WO2012059177A1

WO2012059177A1 - Method for controlling the traction hydraulics of a working machine

Info

Publication number: WO2012059177A1
Application number: PCT/EP2011/005216
Authority: WO
Inventors: Norman Brix; Tobias Mueller
Original assignee: Robert Bosch Gmbh
Priority date: 2010-11-04
Filing date: 2011-10-18
Publication date: 2012-05-10
Also published as: DE102010052065A1

Abstract

The invention relates to a method for controlling the traction hydraulics of a working machine which has a drive machine, working hydraulics driven by the drive machine, and traction hydraulics driven by the drive machine and comprising a hydrostatic two-circuit system, wherein an operating point of the drive machine is set as a function of a power demand at least of the working hydraulics, wherein during traction and working operation, a change in the operating point of the drive machine caused by a change in the power demand of the working hydraulics is responded to, in order to prevent a change in the speed of travel, through a change in the transmission ratio of a hydrostatic transmission of the hydrostatic two-circuit system.

Description

Method for controlling the driving hydraulics of a working machine

description

The present invention relates to a method for driving the drive hydraulics of a work machine.

State of the art

The invention is in the field of mobile working machines, in particular skid steers (so-called skid steer loaders), in which a hydrostatic drive (driving hydraulics) and a working hydraulics are driven by a drive machine, usually an internal combustion engine. The drive hydraulics comprise a hydrostatic two-circuit drive, i. Two hydrostatic circuits (right / left) for the driving function. The

Steering these machines is realized by targeted speed difference between the two circuits. For this purpose, a hydraulic transmission is usually provided with one driven by the drive motor hydraulic pump and an associated hydraulic motor for each page.

It is common, especially in the small work machines, such as the skid steer loaders, that the driver via a selector lever or a pedal, the speed of the drive machine, hereinafter referred to as the diesel engine speed, set as the operating point. Using the selector lever or the gas pedal, the driver sets a constant diesel speed and then moves the vehicle via joysticks, which control the two hydrostatic circuits. The control of the setpoint speed of the engine by an accelerator pedal is described, for example, in DE 101 34 789 C2. A disadvantage of this direct setting is a poor efficiency.

l For large machines, it is known to improve the efficiency by the operating point of the engine is adapted to a current power requirement, as described, for example, in EP 1 754 643 A1. The disadvantage of this, however, is that there is a change in the operating point of the engine during driving to an undesirable change in driving speed. Also, a use of a complex control in small machines is not provided.

It is therefore desirable to increase the efficiency of the control even in the case of small mobile dual-circuit work machines, but not to impair the driving feel.

Disclosure of the invention

According to the invention, a method with the features of patent claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

ADVANTAGES OF THE INVENTION The invention is based on the one hand on the measure of adapting the operating point of the drive machine to the instantaneous power requirement in the case of working machines with a dual-circuit drive hydraulics. This can be done, for example, by determining a maximum speed for the prime mover that satisfies all performance requirements. The implementation of such a basic function is also profitable for small machines. In order to avoid changes in the driving speed due to changed speeds of the prime mover, on the other hand, the drive hydraulics operated so that the traction drive speed remains substantially constant even with changed engine speed. This is preferably done by adjusting the transmission ratio between the hydraulic pump and the hydraulic motor of the drive hydraulics.

The appropriate control of the drive machine, for example. The diesel engine, leads to a reduction in fuel consumption. Furthermore, this results in a reduction of the total noise level, since the drive machine with low requirement only with a low speed is operated. This leads to a cost reduction and an increase in operating comfort, since in particular the speed selector lever can be omitted and the operating costs are reduced due to the improved consumption. The use of a drive suitable for use only becomes possible in practice together with the speed compensation function, since work machines which themselves change the speed during driving would not be accepted, even in view of the advantages mentioned, since the workflow would be strongly adversely affected.

The suitable control of the drive machine (for example of the diesel engine) can be achieved, in particular, via characteristic maps which can be easily parameterized with the actual control of the components, such as, for example, Accelerator pedal, joystick, etc., are coupled. In order to provide the maximum speed required for the current application, all speed requirements of the individual characteristic maps are advantageously connected to one another via a maximum selection.

A particularly easy-to-use adaptation of the transmission ratio between the hydraulic pump and the hydraulic motor of the drive hydraulics is obtained by adjusting the delivery volume of the hydraulic pump and / or the absorption volume of the hydraulic motor. The adaptation can be further simplified if either only the displacement volume or only the delivery volume is changed.

An arithmetic unit according to the invention, e.g. a control device of a working machine is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the invention in the form of software is advantageous because this allows very low cost, especially if an executing processing unit is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

Figure 1 shows schematically a working machine, as the present invention

may be underlying.

Figure 2 shows a preferred way to specify an operating point of the prime mover.

FIG. 3 shows a preferred relationship between the intake volume and delivery volume for specifying a desired transmission ratio.

Before discussing the implementation of the method according to the invention in detail, the construction of a dual-circuit work machine, for example a skid steer loader, will first of all be explained with reference to FIG.

FIG. 1 shows a mobile working machine 1 in which a first hydrostatic transmission 3 and a second hydrostatic transmission 3 'of a driving hydraulics are driven by means of a drive machine, which is designed as a diesel internal combustion engine 2 in the illustrated embodiment. The hydrostatic transmissions 3 and 3 'are constructed substantially the same, so that in the following only the first hydrostatic transmission 3 will be explained in more detail. However, all that has been said applies equally to the second hydrostatic transmission 3 ', whose elements are provided with primed reference numerals. The hydrostatic transmission 3 comprises an adjustable hydraulic pump 5 and an adjustable hydraulic motor 6. The hydraulic pump 5 and the hydraulic motor 6 are connected to each other via a first working line 7 and a second working line 8 in a closed hydraulic circuit.

From the diesel engine 2, a drive torque is generated on a drive shaft 4. The diesel engine 2 is connected to the hydraulic pump 5 via the drive shaft 4 and a transfer case 30, so that the hydraulic pump 5 is driven by the torque generated by the diesel engine 2. According to the adjusted delivery volume of the hydraulic pump 5, pressure medium is conveyed into the first working line 7 or into the second working line 8 by the hydraulic pump. In this way, an output torque is generated in the closed hydraulic circuit as a function of the set intake volume of the hydraulic motor 6. The output torque is transmitted from the hydraulic motor 6 via an output shaft 9 and an optionally provided driving gear 31, for example, to a driven wheel 10.

In addition to the travel drive, the mobile work machine has at least one working hydraulics (not shown), in which a further hydraulic pump driven by the diesel engine 2 is used to supply at least one hydraulic cylinder and / or hydraulic motor. Usually, valves for controlling the

Consumer available. The working hydraulics can, for example, a blade and the like. include.

To adjust the delivery volume of the hydraulic pump 5 and the absorption volume of the hydraulic motor 6, a pump adjustment device 14 or a motor adjustment device 15 is provided. The pump adjusting device 14 and the motor adjusting device 15 each cooperate with an adjusting mechanism of the hydraulic pump 5 and the hydraulic motor 6. In the illustrated embodiment, both the hydraulic pump 5 and the hydraulic motor 6 are carried out starting from a neutral position adjustable in both directions. The hydraulic pump 5 and the hydraulic motor 6 are preferably axial piston machines in swash plate design.

For setting an operating point of the diesel internal combustion engine 2, here a diesel engine speed, an injection pump 13 is given a delivery rate by a control unit 16, which is set up for the implementation of a method according to the invention programmatically. For this purpose, a corresponding signal is transmitted via a bus line 17 from the control unit 16 to the injection pump 13. The adjustment of the operating point is preferably based on a selection of a maximum speed value, as will be explained later with reference to Figure 2.

The setting of the hydrostatic transmission 3 is also carried out by the control unit 16. Accordingly, corresponding control signals are transmitted by the control unit 16 of the pump adjusting device 14 and the engine adjusting device 15. Particularly preferably, the pump adjusting device 14 and the motor adjusting device 15 are designed electroproportionally. In a manner not shown adjusting pressures are generated by control valves, for example, act on an adjusting piston, which cooperates with the respective adjusting mechanism. The setting of the hydrostatic transmission 3 causes the speed of the drive shaft 4 is converted into a corresponding speed of the second drive shaft 9 or in the further course of the wheel 10.

One or more input devices, for example an accelerator pedal or joystick 11, via which a control signal is generated by an operator of the working machine serve to operate the working hydraulics and to predefine the direction of travel and the travel speed. In the present example, the joystick 1 1 is connected to the control unit 13 via the bus 17.

With reference to FIG. 2, a preferred demand-driven activation of the diesel internal combustion engine 2 will be described below. The control takes place via different user preferences 201 to 208, which may include, for example, "forward", "backward", "left", "right", "lift", "lower", "tipping" and "dumping". Each of these user specifications is assigned a required minimum speed via maps 211-218 which are easy to parameterize. In order to provide the speed nosoii necessary for the current use, all speed requirements of the individual maps are connected via a maximum _selection 220, ie the necessary speed 7 _DSo // is the maximum of all requested minimum speeds.

In the following it will be explained how the driving speed can be kept constant with a variation of the diesel speed n _D. To a variation of the speed n _D is due to the demand-driven control during operation of the working hydraulics during the Driving, for example, by lifting, lowering and / or tilting the blade of a skid steer loader.

First, the driving speed request of the operator is interpreted as the output speed desired n _Ab at the wheel 10, so that now gives the task to keep this output speed n _Ab , with changing diesel speeds n _D constant.

The output speed n _Ab , results from the output speed n _{M of} the hydraulic motor 6 via a possibly existing drive gear 31 with a translation i _GFT to:

nU = ⁿ Ah - ⁱ GFT 0)

The transmission ratio r _{Hyd of} the hydrostatic transmission 3 results from the theoretical volume flow balance of the hydraulic pump and the hydraulic motor, neglecting the hydraulic efficiencies:

Q _pump (t) = Q _molor (t) (2)

p - Bo W -epC) ^, _« « - n _M {t) - a _M {t) (3) with:

n _D : input speed of the hydraulic pump

n _M : Output speed of the hydraulic motor

Vg max p ^' ■ maximum delivery volume of the hydraulic pump

g ma w · 'maximum displacement of the hydraulic motor

a _P : swing angle of the hydraulic pump; Volume fraction of [0 ... 1]

a _M : swing angle of the hydraulic motor; Volume fraction of [0 ... 1]

This gives a relationship between the output speed n _Ab and the engine speed n _D. If the output speed n _{Ab is to be} kept constant, a direct relationship is obtained between the pump or motor swivel angles to be set and the current diesel speed n _D :

Preferably, by means of a follow-up adjustment, a desired output rotational speed can be set as a function of the diesel rotational speed via the swivel angle of the hydrostatic drives. A follow-up adjustment is to be understood here as meaning that first, with the maximum displacement of the hydraulic motor, the hydraulic pump is raised from zero to full delivery volume and then the hydraulic motor is reduced from the maximum absorption volume. The basic course of a follow-up adjustment is shown in FIG. In Figure 3, the normalized to 100% or 1 swing angle (ie volume components) a _P and a _{M are} plotted on the ordinate against the transmission ratio r _{Hyd of} the hydrostatic transmission on the abscissa. A ratio _threshold , which is defined by the ratio V _{g max P} IV _g _{max M} between the maximum delivery volume V _{g max P of} the hydrostatic pump (5) and the maximum displacement V _{g max M of} the hydrostatic motor (6), is _denoted by r ₀ .

The swivel angle a _P is 301, the swivel angle a _M is designated 302. For ratios r <r ₀ , the delivery volume of the hydrostatic pump 5 is set between 0% and 100%, while the displacement of the hydrostatic motor 6 is set to 100%. For ratios r> r ₀ , the displacement of the hydrostatic motor 6 is set between 100% and 0% while the delivery volume of the hydrostatic pump 5 is set at 100%. This provides a way to set a desired gear ratio, which is particularly easy to implement. Overall, the invention provides a driving method for mobile dual-circuit machines, with which the consumption can be reduced while still maintaining full functionality.

Claims

claims

1. A method for driving the drive hydraulics (3, 3 ') of a work machine (1), which a drive machine (2), one of the drive machine (2) driven working hydraulics and one of the drive machine (2) driven, a hydrostatic two-circuit system (3 , 3 ') has comprehensive driving hydraulics,

wherein an operating point of the drive machine (2) is set as a function of a power requirement of at least the working hydraulics,

wherein, during a driving and working operation, a change in the operating requirement of the driving machine (2) caused by a change in the power requirement of the working hydraulic system is reacted by a change in the transmission ratio (r _Hyd ) of a hydrostatic transmission (3, 3 ') of the hydrostatic two-circuit system to avoid a change in the driving speed.

2. The method of claim 1, wherein the transmission ratio (r _Hyd ) of the hydrostatic transmission by adjusting the ratio between the delivery volume (a _P ) of a hydrostatic pump (5) and displacement (A _M ) of a hydrostatic motor (6) is adjusted.

3. The method of claim 2, wherein for adjusting the ratio, either only the delivery volume (a _P ) of the hydrostatic pump (5) or only the displacement (A _M ) of the hydrostatic motor (6) is adjusted.

4. The method of claim 3, wherein for a ratio smaller than a ratio threshold (r ₀ ), the delivery volume (a _P ) of the hydrostatic pump (5) between 0% and

100% is set while the displacement (a _M ) of the hydrostatic motor (6) is set to 100%.

5. The method of claim 3, wherein for a ratio greater than a ratio threshold (r ₀ ), the displacement volume (a _M ) of the hydrostatic motor (6) between 0% and

100%, while the delivery volume (a _P ) of the hydrostatic pump (5) is set to 100%.

6. The method of claim 4 or 5, wherein the ratio threshold (r ₀ ) is defined as the ratio between the maximum delivery volume of the hydrostatic pump (5) and maximum displacement of the hydrostatic motor (6).

7. The method according to any one of the preceding claims, wherein for adjusting the operating point of the drive machine (1) the speed (HDS _O //) is set.

8. The method of claim 7, wherein for setting the speed (n _DSo ii) a selection (220) of the largest requested speed is made from a number of speed _requests .

9. The method according to any one of the preceding claims, wherein a driving speed request of the operator specifies an output speed request.

10. computer unit (16) which is adapted to perform a method according to any one of the preceding claims.