CA2625203A1 - Hydrostatic drive with an open hydraulic circuit and a closed hydraulic circuit - Google Patents

Abstract

The invention relates to a hydrostatic drive with an open hydraulic circuit (2) and a closed hydraulic circuit (3). At least one hydraulic load (20, 21) of a working hydraulic system (18) is arranged in the open hydraulic circuit (2). The closed hydraulic circuit (3) comprises at least one working circuit (37) and one travel circuit (36), wherein at least one further hydraulic load (23) is arranged in the working circuit (37).

Description

Hydrostatic drive having an open hydraulic circuit and a closed hydraulic circuit The invention relates to a hydrostatic drive having an open hydraulic circuit and a closed hydraulic circuit.

Utility vehicles are often provided with a hydrostatic drive both for a hydraulic operating unit and for the travel drive of the vehicle. The hydraulic circuits for activating the hydraulic operating unit and for the travel drive are decoupled. For example, in mobile operating machines, in addition to the closed circuit of the travel drive, a hydraulic operating unit is provided and is arranged in the open circuit. In the most simple case, these are lifting cylinders for adjusting an inclination of an extension arm.

Since generally during operational use, that is to say, for example, when activating an extension arm, the vehicle is stationary, the closed hydraulic circuit is not used, whilst in the open hydraulic circuit, a plurality of hydraulic consumers may be active at the same time. This requires significant dimensioning of the hydraulic pump which is arranged in the open circuit. This not only leads to high investment but is also uneconomical during operation of the vehicle.

The object of the invention is therefore to provide a hydrostatic drive which has an open circuit and a closed circuit and which is improved in terms of its cost-effectiveness.

The object is achieved with the hydrostatic drive according to the invention having the features of claim 1.

The hydrostatic drive according to the invention comprises an open hydraulic circuit and a closed hydraulic circuit.
The closed hydraulic circuit has at least one operating circuit and a travel circuit. The open hydraulic circuit is connected to at least one hydraulic consumer of a hydraulic operating unit. In this manner, when the vehicle is stationary, the hydraulic operating unit which comprises a plurality of hydraulic consumers is connected for operation both to a hydraulic pump of the open circuit and to a hydraulic pump of the closed circuit.

The hydraulic operating unit has individual hydraulic consumers. A portion of this hydraulic consumer is associated with the hydraulic pump of the open circuit.
However, at least one additional hydraulic consumer of the hydraulic operating unit is connected to the closed circuit in an operating circuit. This is particularly advantageous since both the open circuit and the closed circuit are generally driven by a common drive engine. In this instance, both hydraulic pumps are generally connected to the drive engine at the same time. When the hydraulic operating unit is activated, the hydraulic pump of the travel hydraulic unit is thus in any case driven at the same time. Owing to the division of the hydraulic consumers of the hydraulic operating unit between the open circuit and the closed circuit according to the invention, the losses are minimised and at the same time it is possible to construct the pump in the hydraulic circuit so as to be smaller in terms of the power thereof. The weight saving which is thereby achieved, in addition to a reduction of the initial investment, also leads to a reduction of the fuel consumption during travel operation, since the overall mass of the vehicle is reduced.

Advantageous developments are set out in the subsidiary claims.

In particular, it is advantageous to provide, in the closed hydraulic circuit, a valve device by means of which it is possible to switch between the operating circuit and the travel circuit. Owing to the valve device, a closed hydraulic part-circuit is consequently formed in each case in which the hydraulic pump is arranged. The second circuit portion which is not required at that time is decoupled.
Decoupling the travel circuit consequently ensures that the drive wheels are not inadvertently driven.

It is particularly advantageous to provide the valve device, together with other valves of the operating circuit in a valve unit. In particular, the operating circuit may contain association valves by means of which a plurality of consumer line branches can be associated with the respective intake or pressure-side operating lines of the closed circuit. In particular, the valve unit may also have a load retaining valve and/or a pressure limitation valve.
Since the valve unit is associated with the operating circuit, it is possible to secure the operating circuit and in particular the hydraulic consumer itself, irrespective of any pressure limitation valves which may in any case be provided for securing the closed circuit.

Preferably, a flush valve is additionally provided in the valve unit.

The hydraulic pumps of the open circuit and the closed circuit, according to another preferred configuration, are mechanically connected to each other so that a rigid coupling is possible between the two pumps. This has the advantage in particular that energy recovery is possible at the additional hydraulic consumer in the event of a load which is most often constituted by pressure. In this instance, the hydraulic pump of the closed circuit is driven by means of the pressure load via the additional hydraulic consumer. Owing to the rigid connection to the hydraulic pump of the open circuit, the torque which is produced in this manner is supplied to the hydraulic pump of the open circuit via the mechanical coupling, whereby the power which has to be produced by a common drive engine is reduced. This leads to a saving of fuel.

Furthermore, it is advantageous for the hydraulic pump of the closed circuit to be adjustable in terms of the supply volume thereof and to be configured to supply pressure medium in two directions. In a variable hydraulic pump of this type, the control of the additional hydraulic consumer is carried out by adjusting the supply direction and the required supply quantity. Complex control using reduction valves and adjustable throttles can consequently be dispensed with. In particular, there is provision for combination with a lifting cylinder as an additional hydraulic consumer.

An embodiment of the hydrostatic drive according to the invention is illustrated in the drawing and explained in greater detail in the description below:

Figure 1 is a schematic illustration of the hydrostatic drive according to the invention.

The hydrostatic drive 1 according to the invention 5 comprises an open circuit 2 and a closed circuit 3. In the closed hydraulic circuit 3 there is provided a hydraulic pump unit 4 which has an adjustable hydraulic pump 5. The adjustable hydraulic pump 5 is coupled to the hydraulic pump unit 4 by means of a supply pump 6. The hydraulic pump 5 is provided to produce a supply flow in the closed hydraulic circuit 3 and is connected to a first operating line 7 and a second operating line 8. The hydraulic pump 5 is configured to supply in both directions.

Before setting out the development of a travel drive according to the invention, the travel drive as known per se for utility vehicles should first be described. The closed hydraulic circuit 3 comprises a hydraulic motor 9 in addition to the hydraulic pump 5, the first operating line 7' and the second operating line 8'. In the embodiment illustrated, the hydraulic motor 9 is adjustable in terms of the intake volume thereof and is connected to the first operating line 7 and the second operating line 8 and consequently to the hydraulic pump 5 by means of a first operating line portion 7' and a second operating line portion 8'.

The hydraulic motor 9 is connected to a differential gear 11 by means of an output shaft 10. The differential gear 11 is, for example, a rear axle gear of a mobile operating machine. In order to drive the vehicle, the torque supplied to the differential gear 11 acts on a first and a second drive wheel 14, 15 by means of a first half-shaft 12 and a second half-shaft 13.

As described above, the connection of the hydraulic motor 9 to the hydraulic pump 5 is carried out via a first operating line 7 and a first operating line portion 7' and via a second operating line 8 and a second operating line portion 8'. The connection between the first operating line 7 and the first operating line portion 7' and the second operating line 8 and the second operating line portion 8' is carried out by means of a valve device which is arranged in a valve unit 16. The structure of the valve unit 16 is described in greater detail below.

In addition to the hydraulic pump 5 of the closed hydraulic circuit 3, an additional hydraulic pump 17 is provided and is arranged in the open circuit 2. The additional hydraulic pump 17 is also adjustable in terms of the supply volume thereof but configured to supply in only one direction. In addition to the travel drive, a hydraulic operating unit 18 is activated by the overall hydrostatic drive 1. In the embodiment illustrated, the hydraulic operating unit 18 comprises a first hydraulic cylinder 20, a second hydraulic cylinder 21 and a third hydraulic cylinder 23. The first and the second hydraulic cylinder 20, 21 are acted on with pressure medium by the additional hydraulic pump 17 of the open hydraulic circuit 2. However, the third hydraulic cylinder 23 is associated with the closed hydraulic circuit 3 and is coupled to the hydraulic pump 5 via the valve unit 16 as long as the closed hydraulic circuit 3 is not required for the travel drive.

The first hydraulic cylinder 20 is constructed in the embodiment illustrated as a dual-action lifting cylinder, a piston 24 being arranged in the first hydraulic cylinder 20 and dividing the first hydraulic cylinder 20 into a piston face space 27 and a piston rod space 28. Accordingly, a second piston 25 is provided in the second hydraulic cylinder 21 and again divides the second hydraulic cylinder 21 into a piston face space 29 and a piston rod space 30.

The third hydraulic cylinder 23 which is associated with the closed hydraulic circuit 3 accordingly has a piston 26 which is arranged so as to be able to be longitudinally displaced in the third hydraulic cylinder 23. Owing to the piston 26, the hydraulic cylinder 23 is also divided into a piston face space 31 and a piston rod space 32. The pistons 24, 25 and 26 can each be acted on with an adjustment pressure at the side of the piston face space 27, 29 and 31 and at the face orientated in the opposite direction in the piston rod space 28, 30, 32. The adjustment pressure for the first operating cylinder 20 and the second operating cylinder 21 is produced by means of the open hydraulic circuit 2 or the additional hydraulic pump 17 which is arranged therein. However, in order to activate the third hydraulic cylinder 23, pressure is produced by the hydraulic pump 5. In order to transfer the movement of the pistons 24, 25 and 26 produced owing to the pressure relationships in the piston face spaces or piston rod spaces 27 to 32, for example, to an extension arm of a crane lorry, the pistons 24, 25 and 26 are connected to the component to be controlled by means of piston rods 33, 34, 35, respectively.

According to a preferred configuration, the closed hydraulic circuit 3 is formed alternately by a travel circuit 36 or an operating circuit 37. The components of the travel circuit 36 have already been discussed above and the circuit comprises the first operating line branch 7', the hydraulic pump 9 and the second operating line branch 8'. The travel circuit 36 forms, together with the first operating line 7 and the second operating line 8 and the hydraulic motor 5, the closed hydraulic circuit 3, if a travel operation is required.

The operating circuit 37 comprises, in addition to the third hydraulic cylinder 23, a first consumer line 38 and a second consumer line 39 which can be connected to the first operating line 7 and the second operating line 8 by means of the valve device of the valve unit 16. As long as the vehicle is stationary, it is possible to switch between the operating circuit 37 and the travel circuit 36. To this end, a first switching valve 40 and a second switching valve 41 are preferably arranged in the valve unit 16 and form the valve device. The first switching valve 40 and the second switching valve 41 are connected to each other by means of a coupling rod 42 so that common activation is possible. In the initial position of the first switching valve 40 and the second switching valve 41 illustrated in Figure 1, the first operating line 7 is connected to the first operating line portion 7'. At the same time, the second operating line 8 is connected to the second operating line portion 8'.

In order to switch to the operating circuit 37, an electromagnetic activation is provided on the first switching valve 40. To this end, the first switching valve 40 is acted on in the direction of the second switching position thereof by means of an electromagnet 43. The movement which the electromagnet 40 produces in the first switching valve 40 is transmitted by means of the coupling rod 42 to the second switching valve 42 which is consequently also displaced into the second switching position thereof. The movement at the first switching valve 40 and the second switching valve 41 is carried out counter to a pressure spring 44 which is provided on the second switching valve 42. If the electromagnet 43 is no longer supplied with electrical power, the second switching valve 41 and consequently the first switching valve 40 is brought into the first switching position thereof again by means of the pressure spring 44. In the second switching position of the first switching valve 40 and the second switching valve 41, the first operating line 7 is connected to the first consumer line 38. At the same time, the second operating line 8 is connected to the second consumer line 39 by means of the second switching valve 41.

In the embodiment illustrated, the first switching valve 40 and the second switching valve 41 are provided purely for switching between the travel circuit 36 and the operating circuit 37. The control of the electromagnet 43 can therefore advantageously be coupled, for example, to an idle sensor. The association of the piston face space 31 and the piston rod space 32 of the third hydraulic cylinder 23 is, however, carried out by means of an association valve unit 48 which is preferably also arranged in the valve unit 16. In order to associate the piston rod space 32 or the piston face space 31 with the first operating line 7 or with the second operating line 8, the association valve unit 48 connects either a first consumer line branch 38' to the first consumer line 38 and at the same time a second consumer line branch 39' to the second consumer line 39 or the first consumer line branch 38' to the second consumer line 39 and the second consumer line branch 39' to 5 the first consumer line 38. The association valve unit 28 can preferably also be produced with simple switching valves. The adjustment speed and the adjustment direction are determined by the variable hydraulic pump 5 being adjusted.

The open hydraulic circuit 2 comprises, in addition to the additional hydraulic pump 17, an intake line 49. The additional hydraulic pump 17 draws pressure medium from a tank space 50 via the intake line 49 and conveys it into a supply line 51. In order to produce an adjustment pressure in the piston face space 27 or the piston rod space 28 of the first hydraulic cylinder 20, the supply line 51 can be connected to a first connection line 54 or a second connection line 55 by means of a first adjustment valve unit 52. Accordingly, it is also possible to convey pressure medium from the supply line 51 into the piston face space 29 or the piston rod space 30 of the second hydraulic cylinder 21 via a third connection line 56 or a fourth connection line 57. The connection of the third connection line 56 or the fourth connection line 57 to the supply line 51 is carried out by means of a second valve unit 53. The first valve unit 52 and the second valve unit 53 are preferably integrated in a common housing. In place of a connection of the supply line 51 to one of the connection lines 54 to 57, it is also possible to produce a connection to a depressurisation line 57 by means of the valve units 52, 53.

If, for example, a lifting movement of the piston 24 of the first hydraulic cylinder 20 is intended to be carried out by applying pressure to the piston face space 27, the first connection unit 54 is connected to the supply line 51 by means of the first valve unit 52. At the same time, in order to allow volume compensation, the second connection line 55 of the piston rod space 28 is connected to the depressurisation line 57. The pressure medium forced from the piston rod space 28 is consequently discharged into the tank space 50.

The activation of the second hydraulic cylinder 21 is carried out in the same manner, so that it is not necessary to describe this again. The first valve unit 52 and the second valve unit 53 can be controlled together or separately and are connected to the supply line 51 and the depressurisation line 57 by means of common connections.

A common drive motor 45 is used in order to drive the hydraulic pumps 5, 6, 17 and is coupled to the hydraulic pumps 5, 6, 17 by means of a drive shaft 46.

In order to produce an initial system pressure, as described above, a supply pump 6 is provided in the hydraulic pump unit 4 in addition to the hydraulic pump 5.
The supply pump 6 also draws pressure medium from the tank space 50 via a supply pump intake line 58 and conveys it to a supply pressure system (not illustrated) via a supply pressure line 59.

In place of the hydraulic cylinder illustrated, it is also possible to use any other hydraulic consumer. In particular, the individual hydraulic consumers of the hydraulic operating unit 18 do not have to have the same configuration. However, it is particularly advantageous to provide a hydraulic cylinder which is generally only acted on with pressure in the closed hydraulic circuit 3. In this instance, it is possible to recover energy, for example, when pressure is applied to the piston rod 35 of the third hydraulic cylinder 23. The weight which presses on the piston rod 35 produces in the piston face space 31 a pressure which is supplied to the hydraulic pump 5 via the second consumer line branch 39' and the valve unit 16 and is supported at that location. Consequently, the hydraulic pump 5 operates as a hydraulic motor and produces a torque which is supplied to the additional hydraulic pump 17 via the drive shaft 46. The common drive engine 45 consequently has to produce only a reduced level of torque to drive the additional hydraulic pump 17, whereby the fuel consumption of the drive motor 45 decreases.

In order to retain a load which has been lifted using the third hydraulic cylinder 23, a load retaining valve is preferably arranged in the association valve unit 48 and disengages the connection between the first and second consumer line branch 38', 39' and the first consumer line 38 and the second consumer line 39. In order to remove pressure medium from the closed circuit 3, a flush valve can preferably also be integrated in the common valve unit 16 which in particular contains all the valves required to operate the travel circuit 36 and the operating circuit 37.

The invention is not limited to the embodiment illustrated.
In particular, under combinations of individual features as they have been explained in the description above are possible without having to implement all the features explained.

Claims (11)

1. Hydrostatic drive having an open hydraulic circuit (2) in which at least one hydraulic consumer (20) of a hydraulic operating unit (18) is arranged, and having a closed hydraulic circuit which comprises at least one operating circuit (37) and a travel circuit (36), at least one additional hydraulic consumer (23) of the hydraulic operating unit (18) being arranged in the operating circuit (37).

2. Hydrostatic drive according to claim 1, characterised in that the closed hydraulic circuit (3) can be switched between the operating circuit (37) and the travel circuit (36) by means of a valve device (40, 41).

3. Hydrostatic drive according to claim 1 or 2, characterised in that, in the closed circuit (3), there is provided a valve unit (16) by means of which an association of a first consumer line branch (38') and/or a second consumer line branch (39') to connections of the hydraulic pump (5) of the closed circuit (3) is determined.

4. Hydrostatic drive according to claim 3, characterised in that a valve device (40, 41) is integrated in the valve unit (16) for switching between the operating circuit (37) and the travel circuit (36).

5. Hydrostatic drive according to claim 3 or 4, characterised in that the valve unit (16) comprises a load retaining valve.

6. Hydrostatic drive according to claims 3 to 5, characterised in that the valve unit (16) comprises at least one pressure limitation valve.

7. Hydrostatic drive according to claims 3 to 6, characterised in that the valve unit (16) comprises a flush valve.

8. Hydrostatic drive according to claims 1 to 7, characterised in that there is provided in the open circuit (2) an additional hydraulic pump (17) which is mechanically connected to the hydraulic pump (5) of the closed circuit (3).

9. Hydrostatic drive according to claim 7, characterised in that the hydraulic pumps (17, 5) of the open and the closed circuit (2, 3) are connected to a common drive engine (45).

10. Hydrostatic drive according to claims 1 to 9, characterised in that the hydraulic pump (5) of the closed circuit (3) can be adjusted in terms of the supply volume thereof and is configured to supply pressure medium in two directions.

11. Hydrostatic drive according to claims 1 to 10, characterised in that the additional hydraulic consumer (23) is a lifting cylinder.