WO2015067426A1

WO2015067426A1 - Method for operating a vehicle powertrain with a drive machine and with an power-split transmission device which can be operatively connected to the drive machine on the input-side

Info

Publication number: WO2015067426A1
Application number: PCT/EP2014/071493
Authority: WO
Inventors: Stephan Schinacher; Jürgen LEGNER; Udo Brehmer; Sven BIEBER; Marcus Hiemer; Robin Cramer; Jan-Frederik Kuhn; Matthias MADLENER
Original assignee: Zf Friedrichshafen Ag
Priority date: 2013-11-08
Filing date: 2014-10-08
Publication date: 2015-05-14
Also published as: DE102013222693A1

Abstract

The invention relates to a method for operating a vehicle powertrain (1) with a drive machine (2) and with an power-split transmission device (3) which can be operatively connected to the drive machine (2) on the input-side, which can be connected to an output (4) on the output side, and the transmission ratio of which can be continuously varied in the region of a variator (21). The vehicle powertrain (1) further comprises a switching element (27) which is arranged in the power flow of the vehicle powertrain (1) between the drive machine (2) and the output (4) and the transmission capacity of which can be continuously adjusted. According to the invention, the transmission capacity of the switching element (27) is varied depending on a respective current torque to be transmitted between the drive machine (2) and the output (4) in the vehicle powertrain (1), and the switching element (27) transitions into a slip operating mode upon applying a torque which exceeds a defined threshold.

Description

A method of operating a vehicle powertrain having a prime mover and having a gearbox unit operatively coupled to the prime mover in operative connection with the prime mover

The invention relates to a method for operating a vehicle drive train with a prime mover and with an input-side engageable with the prime mover in operative connection power-split transmission device according to the closer defined in the preamble of claim 1. Art.

Wheel loaders known from practice are designed, for example, with a reversing gear in conjunction with a hydrodynamic torque converter or in combination with a fully hydrostatic drive. With both drive concepts, a so-called load sensitivity can be represented constructively, by means of which rapid adjustment of a ratio of the reversing gear in the direction of large ratios is possible. This is especially important during a running-in process of a wheel loader in a so-called heap of great importance, during which a blade of the wheel loader is filled. During such a retraction process, a wheel loader is delayed within a fraction of a second from a comparatively high driving speed to almost zero. A drive speed of a drive motor designed as a diesel engine of the wheel loader should, however, be pressed only within very narrow limits during such an operating state course. In addition, the drive motor of a wheel loader should also not be overloaded. This requirement also applies if at the same time auxiliary consumers, such as a working hydraulics, are supplied with power by the working motor.

In gearboxes designed with hydrodynamic torque converters, pressures of the rotational speed of a drive motor and also overloading of a drive motor of a wheel loader are avoided in a simple manner by the identification of the torque converter. This results from the fact that an impeller of a torque converter associated with a diesel engine, depending on the input speed and the current speed conversion, which corresponds to the ratio between a speed of a turbine of the torque converter and the speed of the impeller, only a limited torque. Of the each generated by the impeller oil flow is absorbed by the turbine of the torque converter and passed through a stator of the torque converter back to the impeller. Due to the differences in the blading of pump and turbine wheel, it comes to a torque conversion. This torque conversion can in turn be described by a quotient of the torque acting on the turbine wheel and the torque acting in the region of the impeller. The torque generated in the region of the turbine wheel is introduced via a transmission input shaft of a reversing gear of a wheel loader in the reversing gear. Corresponding to the selected direction of travel and the gear currently engaged in the area of the reverse gear, a corresponding torque is applied in the region of an output.

Since the torque absorption in the region of the pump wheel is directly dependent on the rotational speed of the drive motor and the state of the turbine wheel, the drive motor is therefore not overloaded to the desired extent even with a rapid speed change in the region of the output. This is especially true when currently in the field of reverse gear, a small translation or a large gear at the same time low speed of the drive motor is engaged and a voltage applied in the field of output torque increases rapidly and the output is therefore extremely quickly loaded or if The speed of the output changes rapidly due to external loads.

If a reverse gear is combined with a hydrodynamic torque converter with associated lockup clutch, via which a frictional connection between the pump and the turbine can be produced, and with closed torque converter lockup in the field of high dynamic output a load is built up that the speed of the drive motor of a wheel loader is pressed, the lockup clutch is transferred as fast as possible in an open operating state. The operation of the lockup clutch is usually carried out as a function of present in the range of the drive train of a wheel loader speeds, torques or speed gradients. Fully hydrostatic systems or vehicle drive trains of wheel loaders are known to include swash plate type axial piston pumps, often associated with diesel engines. The axial piston pumps are designed for travel drives with speed controllers and have a so-called twist. Furthermore, so-called high-pressure cut-off functions are activated during operation and high-pressure relief valves are provided. An axial piston pump operated as a pump generates hydraulic power with a corresponding drive, which is forwarded via hydraulic lines to one or more axial piston pumps and converted into mechanical power, the latter axial piston pumps then being operated by a motor. The mechanical power is passed from the motor-driven axial piston pumps via a preferably single or multi-stage gear designed in the direction of the output of a vehicle drive train of a wheel loader.

The power consumption of the axial piston pumps operated as a pump is determined by the high pressure present in the region between the axial piston pumps and the rotational speed of a prime mover or a diesel internal combustion engine. An angle of a swash plate of the axial piston pumps is determined by a control pressure adjusted by the speed. Due to the twist occurring in the region of the axial piston pumps and resulting restoring forces, the swashplate or swashplate pivots back depending on the respective applied high pressure. When a fixed maximum maximum pressure is exceeded, the control pressure of the aforementioned Druckabschneidefunktion is reduced so that the maximum pressure is not exceeded.

If the speed of the return swash of the swash plate such that unacceptably large pressures in the high pressure area, the high pressure is limited by the high-pressure relief valves until the swash plates is adjusted to a pivot position to which the maximum high pressure corresponds to the set by the Druckabschneidefunktion height.

Since the control pressure is set as a function of the speed of the diesel internal combustion engine and thus the maximum power consumption of the pump as a pump Driven axial piston pump is limited, it is ensured that even with set small displacement of the motor-driven axial piston pumps a so-called stalling of the diesel engine is prevented. For design reasons, this also applies if additional auxiliary consumers, such as the working hydraulics, are supplied with torque or power by the diesel internal combustion engine.

Furthermore, vehicle drive trains of wheel loaders are increasingly formed with stepless, power-split transmission systems, which are designed with a variator, a reverse gear and a range group. In the field of reversing gear spur gears or planetary gears are usually provided, wherein a direction of travel of a vehicle is adjusted by appropriate switching of multi-plate clutches. Driving ranges within which a translation of such a continuously variable, power-split transmission via the variator is continuously variable, are represented by coupled planetary gear or spur gears. To display range changes are often used as switching elements also multi-plate clutches. In addition, because of the high power density, the variators are often designed as hydrostatic transmissions with hydrostatic units each operable as a pump or motor in conjunction with a power split. The power split in these transmission systems is done by planetary gear and a summation or inversely.

Basically, a distinction is made between power-split primary and secondary-coupled systems. In the area of the variator input, there is a fixed speed ratio in so-called primary coupled systems and a fixed torque ratio in the area of a variator output. In contrast, a secondary-coupled system is characterized by a fixed torque ratio in the range of the input of the variator and by a fixed speed ratio in the range of Variatorausgangs. Regardless of the respective structural design, in an adjustment of the ratio of a continuously variable, power-split transmission, for example, starting from small translations in the direction of large translations each one or Pass through several driving ranges partially or completely, for which purpose the variator may be to pivot several times over the full range.

The transition from one to the next driving range is known to cause delay times. If, for example, two driving ranges to be traveled through are used as the basis, approximately 0.7 to 1.0 s are required for passing through the driving ranges and another 150 to 200 ms are required for the required driving range change, bringing the total to approximately 0.95 to 1.2 s elapse until a maximum gear ratio has been set in the area of a gearbox. When a wheel loader enters a pile, the load applied from the outside increases in less than 0.5 s. The positioning speed or the rate of change of the ratio in the range of the transmission is therefore disadvantageously too low to avoid inadmissible pressures of the speed of the diesel engine when entering a heap.

In addition, due to legal regulations, the exhaust emissions of internal combustion engines, especially diesel internal combustion engines, are significantly reduced. For this reason, engines have been developed in the recent past, which have a very high torque increase. In addition, current internal combustion engines provide constant power over a wide speed range. This makes it possible that even high speeds at low speeds of a diesel engine or the like can be displayed. Diesel engines are known to operate at correspondingly low speeds each in the range of their consumption-optimal operating points, which is why low speeds are preferred.

This requirement exacerbates the above-described problem with respect to the adjustment of stepless, power-split transmissions. A variator is very widely swung out at typical, preferably low vehicle speeds and at the same time low engine speed during a loading cycle of a wheel loader. The physically maximum possible actuating speed in the range of the hydrostatic units of a variator is not always sufficient in the presence of such an operating state of a vehicle drive train of a wheel loader, to avoid an inadmissible pushing a diesel engine or even stalling a diesel engine can.

The present invention is therefore based on the object of providing a method for operating a vehicle drive train, preferably a wheel loader, with an internal combustion engine and with an input side of the internal combustion engine can be brought into operative continuous stepless power-split transmission device, by means of which during unfavorable operating state curves an impermissible pressure or even a stalling of an internal combustion engine can be avoided.

According to the invention this object is achieved by a method having the features of claim 1.

In the inventive method for operating a vehicle drive train, preferably a wheel loader, with a prime mover and with an input side can be brought into operative connection with the drive power-split transmission device, the output side is connected to an output and the translation in the range of a variator is infinitely variable, and with a Switching element, which is arranged in the power flow of the vehicle drive train between the prime mover and the output and whose transmission capacity is continuously variable, the transmission capability of the switching element is varied depending on a current in the vehicle drive train between the prime mover and the output torque to be transmitted and the switching element is in concern Torque greater than a defined threshold in a slip over.

About the method according to the invention impermissible pressures of the speed of an example designed as an internal combustion engine prime mover of a wheel loader or even stalling such a prime mover in a simple manner thereby avoidable that in a vehicle powertrain between a prime mover and an output torque values greater than a torque, causing an unacceptable squeezing or stalling of the engine, the switching element in a slip operation passes and a voltage applied in the field of the engine torque in the range of the switching element can be limited to a level to which impermissible pressures of the rotational speed of the engine or even a stoppage of the prime mover fail.

In an advantageous variant of the method according to the invention, the ratio of the transmission device is greater than a rise in a torque applied in the region of the output and a resulting deviation between a desired speed and an actual rotational speed of the drive machine corresponding to a depression of the rotational speed Raised limit above which an impermissible depression of the rotational speed of the engine is detected. The transmission capability of the switching element is set in the presence of an inadmissible suppression of the rotational speed of the engine despite a raising of the ratio of the transmission device to a value to which an inadmissible suppression of the rotational speed of the engine is omitted. This, in turn, relieves the drive machine in a simple manner during unfavorable operating state curves and limits the maximum torque that can be displayed in the region of the output.

In order to avoid inadmissible pressures of the rotational speed of the drive machine and / or stalling of the prime mover over the entire operating range of a vehicle drive train to the desired extent, the transmission capability of the switching element in a further advantageous variant of the method according to the invention is currently set in the transmission device ratio and the current output speed varies.

So that the required traction force to be represented in each case in the area of the output can be applied in the area of the output over the prevailing driving speed, the transmission capability of the switching element in the slip mode is to be set such that the torque that can be transmitted via the switching element is less than or equal to a maximum torque that can be predetermined as a function of the operating state.

It can be provided that the maximum torque can be predetermined by an operator. If the torque which can be conducted via the switching element is less than a limit below which damage in the area of torque-transmitting components of the vehicle drive train is avoided, unacceptably high loads in the area of the torque-transmitting components of the vehicle drive train are avoided with little effort.

In a feasible with little control and regulation cost variant of the method according to the invention a current load of the drive machine of the vehicle drive train is determined in dependence on an actual torque of the drive machine. Thus, unacceptably high loads of the drive of a vehicle drive train can be determined with little effort and used for the actuation of the switching element.

Alternatively, or cumulatively, it can also be provided that a current load of the drive machine of the vehicle drive train is determined in dependence of a current load condition in the transmission device and the transmission capability of the switching element is adjusted with little effort to a value to which any impermissible loads in Area of the prime mover can be avoided.

In another variant of the method according to the invention which is likewise simple to carry out, the current load state in the area of the transmission device is determined by metrological determination of a torque guided via the transmission device, preferably by means of a measurement of a high pressure in the region of a hydrostatic variator of the transmission device.

Alternatively, the current load state in the transmission device can also be determined via a qualified load estimation, as is known, for example, from DE 10 2008 043 906 A1.

In order to ensure that the switching element passes into the slip mode without delay when the load is present, the transmission capability of the switching element is adjusted as a function of the rotational speed of the output drive. represents that the switching element begins to slip immediately when the threshold is exceeded.

If the transmission capability of the switching element is set to a value at which a loadable via the switching element torque by a delay-free transition to the slip mode or by increasing the slip in the region of the switching element is set to a predefined value in the presence of a dynamic load condition of the vehicle drive train Transmission capability of the switching element in each case preferably lowered so far that the switching element begins to slip safely and without delay. This can be achieved, for example, by setting or lowering the transmission capability of the switching element as a function of the currently present depression of the drive machine.

It should be noted, however, that the torque capacity of the transmission device decreases at low reciprocal ratios of the transmission device. In such an operating state of a vehicle drive train, the prime mover is no longer pressed to a significant extent or not at all. In particular, in the presence of such operating states, it is important to know the load state of the transmission device, so that the transmission capability of the switching element can be adjusted based on the load state of the transmission device.

In order to avoid impermissible loads in the region of the switching element, the current operating state of the switching element is monitored in a further advantageous variant of the method according to the invention and determines a load of the switching element, wherein the switching element is transferred upon determination of a load greater than a limit in a closed operating state, to which a load of the switching element is less than during a slipping operating condition.

If the ratio of the transmission device is increased when the shift element is slipping, until the slip in the area of the shift element is at least approximately equal to zero, the transmission capability of the shift element being limited to a few seconds. At least approximately slip-free operating state is raised and the switching element is transferred to a slip-free operating state, an impermissible compression of the drive machine as long as the slipping switching element is avoided until the ratio is set in the transmission device to a value to which a suppression in the field of prime mover also is reliably avoided in slip-free operating state of the switching element.

Both the features specified in the claims and the features specified in the subsequent embodiments of the subject invention are each suitable alone or in any combination with each other to further develop the subject invention. The respective feature combinations represent no limitation with respect to the development of the subject matter according to the invention, but essentially have only an exemplary character.

Further advantages and advantageous embodiments of the subject invention emerge from the claims and the embodiments described in principle below with reference to the drawings.

It shows:

Figure 1 is a highly schematic representation of a vehicle drive train with a prime mover, with a continuously variable, power-split transmission device and with an output.

FIG. 2 shows different profiles of operating state variables of the vehicle drive train according to FIG. 1 over a vehicle speed; FIG.

FIG. 3 shows different courses of a plurality of operating state variables of the vehicle drive train according to FIG. 1 during a loading process of a bucket of a wheel loader over time t; FIG.

4 shows two courses of an actuating pressure of a frictionally engaged shifting element of the vehicle drive train according to FIG. ziproken translation of a transmission device of the vehicle drive train;

5 shows a course of a percentage reduction of the actuating pressure of the switching element via a depression of a rotational speed of the drive machine of the vehicle drive train according to FIG. 1; and

Fig. 6 is a limit curve of the torque of the prime mover of the vehicle drive train of FIG. 1 on the reciprocal translation of the transmission device, above which the actuating pressure of the frictional switching element is to reduce an inadmissible pressing the speed of the prime mover with a desired spontaneity reduce or avoid can.

1 shows a schematized representation of a vehicle drive train 1 with a drive device 2 and a continuously variable power-split transmission device 3 coupled thereto. The drive device or drive machine 2 is presently embodied as an internal combustion engine, preferably as a diesel internal combustion engine, and can also be used in other embodiments of the vehicle drive train be formed a combination of an internal combustion engine of any type and an electric machine. On the transmission output side, the transmission device 3 is operatively connected to an output 4, whereby a drive torque provided by the drive device 2 is converted accordingly as output torque in the region of the output 4 as a corresponding tractive power offer depending on the transmission ratio set in the region of the transmission device 3. In the area between the drive device 2 and the transmission device 3, a power take-off 5 or a working hydraulic starting from the drive machine 2 can be acted upon with torque.

In the area of a transmission input shaft 6, the transmission device 3 is rotatably connected to the drive device 2. The transmission input shaft 6 drives via a fixed gear 7 and a fixed gear 8A the power take-off 5, another power take-off 8 and first switching element halves of frictional switching elements 9, 10 at. The frictionally engaged shifting element 9 or the direction-of-travel clutch for downward travel is arranged coaxially with the transmission input shaft 6, while the frictional engagement element 10 or the direction-control clutch for reverse travel is positioned on the shaft of the power take-off 5 arranged parallel to the transmission input shaft 6. In the closed operating state of the frictional switching element 9 drives the transmission input shaft 6 via a loose wheel 1 1, which is rotatably mounted on the transmission input shaft 6, a loose wheel 12, which is rotatably coupled to a planet carrier 13. In the closed operating state of the frictional switching element 10, the transmission input shaft 6 drives the idler gear 12 via a loose wheel 14.

On the planet carrier 13 a plurality of double planetary gears 15 are rotatably mounted. The double planet wheels 15 are connected to a first sun gear 1 6 and a second sun gear 17 and a ring gear 18 in engagement. The first sun gear 16 is rotatably connected to a shaft 19 of a first hydraulic unit 20 of a hydrostatic unit 21. The ring gear 18 is operatively connected via a fixed gear 22 and a fixed gear 23 with a shaft 24 of a second hydraulic unit 25 of the hydrostatic unit 21.

In the area of the infinitely variable power-split transmission device 3, a plurality of transmission ranges are adjustable, within which in turn the ratio of the transmission device 3 can be changed continuously by adjusting the hydrostatic unit 21 or the variator of the transmission device 3. Independently of the illustration according to FIG. 1, the transmission device 3 can be embodied both as a primary and as a secondarily coupled continuously variable power split transmission, wherein the power split can be effected both hydraulically and electrically or by means of a combination thereof.

An output shaft or a transmission output shaft 26 of the transmission device 3 is connected via a coaxial with the transmission output shaft 26 frictional switching element 27 for a first driving range of the transmission device 3, a loose wheel 28 and a fixed gear 29 with the second shaft 24 of the hydrostatic unit 21 connectable. Furthermore, the transmission output shaft 26 via a fixed gear 30, a fixed gear 31 and another frictional switching element 32 for a second driving range of the transmission device 3 and a loose wheel 33 and a fixed gear 34 with the second sun gear 17 coupled. The fixed gear 34 is arranged coaxially with the second sun gear 17, while the fixed gear 31, the frictional switching element 32 for the second driving range and the idler gear 33 are arranged coaxially with each other. The fixed gear 30, the frictional switching element 27 for the first driving range and the idler gear 28 are in turn provided coaxially with the transmission output shaft 26. In addition, the fixed gear 30 meshes with both the fixed gear 31 and the fixed gear 34 of a shaft 35, which in turn is connectable to the drivable vehicle axle or with several drivable vehicle axles of the output 4.

The direction of travel clutches 9 and 10 are in the present case designed as wet clutches, which are not only provided for producing the power flow between the drive device 2 and the output 4, but at the same time determine the direction of travel. According to their capacitive design, the frictional switching elements 9 and 10 of the vehicle drive train 1 can also be used as starting elements. This is the case when, starting from a neutral operating state of the transmission device 3, to which the shift elements 27 and 32 are opened, a driving direction is engaged by a driver and at the same time an accelerator pedal is actuated to deliver a speed request. The frictional switching elements 9 and 10 are presently designed such that they also change the direction of travel or a so-called reversing is possible starting from higher speeds in the forward or reverse direction.

During such a reversing process, a vehicle speed is first reduced starting from the current vehicle speed in the direction of zero, for which both the transmission capability of the frictional

Switching element 9 and the transmission capability of the frictional switching element 10 is set to a corresponding extent. The two frictional switching elements 9 and 10 are operated predominantly slipping during the reversing process. If the vehicle speed is substantially equal to zero, the transmission capabilities of the two switching elements 9 and 10 are set such that the vehicle is approached in the opposite direction opposite to the previously operated direction of travel until the requested vehicle speed is reached. In order to be able to display a starting process based on a vehicle standstill and the neutral operating state of the transmission device 3 within short operating times and essentially without delay, the switching element 27 of the first transmission range of the transmission device 3 is closed and, in addition, the switching element 9 or the shifting element 10 as a function of the respectively present driver's request for forward or reverse driving in its closed state. During the connection of the switching element 27 and the switching element 9 or 10, the two hydraulic units 20 and 25 are adjusted via an adjustable yoke 36 such that the desired Anfahrübersetzung is set in the transmission device 3. The two hydraulic units 20 and 25 of the oblique-axis design variator 21 are arranged at an angle of 44 ° to each other and connected to the housing or the double yoke 36 with high strength. The transmission capability of the frictional switching element 9 or 10 is set to values greater than zero during the representation of the Anfahrübersetzung the transmission device 3 in order to start a executed with the vehicle drive train 1 vehicle already during a closing operation of the frictional switching element 9 or 10 can.

So that a running with the vehicle drive train 1 vehicle is operable with a driver's expected behavior, a recording power of the transmission device 3, taking into account in the direction of the PTO 5 and the other power take-off 8 guided torque and a rotational speed of the drive device 2 and in dependence of Actually present driving situation of the vehicle by changing the ratio of the transmission device 3 and / or defined by limiting a high pressure in the range of the hydrostatic unit 21 and the variator of the transmission device 3 set. In this case, the torque guided in the direction of the power take-off 5 and / or the additional power take-off 8 is determined from the difference between the torque currently provided by the drive device 2 and a torque applied to the transmission device 3 in the region of the transmission input shaft 6. If it is detected that the torque guided in the direction of the power take-off 5 and / or the additional power take-off 8 and the torque applied due to a driver-side request in the region of the transmission input shaft cause an impermissible depression of the drive device 2, the transmission device 3 is translated by adjusting the hydrostatic drive 21 and thus increases a change in the overall ratio of the transmission device 3 and reduces the transmission receiving power. This ensures that the torque required by the power take-off or by the additional power take-off 8 is at least approximately to the desired extent of the drive device 2 available, while a run with the vehicle drive train 1 vehicle is slower or decreases a vehicle speed. This also ensures that a working hydraulics can be operated to the desired extent and at the same time a traction power in the range of the output of the vehicle drive train 1 can be maintained at least approximately and an expected for a driver driving behavior is available.

The operation of the vehicle drive train 1 described below is based on the clarity of a constant speed of the prime mover 2 basis.

Basically, the double yoke 36 with closed frictional switching element 9 or 10 and in the vehicle via the switching element 27 inserted first driving range in the present case by definition not pivoted and is in the 0 ° position. This means that the first hydraulic unit 20 is in the non-pivoted operating state, while the second hydraulic unit 25 is pivoted by the full pivoting angle, which in the present case is 44 °. The power flow in the transmission device 3 is divided over the double planet carrier 15, the first sun gear 16 and the ring gear 18 and summed up again in the region of the shaft 24 and then forwarded in the direction of the output 4.

In the region of the switching element 32 is in the latter operating state of the transmission device 3 between the switching element halves before the maximum differential speed. At the same time, the speed is in the range of the first hydraulic No 20 maximum. The speeds in the range of the second hydraulic unit 25 and the speed of the output 4 are equal to zero in the vehicle standstill. In the area of the variator 21, the maximum high pressure is reached and there is a maximum traction power supply. If the swivel angle in the region of the double yoke 36 is increased, the rotational speed in the region of the first hydraulic unit 20 decreases and the differential rotational speed in the region of the switching element 32 decreases. At the same time, the rotational speed increases in the region of the second hydraulic unit 25, which also causes an increase in the rotational speed in the region of the output 4. In nearly fully swung-out state of the double yoke 36, to which the pivot angle in the range of the second hydraulic unit 25 is now by definition substantially equal to zero, the switching element 32 is substantially in the synchronous operating state, in which the speed in the first hydraulic unit 20 substantially is equal to zero and in the region of the second hydraulic unit 25 is substantially maximum. Then the maximum achievable when the first driving range high pressure in the range of the variator 21 is the lowest.

If now the switching element 27 is opened and the switching element 32 is closed, the power flow changes in the transmission device 3, which is then guided via the second sun 17 and the switching element 32 in the direction of the output 4. Due to the load transfer from the switching element 27 in the direction of the switching element 32, the Getriebegesamtübersetzung in the area of the transmission device 3 does not change initially. When inserted in the transmission device 3 second driving range is in the last described operating state of the transmission device 3, the maximum achievable high pressure at the greatest and the available traction maximum. If, in turn, the pivoting angle of the double yoke 36 is reduced, the rotational speeds increase in the region of the output 4 and in the region of the first hydraulic unit 20, which in turn leads to an increase in the differential rotational speed in the region of the switching element 27.

If the double yoke 36 in turn has a swivel angle close to zero, the vehicle implemented with the vehicle drive train 1 is operated essentially at its terminal speed. The speed is again zero in the area of the second hydraulic unit 25, while the speed in the area of the first hydraulic unit 25 is zero. unit 20 as the differential speed in the range of the switching element 27 is maximum.

The amount of each adjusting in the range of the vehicle drive train 1 speeds is significantly dependent on the amount or the amount of speed of the prime mover 2. The lower the selected speed of the prime mover 2, the lower is the possible driving speed or the speed of the output 4. The smaller is also the required ratio, which is set in the transmission device 3 to a certain vehicle speed or a certain Speed of the output 4 to be able to represent.

FIG. 2 shows different courses of the aforementioned operating state variables of the vehicle drive train 1 over the vehicle speed v_fzg. It is apparent from the illustration of FIG. 2 that an output torque m41 and m42 decreases when the first driving range and when the second driving range is engaged at a constant rotational speed n2 of the engine 2 with increasing vehicle speed v_fzg. At the same time, the maximum pressures pHD1 or pHD2 which can be achieved in the region of the variator 21 with the first driving range engaged and the second driving range engaged are also reduced with increasing vehicle speed vfzg. The course pHD1 represents the maximum pressure that can be reached when the first operating range is engaged, while the curve pHD2 graphically shows the maximum pressure that can be achieved, which is the maximum possible when the second operating range is engaged.

FIG. 3 likewise shows different progressions of a plurality of operating state variables of the vehicle drive train 1 over time t, which occur during a loading operation of a blade of a wheel loader designed with the vehicle drive train, if the vehicle drive train 1 according to the invention is designed to prevent inadmissible depression of the rotational speed n 2 of the drive machine 2 is operated.

At a point in time T1, the first driving range is engaged in the region of the transmission device 3 and the wheel loader is operated at a constant output rotational speed n4. An output torque m4 is relatively low, which is why an actuation torque pressure p27 of the switching element 27 is set at a lower level, to which the switching element 27 is held with a security of at least one or slightly above one in completely slip-free operating condition. A corresponding reciprocal translation of the transmission device 3 is comparatively large. A course of a requested by a driver speed n2com the prime mover 2, a target speed n2soll the prime mover 2 and an actual speed n2ist the prime mover 2 correspond to each other at time T1. In addition, a curve of a torque m2 of the drive machine 2 is shown in FIG.

At a time T2, a load applied in the region of the output 4 increases, for which reason the torque m4 in the region of the output 4 increases from the time T2. The increase of the output torque m4 leads to an increase of the drive torque m2 of the prime mover 2 in order to be able to represent the traction power demanded in the region of the output 4.

The load applied in the region of the output 4, in conjunction with the gear ratio currently set in the region of the transmission device 3, results in the actual rotational speed n2 being of the engine 2 decreasing. The decrease in the actual rotational speed n2 of the engine 2 is detected as a depression of the engine 2. In order to reduce or avoid the pressure in the region of the drive machine 2, the ratio in the region of the transmission device 3 is increased from the point in time T3. At the same time, the actuating pressure p27 of the switching element 27 is raised in order to be able to transmit the torques transmitted in the vehicle drive train 1 initially in the slip-free operating state of the switching elements 27.

In the present case, the output 4 from a time T2 at low actual engine speed n2ist and simultaneously high speed or output speed n4 abruptly heavily loaded by a corresponding external load, resulting in the increase of the drive torque m2 results and the prime mover 2 is pressed. By adjusting the ratio of the transmission device 3 in the direction of short or greater transmission values of the transmission device 3, the drive-side load is reduced and the output torque m4 is increased. However, the speed of the system in the field of the transmission device 3 is not sufficient, which is why In the area of the drive machine 2, an impermissible depression of the speed n2 occurs. For this reason, in the manner shown in FIG. 3, the switching pressure p27 of the switching element 27 is reduced so as to be reduced in the region of the target pressure p27soll at which the switching element 27 is securely held in the closed operating state Switching element 27, the torque to be transmitted is no longer supportable and the switching element 27 passes into a slip mode. As a result, the engine 2 is relieved and limits the maximum torque m4 in the region of the output 4 from a time T5 in the illustrated manner.

In order to achieve the required tensile force in the region of the output 4 above the driving speed and at the same time to avoid an impermissible depression of the engine 2, the pressure p27 of the now slipping switching element 27 is correspondingly modulated. In this case, the transmission capability of the slipping switching element 27 is adjusted so that as far as possible a maximum permissible torque is feasible via the switching element 27 at currently set in the field of the transmission device 3 Getriebeegesamtübersetzung, but without generating an impermissible pressure in the region of the drive machine 2.

The maximum permissible torque corresponds, for example, to a traction force specified by a driver or to a torque requested by a driver, which is to be displayed in the region of the output 4. This means that in the case of a maximum driver-side power requirement, the respective full or maximum possible torque in the area of the output 4 is to be made available. If the driver requests, for example, only 50% of the power, the switching element 27 is acted upon by a corresponding actuating pressure in order to apply only 50% of the traction in the region of the output. In principle, operating pressure p27 is always set to a value depending on the state of operation in vehicle drive train 1 in the vehicle drivetrain 1 and is not exceeded in order to cause damage in the region of the torque-carrying components of vehicle drive train 1 safe to avoid. The detection of whether an impermissible load of the drive machine 2 is present is determined by a comparison between a operating state-dependent varying limit value and the currently present load of the drive machine 2. In this case, the current drive torque m2 of the prime mover 2 is monitored. As an alternative to this, it is also possible to determine the currently present pressure, which corresponds to the difference between the desired rotational speed n2setpoint and the actual rotational speed n2actual, and to use this to determine an impermissible load on the drive engine 2. Deviating from this, it is also possible to determine an impermissible load on the drive machine 2 as a function of the currently present load state in the area of the transmission device 3, wherein the current load state can be based on the currently existing high pressure in the range of the variator 21 or a qualified load estimate.

In order to ensure that the switching element 27 passes without delay into the slip operation under appropriate load, the actuation pressure p27 is always above the vehicle speed vfzg or the output speed m4 nachzuführen that the switching element 27 is acted upon in normal driving operation with an actuating pressure to which the Switching element 27 is operated slip-free at currently applied torque and an increase in the torque applied to the switching element 27 has a transition of the switching element 27 in the slipping operating state result. In this case, the actuation pressure p27 is also to be changed in the manner shown in FIG. 4 as a function of the reciprocal ratio irez of the transmission device 3. The course of the actuating pressure p27 in turn indicates the pressure values above the reciprocal ratio irez, to which the switching element reliably transitions into the slipping operating state above a torque applied to the switching element 27. In contrast to this, curve p27S1 indicates the pressure values of the actuating pressure at which switching element 27 is operated at the same torque values applied to switching element 27 with safety 1 in a slip-free operating state.

Upon detection of a dynamic load state, which requires a transition of the switching element 27 in the slip mode, the transmission capability of the switching element 27 is to be changed by appropriately adjusting the actuating pressure p27 so that the switching element 27 safe and delay freely in the slipping operating condition passes. This is achieved, for example, by the actuation pressure p27 of the switching element 27 being reduced as a function of the pressure in the area of the drive machine 2. It should be noted, however, that the torque absorption of the transmission device 3 decreases at low reciprocal translations irez. 5 shows a course of a required reduction of the actuating pressure p27 in percent over the depression of the rotational speed n2 of the engine 2. It is apparent from the representation according to FIG. 5 that the percentage reduction of the actuating pressure p27 is reduced with decreasing engine droop.

With increasing gear ratio in the transmission device 3, the pressure of the diesel engine or the engine 2 increasingly decreases until a suppression of the engine 2 completely omitted. In this operating range of the vehicle drive train, it is important to know the load state of the transmission device 3 so that the actuation pressure p27 of the switching element 27 can be lowered on the basis of the load state of the transmission device 3.

During the entire operation of the switching element 27, the load in the region of the switching element 27 is monitored. During the slip operation of the switching element 27, the ratio in the range of the transmission device 3 is adjusted as long as short or raised until the differential speed of the slipping operated switching element 27 is substantially zero or equal to zero. In the synchronous operating state or in the presence of the synchronous speed in the region of the switching element 27, the switching element 27 is again acted upon by an actuating pressure p27 to which the switching element 27 is present in the closed operating state with a safety margin equal to one or greater. This is the case in this case at a time T6.

FIG. 6 shows a profile of a limit torque m2grenz of the drive machine 2 over the reciprocal ratio irez of the transmission device 3. Above the course m2grenz the actuation pressure p27 of the switching element 27 is to be reduced accordingly to ensure at a sudden increase in the voltage applied to the switching element 27 torque that the switching element 27 passes to the desired extent in the slip mode. This is an im Area of the prime mover 2 applied torque with little control and control effort limited and unacceptable squeezing the prime mover 2 avoidable.

Notwithstanding the above description, an impermissible pressure in the region of the engine 2 is also avoidable with a frictionally engaged shifting element arranged at another point of the vehicle driveline 1, which is transferred to the above-described extent with inadmissibly high loads on the engine 2 by appropriately setting the transmission capability into a slip operation. Thus, for example, it is possible to operate the travel direction clutch 9 or 10 which is currently connected to display the direction of travel to the same extent as the switching element 27. Alternatively, it may also be provided that in the area between the transmission device 3 and the output 4, a corresponding additional frictional engagement element is provided, which is controlled and regulated operated in the proposed scope.

Attribution mark vehicle drive train

driving means

transmission device

output

PTO

Transmission input shaft

fixed gear

another power take-off

fixed gear

frictional shifting element frictionally engaged shifting element loose wheel

Losrad

planet carrier

Losrad

Double-pinion carrier

first sun gear

second sun wheel

ring gear

wave

first hydraulic unit

hydrostatic unit

fixed gear

wave

second hydraulic unit

Transmission output shaft frictional shift element idler gear

fixed gear

fixed gear 32 frictional switching element

33 idler gear

34 fixed wheel

35 wave

36 adjustable yoke

irez reciprocal transmission gear ratio m4, m41, m42 output torque

m2 drive torque

m2grenz Course of the limit torque of the engine 2 n4 output speed

n2com requested target speed of the prime mover n2is actual speed of the prime mover

n2soll Target speed of the prime mover

p27 Course of the actuating pressure of the switching element p27S1 Course of the actuating pressure of the switching element

T1 to T6 discrete time

t time

vfzg vehicle speed

Claims

claims

1 . Method for operating a vehicle drive train (1) having a drive machine (2) and having a power-split transmission device (3) which can be brought into operative connection with the drive machine (2), which can be connected to an output (4) on the output side and whose transmission in the range a variator (21) is infinitely variable, and with a switching element (27) disposed in the power flow of the vehicle drive train (1) between the engine (2) and the output (4) and whose transmission capacity is continuously variable, characterized in that the Transmission capability of the switching element (27) in response to each currently in the vehicle drive train (1) between the engine (2) and the output (4) to be transmitted torque is varied and the switching element (27) upon application of a torque greater than a defined threshold in one Slipping operation passes.

2. The method according to claim 1, characterized in that at an increase in the region of the output (4) applied torque (m4) and a resulting deviation between a target speed (n2soll) and an actual speed (n2ist) of the prime mover (2) greater than a limit above which an impermissible depression of the rotational speed (n2) of the prime mover (2) is detected, the ratio of the transmission device (3) is raised, wherein the transmission capacity of the switching element (27) in the presence of an impermissible pressure of Speed (n2) of the drive machine (2) is set despite the increase in the ratio of the transmission device (3) to a value at which an impermissible depression of the speed (n2) of the drive machine (2) is omitted.

3. The method according to claim 1 or 2, characterized in that the transmission capability of the switching element (27) in dependence of the currently in the range of the transmission device (3) set ratio and the current output speed (m4) is varied.

4. The method according to any one of claims 1 to 3, characterized in that the transmission capability of the switching element (27) is set in the slip mode so that the via the switching element (27) feasible torque smaller or is equal to a maximum operating state dependent predetermined maximum torque.

5. The method according to claim 4, characterized in that the maximum torque can be predetermined by an operator.

6. The method according to any one of claims 1 to 5, characterized in that via the switching element (27) feasible torque is less than a limit, below the damage in the range of torque transmitting components of the vehicle drive train (1) omitted.

7. The method according to any one of claims 1 to 6, characterized in that a current load of the drive machine (2) of the vehicle drive train (1) in dependence of a current torque (m2) of the drive machine (2) is determined.

8. The method according to any one of claims 1 to 7, characterized in that a current load of the drive machine (2) of the vehicle drive train (1) in dependence of a current load condition in the region of the transmission device (3) is determined.

9. The method according to claim 8, characterized in that the current load state in the region of the transmission device (3) by metrological determination of a via the transmission device (3) guided torque, preferably by means of a measurement of high pressure in the region of a hydrostatic variator (21) of the transmission device (3).

10. The method according to any one of claims 3 to 9, characterized in that the transmission capability of the switching element (27) in response to the output speed (n4) is set so that the switching element (27) passes directly into the slip mode when the threshold value is exceeded.

1 1. Method according to one of claims 1 to 10, characterized in that the transfer capability of the switching element (27) in the presence of a dyna- Mixing load state of the vehicle drive train (1) is set to a value at which the via the switching element (27) feasible torque by a delay-free transition to the slip mode or by increasing the slip in the region of the switching element (27) is set to a predefined value.

12. The method according to any one of claims 1 to 1 1, characterized in that the current operating state of the switching element (27) monitors and a load of the switching element (27) is determined, wherein the switching element (27) upon determination of a load greater than a limit value is converted into a closed operating state.

13. The method according to any one of claims 1 to 12, characterized in that the ratio of the transmission device (3) in schlupfendem switching element (27) is increased until the slip in the region of the switching element (27) is at least approximately equal to zero, wherein the transmission capability of the switching element (27) raised in at least approximately slip-free operating condition and the switching element (27) is transferred to a slip-free operating state.