DE102012223867A1 - Method for holding motor vehicle on inclined surface, involves holding motor vehicle by motoring torque that is generated by electric drive machine of motor vehicle, where efficiency of electric drive system is monitored - Google Patents

Abstract

The method involves holding the motor vehicle by motoring torque that is generated by an electric drive machine (EM) of the motor vehicle, where the efficiency of the electric drive system comprising the electric drive machine is monitored. An alternative holding system is activated for holding the motor vehicle if the efficiency drops to a certain level. The available torque of the electric machine is monitored for monitoring the efficiency of the electric drive system.

Description

The invention relates to a holding of a motor vehicle on an inclined surface, which comprises an electric drive system with an electric drive machine.

For the purposes of the application, the term "motor vehicle with an electric drive system with an electric drive machine" comprises both an electric vehicle loadable via an external electrical energy supply with an optional internal combustion engine range extender and a hybrid vehicle with an internal combustion engine and an electric drive machine. In a motor vehicle with an electric drive system, the electric drive machine can impress a mechanical torque in the drive train.

In motor vehicles when stopping the motor vehicle on an inclined surface, the service brake must be operated depending on the inclination, so that the vehicle does not roll, for example, so that the vehicle does not roll back when stopping uphill.

In a current concept for electric vehicles, a pronounced deceleration delay when releasing the accelerator pedal is provided until the vehicle is stopped, with a correspondingly high recuperation of the electric drive machine is set so that the driver by pressing the accelerator pedal both accelerate as well as release the accelerator pedal a desired delay pretend. This leads to a so-called "one-pedal feeling", d. H. the feeling of being able to control the vehicle only with the accelerator pedal. This "one pedal feeling" reduces the use of the brake pedal considerably. In this concept, unlike typical automatic vehicles, the electric vehicle also has no creep, i. H. the motor vehicle does not move in a forward direction on a flat surface without inclination in an engaged gear (typically called a D-drive) associated with the forward direction of the vehicle; the same applies to the reverse direction. The creep of a motor vehicle is incompatible with the "one-pedal feeling", since this requires, for example, the frequent operation of the brake pedal to prevent the crawl of the vehicle.

In such an "one-pedal-feeling" electric vehicle, the vehicle noticeably decelerates upon release of the accelerator pedal and stops on a non-inclined surface without operating the brake pedal. When stopping in the D range (D-Drive) on a positive slope surface, when the accelerator pedal is released, the vehicle decelerates to a stop and then rolls back depending on the degree of the positive slope. Conversely, in the reverse gear (R reverse) mode, when stopping on a negative slope surface, the vehicle is coasting to a stop when reversing the vehicle and then rolling in the forward direction depending on the degree of negative slope. To avoid rolling, the driver must depress the brake pedal, which reduces the "one-pedal feeling".

The described disadvantage that the driver has to operate the brake pedal when stopping on an inclined surface in order to prevent rolling is a general problem of motor vehicles; in electric vehicles with "one-pedal feeling" a solution is particularly desirable because it is dispensed with an operation of the brake pedal in many cases. In conventional vehicles with an internal combustion engine and automatic transmission, this problem is slightly different, since due to a generated via the torque converter and acting in the direction of the engaged speed creep the brake pedal must also be operated to hold in the plane.

For vehicles having an electric drive system, for holding the vehicle on a slope, it is known to maintain a fixed angular position of the rotor of the electric machine via a controller for controlling the angular position, so that the vehicle is held on the slope. This is for example in the document EP 0 921 028 A2 described. The disadvantage of this is that the performance of the electric drive system, for example due to the heat or the state of charge of the battery is reduced in time, so that at a certain time, the electric machine can no longer hold the vehicle and the vehicle starts to roll.

It is an object of the invention to provide an improved method for holding a motor vehicle on an inclined surface, which eliminates this disadvantage.

The object is solved by the features of claim 1. Advantageous embodiments are described in the dependent claims.

In the method according to claim 1 of the invention, the motor vehicle, in particular in the form of an electric vehicle, initially held by a generated by means of the electric drive motor motor torque which acts counter to the slope force. Here, the performance of the electric drive system is monitored.

If it is determined that the performance of the electric propulsion system at a certain degree or falls to a certain extent, according to the invention an alternative holding system for holding the motor vehicle is activated, for example, an electric parking brake, a parking brake or the hydraulic service brake of the vehicle. For example, a complete transfer to the alternative holding system can then take place so that the vehicle is held by the alternative holding system and no longer by a torque of the electric machine acting in the direction of travel of the engaged driving stage. Alternatively, the alternative holding system can then hold the motor vehicle next to the electric machine on the inclined surface, so that the electric drive machine is supported in its holding function by the alternative holding system; the electric drive machine then operates preferably with reduced torque.

The background to this is that when the motor vehicle is held over the electric machine, a degradation in the electric drive system with respect to its performance can occur, so that the required holding torque is no longer available over time. In this case, an alternative holding system is activated to ensure the hold function.

By monitoring the performance of the electric power and activating an alternative holding system according to the present invention, if the performance drops, maintaining the motor vehicle on the inclined surface can be ensured even if the electric machine can no longer provide a sufficient motor torque due to performance degradation Motor vehicle to hold against the slope force.

The holding of the motor vehicle by means of the electric drive machine is preferably carried out via a controller as part of a control loop, which controls the speed of the electric drive machine when rolling against the direction of travel of the engaged gear to zero; Alternatively, a characteristic of the speed variable (for example, the vehicle speed) can be controlled in an appropriate way; the controller is preferably a controller with an I-element, for example a PI controller, an I controller or a PID controller. In the event that the vehicle begins to roll backwards after stopping on a positive slope surface and with the D-speed engaged, the governor controls the speed of the electric machine to zero to avoid further rolling. The holding of the motor vehicle by means of the electric drive machine is preferably carried out in the manner described in another patent application "device for avoiding rolling for a motor vehicle comprising an electric drive system on a sloping surface", which on the same day as the present application German Patent and Trademark Office was filed by the applicant. The disclosure of this other patent application is hereby incorporated by reference into the disclosure of the present application.

According to a preferred embodiment, the performance of the electric drive system is monitored by monitoring an available torque of the electric machine as a measure of performance. The available torque is a torque magnitude indicative of a torque that is potentially adjustable via the electric drive engine. It is therefore a retrievable torque of the electric machine; Preferably, both negative and positive available torque are determined. Typically, the available torque from one or more characteristics of the electric drive system, in particular the energy storage determined. For example, the available torque can be determined as a function of the temperature, the state of charge, the current voltage level, the available DC current of the electric energy storage device supplying the electric drive machine. The available torque can be determined, for example, as a function of the available DC current of the energy store and the current voltage value of the energy store. The amount of available energy storage DC current is a function of the energy storage temperature (storage cell temperature): at both low and high energy storage temperatures, the available DC current in both directions (discharging the energy storage and charging the energy storage) is typically lower , Among other things, the current memory value is typically a function of the state of charge of the energy store. This also applies to the DC current for charging the energy storage.

The available torque is preferably not exactly related to the situation at the time of calculating the available torque, but the available torque is predicted relative to a near future time, which is preferably a few seconds in the future. The available torque is therefore preferably calculated for a few seconds in advance, for example for 2 s.

The activation of the alternative holding system is triggered, for example, when the available (positive) torque has fallen to a certain value or by a certain value.

To monitor performance, the available torque becomes a threshold compared and triggered the activation of the alternative holding system depending on the comparison. For example, the activation is triggered when the available (positive) torque reaches or falls below a certain threshold.

Preferably, there is a positive and negative value for the available torque. The positive value of the available torque indicates a potentially adjustable torque in one direction of rotation of the electric machine, while the negative value of the available torque indicates a potentially adjustable torque in the other direction of rotation of the electric machine.

The threshold value with which the available torque is compared results, for example, from the sum of a torque for holding the vehicle and an additional torque reserve. The additional torque reserve preferably comprises a torque reserve for starting the substantially stationary vehicle in the direction of travel of the engaged gear on the inclined surface. Ie. the torque reserve M _VH is dimensioned so that it allows a start of the substantially stationary vehicle in the direction of travel of the engaged gear on the inclined surface. The torque reserve, in addition to the lead to start the vehicle or one or more other components include, for example, a Vorhaltkomponente for starting a range extender (it should be noted that the range extender is typically not started via the electric drive machine, but via another electric machine, which is supplied with energy from the electrical energy storage for starting the range extender). Other possible Vorhaltkomponenten concern the fulfillment of a necessary for the electric drive system (electric machine, power electronics or storage) cooling capacity or ensuring a desired by the driver for the interior climate or heating capacity.

Preferably, a controller for controlling the rotational speed of the electric machine to zero or for meaningful control of a characteristic of the rotational speed variables are provided for holding the motor vehicle, by means of which a torque input for the electric machine is determined. The torque for holding the vehicle, for example, corresponds to or results from the torque command determined by means of the controller.

Thus, it is preferably determined when the available torque has dropped to the torque for holding plus a torque reserve or has fallen below the torque required for holding plus a torque reserve. If so, the alternate holding system is activated.

The monitoring of the performance and activation of the alternative holding system can be performed by a software function in the engine control unit, which takes into account the torque inventory necessary for starting in determining the activation time.

An activation of the alternative holding system is preferably carried out only from a holding state in which the vehicle is held by the electric machine on the inclined surface at a standstill and not from rolling conditions in which, for example, the torque set via the controller is not sufficient to hold the motor vehicle and the Vehicle rolls. For example, an upper limit is defined for the amount of torque (eg, 70 Nm relative to the rotor of the electric machine) of the hold function that allows holding up to a certain grade (eg, about 8% slope for a given vehicle weight with payload). Downhill forces corresponding to torques greater than this upper limit are not fully compensated so that the vehicle will not be stalled in these situations and will roll back due to the slope drive force with a counter torque equal to the maximum value with D gear engaged or with the R gear selected forward rolls. From such rolling situations, preferably no activation of the alternative holding system should take place.

It is conceivable to insert a mechanical parking lock in the transmission (transmission lock) as an alternative holding system. This is done, for example, by sending a signal to the transmission controller to engage the transmission position P (P-parking) with the parking lock being engaged. The disadvantage of this is that the driver after insertion of the automatic transmission position P to start again the gear D (or R when starting in reverse direction) must insert. If the electric parking brake is used as an alternative holding system, this disadvantage does not exist, since typically an automatic deactivation function for the parking brake is activated when the accelerator pedal is actuated.

The invention will be described below with reference to the accompanying drawings with reference to an embodiment. In these show:

1 an exemplary control circuit for controlling the rotational speed of the electric drive machine to the vehicle by means of a to keep the electric drive machine generated motor torque against the slope force;

2 an exemplary implementation of a feedforward control;

3 a timing of the torque command M _G processed by the drive controller for driving the electric machine and a time course of the vehicle speed v when stopping in three different situations;

4 an exemplary implementation of the in 1 illustrated control loop;

5 an embodiment of the inventive method; and

6 an exemplary profile of the available torque M _V over time t.

1 shows a schematic embodiment of a control loop to prevent rolling against the direction of travel of the engaged gear. Here, a speed regulator R is provided, the rotation speed n _is an electric motor EM to a target speed n _soll = regulates 0th The controller R is preferably a proportional integrating PI controller; however, it would also be possible to use any other type of regulator with an I-element, for example an I-regulator or a PID-regulator. The controller R is used to generate a controller-side torque input M _R (target torque) for the electric drive machine EM of the motor vehicle. The controller R receives a speed deviation .DELTA.n = _n - n _to counter; since the target speed n _should be set to zero to avoid rolling, then: .DELTA.n = _n - n _to - 0 = _n. Here, the actual speed n _is positive in the forward direction of the vehicle and negative in the reverse direction of the vehicle.

In diagram a) in the lower part of 1 only the P component (proportional term) of the torque command M _R 'at the output of the regulator R to the rotational speed deviation .DELTA.n = n _is shown; the I component was not taken into account in diagram a) for reasons of simplified presentation.

However, it should not be forgotten that the I component holds the vehicle on a slope, whereby the speed n _{is kept} at zero by the I component; the controller R learns the I component during the initial backward roll.

In the example of 1 acts a positive torque command in the forward direction of the vehicle, ie when D-speed step in the direction of the D-speed and with engaged R-drive counter to the direction of the R-drive level. Conversely, a negative torque specification acts in the reverse direction of the vehicle, ie, when the D-speed step is engaged, counter to the direction of travel of the D-speed step and when the R-speed step is engaged in the direction of travel of the R-speed level.

As can be seen from the diagram a), is at a negative speed deviation .DELTA.n = n _{(that is} n for a negative actual speed, which acts in the rearward direction of the vehicle), the torque command M _R 'is positive and at a positive speed deviation .DELTA.n = n _{(that is} at a positive actual speed n, which acts in the forward direction of the vehicle), the torque command M _R 'negative. This also applies if the I component is taken into account.

Further, a limiter LIM for limiting the output of the regulator R is provided. The limiter LIM limits the output signal M _R 'of the regulator R upward by an upper regulator limit RegG _o and down by a lower regulator limit RegG _u . In the present example the upper governor limit RegG _{o is} a value ≥ 0 and the lower governor limit RegG _{u is} a value ≤ 0. If the torque command M _R 'is greater than the upper governor limit RegG ₀ , the torque default M _R at the output of the limiter LIM corresponds to upper controller limit RegG _o . If the torque input M _R 'is smaller than the lower controller limit RegG _u , the torque input M _R corresponds to the output of the limiter LIM of the lower controller limit RegG _u . With values M _R 'at the input of the limiter LIM between the upper regulator limit RegG _o and the lower regulator limit RegG _u , M _R = M _R '.

The upper controller limit RegG _o and the lower controller limit RegG _u are variable.

When the D drive is engaged _, a positive maximum value M _{R, max} is set for the upper governor limit RegG _{o and} the value 0 for the lower governor limit RegG _u , with the torque input rising through this positive maximum value M _{R, max} and down through the value 0 is limited. This is in the diagram b) below in 1 shown schematically.

When the R range is engaged, the negative of the maximum value M _{R, max is} set for the lower controller limit RegG _u , ie RegG _u = -M _{R, max} , and for the upper controller limit RegG _o the value 0 is set the value M _{R, max} and upwards by the value 0 is limited. This is in the diagram c) below in 1 shown schematically.

Both when the D-speed step is engaged and when the R-speed step is engaged, the amount of the torque input M _R in the direction of travel of the engaged drive level is limited to the value M _{R, max} .

Due to the lower governor limit RegG _u = 0 in the case of an engaged D-speed step or the upper governor limit RegG _o = 0 in the case of an engaged R-speed only values for the torque input M _R 'are used at the output of the controller, in the direction of travel engaged gear stage, ie positive torque values with engaged D-speed step or negative torque values with engaged R-speed step. Values of the torque input M _R '(ie negative torque values M _R ' when the D drive speed is engaged or positive torque values M _R 'when the R drive speed is engaged) are excluded by the limiter LIM and not for controlling the speed n _is used.

Due to the lower governor limit RegG _u = 0 in the case of an engaged D-speed step or the upper governor limit RegG _o = 0 in the case of an engaged R-speed, the controller R affects the speed n _is not, if the speed n _is in the direction of travel of the inserted gear acts (ie, in the case of D-driving position when reversing rollers and thus positive at a rotational speed _n = .DELTA.n; in the case of the R-drive position for forward rollers and negative rotational speed _n = an). At such speeds n _is the torque default M _R = 0 (see the diagrams b) and c) in 1 ), so that the controller R at such speeds n _is not engaged. By contrast, n at a rotational speed _is opposite to the direction of travel of the driving stage (ie, in the case of D-driving position when reversing rollers and _is therefore n a negative speed = .DELTA.n; in the case of the R-drive position for forward rollers and thus a positive rotation speed _is n = An) the torque default M _{R is} equal to zero, so that the controller at such speeds n _is the speed n _is zero.

Since the amount of the torque input M _R in the direction of the gear is limited to the value M _{R, max} when the D drive speed is engaged as well as when the R drive speed is engaged, the holding torque which can be set via the control R is limited. The maximum amount of the holding torque of the regulator R can be, for example, at M _{R, max} = 70 Nm (based on the rotor of the electric machine). If this maximum amount for holding the vehicle against the slope driving force is insufficient, there will be a rollback in the D-drive stage with a set torque setting M _R = M _{R, max of} the controller or to a forward rolling in the R-drive stage with a set torque command M _R = -M _{R, max of} the controller. Assuming a vehicle weight, the maximum amount of holding torque corresponds to a maximum slope up to which the vehicle can be held on the slope without rollers, for example, about 8%.

It comes so above this maximum slope to a controlled backward rolling in a D-drive or to a controlled forward rolling in the R-drive.

The control loop preferably further comprises a feedforward control VS, which determines a pilot-controlled torque input M _VS 'as a function of a vehicle speed v' related to the direction of travel of the engaged drive stage. Alternatively, the torque input M _VS 'could also be determined as a function of the rotational speed n _{ist of} the electrical machine. The speed v 'has a positive sign in the direction of travel of the engaged gear and a negative sign contrary to the direction of travel of the engaged gear. The vehicle speed v 'related to the direction of travel of the engaged gear is determined from the absolute vehicle speed v and the engaged gear FS by inverting the absolute vehicle speed v in the case of the R gear and not inverted in the case of the D gear (see FIG. the inverter block INV1 in 1 which only inverts the speed v when the R-speed step is engaged).

The feedforward control VS comprises an in 1 not shown accelerator pedal interpreter, the pilot-controlled torque command M _VS 'depends on an accelerator pedal signal FP, which indicates the degree of actuation of the accelerator pedal. The rollback prevention should intervene in particular when the accelerator pedal is not actuated. When the accelerator pedal is not actuated, the course of the precontrolled torque input M _VS 'of the precontrol VS preferably corresponds in its essential characteristic to that in FIG 1 The pre-controlled torque input M _VS 'corresponds to approximately 0 at a value of v' = 0, ie in the controlled state when the vehicle is not rolling, the pre-controlled torque command M _VS '= 0. At values for v' against the direction of travel of the engaged gear (ie, for negative values for v '), the pilot-controlled torque command M _VS ' is positive and increases as the magnitude of v 'increases. The torque input M _VS 'is either inverted or not inverted as a function of the engaged speed stage FS: when the R speed range is engaged: M _VS = -M _VS '; when the D gear is engaged: M _VS = M _VS '(see the inverter block INV2 in 1 which only inverts the pre-controlled torque input M _VS 'when the R drive speed is engaged).

The torque input M _{R of} the controller and the pilot-controlled torque input M _VS are added and the resulting torque command M _G = M _VS + M _{R received} from a drive controller AS (including the power electronics), which controls the electric drive machine EM so that the torque input M _G is implemented by the electric drive machine EM. With a measuring device ME, the actual speed n _is the electric machine determined.

The amount of the torque input M _{R of} the controller R is preferably taken into account in the accelerator pedal interpretation of the pilot control VS, as shown in 1 is indicated. The torque input M _{R of} the controller R is namely added as an offset to the pilot-controlled torque M _VS in the control of the electric machine EM, so that the torque input M _{R of} the regulator R in the accelerator pedal interpretation in the feedforward VS is calculated out again.

When the motor vehicle is held by the torque input M _{R of} the controller, the accelerator pedal is not always accelerated in the direction of travel of the engaged gear, but it is only accelerated in the direction of travel of the engaged gear when the magnitude of the torque input in the accelerator pedal interpretation is greater than that The amount of the torque input M _{R of} the controller is, in which case the same reference point for the torque input from the accelerator pedal interpretation and the torque input M _{R of} the controller is assumed (for example, for both torque specifications as a reference point of the rotor or the drive axle). This means that operation of the accelerator pedal, the amount of holding torque M _R already made by the regulator R must be achieved first of all and only then if the amount of torque command from the accelerator pedal interpretation exceeds the amount of the controlled via the regulator holding torque M _R more Moment is placed on the electric machine EM, as is needed just to hold, and accelerates the vehicle in the direction of travel of the engaged gear and moves it.

In order to implement this behavior, the torque command M _R determined by the controller _{R is} subtracted from a torque command determined at the accelerator pedal interpretation. This is exemplary in 2 which shows a possible implementation of the feedforward VS in a schematic way. Part of the feedforward controller VS is the accelerator pedal interpretation (accelerator pedal evaluation). The block KLFP100% gives a torque M _100% as a function of the vehicle speed v 'assuming a maximum actuation of the accelerator pedal (FP = 100%); the block KLFP0% predicts a moment M _0% assuming a non-actuation of the accelerator pedal (FP = 0%) as a function of the vehicle speed v ', wherein the characteristic of the torque M is _0% above the driving speed v' substantially that associated with 1 discussed characteristic of the pilot-controlled torque M _VS 'corresponds to non-actuation of the accelerator pedal. Via a cross-fader MIX, depending on the position FP of the accelerator pedal, a driver desired torque M _{FW is} determined, which, depending on the position FP of the accelerator pedal between the torque M is _100% at maximum actuation of the accelerator pedal and the torque M _0% when the accelerator pedal is not actuated. When the accelerator pedal is not actuated, the driver's desired torque M _FW corresponds to the moment M _0% ; ie M _FW = M _0% .

The driver command torque M _FW is a wheel torque, whereas the torque input M _{R of} the controller R represents a torque related to the rotor axis. In order to subtract the torque input of the controller R from the driver request torque M _FW resulting from the accelerator pedal interpretation, the torque input M _{R of} the controller R is converted into a wheel torque. For this purpose, the torque input M _{R of} the controller is multiplied by a ratio i. Furthermore, via the inverter block INV3, when the R drive speed is engaged, the resulting torque is inverted (since the holding torque is negative in this case), the torque is not inverted when the D drive speed is engaged.

After the torque input M _{R of} the controller R has been converted into a wheel torque M _{R, V} and was inverted with engaged R-speed, the resulting torque command M _{R, V of} the controller R is subtracted from the determined in the accelerator interpretation driver input torque M _FW , where a modified driver request torque M _FW 'is obtained. If the driver's desired torque M _{FW is} greater than the resulting torque input M _{R, V of} the controller R, the modified driver's desired torque M _FW 'is positive. If the driver's desired torque M _{FW is} smaller than the resulting torque input M _{R, V of} the controller R, the modified driver's desired torque M _FW 'is negative. The resulting modified driver desired torque M _FW 'is given to a limiter LIM0 with a lower limit of 0 Nm, which forwards a resulting modified driver desired torque M _FW ' greater than or equal to 0 Nm (unchanged) and a resulting modified driver desired torque M _FW 'less than 0 Nm Driver torque limited from 0 Nm down. This means that only for the case M _FW > M _{R, V} at the output of the limiter LIM0 a driver's desired torque is greater than zero. Furthermore, an optional torque structure MS is provided by means of which the torque specification is adapted to different torque requirements of the vehicle. Subsequently, the resulting torque specification is converted into a torque command M _VS 'related to the rotor.

In 3 the time characteristic of the torque input M _G (see in each case the solid line) processed by the drive control system AS for actuating the electric machine EM and the time profile of the vehicle speed v (see in each case the dotted line) are schematically sketched when stopping in three different situations. In subdiagram a), the time lapses are on hold and then holding the vehicle against the slope force with D-drive stage and a roadway with positive slope (positive inclination angle) shown, with the vehicle when stopping according to the indicated direction arrow moves uphill in the forward direction. In subdiagram b) the time courses when stopping the vehicle with the D-speed step engaged are shown on a roadway without a gradient. In sub-diagram c), the time courses when stopping and then holding the vehicle against the downhill force with the R-drive stage on a roadway with a negative slope (negative inclination angle) are shown, the vehicle when stopping in the reverse direction according to the indicated direction arrow moves uphill.

When stopping with the D-drive stage in sub-diagram a), when the accelerator pedal is released, the torque input M _{G is} reduced, resulting in a negative torque input M _G and the vehicle brakes, thus reducing the speed v. Shortly before reaching the speed v = 0, the negative torque input M _{G is increased} to 0 Nm. In addition, when reaching or falling below a limit speed (for example, 2 km / h) the roll avoidance via the regulator R is activated by the upper regulator limit RegG ₀ of RegG _{0 is set} equal to 0 to a positive value not equal to 0, for example to 70 Nm. The lower controller limit RegG _u is left at 0. Since the lower controller limit RegG _u is 0, despite the speed deviation Δn> 0 via the controller R no negative torque command M _{R can be} impressed, which would slow down the vehicle. If the vehicle comes on the road with positive slope to hold with v = 0, the drawn stop stops. If the vehicle then rolls backwards against the D shift speed engaged and the vehicle speed v becomes negative, the drawn-in holding phase begins. The negative vehicle speed v causes a negative rotational speed _n and a speed deviation .DELTA.n <0, which arise over the feedforward control, a positive pre-torque M _VS and the control, a positive torque command M _R of the controller. The (negative) vehicle speed v increases again due to the resulting positive torque input M _G , and as the vehicle speed v increases, the positive pilot torque M _VS decreases and the torque specification M _{R of} the controller R increases. If the driving speed has been adjusted to v = 0 km / h, the pre-control torque M _{VS has} dropped to 0, wherein the torque command M _{G is} generated substantially completely via the controller R, ie M _G = M _R. The torque input M _G = M _R compensates the downgrade force. If the slope requires a torque input M _R greater than the upper controller limit RegG _o , the vehicle can not be held and rolls backwards, since the torque input M _{R of} the controller R is limited to the upper controller limit RegG _o . During backward rolling of the vehicle increases with increase in the speed v counter to the desired direction of travel amount of the pilot torque to M _VS (s. Characteristic of the pilot torque M _VS '), whereby the amount of braking torque command then M _G increases. As a result, a braking recuperation torque is built up on the electric machine EM.

The roll-preventing function via the regulator R is deactivated (for example, by setting the upper regulator limit RegG ₀ to zero) when the driver actuates the brake pedal and builds a brake pressure corresponding to the holding torque of the electric motor.

After starting the motor vehicle (not shown) in the forward direction, the torque setting M _{R of} the regulator R is set to zero by the upper regulator limit RegG _{o is set} to zero. This effectively deactivates the function of rollback prevention. In addition, the governor component M _{R, V} considered in the accelerator pedal interpretation is thereby set to 0, so that the driver's request M _{FW is} no longer reduced by the controller component M _{R, V.}

Partial diagram c) shows the situation when stopping with engaged R-drive. Since the vehicle is backing uphill when stopped, the torque default M _{G is} initially negative. For deceleration, a positive torque command M _{G is} set, so that the speed v increases in the direction 0. Shortly before reaching the speed v = 0, the positive torque command M _{G is} reduced to 0 Nm. In addition, when reaching or falling below a limit speed (for example, -2 km / h), the roll avoidance via the regulator R is activated by the lower regulator limit RegG _u of RegG _{u is} set to 0 to a negative value other than 0, for example to -70 Nm. The upper controller limit RegG _o is left at 0. When the vehicle then against the inserted R-gear forward rolls and the vehicle speed v is positive, there is a positive rotational speed _n and a speed deviation .DELTA.n> 0, whereby on the feedforward control a negative torque specification M _VS and the control a negative Torque input M _{R of} the controller. The vehicle speed v decreases again due to the resulting negative torque input M _G , whereby the amount of the negative pilot torque M _VS decreases as the vehicle speed v decreases, and the magnitude of the negative torque input M _{R of} the controller R increases. If the driving speed has been adjusted to v = 0 km / h, the pre-control torque is M _VS at zero, wherein the torque command M _{G is} completely generated via the controller R, ie M _G = M _R.

In 1 to 3 It was assumed that the target speed n _{soll is} set to 0 as the reference variable of the control loop for roll avoidance. If in a roll avoidance with n _soll = 0, the vehicle due to a low friction between the tire and the road (for example, due to icy road) slips in stationary rear wheels, it can be provided that the target speed n _is adapted to the slipping, so that the wheels of the driven axle can rotate with the skid and the vehicle is better steerable. A slippage of the vehicle with stationary wheels of the driven axle can be determined, for example, by turning the wheels of the non-driven axle counter to the direction of travel of the engaged driving gear. When the vehicle is slipping, the target speed n _soll is changed so that the wheels of the driven axle rotate with the vehicle movement. The target speed n _soll is for this purpose changed from n _soll = 0 to, for example, a value which, taking into account the ratio between the wheel and rotor axis of the speed of the non-driven wheels or whose amount is slightly less than the speed of the non-driven wheels; the wheels of the driven axle then turn so fast or slightly slower than the wheels of the non-driven axle. In the case of a reverse slip with the D-speed engaged, in 1 a speed n _{should be set} to a negative value; in the case of a forward slide with engaged R-speed, is in 1 then a speed n _{should be set} with a positive value.

In 4 is an exemplary breakdown of the in 1 shown control circuit shown on several control units. A drive electronics AE for the electric drive machine EM comprises a speed controller R with additional torque control via the pre-control torque input M _VS (combined speed control and torque control). In addition, the drive electronics AE includes the drive controller AS, which converts the torque input M _G into corresponding drive variables of the electric machine EM. The drive electronics AE is connected via a vehicle bus B with an engine control unit eDME. The engine control unit eDME serves inter alia to determine the pre-control torque input M _VS as a function of the accelerator pedal position FP, which is further processed in the drive electronics AE. The engine control unit eDME further informs the drive electronics AE of the upper controller limit RegG _o , the lower controller limit RegG _u and the target speed n _soll with. To implement the roll avoidance function, the target speed n _{soll is set} to zero, other operating cases may be provided in which the target speed n _{soll is set} to a value other than zero. The variables n _soll , RegG _o and RegG _u are specified by a controller S. The engine control eDME receives the torque input M _{R of} the controller R to take into account this variable in the accelerator pedal interpretation. In addition, the engine control unit eDME is notified of the actual torque M _{i of} the electric machine EM. The actual torque M _i is calculated from the current of the electric machine EM.

Furthermore, the engine controller eDME receives the available torque M _{v of} the electric machine EM, ie a potentially steeper moment M _{v of} the electric machine EM, which describes the performance of the electric drive system. Preferably, both a positive value for the available torque M _{v is} received, which indicates a potentially adjustable torque in the forward direction of the vehicle, as well as a negative value for the available torque M _V receive, indicating a potentially adjustable torque in the reverse direction of the vehicle. At a certain degradation in performance, ie degradation of the available torque M _v , an alternative holding system, in particular an electric parking brake, a parking brake or a service brake, triggered. The holding function is then preferably substantially completely transferred to the alternative holding system. The triggering of the alternative holding system is done via the digital signal RQ, which is sent via the bus B to a control unit, here the brake control unit DSC, and switches in this case, so that the control unit DSC is signaled, an alternative holding system, such as an electric parking brake ePB to turn on. It can be provided that the control unit DSC itself decides upon receiving the digital signal RQ, whether an electric parking brake or a mechanical parking brake is to be inserted.

However, it is not necessary to go to activate the alternative holding system via the brake control unit DSC; the engine control unit eDME can trigger the mechanical parking lock, for example via a transmission control unit (not shown). The digital signal may be, for example, a gear selection signal for engaging the gear position P (P-parking), which is sent to a transmission controller; As a result, the mechanical parking lock is engaged.

In a special embodiment, in which the parking brake is used as an alternative holding system, the brake control unit DSC is first informed via the signal RQ that the vehicle can no longer be held by the electric drive machine (soon). The brake control unit DSC then delivers a warning signal to the engine control unit eDME back that the electric Parking brake is not activated. The warning signal is then forwarded by the engine control unit eDME to a gearbox control unit, whereupon the P-gear stage is engaged. and thus the parking lock is engaged. If the engine control unit eDME determines that the vehicle is being held over the parking lock, the holding function realized via the electric drive machine is deactivated, for example by the upper governor limit RegG _o when the D driving position is engaged or by the lower governor limit RegG _u when the R driving step is engaged set to zero.

The monitoring of the available torque M _v takes place in the function block MON of the engine control unit eDME.

In 5 an embodiment of the inventive method is shown, wherein the steps 130 . 140 . 150 for example, in the function block MON 4 expire. After starting the method, the vehicle is held by a torque generated by the electric machine EM (see step 110 ). For this purpose, the torque input M _R is preferably generated by means of the controller R, which controls the speed n _is the electric drive machine EM when rolling against the direction of travel of the engaged gear to zero. In step 120 a current value for the available moment M _{v is} determined. Preferably, both a positive value for the available torque M _{V is} determined, which indicates a potentially adjustable torque in the forward direction of the vehicle, as well as a negative value for the available torque M _V , which indicates a potentially adjustable torque in the reverse direction of the vehicle. In addition, a threshold value M _S for the available torque M _{v is} calculated (see step 130 ). The threshold value M _S results from the sum of a torque for holding the vehicle (here the torque input M _{R of} the controller) and a torque reserve M _VH . For the calculation of M _{s is} the torque command M _G, instead of M _R could be used which still has the pilot portion M _VS additionally _(n by adjusting the rotational speed to zero, the pilot fraction M _VS is already zero, so that M _G = M _R applies) ,

At the junction 140 a threshold value comparison of the available torque M _v with the threshold value M _{S is} performed. Preferably, a distinction is made here between holding with the D-speed step engaged, with the vehicle being prevented from rolling back over a positive torque command M _R , and holding with the R-speed step engaged, the vehicle being held against forward rolling via a negative torque command M _R , When the D-speed step is engaged, it is checked whether the available (positive) torque M _{v has} already dropped so far that the available torque M _{v is} less than or equal to the (positive) threshold value M _S. If so, the alternate holding system is activated. Otherwise, the holding of the motor vehicle is continued via the electric drive machine EM. When the R-drive stage is engaged, it is checked whether the available (negative) torque M _{v has} already increased so far in the direction of zero that the available (negative) torque M _{v is} greater than or equal to the (in this case negative) threshold value M _s . If so, the alternate holding system is activated. Otherwise, the holding of the motor vehicle is continued via the electric drive machine EM. In addition, the holding is deactivated by a torque generated by the electric machine EM (see step 160 ). Preferably, the deactivation takes place after the activation of the alternative holding system. In this case, it can optionally be provided that it is initially waited until it has been confirmed that the vehicle is being held by the alternative holding system, and only after the confirmation has the holding been deactivated via the electric machine EM.

Preferably, prior to activating the alternative retention system (in 5 in the branch 140 ) is still checked whether there is no rolling of the vehicle due to the holding torque limitation (see RegG _o with the D-drive step engaged and RegG _u with the R-drive step engaged). For this purpose, for example, the speed of the vehicle or the rotational speed of the electric machine EM can be evaluated. The rollers can also be detected indirectly by evaluating the preset torque M _R, by checking whether the amount of M _R already the controller limit RegG _o (at D-speed gear stage) or RegG _u corresponds (at R-speed gear stage). If this additional test is performed, the alternate restraint system will only be activated if it is determined that there is no vehicle rolling.

In 6 the course of the (positive) available torque M _{V of} the electric machine over the time t when holding the motor vehicle against the slope force is shown. The available torque M _V is hereby preferably calculated for a few seconds in advance, for example for 2 s. It is assumed that the D-speed is engaged. In the case of an engaged R-drive stage, the curve of the negative available torque is mirrored on the X-axis and all the variables shown on the Y-axis are negative, and instead of the upper positive controller limit RegG _o then the lower negative controller limit RegG _u would be drawn. Due to the increase in the temperature and / or the decrease in the state of charge of the electrical energy storage, there is a degradation of the performance of the electric drive system and thus the available torque M _{V of} the electric drive machine EM. During the holding is checked again and again, whether the available torque M _{V of} the electric machine has already dropped to the threshold value M _S or has fallen below this threshold. The threshold. M _S results from the sum of the determined by means of the controller R torque default M _R for the electric machine EM for holding the motor vehicle and a torque reserve M _VH . The torque reserve M _VH is dimensioned so that it allows a start of the stationary vehicle in the direction of travel of the engaged gear (here uphill in the forward direction with D-drive level) on the inclined surface with a certain driving dynamics. The torque reserve M _VH may comprise one or more further components in addition to the derivative for starting the vehicle, for example a torque reserve for starting a range extender. For example, the torque reserve M _{VH has} a value of 100 Nm when the D-speed step is engaged (when the R-speed step is engaged, the torque reserve M _{VH is,} for example, -100 Nm). It can be provided that the torque reserve varies as a function of a plurality of operating parameters, for example as a function of the temperature or the state of charge of the energy store. At the time t _exit , the available torque M _{V reaches} the threshold value M _S and an instruction for activating the alternative holding system is given. For this purpose, for example, the signal RQ is sent to the brake control unit DSC by the engine control unit eDME. Thereafter, the holding is deactivated via the electric machine EM.

The above-described activation of the alternative holding system is motivated by the fact that degradation in the electric drive system can occur due to thermal and / or stress, so that it is possible that the desired holding torque is no longer available over time. In this case, an alternative holding system is activated in good time to ensure the holding function for the vehicle, in particular, it is handed over in good time to an alternative holding system. This is preferably coordinated by a software function in the engine control system eDME, which also takes into account, for example, the torque inventory necessary for start-up driving in the determination of the transfer time.

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

• EP 0921028 A2 [0007]

Claims (9)

Method for holding a motor vehicle comprising an electric drive system with an electric drive machine (EM) on an inclined surface, comprising the steps of: - holding ( 110 ) of the motor vehicle by a motor torque generated by means of the electric drive machine (EM), wherein the performance (M _v ) of the electric drive system is monitored; and if the performance (M _v ) falls to a certain extent or to a certain extent, activate ( 150 ) of an alternative holding system (ePB) for holding the motor vehicle. The method of claim 1, wherein for monitoring the performance of the electric drive system, an available torque (M _v ) of the electric machine (EM) is monitored. A method according to claim 2, wherein the available torque (M _v ) of the electric machine (EM) is determined as a function of one or more parameters of the electric drive system, in particular depending on the temperature, the state of charge, the current voltage level, the available DC current the electric machine with electric energy supplying electric energy storage. Method according to one of claims 2-3, wherein the available torque (M _v ) is compared with a threshold value (M _S ) and, depending on the comparison, the alternative holding system (ePB) is activated to hold the motor vehicle. Method according to Claim 4, wherein the threshold value (M _S ) results from the sum of a torque (M _R ) for holding the vehicle and - a torque reserve (M _VH ). A method according to claim 5, wherein - for holding the motor vehicle, a controller (R) for controlling the speed of the electric machine to zero or for meaningful control of a characteristic of the speed is provided by means of which a torque input (M _R ) for the electric Engine is determined and - the torque for holding the vehicle results from the torque specification (M _R ) for the electric machine or the torque specification (M _R ) corresponds. Method according to one of claims 5 or 6, wherein the torque reserve (M _VH ) comprises a torque reserve for starting the vehicle in the direction of the engaged gear. Method according to one of the preceding claims, wherein the holding by the electric machine after activation of the alternative holding system is deactivated. Method according to one of the preceding claims, wherein the alternative holding system (ePB) is an electric parking brake, a parking brake or a service brake.

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