WO2010118816A1

WO2010118816A1 - Hydrostatic transmission

Info

Publication number: WO2010118816A1
Application number: PCT/EP2010/001905
Authority: WO
Inventors: Marcus Simon; Andreas Illmann; Michael Gaumnitz; Klaus Meyer
Original assignee: Robert Bosch Gmbh
Priority date: 2009-04-16
Filing date: 2010-03-26
Publication date: 2010-10-21
Also published as: DE102009060224A1

Abstract

The invention relates to a hydrostatic transmission having a primary unit and a secondary unit, said units being provided with a constant displacement/suction volume by a plurality of hydraulic machines. The primary and secondary units can be operated in a closed hydraulic circuit.

Description

description

Hydrostatic transmission

The invention relates to a hydrostatic transmission according to the preamble of claim 1.

Such hydrostatic transmissions have a primary unit formed by at least one pump and a secondary unit formed by a hydraulic motor, which are hydraulically coupled. In this case, the primary and secondary units can be operated in an open circuit, being sucked via the pump pressure fluid from a tank and the pressurized pressure medium flow to the hydraulic motor of the secondary unit is passed and flows from there to the tank.

In a closed circuit, the primary unit and the secondary unit are directly connected, so that the pressure center! from the drain port of the secondary unit to the suction or low pressure port of the primary unit is performed and only pressure fluid losses are compensated via a feed pump or the like.

In DE 937 862 a hydrostatic transmission for a machine tool is shown, in which the primary unit is formed by a plurality of pumps, which can be designed as constant pumps or variable displacement pumps. In the pressure medium flow path between the pressure port of the pump and the inlet port of the secondary unit, which is formed in this known solution by hydraulic cylinders, a valve arrangement is provided, via which one or more of the pumps is adjustable to non-pressurized circulation, so that the pressure medium supply to the secondary unit in dependence Operating state across all pumps or a subset of these pumps can be made to adjust the feed rate of the secondary unit. The pressure medium flows from the secondary unit to a tank from where the pumps are supplied with pressure medium - it is thus an open circuit. In DE 198 50 162 C1 an embodiment of a hydrostatic transmission with open circuit is shown, in which the primary unit and the secondary unit are each formed by adjustable hydraulic machines, so that the displacement volume of the secondary unit can be adapted to the pressure of the primary unit to a desired Set the speed of the hydraulic motor.

In EP 0 494 236 B1 a hydrostatic transmission with a primary and secondary unit is shown, each of which is constructed according to the DDU principle (Digital Displacement Unit). The primary and secondary units are each designed as hydraulic machines in axial or radial piston construction, which thus have a discontinuous conveying characteristic. The pressure medium supply and removal to work rooms of these hydraulic machines are controlled by electrically unlockable or lockable check valves, which are controlled by the pump control to operate the respective working space in "fill mode", "partial mode" or "idle mode". As a result, the delivery or absorption volume of the primary / secondary units can be adjusted in the first approximation continuously from a maximum value to zero, wherein the activation takes place in such a way that a low-pulsation sum flow volume flow or total displacement flow volume is achieved Control (DDU) is that the low pressure and high pressure side valves can be switched with high dynamics so that the pressure medium flow paths to or from the working space can be very quickly shut off or released for passage holding valves, preferably designed in a seat design, which are actuated for example by a solenoid actuator.

The disadvantage of this solution is that the adjustment of the displacement / delivery volume on the fast-switching valves requires a considerable control engineering and device-technical effort.

A disadvantage of the solution described in DE 937 862 is that adaptation of the absorption volume of the secondary unit is not possible. In the hydrostatic transmission described in DE 198 50 162 C1, the adjustment of the primary and secondary units can only be carried out relatively slowly, so that adjustments with high dynamics are not possible. Furthermore, a significant device-technical effort for the realization of the adjustable hydro- machine is required.

In contrast, the present invention seeks to provide a simple design hydrostatic transmission, which is adaptable to different operating conditions with high dynamics.

This object is achieved by a hydrostatic transmission with the features of claim 1.

Advantageous developments of the invention are the subject of the dependent claims.

According to the invention, the hydrostatic transmission is designed with a primary unit and a secondary unit, one of which is operated as a pump arrangement and the other as a hydraulic motor arrangement. The pump assembly has a plurality of parallel connected, driven by a common drive shaft pumping units, which are selectively connected via a valve arrangement hydraulically connected to the hydraulic motor assembly, which in turn is in operative connection with an output shaft. Between the secondary unit and the primary unit, a directional control valve is provided for adjusting the direction of rotation of the secondary unit. According to the invention, the secondary unit has a plurality of hydraulic motor units whose inlet connections can be connected in each case via the valve arrangement to a pressure line fed by the pump units or to a low-pressure line.

Accordingly, in the hydrostatic transmission according to the invention, both the primary unit and the secondary unit are formed by a plurality of hydraulic machine units, which are preferably designed as constant units. By selectively switching on or off one or more pumping units or hydraulic machine units, both the displacement volume and the delivery volume of the secondary / primary units can be adapted to different operating conditions, wherein suitable adaptation of the pressure medium connection controlling valve arrangement allows adaptation to different pressures and flow rates with high dynamics.

In a preferred embodiment, each hydromotor unit is assigned an inlet valve on the inlet side and / or a drain valve in one position, which in one position the inlet connection with the pressure line or a drain connection with a drain line and in another position, the inlet connection and the drain connection with a common hydraulic motor units Drain line is connectable. In this way, it is possible with little effort to switch the individual hydraulic machines to non-pressurized circulation, so that it provides no contribution to the drive of the hydrostatic transmission associated consumer.

Correspondingly, a low-pressure valve and / or a high-pressure side pressure valve can be associated with each pump unit, which in one position a low-pressure connection with the low-pressure line or the pressure connection with the pressure line and in another position the low-pressure connection or the pressure connection with all pumping units common Low pressure line connects. By this variant, one or more of the pumping units can be adjusted accordingly to non-pressurized circulation in order to adjust the delivery volume flow accordingly.

In a particularly simple embodiment, a low-pressure valve is assigned to all or more of the pumping units, so that all these pumping units are controlled in the same way.

Accordingly, one or more of the hydraulic motor units can be assigned a common drain valve, so that they can be switched on or off accordingly.

In a particularly simple design solution, the inlet, drain, suction or pressure valves are designed as electrically or electro-hydraulically actuated directional control valves with a flow position and a circulation position, wherein in the latter the respective connection of the primary or secondary unit is connected to low pressure. Such valves can be performed with a very low cost, so that the device complexity is minimal.

For storing braking energy, for example during braking of the secondary unit, the hydrostatic transmission can be designed with a hydraulic accumulator, which can be connected to the low-pressure line via a storage charging valve.

In a variant of the invention, the hydrostatic transmission can be provided with the function of a parking brake when the directional control valve is designed with a blocking position in which the hydraulic connection between the primary and secondary unit is shut off.

In a particularly compact design, the solution or valves provided in the inlet or outlet of the hydraulic motor units and on the low-pressure side and high-pressure side of the pump units are each combined to form a valve.

Such a valve is preferably designed with a circulation position, in which the respective connections are connected to the low-pressure or discharge line.

In another embodiment, for example, for load-free start / run of the primary unit driving motor, a valve of the aforementioned type can be used, which is biased in the direction of its circulating position.

A further improvement of the efficiency in the part-load range can be achieved if the units that are in the non-pressurized circulation, are separated by a coupling of the associated shaft (drive shaft / output shaft).

According to the invention, it is preferred if the primary unit is driven by an internal combustion engine and the output shaft is in operative connection with a differential gear or the like. In a further embodiment of the invention, the delivery or absorption volume of the units is designed differently on the primary or secondary side.

The primary unit and the secondary unit may be arranged either in a closed circuit or in an open circuit. In a closed circuit, the drain lines of the hydraulic motor units are connected to the inlet lines of the pump units. Such a variant has the advantage that the secondary unit can be supported in a thrust reverser, for example, when driving downhill on the primary engine unit side of the combustion engine, so that the required in an open circuit device complexity for hydraulic support is minimized.

To compensate for leakage, the closed circuit is preferably associated with a feed pump via which pressure medium can be fed to a low-pressure side of the primary or secondary unit.

In order to allow a better flushing and cooling of the pump units and hydraulic motor units in the non-pressurized circulation, in one embodiment of the invention, the motor and hydromotor side ports are separately connected to a tank.

Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. Show it:

Figure 1 is a circuit diagram of a first embodiment of a hydrostatic transmission with an open hydraulic circuit;

Figure 2 is a simplified variant of the embodiment of the hydrostatic transmission according to Figure 1;

FIG. 3 shows a further simplified variant, in which the valves on the primary side of the primary unit and the discharge-side valves of the secondary unit are each combined into a single valve; Figure 4 shows a variant in which the low pressure and high pressure side valves of a unit are combined to form a common valve;

Figure 5 shows a variant of the embodiment of Figure 4, wherein this valve is energized energized in a circulating position;

Figure 6 shows a variant of a hydrostatic transmission with the function of a parking brake;

FIG. 7 shows an exemplary embodiment in which pump units of the primary unit and hydraulic motor units of the secondary unit can be separated from the drive or output line via couplings;

FIG. 8 shows a transmission of the basic construction according to the exemplary embodiment according to FIG. 1, in which the primary and secondary units are operated in a closed hydraulic circuit;

9 shows a hydrostatic transmission with a closed hydraulic circuit and a feed pump and

FIG. 10 shows a variant of the hydrostatic transmission according to FIG. 9.

Figure 1 shows a circuit diagram of a hydrostatic transmission 1, via which, for example, a vehicle, a mobile implement, a machine tool or the like can be driven. The hydrostatic transmission 1 consists essentially of a driven by an internal combustion engine 2 primary unit 4, which is connected via a directional control valve 6 hydraulically connected to a secondary unit 8, which in turn is mechanically connected to a differential gear 9 of a motor vehicle. In the exemplary embodiment illustrated, the primary unit 4 has at least four hydraulic machines designed with constant delivery volume, hereinafter referred to as pump units 10a, 10b, 10c, 10d, which are driven by the internal combustion engine 2 via a drive shaft 12 common to all pump units 10. The units 10, 14 are operable in both directions of rotation. In the exemplary embodiment illustrated, the secondary unit 8 has at least four hydraulic machines, hereinafter referred to as hydraulic motor units 14a, 14b, 14c, 14d, which are mechanically connected to the differential gear 9 via an output shaft 16.

The hydrostatic transmission 1 is designed in the embodiments according to Figures 1 to 8 as an open hydraulic circuit. When the primary unit 4 is driven by the pump units 10a, 10b, 10c, 10d, pressure medium is sucked from a tank T via a common low-pressure line 18, branching from the branch lines 20a, 20b, 20c, 20d to low-pressure connections of the pump units 10. In each of these low-pressure branch lines 20, a low-pressure valve 22a, 22b, 22c, 22d is arranged in the illustrated embodiment. This is designed as a 3/2-way valve, which allows in a spring-biased position (a), the flow through the low-pressure branch line 20 and when energizing an electromagnet 24 a, 24 b, 24 c, 24 d in a circulating position (b) is adjustable, in which here as Suction connection of the respective pump unit 10 a, 10 b, 10 c, 10 d designated connection with a branching drain line 26 connects, which opens into the tank T. By switching the low-pressure valve 22 assigned to a pump unit 10, the respective low-pressure connection of the pump unit 10 can be connected directly to the tank T. In the event that the pump units 10 act as hydraulic motors, then the "low pressure port" would be the drain port of the hydraulic machine 10 - this applies to the other units / hydraulic machines 10, 14 accordingly.

The pressure connections of the pumping units 10 are connected via pressure branch lines 28a, 28b, 28c, 28d to a common pressure line 30. Corresponding to the low-pressure side, a pressure valve 32a, 32b, 32c, 32d, whose construction corresponds to that of the low-pressure valves 22, is also arranged in the pressure medium flow path between the respective pressure connection of the pump units 10 and the pressure line 30. That is, these pressure valves 32 are biased in an open position (a) in which the pressure medium from the Druckanschius of the pumping units 10 can flow into the common pressure line 30. By energizing an electromagnet 34 a, 34 b, 34 c, 34 d, each pressure valve 32 can be adjusted to a circulating position (b), in which the respective Druckanschius the pumping units 10 with a to the pressure valves 32 out connect branching pressure-side drain line 36, which opens into a main drain line 38. In the illustrated embodiment, the drain lines 26, 38 are designed as separate lines, but in principle these lines and also the line 36 may be designed as a common drain line.

The pressure line 30 is guided to a pressure port P of the direction of rotation valve 6. This is in the illustrated embodiment designed as a 4/2-way valve that connects in its spring-biased position (a) the pressure port P with a working port A and the main drain line 38 with another working port B. By energizing an electromagnet 40, the direction-of-rotation valve 6 can be switched over to a switching position (b) for reversing, in which the pressure port P is connected to the working port B and the working port A is connected to the port T.

To the working port A, a feed line 42 is connected, branch off from the inlet branch lines 44a, 44b, 44c, 44d to feed ports of the hydraulic motor units 14a, 14b, 14c, 14d. Similar to the primary unit 4, an inflow valve 46a, 46b, 46c, 46d, which in turn has the same construction as the low-pressure valves 22 and the pressure valves 32, are provided in the inlet to the hydraulic motor units 14. Accordingly, these inlet valves 46 are biased by a spring into an open position (a), in which the supply line 42 is connected to the respective inlet port of the associated hydraulic motor unit 14. When an electromagnet 48a, 48b, 48c, 48d is energized, the respective inlet connection of the associated hydraulic motor unit 14a, 14b, 14c, 14d is connected to an inlet-side outlet line 50 which is common to all units and also opens into the tank T. By switching the inlet valves 46, the inlet connection of the hydraulic motor units 14 can thus be connected to the tank T (non-pressurized circulation).

The low-pressure-side drain connections of the hydraulic motor units 14a to 14d are connected via return branch lines 52a, 52b, 52c, 52d to a common return line 54 connected to the working connection B. In each of the return branch lines 52, a drain valve 56 a, 56 b, 56 c, 56 d is provided, whose basic structure in turn that of those designated by the reference numeral 22, 32, 46th Corresponds to valves. Accordingly, the drain valves 56 are designed as 3/2-way valves, which are biased into an open position (a) and by means of a solenoid 58a, 58b, 58c, 58d switchable to a circulation position (b), in which the drain port of Hydraulic motor units 14a, 14b, 14c, 14d are each connected to a branching out to the drain valves 56 outflow-side drain line 60, which is connected to the inflow-side drain line 50 opening into the tank T. Accordingly, by switching the drain valves 56 to the switching position (b), the drain port of the associated hydraulic motor units 14 is directly connected to the tank T.

As stated above, each of the units 10, 14, each of the above-described 3/2-way valves 56, 46, 32, 22 arranged low pressure and high pressure side, so regardless of whether the unit 10,14 as a motor or pump will operate, the unit in question 10, 14 can be switched to non-pressurized circulation.

According to Figure 1, a storage valve 62 is provided in the low-pressure line 18, which is designed as a 3/2-way valve and is biased by a spring in a basic position (a) in which the low pressure line 18 opens into the tank T. By energizing a switching magnet 64, the accumulator charging valve 62 can be adjusted to a position (b), in which the low-pressure line 18 is connected to a hydraulic accumulator 66, the function of which will be explained below.

In the "normal" operating state (forward drive), the internal combustion engine 2 drives the pump units 10 of the primary unit 4 via the drive shaft 12. These pump units 10 are designed as constant pumps in the illustrated embodiment and can be designed, for example, by gear pumps, vane pumps, gerotors or by piston pumps Initially explained, the number of pumping units can be chosen arbitrarily depending on the task, wherein the pumping units 10 need not necessarily be designed with the same delivery volume. In the "normal" operating state, all the valves 22, 32, 46, 56 are in their opening positions (FIG. a) connected (solenoids 24, 34, 48, 58 without current). The pressure medium is sucked in via the pump units 10 and the low pressure line 18 from the tank T and pressurized via the open pressure valves 34 in the pressure line 30 promoted. During the forward travel of the vehicle, the direction of rotation valve 6 is switched to its basic position (a) (switching magnet 40 de-energized), so that the pressure medium conveyed by the primary unit 4 via the supply line 42 and the inlet branch lines 44 branching off from it and the respectively open inlet valves 46 to the inflow port of Hydraulic motor units 14 is promoted. About the hydraulic units 14, the output shaft 16 and thus the differential gear 9 is then driven. The pressure medium flowing away from the outlet connection of the hydraulic motor units 14 flows via the open discharge valves 56 and the return branch lines 52 into the common return line 54 and via the working connection B and the tank connection T of the direction of rotation valve 6 into the main drain line 38 and from there back into the tank T. The above-described operating state is set, for example, when the vehicle is to travel at a comparatively high speed, in which the maximum absorption volume of the secondary unit 8 is utilized.

By reversing the direction of rotation valve 6 into the switching position indicated by (b), a reverse drive of the vehicle can be set. In this case, then the return line 54 and the return valves 56 are in the pressure medium inlet, while the inlet valves 46 and the supply line 52 are in the process.

For starting the vehicle or during slow driving individual pumps of the primary unit 4 can be switched by switching the valves 24 and 36 in their designated (b) circulation positions to non-pressurized circulation, so that both the low pressure side and the pressure side of the pumping units 10 with the tank T are connected. In a corresponding manner, the displacement of the secondary unit 8 can also be reduced by switching the inlet valves 46 and the outlet valves 56 into their respective circulating position (b). This circuit reduces the losses of the primary unit 4 and the secondary unit 8 in the region of low volumetric flow demand, so that a comparatively high efficiency is achieved, in particular in the partial load range. In a hydraulic braking of the vehicle, the braking energy can be converted via a circuit not shown in hydraulic energy by pressure medium during the braking process by switching the storage valve 62 is fed into the hydraulic accumulator 66 so that it is charged. The energy stored in the hydraulic accumulator 66 can then be used, for example, during a starting process of the vehicle to support the internal combustion engine 2.

In the case where the braking energy of the vehicle is converted into hydraulic energy, the units denoted 14 in FIG. 1 then act, so to speak, as a primary unit (pump), via which the hydraulic accumulator 66 can be charged.

2 shows a simplified embodiment is shown, the basic structure of which corresponds to that of Figure 1. The only difference is that the pump units 10a, 10b, 10c, 10d of the primary unit 4 instead of each low pressure valve 22a, 22b, 22c, 22d only one common pumping units 10 common low-pressure valve 22 is assigned, the marked in Figure 2 with A Off - Connected via a suction line 68 to the low-pressure ports of the pumping units 10a to 10d. That the primary unit 4 can be switched low-pressure side by switching a single low-pressure valve 22 in its circulation position (b).

Figure 3 shows a comparison with the variant in Figure 2 further simplified solution in which instead of the three drain-side drain valves 56a, 56b, 56c, 56d of the secondary unit 8, a single drain valve 56 is provided, the hydromotorseitiger input terminal A via a line 70 with the Outlets of the hydraulic motor units 14a to 14d is connected. The output terminal of the discharge valve 56 marked T is then connected to the working connection B of the direction-of-rotation valve 6, as in the exemplary embodiment according to FIG. Incidentally, this embodiment corresponds to that of Figure 2, so that further explanations are unnecessary. The simplification shown in FIG. 3 restricts the functionality for the reversing mode and also for the storage of the braking energy. FIG. 4 illustrates an exemplary embodiment with reference to a pump unit 10a of the hydrostatic transmission according to FIG. 1, in which the low-pressure valves and pressure valves designated by the reference symbols 22 and 32 in FIG. 1 are combined to form a single combination valve 72. This is designed as a 4/2-way valve, in its spring-biased position (a) the pressure line 30 (see Figure 1) connected to the pressure port of the pump unit 10 a pressure branch line 28 a and the low pressure line 18 with the connected to the low pressure port of the pump unit 10 a Low pressure branch line 20a connects. Accordingly, in the switching position (a) of the combination valve 72, the functionality provided in the basic positions (a) of the low-pressure valve 22 and the pressure valve 32 in the embodiment of FIG. 1 is provided. In other words, in the basic position (a) of the combination valve 72, pressure medium is sucked out of the tank T via the low-pressure line 18 and pressurized via the pump unit 10 driven by the internal combustion engine 2 and conveyed to the secondary unit 8 via the pressure branch line 28a and the pressure line 30. Of course, the secondary unit side, each associated with a hydraulic motor unit 14 inlet and outlet valves 46, 56 are executed as a combination valve 72 according to Figure 4.

By adjusting the combination valve 72 in its (b) marked circulation position, both the pressure branch line 28a and the low pressure branch line 20a connected to the low pressure line 18 or a drain line, so that the pump unit 10a is connected to non-pressurized circulation.

FIG. 5 shows a variant in which the internal combustion engine 2 can be started substantially without load or brought to rotational speed. Such a variant can also be used for a failsafe function. In this variant, the combination valve 72 is biased in a basic position (a), in which the pressure branch line 28a and the low-pressure branch line 20a are both connected to the low-pressure line 18, so that the pump unit 10a is switched to de-energized circulation with de-energized solenoid 74. That is, in case of power failure or not energized solenoid 74, the secondary unit 8 is not supplied with pressure medium. This pressure medium supply takes place only after switching to the switching position (b) by means of the switching magnet 74, in which then the pressure branch line 28a with the pressure line 30 and the low pressure line 18 is connected to the low pressure branch line 20a. Of course, the combination valve 72 shown in Figure 5 can be used with an idle circulation position in the hydraulic motor units 14 of the secondary unit 8. That is, the combination valves can be realized both in the resolved valve construction of Figure 1 and in the simplified embodiments according to Figures 2 and 3.

FIG. 6 shows an embodiment corresponding to the hydrostatic transmission according to FIG. 1, in which the function of a parking brake can be represented via the directional control valve 6. In this embodiment, the Drehrich- tuhgsventil 6 is designed as a 4/3-way valve, with a spring-biased home position (0) in which the supply line 42, the return line 54, the main drain line 38 and the pressure line 30 are shut off against each other, so that the hydraulic Connection between primary unit 4 and secondary unit 8 is interrupted. By energizing the two solenoids 40a, 40b, the directional control valve 6 can be adjusted to set the forward drive to the position indicated by (a) and to set the reverse drive to the shift position indicated by (b). In these switching positions (a), (b), the function corresponds to that of the embodiment of Figure 1, so that reference may be made to the relevant embodiments.

Figure 7 shows a variant over which the efficiency in the partial load range, ie in the area in which some of the hydraulic motor units 14 and the pump units 10 are connected to non-pressurized circulation can be further improved. For this purpose, each of the pump units 10a to 10d and the hydraulic motor units 14a to 14d are each associated with a clutch 76a, 76b, 76c, 76d in the primary-side driveline or a clutch 78a, 78b, 78c, 78d in the secondary-side driveline Circulation switched pump units or hydraulic motor units by disengaging the associated clutch 76, 78 mechanically separated from the drive shaft 12 and the output shaft 16 can be separated. These couplings 76, 78 can be designed in any desired manner, for example by mechanical, hydraulic or pneumatic couplings. In this variant, the units 10, 14 arranged on the left in the illustration are then switched to depressurized circulation and, in order to minimize the mechanical losses, the associated couplings 76, 78 are also opened, so that only the units 10, 14 lying to the right are effective. Of course, the valve variants explained with reference to FIGS. 4, 5 and 6 can be used in all described exemplary embodiments.

In the above-described embodiments, the secondary unit 8 and the primary unit 4 are operated in an open hydraulic circuit. Exemplary embodiments are explained with reference to FIGS. 8 to 10, in which these units are arranged in a closed hydraulic circuit.

FIG. 8 shows the basic structure of a hydrostatic transmission 1 according to FIG. 1 with a closed hydraulic circuit, wherein in principle the structure of the primary and secondary units 4 and 8 is the same as in the previously described exemplary embodiments, so that a description of the individual components is dispensed with. An essential difference is that the return line 54 is connected directly to the low pressure line 18 of the primary unit 4 in the basic position of the directional control valve 6 shown in FIG. h., The suction side of the pumping units is always connected to the discharge side of the hydraulic motor units.

The hydraulic accumulator 66 is connected to an input of the shuttle valve 80 via the accumulator valve 62 when the switching magnet 64 is energized and a storage line 82 leading to the output of a shuttle valve 80. The two inputs of the shuttle valve 80 are connected on the one hand to the supply line 42 of the secondary unit 8 and on the other hand to the low pressure line 18 of the primary unit 4, so that the storage line 82 is always connected to the higher pressure line leading the two lines 18 and 42.

The function of the hydrostatic transmission 1 in Figure 8 corresponds to that of the above-described embodiments - as mentioned, the only difference is that the return of the secondary unit 8 (hydraulic motor units 14) is connected to the inlet of the primary unit 4 (pumping units 10). By switching the direction of rotation valve 6 from the illustrated home position, the direction of rotation of the secondary unit 8 can be reversed, so that a reverse drive of the vehicle is set. To start the vehicle or during slow driving individual pump units 10 can be switched by switching the associated valves 22 and / or 32 to non-pressurized circulation, in which case the inlet and / or the flow of the pump unit 10 - as described above - connected to the tank T. is.

In the solution shown in solid line in Figure 8, the circulation ports of the inlet valves 46 via the common drain line 50 and the circulation ports of the drain valves 56 via a common further drain line 84 to the tank T are connected. Correspondingly, the circulation ports of the pressure valves 32 are connected via a common drain line 86 and the circulation ports of the low pressure valves 22 of the primary unit 4 via the drain line 26 to the tank T, so that due to the separate drain lines 50, 84; 86, 26 in the respective circulating position of these valves 46, 56; 32, 22 a better flushing and cooling of the associated pump units 10 and hydraulic motor units 14 is achieved. Instead of this separate connection of the circulation connections can also - as shown in dashed lines in Figure 8 and explained in more detail with reference to the embodiment 9 - are dispensed with a separate connection to the tank, so that the circulation ports of the valves 22, 32 of the primary unit 4 and the valves 56, 46 of the secondary unit 8 via common drain lines (dashed lines in Figure 8) are connected to the tank T.

In the circulation circuit (idling circuit) described above, the losses of the pump / motor combination are reduced in the region of low volumetric flow requirements, and thus a higher efficiency is achieved, in particular in the partial load range.

For hydraulic braking, the storage valve 62 is switched so that the hydraulic accumulator 66 is charged. The stored braking energy can then z. B. be used when starting the vehicle or to start the internal combustion engine 2.

During thrust reversal, the wheels of the vehicle drive the hydraulic motor units 14 via the output shaft 16 faster than by the currently set Pressure fluid flow over the pumping units 10 would be the case - the hydraulic motor units 14 then switch to the pumping mode and the pumping units 10 in the hydraulic motor mode, so that also change the pressure and suction side of these hydraulic machines and the vehicle mass is supported on the internal combustion engine 2 and the hydraulic accumulator 60 is charged with switched storage valve 62. It is ensured by the shuttle valve 80 that the hydraulic accumulator 60 is always connected to the higher pressure line leading. Also in this mode of operation, the suction side of the "pumps" (hydraulic motor units 14) is connected to the discharge side of the "motors" (pumping units 10).

The solution shown in FIG. 8 is preferably used when using external or internal gear machines for the pump units 10 or the hydraulic motor units 14, since the leakage losses there are minimal.

To compensate for the leakage losses, the hydrostatic transmission can be executed in a closed circuit with a feed pump 88 according to FIG. 9, via which pressure medium is fed into the low-pressure side of the closed hydraulic circuit to compensate for leaks. The pressure connection of the feed pump 88 can be connected via a feed line 90 and two check valves 94, 96 to the low-pressure line 18 or pressure line 30. The check valves 94, 96 close to the feed pump 88 so that it is always connected to the lower pressure line 18, 30. The maximum feed pressure in the feed line 90 is limited by a feed pressure limiting valve 98. In the variant shown in FIG. 9, the circulation connections of the secondary side 8 and primary side 4 are each connected to the tank T via a common discharge line 50 or 26.

Finally, FIG. 10 shows an exemplary embodiment which corresponds to that of FIG. 9, wherein-similarly to the exemplary embodiment according to FIG. 8-the circulation connections of the valves 46 are via the drain line 50, the drain valves 56 via the drain line 84, the pressure valves 32 via the drain line 86 and the low pressure valves 22 via the drain line 26 separately connected to the tank T. are. Incidentally, the embodiment according to FIG. 10 corresponds to that of FIG. 9, so that further explanations are unnecessary.

Disclosed is a hydrostatic transmission with a primary unit and a secondary unit, which are each carried out by a plurality of hydraulic machines with constant delivery / displacement, which are operable in both directions of rotation. The primary and secondary units can be operated in a closed hydraulic circuit.

Claims

claims

1. Hydrostatic transmission with a primary unit (4) and a secondary unit (8), one of which is operated as a pump assembly and the other as a hydraulic motor assembly, wherein the pump assembly comprises a plurality of parallel, driven by a common drive shaft (12) pumping units (10a , 10b, 10c, 10d) which are hydraulically connectable via a valve arrangement to the hydraulic motor arrangement (14a, 14b, 14c, 14d) which is in operative connection with an output shaft (16), whereby between primary unit (4) and secondary unit (8) a directional control valve (6) for adjusting the direction of rotation of the secondary unit (8) is arranged, characterized in that the secondary unit (8) has a multiplicity of hydraulic motor units (14a, 14b, 14c, 14d) whose inlet connections are respectively via the valve arrangement (46) with one of the pump units (10a, 10b, 10c, 10d) fed supply line (42) or with a drain line (50) are connectable.

2. Hydrostatic transmission according to claim 1, wherein each hydraulic motor unit (14a, 14b, 14c, 14d) on the inlet side an inlet valve (46a, 46b, 46c, 46d) and / or outlet side associated with a drain valve (56a, 56b, 56c, 56d) is that in one position (a) connects the inlet connection with the inlet line (42) or the outlet connection with a return line (54) and in another position (b) the inlet connection or the drain connection with a drain line (50, 60) ,

3. Hydrostatic transmission according to claim 1 or 2, wherein each pump unit (10a, 10b, 10c, 10d) the low pressure side, a low pressure valve (22a, 22b, 22c, 22d) and / or high pressure side associated with a pressure valve (32a, 32b, 32c, 32d) is, in a position (a) a low pressure port of the pump unit (10a, 10b, 10c, 10d) with a low pressure line (18) and a pressure port of the pump unit (10a, 10b, 10c, 10d) with a pressure line (30) and in another position (b) connects the low pressure port and the pressure port with a drain line (36, 26).

4. Hydrostatic transmission according to claim 2 or 3, wherein a low-pressure valve (22) and / or a drain valve (56) all or a plurality of pumping units (10a, 10b, 10c, 10d) and hydraulic motor units (14a, 14b, 14c, 14d ) assigned.

5. Hydrostatic transmission according to one of the preceding claims, wherein the inlet, drain, low pressure or pressure valve (22, 32, 46, 56) is an electrically or electro-hydraulically actuated directional control valve with a flow position (a) and a circulating position (b) in which the respective connection of the primary or secondary unit (4, 8) is connected to low pressure.

6. Hydrostatic transmission according to one of the preceding claims, with a low pressure side arranged hydraulic accumulator (66) which is connectable via a storage valve (52) with the low pressure line (18).

7. Hydrostatic transmission according to one of the preceding claims, wherein the direction of rotation valve (6) has a blocking position (0).

8. Hydrostatic transmission according to one of the claims 2 to 7, wherein the respective one unit (10, 14) associated valves (22, 32, 46, 56) are each combined to form a combination valve (72).

9. Hydrostatic transmission according to claim 8, wherein the combination valve (72) has a circulation position in which the respective port is connected to low pressure.

10. Hydrostatic transmission according to one of the preceding claims, wherein each pump unit (10) and / or hydraulic motor unit (14) each having a coupling (76, 78) is assigned, via which the associated unit is separable from the drive or output train.

11. Hydrostatic transmission according to one of the preceding claims, wherein the primary unit (4) by an internal combustion engine (2) is driven and the output shaft (16) with a differential gear (9) or the like is in operative connection.

12. Hydrostatic transmission according to one of the preceding claims, wherein the primary and secondary units by continuously conveying Hydromachines are formed with two directions of rotation, for example, with internal or external gear machines.

13. Hydrostatic transmission according to one of the preceding claims, wherein the delivery / absorption volume of the hydraulic machines (10, 14) is designed differently.

14. Hydrostatic transmission according to one of the preceding claims, wherein the secondary unit (8) and the primary unit (4) are operated in an open or closed hydraulic circuit.

15. Hydrostatic transmission according to claim 14, second alternative, wherein a return line (54) of the secondary unit (8) with a low-pressure line (18) of the primary unit (4) is connected.

16. Hydrostatic transmission according to claim 15, with a feed pump (88) for supplying pressure medium in the low pressure side of the closed circuit.

17. Hydrostatic transmission according to claim 5 or one of the claims back to this, wherein circulation ports of the valves (22, 32, 46, 56) via separate drain lines (26, 50, 84, 86) are connected to the low pressure (T).