Deceleration of an electric motor vehicle

Abstract

Method for decelerating an electric motor vehicle, which comprises an accelerator pedal and a brake pedal actuated by the driver, with the following steps performed by the motor vehicle: Detecting (110) the termination of the operation of the accelerator pedal; upon detection of the termination of the operation of the accelerator pedal, setting (120) a coasting recuperation torque (M Sreku,m ) as part of a coasting recuperation to decelerate the vehicle; when the brake pedal is actuated, increasing (130) the deceleration of the motor vehicle while maintaining the coasting recuperation, wherein a coasting recuperation torque (M Sreku,m ) is preserved; Detecting (140) a subsequent withdrawal of the brake pedal actuation; when detecting the release of the brake pedal, reducing (150) the coasting recuperation torque (M Sreku ) based on a coasting recuperation torque (M Sreku,m ), where, upon detection of the withdrawal of the brake pedal, the coasting recuperation torque (M Sreku ) is reduced as a function of a quantity characteristic of the actuation of the brake pedal.

Description

The invention relates to the deceleration of a motor vehicle with an electric drive, for example a purely electrically operated vehicle or a hybrid vehicle with an electric drive and an internal combustion engine.In motor vehicles with an electric drive, kinetic energy of the motor vehicle can be converted into electrical energy during the generator operation of an electric machine of the electric drive and fed into the electrical energy store (typically a battery or a capacitor) of the electric drive. This conversion of the kinetic energy of the motor vehicle into electrical energy is also referred to as (electrical) recuperation. For recuperation, a recuperation torque is set on the electric machine, which counteracts the movement of the motor vehicle and decelerates the latter.The recuperation by means of the electric drive can be used for decelerating the motor vehicle during active braking when the brake pedal is actuated. Furthermore, recuperation can also be used in coasting operation for decelerating the vehicle. In this case, when the actuation of the accelerator pedal is ended, a thrust recuperation torque of the vehicle is set, as a result of which the motor vehicle is decelerated.It can be provided that a thrust recuperation torque M Sreku is already set not only when the actuation of the accelerator pedal is completely ended, but already when the actuation of the accelerator pedal is released and the accelerator pedal actuation is still low; in this case, the amount of the thrust recuperation torque M Sreku increases with decreasing accelerator pedal actuation and reaches its maximum value M Sreku,m. when the actuation of the accelerator pedal is ended. By reducing the actuation of the accelerator pedal, the vehicle can thus be decelerated in a dosed manner. For this purpose, FIG. 1 schematically shows an exemplary profile of the drive torque M over the accelerator pedal angle FPW. At small accelerator pedal angles FPW of less than FPW TH a negative drive torque results, the magnitude of which corresponds to the thrust recuperation torque M Sreku. At an accelerator pedal angle FPW of 0° (i.e. upon termination of the actuation of the accelerator pedal), the maximum thrust recuperation torque M Sreku,m; is obtained; this is associated with the non-actuation of the accelerator pedal. The maximum thrust recuperation torque M Sreku,m assigned to the non-actuation of the motor vehicle can optionally be speed-dependent, wherein the thrust recuperation torque M Sreku,m is typically lowered in the medium or upper speed range.Recuperation in coasting mode is also referred to as coasting recuperation. For thrust recuperation, reference is also made, for example, to the publication DE 10 2011 108 446 A1.DE 196 07 823 C1 discloses a brake control which enables a combination of friction braking with regenerative braking via at least one of the drive motors of the vehicle, which is triggered by the detection of the release of the accelerator pedal and the actuation of the brake pedal. Regenerative braking is activated as a function of the release of the accelerator pedal and is independent of the actuation of the brake pedal, and frictional braking is activated as a function of the actuation of the brake pedal, independent of the release of the accelerator pedal.Document DE 10 2011 119 007 A1 discloses a method for operating a vehicle, a control device and a vehicle. A coasting path of a vehicle is determined. An initial speed and a target speed of the vehicle are determined. The coasting distance of the vehicle, in which the vehicle decelerates from the initial speed to the target speed in a free-wheeling operating state or in a deceleration fuel cut operating state, is determined. The determination of the coasting distance comprises an evaluation of at least one coasting distance function which specifies the coasting distance in a closed form as a function of the initial speed, the target speed and a plurality of driving resistance parameters.DE 10 2007 018 733 A1 discloses a method for determining a speed function for decelerating a vehicle in which a speed function describing a speed of the vehicle from an initial speed to a target end speed over a deceleration path is determined such that a deceleration time required for decelerating the vehicle using the speed function becomes maximum.Document DE 10 2011 108 446 A1 discloses a method and apparatus for recuperation for a vehicle. A vehicle comprises an electric motor for driving the vehicle and a high-voltage battery for supplying the electric motor. A gradient of a road on which the vehicle travels is automatically detected. For recuperation for the vehicle, a recuperation power of a recuperation of the vehicle is set as a function of the detected gradient.FIG. 2 schematically illustrates an exemplary profile of a deceleration torque M V and of the thrust recuperation torque M Sreku over time t in a conventional concept for utilizing the thrust recuperation; here, the deceleration torque M V serves for decelerating the vehicle and is directed opposite to the drive torque. The deceleration torque M V corresponds to the broken line; the thrust recuperation torque M Sreku corresponds to the dotted line. At the time t 1 the actuation of the accelerator pedal is ended, so that thereupon as deceleration torque M V a thrust recuperation torque M Sreku= M Sreku,m is set at the electric drive, which torque acts counter to the direction of movement of the moving vehicle and thereby decelerates the vehicle. When the driver actuates the brake pedal at time t 2 the deceleration already established by the thrust recuperation is increased. By actuating the brake pedal, for example, the hydraulic service brake is triggered. The braking torque M B of the service brake acts in this case in addition to the thrust recuperation torque M Sreku,m= M Sreku,m of the electric drive which has already been set and is kept still.It should be noted here that the level M Sreku,m of the thrust recuperation torque M Sreku at this point in time may be somewhat increased compared to the point in time directly after the build-up of the thrust recuperation torque M Sre-ku= M Sreku,m( shortly after t 1) since the thrust recuperation torque level M Sreku,m may be speed-dependent.Optionally, in addition to the thrust recuperation, a brake recuperation which can be metered by way of the brake pedal can also be triggered at the time t 2 wherein an additional brake recuperation torque is set on the electric drive in addition to the thrust recuperation torque M Sreku= M Sreku,m (not illustrated). In contrast to the thrust recuperation torque level M Sreku,m the brake recuperation torque is dependent on the position of the brake pedal and can thus be metered by the driver. The recuperation torque at the electric drive is then obtained from the sum of the thrust recuperation torque M Sreku= M Sreku,m and the brake recuperation torque.At the time t 3 the driver decreases the brake actuation again, in this case the deceleration torque M V is reduced in that the braking torque M B built up via the service brake is reduced (and a brake recuperation torque is possibly reduced). After the brake pedal has ended being actuated at the time t 4 the thrust recuperation torque M Sreku= M Sreku,m associated with the non-actuation of the accelerator pedal continues to remain effective and the vehicle continues to brake with this deceleration torque M V= M Sreku,m.It should also be noted here that the level of the thrust recuperation torque M Sreku,m at the time t 4 can be somewhat increased compared to the time directly after the build-up of the thrust recuperation torque M Sreku,m( shortly after t 1) since the thrust recuperation torque M Sreku,m can be speed-dependent.If the driver wishes to reduce the deceleration torque M V below the thrust recuperation torque level M Sreku,m after the brake pedal has ended being actuated, for example for a target braking to a specific target stopping point, the driver must again actuate the accelerator pedal in order to be able to perform a targeted braking at a low level by actuating the accelerator pedal. This occurs in FIG. 2 from the time t 5.This described necessary change from the brake pedal to the accelerator pedal for generating deceleration torques M V smaller than the thrust recuperation torque level M Sreku,m however means an additional circumstance for the driver. This is all the more true if the thrust recuperation torque level M Sreku,m and thus the remaining deceleration torque M V= M Sreku,m is high after the brake pedal has ended. If the thrust recuperation torque level M Sreku,m is high, decelerations in the lower deceleration range can be generated within the scope of a single-pedal operation by removing the actuation of the accelerator pedal, and the brake pedal must be actuated only at higher decelerations. However, after the end of an actuation of the brake pedal, a high thrust recuperation torque level M Sreku,m is then maintained, which can only be reduced by an additional actuation of the accelerator pedal.It is an object of the invention to specify methods for decelerating a motor vehicle in which even without renewed actuation of the accelerator pedal a deceleration below the thrust recuperation torque value M Sreku,m is achieved after the actuation of the brake pedal has ended. The invention is also directed to specifying correspondingly designed control devices for a motor vehicle.A first aspect of the invention relates to a method for decelerating an electric drive motor vehicle. The motor vehicle comprises an accelerator pedal and brake pedal that can be actuated by the driver. The motor vehicle allows a thrust recuperation, wherein the motor vehicle is designed such that, when the actuation of the accelerator pedal is ended, a thrust recuperation torque assigned to the non-actuation of the accelerator pedal is set on the electric drive (see, for example, the thrust recuperation torque level M Sreku,m in FIG. 1 ).The method has the following steps: in a first step, it is determined by the vehicle that the driver has finished actuating the accelerator pedal; this can be carried out, for example, by evaluating the accelerator pedal angle or another variable which is characteristic of the position of the accelerator pedal. A thrust recuperation torque associated with the non-actuation of the accelerator pedal is then set within the framework of the thrust recuperation (for example setting M Sreku,m in FIG. 2 after the time t 1). It is possible that a thrust recuperation torque is already set beforehand when the actuation of the accelerator pedal is released when the actuation of the accelerator pedal is small, but this torque is less than the thrust recuperation torque which is assigned to the non-actuation of the accelerator pedal and is set later (see in this respect, for example, FIG. 1 ).The brake pedal is then actuated by the driver (see, for example, the time t 2 in FIG. 2 ). After actuation of the brake pedal, the deceleration of the motor vehicle increases, wherein a thrust recuperation torque associated with the non-actuation of the accelerator pedal is still maintained.The increase in the deceleration can be caused, for example, by a braking torque of the hydraulic service brake and / or a braking recuperation torque of the electric drive which is additional to the thrust recuperation torque already set, as was explained in connection with FIG. 2.It is then determined by the vehicle that the driver cancels the actuation of the brake pedal (see, for example, the time t 3 in FIG. 2 ). This can be done, for example, by evaluating a variable characteristic of the position of the brake pedal (e.g., brake pedal travel or brake pedal angle) or by evaluating the admission pressure between the tandem master brake cylinder and the hydraulic unit of the hydraulic service brake.After removal of the brake pedal, the deceleration of the motor vehicle is reduced by, for example, reducing the braking torque of the hydraulic service brake and / or the braking recuperation torque of the electric drive. In contrast to the approach shown in FIG. 2, however, according to the invention, within the scope of the reduction of the deceleration, the set thrust recuperation torque is also reduced starting from the thrust recuperation torque (see M Sreku,m in FIG. 2 ) assigned to the non-actuation of the accelerator pedal.Because, when the actuation of the brake pedal is released, the set thrust recuperation torque is also reduced, the driver can dose the deceleration torque in a greater range via the brake pedal and also specify deceleration torques smaller than a thrust recuperation torque (see M Sreku,m in FIG. 2 ) assigned to the non-actuation of the accelerator pedal. As a result, the driver can also stop precisely, in particular purely by actuating the brake pedal, without having to actuate the accelerator pedal again, if the driver wishes to set a deceleration torque less than a thrust recuperation torque assigned to the non-actuation of the accelerator pedal. The driver can therefore also dose the thrust recuperation by the brake pedal in addition to the braking by the service brake.Upon removal of the actuation of the brake pedal, the thrust recuperation torque can be reduced substantially in proportion to a variable characteristic for the actuation of the brake pedal. For example, the torque recuperation during the removal of the actuation of the brake pedal can be reduced in proportion to the brake pedal travel or to the brake pedal angle. If, for example, the brake pedal travel or the brake pedal angle is reduced by 10% compared to the currently actuated position, the thrust recuperation torque is preferably also reduced substantially by 10%. Alternatively to the brake pedal travel or to the brake pedal angle, the thrust recuperation torque can also be reduced in proportion to the admission pressure between the tandem brake cylinder and the hydraulic unit of the hydraulic service brake. The preliminary pressure is a variable which is characteristic for the actuation of the brake pedal and can be determined by means of a so-called preliminary pressure sensor.The reduction of the thrust recuperation torque when the actuation of the brake pedal is released is preferably carried out in such a way that, when the actuation of the brake pedal is ended, the thrust recuperation torque is substantially reduced to zero. When the actuation of the brake pedal is ended, for example, both the braking torque of the service brake and the thrust recuperation torque are substantially reduced to zero.If the driver has to step back again during the deceleration reduction by releasing the brake pedal in order to increase the deceleration again, the thrust recuperation and thus the amount of the thrust recuperation torque can likewise be increased in proportion to a variable characteristic for the actuation of the brake pedal, for example in proportion to the preliminary pressure. Alternatively, the thrust recuperation can also remain at the level achieved by the deceleration reduction, and the driver generates the desired increased deceleration mainly via the hydraulic braking force and, if applicable, the brake recuperation.A second aspect of the invention relates to a method for decelerating a motor vehicle with an electric drive, wherein, in principle, when an actuation of the accelerator pedal via the electric drive is ended, a thrust recuperation torque assigned to the non-actuation of the accelerator pedal is built up within the scope of a thrust recuperation for decelerating the vehicle.If, on the other hand, a so-called actuation change from the accelerator pedal to the brake pedal is detected (in particular a rapid and / or forceful actuation change), the build-up of the thrust recuperation torque assigned to the non-actuation of the accelerator pedal is prevented (this does not have to be the case for each actuation change, however). As a result, depending on the implementation of the method, either the result is that no thrust recuperation torque at all is then present at all in the stationary state, or that a thrust recuperation torque is present in the stationary state, which is lower than the otherwise set thrust recuperation torque. It can be provided that no thrust recuperation takes place at all due to the prevention, or that an beginning thrust recuperation is reduced again to zero with an increasing thrust recuperation torque due to the prevention, or that the build-up of the thrust recuperation torque is stopped due to the prevention and the thrust recuperation torque that has been built up up up until now remains at a level below the thrust recuperation torque associated with the non-actuation of the accelerator pedal (see M Sreku,m in FIG. 2 ).If the method cannot react fast enough and the thrust recuperation torque assigned to the non-actuation of the accelerator pedal has already been built up when the actuation change is detected, this may alternatively also be reduced, in particular completely to zero or alternatively also to a lower value which is lower than the thrust recuperation torque assigned to the non-actuation of the accelerator pedal.The thrust recuperation is therefore either masked or reduced during the braking by the brake pedal in this case.Since, in the event of a change in actuation from the accelerator pedal to the brake pedal, the build-up of the thrust recuperation torque assigned to the non-actuation of the accelerator pedal is prevented or this torque is reduced again, the deceleration torque which can be adjusted via the brake pedal is not limited downward by the thrust recuperation torque assigned to the non-actuation of the accelerator pedal. Instead, deceleration torques smaller than this thrust recuperation torque can also be set via the brake pedal. The driver can thus meter the deceleration torque over a larger range by actuating the brake pedal, which is advantageous in particular for target braking. For deceleration, when the brake pedal is actuated, as an alternative or in addition to braking via the hydraulic service brake, a brake recuperation which can be metered via the brake pedal can be used.The concept of building up a thrust recuperation torque assigned to the non-actuation of the accelerator pedal, in principle, when an actuation of the accelerator pedal is ended, brings about a low energy loss during the deceleration due to the regenerative of the recovered energy into the energy store of the electric drive in comparison with the deceleration without permitting thrust recuperation. However, if an actuation change to the brake pedal is detected, this structure is prevented or the thrust recuperation is reduced again, so that the driver can dose the deceleration torque over a relatively large range via the brake pedal without having to actuate the accelerator pedal again for this purpose.According to a preferred embodiment, the build-up of the thrust recuperation is not prevented or the thrust recuperation is reduced again during each actuation change, but only during actuation changes that meet one or more specific criteria. For example, a build-up or a reduction in the thrust recuperation is to be prevented or a reduction is to be initiated if a dangerous braking is involved which is characterized by a rapid change in confirmation and a forceful braking actuation.For example, the presence of a sufficiently fast actuation change is determined on the basis of one or more criteria. The prevention or the removal is carried out only if the actuation change is carried out sufficiently quickly. For a sufficiently rapid change of actuation, for example, the following criteria must be cumulatively fulfilled:the amount of the gradient of the accelerator pedal angle or of the gradient of another variable characteristic of the position of the accelerator pedal is greater than a specific threshold value,detecting the zero position of the accelerator pedal (for example via the accelerator pedal angle), andthe time duration Δt between the detection of the zero position of the accelerator pedal until the actuation of the brake pedal is smaller than a threshold value.Additionally (or alternatively), the presence of a sufficiently powerful brake pedal actuation is determined on the basis of one or more criteria. The prevention or the removal takes place only if the brake pedal actuation was sufficiently forceful. This is intended to prevent the thrust recuperation from being prevented or reduced when the brake pedal is slightly actuated. For a sufficiently powerful brake pedal actuation, for example, the following criteria must be cumulatively fulfilled:a braking gradient (for example the gradient of the admission pressure of the hydraulic brake system or the gradient of the brake pedal travel) is greater than a specific threshold value, andthe braking level (for example the preliminary pressure or the brake pedal travel) is greater than a threshold value.In the event of a sufficiently rapid change from the accelerator pedal to the brake pedal and a correspondingly powerful brake pedal actuation, the acceleration recuperation which is developing or the acceleration recuperation which is developing can be thrown off, so that the driver takes over the braking via the brake pedal and can meter the vehicle deceleration over a relatively large range.For both methods according to the first and second aspect of the invention, it can be provided that after termination of the actuation of the brake pedal, when the driver is not walking on the accelerator pedal and the vehicle is still rolling, the thrust recuperation and thus the thrust recuperation torque are blended in again. The pushing recuperation torque can be blended in with a specific ramp over time or over the route, the gradient of which can depend on one or more different boundary conditions, such as the current gradient of the route (travel in the level or downhill).Accordingly, it may be provided that it is checked that the actuation of the brake pedal has been ended, that the accelerator pedal is not subsequently actuated, and that the vehicle is still rolling. If all of these conditions are fulfilled, the thrust recuperation torque is increased again, in particular to a thrust recuperation torque associated with the non-actuation of the accelerator pedal. As explained above, the increase can take place ramp-like over time or over the route.A third aspect of the invention is directed to a control device for carrying out the method according to the first aspect of the invention.The control device is configured to determine the termination of the actuation of the accelerator pedal, for example by evaluating the accelerator pedal angle or another variable characteristic of the position of the accelerator pedal. When the end of the actuation of the accelerator pedal is detected, a thrust recuperation torque associated with the non-actuation of the accelerator pedal is set by the control device within the scope of a thrust recuperation for decelerating the vehicle. Even when the brake pedal is subsequently actuated, a thrust recuperation torque associated with the non-actuation of the accelerator pedal is still maintained. If the brake pedal has been actuated, a removal of the actuation of the brake pedal is subsequently ascertained by the control device, for example by evaluating the brake pedal position. When the removal of the brake pedal is detected, the thrust recuperation torque is reduced on the basis of a thrust recuperation torque assigned to the non-actuation of the accelerator pedal.The control device is, for example, a drive control unit and a brake control unit. The drive control unit detects the termination of the actuation of the accelerator pedal and sets a thrust recuperation torque associated with the non-actuation of the accelerator pedal. The brake control unit detects an actuation and subsequent removal of the brake pedal. Upon removal of the actuation of the brake pedal, the brake control unit gives the drive control unit a specification (for example a setpoint torque) to reduce the set thrust recuperation torque.The control device is configured to build up, upon termination of an actuation of the accelerator pedal, a thrust recuperation torque associated with the non-actuation of the accelerator pedal within the scope of a thrust recuperation for decelerating the vehicle. However, if an actuation change, in particular a rapid and / or forceful actuation change, is detected from the accelerator pedal to the brake pedal by the control device, the build-up of the thrust recuperation torque assigned to the non-actuation of the accelerator pedal is prevented or the thrust recuperation torque assigned to the non-actuation of the accelerator pedal is reduced, provided that the thrust recuperation torque assigned to the non-actuation of the accelerator pedal was already built up.The control device is, for example, a drive control unit and a brake control unit. The drive control unit provides, for example, the information about the accelerator pedal gradient and the zero position of the accelerator pedal to the brake control unit. The brake control unit detects the actuation of the brake pedal and measures the time duration between zero position of the accelerator pedal and actuation of the brake pedal. The brake control unit also measures, for example, the brake gradient and the brake pressure level. The brake control device then decides on the basis of this information whether a sufficiently rapid and sufficiently forceful change of actuation from the accelerator pedal to the brake pedal has taken place. If this is the case, the brake control unit gives the drive control unit the specification to prevent the build-up of the thrust recuperation torque or to reduce the thrust recuperation torque.The above explanations relating to the method according to the invention according to the second aspect of the invention also apply in a corresponding manner to the control device according to the invention according to the fourth aspect of the invention. Advantageous exemplary embodiments of the control device according to the invention that are not explicitly described at this point correspond to the described advantageous exemplary embodiments of the method according to the invention.The invention is described below with the aid of the appended drawings with reference to a plurality of exemplary embodiments. In these show: FIG. 1 shows an exemplary schematic profile of the drive torque M over the accelerator pedal angle FPW; FIG. 2 shows an exemplary schematic profile of the deceleration torque M V and the thrust recuperation torque M Sreku over time t in a conventional concept for utilizing the thrust recuperation; FIG. 3 shows a flow diagram of an exemplary embodiment of the method according to the invention according to the first aspect of the invention; FIG. 4 shows an exemplary schematic profile of the deceleration torque M V and the thrust recuperation torque M Sreku over time t in an exemplary embodiment of the method according to the invention according to the first aspect of the invention; and FIG. 5 shows an exemplary schematic profile of the deceleration torque M V and of the thrust recuperation torque M Sreku over time t in an exemplary embodiment of the method according to the invention according to the second aspect of the invention.FIGS. 1 and 2 have already been described above.In the following, with the aid of FIGS. 3 and 4, an exemplary embodiment of the method according to the invention according to the first aspect of the invention is described. FIG. 3 shows an exemplary sequence of the method. FIG. 4 shows an exemplary schematic profile of the deceleration torque M V and the thrust recuperation torque M Sreku over time t in the exemplary embodiment. The deceleration torque M V corresponds to the broken line; the thrust recuperation torque M Sreku corresponds to the dotted line. The above explanations relating to FIG. 2 also apply to FIG. 4 up to the point in time t 3.In step 110 of FIG. 3, the termination of the actuation of the accelerator pedal is ascertained, for example, by evaluating the accelerator pedal angle FPW, and a thrust recuperation torque M Sreku= M Sreku,m corresponding to the accelerator pedal angle FPW=0 is then built up starting from the time t 1 in FIG. 4 (see step 120). Previously, already upon removal of the actuation of the accelerator pedal at small accelerator pedal angles, a thrust recuperation torque can be predefined, the magnitude of which is less than M Sreku,m( see FIG. 1 ).When the driver operates the brake pedal at time t 2 the deceleration already established by the thrust recuperation is increased (see step 130). By actuating the brake pedal, for example, the hydraulic service brake is triggered and a braking torque M B is built up, which is added to the thrust recuperation torque level M Sreku,m of the electric drive. The thrust recuperation torque level M Sreku,m continues to be maintained after actuation of the brake pedal.The increase in the deceleration can, for example, also be caused, additionally or alternatively to the braking torque of the hydraulic service brake, by a braking recuperation torque of the electric drive which is additional to the thrust recuperation torque which is already set, as was explained in connection with FIG. 2.At time t 3 the driver begins to resume brake pedal actuation. This is detected in step 140, for example by evaluating the signal of a brake pedal travel sensor or the signal of a preliminary pressure sensor of the preliminary pressure between the tandem master brake cylinder and the hydraulic unit. After the brake pedal is released, the brake pressure is reduced via the tandem master brake cylinder and thus the braking torque M B built up via the service brake is reduced. In addition, in step 150, the thrust recuperation torque M Sreku is reduced, starting from the thrust recuperation torque level M Sreku,m in proportion to a variable characteristic for the actuation of the brake pedal, for example in proportion to the brake pedal travel or to the admission pressure between the tandem master brake cylinder and the hydraulic unit. After the brake pedal has ended being actuated at the time t 4 the braking torque M B of the service brake is substantially reduced to zero (in the case of the use of a brake recuperation torque, this would also be reduced to zero). In addition, the thrust recuperation torque M Sreku is reduced substantially to zero.After the brake pedal has been actuated, the thrust recuperation torque M Sreku is increased in a ramp-like manner over time t to the thrust recuperation torque level M Sreku,m if the accelerator pedal is subsequently not actuated and the vehicle is still rolling (see FIG. 3 and step 160). At time t 5 the thrust recuperation torque level M Sreku,m is reached. The ramp-shaped increase of the thrust recuperation torque M Sreku can also be started only after a specific time duration has elapsed after the time t 4 has elapsed.In the following, with the aid of FIG. 5, an exemplary embodiment of the method according to the invention according to the second aspect of the invention is described.FIG. 5 shows an exemplary schematic profile of the deceleration torque M V and the thrust recuperation torque M Sreku over time t in the exemplary embodiment. The deceleration torque M V corresponds to the broken line; the thrust recuperation torque M Sreku corresponds to the dotted line.At time t 9 the driver begins to decrease the actuation of the accelerator pedal. At time t 10 the actuation of the accelerator pedal is ended. By ending the actuation of the accelerator pedal, a thrust recuperation torque M Sreku is built up with the target value M Sreku,m (before t 10 a thrust recuperation torque M Sreku can already be built up with a lower target value). In this exemplary embodiment, the torque M Sreku which builds up is reduced back to zero if it is determined that a rapid change of actuation from the accelerator pedal to the brake pedal is carried out, in which additionally the actuation of the brake pedal is effected forcibly. The actuation of the brake pedal begins at the time t 11; shortly thereafter the braking torque M B of the service brake increases, wherein the deceleration torque then results from the building-up thrust recuperation torque M Sreku and the building-up braking torque M B.After it has been determined that a rapid change from the accelerator pedal to the brake pedal has taken place and the brake pedal has been actuated in a powerful manner, a reduction of the increasing thrust recuperation torque M Sreku to the value zero begins at the time t 12. The reduction can take place very quickly, in particular abruptly, or in accordance with a ramp. The deceleration torque M V is then formed at M Sreku= 0 by the braking torque M B. At time t 13 the driver decreases the actuation of the brake pedal again, at time t 14 the driver has ended the actuation of the brake pedal. After the brake pedal has been actuated, the thrust recuperation torque M Sreku is increased in a ramp-like manner over the time t to the thrust recuperation torque value M Sreku,m if the accelerator pedal is subsequently not actuated and the vehicle is still rolling. The ramp-shaped increase of the thrust recuperation torque M Sreku can also be started only after a specific time duration has elapsed after the time t 14 has elapsed.The above-described reduction of the building-up thrust recuperation torque M Sreku at the time t 12 takes place only if the actuation change is carried out sufficiently quickly and the subsequent brake pedal actuation is sufficiently forceful.In order to establish a sufficiently rapid change in actuation, it is checked, for example, whether the following criteria are cumulatively fulfilled:the amount of the gradient of the accelerator pedal angle is greater than a specific threshold value,the zero position of the accelerator pedal was detected (for example via the accelerator pedal angle), andthe time duration Δt between the detection of the zero position of the accelerator pedal until the actuation of the brake pedal is smaller than a threshold value; the actuation of the brake pedal can be detected via a signal of the brake light switch, a signal of the preliminary pressure sensor between tandem master cylinder and hydraulic unit or a signal of a brake pedal travel sensor.In order to determine a sufficiently powerful brake pedal actuation, it is checked, for example, whether the following criteria are cumulatively fulfilled:a braking gradient (for example the gradient of the admission pressure of the hydraulic brake system or the gradient of the brake pedal travel) is greater than a specific threshold value, andthe braking level (for example the preliminary pressure or the brake pedal travel) is greater than a threshold value.

Claims

Method for decelerating an electric-drive motor vehicle, which comprises an accelerator pedal which can be actuated by the driver and a brake pedal, having the steps carried out by the motor vehicle: establishing (110) the termination of the actuation of the accelerator pedal; upon establishing the termination of the actuation of the accelerator pedal, setting (120) a thrust recuperation torque (M Sreku,m) which is associated with the non-actuation of the accelerator pedal, as part of a thrust recuperation for decelerating the vehicle; upon actuation of the brake pedal, increasing (130) the deceleration of the motor vehicle while maintaining the thrust recuperation, wherein a thrust recuperation torque (M Sreku,m) which is associated with the non-actuation of the accelerator pedal is furthermore maintained; determining (140) a subsequent removal of the actuation of the brake pedal; upon determining the removal of the brake pedal, reducing (150) the thrust recuperation torque (M Sreku) starting from a thrust recuperation torque (M Sreku,m), assigned to the non-actuation of the accelerator pedal, wherein upon determining the removal of the actuation of the brake pedal, the thrust recuperation torque (M Sreku) is reduced as a function of a variable characteristic for the actuation of the brake pedal.Method according to Claim 1, wherein the thrust recuperation torque (M Sreku) is reduced substantially in proportion to a variable characteristic for the actuation of the brake pedal.Method according to one of the preceding claims, wherein, when the actuation of the brake pedal is ended, the thrust recuperation torque (M Sreku) is reduced substantially to zero.Control device for a motor vehicle with electric drive, which comprises an accelerator pedal which can be actuated by the driver and a brake pedal, wherein the control device is configured to ascertain the termination of the actuation of the accelerator pedal; if the termination of the actuation of the accelerator pedal is ascertained, to set a thrust recuperation torque (M Sreku,m) which is associated with the non-actuation of the accelerator pedal, within the scope of a thrust recuperation for decelerating the vehicle, wherein even if the brake pedal is subsequently actuated, a thrust recuperation torque (M Sreku,m) which is associated with the non-actuation of the accelerator pedal continues to be retained, to ascertain a removal of the actuation of the brake pedal; and upon detecting the removal of the brake pedal, to reduce the thrust recuperation torque (M Sreku) on the basis of a thrust recuperation torque (M Sreku,m) associated with the non-actuation of the accelerator pedal, wherein upon detecting the removal of the actuation of the brake pedal, the thrust recuperation torque (M Sreku) is reduced as a function of a variable characteristic for the actuation of the brake pedal.

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