DE102009039614A1 - Deceleration system controlling method for e.g. hybrid vehicle, involves reducing reference-recuperation torque in overrun mode during detection of stability-critical condition or during assuming future stability critical condition - Google Patents

Abstract

The method involves determining reference-recuperation torque based on preset characteristic curves and/or parameters in an overrun mode of a motor vehicle e.g. hybrid vehicle. The recuperation torque actually applied by an electrical-regenerative system is reduced in the overrun mode during detection of a stability-critical condition or during assuming a future stability critical condition. A constant or variable value is provided as preset maximum allowed, reduced reference-recuperation torque. The maximum allowed torque is provided based on preset operating parameters of the vehicle.

Description

The invention relates to a method for controlling a deceleration system for a motor vehicle having an electrically regenerative drive system according to the preamble of claim 1.

In particular, in hybrid vehicles or purely electrically driven vehicles, an electric machine is provided for driving the vehicle, which is used during certain operating conditions of the vehicle in which the vehicle is to be decelerated, as a generator for energy recovery (recuperation). The purpose of such an electrical-regenerative system or of a generator is to recover at least part of the energy converted during deceleration in the vehicle and, if necessary, to store it. This stored energy can then be used for the drive or other systems of the vehicle.

At present, various operating concepts are conceivable when the electric machine is operated as a generator. This can always be done as soon as the accelerator pedal is released or no power is requested from the drive (= Schubrekuperation). Alternatively, the recuperation of the electric machine can only be activated when a braking operation is initiated, either because of a driver's specification on the brake pedal or a system-related brake specification, as they are requested. For vehicles with cruise control systems (= Bremsrekuperation). In addition, a superposition of the described thrust and Bremsrekuperation take place.

The (additional) delay effect of the electric regenerative system and the associated additional longitudinal forces may u. U. adversely affect the driving dynamics of the vehicle. Thus, a longitudinal force distribution can be set between the axles by the (additional) braking effect of the electric regenerative brake, which acts only on the drive axle, which deviates significantly from the "installed" brake force distribution due to the design of the brake system. This effect also occurs in conventional vehicles with internal combustion engine and without recuperative drive / brake system and can be corrected as needed by an existing stabilization system, in particular by an engine drag torque control. Such a regulation can also be used in vehicles with electrified drives.

For vehicles with a recuperative drive or deceleration system, stronger effects are to be expected due to the desire to recover as much braking energy as possible. Depending on the level of the generator torque and depending on the driving situation, the recuperation torque can have a detrimental effect on driving dynamics. In particular, on smooth roads and in the vicinity of the dynamic driving limit range, it may happen that the drive wheels (on which the electric regenerative system acts) can not sufficiently transmit the recuperative deceleration required due to the current Schubrekuperationsmoments. In front wheel drive vehicles, this can lead to understeer of the vehicle and oversteer in vehicles with rear wheel drive.

So revealed the DE 103 32 207 A1 a method for controlling a brake system with a friction brake system and a recuperation brake system or an electric regenerative braking system. In this case, when a requested brake intervention (ie in Bremsrekuperationsbetrieb) exclusively the friction brake system is controlled to decelerate the vehicle when a predetermined shutdown condition for the recuperation brake system is met. Such a switch-off condition is met when a longitudinal dynamic quantity describing the vehicle longitudinal dynamics is outside an admissible range, or when the wheel speed difference of the driven wheels of a vehicle axle is greater than a speed threshold value.

The object of the invention is now to provide a method for controlling an electrically regenerative deceleration system, which ensures a stable vehicle condition in Schubrekuperation.

This object is achieved by the subject matter of independent claim 1. Advantageous developments emerge from the subject matters of the dependent claims.

In the invention, it is assumed that a motor vehicle with an electric regenerative system, on the one hand as a drive unit for driving the vehicle and on the other hand in overrun operation as a deceleration system for braking or deceleration of the vehicle by applying a Rekuperationsmoments can be used. The point of attack of the electric regenerative system is at least one drive wheel, but in particular two or more drive wheels of the vehicle or is at least one drive axle of the vehicle, d. H. by applying the Rekuperationsmoments the vehicle is delayed by acting on the drive wheels.

In overrun operation of the motor vehicle (ie no positive or driving drive torque is requested), a setpoint characteristic is determined on the basis of predefined characteristic curves and / or parameters. Schubrekuperationsmoment determined and - if possible - applied (at least initially) by the electric regenerative system.

The invention is characterized by the fact that in the presence of predetermined reduction conditions in overrun, in particular upon detection of a stability-critical state or assuming a future (or an indication of an impending) stability-critical state in overrun the applied by the electric regenerative system (Soll -) Recuperation torque is reduced, so that instability of the vehicle is prevented. This method is suitable for all vehicles equipped with a corresponding electric regenerative (propulsion) system, i. H. It can be used both in vehicles with purely electric drive as well as in vehicles with hybrid drive from internal combustion engine and electrical system.

Advantageously, in addition to the evaluation of the current stability of the driving state, the recognition of an imminent stability-critical state can be carried out by evaluating at least one predetermined preventive signal. A preventive signal is to be understood as meaning those signals or parameters which change or are changed in such a way as to destabilize the vehicle in such a way that a future destabilization of the vehicle can be recognized or assumed. Such a preventive signal may be a driver specification or a driving condition parameter that adjusts or changes on the basis of a driver specification or a vehicle condition parameter.

Advantageously, based on an evaluation of the following preventive criteria (driver specifications and / or current driving condition parameters) on a future stability critical state of the vehicle are concluded: steering angle speed, steering angle, brake pressure generated, brake pedal travel and / or accelerator pedal angle, release gradient of the accelerator pedal and / or actuation gradient of the brake pedal and / or the vehicle deceleration desired by the driver. Alternatively or additionally, such signals can be evaluated, which correlate with the current driving situation, such. B. the vehicle or wheel speed, the wheel slip, the Fahrbahnreibwert, the speed and / or torque of the drive unit, the longitudinal and lateral acceleration and the yaw rate of the vehicle and / or the error status or the activation state of a stabilization system. In addition, for example, information from existing driver assistance systems, such. B. a collision warning to be evaluated.

In order to be able to ensure a stable state, the currently applied (setpoint) recuperation torque can be reduced to zero or a maximum permissible, reduced nominal recuperation torque, in which case a constant or a variable value can be preset. If the method is used for stabilizing or maintaining stability in a vehicle whose drive is composed, for example, of a hybrid drive consisting of an internal combustion engine and the electric regenerative system designed as a drive unit, it may be necessary to do so on the basis of the stability state of the vehicle Reduction of Rekuperationsmoments in overrun operation still a deceleration torque of the engine acts, the target recuperation be reduced in the simplest embodiment to zero. However, this results in that during this operating state no energy can be recovered. However, if the vehicle is delayed in overrun only by the application of the recuperation torque (as is the case, for example, in pure electric vehicles without an internal combustion engine), the recuperation torque in the stability-critical state should only be reduced to such a stability recuperation torque that a deceleration torque ensues a deceleration torque to be achieved in a vehicle with internal combustion engine at the same operating conditions in overrun operation is at least almost identical or that the recuperative deceleration torque is not reduced to zero, so that a certain minimum delay is maintained.

In order to be able to provide maximum energy recovery, the (applied) recuperation torque currently applied should advantageously not be reduced to zero, but only to a torque level such that the stability of the vehicle can at least just be guaranteed when it is implemented (ie a given stability condition is satisfied) is or remains satisfied). The corresponding, maximum permissible, reduced nominal recuperation torque can be predefined, for example, as a function of the above-mentioned driver specifications, driving state and / or vehicle state parameters.

If a stability-critical condition of the vehicle is still recognized or suspected in hybrid or electric vehicles despite the reduction of the recuperation torque, the stabilization functions known from conventional vehicles must intervene and restore a stable driving condition. For example, in vehicles with hybrid drive despite reducing the recuperation (to zero) continues to recognize or suspected a stability-critical condition of the vehicle, to achieve - or holding - a stable vehicle condition, a corresponding Motor Schleppregelung the internal combustion engine, possibly also other stabilization functions, as is already common in conventional vehicles are made. This means that the motor drag control, for example, engages only when the reduction of the regenerative drag torque, as proposed here, is not sufficient to ensure vehicle stability.

Advantageously, the maximum permissible, reduced setpoint recuperation torque in overrun operation (for stabilizing the vehicle) can be increased again if an increase is permitted on the basis of predetermined conditions and / or operating parameters of the vehicle. In particular, the recuperation torque can then be increased again to the initially specified desired recuperation torque. The given conditions may, for example, be a stability condition already mentioned above, which is considered fulfilled if no stability-critical condition of the vehicle (possibly for a predefined period of time) is detected or suspected.

In a particularly advantageous embodiment of the invention, the target recuperation torque can be variably set or controlled in overrun mode of the vehicle depending on the position of the accelerator pedal, d. H. the applied during overrun operation of the vehicle recuperation is metered by the position of the accelerator pedal. The accelerator pedal thus becomes a "delay control element". The desired recuperation torque can then be set differently within a certain pedal travel from the point of "free rolling" (neither a driving, nor a decelerating drive torque is requested) to the complete release of the accelerator pedal (corresponds to a maximum requirement of the target Rekuperationsmoments). The relationship between the amount of accelerator pedal operation and the amount of recuperation required to be requested may, for. B. be determined suitably over curves or maps.

Similarly, the required for avoiding a stability-critical condition of the vehicle stability-recuperation in overrun depending on the position of the accelerator pedal can be specified.

Thus, the invention offers the advantage that the number of otherwise necessary stabilizing control interventions of the otherwise necessary by the preventive avoidance or the early (reactive) detection of destabilization of the vehicle in overrun and the resulting need-based reduction of the applied by the electric regenerative unit Rekuperationsmoments Stabilization system can be reduced and yet a high degree of driving stability can be achieved. The proposed method, which can be implemented as a function in a control unit, allows the compromise between optimum energy efficiency through the best possible use of Rekuperationspotentials and ride comfort by avoiding uneven delays and possibly uncomfortable control actions on the one hand, and ensuring the driving stability on the other.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 10332207 A1 [0006]

Claims (9)

A method for controlling a deceleration system for a motor vehicle with an electric regenerative system for braking the vehicle by applying a Rekuperationsmoments to at least one drive wheel or at least one drive axle of the motor vehicle, wherein in coasting mode of the motor vehicle based on predetermined characteristics and / or characteristics determines a target Rekuperationsmoment and is applied by the electric regenerative system, characterized in that upon detection of a stability-critical state or assuming a future stability-critical state in overrun the actual regenerative applied by the electric regenerative system target recuperation is reduced. A method according to claim 1, characterized in that the currently applied target recuperation torque is reduced to zero or a predetermined, maximum allowable, reduced target recuperation torque. Method according to Claim 2, characterized in that a constant or variable value is specified as the maximum permissible, reduced nominal recuperation torque. A method according to claim 2 or 3, characterized in that the maximum allowable reduced target recuperation torque is predetermined in dependence on predetermined operating parameters of the vehicle. Method according to one of claims 2-4, characterized in that in vehicles with purely electric drive with reduction of the currently applied target recuperation due to the detection or assumption of a stability-critical state, the stability Rekuperationsmoment is set such that sets a deceleration torque greater than zero which is at least almost identical to a deceleration torque to be achieved in a vehicle with internal combustion engine under the same operating conditions in overrun operation. Method according to one of claims 2-4, characterized indicates that the maximum allowable reduced target recuperation torque is predetermined such that a predetermined stability condition is met and / or satisfied. Method according to one of the preceding claims in vehicles with hybrid drive, which is composed of an internal combustion engine and an electric drive or in vehicles with pure electric drive, characterized in that under the condition that despite reducing the recuperation a stability-critical state of the vehicle continues to be recognized or future is assumed, to achieve or maintain a stable vehicle state, a dynamic driving control intervention by a stabilization system, in particular a dynamic driving control intervention is performed by the brake hydraulic. Method according to one of the preceding claims, characterized in that the reduced recuperation torque applied upon detection or presumption of the stability-critical state is increased again, in particular is increased to the predetermined desired recuperation moment, if an increase is permitted due to predetermined conditions and / or operating parameters of the vehicle , Method according to one of the preceding claims, characterized in that the target Rekuperationsmoment in overrun operation of the vehicle as a function of the position of the accelerator pedal is set, in particular such that the desired Rekuperationsmoment is set larger with less deflection of the accelerator pedal.