Method for operating a hydraulic pump with adjustable delivery volume

Abstract

The invention relates to a method for operating a hydraulic pump (24) of a hydrostatic auxiliary drive (20) of a motor vehicle. The hydraulic pump (24) can be drivenly coupled to a main drive (10) of the motor vehicle by means of a coupling device (32). Furthermore, the delivery volume of the hydraulic pump (24) can be selectively set to either a first delivery volume value or a second delivery volume value that is greater than the first delivery volume value. The method includes commissioning the hydraulic pump (24), wherein the commissioning includes setting the delivery volume of the hydraulic pump (24) to the first delivery volume value. The commissioning also includes drivingly coupling the hydraulic pump (24) to the main drive (10) by means of the coupling device (32).Furthermore, the commissioning process involves mechanically driving the hydraulic pump (24), which is set to the first delivery volume value and coupled to the main drive (10), by means of the main drive (10). Finally, the commissioning process involves changing the delivery volume of the driven hydraulic pump (24) from the first delivery volume value to the second delivery volume value.

Description

[0001] The invention relates to a method for operating a hydraulic pump of a hydrostatic auxiliary drive, a drive device for a motor vehicle designed to carry out the method, and a motor vehicle with such a drive device.

[0002] It is generally known to equip motor vehicles with a hydrostatic auxiliary drive to power an auxiliary drive axle. This auxiliary drive can usually be engaged temporarily as needed, for example, when driving on slippery surfaces, mud, and / or gravel, to provide traction support to the vehicle's main drive axle.

[0003] The hydrostatic auxiliary drive can be designed such that a hydraulic pump is connected via a pipe system to at least one hydraulic motor of the auxiliary drive axle. Preferably, the hydraulic pump is driven by the main drive of the vehicle. For example, the hydraulic pump can be driven via a transmission in a fixed ratio to the main drive. Since traction assistance is primarily required at low speeds, the hydraulic pump is advantageously coupled to the main drive via a coupling device, e.g., with one or more clutches. This allows the hydrostatic traction assistance to support the main drive axle at low vehicle speeds, and then disengage from the main drive at a preselected speed.

[0004] The clutch assembly for connecting the hydraulic pump to the main drive is advantageously switchable when the vehicle is stationary or while driving, possibly under load. Depending on the type of clutch, further limitations arise when shifting under load, for example, in the form of torque limits. Generally, the lowest possible torque is desired when shifting the clutch assembly, as this allows for a simpler, lighter, and more compact design. A significant portion of the torque present at the clutch assembly in the hydrostatic auxiliary drive described above, particularly during start-up, is generated by the hydraulic pump (e.g., due to stick-slip effects) and by the viscosity of the hydraulic fluid.

[0005] The positioning of the coupling device for connecting and disconnecting the hydraulic pump to and from the main drive can, in principle, be arbitrary. However, the boundary conditions for the component change due to the gear ratio: The torque is lowest and the rotational speed is highest near the hydraulic pump. The larger the gear ratio between the hydraulic pump and the coupling device, the greater the torque and the lower the rotational speed at the coupling.

[0006] For reasons of installation space and / or other factors, it can be advantageous to position the clutch assembly as far away from the hydraulic pump as possible. However, this increases the drag torque due to the gear ratio or the transmission assembly up to the clutch assembly. This is particularly disadvantageous if the clutch assembly is designed in such a way that a distinction is made between starting and operating torque transmission (e.g., a factor 10 greater than the starting torque).

[0007] The object of the invention is to provide a solution that enables improved operation of a hydraulic pump of a hydrostatic auxiliary drive. A preferred object of the invention is to provide a solution that simplifies the commissioning of the hydraulic pump, in particular by reducing the drag torque of the hydraulic pump during commissioning, thereby facilitating the switching operation of a coupling device arranged between the hydraulic pump and the drive.

[0008] These problems can be solved using the features of the independent claims. Advantageous embodiments and applications of the invention are the subject of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

[0009] According to a first independent aspect of the present disclosure, a method for operating a (e.g., high-pressure) hydraulic pump of a (e.g., switchable) hydrostatic auxiliary drive of a motor vehicle (e.g., a commercial vehicle) is provided. The hydraulic pump, which may also be referred to as a hydraulic pump, can be designed, for example, as a radial piston pump, axial piston pump, or rotary lobe pump. The hydraulic pump can be fluidically connected, or connected, to at least one hydraulic motor of the hydrostatic auxiliary drive via a piping system of the hydrostatic auxiliary drive.

[0010] The hydraulic pump can be drivenly coupled to a main drive (e.g., an internal combustion engine and / or electric motor) of the motor vehicle by means of a coupling device (e.g., positive locking and / or friction locking). For example, the hydraulic pump and the main drive can be selectively drivenly connected or disconnected from each other by means of the coupling device.

[0011] Furthermore, it is provided that the (e.g., geometric) delivery volume of the hydraulic pump can be selectively set to either a first delivery volume value or a second delivery volume value. Preferably, the second delivery volume value is greater than the first delivery volume value. For example, the first delivery volume value can be a minimum delivery volume value of the hydraulic pump, while the second delivery volume value can be a maximum delivery volume value of the hydraulic pump.

[0012] The delivery volume, which can also be referred to as displacement volume, can be, for example, the volume of hydraulic fluid delivered per revolution of the hydraulic pump (or its drive shaft) (e.g., in cm³). 3 The delivery volume can be calculated, for example, from the geometric dimensions of the displacement chambers of the hydraulic pump or by measurements. The product of delivery volume and rotational speed is also referred to as delivery rate or volume flow rate.

[0013] The procedure involves starting up the (e.g., stationary) hydraulic pump.

[0014] The commissioning of the hydraulic pump involves setting its delivery volume to the first (e.g., smaller) delivery volume value. This is preferably done to reduce or minimize the hydraulic pump's drag torque.

[0015] Furthermore, starting up the hydraulic pump involves connecting it to the (e.g., running) main drive via the coupling device. This can be achieved, for example, by closing a clutch in the coupling device.

[0016] Furthermore, the commissioning of the hydraulic pump involves mechanically driving the pump, which is set to the first delivery volume value and coupled to the main drive, by means of the main drive. For example, the main drive can mechanically and / or rotaryly drive a drive shaft of the hydraulic pump. Preferably, the mechanical drive is used to pump hydraulic fluid (e.g., hydraulic oil) via the hydraulic pump.

[0017] Furthermore, commissioning the hydraulic pump involves adjusting the delivery volume of the driven hydraulic pump to the second (e.g., larger) delivery volume value. For example, this adjustment can involve changing the delivery volume of the driven hydraulic pump from the first (e.g., smaller) delivery volume value to the second (e.g., larger) delivery volume value. This change in delivery volume can occur, for instance, when the rotational speed of the driven hydraulic pump exceeds a predetermined target speed. Preferably, adjusting the delivery volume to the second (e.g., larger) delivery volume value serves to build up working pressure in the hydrostatic auxiliary drive, e.g., in the hydraulic auxiliary drive's piping system.

[0018] This advantageously ensures that the hydraulic pump exerts minimal drag torque on the coupling device during engagement or closure, as the low flow rate of the hydraulic pump results in minimal flow losses. Only after engagement is the flow rate increased to ensure reliable operation of the hydrostatic auxiliary drive, and the resulting fluctuations in drag torque are tolerated by the components involved. Furthermore, minimizing the drag torque allows for the advantageous use of a coupling device primarily operating on the positive locking principle, which can generally be designed to be smaller and more compact than, for example, a purely friction-based coupling device. This saves costs, installation space, and weight, and can also improve the operational reliability of the coupling device.

[0019] From a first perspective, the delivery volume of the driven hydraulic pump can be adjusted to the second delivery volume value depending on the pump's rotational speed (e.g., detected by a speed sensor). For example, the delivery volume of the driven hydraulic pump can be adjusted to the second delivery volume value depending on the pump's rotational speed when the pump's rotational speed reaches a (e.g., predetermined) target speed. Advantageously, this ensures reliable adjustment of the hydraulic pump using a parameter that is easily detectable (e.g., by a speed sensor).

[0020] According to another aspect, the first delivery volume value can be a minimum delivery volume value of the hydraulic pump and / or result in zero delivery by the hydraulic pump. For example, when the hydraulic pump operates at the first delivery volume value, essentially only a very small amount of hydraulic fluid may be delivered (e.g., to compensate for leakage losses) or essentially no hydraulic fluid may be delivered by the hydraulic pump. This advantageously minimizes flow losses in the hydraulic pump and thus its drag torque.

[0021] Alternatively, or in addition, the second delivery volume value can be the maximum delivery volume of the hydraulic pump. For example, when the hydraulic pump is operated at the second delivery volume value, the maximum possible volume of hydraulic fluid can be delivered by the hydraulic pump per revolution. This advantageously ensures an adequate supply of hydraulic fluid to the hydrostatic auxiliary drive.

[0022] Alternatively, or in addition, the delivery volume of the hydraulic pump can be set exclusively to either the first or second delivery volume value. For example, the delivery volume of the hydraulic pump can be set exclusively or digitally to the minimum or maximum delivery volume. This advantageously allows for the simplest possible adjustment of the hydraulic pump.

[0023] Another aspect of starting up the hydraulic pump can involve hydraulically short-circuiting a suction side of the pump with a pressure side before the pump is coupled to the main drive. Preferably, this hydraulic short-circuiting is achieved by returning hydraulic fluid pumped by the pump (e.g., in a closed circuit) directly back to the pump (e.g., without supplying a consumer of the hydrostatic auxiliary drive). By way of example, the hydraulic short-circuiting can also be accomplished via a suitable bypass circuit in the piping system connecting the suction and pressure sides of the pump. This bypass circuit can be implemented as needed, for instance, by appropriately switching one or more control valves in the piping system. This advantageously minimizes the drag torque of the hydraulic pump acting on the coupling device.

[0024] According to another aspect, the clutch assembly can have a positive-locking clutch (e.g., a dog clutch) with a synchronizer (e.g., friction-locking) (e.g., a multi-plate synchronizer). The synchronizer advantageously compensates for speed differences during the shifting process, at least partially, thereby ensuring the lowest possible wear on the clutch assembly. A further advantage is that the aforementioned clutch assembly design allows for a very compact and small clutch geometry.

[0025] Furthermore or alternatively, when the hydraulic pump is coupled to the main drive, the hydraulic pump can be coupled to the main drive via a transmission device (e.g., arranged between the coupling device and the hydraulic pump). Preferably, the transmission device has a fixed (or unchanging) gear ratio. This ratio can be determined, for example, as a function of the hydraulic pump's delivery volume, the displacement of at least one hydraulic motor of the hydrostatic auxiliary drive, and / or the gear ratio of a main drive axle of the vehicle. This advantageously allows the torque / speed ratios acting on the coupling device to be adjusted.

[0026] Another aspect is that the hydraulic pump can have an actuating element (e.g., a mechanical actuator) for adjusting its delivery volume. For example, the actuating element can change the pump's swivel angle. This actuating element can, in turn, be coupled to a hydraulic control circuit. For instance, it can be operatively connected to a hydraulic actuator within that circuit. Adjusting the hydraulic pump's delivery volume can then be achieved by actuating the actuating element via the hydraulic control circuit. This advantageously ensures reliable adjustability of the hydraulic pump's delivery volume.

[0027] In one embodiment, the hydraulic control circuit can include a feed pump for supplying a control fluid. Preferably, the feed pump can be mechanically driven (e.g., via a torque transmission device) by the main drive and / or by a pump drive (e.g., an electric pump motor) that is directly connected to the feed pump and / or separate from the main drive.

[0028] Furthermore, the hydraulic control circuit can include a hydraulic actuator that is coupled (e.g., connected) to the actuating element and can be actuated with the control fluid supplied by the feed pump via a fluid connection. For example, the hydraulic actuator coupled to the actuating element can be configured to hold the actuating element in a first position when unactuated and to hold the actuating element in a second position when actuated.

[0029] Furthermore, the hydraulic control circuit can include a valve assembly through which the fluid connection (between the hydraulic actuator and the feed pump) can be selectively opened or closed, preferably to selectively supply the hydraulic actuator with control fluid or not. This advantageously ensures reliable adjustability of the hydraulic pump's delivery volume.

[0030] According to another aspect, the hydrostatic auxiliary drive can serve to drive an auxiliary drive axle of the motor vehicle. An axle, as defined in B. Heißing (ed.) et al., Fahrwerkshandbuch (DOI 10.1007 / 978-3-8348-8168-7), Chapter 4, can be understood, for example, as the entire connection between two wheels and the wheel suspension for individual wheels, including its connection to the chassis or chassis frame. A typical passenger car therefore usually has two axles and four wheel suspensions. Preferably, the auxiliary drive axle can be a (e.g., steerable) front axle, a liftable rear axle, a leading axle, or a trailing axle of the motor vehicle. This advantageously provides hydrostatic traction support for driving on difficult surfaces such as mud and / or gravel.

[0031] In addition, or alternatively, the main drive can serve to drive a main drive axle of the motor vehicle. For example, the main drive axle can be a (e.g., unsteered) rear axle of the motor vehicle.

[0032] In addition or alternatively, the main drive can consist of an internal combustion engine and / or an electric motor.

[0033] According to another aspect, the hydrostatic auxiliary drive can comprise at least one hydraulic motor (e.g., at least one radial piston wheel hub motor) and a (e.g., hydraulic) piping system. The hydraulic pump and the at least one hydraulic motor can be hydraulically connected or linked to each other via the piping system. For example, hydraulic fluid can be exchanged between the at least one hydraulic motor and the hydraulic pump via the piping system. The at least one hydraulic motor, in turn, can preferably be assigned to an auxiliary drive axle of the vehicle and / or be designed to convert the hydraulic energy of the hydraulic fluid into mechanical energy, which can then be used, for example, to drive the auxiliary drive axle or to propel the vehicle. As mentioned above, this advantageously enables hydrostatic traction support when required.

[0034] In one embodiment, the at least one hydraulic motor can comprise two hydraulic motors, each preferably assigned to a wheel of the vehicle. For example, one of the two hydraulic motors can be assigned to a left wheel of the vehicle and the other to a right wheel. Preferably, the two hydraulic motors are two wheel hub motors, and particularly preferably two radial piston wheel hub motors.

[0035] According to another aspect, the at least one hydraulic motor can be operated as a (e.g., hydraulic) pump by mechanical drive (e.g., via a rolling motion of the associated wheel). For example, hydraulic fluid, preferably in the piping system, can be conveyed by means of the at least one hydraulic motor by mechanically and / or rotaryly driving an (actual) output shaft of the hydraulic motor.

[0036] Another aspect is that the drive coupling can occur depending on a speed difference (detected, for example, by speed sensors) between a main drive-side input of the clutch assembly and a hydraulic pump-side output of the clutch assembly. Preferably, the drive coupling occurs when the speed difference falls below a (e.g., predetermined) limit value. This advantageously ensures wear-free shifting of the clutch assembly.

[0037] According to another aspect, the at least one hydraulic motor can have an operating state in which it couples the hydraulic fluid and an output (e.g., an output shaft or a rotor housing) of the at least one hydraulic motor in a force-transmitting manner. Furthermore, the at least one hydraulic motor can have a free-running state in which the output is freely rotatable and / or no force transmission occurs between the output and the hydraulic fluid. For example, the at least one hydraulic motor can be designed as a radial piston wheel hub motor, comprising at least one extendable and retractable radial piston and a cam ring, wherein the at least one radial piston is extended in the operating state and runs against the cam ring, and is retracted in the free-running state and has no contact with the cam ring.This advantageously allows power transmission between the roadway and the hydrostatic auxiliary drive to be selectively enabled or interrupted as needed.

[0038] In one embodiment, starting up the hydraulic pump before pumping hydraulic fluid can further involve moving the at least one hydraulic motor (e.g., from the free-running state) into the operating state. For example, the at least one radial piston of the at least one hydraulic motor can be extended for this purpose. Advantageously, this enables a trailing or push-type operation of the at least one hydraulic motor.

[0039] Furthermore, or alternatively, the commissioning of the hydraulic pump after the drive coupling can also involve moving the at least one hydraulic motor (e.g., from its operating state) into a free-running state. For example, the at least one radial piston of the at least one hydraulic motor can be retracted for this purpose. Preferably, the at least one hydraulic motor is moved into a free-running state to terminate the hydraulic drive of the hydraulic pump. This advantageously allows for the most energy-efficient operation of the hydraulic pump in operating conditions where no traction support from the hydrostatic auxiliary drive is required.

[0040] Another aspect is that the delivery volume of the hydraulic pump can be adjusted (e.g., continuously) to several different delivery volume values ​​between the first and second delivery volume values. For example, the delivery volume of the hydraulic pump can be adjusted continuously or in several steps between a minimum and a maximum delivery volume value.

[0041] Furthermore, in this context, commissioning the hydraulic pump before the drive coupling can involve changing the delivery volume of the hydraulic pump (e.g., hydraulically driven and / or set to the first delivery volume) from the first delivery volume value to one of several further delivery volume values. Accordingly, the delivery volume of the hydraulic pump can preferably be increased (e.g., incrementally) even before the drive coupling. Preferably, the aforementioned change in the delivery volume of the driven hydraulic pump is carried out in such a way that (e.g., by the corresponding further delivery volume value) the speed difference between the main drive-side input of the coupling device and the hydraulic pump-side output of the coupling device is minimized. For example, the change in the delivery volume can be carried out by means of an optimization method (e.g.,(using gradient-based Newton methods, dynamic programming, heuristics and / or using a neural network), the delivery volume value is selected from the several other delivery volume values ​​which minimizes the speed difference between the main drive-side input of the clutch device and the hydraulic pump-side output of the clutch device.

[0042] According to another aspect, the method can include deactivating the hydraulic pump (e.g., set to the second delivery volume value and / or coupled to and driven by a main drive via the coupling device). Deactivating the hydraulic pump can, for example, occur after commissioning it. However, the features related to deactivation should also be disclosed and claimable independently of commissioning. In other words, the method for operating the hydraulic pump can, in principle, consist solely of deactivating the hydraulic pump without the corresponding commissioning steps, whereby the features described herein in connection with commissioning should also be disclosed and claimable independently of the actual commissioning, but only in connection with deactivation.

[0043] The aforementioned deactivation can optionally involve a hydraulic short-circuiting of one (or both) suction side of the hydraulic pump with one (or both) pressure side of the hydraulic pump (which may be set to the second delivery volume value and / or coupled to a main drive via the coupling device and / or driven by the main drive). Preferably, the hydraulic short-circuiting is carried out such that hydraulic fluid pumped by the hydraulic pump (e.g., in a closed circuit) is returned directly to the hydraulic pump (e.g., without supplying a consumer of the hydrostatic auxiliary drive). This advantageously reduces the drag torque of the hydraulic pump acting on the coupling device.

[0044] The aforementioned shutdown can (furthermore) involve adjusting the delivery volume of the hydraulic pump (e.g., hydraulically short-circuited and / or set to the second delivery volume value and / or driven by a main drive via the coupling device and / or driven by the main drive) to the first delivery volume value. For example, adjusting the delivery volume can involve changing the delivery volume from the second delivery volume value to the first delivery volume value. Preferably, the first delivery volume value is a minimum delivery volume value of the hydraulic pump. Furthermore, preferably, the delivery volume is adjusted to reduce the drag torque of the hydraulic pump (e.g., further).

[0045] The decommissioning process can further involve the decoupled operation of the hydraulic pump, set to the first delivery volume value, from the main drive by means of the coupling device. This can be achieved, for example, by opening a clutch within the coupling device. Advantageously, this ensures that the hydraulic pump exerts the lowest possible drag torque on the coupling device during decoupling or opening, since only minimal flow losses occur in the hydraulic pump due to the low delivery volume.

[0046] Another independent aspect of the present disclosure relates to a drive device for a motor vehicle (e.g. a commercial vehicle).

[0047] The drive system includes a main drive (e.g., for driving a main drive axle of the motor vehicle). For example, the main drive can be an internal combustion engine and / or an electric motor.

[0048] Furthermore, the drive device includes a (e.g., switchable) hydrostatic auxiliary drive (e.g., for driving an auxiliary drive axle of the motor vehicle). The hydrostatic auxiliary drive, in turn, includes a (e.g., high-pressure) hydraulic pump whose delivery volume is adjustable between a first delivery volume value and a second delivery volume value, with the second delivery volume value preferably being greater than the first delivery volume value. For example, the first delivery volume value can be a minimum delivery volume value of the hydraulic pump, while the second delivery volume value is a maximum delivery volume value of the hydraulic pump.

[0049] The drive device also has a coupling device (e.g., positive locking and / or friction locking) by means of which the hydraulic pump can be coupled to the main drive.

[0050] The drive device further comprises a processing unit (e.g., control unit) by means of which the delivery volume can be adjusted and the coupling device engaged. Preferably, the processing unit can also be used to initiate operation of the main drive and / or switching of the piping system and / or selectively placing the at least one hydraulic motor into the operating or freewheeling state. For example, the processing unit can be connected to the main drive and / or the components of the auxiliary drive (e.g., the hydraulic pump) and / or the coupling device via appropriate signal lines. The processing unit is configured to execute a method as disclosed herein (e.g., automatically). Consequently, the features described above in connection with the method are also disclosed and claimable in connection with the drive device.The same should apply in reverse.

[0051] Another independent aspect of the present disclosure relates to a motor vehicle comprising a drive device as described herein. Preferably, the motor vehicle is a commercial vehicle. A commercial vehicle can generally be understood to be, for example, a vehicle that, by its design and equipment, is specifically designed for the transport of persons, the transport of goods, or the towing of trailers. For example, the commercial vehicle can be a truck, a semi-trailer truck, a construction vehicle, and / or a bus.

[0052] The embodiments and features described above can be combined in any way. Further details and advantages are described below with reference to the accompanying drawings. These show: Fig. 1 a schematic sectional view of a drive device for a motor vehicle according to one embodiment; Fig. 2 a schematic sectional view of a drive device for a motor vehicle according to a further embodiment; and Fig. 3 a flowchart of a method for operating a hydraulic pump by means of a drive device according to an embodiment.

[0053] The in the Fig. 1 and Fig. The two embodiments shown are at least partially identical, so that similar or identical parts are provided with the same reference numerals and, to avoid repetition, reference is also made to the description of the other embodiments or figures for their explanation.

[0054] The Fig. 1 and Fig. Figure 2 each shows a drive device 30 for a motor vehicle. The motor vehicle can be, for example, a commercial vehicle such as a truck, semi-trailer truck or bus.

[0055] The motor vehicle can have multiple axles. For example, the motor vehicle can have at least one main drive axle 1 with a left and right wheel 3, and at least one auxiliary drive axle 2 with a left and right wheel 3. By way of example only, as shown, the at least one main drive axle 1 can comprise a non-steered (or rigid) rear axle, while the at least one auxiliary drive axle 2 can comprise a steerable front axle. In addition, or alternatively, the at least one auxiliary drive axle 2 can also have, for example, a liftable rear axle, a leading axle, and / or a trailing axle. Furthermore, the at least one main drive axle 1 can also have a front axle in addition to, or as an alternative to, the non-steered rear axle.

[0056] The drive device 30 has a main drive 10, a hydrostatic auxiliary drive 20, a coupling device 32 and a processing device 34.

[0057] Preferably, the main drive 10 serves to drive the main drive axle 1 of the motor vehicle. For this purpose, the main drive 10 can be connected, or be connectable, to an input of a differential 16 of the at least one main drive axle 1, for example, via a vehicle transmission 12 and an output shaft 14. The main drive 10 can be, for example, an internal combustion engine or an electric motor. The main drive 10 can be configured to drive the motor vehicle on its own and / or to propel the motor vehicle on its own.

[0058] The hydrostatic auxiliary drive 20 is preferably designed to provide traction support to the main drive 10 (e.g., on a temporary and / or demand-based basis). For example, the hydrostatic auxiliary drive 20 can be manually engaged by the driver when driving on slippery surfaces, mud, and / or gravel. However, the hydrostatic auxiliary drive 20 can also be automatically activated by the vehicle if, for example, traction support is determined to be necessary or advantageous based on sensor data.

[0059] The hydrostatic auxiliary drive 20 can be used to drive the auxiliary drive axle 2. Accordingly, the motor vehicle can be driven by means of the hydrostatic auxiliary drive 20, preferably in addition to the main drive 10, and / or propulsion of the motor vehicle can be effected.

[0060] The hydrostatic auxiliary drive 20 preferably comprises a hydraulic pump 24, at least one hydraulic motor 26 and a (e.g. hydraulic) piping system 28.

[0061] The hydraulic pump 24 can be driven by the coupling device 32 and connected to the main drive 10. For example, a drive shaft of the hydraulic pump 24 can be connected to the output shaft 14 via the coupling device 32, so that torque generated by the main drive 10 can be transmitted to the hydraulic pump 24. Accordingly, the hydraulic pump 24 can be driven indirectly by the main drive 10, either mechanically and / or by rotation.

[0062] The coupling device 32 can, for example, have a positive-locking coupling (e.g., a jaw coupling) with friction-based synchronization. Alternatively, or in addition, the coupling device 32 can also have a conical friction coupling.

[0063] Furthermore, it is possible that a transmission device 33, e.g., comprising several meshing gears, is arranged between the hydraulic pump 24 and the coupling device 32 or between the coupling device 32 and the main drive 10. Preferably, the transmission device 33 has a fixed gear ratio. The (fixed) gear ratio can, for example, be determined depending on the design of the components of the hydrostatic auxiliary drive 20.

[0064] The hydraulic pump 24 and the at least one hydraulic motor 26 can be hydraulically connected or linked to each other via the aforementioned piping system 28. For example, the piping system 28 can comprise several pipe, hose, and / or line sections. Hydraulic fluid can be exchanged between the hydraulic pump 24 and the at least one hydraulic motor 26 via the piping system 28. For example, the hydraulic pump 24 can supply the at least one hydraulic motor 26 with hydraulic fluid pumped by the hydraulic pump 24 via the piping system 28.

[0065] The at least one hydraulic motor 26 can be assigned to a wheel 3 of the motor vehicle and / or be driven by a wheel 3 of the motor vehicle. For example, the at least one hydraulic motor 26 can have an output that is connected to the corresponding wheel 3 of the motor vehicle. The output can be designed, for example, in the form of an output shaft or in the form of a rotor housing. By means of the at least one hydraulic motor 26, the wheel 3 can thus be driven or propulsion of the motor vehicle can be effected.

[0066] The at least one hydraulic motor 26 can be designed for motor operation. Accordingly, the at least one hydraulic motor 26 can be configured to convert the hydraulic energy of the hydraulic fluid pumped by the hydraulic pump 24 into mechanical energy, e.g., into a rotary motion of the output. This process can also be referred to as hydraulic drive. However, the at least one hydraulic motor 26 can also be operated, at least temporarily, as a (e.g., hydraulic) pump. For example, by means of a (e.g., external) mechanical drive of the at least one hydraulic motor 26, hydraulic fluid can also be pumped, at least temporarily, by means of the at least one hydraulic motor 26. Accordingly, in this pump operation, mechanical energy can be converted into hydraulic energy by means of the at least one hydraulic motor 26.

[0067] The mechanical driving of the at least one hydraulic motor 26 or its output shaft can be effected, for example, by a driving movement of the motor vehicle.

[0068] In other words, the at least one hydraulic motor 26 can be towed by the motor vehicle during pump operation and / or operated in a push-pull mode. In this case, a rotary movement of the corresponding wheel 3, resulting from the movement of the motor vehicle (e.g., driven by the main drive 10), can be introduced via the output shaft into the at least one hydraulic motor 26 and converted there into hydraulic energy or the delivery of hydraulic fluid.

[0069] As in the Fig. 1 and Fig. As shown in Figure 2, the at least one hydraulic motor 26 preferably comprises (at least) two hydraulic motors 26, wherein one of the two hydraulic motors 26 can be drivenly connected to the left wheel 3 and the other of the two hydraulic motors 26 to the right wheel 3 of the auxiliary drive axle 2.

[0070] The two hydraulic motors 26 can each be designed, for example, as wheel hub motors or wheel-mounted motors. Preferably, the two hydraulic motors 26 are each designed as radial piston wheel hub motors. Each of the radial piston wheel hub motors can have a cylinder block which can be rotationally fixed to the output shaft of the respective radial piston wheel hub motor (e.g., by means of an internal gear). Furthermore, each of the radial piston wheel hub motors can have several radially extendable and retractable radial pistons, which can be arranged star-shaped in the cylinder block and surrounded by a cam ring. In an operating state, the respective radial pistons can be loaded and unloaded with hydraulic fluid to execute a stroke movement, whereby the respective radial pistons can slide along an inner contour of the cam ring.This allows the linear stroke motion of the radial pistons to be converted into a rotary motion of the cylinder block and the associated output shaft. Accordingly, in the operating state, the hydraulic fluid and the output can be coupled to each other in a force-transmitting manner.

[0071] For example, by applying pressure to the respective control chamber of the radial piston wheel hub motors, the radial piston wheel hub motors can also be brought into a free-running state. In this state, the respective radial pistons can have no contact with the cam ring and the output can rotate freely. Accordingly, in the free-running state, the hydraulic fluid and the output can be decoupled from each other in terms of force transmission.

[0072] To supply the two hydraulic motors 26 with hydraulic fluid, each motor can have a hydraulic fluid inlet and a hydraulic fluid outlet. As shown, hydraulic fluid pumped from the hydraulic pump 24 to a pressure side of the hydraulic pump 24 can be supplied to the respective hydraulic fluid inlets of the hydraulic motors 26 via the line system 28. Furthermore, hydraulic fluid discharged from the respective hydraulic fluid outlets can be returned to the suction side of the hydraulic pump 24 via the line system 28.

[0073] As in Fig. As shown in Figure 1, the hydrostatic auxiliary drive 20 or the piping system 28 can have at least one control valve 22, for example, in the form of a 4 / 2-way valve. By means of the at least one control valve 22, a hydraulic connection and / or a power transmission between the hydraulic pump 24 and the at least one hydraulic motor 26 can be selectively interrupted or enabled. For example, the at least one control valve 22 can have a first switching state in which the pressure and suction sides of the hydraulic pump 24 are hydraulically short-circuited (e.g., in a closed circuit). In this first switching state, the hydraulic fluid pumped by the hydraulic pump 24 can be returned directly and / or with virtually no loss (e.g., via a nearly resistance-free short-circuit path) to the hydraulic pump without supplying the at least one hydraulic motor 26 with hydraulic fluid.By appropriately dimensioning the short-circuit path, power losses of the circulating hydraulic fluid can be kept low, so that the hydraulic pump 24 is preferably in a quasi-free-running state. Due to the pressure equalization between the supply and return lines, no pressure, and consequently no torque, can build up on the at least one hydraulic motor 26 and on the hydraulic pump 24 in the first switching state. Preferably, the at least one hydraulic motor 26 is in a free-running or "disengaged" state, so that no hydraulic fluid flows over and / or through the at least one hydraulic motor 26. The branch of the hydrostatic auxiliary drive 20 between the control valve 22 and the auxiliary drive shaft 2 can therefore be connected to the hydraulic pump 24, but the hydraulic fluid remains stationary in this part of the circuit, and circulation only takes place between the hydraulic pump 24 and the control valve 22.

[0074] Furthermore, the at least one control valve 22 can have a second switching state in which the at least one hydraulic motor 26 is arranged as a consumer between the pressure and suction sides of the hydraulic pump 24. Accordingly, in the second switching state, the at least one hydraulic motor 26 can be supplied with or have a flow through it with hydraulic fluid pumped by the hydraulic pump 24.

[0075] Optionally, the hydrostatic auxiliary drive 20 or the piping system 28 can also include an overpressure relief unit 23. This unit can be arranged between the pressure and suction sides of the hydraulic pump 24, parallel to the at least one hydraulic motor 26. The overpressure relief unit 23 can include two pressure relief valves and two check valves. The two pressure relief valves can be arranged in series with opposite orientations, with each check valve positioned parallel to one of the pressure relief valves and acting in a different direction relative to the respective pressure relief valve. The overpressure relief unit 23 allows the maximum hydraulic pressure of the suction side and the maximum hydraulic pressure of the pressure side of the hydraulic pump 24 to be set.

[0076] The aforementioned hydraulic pump 24 is preferably a variable displacement hydraulic pump. For example, the delivery volume of the hydraulic pump 24 can be selectively set to either a first delivery volume value or a second delivery volume value. The first delivery volume value and the second delivery volume value should be different. Preferably, the second delivery volume value is greater than the first delivery volume value. For example, the first delivery volume value can be a minimum delivery volume value of the hydraulic pump 24 and / or result in zero delivery from the hydraulic pump. In addition, or alternatively, the second delivery volume value can be a maximum delivery volume value of the hydraulic pump 24.

[0077] In one embodiment, the delivery volume of the hydraulic pump 24 can be set exclusively to the first or second delivery volume value. In this context, it can also be referred to as a digital variable displacement hydraulic pump with only two positions.

[0078] Alternatively, the delivery volume of the hydraulic pump 24 (e.g., continuously or in stages) can be adjusted to at least one further delivery volume value between the first and second delivery volume values. Preferably, the at least one further delivery volume value has several further delivery volume values, so that the delivery volume of the hydraulic pump 24 (e.g., continuously or in stages) can preferably be adjusted to several further delivery volume values ​​between the first and second delivery volume values.

[0079] In all cases, adjusting the delivery volume of the hydraulic pump 24 can be achieved, for example, using techniques known in the prior art. For instance, the delivery volume of the hydraulic pump 24 can be adjusted by pivoting a rotary disk of the hydraulic pump 24 (e.g., if it is designed as an axial piston pump) or by eccentric adjustment of the stroke ring of the hydraulic pump 24 (e.g., if it is designed as a radial piston pump). In principle, the delivery volume of the hydraulic pump 24 can also be adjusted by changing the geometry of the displacement chamber(s) of the hydraulic pump 24. Accordingly, the hydraulic pump 24 can have at least one displacement chamber whose geometric dimensions can be varied.

[0080] To adjust the delivery volume of the hydraulic pump 24, it can be equipped with an (e.g., mechanical) actuating element 25. For example, the actuating element 25 can be used to change the swivel angle of the hydraulic pump 24 or to adjust a stroke ring of the hydraulic pump 24. The actuating element 25 can, for example, be hydraulically actuated. As in Fig. As shown in Figure 2, the actuator 25 can be coupled to a hydraulic control circuit 40.

[0081] The hydraulic control circuit 40 can include a pressure relief valve 41, a feed pump 42, a filter 43, a hydraulic actuator 44, a control fluid reservoir 45, a fluid connection 46, a valve assembly 48 and / or a check valve 49.

[0082] Control fluid can be pumped from the control fluid reservoir 45 by means of the feed pump 42. The hydrostatic auxiliary drive 20 can also be supplied with hydraulic fluid from the control fluid reservoir 45. Accordingly, the control fluid and hydraulic fluid can, for example, be the same fluid, which, for better differentiation, is referred to as control fluid or hydraulic fluid, depending on whether it circulates in the hydraulic control circuit 40 or in the hydrostatic auxiliary drive 20.

[0083] The feed pump 42 can be connected to the main drive 10 or to a separate (e.g., electric) pump drive. The control fluid pumped by the feed pump 42 can then be returned to the control fluid reservoir 45 via the valve assembly 48 or supplied to the hydraulic actuator 44 via the fluid connection 46.

[0084] For example, the valve assembly 48 can be configured as a 4 / 2-way valve. The valve assembly 48 can, for instance, have a first switching state in which a pressure side of the feed pump 42 is connected to the control fluid reservoir 45 via the filter 43. The valve assembly 48 can also have a second switching state in which the pressure side of the feed pump 42 is connected to the hydraulic actuator 44 via the fluid connection 46. In this switching state, the hydraulic actuator 44 can be supplied with control fluid and thereby moved.

[0085] The hydraulic actuator 44 can be connected to the actuating element 25 such that, in an unpowered state of the hydraulic actuator 44, the actuating element 25 is held in a first position, and in a powered state of the hydraulic actuator 44, the actuating element 25 is held in a second position. The first and second positions are each assigned to different delivery volumes of the hydraulic pump.

[0086] In addition to or as an alternative to the exemplary hydraulic actuation of the actuator 25 described above, the actuator 25 can in principle also be pneumatically, electrically and / or mechanically actuated.

[0087] The drive device 30 can further comprise one or more speed sensors 36. These can be designed to detect the rotational speed of a rotating component of the drive device 30. For example, one of the speed sensors 36 can be arranged and designed to detect the rotational speed of the hydraulic pump 24 or its drive. Another speed sensor 36 can, for example, measure the rotational speed at the main drive-side input of the clutch assembly 32.

[0088] As mentioned above, the drive device 30 has a processing unit 34. The processing unit 34 can be connected to the other components of the drive device 30 via appropriate signal lines. In particular, the processing unit 34 can be connected via the appropriate signal lines to the speed sensors 36, the hydraulic pump 24, the clutch assembly 32, the at least one control valve 22, and the valve assembly 48.

[0089] The processing unit 34 can, for example, trigger an adjustment of the delivery volume of the hydraulic pump 24. The processing unit 34 can be configured, for instance, to output corresponding adjustment signals directly to the hydraulic pump 24 or to the valve assembly 48 of the hydraulic control circuit 40, thereby allowing the delivery volume of the hydraulic pump 24 to be adjusted directly or indirectly. Alternatively, the processing unit 34 can also be configured to output corresponding adjustment signals to the valve assembly 48, enabling it to selectively assume either the first or second switching state. Alternatively, the processing unit 34 can also be configured to output corresponding coupling signals to the coupling assembly 32, allowing it to be selectively switched to an open or closed state.

[0090] Furthermore, the processing unit 34 is configured to execute a procedure as described herein (e.g., automatically). An example of such a procedure is now given below with reference to the Fig. 3 and Fig. 4 described in more detail.

[0091] Fig. Figure 3 shows a flowchart of a method for operating a hydraulic pump 24 by means of a drive device 30, as e.g. in connection with Fig. 1 and Fig. 2 described, according to one embodiment.

[0092] In step S1, the hydraulic pump 24 is put into operation.

[0093] The commissioning process, in turn, comprises in one step S11 setting the delivery volume of the hydraulic pump 24 to the first delivery volume value. For example, the processing unit 34 can output a corresponding setting signal directly to the hydraulic pump 24 or to the valve assembly 48 of the hydraulic control circuit 40, whereby the valve assembly 48 can, for example, assume the second switching state. Preferably, the first delivery volume value is a minimum delivery volume value of the hydraulic pump 24 and / or essentially results in zero delivery by the hydraulic pump 24.

[0094] The commissioning process can further include, in an optional step S12, a hydraulic short-circuiting of the suction side of the hydraulic pump 24 with the pressure side of the hydraulic pump, preferably such that hydraulic fluid pumped by the hydraulic pump 24 is directly returned to the hydraulic pump 24. For example, the processing device 34 can output a corresponding setting signal to the at least one control valve 22, which can then, for example, assume the first switching state.

[0095] The commissioning process further comprises, in step S13, the mechanical coupling of the hydraulic pump 24 to the main drive 10 by means of the coupling device 32. For example, the processing unit 34 can output a corresponding coupling signal to the coupling device 32, thereby, for example, closing the positive-locking coupling and synchronizing the coupling device 32. Since the hydraulic pump 24 has a small delivery volume and is preferably short-circuited, only a small drag torque acts at the hydraulic pump-side output of the coupling device 32, thus enabling switching that is as gentle on the components as possible.

[0096] The commissioning process further comprises, in step S14, the mechanical driving of the hydraulic pump 24, which is set to the first delivery volume value and coupled to the main drive 10, by means of the main drive 10. For example, torque can be transmitted from the main drive 10 to the hydraulic pump 24 via the coupling device 32. Since the hydraulic pump 24 has a small delivery volume and is preferably short-circuited, only a small drive power is advantageously required.

[0097] Furthermore, commissioning also includes, in step S15, adjusting the delivery volume of the driven hydraulic pump 24 to the second (e.g., larger) delivery volume value. For example, the processing unit 34 can output a corresponding setting signal directly to the hydraulic pump 24 or to the valve assembly 48 of the hydraulic control circuit 40, allowing the valve assembly 48 to assume, for example, the first switching state. Preferably, the second delivery volume value is a maximum delivery volume value of the hydraulic pump 24 and / or causes the establishment of the working pressure of the hydrostatic auxiliary drive 20.

[0098] Preferably, the delivery volume of the driven hydraulic pump 24 is adjusted to the second delivery volume value as a function of the rotational speed of the hydraulic pump 24. For example, the delivery volume of the driven hydraulic pump 24 can be adjusted to the second delivery volume value as a function of the rotational speed of the hydraulic pump 24 when the rotational speed of the hydraulic pump 24 reaches a (e.g., predetermined) target speed value. This target speed value can be determined, for example, through appropriate preliminary tests and / or be defined as a function of the delivery volume of the hydraulic pump 24, a function of the displacement volume of the at least one hydraulic motor 26, and / or a function of the gear ratio of the transmission device 33. Preferably, the target speed value is greater than a minimum rotational speed of the hydraulic pump 24 and less than a maximum rotational speed of the hydraulic pump 24.

[0099] The commissioning process can also include, in an optional step S16, a hydraulic connection of the hydraulic pump 24 and the at least one hydraulic motor 26 via the piping system 28. For example, the processing unit 34 can output a corresponding setting signal to the at least one control valve 22, which can then, for example, assume the second switching state. Accordingly, the hydraulic short circuit can be removed in step S16.

[0100] In addition to or as an alternative to commissioning, the method can also include decommissioning the hydraulic pump 24 in a step S2. Preferably, the decommissioning is carried out in the reverse order of commissioning the hydraulic pump 24.

[0101] Accordingly, in an optional step S21, the deactivation can include a hydraulic short-circuiting of the suction side of the hydraulic pump 24 with the pressure side of the hydraulic pump 24, preferably such that hydraulic fluid pumped by the hydraulic pump 24 is returned directly to the hydraulic pump 24. For example, the processing device 34 can output a corresponding setting signal to the at least one control valve 22, which can then, for example, assume the first switching state.

[0102] Furthermore, the deactivation in step S22 can include adjusting the delivery volume of the hydraulic pump 24, preferably hydraulically short-circuited, to the first delivery volume value. For example, the processing device 34 can output a corresponding setting signal directly to the hydraulic pump 24 or to the valve device 48 of the hydraulic control circuit 40, whereby the valve device 48 can, for example, assume the second switching state.

[0103] Furthermore, in step S23, the decommissioning can include the drive-related decoupling of the hydraulic pump 24, set to the first delivery volume value, from the main drive 10 by means of the coupling device 32. For example, the processing device 34 can output a corresponding coupling signal to the coupling device 32, which, for example, opens the positive-locking coupling and synchronizes the coupling device 32.

[0104] Although the invention has been described with reference to specific embodiments, it is apparent to a person skilled in the art that various modifications can be made and equivalents can be used as substitutes without departing from the scope of the invention. Consequently, the invention is not intended to be limited to the disclosed embodiments, but rather to encompass all embodiments falling within the scope of the appended claims. In particular, the invention also claims protection for the subject matter and features of the dependent claims independently of the referenced claims. All scope specifications herein are to be understood as disclosed in such a way that all values ​​falling within the respective scope are disclosed individually, e.g., also as preferred narrower outer limits of the respective scope. Reference symbol list 1 Main drive axle 2 Auxiliary drive axle 3-wheeler 10 Main drive 12 Vehicle transmissions 14 Output shaft 16 Differential 20 Auxiliary drive 22 Control valve 23 Overpressure protection unit 24 Hydraulic pump 25 Actuator 26 Hydraulic motor 28 piping system 30 Drive device 32 Coupling device 33 Gearbox unit 34 Processing unit 36 Speed ​​sensor 40 Hydraulic control circuit 41 Pressure relief valve 42 Pump 43 filters 44 Hydraulic actuator 45 control fluid reservoirs 46 Fluid connection 48 Valve assembly 49 Check valve QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] B. Heißing (ed.) et al., Fahrwerkshandbuch (DOI 10.1007 / 978-3-8348-8168-7

[0030]

Claims

[1] Method for operating a hydraulic pump (24) of a hydrostatic auxiliary drive (20) of a motor vehicle, wherein the hydraulic pump (24) can be drivenly coupled to a main drive (10) of the motor vehicle by means of a coupling device (32); and wherein a delivery volume of the hydraulic pump (24) can be optionally set to a first delivery volume value or to a second delivery volume value which is greater than the first delivery volume value; wherein the method includes commissioning the, preferably stationary, hydraulic pump (24) and includes the commissioning: - Adjusting the delivery volume of the hydraulic pump (24) to the first delivery volume value, preferably to reduce a drag torque of the hydraulic pump (24); - Driving coupling of the hydraulic pump (24) with the main drive (10) by means of the coupling device (32); - Mechanical driving of the hydraulic pump (24), which is set to the first delivery volume value and coupled to the main drive (10), by means of the main drive (10); and - Adjusting the delivery volume of the driven hydraulic pump (24) to the second delivery volume value, preferably to build up a working pressure in the hydrostatic auxiliary drive (20). [2] Method according to claim 1, wherein: The adjustment of the delivery volume of the driven hydraulic pump (24) to the second delivery volume value is carried out as a function of a speed of the hydraulic pump (24), preferably when the speed of the hydraulic pump (24) reaches a predetermined target speed value. [3] Method according to claim 1 or 2, wherein: the first delivery volume value is a minimum delivery volume value of the hydraulic pump (24) and / or results in zero delivery of the hydraulic pump (24); and / or the second delivery volume value is a maximum delivery volume value of the hydraulic pump (24); and / or The delivery volume of the hydraulic pump (24) can be optionally set exclusively to the first or second delivery volume value. [4] Method according to any one of the preceding claims, wherein the commissioning further comprises: - Hydraulic short-circuiting of a suction side of the hydraulic pump (24) with a pressure side of the hydraulic pump (24) before the hydraulic coupling of the hydraulic pump (24) with the main drive (10), preferably such that hydraulic fluid pumped by the hydraulic pump (24) is returned directly to the hydraulic pump (24). [5] Method according to any one of the preceding claims, wherein: the coupling device (32) has a positive-locking coupling, preferably a claw coupling, with a synchronization, preferably friction-locking. [6] Method according to any one of the preceding claims, wherein: In the actuarial coupling of the hydraulic pump (24) with the main drive (10), the hydraulic pump (24) is actuarially coupled to the main drive (10) via a transmission device (33), wherein the transmission device (33) preferably has a fixed ratio. [7] Method according to any one of the preceding claims, wherein: the hydraulic pump (24) has an actuating element (25) for adjusting the delivery volume of the hydraulic pump (24), which is coupled to a hydraulic control circuit (40); and The adjustment of the delivery volume of the hydraulic pump (24) is carried out by actuating the actuating element (25) by means of the hydraulic control circuit (40). [8] Method according to claim 7, wherein the hydraulic control circuit (40) comprises: a feed pump (42) for conveying a control fluid, which is preferably mechanically driven by the main drive (10) and / or by a pump drive, preferably separate from the main drive (10); a hydraulic actuator (44) which is coupled to the actuating element (25) and which can be actuated via a fluid connection (46) with the control fluid supplied by the feed pump (42); and a valve device (48) by which the fluid connection (46) can be selectively opened or closed, preferably in order to selectively supply the hydraulic actuator (44) with control fluid or not. [9] Method according to any one of the preceding claims, wherein: the hydrostatic auxiliary drive (20) serves to drive an auxiliary drive axle (2) of the motor vehicle, wherein the auxiliary drive axle (2) is preferably a steerable front axle, a liftable rear axle, a leading axle or a trailing axle of the motor vehicle; and / or the main drive (10) serves to drive a main drive axle (1) of the motor vehicle, wherein the main drive axle (1) is preferably an unsteered rear axle of the motor vehicle; and / or the main drive (10) comprises an internal combustion engine and / or an electric motor. [10] Method according to any one of the preceding claims, wherein: the hydrostatic auxiliary drive (20) has at least one hydraulic motor (26) and a piping system (28) via which the hydraulic pump (24) and the at least one hydraulic motor (26) can be hydraulically connected to each other, wherein preferably: the at least one hydraulic motor (26) has two hydraulic motors (26), preferably two wheel hub motors, particularly preferably two radial piston wheel hub motors, wherein the two hydraulic motors (26) are each assigned to a wheel (3) of the motor vehicle. [11] Method of one of the preceding claims, wherein: The coupling of the hydraulic pump (24) with the main drive (10) takes place depending on a speed difference between a main drive-side input of the coupling device (32) and a hydraulic pump-side output of the coupling device (32), preferably when the speed difference falls below a predetermined limit value. This speed difference is preferably detected by means of speed sensors (36). [12] Method according to claim 11, wherein: the delivery volume of the hydraulic pump (24), preferably continuously, is adjustable to several further delivery volume values ​​between the first and second delivery volume value and further features commissioning before the hydraulic pump (24) is coupled to the main drive (10): - Changing the delivery volume of the driven hydraulic pump (24) from the first delivery volume value to one of the several further delivery volume values, such that the speed difference between the main drive-side input of the clutch device (32) and the hydraulic pump-side output of the clutch device (32) is minimized. [13] Method of one of the preceding claims, wherein: the method comprises a disabling of the hydraulic pump (24), which is preferably coupled to a main drive (10) by means of the coupling device (32) and driven by the main drive (10), and includes the disabling of: - Preferably: Hydraulic short-circuiting of a suction side of the hydraulic pump (24) with a pressure side of the hydraulic pump (24) such that hydraulic fluid pumped by the hydraulic pump (24) is returned directly to the hydraulic pump (24); - Adjusting the delivery volume of the hydraulic pump (24), preferably hydraulically short-circuited, to the first delivery volume value, preferably in order to reduce a drag torque of the hydraulic pump (24); and - Decouple the hydraulic pump (24) set to the first delivery volume value from the main drive (10) by means of the coupling device (32). [14] Drive device (30) for a motor vehicle, preferably a commercial vehicle, wherein the drive device (30) comprises: a main drive (10), preferably for driving a main drive axle (1) of the motor vehicle; a hydrostatic auxiliary drive (20), preferably for driving an auxiliary drive axle (2) of the motor vehicle, wherein the hydrostatic auxiliary drive (20) has a hydraulic pump (24) whose delivery volume is adjustable between a first delivery volume value and a second delivery volume value, which is greater than the first delivery volume value; a coupling device (32) by means of which the hydraulic pump (24) can be coupled to the main drive (10); and a processing device (34) by means of which an adjustment of the conveying volume and a coupling of the coupling device (32) can be triggered, wherein the processing device (34) is configured to carry out a method according to one of the preceding claims, preferably automatically. [15] Motor vehicle, preferably commercial vehicle, comprising a drive device (30) according to claim 14.

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