EP2238350A1

EP2238350A1 - Method for controlling a hydrostatic drive

Info

Publication number: EP2238350A1
Application number: EP08866733A
Authority: EP
Inventors: Steffen Mutschler; Markus Weber; Matthias Müller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-12-28
Filing date: 2008-12-22
Publication date: 2010-10-13
Also published as: US20100324791A1; US8380407B2; CN101910634B; DE102007062888A1; CN101910634A; WO2009083222A1; JP2011508142A

Abstract

The invention relates to a method for controlling a hydrostatic drive having at least one first hydraulic consumer and one second hydraulic consumer. The two hydraulic consumers are driven by a common drive machine. First of all, a first power requirement of the first hydraulic consumer is determined (20). Proceeding from the determined first power requirement, the free power which is available as a result of the common drive machine is determined (21). This available free power of the common drive machine is scaled onto a possible actuating path of a control transmitter for the working hydraulics (22). A position of the control transmitter for actuating the second hydraulic consumer is determined (23) and a power requirement is assigned on the basis of the scaled available free power. An operating point of the common drive machine is fixed from the first power requirement and the second power requirement (24).

Description

Method for controlling a hydrostatic drive

The invention relates to a method for controlling a hydrostatic drive with at least a first hydraulic consumer and a second hydraulic consumer, which are driven by a common drive machine.

From DE 103 07 190 Al a hydrostatic drive is known. The hydraulic system of the mobile work machine proposed there comprises a travel drive and at least one working hydraulics. Both the traction drive and the working hydraulics represent hydraulic consumers, which are driven by a common drive machine. The common drive machine is designed as a diesel engine. During operation of the mobile work machine, the drive power provided by the diesel engine must be divided between the drive and the work hydraulics. For this purpose, for the corresponding accelerator pedal position or the position of a joystick to operate the working hydraulics of the respective with the

Diesel engine connected hydrostatic pumps recorded power recorded. From the respectively due to the accelerator pedal position or the joystick position to be absorbed power of the hydraulic load so the connected hydrostatic pumps a to be provided by the internal combustion engine power is determined. Subsequently, the internal combustion engine is set to an operating point capable of satisfying the power demand.

The described system has the disadvantage that the rated power of the diesel engine is selected It must be ensured that, with the accelerator pedal fully depressed as well as with an end-position joystick, the diesel engine is able to meet the power requirement. But if one refrains from this, an unnecessary oversizing of the

To avoid diesel engine, the problem arises that, for example, at a high demand due to the traction drive, the power requirement of the working hydraulics can no longer be met. The power that is available to the working hydraulics is small and a movement of the joystick in the direction of greater power for the working hydraulics is perceived by a user as an idle travel.

The invention is therefore based on the object to provide an improved control for a hydrostatic drive, in which in particular a feedback on the power components available for each of the working hydraulics is possible.

The object is achieved by the method having the features of claim 1.

In the method according to the invention for controlling a drive, which comprises a common drive machine and at least one first hydraulic load and a second hydraulic load, a first power requirement of the first hydraulic load is first determined. This will usually be the propulsion of a mobile work machine. at

Knowing this first power requirement, which must be realized by the common drive machine, then the available free power of the common drive machine can be determined. The available free power is the difference between a power that can be represented by the drive engine and the determined first power requirement. This available free power of the common drive machine is limited to a possible travel of the control encoder, z. B. one Joysticks, scaled. Thus, between a zero position of the control transmitter and the maximum deflection of the control transmitter, which is provided for example for actuating the working hydraulics, the actual available power is scaled. As a result, in each case a movement of the control transmitter is converted into a change in the power consumption of the second hydraulic consumer. After scaling the available free power, a determined position of the controller is assigned a second power requirement. On the basis of this second power requirement and the determined first power requirement then the operating point of the common drive machine is determined. Thus, the common prime mover can be set to a favorable operating point in each case due to the actual power requirement, nevertheless due to the scaling of theoretically still available free power of the operator receives a feedback on a movement of the control transmitter due to the system reaction, how high the available power reserves for the working hydraulics.

In the dependent claims advantageous developments of the method according to the invention are carried out.

In particular, it is advantageous to set a maximum value for the first power requirement. Setting such a maximum value ensures that it is not possible to use the complete drive power of the common drive machine for the traction drive. Accordingly, a minimum performance is always available for other connected hydraulic consumers, ie in particular the working hydraulics in a mobile work machine.

Furthermore, it is advantageous to calculate the available free power from the difference of the absolute maximum power (nominal power) of the common machine and the determined first power requirement. As an alternative to this, it would also be possible to determine the free power of the common operating machine which is available in a respectively set operating point. Furthermore, a transmission ratio of the hydrostatic drive is preferably determined from the position of the driving command setting device. In order for an automotive driving the mobile machine is made possible and in particular the operation is greatly simplified by an operator. Above all, the method according to the invention also makes it possible to dispense with a so-called "inching pedal", which is generally used to flexibly adjust the power components between the working hydraulics and the traction drive, but requires user intervention.

An advantageous embodiment is shown in the drawing and will be explained in detail in the following description. Show it:

Figure 1 is a schematic representation of a hydraulic system of a mobile work machine;

Figure 2 is a schematic representation of the power distribution between a

Working hydraulics and a traction drive;

Figure 3 is a simplified representation of

Procedure for controlling a hydrostatic drive.

In FIG. 1, a hydrostatic drive (1) of a mobile working machine, such as an excavator, is shown in a greatly simplified manner. The hydrostatic drive 1 comprises a

Diesel engine 2, which is used as a common drive machine. The

Diesel engine 2 is connected to a transfer case 3 via which the diesel engine 2 generated torque can be distributed to several consumers.

With the transfer case 3 is the first hydraulic consumer, a hydrostatic transmission 4 of the

Mobile drive connected to the mobile machine. The hydrostatic transmission 4 comprises a variable displacement pump 5 and an adjusting motor 6. The adjusting motor 6 is connected via an output shaft to a driven axle of the mobile working machine. The connection with only one driven axle is to be understood as an example. As well, of course, another drive concept such as a four-wheel drive can be realized.

The transfer case 3 is connected via a first drive shaft 8 with the variable displacement pump 5 and connected via a second drive shaft 9 with a further variable displacement pump 10. The further variable displacement pump 10 is connected via a delivery line 11 to a working hydraulics, for example a lifting cylinder and forms a second hydraulic consumer.

The diesel internal combustion engine 2 thus drives a first hydraulic consumer in the form of the first variable displacement pump 5 and a second hydraulic consumer in the form of the further variable displacement pump 10 of the working hydraulics.

The variable displacement pump 5 and the adjusting motor 6 of the hydrostatic transmission 4 are each adjustable in their stroke volume and preferably designed as a swash plate or oblique axis machine. To set the stroke volume, an electronic control unit is provided, which is referred to below as traction drive control 12. The

Traction drive control 12 generates a first control signal for adjusting the delivery volume of the variable displacement pump 5 and a second control signal for adjusting the absorption volume of the hydraulic motor 6. The first control signal is transmitted to a first adjusting device 13 and the second control signal to a second adjusting device 14. The adjusting devices 13, 14 each interact with the adjusting mechanisms of the variable displacement pump 5 and the hydraulic motor 6 and thus set them in accordance with the control signal to a desired ratio of the hydrostatic transmission 4.

Another electronic control unit is referred to below as the working hydraulic control 15. The working hydraulic control 15 is connected to a third adjusting device 16 via a signal line. The third adjusting device 16 adjusts the delivery volume of the further variable displacement pump 10 and thus regulates the power consumption of the further variable displacement pump 10.

To set an operating point of the diesel engine 2, another control unit, the diesel control unit 17 is provided. The diesel control unit 17 specifies an operating point and thus controls a setpoint speed of the diesel engine 2. For this purpose, a control signal is transmitted to the injection system 18 of the diesel engine 2. The diesel control unit 17 is connected to the

Work hydraulic control 15 and the traction drive control 12 in conjunction.

The traction drive control 12 is to be able to determine a first power requirement, a signal of

Accelerator pedal 19 transmitted. The accelerator pedal 19 is merely an example. Just as well, a driving lever or another driving command default device can be provided. In the illustrated embodiment, the accelerator pedal 29 can be swung out of a neutral position in two opposite directions to realize an automotive driving operation. The respectively set angle α, which characterizes the position of the accelerator pedal 29, is determined by means of a position detector 30 determined and transmitted a position signal to the traction drive control 12. Based on this position signal, the traction drive controller 12 determines a first power requirement and transmits this power requirement to the diesel control unit 17

Diesel control unit 17 is determined on the basis of the determined first power demand, the available free power of the diesel engine 2. This available free power is at most equal to the difference between the absolute maximum power of the diesel engine which it can produce at rated speed and the determined first power demand. The information about the available free power is transmitted from the diesel control unit 17 to the working hydraulic control 15.

In order to control the power consumption of the further variable displacement pump 10, a control transmitter is provided, which in the illustrated embodiment is realized as an operating lever 31. The operating lever 31 is adjustable starting from its neutral position shown in the figure 1 in two directions up to each end position. The adjustment paths up to the first end position and the opposite second end position may be different and are in the figure 1 by the

Angle ß and ß 'marked. The respective position of the operating lever 21 is detected by a further position sensor 32 and the position signal of the working hydraulic control 15 is supplied. The working hydraulic control 15 scales on the adjustment path ß of the operating lever 21 between its neutral position and one end position the available power of the diesel engine 2. Thus it is ensured that for each determined position of the other position sensor 32 in the direction of the maximum deflection of the operating lever 21 nor a power reserve of the diesel engine 2 provides to a reaction of the working hydraulics or the Allow working hydraulic supply further variable displacement pump 10.

As can be seen by the direct connection between the drive hydraulic control 15 and the

Travel drive control 12 is shown, can also be set by the working hydraulic control 15, a maximum value for the power requirement of the traction drive. This maximum power requirement, which can then be at most the traction drive, can be parameterized. For this purpose, a corresponding limit value is set via the drive hydraulic control 15, z. B. stored in an integrated memory. The maximum value for the traction drive control 12 thus establishes an upper limit for the output of the diesel internal combustion engine 2 to be requested by the traction drive, so that there is always a minimum output of the diesel internal combustion engine 2 available for the working hydraulics.

This will be clarified again below with reference to FIG. FIG. 2 shows the rated power P _{Nenn of} the diesel engine 2. Furthermore, a maximum value P _{max is} entered. The travel drive can only be set in the range between zero and P _max . In fact, however, if the determined first power requirement of the traction drive is less than P _{max /} for example P _FA , then there is an available free power, which results from the difference between Pu ^{unc unc} * P _F A. This is indicated by the arrow 19 in FIG. This available free

Power 19 is scaled to the adjustment path ß of the operating lever 31. In the simplest case, a linear scaling takes place.

FIG. 3 once again simplifies the method according to the invention. First, in step 20, the first power requirement is determined. The first power requirement is in the described Auführungsbeispiel, in which the first hydraulic Consumer is the hydrostatic transmission 4, the power requirement of the drive. This is determined on the basis of the accelerator pedal position α. Taking into account the first power requirement, the available free power is determined in step 21. For this purpose, the first power requirement is transmitted from the traction drive control to the diesel control unit 17. This determines the available free power from the first power requirement and the maximum power of the diesel engine 2 and communicates it to the working hydraulic control 15. The

Work hydraulic control 15 scales the available free power in step 21 to the possible adjustment path ß of the operating lever 21. Subsequently, in step 23, the position of the operating lever 21 is determined by means of the further position sensor 22. This determined position is assigned a second power requirement of the working hydraulics on the basis of the scaled available free power. On the basis of the determined first power requirement and the determined second power requirement, an operating point for the

Diesel engine 2 fixed. To determine the operating point, a map of the diesel internal combustion engine 2 stored in the diesel control unit 17 is preferably used. Here, an operating point is selected under consumption-optimized aspects, which is sufficient for the realization of the determined total power demand.

When changing the power requirement either by the travel drive or by the working hydraulics, a new operating point is set accordingly. If the power requirement increases, this will generally lead to a speed increase of the diesel internal combustion engine 2. Based on the set operating point, a setpoint speed for the diesel internal combustion engine 2 is determined by the diesel control unit 17 and the injection system 18 of the diesel engine 2 is supplied with a corresponding control signal. The injection system 18 sets the diesel engine to this target speed. Furthermore, the transmission ratio of the hydrostatic transmission is determined by the traction drive control 12 and adjusted by means of the adjusting devices 13 and 14 each have a delivery volume of the variable displacement pump 5 and a displacement of the hydraulic motor 6. By the working hydraulic control 15, a delivery volume of the variable displacement pump 10 is further determined and adjusted with the aid of the adjusting device 16.

The adjustment of the variable displacement pumps 5, 10 and the hydraulic motor 6 by means of the adjusting devices 13, 14 and 16 takes place in a known manner, for example via electro-proportional adjusting devices.

The exemplary embodiment shows in a simple form the method according to the invention for a hydrostatic drive 1 with a travel drive as the first hydraulic consumer and a further variable displacement pump 10 as a second hydraulic consumer. However, it is readily apparent that 3 more power consumers can be arranged on the transfer case. These are then taken into account accordingly via further control devices, which essentially correspond to the working hydraulic control unit 15. This extra

Performance requirements are then determined individually and fed to the diesel control unit 17. The diesel control unit 17 then also takes into account the further performance requirements.

The invention is not limited to the illustrated embodiment. In particular, individual features of the embodiment explained in detail can advantageously be combined with one another.

Claims

claims

Method for controlling a hydrostatic drive with at least one first hydraulic consumer (5) and a second hydraulic consumer (10) which are driven by a common drive machine (2), comprising the following method steps: determining a first power requirement (20) of the first hydraulic consumer (5),

Determining a free power (21) available by the common drive machine (2),

- Scaling the available free power (22) of the common drive machine (21) to a possible

Travel (ß) of a control transmitter (31),

- Determining a position (23) of a control transmitter (31) for controlling the second hydraulic consumer (10), - Assigning a second power requirement (23) to the determined position of the control transmitter (31), and

- Setting an operating point (24) of the common drive machine (2) taking into account the first and the second power requirement.

2. The method according to claim 1, characterized in that a maximum value (P _ma χ) for the first power requirement (P _FA ) is set.

3. The method according to claim 1 or 2, characterized in that the available free power (19) from the difference between an absolute maximum power (PNenn) of the common drive machine (2) and the determined first power requirement (P _FA ) is calculated.

4. The method according to any one of claims 1 to 3, characterized in that for determining the first power requirement (PF _A ) a position (α) of a Fahrbefehlvorgabevorrichtung (29) is determined.

5. The method according to claim 4, characterized in that from the position (α) of the Fahrbefehlvorgabevorrichtung (29) a

Transmission ratio of a hydrostatic transmission (4) of a traction drive is determined.