Hydrostatic Drive

Abstract

A hydrostatic drive includes a diesel engine and a hydrostatic adjustable machine which supplies multiple consumers in normal operation as a pump. The machine has a pressure/flow regulator to which is communicated, according to the load-sensing principle, the highest load pressure of the consumers, in particular when the machine is operated as a pump. In order to realize a start/stop function of the diesel engine, a previously charged high-pressure reservoir supplies the hydrostatic machine, which then acts as a starter motor for the diesel engine. In order to switch from pump to starter motor, the hydro-machine is adjusted over zero. In order for this switch to take place quickly and reliably, the pressure/flow regulator is deactivated by means of a switching valve and the adjustment device is supplied with an adjustment pressure medium via the switching valve, which medium is taken from the high-pressure reservoir or from an auxiliary reservoir.

Claims

1. A hydrostatic drive for starting an internal combustion engine, comprising: a hydraulic machine with a swept volume, the hydraulic machine is (i) adjustable in the swept volume by a hydraulic adjustment device, (ii) operable as a pump and as a motor, and (iii) configured to drive the internal combustion engine in a mode as a motor; at least one high pressure accumulator from which the hydraulic machine is suppliable with pressure medium via a pump line, the pump line running between a working connection of the hydraulic machine and the high pressure accumulator for the mode as a motor; and an accumulator shut off valve having a first position and a second position, the accumulator shut off valve is arranged in the pump line such that a fluidic connection from the high pressure accumulator to the hydraulic machine is open in the first position and is shut off in the second position, wherein the hydraulic machine is adjustable by the adjustment device from a positive swept volume and pump mode via a zero position, in which the swept volume is zero, to a negative swept volume and motor mode, and wherein, for an adjustment to a negative swept volume, the adjustment device is suppliable with pressure medium from a pressure medium source via a control valve independently of the working connection of the hydraulic machine.

2. The hydrostatic drive as claimed in claim 1, wherein, for an adjustment to a negative swept volume, the adjustment device is suppliable with pressure medium from the high pressure accumulator via the control valve.

3. The hydrostatic drive as claimed in claim 1, wherein, for an adjustment to a negative swept volume, the adjustment device is suppliable with pressure medium from an auxiliary hydraulic accumulator via the control valve.

4. The hydrostatic drive as claimed in claim 1, wherein, during an adjustment to a negative swept volume, first of all the adjustment device is acted upon with actuating pressure via the control valve, and the working connection of the hydraulic machine is then only supplied with pressure medium from the high pressure accumulator when the hydraulic machine is adjusted to a negative swept volume.

5. The hydrostatic drive as claimed in claim 4, wherein, during an adjustment to a negative swept volume, first of all the adjustment device is acted upon with actuating pressure via the control valve and the accumulator shut off valve is brought into its first position with a time delay.

6. The hydrostatic drive as claimed in claim 1, wherein the control valve is a seat valve with an inlet that is fluidically connected to the pressure medium source, and with an actuating pressure outlet that is connected to an actuating pressure inlet of the adjustment device, and wherein the control valve has a first position in which the inlet is shut off in an at least approximately leakage-free manner, and a second position in which the inlet is fluidically connected to the actuating pressure outlet.

7. The hydrostatic drive as claimed in claim 1, wherein the high pressure accumulator is superchargeable by the hydraulic machine in the mode as a pump.

8. The hydrostatic drive as claimed in claim 1, wherein: for the mode as a pump, the hydraulic machine is assigned a hydraulic regulating device with an actuating pressure outlet, the control valve is a 3/2-way valve with a first inlet that is fluidically connected to the actuating pressure outlet of the hydraulic regulating device, with a second inlet that is fluidically connected to the pressure medium source, and with an outlet that is connected to an actuating pressure inlet of the adjustment device, and the control valve has a first position, in which the outlet is fluidically connected to the first inlet and the second inlet is shut off, and a second position in which the outlet is connected to the second inlet and the first inlet is shut off.

9. The hydrostatic drive as claimed in claim 8, wherein the hydraulic regulating device is a load-sensing regulating valve which is acted upon by the pump pressure, with the effect of a pressure medium inflow to the actuating pressure chamber of the adjustment device, and is acted upon by a spring and an LS pressure, which is present at an LS connection, with the effect of a pressure medium outflow from the actuating pressure chamber.

10. The hydrostatic drive as claimed in claim 9, wherein an adjustable pressure limiting valve is connected to the LS connection between the latter and a nozzle.

11. The hydrostatic drive as claimed in claim 9, wherein in the mode as a pump, apart from the high pressure accumulator at least one further hydraulic consumer is suppliable with pressure medium by the hydraulic machine, the hydraulic machine operated as a pump is regulable depending on a highest load pressure of the at least one consumer, said load pressure being present in a common LS indicator line, for which purpose the LS indicator line is connected to an LS connection of the LS regulating device, and the pump line is also connectable to the LS indicator line or directly to the LS connection via an LS valve.

12. The hydrostatic drive as claimed in claim 11, wherein the LS valve is a switching valve which, in a basic position pretensioned by a spring, shuts off the pump line to the LS indicator line or to the LS connection, and which, in a switching position, connects the pump line to the LS indicator line or to the LS connection.

13. The hydrostatic drive as claimed in claim 11, wherein a first shuttle valve is arranged in the LS indicator line, at the first inlet of which shuttle valve the highest load pressure of the at least one consumer is present, and to the second inlet of which shuttle valve the LS valve is connected.

Description

[0027] A plurality of exemplary embodiments of a hydrostatic drive according to the invention are illustrated in the drawings. The invention is now explained in more detail with reference to the figures of said drawings.

[0028] In the drawings

[0029] FIG. 1 shows a circuit diagram of a first exemplary embodiment,

[0030] FIG. 2 shows a circuit diagram of a second exemplary embodiment, and

[0031] FIG. 3 shows a detail of a circuit diagram of a third exemplary embodiment.

[0032] FIG. 1 shows a circuit diagram of the first exemplary embodiment which, apart from starting a diesel engine, is also provided for steering and for actuating an item of equipment on a mobile working machine and, for this purpose, comprises a hydrostatic steering system 1 and further hydraulic consumers 2. The drive is used in combination with a diesel engine 4, the crankshaft 6 of which can be coupled to a drive shaft 8 of a hydraulic machine 10 which is adjustable via a zero position and is designed as a fully pivotable axial piston machine. The housing 12 of said hydraulic machine has a tank connection T and a pump connection P for the main volume flow of the hydraulic machine 10, wherein said two connections T, P are permanently and unambiguously assigned high pressure and tank pressure.

[0033] The pump connection P is connected to the steering system 1 and to the further consumers 2 and to a high pressure accumulator 16 via a branched pump line 14, which can also be referred to more generally as the working line. For this purpose, the pump line 14 has a branch 18. A consumer shut off valve 20 which is designed as a 2/2-way switching valve is provided between the branch 18, on the one hand, and the steering system 1 and the further consumers 2, on the other hand. In a blocking position pretensioned by a spring, said consumer shut off valve separates the steering system 1 and the further consumers 2 from the hydraulic machine 10 and the high pressure accumulator 16, while it opens the pump line 14 in a switching position.

[0034] Provided in the pump line 14 between the branch 18 and the high pressure accumulator 16 is an accumulator shut off valve 22 which, in a basic position pretensioned by a spring, shuts off the accumulator 16 in relation to the branch 18 and the hydraulic machine 10, and which opens the pump line 14 in a switching position.

[0035] The hydraulic machine 10 is designed as a fully pivotable axial piston machine. For this purpose, it has an adjustment device which essentially has an actuating cylinder 26 which acts counter to a mating cylinder 28 and a spring and the actuating pressure chamber 30 of which can be filled via an actuating pressure inlet 32. When the hydraulic machine is at a standstill, the pressures in the adjustment device and at the high pressure connection of the hydraulic machine dissipate relatively rapidly because of leakage, and therefore the hydraulic machine is set by the spring to a maximum positive swept volume. During filling of the actuating pressure chamber 30, the hydraulic machine 10 is pivoted back, as a result of which its swept volume is reduced. During more substantial filling of the actuating pressure chamber 30, the hydraulic machine 10 is pivoted through zero and fully pivoted when configured as an axial piston machine. The displacement volume of the hydraulic machine 10, which is now operable as a starter motor for the diesel engine 4, is then increased.

[0036] The actuating pressure chamber 30 can be filled—in the manner known in principle from the prior art—via a pressure delivery flow regulator 34 which has a load-sensing regulating valve which is acted upon by the pump pressure, with the effect of a pressure medium inflow to the actuating pressure chamber 30 of the adjustment device (26) and by a spring and an LS pressure, which is the highest load pressure of the consumers 1, 2 that is indicated at the LS connection X or is a predetermined control pressure, with the effect of a pressure medium outflow from the actuating pressure chamber 30. The pressure equivalent of the spring determines the difference in pressure by which the pump pressure lies above the LS pressure. The highest load pressure of the consumers 1, 2 is tapped off via a cascade of shuttle valves (not shown in FIG. 1) and transmitted to the LS connection X via a common LS indicator line 36.

[0037] A shuttle valve 38 is arranged in the LS indicator line 36, at the first inlet 40 of which shuttle valve the highest load pressure of the consumers 1, 2 is present and to the second inlet 42 of which shuttle valve the pump line 14 is connectable via an LS valve 44. In a basic position pretensioned by a spring, said LS valve shuts off the pump line 14 to the LS indicator line 36. In a switching position of the LS valve 44, the pressure of the pump line 14 is indicated to the shuttle valve 38 and, if said pressure is higher than the highest load pressure of the consumers 1, 2, is indicated to the LS connection X of the pressure delivery flow regulator 34. A hydraulic short circuit can therefore be produced and the pressure delivery flow regulator 34 discharges pressure medium from the actuating pressure chamber 30, as a result of which the delivery volume flow of the hydraulic machine 10 acting as a pump is increased. The high pressure accumulator 16 can therefore be charged.

[0038] Provided between an actuating pressure outlet 46 of the pressure delivery flow regulator 34 and the actuating pressure inlet 32 of the actuating cylinder 26 is a 3/2-way switching valve 48 via which the pressure delivery flow regulator 34 can be circumvented and instead the pressure medium thereof can be supplied from the high pressure accumulator 16 to the actuating pressure inlet 32. For this purpose, the 3/2-way valve 48 has a first inlet 66 which is connected to a portion of the pump line 14 that connects the accumulator shut off valve 22 to the high pressure accumulator 16. A second inlet of the 3/2-way valve 48 is connected to the actuating pressure outlet 46 of the pressure delivery flow regulator 34. An actuating pressure outlet of the 3/2-way valve 48 is connected to the actuating pressure inlet 32 of the actuating cylinder 26.

[0039] In a spring-pretensioned basic position of the 3/2-way valve 48, the pressure delivery flow regulator 34 is connected to the actuating pressure inlet 32 via the 3/2-way valve 48, and therefore the pressure delivery flow regulator 34 can implement the regulation of the hydraulic machine 10—in the manner known from the prior art. By switching over, brought about by an attracting solenoid, of the 3/2-way valve 48 into its switching position, the high pressure accumulator 16 is connected to the actuating pressure inlet 32, and therefore the hydraulic machine 10 is rapidly adjusted over the zero position and is subsequently available as a starter motor for the diesel engine 4.

[0040] An electronic control unit 50 which monitors the start-stop function of the drive shown is shown in the first exemplary embodiment according to FIG. 1. For example, when the stopped diesel engine 4 is restarted via the control unit 50, first of all the consumer shut off valve 20 is closed, and therefore the consumers 1, 2 are not moved unintentionally. Furthermore, the 3/2-way valve 48 is switched, and therefore the hydraulic machine 10 is rapidly adjusted from its position with a maximum positive swept volume over the zero position. Only then is the accumulator shut off valve 22 opened such that the pressure medium can flow from the charged high pressure accumulator 16 via the pump line 14 to the pump connection P of the hydraulic machine 10 and supplies the latter with pressure medium. Via the hydraulic machine 10 acting as a starter motor, the diesel engine 4 can be started with a correct direction of rotation without high connection and tank connection on the hydraulic machine having been mixed up.

[0041] An electronic control unit 50 which monitors the start-stop function of the drive shown is shown in the first exemplary embodiment according to FIG. 1. For example, when the stopped diesel engine 4 is restarted via the control unit 50, first of all the consumer shut off valve 20 is closed such that the consumers 1, 2 are not unintentionally moved. Furthermore, the 3/2-way valve 48 according to the invention is switched, and therefore the hydraulic machine 10 is rapidly adjusted over zero. The accumulator shut off valve 22 is then opened, and therefore the pressure medium can flow out of the charged high pressure accumulator 16 via the pump line 14 to the pump connection P of the hydraulic machine 10 and supplies the latter with pressure medium. Via the hydraulic machine 10 acting as a starter motor, the diesel engine 4 can be started in the direction in which it was previously operated.

[0042] After the diesel engine 4 has been started, in addition to the supply of the consumers 1, 2, the high pressure accumulator 16 can also be recharged via the nonreturn valve 24. The accumulator shut off valve 22 is closed here. During the supply of the consumers 1, 2, the high pressure accumulator 16 can be supercharged up to the highest achieved load pressure of the consumers, wherein the maximum value of the highest load pressure can be determined by a pressure limiting valve which is assigned to the consumers 1, 2. However, the high pressure accumulator is intended to be supercharged to a higher level for a following starting operation than said maximum value of the highest load pressure. Therefore, active supercharging of the high pressure accumulator always precedes the internal combustion engine being switched off. For this purpose, the consumer shut off valve 20 is closed and the LS valve 44 is switched and therefore opened, and therefore the pump pressure or accumulator pressure prevailing at the branch 18 is indicated to the LS connection X of the pressure delivery flow regulator 34 via the first shuttle valve 38. The pump then pivots to a maximum positive swept volume and therefore supercharges the high pressure accumulator to the desired, pressure. If the accumulator pressure which is detected by a pressure sensor has reached the desired value, the LS valve 44 is closed.

[0043] FIG. 2 shows a second exemplary embodiment of a hydrostatic drive according to the invention. The essential difference with respect to the first exemplary embodiment according to FIG. 1 can be seen in the fact that a start-stop valve block 52 is formed in which the consumer shut off valve 20, with which a connection between two connections P1 and P2 of the start-stop valve block 52 can be made and interrupted, the accumulator shut off valve 22, the LS valve 44 and the first shuttle valve 38 are arranged. Furthermore, a second shuttle valve 54 is accommodated in the start-stop valve block 52, said second shuttle valve being connected firstly to an LS indicator line of the steering system 1 and secondly to an LS indicator line of the other consumers 2. In more precise terms, an LD connection LD of a valve block 56 of the steering system 1 and an LS connection LS of a valve block 58 of the other consumers 2 are connected to the second shuttle valve 54 in such a manner that the higher load pressure is indicated to the first inlet 40 of the first shuttle valve 38.

[0044] The two valve blocks 56, 58 furthermore have a pump connection P and a tank connection T. The pump line 14 branches via a priority valve 60 to the two pump connections P of the two valve blocks 56, 58, as a result of which the steering system 1 is favored in the event of a deficient supply.

[0045] Furthermore, in a departure from the first exemplary embodiment according to FIG. 1, four high pressure accumulators 16 switched parallel to one another are shown in the second exemplary embodiment according to FIG. 2, in order thereby to provide a particularly large pressure medium store and energy store for starting the diesel engine 4. For the active supercharging of the hydraulic accumulators 16, the consumer shut off valve is again closed. An LS pressure which is transmitted to the LS connection X of the pressure delivery flow regulator 34 is produced at the LS connection X of the start-stop valve block 52. For this purpose, the pump pressure transmitted to the outlet of the first shuttle valve 38 is reduced with the aid of a nozzle 64 and a proportionally adjustable pressure limiting valve 62 before the pressure is transmitted to the LS connections X of the start-stop valve block 52 and of the pressure delivery flow regulator 34. The nozzle 62 is arranged in a line portion between the outlet of the first shuttle valve 38 and the pressure limiting valve 62. The pressure limiting valve 62 is adjusted to ever higher pressures during the charging. The pump pressure is in each case higher by the pump Δp. In this manner, the speed of the charging operation and the maximum accumulator pressure can therefore be predetermined.

[0046] The LS valve 44 of the second exemplary embodiment according to FIG. 2 is designed as a 3/2-way valve and, in the basic position shown, which said valve takes up under the action of a spring, provides relief of the second inlet 42 of the first shuttle valve 38 to the tank T. A nozzle is arranged between the second inlet of the first shuttle valve 38 and the LS valve 44. Said nozzle can also be omitted.

[0047] By integration of the consumer shut off valve 20 in the start-stop valve block 52, the latter has two pump connections P, of which one is assigned to the hydraulic machine 10 and the other to the consumers 1, 2. Two lifting cylinders are shown as examples of further consumers 2.

[0048] In a departure from the first exemplary embodiment according to FIG. 1, the nonreturn function, which is used for recharging the high pressure accumulator 16 even when the accumulator shut off valve 22 is closed, is integrated in the accumulator valve 22.

[0049] FIG. 3 shows a third exemplary embodiment of a hydrostatic drive according to the invention, wherein the pressure delivery flow regulator 34 and the 3/2-way valve 48 are accommodated in a common housing 70 which is fitted on the housing 12 of the hydraulic machine 10 and, at the interface, forms the two connections for the pump pressure and for the actuating pressure medium. Furthermore, the common housing 70 of the pressure delivery flow regulator 34 and of the 3/2-way valve 48 has the LS connection X and the first inlet 66 described. In a departure from the first two exemplary embodiments according to FIGS. 1 and 2, the actuator of the 3/2-way valve 48 is arranged on the valve body opposite the spring and therefore said actuator is designed as a repelling solenoid.

[0050] The start-stop valve block 52 comprises the accumulator shut off valve 22 which is designed as a continuously adjustable seat valve and forms a block in its inoperative position. An adjustable throttle 74, a pressure reducing valve 76 and a nonreturn valve 78 opening from the pressure reducing valve 76 to the high pressure accumulator 16 are arranged in a parallel line 72 parallel to the accumulator shut off valve 22. Passive and active supercharging of the high pressure accumulator up to a highest value, which is predetermined by the adjustment of the pressure reducing valve 76, is possible via the throttle 74, the pressure reducing valve 76 and the nonreturn valve 78.

[0051] The continuous adjustability of the accumulator shut off valve affords the advantage that the volumetric flow flowing to the hydraulic machine 10 from the high pressure accumulator 16 are increased in a ramp-like manner starting from the closed valve. The effect which can be achieved by this is that the pressure rise in the pump line and at the hydraulic machine does not become too steep and the valves are not overloaded by an initially excessively high volume flow.

[0052] A hydrostatic drive is disclosed which is provided in particular for starting an internal combustion engine, and which is provided with a hydraulic machine which is adjustable in its swept volume by means of a hydraulic adjustment device, is operable as a pump and as a motor, and in a mode as a motor, is provided for driving the internal combustion engine, with at least one high pressure accumulator from which the hydraulic machine is suppliable with pressure medium via a pump line, which runs between a working connection of the hydraulic machine and the high pressure accumulator for the mode as a motor, and with an accumulator shut off valve having a first position and a second position, which is arranged in the pump line and by means of which a fluidic connection from the high pressure accumulator to the hydraulic machine is open in the first position and is shut off in the second position. In order to ensure rapid and reliable starting of the internal combustion engine without a great outlay, the hydraulic machine is adjustable by the adjustment device from a positive swept volume and pump mode via a zero position, in which the swept volume is zero, to a negative swept volume and motor mode. For an adjustment to a negative swept volume, the adjustment device is suppliable with pressure medium from a pressure medium source via a control valve independently of the working connection of the hydraulic machine.

LIST OF DESIGNATIONS

[0053] 1 Steering hydraulics [0054] 2 Other consumers [0055] 4 Diesel engine [0056] 6 Crankshaft [0057] 8 Drive shaft [0058] 10 Hydraulic machine [0059] 12 Housing [0060] 14 Pump line [0061] 16 High pressure accumulator [0062] 18 Branch [0063] 20 Consumer shut off valve [0064] 22 Accumulator shut off valve [0065] 24 Nonreturn valve [0066] 26 Actuating cylinder [0067] 28 Mating cylinder [0068] 30 Actuating pressure chamber [0069] 32 Actuating pressure inlet [0070] 34 Pressure delivery flow regulator [0071] 36 LS indicator line [0072] 38 First shuttle valve [0073] 40 First inlet [0074] 42 Second inlet [0075] 44 LS valve [0076] 46 Actuating pressure outlet [0077] 48 3/2-way valve [0078] 50 Electronic control unit [0079] 52 Start-stop valve block [0080] 54 Second shuttle valve [0081] 56, 58 Valve block [0082] 60 Priority valve [0083] 62 Adjustable pressure limiting valve [0084] 64 Nozzle [0085] 66 Inlet of 48 [0086] 70 Housing [0087] 72 Parallel line [0088] 74 Adjustable throttle [0089] 76 Pressure reducing valve [0090] 78 Nonreturn valve [0091] A, B Working connection [0092] LD LD connection [0093] LS LS connection [0094] T Tank, tank connection [0095] P Pump connection [0096] PS Control pressure outlet [0097] X LS connection