DE102008025683B4 - Procedure for controlling a travel drive - Google Patents

Abstract

Method for controlling a travel drive (1) with a primary drive machine (2) and a hydrostatic transmission (3) connected thereto, with the following method steps: - Detecting a position of a driving command specification device (13) - Determining an operating point (A, B, C) for a primary drive machine (2) on the basis of a driving command (13, S4) and a current vehicle state,- determining a transmission ratio (r) of the hydrostatic transmission (3), characterized in that based on the detected position of the driving command specification device (13) a vehicle target torque (MFzg,soll) of the travel drive (1) is determined, from which a required drive power is determined (S3), the operating point (A, B, C) of the primary drive machine (2) being defined on the basis of the required drive power.

Description

The invention relates to a method for controlling a travel drive with a primary drive machine and a continuously variable transmission connected to it.

A method for controlling a hydrostatic drive is from DE 38 06 194 A1 famous. The control described there is self-learning and processor-controlled. A speed for a diesel engine is specified by means of a sensor, for example an accelerator pedal. The control contains adjustable characteristic curves with which a maximum permissible pressure can be set depending on the specified diesel speed. A delivery volume of the hydrostatic pump of the hydrostatic transmission is set as a function of the pressure actually resulting from the load condition.

The problem with the known control is that changes to the characteristics of the control behavior are difficult to implement. For example, an idling curve of the drive unit must be recorded by the self-learning process. The flexibility is limited to adjusting the permissible maximum pressure of the diesel internal combustion engine.

It is therefore the object of the invention to provide a control method for a hydrostatic travel drive in which easy intervention in the control characteristics is possible.

The object is solved by the method with the features of claim 1.

In the method according to the invention, a driving command and a vehicle state are first determined in order to control a travel drive with a continuously variable transmission, in particular a hydrostatic transmission. It will e.g. B. detects a position of a drive command setting device and a vehicle speed. Such a driving command specification device can be a driving lever or a driving pedal. A vehicle setpoint torque and from this an operating point for a primary drive machine are determined from the detected position of the driving command specification device. At the determined operating point, it is ensured that the primary drive machine generates sufficient power to meet the requirements according to the throttle lever specification. In addition to the operating point, the setting of the hydrostatic transmission, i.e. its transmission ratio, is also determined. According to the invention, a target output torque of the traction drive is determined on the basis of the detected position of the drive command specification device, from which a required drive power and ultimately the operating point of the primary drive machine is determined. In contrast to the prior art, a setpoint speed for the primary drive machine, which is usually designed as a diesel internal combustion engine, is no longer simply specified by means of the position of the driving command specification device. Rather, a driving lever position set by an operator is initially assigned by the operator to a torque requirement, the target output torque. On the basis of this torque requirement, ie the target output torque of the traction drive, in a second step that required drive power of the primary drive machine that is required to implement the target output torque is then determined.

Finally, an operating point of the primary drive machine is defined according to the determined required drive power. In the case of diesel internal combustion engines in particular, there is no direct connection between the position of the drive command specification device and a setpoint speed of the diesel internal combustion engine. Rather, the operating point is determined from the characteristics map of the diesel internal combustion engine, with one selection criterion being the previously determined required drive power. The determination of the operating point in the map can thus take place much more flexibly and, in particular, areas with particularly favorable fuel consumption can be taken into account. For the sake of simplicity, only one hydrostatic transmission is used below to represent other continuously variable transmissions.

Advantageous developments of the method according to the invention are set out in the dependent claims.

It is advantageous to first determine a target vehicle speed based on a physical model of the drive train or the entire vehicle from the target output torque of the traction drive. The transmission ratio of the hydrostatic transmission is then determined from this target vehicle speed. Determining the transmission ratio of the hydrostatic transmission from the target output torque via the target vehicle speed has the advantage that instead of taking an acceleration torque into account, which is time-consuming, the actual vehicle speed can be simply added can be done. This simplifies the calculation and in particular the parameterization of the control algorithm.

According to a further preferred embodiment, a value from 0 to a torque resulting from the rated output of the drive machine is assigned to the respectively determined position of the driving command specification device in order to determine the target output torque. However, this results in a relatively high sensitivity to load, since the power actually available at a speed, taking into account the compression of the diesel internal combustion engine, is increasingly below the nominal power of the diesel internal combustion engine as the speed increases.

In another, particularly preferred embodiment, therefore, each detected position of the drive command specification device is assigned a value from 0 to a torque resulting from an actual operating point of the drive machine. This ensures in each case that, regardless of the position of the drive command specification device, the free drive power that is actually still available is available to the primary drive machine for the remaining pedal travel or lever travel of the drive command specification device. Therefore, at each drive command setting device position, the operator "feels" what additional power the prime mover is still offering him.

A vehicle load torque is preferably also taken into account when determining the transmission ratio of the hydrostatic transmission. The vehicle load moment is determined in particular from the compression of the engine. The deviation of the actual speed from a target speed of the primary drive machine is referred to as pressure. The determination of the vehicle load torque from the compression of the engine has the advantage that only a deviation of the actually resulting engine speed from the specified target speed is required. This is already made possible by using a simple speed sensor.

According to a further preferred embodiment, the vehicle load torque is read out directly from the control unit of the primary drive machine. However, such a procedure is only possible if the control unit, for example, provides the injection system of a diesel internal combustion engine with a corresponding signal about the vehicle load torque or the drive power actually delivered by the diesel internal combustion engine.

The vehicle setpoint speed is preferably determined by integrating an initially determined vehicle setpoint acceleration. In this case, the relationship between the target output torque and the target acceleration is used in a particularly simple manner. The calculation of the target vehicle speed by integrating the target vehicle acceleration ensures that practically the entire determination of the transmission ratio of the hydrostatic transmission can be carried out by calculation. The pressure-controlled adjusting devices, which are necessary, for example, in the case of an otherwise conventional speed-dependent high-pressure adjustment, can thus be omitted. The method for controlling the traction drive is therefore essentially to be integrated into a control unit and can be parameterized accordingly in a simple manner.

According to the preferred embodiment, the transmission ratio for the hydrostatic transmission is finally determined from the desired vehicle speed determined by integration and the actual speed of the primary drive machine. In this way, the transmission ratio of the hydrostatic transmission to be set can also be determined purely by calculation, with individual characteristic curves being established on the basis of the transmission ratio in order to set the pump swivel angle or the motor swivel angle.

It is particularly preferred that the integration of the target vehicle acceleration for determining the target vehicle speed takes place over the entire time since the system was started.

• 1 eine schematische Darstellung eines zur Ansteuerung gemäß dem erfindungsgemäßen Verfahren genutzten hydrostatischen Fahrantriebs;
• 2 ein beispielhaftes Kennfeld zur Skalierung der Position der Fahrbefehlvorgabevorrichtung;
• 3 einen Signalflussplan zur Verdeutlichung der Durchführung des erfindungsgemäßen Verfahrens;
• 4 ein beispielhaftes Kennfeld einer Dieselbrennkraftmaschine ausgeführten primären Antriebsmaschine.

A preferred exemplary embodiment of the method according to the invention is explained in detail in the following description with reference to the figures. Show it:

• 1 a schematic representation of a hydrostatic travel drive used for control according to the method according to the invention;
• 2 an exemplary map for scaling the position of the drive command setting device;
• 3 a signal flow chart to illustrate the implementation of the method according to the invention;
• 4 an exemplary map of a diesel engine executed primary drive machine.

In the 1 a traction drive 1 for carrying out the method according to the invention can be seen in a schematic representation. The travel drive 1 includes a primary drive machine, which is designed as a diesel internal combustion engine 2 in the exemplary embodiment shown. The diesel internal combustion engine 2 is connected to a hydrostatic transmission 3 .

The hydrostatic transmission 3 includes an adjustable hydraulic pump 4 and a likewise adjustable hydraulic motor 5 . In the illustrated embodiment, the hydrostatic transmission 3 is realized by connecting the hydraulic pump 4 and the hydraulic motor 5 in a closed circuit. Both hydrostatic machines, which are preferably axial piston machines with a bent axis or swash plate design, are designed for operation in two opposite directions of flow. This allows the direction of travel to be adjusted without the need for a mechanical transmission by changing the delivery direction of the hydraulic pump 4 .

The diesel internal combustion engine 2 is connected to the hydraulic pump 4 via a drive shaft 6 . Instead of the direct drive of the hydraulic pump 4, a transmission arranged between the diesel internal combustion engine 2 and the hydraulic pump 4 can also be provided. The transmission can be designed as a transfer case, which is provided, for example, a power take-off to drive other possibly also hydraulic consumers.

To drive the vehicle, the hydraulic motor 5 is connected to a driven vehicle axle 8 via an output shaft 7 . The representation of the individual driven vehicle axles is only an example. Likewise, the output shaft 7 can be connected to a further transfer case in order to implement a multi-axle drive, for example.

An injection system 9 is provided to implement a determined operating point of diesel internal combustion engine 2 . The injection system 9 can, for example, have its own injection control device, via which the injection quantity of an injection pump of the injection system 9, which is not explicitly shown, is adjusted.

A first adjusting device 10 is provided for setting the delivery volume of the hydraulic pump 4 . A second adjustment device 11 is provided in a corresponding manner for setting the displacement of the hydraulic motor 5 . The first adjusting device 10 and the second adjusting device 11 can, for example, be electro-proportional adjusting devices, as are known for controlling swash plate angles in axial piston machines.

Both the injection system 9 and the first and the second adjustment device 10, 11 of the hydrostatic transmission 3 are controlled by means of a central control unit 12, in which the control method according to the invention essentially runs. For this purpose, default values are determined by the central control device 12, which are transmitted to the injection system 9, the first adjusting device 10 and the second adjusting device 11 via corresponding lines, for example a bus system.

The central control unit 12 determines for the diesel internal combustion engine 2 an operating point defined by a setpoint speed n _D, setpoint and for the first adjustment device 10 and the second adjustment device 11 a control signal, for example for a proportional magnet in the case of an electro-proportional adjustment of the hydraulic pump 4 and the hydraulic motor 5.

To determine the control signals, a position of a driving command specification device is determined by the central control unit 12 . In the illustrated embodiment of the 1 the drive command specification device is an accelerator pedal 13. The position of the accelerator pedal 13 is determined via an accelerator pedal sensor 14 and corresponds to a value of 0 to 100%. In addition, the central control unit 12 is supplied with the actual speed n _D, actual of the diesel internal combustion engine 2 . This can be done, for example, via a correspondingly returned signal from the injection system 9 . If such a signal is not available from the injection system 9, a speed sensor should be provided, for example on the drive shaft 6, and its signal fed to the central control unit 12. The accelerator pedal 13 can also be adjustable from a basic position to -100% and +100%.

Furthermore, the vehicle speed v actual _is determined by means of a vehicle speed sensor 15 . This can, for example, determine the rotational speed of the output shaft 7 and pass it on to the central control unit 12, where the actual vehicle speed v actual _is determined from this, taking into account the wheel gear ratios and/or an axle gear ratio.

In order to carry out the method according to the invention, a vehicle setpoint torque M _Fzg,soll is first determined for a specific position of the drive command specification device determined by accelerator pedal sensor 14 . In general, a vehicle torque is calculated according to the following equation: $$M_{f\mathrm{e.g}G}=\frac{M_D}{\mathrm{right}}{i}_{\mathrm{right}a\mathrm{i.e}}$$

M _Fzg is the vehicle torque, M _D is the drive torque of the diesel engine 2 actually supplied to the hydrostatic transmission 3, r is the transmission ratio of the hydrostatic transmission 3 as the ratio of the swept volume of the hydraulic pump V _gP to the swept volume of the hydraulic motor 5 V _gM and i _rad is the wheel gear reduction, which is defined as the speed of the hydraulic motor 5 to the speed of the driven wheel. At the same time, this definition also takes into account an axle ratio.

There are two ways of assigning a vehicle setpoint torque to the determined position of accelerator pedal 13 . In general, the following relationship between the vehicle torque and the power of the primary drive machine is initially used: $$M_{f\mathrm{e.g}G}=\frac{M_D{n}_{D,ist}}{v_{f\mathrm{e.g}G,is\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102008025683B4\_0012.png,DE102008025683B4\_0013.png"\; state="\{\{state\}\}">t</figure-callout>}}}2\pi {\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}=\frac{P_D-\left(P_{NV}\right)}{v_{f\mathrm{e.g}G,is\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102008025683B4\_0012.png,DE102008025683B4\_0013.png"\; state="\{\{state\}\}">t</figure-callout>}}}2\pi {\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}$$

Where n _{D,ist is} the actual speed of the primary drive machine, v _vehicle,is the actual speed of the vehicle and r _rad is the radius of the driven wheels. In the right-hand part of the equation, the dependency of the vehicle torque M _Fzg on the power of the primary drive machine P _D can be seen, taking into account the power of any secondary consumers P _NV that may be present.

Since the vehicle torque would approach infinity with decreasing vehicle speeds v _Fzg,actual, the maximum torque should be limited by pressure relief valves in the hydrostatic transmission 3 . This limitation occurs according to the equation: $$M_{f\mathrm{e.g}G,\text{Max}}=\frac{V_{G\mathrm{<figure-callout\; id="2"\; label="M\; p\; Max"\; filenames="DE102008025683B4\_0012.png,DE102008025683B4\_0013.png"\; state="\{\{state\}\}">M</figure-callout>}}{p}_{\text{Max}}{}_{}}{2\pi }{i}_{\mathrm{right}a\mathrm{i.e}}$$

M _Fzg,max is the maximum vehicle torque, V _gM is the displacement of the hydraulic motor 5 and p _max is the maximum working pressure permitted by the pressure relief valves in the closed circuit of the hydrostatic transmission 3 .

According to a first, simple embodiment, the determined accelerator pedal position is scaled in such a way that when the accelerator pedal is fully depressed (100% position), the vehicle setpoint torque is determined according to the above equation, taking into account the absolute maximum drive power P _D,max,abs of the diesel internal combustion engine 2. In the rest position of the accelerator pedal 13 (0% position), the vehicle setpoint torque M _{Fzg, setpoint is,} however, equal to zero. The scaling can e.g. B. done linearly.

However, this determination of a vehicle setpoint torque assigned to the position of the accelerator pedal 13 does not take into account the fact that the actually available power P _D,max (n _D, actual ) depends on the actual speed of the diesel internal combustion engine 2 and its pressure and is less than with increasing pressure the absolute maximum power P _D,max,abs of the diesel engine 2.

For this first possibility is in the 2 a map for scaling the accelerator pedal 13 is shown. From the diagram of 2 It can be seen that the accelerator pedal 13 can be swiveled out in two directions, starting from its zero position, which corresponds to driving forwards or driving backwards. The limitation of the maximum vehicle torque M _Fzg by the pressure relief valves can also be seen. The diagram shows the desired vehicle torque M _Fzg,soll specified by an operator using the accelerator pedal 13 as a function of the actual vehicle speed v _Fzg,act .

According to a second, particularly preferred embodiment, when scaling the vehicle pedal when the accelerator pedal 13 is fully depressed (100% position), it is not the nominal power of the primary diesel internal combustion engine 2 that is taken into account, but rather the drive power actually available at the set operating point. The 100% position of the accelerator pedal 13 is thus assigned a vehicle setpoint torque M _{Fzg,setpoint,} which takes into account the maximum torque M _D,max available at the actual diesel speed n _D, actual. In the 0 ö position of the accelerator pedal 13, of course, the assigned vehicle setpoint torque M _{Fzg,setpoint is} again equal to zero. The latter possibility has the advantage that the torque scaling of the usable torque of the diesel internal combustion engine 2 always takes place over the entire accelerator pedal travel. The remaining pedal travel of the accelerator pedal 13 is thus always assigned to the currently still available power reserve of the diesel internal combustion engine 2 . In contrast to the first-mentioned scaling example, there is therefore no dead pedal travel in which an operator changes the position of the accelerator pedal 13, but the vehicle does not react.

The course of the method according to the invention is described below with reference to the 3 explained. First, as already explained above, an assigned vehicle setpoint torque M _Fzg ,nom _is determined for each position of accelerator pedal 13 in central control unit 12 . The scaling is indicated schematically with step 1. In step S2, this vehicle setpoint torque M _Fzg , _{soll is} freed from the load torque of the vehicle. In the example shown, the load torque is determined from the pressure on diesel internal combustion engine 2 . For this purpose _, a setpoint speed n _D, setpoint of the diesel internal combustion engine 2 is first determined on the basis of the vehicle setpoint torque M _Fzg ,setpoint. This setpoint speed n _D, setpoint is also determined by the central control unit 12 and supplied to the injection system 9 of the traction drive 1 as a control variable.

To determine the setpoint speed n _D, setpoint of the diesel internal combustion engine 2 _, the drive power required to realize this torque is first determined from the vehicle setpoint torque M _Fzg ,setpoint (S3). The setpoint speed n _D, setpoint is then specified using a characteristic map of the diesel internal combustion engine 2. This is explained below with reference to FIG 4 still explained. After the setpoint speed for the diesel internal combustion engine 2 has been determined in step S4, the actual speed n _D, actual of the diesel internal combustion engine 2 is also determined, for example by means of a speed sensor (not shown). In step S5, the speed reduction Δn _D is determined from the setpoint speed n _D,soll and the actual speed n _D, actual. From the pressure Δn _D and the actual diesel speed n _D, actual, the torque M _D, actual actually generated by the diesel internal combustion engine 2 is determined using a known relationship that is stored as a characteristic diagram in the central control unit 12 . From the torque M D,act provided by the diesel internal combustion engine 2, a simplified vehicle load torque M _{Fzg,est is} calculated taking into account the transmission ratio r of the hydrostatic transmission 3 and the wheel transmission ratio i _rad in step S7 and other factors influencing the torque, such as friction losses estimated, which disregards a portion attributable to the actual acceleration. This estimated simplified vehicle load torque M _Fzg,est is subtracted from the desired vehicle torque M _Fzg,soll determined from the accelerator pedal position and a simplified desired vehicle acceleration a′ _{Fzg,soll is} calculated from the difference torque thus obtained in step S9.

This generated torque M _D, actual corresponds to the drive torque actually made available by the diesel internal combustion engine to the hydrostatic transmission 3 if there are no secondary consumers. In general, the input torque of the hydrostatic transmission 3 corresponds to the following relationship: $$M_{D,ist}=ƒ\left(\left(n_{D,sOll}-n_{D,ist}\right)p,n_{D,ist}\right)-\left(M_{NV}\right)$$

Here, M _NV is the load torque of the secondary consumers and f ((n _D, setpoint −n D,actual ) p,n _{D ,} actual ) is the relationship, stored as a map, between the torque generated by the diesel internal combustion engine 2 and the determined diesel pressure Δn _D at a certain diesel speed n _D, actual.

In general, the relationship between the vehicle load torque M _{vehicle, load} is given by the following equation: $$M_{f\mathrm{e.g}G,Last}=\frac{M_{D,ist}}{\frac{V_{GP}}{V_{GM}}}{i}_{\mathrm{right}a\mathrm{i.e}}-a_{f\mathrm{e.g}G,ist}m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}$$

The first term on the right-hand side indicates the simplified vehicle load torque M _Fzg,est and the second term indicates a part of the load torque of the vehicle attributable to the actual acceleration a _Fzg, actual. Where m is the total vehicle mass and r _rad is the radius of the driven wheel.

A setpoint acceleration a _Fzg,setpoint for the vehicle can be calculated from the difference between the vehicle setpoint torque M _Fzg,setpoint and the vehicle load. When calculating the difference between the vehicle setpoint torque M _{Vehicle,setpoint} and the vehicle load M _Vehicle,Last , as calculated using the above equation, this also takes into account the load torque attributable to the acceleration component and is calculated according to the following relationship: $$a_{f\mathrm{e.g}G,sOll}=\frac{M_{f\mathrm{e.g}G,sOll}-M_{f\mathrm{e.g}G,Last}}{m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}}=\frac{M_{f\mathrm{e.g}G,sOll}-\left(\frac{M_{D,ist}}{\frac{V_{GP}}{V_{GM}}}{i}_{\mathrm{right}a\mathrm{i.e}}-a_{f\mathrm{e.g}G,ist}m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}\right)}{m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}}$$

The respective target vehicle speed v _Fzg,soll results from integration of the vehicle target acceleration a _Fzg,soll determined according to the above relationship by integration. If one chooses integration limits from the start of the system (t = 0) to the current time t, the following relationship results: $$v_{f\mathrm{e.g}G,sOll}={\displaystyle \underset{0}{\overset{t}{\int }}{a}_{f\mathrm{e.g}G,sOll}\mathrm{i.e}t}$$

wobei die tatsächliche Dieseldrehzahl n_D,ist zu berücksichtigen ist.The relationship between this target vehicle speed v _Fzg,setpoint and the transmission ratio r to be set for the hydrostatic transmission 3 results from the equation: $$\mathrm{right}=\frac{v_{f\mathrm{e.g}G,sOll}{i}_{\mathrm{right}a\mathrm{i.e}}}{n_{D,ist}{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}2\pi },$$

where the actual diesel speed n _{D,actual must} be taken into account.

When calculating the target vehicle speed v _{Fzg,setpoint, it} also shows that due to the relationship according to Equation VI, the integration over the target vehicle acceleration a _Fzg,setpoint can ultimately be reduced to an addition of the actual vehicle speed. The vehicle target speed v _Fzg,soll results in: $$v_{f\mathrm{e.g}G,sOll}={\displaystyle \underset{0}{\overset{t}{\int }}\left(\frac{M_{f\mathrm{e.g}G,sOll}-\frac{M_{D,ist}}{\frac{V_{GP}}{V_{GM}}}{i}_{\mathrm{right}a\mathrm{i.e}}}{m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}}\right)}\mathrm{i.e}t+{\displaystyle \underset{0}{\overset{t}{\int }}{a}_{f\mathrm{e.g}G,ist}}\mathrm{i.e}t={\displaystyle \underset{0}{\overset{t}{\int }}\left(\frac{M_{f\mathrm{e.g}G,sOll}-\frac{M_{D,ist}}{\frac{V_{GP}}{V_{GM}}}{i}_{\mathrm{right}a\mathrm{i.e}}}{m{\mathrm{right}}_{\mathrm{right}a\mathrm{i.e}}}\right)}\mathrm{i.e}t+v_{ist}$$

Coming back to the presentation of the method in the 3 the result is that in step S2 the simplified vehicle load torque M _{Fzg,est is} subtracted from the vehicle target torque M Fzg,setpoint , since instead of integrating the actual vehicle acceleration a _{Fzg,setpoint ,} the actual vehicle speed v _Fzg,actual can be added at a later point in time .

From the difference between the vehicle setpoint torque M _Fzg,setpoint and the simplified vehicle load torque M _Fzg,est , a simplified vehicle setpoint acceleration a' _{Fzg,setpoint is} determined in step S9. After this simplified target vehicle acceleration a' _Fzg,soll has been integrated in the further step S10, the actual vehicle speed v _{Fzg,actual is} then added. This actual vehicle speed v _Fzg,act can be determined in a simple manner, for example via the speed sensor 15 . An integration with regard to this component when determining the vehicle setpoint speed v _Fzg,setpoint can thus be avoided.

Using the actual diesel speed n _D, actual, the transmission ratio r is then determined from the vehicle _{setpoint speed VFzg,setpoint} . With the help of this transmission ratio r, the delivery volume V _gP for the hydraulic pump 4 and a second characteristic curve the displacement V _gM of the hydraulic motor 5 are then determined by means of a first characteristic curve. These are given as an example in method step S12. The displacement V _gM of the hydraulic motor 5 is initially kept at its constant, maximum value, while the pivoting angle of the hydraulic pump 4 is linearly increased along a ramp from a minimum value up to the maximum delivery volume. When the maximum delivery volume of the hydraulic pump 4 is reached, the displacement V _gM of the hydraulic motor 5 is then reduced along the second part of the curve shown in dashed lines, and the vehicle is thus further accelerated.

In the 4 a characteristic map of a diesel internal combustion engine 2 is shown as an example. After a performance requirement has been defined in the diesel map, which is made up of the traction drive 1 and the additional consumers present, an optimum diesel speed is determined, taking into account the specific fuel consumption. In addition to the diesel speed, the efficiencies of the hydrostats 4, 5 are also taken into account. Instead of increasing the power of diesel engine 2 along points 16 to 23, which would allow an increase in diesel power or the torque delivered at a constant speed, the diesel speed is increased from point A (idle) to point B. This increase in the diesel speed has the advantage that the hydraulic motor 5 can be operated in the range of improved efficiency. By increasing the diesel speed, larger motor swivel angles of the hydraulic motor 5 can be implemented, with the efficiency of the hydraulic motor 5 improving in the process. From point B, the speed of the diesel internal combustion engine 2 is increased in the direction of point C in such a way that the piston engines 4, 5 of the hydrostatic transmission 3 can be operated in a good efficiency range for as long as possible. The exact adaptation of the curve and the necessary support points are determined with the help of an optimization function, which also takes into account the driving comfort and/or the driving performance to be achieved in addition to the consumption. Instead of the optimization function, a map can also be used, which also includes the speed in addition to consumption and performance.

wobei p_SpHD der aktuelle Druck in dem Hochdruckspeicher und p_SpND der Druck im Niederdruckspeicher ist, der zum Volumenstromausgleich erforderlich ist. Bei dem beschriebenen Ausführungsbeispiel ist der Fahrantrieb 1 mit einer Druckwiege bestehend aus einem Hochdruckspeicher und einem Niederdruckspeicher verbunden. Die oben angegebene Beziehung gilt ohne Berücksichtigung der Wirkungsgrade. Gleichzeitig muss sichergestellt werden, dass die Dieselbrennkraftmaschine 2 nicht in den Schubbetrieb geht. Der Motorschwenkwinkel des Hydromotors 5 muss daher folgende Bedingung erfüllen: $$V_{gM}\le \frac{M_{Fzg,soll}2\pi }{i_{rad}\left(p_{SpHD}-p_{SpND}\right)}$$

In a vehicle with a traction drive 1 braking energy can also be recovered in a simple manner. For this purpose, a high-pressure accumulator (not shown) is connected to the suction side of the hydraulic pump 4 . The drive torque to be made available by the diesel internal combustion engine 2 is reduced accordingly because of the high pressure made available. In this case, the vehicle target torque is calculated as follows: $$M_{f\mathrm{e.g}G}=\left(\frac{2\pi M_{D,ist}}{V_{sP}}+p_{SpHD}-p_{SpND}\right)\frac{{\mathrm{<figure-callout\; id="2"\; label="V\; G\; M"\; filenames="DE102008025683B4\_0012.png,DE102008025683B4\_0013.png"\; state="\{\{state\}\}">V</figure-callout>}}_{GM}}{2\pi }{i}_{\mathrm{right}a\mathrm{i.e}}$$

where p _{SpHD is} the current pressure in the high-pressure accumulator and p _{SpND is} the pressure in the low-pressure accumulator, which is required to balance the volume flow. In the exemplary embodiment described, the travel drive 1 is connected to a pressure cradle consisting of a high-pressure accumulator and a low-pressure accumulator. The above relationship applies without taking efficiencies into account. At the same time, it must be ensured that the diesel internal combustion engine 2 does not go into overrun mode. The motor swivel angle of the hydraulic motor 5 must therefore meet the following condition: $$V_{GM}\le \frac{M_{f\mathrm{e.g}G,sOll}2\pi }{i_{\mathrm{right}a\mathrm{i.e}}\left(p_{SpHD}-p_{SpND}\right)}$$

The invention is not limited to the illustrated embodiment. Rather, individual features of the method according to the invention can also be combined with one another.

Claims (10)

Method for controlling a travel drive (1) with a primary drive machine (2) and a hydrostatic transmission (3) connected thereto, with the following method steps: - detecting a position of a driving command specification device (13) - determining an operating point (A, B, C) for a primary drive machine (2) on the basis of a driving command (13, S4) and a current vehicle condition, - determining a transmission ratio (r) of the hydrostatic transmission (3), thereby marked net that on the basis of the detected position of the drive command specification device (13) a vehicle setpoint torque (MFzg,soll) of the travel drive (1) is determined, from which a required drive power is determined (S3), the operating point (A, B, C) of the primary prime mover (2) is set. procedure after claim 1 , characterized in that from the target output torque (M _Fzg,soll ) a vehicle target speed (v _Fzg,soll ) is determined based on a physical model of a drive train or the vehicle (S10) and the transmission ratio (r) of the hydrostatic transmission (3). of the target vehicle speed is determined (S11). procedure after claim 1 or 2 , characterized in that to determine the vehicle target torque (M _Fzg,soll ) the determined position of the drive command specification device (13) is assigned a value from zero to a torque resulting from the rated power of the drive engine (S1). procedure after claim 1 or 2 , characterized in that to determine the vehicle target torque (M _Fzg,soll ) of the determined position of the drive command specification device (13) a value from zero to a value derived from the at an actual operating point (A, B, C) of the engine (2) resulting moment is assigned (S1). Procedure according to one of Claims 1 until 4 , characterized in that to determine the transmission ratio (r) of the hydrostatic transmission (3), a vehicle load torque (M _Fzg,est ) is taken into account. procedure after claim 5 , characterized in that the vehicle load torque (M _{Fzg, est} ) is determined from a depression of the engine. procedure after claim 5 , characterized in that the vehicle load torque (M _{Fzg, est} ) is read out from a control unit (g) of the drive motor (2). procedure after claim 2 , characterized in that the desired vehicle speed v _Fzg,soll ) is determined from an initially determined desired vehicle acceleration (a _Fzg,soll ) by integration (S10). procedure after claim 8 , characterized in that the transmission ratio (r) for the hydrostatic transmission (3) is determined from the desired vehicle speed (v _Fzg,soll ) and the actual speed (n _D, actual ) of the primary drive machine (2). procedure after claim 8 or 9 , characterized in that the integration of the vehicle setpoint acceleration (a _Fzg,soll ) takes place over the entire time since the system was started (0-t).

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