DE112010002845T5 - Method and system for controlling a vehicle - Google Patents

Abstract

The present invention relates to a method for driving a vehicle when the vehicle starts, the vehicle having at least one driven wheel for driving the vehicle and also comprising an electric motor which is designed to generate a torque for driving the driven wheels. The method comprises the steps of: a) using the electric motor to transmit a torque that drives the driven wheels in a first direction, b) determining a representative value for adhesion of the driven wheels on a tread, and c) reversing the direction of rotation of the electric motor to transmit a torque that drives the driven wheels in an opposite direction to the first direction when the representative value for the adhesion of the driven wheels to the tread meets a first criterion.

Description

Field of the invention

The present invention relates to a system for controlling a vehicle when starting in unfavorable tread conditions. In particular, the present invention relates to a method according to the features of the preamble of claim 1. The invention also relates to a system according to claim 11 and a vehicle according to claim 12.

Background of the invention

It is known that vehicles in general and trucks in particular can get stuck when starting from a standstill in situations with unfavorable road or tread conditions. Such unfavorable tread conditions may be, for example, snow or soft treads such as sand, soil, etc.

When a vehicle is to start up in such conditions, usually in situations where one or more of the driven wheels has become stuck in a cavity or furrow, the wheels spin before they go out due to the engine torque applied to move the wheels come out of the cavity / furrow. As a result, the cavity / groove is deeper and it is the more difficult it is to drive out of the vehicle.

When such situations occur, one or more "proven" methods of freeing the vehicle are often used. For example, the vehicle's air suspension system may be used and / or the trailing axle raised to increase the load on the driven wheels, thereby making it easier for the wheels to maintain grip on the tread. Another method often used in the case of such cavities / furrows is a rocking-up method wherein the driver attempts to free the vehicle by increasing the force applied to the driven wheels, preferably with a relatively high engaged gear, until the wheels spin freely , Thereafter, the driver immediately stops the acceleration and, if applicable, disengages the clutch so that the vehicle rolls back. This process is then repeated when the movement in the opposite direction is omitted. The continuous rocking of the vehicle in this way can lead to a sufficiently large force to move the vehicle out of the cavity / furrow.

The probability of success with such a rocking process varies from driver to driver and with the experience of the driver. For this reason, systems have been developed in which the Aufschaukelfunktion is automated. An example of such a function is in the document WO 2004/098940 A1 (Volvo Lastvagnar AB). This document describes the automatic control of a vehicle drive system for use when starting under adverse tread conditions. The driving force is applied across the driveline of the vehicle to at least one driven wheel until a condition such as spin of the wheels is detected, whereupon application of the driving force is stopped and effected in the opposite direction.

The function described in the above-mentioned document has the advantage that the driving force for application to the driven wheels of the vehicle for Aufzuschkelzwecke can act not only in one direction, but in both directions in order to try to improve the chances of driving away the vehicle to be able to. However, the solution described has the disadvantage that the change of direction in which the driving force is exerted, a first disconnection of the vehicle drive train and then a gear change includes to be able to exert the driving force in the opposite direction. Although such a process works well in principle, disconnecting the powertrain, then changing gears, and re-connecting the powertrain are relatively time consuming operations. As a result, the change of direction in which the driving force is applied is often too late to take full advantage of it.

There is therefore a need, at least in certain situations, for an improved method for freeing a stuck vehicle.

Outline of the invention

It is an object of the present invention to propose a method of controlling a vehicle at startup, which solves the problem described above. This object is achieved by a method according to claim 1.

The present invention relates to a method for driving a vehicle at startup, the vehicle including at least one driven wheel for driving the vehicle and including an electric motor configured to generate a drive torque that acts on the driven wheel. The electric motor is used to apply a drive torque to the driven wheel in a first direction, a representation value for the grip Adhesion of the wheel on the tread is detected, and the direction of rotation of the motor is reversed to apply drive torque to the wheel in an opposite direction to the first direction when the representation value for the grip on the tread is a first criterion Fulfills.

The present invention has the advantage that by using an electric motor for generating the driving torque, for example, to effect the above-described Aufschaukelfunktion, unlike the prior art, it is possible to turn over the moment acting on the wheel very quickly, if at least one the driven wheels of the vehicle loses its grip on the tread, which can be determined, for example, by detecting wheel spin / a large increase in the speed of the wheel (s). In this case, the spinning wheel (s) may be stopped quickly and the driving torque applied in the opposite direction to assist the vehicle movement in an opposite direction to thereby increase the rocking, resulting in a higher probability of the vehicle closing to free. The present invention therefore makes it possible for a driver to rescue a vehicle from a situation otherwise requiring a release or other form of assistance, such as attempting to place something under the wheels. The invention has the further advantage that no further new components are needed in vehicles with existing electric motor systems.

The above-described steps involving the reversal of the direction of the moment may be repeated until the method is stopped by, for example, a driver of the vehicle or until the control system of the vehicle determines that the vehicle has been cleared and actually started up.

According to one embodiment, the electric motor is connected to the driven wheel via a transmission. The present invention has the advantage that even when the engine is connected to the wheel via the transmission, the transmission can still be operated in both directions, which means that the same gear can be used in carrying out the method according to the present invention so no time is needed to separate a gear and engage another gear.

The invention is suitable for parallel hybrid vehicles and other types of vehicles in which an electric motor can be used for driving. The invention may be used, for example, in hybrid serial vehicles and in vehicles in which one or more electric motors drive the drive wheels of the vehicle directly without intermediate gears, as in pure electric vehicles.

Further features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

Brief description of the figures

1 shows a powertrain of a hybrid vehicle, with which the present invention can be used advantageously.

2 illustrates an example of a method according to the present invention.

3 FIG. 4 illustrates an example of a rocking method according to the present invention.

Detailed Description of Exemplary Embodiments

As described above, in automated upshifting functions, it is difficult to disengage an automatic clutch at the right time, i. H. precisely when the wheels start to spin. When the driven wheels of the vehicle begin to spin, the grip on the tread is lost, and if the wheels have come out of a cavity / furrow on the way, the vehicle will move in the opposite direction, i. H. back into the cavity or furrow. In this situation, it is desirably possible to quickly engage a gear for moving in the opposite direction, so that an advantage can be drawn from the gravitational effect which occurs when the wheels roll back into the cavity and this can be used to move in an opposite direction To get out of the cavity. Disconnecting the output shaft of the engine from the input shaft of the transmission, which is involved in a gear change, means that such a solution does not take up little time and makes optimal operation impossible.

In contrast, the present invention does not lead to this problem. The invention described below will first be described with reference to a parallel hybrid system and the Aufschaukelfunktion according to the present invention makes it possible to disconnect an internal combustion engine, for example by means of a conventional clutch from the input shaft of the transmission, so that only the electric motor for driving the driven wheels is used during the Aufschaukelverfahrens. The direction and speed of an electric motor are controlled by the frequency of the voltage to supply it. The use of an electric motor therefore offers the advantage that, unlike an internal combustion engine, the electric motor can rotate in both directions. Thereby, it is achieved according to the present invention that by reversing the direction of rotation of the electric motor in principle any desired gear can be inserted, since the driven wheels can be driven in both directions with the same gear engaged. Therefore, according to the present invention, there is no need for a gearshift and thus no need to spend time on such a gearshift. The present invention therefore makes it possible, at least in principle, to switch the drive torque directly from forward to reverse (or vice versa).

1 provides a powertrain in a hybrid vehicle 100 According to a first embodiment of the present invention, various types of hybrid vehicles exist and the illustrated vehicle is a parallel hybrid vehicle.

The powertrain of the in 1 shown parallel hybrid vehicle has an internal combustion engine 101 on, in a conventional manner via an output shaft 102 of the internal combustion engine 101 via a friction element (coupling) 106 with a gear 103 connected is. The vehicle further includes drive shafts 104 . 105 that with the driven wheels 113 . 114 the vehicle are connected and, as in a conventional internal combustion engine system, by means of an output shaft 107 the transmission are driven by a final drive, for example, in conventional differential 108 can be.

Unlike conventional vehicles, this features in 1 shown vehicle also has an electric motor 110 on that with an input shaft 109 of the transmission 103 "Downstream" of the clutch 106 connected is. The parallel hybrid vehicle can therefore simultaneously force from two separate drive sources to the drive wheels 113 . 114 transferred, ie from both, the internal combustion engine 101 and the electric motor 110 , Alternatively, the vehicle may be driven by one or the other of the drive sources, ie either by the internal combustion engine 101 or the electric motor 110 ,

As those skilled in the art know, there are various types of electric motors that can be used in hybrid vehicles. Accordingly, the electric motor 110 be of any desired, suitable type. The motor used by way of example in the following description is a three-phase motor and the power supply is a three-phase supply. Three-phase motors can be so-called asynchronous or synchronous types, with synchronous motors having the advantage that an exact determination of the speed is possible. In vehicle applications, it is naturally preferable to be able to vary the rotational speed of the driven wheels and thus of the electric motor in addition to the changes achieved by the conventional gear changes via the transmission. Therefore, the engine must conventionally be speed controlled. The speed of the electric motor is generally controlled by the frequency of the supply voltage through which the motor is driven. The speed of the motor is directly proportional to this frequency. The speed control of an electric motor thus includes the change in the voltage supplied to the motor. In the case of an AC motor, this means that the frequency of the AC power supply must be changeable.

The in 1 illustrated engine 110 is therefore powered by a three-phase supply of variable frequency, which is achieved by using a power electronics device 111 which, in the case of hybrid vehicles, can also be used in a known manner for various other functions which will not be described in detail here.

The power electronics device 111 works with an energy store 112 together, for example, one or more batteries, supercapacitors, etc., wherein the energy storage must be loadable in various ways, for example by regenerative braking by means of the electric motor 110 and / or by plugging in an external power source, for example a conventional electricity grid.

The illustrated power electronics device 111 may be of the type conventionally used in hybrid vehicles and therefore will not be described in detail. In general, however, it can be stated that in the case of AC motors, the power electronics device 111 the direct current of the energy storage 112 converted into AC voltage. The conversion is effected by a converter, which may comprise, for example, a number of insulated gate bipolar transistors (IGBTs), which by means of suitable switching, a three-phase voltage of a preferred and variable amplitude and frequency for driving the electric motor 110 and thus the driven wheels 113 . 114 can provide the vehicle.

The electric motor 110 can by controlling the engine 110 supplied frequency from 0 Hz up to a frequency corresponding to the maximum speed of the vehicle (or of the internal combustion engine in the case of a common operation with the Internal combustion engine) at speeds of a vehicle in a range of 0 to maximum speed.

1 also provides a control unit 115 which can be used to control the method according to the present invention. The control unit 115 forms part of the control system of the vehicle, vehicle control systems in modern vehicles conventionally comprise a communication bus system formed by one or more communication buses for connection to various electronic control units and components located in the vehicle. For example, signals to / from an electric motor control unit / power electronics and other vehicle functions used in the method according to the invention may be supplied to / from the control unit 115 be routed through suitable communication buses. The vehicle control unit 115 may for example be an existing control unit. In this case, the present invention can be easily integrated at a low cost.

An embodiment according to the present invention will be described below with reference to FIG 2 in which a Aufschaukelverfahren generally with 200 is designated. The procedure begins with step 201 which determines whether the upshift function is activated. This can be determined in different ways. For example, after the stoppage of the vehicle has been detected, the driver may activate the function by means of a button or lever or some other means, for example via a function that can be selected via a display.

The function may also be configured to be automatically activated, for example if the vehicle control system detects wheel spin. For security reasons, however, it may be preferable for the function to be activated manually. The invention will therefore be described below with reference to a manual activation.

If it has been determined that a roll-over function should be initiated, the method continues with step 202 in which it is determined whether the function should actually be executed. This determination is not necessary, but preferred, to prevent "independent execution" of the vehicle immediately after activation of the upshift function. For example, the embodiment may be located downstream of the operator depressing the accelerator pedal or the display in another way, for example by means of a compliant knob or lever, so that the Aufschaukelfunktion is actively effected. This may also be combined with the selection of a preferred direction (forwards or backwards) in which the vehicle is to be preferentially approached by the driver to assist the desired continuous ride.

This is desirable, for example, in situations where continuous operation is possible only in one direction, for example due to obstacles in front of or behind the vehicle. For example, the driver may indicate the preferred direction of travel by using the gear selector to select a forward or reverse direction. Whatever his / her choice is, then the control system selects a suitable gear in the transmission which is subsequently used during the upshift function.

Will in step 202 detects that the Aufschaukelfunktion is actually executed, the method goes to step 203 fort (for safety reasons, the Aufschaukelfunktion can be advantageously designed such that it is stopped immediately when the driver releases the accelerator pedal and / or presses the brake). In step 203 a suitable gear is selected for use during the upshift function. This gear will normally be one of the lower gears of the transmission. Whether this gear is intended to propel the vehicle forwards or backwards makes no difference to the process, but may be crucial to the continuous movement of the vehicle when it has been released from the cavity / furrow. For example, it may be advantageous that the gear selected by the Aufschaukelfunktion can also be used for continuously driving the vehicle, so that there is no risk of reconnection due to an unavoidable interruption of the drive torque that occurs at a gear change and at low speed can result in a stop of the vehicle and can lead to a renewed sticking.

Therefore, it may be advantageous to select a gear for driving the vehicle in the direction indicated by the driver. Another parameter to be considered in selecting the gear for use in the method according to the invention is that the gear selection must result in achieving the desired control characteristics, i. H. the selected gear must be capable, together with the electric motor, of achieving the preferred speed of the driven wheels (this selection can be controlled at least in part based on the torque of the electric motor relative to the engine torque and the larger the electric motor, the larger Degree of freedom to choose the gear).

When in step 203 a suitable gear has been selected, the method goes to step 204 by generating a torque resulting from a movement in a preferred direction by the electric motor. By means of the power electronics (controlling the voltage and frequency of the power supply of the motor), the speed of the motor from standstill can be controlled in a controlled manner, while at the same time the torque provided by the motor can be controlled from 0 Nm to the maximum torque. The control devices of the engine make it possible that the speed and the torque can be provided increasingly stepless or ramped.

It must be considered that as long as the torque input is lower than the torque required to move the driven wheels of the vehicle, the shaft of the electric motor will remain stationary, regardless of the frequency supplied. One possible control method therefore involves increasing the torque provided by the engine at low speed until the shaft begins to move, whereupon the rotational speed of the engine progressively increases as the driven wheel (s) of the vehicle have begun to move. The increase in the rotational speed may be continued until the representation of the adhesion of the driven wheel (s) on the tread satisfies a first criterion, for example, if a loss of grip in wheel spin is detected, whereupon the method continues with step 205 continues, or alternatively until the rocking is completed, whereupon the method with step 206 continues. In parallel with the increase in rotational speed can be as in 3 shown, the torque can also be increased progressively. The spinning of the wheels can be detected, for example, by determining the rotational speed of the electric motor. If the speed increases rapidly, it means that the speed of the driven wheel or wheels is also increasing rapidly. This can be determined by comparing the speed of the driven wheels with the speed of the idle wheels. For example, it is possible to determine whether a difference in the rotational speed of the driven wheels and at least one non-driven wheel of the vehicle exceeds a first value.

Alternatively or additionally, the wheel spin may be detected by determining whether the speed of the driven wheels has reached a first speed.

3 FIG. 10 is a graph of torque and wheel speed / motor speed during an example of a rocking operation. FIG. It must be noted that in 3 described method very schematically and the actual process may differ significantly from, for example, depending on the choice of the control principles and how fast the driven wheels of the vehicle freewheel. The rocking process begins at time T = 0 and the torque of the electric motor increases until its shaft (and thereby also the driven wheels of the vehicle) begins to rotate at T = T1. Between the time T = T1 and the time T = T2, the speed of the wheels increases, while at the same time the torque increases at least in a part of the time range. The increase in torque is preferably torque limited, ie, the torque increases only to a predetermined level to prevent too rapid occurrence of wheel spin. The speed achieved with the corresponding torque is then maintained until the time T = T3, at which a rapid increase of the speed starts. The continuous monitoring of the rotational speed of the electric motor and / or the driven wheels makes it possible in principle to directly determine that the rotational speed is increasing. The continuous monitoring of the rotational speed of the electric motor and / or the driven wheels can be done in various ways, some of which will be described below. The speed increase starting at time T = T3 indicates wheel spin. In this case, the rotation direction of the motor becomes T = T4, step 205 , in principle, directly reversed by means of the three-phase voltage generated by the power electronics. For example, by changing the phase sequence of the three phases driving the electric motor, it is possible in principle to directly reverse the direction of the torque flow generated in the motor, which flux drives the rotor of the motor, whereupon the spinning of the driven wheels is braked very quickly to rotate in the opposite direction to the time T = T5 to begin. In principle, since the moment acting on the driven wheels can be reversed immediately, the electric motor can advantageously drive the driven wheels in the reverse direction, thereby assisting the acceleration of the vehicle in the opposite direction as it begins to slide back into the cavity / groove , The process returns to step after reversing the direction of rotation 204 back. When the wheels spin again, step 204 is detected in the opposite direction, the torque of the engine at T = T6 is reversed again, whereby a permanent drive of the specified wheels is achieved, which is advantageous for the liberation of the vehicle from the cavity / furrow.

As shown in the diagram, the maximum applied to the driven wheels Torque be increased progressively when the rocking process continues.

The determination of the torque provided by the electric motor, which simultaneously determines the speed of the driven wheels / motor, makes it possible to use the torque increase along with the increase in speed to determine if the vehicle is out of the cavity or Mulde has come out and therefore continue his journey. This is exemplified at the time T = T7 at which the speed of the driven wheels exceeds a level N1, while at the same time the speed increases so slowly despite the applied motor torque that the drive advances. This can be determined, for example, by determining a derivative of the speed. If the derivative exceeds a threshold, this may be interpreted as spinning the wheels, whereas if the derivative is below a certain threshold, the driven wheels of the vehicle may be considered as driving the vehicle. The threshold does not have to be set throughout the operation but may, for example, depend on the torque provided by the electric motor at the time. The higher the torque, the greater the relative speed increase that is possible without being judged as spinning the wheels.

When the speed of the vehicle has reached a certain level, for example the speed N1, the control system may decide that the Aufschaukelfunktion is stopped, step 206 , and that the normal journey continues. If so, and the vehicle is moving normally (if that direction has been selected by the driver, for example, by placing the gear selector in a position "D" or reverse if the gear selector has been placed in position "R") the clutch is closed and the vehicle now moves forward driven by the diesel engine. The diesel engine preferably runs during the rocking operation so that it is quickly usable for continuous driving when the vehicle has been released.

As described above, it may be disadvantageous to effect a gear change when the vehicle has begun to move. Therefore, the control system prevents any gear change until a certain speed is reached, with the aim of preventing further stopping due to the unavoidable torque gap in gear changes. In one embodiment, the separation of the automatic transmission may be controlled by the driver, for example by preventing a gear change as long as he / she presses the accelerator pedal, so that a gear change is only effected if he / she specifies that the gear change without risk of further Halt can be made and therefore releases the accelerator pedal.

The present invention therefore offers the advantage of making very fast control processes possible as a result of the operation of a conventional transmission in both directions. Therefore, there is no need for time-consuming gear changes. In principle, since the direction of the torque provided by the electric motor can be directly reversed when the wheel spin is detected, a very accurate torque control is possible and therefore a good Aufschaukelfunktion.

In the in 3 illustrated control method, the speed control is combined with a limitation of the torque. However, the above control can also be performed by monitoring the rotational speed of the driven wheels / the electric motor alone. The torque limit can still be used to ensure that the driven wheels do not rotate freely undesirably fast. The above upshift function can also be advantageously combined with an automatic application of all other devices that are available when the vehicle is stuck. For example, existing differential locks may be automatically engaged (or a message for the driver may be generated to cause him / her to engage the differential locks). The automatic speed change function can also be disconnected as described above.

The wheel spin can be detected in several different ways. For example, a sensor may be provided on the output shaft of the transmission to provide signals representing the speed of the output shaft. Alternatively, one or more wheel speed sensors may be used (eg, all wheel speed sensors of the vehicle may be used for detection to achieve the most accurate detection possible). A speed sensor may also be provided on the shaft of the electric motor. It is also possible to detect the speed of the motor by superimposing the high frequency signals of its energy supply. The superimposed high-frequency signal can then be used not only to detect the engine speed, but also to detect its condition. This allows precise detection of when the driven wheels start to turn. Thus, a very good torque control based on the rotational speed of the driven wheels can be achieved. It can too be advantageous to use the signals of some or all of the above sensors in order to achieve a reliable as possible determination.

It is of course possible that the vehicle is freed from the cavity / furrow in a "wrong" direction. The software that controls the function may therefore be provided with a locking device that, for example, prevents greater movement than a maximum of 30 cm in a wrong direction. The function can also be combined with clear warnings and acoustic / light signals to indicate retraction as the vehicle also moves backwards during the upshift function, regardless of the direction in which it is finally released.

The invention has been described above with reference to a parallel hybrid vehicle, but may equally be used with all other types of vehicles in which an electric motor can be used for driving. For example, the invention may be used in a serial hybrid vehicle in which the internal combustion engine is used only for driving a generator that charges an energy storage used to drive the electric motor to drive the driven wheels. The electric motor in hybrid serial solutions is propelled in a similar manner to that described above, so the above principles are equally applicable to this type of vehicle, with the only difference that no gear must be selected if, as is often the case, the electric motor in a serial hybrid vehicle is directly connected to a final drive gear, for example a differential.

The invention is also applicable to vehicles in which one or more electric motors drive the driven wheels of the vehicle directly without intermediate gears, ie, pure electric vehicles.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2004/098940 A1 [0005]

Claims (12)

A method of driving a vehicle when the vehicle is traveling on a tread, the vehicle having at least one driven wheel for driving the vehicle and including an electric motor configured to generate a torque for driving the driven wheels, characterized in that the method the steps comprises: a) using the electric motor to transmit a torque that drives the driven wheels in a first direction, b) determining a representation value for the adhesion of the driven wheels to the tread, and c) reversing the direction of rotation of the electric motor Transmit torque that drives the driven wheels in the opposite direction to the first direction, when the representation value for the adhesion of the driven wheels on the tread meets a first criterion. The method of claim 1, wherein the first criterion includes determining whether the driven wheels lose their grip on the tread. Method according to one of claims 1 or 2, wherein the representation value for the adhesion on the running surface is a rotational speed of the driven wheels. Method according to one of claims 1 to 3, wherein the first criterion comprises a determination of whether the rotational speed of the driven wheels has reached a first speed. Method according to one of claims 1 to 4, wherein the first criterion comprises a determination of whether a speed difference between the driven wheels and at least one provided on the vehicle, the non-driven wheel exceeds a first value. Method according to one of claims 1 to 5, wherein the representative value for the rotational speed of the driven wheels comprises different parameter values representing the rotational speeds of the driven wheels at different times, The method of claim 6, wherein the criterion includes determining a change in rotational speed of the driven wheels between two consecutive times. Method according to one of claims 1 to 7, wherein the steps b) and c) are repeated until a second criterion is met. The method of claim 8, wherein the second criterion comprises one of the following: the procedure is stopped by the driver of the vehicle; a control unit provided in the vehicle detects that repeating the steps b) and c) for continuously driving the vehicle is not necessary. Method according to one of claims 1 to 9, wherein the electric motor is connected via a gear with the driven wheels. A system for driving a vehicle when the vehicle starts, the vehicle having at least one driven wheel for driving the vehicle and including an electric motor configured to generate a torque for driving the driven wheels, characterized in that the system comprises means for: Using the electric motor to transmit a torque to drive the driven wheels in a first direction; Determining a representation value for adhesion of the driven wheels to the tread, and Reversing the rotational direction of the electric motor to transmit a torque that drives the driven wheels in an opposite direction to the first direction when the adhesion of the driven wheels on the tread satisfies a first criterion. Vehicle, characterized in that it comprises a system according to claim 11.

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