first proportional electromagnet 21 from its median position in one direction; after this movement, the first adjustment chamber 16 is connected to the hydraulic liquid supply connection and the second adjustment chamber 17 is connected to the tank connection. A second proportional electromagnet 22 moves the adjusting piston from its middle position in the opposite direction; after this adjustment, the second adjustment chamber 17 is connected to the hydraulic fluid supply connection and the first adjustment chamber 16 is connected to the tank connection. The displacement of the adjusting piston 15 is connected in a known manner by a lever 23 to the spring device 20 of the regulating valve 19. Thus, the angle of the swash plate 14 will be adjusted according to the proportional supply of the 'electro magnet. The nature of the regulation of the pump 10 is called electro-proportional regulation (EP regulation).

The control valve 19 has a separate housing 26 which is installed on the housing 27 of the pump 10.

The housing 27 of the pump comprises two active channels 28, 29 to the AB connections. Depending on the mode of operation one of the two active channels is the high pressure channel and the other is the low pressure channel. The primary module 10 comprises a fixed constant feed pump 30 which delivers in a supply channel 31 supplying the respective active channels, in hydraulic liquid, a shut-off valve 32. The feed channel 31 comprises a supply pressure limiting member 33 which adjusts the supply pressure in the channel 31 as the case may be around 30 bar, for example 30 bar. Thus, the feed pump 30 feeds one of the active channels 28, 29 and thus an active line 12, 13 if the pressure in the channel / line drops below the pressure set on the pressure limiting valve. 33.

The feed pump 30 feeds the control valve 19 with hydraulic fluid and for this the hydraulic fluid supply connection is connected by the liquid path 34 to the feed channel 31. The path 34 comprises a control member. constant throttle 35 and an adjustable throttle 36 in the liquid path 34. This adjustable throttle may open the throttled connection from the path 34 to the reservoir. The movable valve of the adjustable throttling member 36 is urged in the closing direction by a spring 37 and in the opening direction, by the highest pressure applied to it by the two active channels. The highest pressure is chosen by the alternative valve 38. As long as the highest pressure is less than the value defined by the pressure equivalent of the spring 37, for example below 300 bar, adjustable throttle 36 remains closed. When the higher pressure exceeds a certain value, the adjustable throttle member opens and this opening section will be larger the higher the pressure. The constant throttle member 35 and the adjustable throttle member 36 constitute a pressure divider whereby the pressure applied to the hydraulic fluid supply branch of the regulating valve 19 drops below the pressure of supply and the swash plate 14 of the pump 10 returns. Indeed, it is not always possible to maintain the previous position of the swash plate in one of the adjustment chambers 16, 17. Thus, the adjustable throttling member 36 with the alternative valve 38 ensures that the pressure in the active line will not exceed a preset value. The combination of the adjustable restrictor 36 and the alternate valve 38 is hereinafter referred to as the pressure cutoff valve.

The hydraulic fluid passing through the supply pressure limiting valve 33 and the throttle member 36 enters the pump housing 27 and thence into the reservoir through the tank connection T.

Finally, the pump 10 comprises two high-pressure limiting valves 39, 40. The high-pressure limiting valve 39 is connected to the active channel 28 and the high-pressure limiting valve 40 is connected to the active channel 29. high pressure limiting are set at a level higher than that of the adjustable throttle 36. Their outputs are connected to the supply line 31. When the high pressure limiting valve 39 or 40 is requested, only the Hydraulic fluid exiting the high pressure limiting valve of one channel can escape through one of the two check valves 32 into the other active channel. A high pressure relief valve and a shut-off valve are combined and will be referred to as "high pressure relief valve and shut-off valve".

The functional embodiment of the hydraulic motor 11 appears in more detail in FIG. 3. The hydraulic motor comprises a motor housing 45 in which the active lines 12, 13 are extended in the form of active channels 46, 47. A control valve 48 and a rinsing unit 49 are mounted on the housing 45 of the engine. The rinsing unit comprises a rinsing diaphragm 50, a rinsing valve 51 connecting the active channel 46 or 47 which is at the low pressure and the rinsing diaphragm 50 as well as a pressure maintaining valve 52 which is the valve with drawers for adjusting the pressure between the rinsing diaphragm and the interior volume of the motor housing 45 in the tank; this slide valve is biased by a spring towards its closed rest position and by the pressure upstream of the diaphragm 50 in the direction of its open position. The pressure-maintaining valve 52 opens only for a pressure greater than that prevailing in the reservoir, in the active channel of low pressure, for example a pressure of 16 bar, so that the rinsing liquid will only come out if this pressure reigns in active driving.

The hydraulic motor 11 further comprises a setting device for adjusting the angular position; it is equipped with delivery pistons; this position is set in relation to Drive shaft tax. Thus, the cylindrical drum 54 can only pivot on one side between a maximum flow rate and a minimum flow rate, that is to say not a zero angle with respect to the drive shaft. The adjusting device comprises a double-acting regulating piston 55 with two regulating chambers 56, 57. The regulating piston 55 is provided on one side with a rod 58 so that the regulating chamber 57 is a chamber annular shape adjustment. This chamber is urged by pressure through two nonreturn valves 59 constituting a selector device. The applied pressure is the highest pressure of the active channel 46 or 47. The arrival and the exit of hydraulic liquid in the control chamber 56 are controlled by the control valve 48 made in the form of a distributor with drawers. 3/2 channels with passage through 0 and return to the rest position by a device of springs 60; in this position the adjustment chamber 56 is discharged to the interior of the housing 45 of the engine. The supply of the proportional electromagnet 61 sets the regulating piston 62 of the regulating valve 48 into a setting position in which the connections are covered up to a setting position in which the regulating chamber 56 receives passing hydraulic liquid. by one of the non-return valves 59 from the active channel which is at a higher pressure.

The spring device 60 has a first spring 63 on a fixed pretensioning force which regulates the start of the regulation and a regulating spring 64 mounted between the regulating piston 62 of the regulating valve 48 and the piston rod 58. that is the adjustment piston 55.

In this arrangement, the position of the adjusting piston 55 and thus the flow rate of the hydraulic motor 11 directly depend on the force developed by the electromagnet 61, that is to say the intensity of the current flowing through the coil of the electro magnet.

In the regulated state, it is indeed necessary that on the one hand, the adjusting piston 55 is at rest and that, on the other hand, independently of the position of the adjusting piston in its rest position, the regulating piston 62 of the regulating valve 48 is at the equilibrium of the forces. The sum of the forces exerted by the two springs 63, 64 must be equal to the force developed by the electromagnet 61. The force of the spring 63 is always the same in the regulation position of the regulating piston. Thus, depending on the force developed by the electromagnet, the force of the spring 64 will have to be different. This different force of the spring 64 depends on the different positions of the adjusting piston 55 according to the electromagnetic force. This type of adjustment is also called electro-proportional adjustment. The hydrostatic drive shown comprises a second pump 70 which is a pump for an adjustable flow open circuit having a housing or pump body 71 with a suction connection S and a pressure connection P which provides the pressure of the pump. The pump 70 is preferably an axial piston pump with a swashplate. The pressure line 72 connected to the pressure connection P allows the pump 70 to supply hydraulic users of the mobile machine with the hydraulic fluid necessary for the work functions.

The swash plate 73 of the pump 70, indicated by a double arrow cooperating with two adjustment cylinders 74, 75 can be tilted between a maximum flow and a zero flow. The adjustment cylinders are for example differential cylinders having an adjusting piston 76 or a counter-piston 77 and a piston rod 78 applied against the inclined plate 73. The pressure is applied only to the rod-side adjustment chamber of piston actuators. The surface of the counter-piston 77 of the adjusting jack 75 is smaller than the surface of the adjusting piston 76 of the other adjusting jack 74. Thus, the deployment of the piston rod 78 of the adjusting jack 74 reduces the swing angle of the swash plate 73 and thus the flow rate of the adjustable pump 70 while the deployment of the piston rod 78 of the adjusting jack 75 increases the tilting angle of the swash plate 73 and thus the flow rate of the adjustable pump 70 .

The adjusting chamber of the adjusting cylinder 75 is permanently connected to the pressure connection P. Thus, the pressure in this setting chamber is the same as in the pressure line 72. The inlet or the outlet of the hydraulic fluid of the control cylinder adjusting chamber 74 is controlled by the pump control valve unit 80 installed on the pump housing 71 and having an external branch LS to which a charge signaling line 81 is connected. This unit comprises substantially two slide valves, proportional to 3/2 ways, one being the pump control valve 82 and the other the pressure regulating valve 83 which sets a pressure higher than the usual charging pressures. The pressure control valve 83 has a first branch connected by a discharge line 84 to the tank 11. The second branch of the pressure control valve 83 is connected to the pressure branch P. The third branch connected to the first or second The branch is connected to the control cylinder adjusting chamber 74. The first connection of the pump control valve 82 is connected to the discharge line 84; the second connection is connected to the pressure connection P. The third connection of the valve 82 is connected to its first or second connection and permanently to the first connection of the valve 83. The unreferenced valve of the valve 83 is pushed by the spring compressor 85 in the direction of increasing the tilt angle and by the pressure of the pump in the direction of the reduction of this tilting angle of the pump 10. The unreferenced slide of the pump control valve 82 is biased in the direction of increasing the pivoting angle of the pump 71 by the compression spring 86 and the pressure in the load-indicating duct 81 in the direction of a reduction of the angle of tilting of the pump tray. The valve slide 82 is in equilibrium when the pressure of the pump and that in the charge signaling pipe 81 differ from a force corresponding to the force developed by the spring 85. Usually, this pressure difference is between 10 bars and 25 bars. At standstill, the second pump 70 is moved for maximum flow under the effect of the return spring 87 of the inclined plate 73.

When the pump is driven and the tank pressure is applied to the LS branch of the pump control valve unit, the pump flow is very low. The pump delivers only what is necessary to make the line 72 prevail, for example at a pressure of 20 bar. This pressure corresponds to the compression equivalent of the compression spring 86 and is called the rest pressure or the pump pressure difference (difference Δρ).

The second pump 70 is not used to supply users of hydraulic fluid to supply them with fluid under pressure, but to inject hydraulic fluid into the first active conduit 12 of the closed circuit and supply the hydraulic motor with a quantity of hydraulic fluid. exceeding the flow demanded by the first pump 10 and thus maintaining a high speed of circulation of the mobile machine.

For this purpose there is first a continuously adjustable slide valve 90 constituting the active valve, connected by a pressure connection to the pressure line 72. The tank connection connects the slide valve 90 to the tank. In addition, the spool valve has an active branch 91 which connects it to the first active line 12 by a supply line 92 and a shutoff valve 93 closing in the direction of the active branch.

The slide valve 90 can assume two different functional positions. In the rest position of the dispenser takes under the action of the compression spring 94, the active branch 91 and the branch 95 are connected to the reservoir. The slide valve can be put into different active positions by the hydraulic control from the rest position; in these positions, the metering diaphragm 96 opens differently between the pressure branch and the active branch 91; the tank connection is closed. In an active position, the branch 95 is connected by a nozzle to the active branch 91. The branch 95 is connected to the first inlet of an alternative valve 97 to the other inlet of the alternative valve 97 is controlled by the strongest pressure load of all hydraulic users operated in common of the working hydraulic circuit or, if no user is commanded, it receives the pressure of the tank. The outlet of the reciprocating valve is connected to the charge signaling duct 81. Thus, the reciprocating valve signals the highest load pressure of the hydraulic consumers controlled from the hydraulic circuit or the pressure applied to the first active pipe 12 towards the valve of the hydraulic system. LS pump control.

The quantity of hydraulic fluid injected by the second pump 70 in addition into the first active conduit 12 of the closed hydraulic circuit, can be discharged from the closed hydraulic circuit at the level of the second active conduit 13. For this, the second active pipe 13 has a pressure control valve 100 pre-ordered, having a main stage 101, a pilot stage 102 and a pressure cutoff device 103 connected to the inlet 104. Details of construction of this valve known per se appear in Figure 5. On recognizes the main tasks 101 with a seat of large diameter for the main closure member 105 biased in the closing direction by a weak spring 106 and the pressure in the spring chamber, connected by a hydraulic fluid nozzle command 107 at the input 104. The driver stage 102 has a smaller diameter seat for the driver shutter member 108 which is not required. in the closing direction by the greater force of a closing spring 109. The spring chamber of the pilot stage is discharged to the tank. The closing spring 109 is supported by means of a rod 110 against a cut-off piston 111 of the pressure cut-off device 103; the piston is pushed against a first stop by a compression spring 112 developing a greater force than that of the closing spring 109. When the cut piston 111 is applied against the first stop, the closing spring 109 is strongly prestressed. The pressure limiting valve is then set to a high pressure, for example 400 bar. In the chamber receiving the spring 112 which is relieved of pressure, on the opposite side of the cutoff piston 111, a pressure chamber 113 receives pressurized liquid by a control connection 114 which can also evacuate the hydraulic liquid. When hydraulic fluid arrives, the cutoff piston 111 is pushed against the force of the compression spring 112 to a second stop; the closing spring 109 of the pilot stage 102 pushes the rod 110 and relaxes. The pressure limiting valve is set at a low pressure, for example at 25 bar. The supply and discharge of hydraulic fluid from the pressure chamber 113 are controlled by a control valve 120 cooperating with a constriction 121. The control valve 120 is a 2/2-way hydraulically operated slide valve. having two connections and two switching positions. An inlet branch 122 is connected by a pipe 123 equipped with a throat 124 to the supply channel 31 of the first pump 10. The outlet branch 125 of the control valve 120 is connected via a line 126 to the branch of control 114 of the pressure limiting valve 100. A discharge line 127 provided with a constriction 121 connects the pipe 126 to the reservoir.

The control valve is biased by a spring 129 and by the pressure prevailing in the pipe 127 towards the rest position in which the outlet branch 125 is cut off from the inlet connection 122. The control connection 130 of the valve 120 is connected by a line 131 to the segment of the supply line 92 between the slide valve 90 and the non-return valve 93. It may be advantageous to connect the chamber of the spring of the control valve 120 to the reservoir. .

The pressure of the outlet connection of the pressure limiting valve 100 is set to a prestressing value of, for example, 5 bar, by a pre-stressing valve 135 in the form of a non-return valve having a strong spring. Between the pressure limiting valve 100 and the prestressed valve 135, the bypass of a pipe 136 is connected to the first active pipe 12 and comprises a non-return valve 137 opening towards the first active pipe 12.

In rolling mode when the mobile machine is traveling at a slow speed, the slide valve 90 is in the rest position; in this position, the segment of the supply line 92 between the slide valve 90 and the non-return valve 93 is connected to the reservoir. Thus, the control valve 120 is also in the rest position in which the pipe 126 is cut off from the pipe 123 and discharges through the nozzle 121 into the tank. The pressure chamber 113 of the cutoff piston 111 of the pressure limiting valve 100 is also discharged so that the pressure limiting valve is set to a high pressure level. This pressure is for example equal to 20 bar, it is greater than the pressure set on the high-pressure limiting valves 39 and 40 of the pump 10. Thus, at slow speed, the limiting valve 100 does not influence the operation. of the hydrostatic drive composed of the pump 10 and the hydraulic motor 11.

When the slide valve 90 is closed, completely independently of the machine that is circulating or is stopped, the hydraulic fluid delivered by the second pump 70 is completely available to supply the hydraulic users of the active circuit.

When the hydraulic motor 11 is supplied with hydraulic fluid only by the first pump 10, the maximum circulation speed of the machine is determined from the flow rate and the rotation speed of the first pump 10 as well as the minimum flow rate of the hydraulic motor. 11 for the maximum pressure in one of the active lines 12 or 13 to generate the torque necessary for the circulation of the machine.

If it is desired to circulate more rapidly, the slide valve 90 is adjusted in proportion to the operating stroke of a manually controlled electric control generator, for example a pedal; thus the dosing diaphragm 96 is open to a certain extent, proportionally to the actuating stroke. The pressure in the supply line is signaled by the alternative valve 97 to the LS branch of the control pump unit 80 in that no higher load pressure of a hydraulic user of the active circuit is applied to the the alternative valve. Normally this is not the case because while the vehicle is moving quickly, the working hydraulics are not solicited.

The second pump then delivers hydraulic fluid into the supply line 92 and the check valve 93 into the first active line 12 of the closed hydraulic circuit. The pressure which is established on the LS connection of the control pump unit if negligible pressure drops are not taken into account on the check valve 93, is equal to the pressure in the active line 12. Because of the regulation LS by the pump control valve 82, the second pump 70 will have a flow rate so that the pressure in the pressure line 72 is always greater than the pressure of the supply line 92 corresponding to the pressure difference of Δρ pump which is 20 bars. The pressure drop across the dosing diaphragm 96 is always the same so that with only the control of the opening section of the dosing diaphragm the flow of hydraulic fluid transferred by the second pump can be determined. 70 in the active line 12. As soon as the slide valve 90 is opened, the pressure in the supply line 92 increases, the control valve 120 in the control branch 130 connects to the supply line 92. by the pipe 131, opens so that the cut piston 111 urges the pressure limiting valve 100 with the supply pressure and away from the first stop towards the second stop. The pressure limiting valve 100 is thus set to a low pressure which in the present example is a pressure of 25 bar. This pressure corresponds to the pressure difference between the inlet and the outlet of the pressure limiting valve; this pressure is lower than the supply pressure (30 bar). As, however, downstream of the pressure-limiting valve 100, there is still the prestressing valve 135 whose pressure is of the order of 5 bars applied to the outlet of the pressure-limiting valve, the inlet the pressure limiting valve is maintained at a pressure of 30 bar. This pressure is equal to the supply pressure so that the switching of the pressure limiting valve 100 does not change the pressure in the second active line 13 and the supply pressure.

The flow of hydraulic fluid that returns to the hydraulic motor 11 by the first active conduit 12 passes through the hydraulic motor 11 and arrives in the second pipe 13. The first pump 10 receives from the second active pipe, the flow which is the usual maximum flow rate for the rapid movement and which is defined by its speed of rotation. The excess amount returns through the pressure limiting valve 100 and the prestressing valve 135 to the reservoir.

For a braking demand of the machine and the corresponding reduction in the metering diaphragm passage section or the complete closure of this diaphragm, the pressure in the supply line 92 decreases as the hydraulic motor 11 rotates more rapidly. The control valve 120 arrives in its rest position; the pressure chamber 113 of the breaking piston 111 is relieved of pressure and the pressure limiting valve switches to its high pressure stage. The pressure thus increases in the second active line 13 and produces the braking, the second hydraulic motor 11 functioning as a pump.

If the pressure in the first active line should increase due to a sudden reduction of the volume transferred in this active line, for example by the rapid closing of the slide valve 90 from a position of large section of the metering diaphragm 96 , the hydraulic fluid passing through the pressure limiting valve 100 will be injected by the check valve 137 to the prestressing pressure of the prestressing valve 135 in this first active conduit to avoid with certainty, cavitation.

The control valve 120 can also be operated other than by pressure. For example, it can be actuated by an electromagnet and in this case the side of the spring must open towards the tank. The control valve 120 can also be proportionally adjusted. It is also possible to replace the control valve 120 made in the form of a 2/2-way valve with the throttle 121 by a 3/2-way spool valve also having a connection to the reservoir.

Some or all of the valves 100, 120, 135, 137 can be integrated in the hydraulic motor 11.

In the exemplary embodiment, the arrival of hydraulic fluid to the hydraulic motor 11 from the pumps 10, 70 through the active conduit 12 corresponds to a forward movement. It is also possible to envisage, for the reverse direction, that is to say in the working direction 13, the injection by the pump 70. The slide valve LS may also have another active position and be connected by a second active connection to the active line 13.

NOMENCLATURE OF THE MAIN ELEMENTS 9 Circuit 10 Pump 11 Hydraulic motor 12 First active line 13 Second active line 14 Inclined plate / swash plate 15 Adjustment piston 16 First control chamber 17 Second control chamber 18 Centering spring 19 Control valve 20 Control unit springs 21 Proportional solenoid 22 Proportional solenoid 23 Lever 24 Control valve housing 27 Pump housing 28 First active channel 29 Second active channel 30 Supply pump 31 Supply channel 32 Check valve 33 Pressure relief valve 34 Liquid path 35 Fixed throttle 36 Adjustable throttle body 37 Spring 38 Alternative valve 39 High pressure relief valve 40 High pressure relief valve 45 Motor housing 46 Active channel 47 Active channel 48 Valve control 49 Rinsing unit 50 Rinsing diaphragm 52 Holding valve pressure 54 Drum cylinder 55 Control piston 56 Adjustment chamber 57 Adjustment chamber 58 Piston rod 59 Resistor device 61 Proportional solenoid 62 Control piston 63 Spring 64 Control spring 70 Second pump 71 Pump housing 72 Pressure line 73 Tray inclined / swashplate 74 Adjustment cylinder 75 Adjustment cylinder 76 Adjustment piston 77 Counter-piston 78 Piston rod 80 Pump control valve unit 81 Charge transmission line 82 Load sensing control valve 83 Control valve pressure 84 Discharge line 85 Compression spring 86 Compression spring 90 Spool valve 91 Active connection 92 Supply line 93 Non-return valve 94 Compression spring 95 Connection 96 Dosing diaphragm 97 Alternative valve 100 Pressure relief valve 101 Main stage of the valve 100 102 Pilot stage of the valve 100 103 orpressure pressure 104 Valve inlet 100 105 Main shut-off member 106 Spring 107 Control fluid nozzle 108 Pilot shut-off device 109 Closing spring 110 Rod 111 Cut-off piston 112 Compression spring 113 Compression chamber 114 Connection to control 120 Control valve 121 Restrictor 122 Inlet connection 123 Conduit 124 Restrictor 125 Output connection 126 Conduit 127 Discharge line 129 Spring 130 Control connection 131 Line 135 Prestressed valve 136 Line 137 Check valve

Claims (11)

1) hydrostatic drive system having: - a first pump (10) adjustable between a positive and negative flow through a neutral position, - a hydraulic motor (11) connected to the first pump (10) by a circuit closed hydraulic motor (9) via a first active conduit (12) whereby, in an operating state, the hydraulic motor (11) receives hydraulic fluid from the first pump (10) and a second pipe active (13) whereby, in the same operating state, the hydraulic fluid passes from the hydraulic motor (11) into the pump (10), - an open hydraulic circuit having a second pump (70) provided with a connection suction (S) for drawing hydraulic fluid from the tank and a high pressure connection (P) through which the hydraulic fluid is injected into the first active line (12) of the closed hydraulic circuit (9), and - a valve device switched by QU el, while maintaining a minimum pressure in the second active line (13), the hydraulic fluid is transferred from the second active line (13) into the tank when the second pump (70) delivers into the first active line (12), characterized in that the switched valve device comprises a pressure limiting valve device (100) switched between two pressure settings. Hydrostatic drive system according to claim 1, characterized in that the switched pressure relief valve device comprises a pre-ordered first pressure relief valve (100) having a main stage (101) and a driver stage (102) and a switching piston (111) receiving the control pressure for setting the driver stage (102), and having two end positions, and - the driver stage (102) and thus also the main stage (101) are set in a first end position of the switched piston (111) on a low pressure level and in a second end position of the switched piston (111) on a high pressure level . 3) hydrostatic drive system according to claim 2, characterized in that the switching piston (111) is loaded by a spring (112) to its second end position and by the control pressure to pass its second end position in its first end position. 4) Hydrostatic drive system according to Claim 1, characterized in that the closed hydraulic circuit (9) comprises a supply circuit provided with a feed pump (30) and a pressure relief valve. pressure (33) limiting the supply pressure and which is supplied by the pressure liquid of an active line (12, 13) when the pressure in this active line (12, 13) falls below the pressure of supply, - a control valve (120) which, depending on its position, discharges the pressure chamber (113) from the pressure limiting valve device (100) to adjust the level of the discharge pressure or is supplied by the supply pressure, and - the low pressure level of the pressure limiting valve device (100) has a value such that the pressure in the second active line and thus the pressure in the supply circuit does not fall below the pressure nece ssary to the setting of the pressure relief valve device (100). Hydrostatic drive system according to Claim 4, characterized in that the low pressure level of the pressure limiting valve device (100) has a value such that the pressure in the second active line (13) is limited to less than the set value of the supply pressure limiting valve (33). Hydrostatic drive system according to Claim 4 or 5, characterized in that the second pump (70) transfers hydraulic fluid via a shut-off valve (93) into the first active conduit (12) of the closed hydraulic circuit. (9) and the control valve (120) has a control connection (130) fluidly connected to the line (92) between the second pump (70) and the check valve (93). 7 °) hydrostatic drive system according to claim 6, characterized by a distributor (90) between the second pump (70) and the shut-off valve (93) which, in a first position, connects the shut-off valve ( 93) to the second pump (70) and in a second position, intersects the pipe segment (92) between it and the shut-off valve (93) to the second pump (70) and discharges it to the reservoir, and the Control branch (130) of the control valve (120) is connected to the line segment (92) between the distributor (90) and the check valve (93). Hydrostatic drive system according to claim 1, characterized in that downstream of the pressure limiting valve device (100) a prestressed check valve (135) maintains the pressure downstream of the valve device. pressure limiting device (100) at a level higher than the pressure in the reservoir, and the inlet of a shut-off valve (137) is connected to the fluid connection between the pressure limiting valve device (100) and the prestressed valve (135), its output being connected to the first active conduit (12). Hydrostatic drive system according to claim 8, characterized in that the low pressure level of the pressure limiting valve device (100) is less than the set pressure in the supply pressure limiting valve (33). ). 10 °) hydrostatic drive system according to claim 1, characterized in that the second pump (70) is adjustable flow rate which is adjusted to inject different amounts of hydraulic fluid into the first active conduit (12). Hydrostatic drive system according to claim 10, characterized in that the second pump (70) has a load sensing control valve (82) and between the high pressure connection (P) of the second pump ( 70) and the first active line (12), a metering diaphragm (96) is preferably continuously set to different non-zero opening sections and the load sensing control valve (82) is biased by the prevailing pressure. in the first active conduit (12).