DE102013011230A1 - Method for improving the traction of vehicles - Google Patents

Abstract

The present invention relates to a method and a corresponding device for improving the traction of vehicles by controlling the drive torque. In order to remedy against vehicle occupants noticeable and perceived as a comfort reduction control interventions, it is proposed that a model-based feedforward control of the drive torque is used taking into account various parameters of a motor vehicle for calculating the deductible in an optimal situation forces. Practically, under the never optimal conditions of reality, only a smaller force can be deducted so that a force determined on the basis of the model can be used as an upper limit for an engine torque when starting in a stationary state.

Description

The present invention relates to a method and a corresponding device for improving the traction of vehicles by controlling the drive torque.

To transfer the power of a vehicle drive efficiently on a roadway, a traction control system, short ASR, an integral part of today's motor vehicles. The ASR prevents the wheels from spinning if the drive torque exceeds the maximum longitudinal force that can be removed from the wheel. For this purpose, the speeds of the wheels are constantly monitored and compared with the current vehicle speed. In the case of too large a deviation of the wheel speeds, the engine torque is withdrawn and optionally initiated an additional brake intervention.

Various approaches are known from the prior art for the purpose mentioned above, which are intended to improve the traction of vehicles by controlling the drive torque while reducing or avoiding slippage. So revealed the DE 196 34 203 A1 a method in which a prediction of an acceleration slip on the basis of several measured values is concerned: If a drive wheel speed is less than a target drive speed and at the same time a throttle opening speed and a throttle opening degree greater than or equal to respective thresholds, the risk of occurrence of acceleration slippage is seen and triggers appropriate interventions on an internal combustion engine.

Furthermore, from the EP 0 554 838 A1 Among other things, the use of a slip rate calculation means known to prevent excessive slip of the drive wheel by the drive and vehicle speed are used to calculate a slip rate. A reduction of the torque then takes place via a throttle valve of an internal combustion engine whose initial opening degree is determined taking into account a current vehicle behavior in order to avoid abrupt changes in vehicle behavior.

According to the teaching of US 5,406,486 A1 For example, vehicle acceleration is optimized from a starting point by always accurately estimating a coefficient of friction between a wheel and a respective road surface in order to stabilize a start acceleration under the control of a slip.

The torque supply of the drive train exceeds just when starting a vehicle in the longitudinal direction maximum deductible wheel forces on one side or even on both sides. This results in an excessive wheel slip, which weakens the traction potential of a particular tire. The result is loss of traction and negative influence on directional stability and acceleration of the vehicle.

By controlling the drive in one of the ways described above, there is a fundamental drawback: Due to the signal feedback required for the control, it is first necessary to set a fault in the form of too high a slip, which can then only be compensated afterwards. These control interventions are noticeable to vehicle occupants and are perceived as a comfort reduction.

The object of the present invention is to provide a remedy in the form of a method by the use of which regulating interventions are considerably less noticeable.

This object is achieved by the features of claim 1, characterized in that a model-based feedforward control of the drive torque, taking into account various parameters of a motor vehicle for calculating the deductible in an optimal situation forces is used. By such a limitation of the drive torque, the probability of occurrence of slippage can be substantially reduced even when starting the vehicle in question from the state, with a ride comfort and an available dynamics are not excessively impaired.

Advantageous developments are the subject of the dependent claims. Accordingly, a model-based precontrol preferably takes place on the basis of a simplified vehicle model taking into account a kinematics, elastokinematics and tire properties of a respective vehicle, but also a current position of the stationary vehicle with respect to a normal plane.

Preferably, each current driver input, as z. B. is given by steering wheel angle or accelerator pedal position, used to calculate abzustbaren in a Bestfall on the tires on the road forces.

Particularly advantageously, the method is performed while covering all foreseeable influences with internal mapping of an optimal situation between the wheel and the road surface in the model. Foreseeable influences, for example, engine torque, transmission characteristics of the drive train in automatic drive, position of the clutch in manual transmission and other vehicle-specific characteristics are considered. Through a model-based approach Thus, according to the invention, a drive torque which can be maximally reduced under optimum conditions and / or a required blocking torque of a possibly slipping wheel, including, for example, B. the process of a Radlastverlagerung be calculated for a respective motor vehicle. This calculation can be done individually for each wheel as well as continuously.

Particularly advantageously, in one embodiment of the invention, a current or prevailing at a current location of the vehicle friction coefficient is used. This current or prevailing at a current location coefficient of friction can be determined from a stored short-term history with previous deceleration in the state or shortly previous approach and used for the feedforward control to determine a fictitious optimal situation for a start from a stand.

In a preferred embodiment of the invention takes place in the context of feedforward and the construction of a locking torque by a controlled brake pressure build-up, with a prediction of Radlastverlagerungen z. B. on the basis of a current steering angle and / or a road position in this feedforward control is taken into account. By temporally upstream model-based calculation of each applied drive torque can be achieved by targeted braking interventions even from the stoppage of the vehicle already a traction improvement, since already in the approach, an excessive longitudinal slip of the tire is prevented. On the basis of a total torque balance, the drive torque can advantageously be further limited by this type of feedforward control and the braking torque can be compensated.

A combination of a method according to the invention with a wheel slip-based control advantageously results in new operating points being able to be taken over by the precontrol in the case of a required intervention of the conventional slip control. In this way, a wheel slip-based control can also be adapted to new conditions by an algorithm according to the invention, so that an approach which is basically known from the prior art thus becomes capable of learning.

Further features and advantages of embodiments according to the invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing. Therein show in a schematic representation:

1 a side view of a passenger car showing a static force distribution on front and rear axles with an indication of their displacement by a starting acceleration;

2 : A front view of a passenger car showing a static power distribution on the left and right wheels with an indication of their displacement by a starting acceleration when turning slightly turned steering and

3 : a course of an available braking torque in a motor vehicle, showing a possible influence of a pilot control according to the invention.

Throughout the various illustrations, the same reference numerals are always used for the same elements.

1 shows a side view of a passenger car K. A weight G has been drawn in an assumed center of gravity of the passenger car K. For a static case, this weight G is distributed evenly on wheels V of a front axle and wheels H of a rear axle. Therefore, these dashed arrows are the same size. Upon application of the passenger vehicle K from the state (v = 0) with an acceleration force F = m · a _x in a vehicle longitudinal direction x, a displacement of this force distribution is effected in a manner known to the person skilled in the art: A force F _v at the front axle is compared a force F _h at the rear axle reduced. By this indicated displacement by the starting acceleration a driven front wheels V can slip faster than possibly also driven rear wheels H.

The sketch of 2 shows a front view of a passenger car K, in which a static distribution of the weight G on a left front wheel V _l and a right front wheel V _{r is} again indicated by dashed lines. In the state at v = 0, the steering is taken to the left, so that the Ackermann condition, corresponding to a left front wheel V _l stronger than right front wheel V _r is taken. By an acceleration acceleration a at turning to the left turned steering, in turn, a shift of the forces acting on the left front wheel V _l and the right front wheel V _r forces F _l , F _r caused. In this case, this displacement or displacement of the forces acts in such a way that the left-hand front wheel V ₁ lying inside is clearly relieved from the outer right-hand front wheel V _r . Thus, in a driven only at the front axle passenger car K, the left front wheel V _l over the right front wheel V _{r would have} a significantly increased tendency to slippage.

A shift comparable to the situations described above could also occur result in that the passenger vehicle K is inclined in its longitudinal and / or transverse axis, for example on a ramp, on one side on a curb-edge or within a greatly exaggerated curve.

Every discharge of a driven wheel increases its tendency to slip. An approximate knowledge of such displacements achieved on the basis of the aforementioned model makes targeted intervention possible even when the vehicle is at a standstill, not just on corresponding sides of a vehicle, but in relation to a respective driven wheel of the vehicle. This makes it possible to control the vehicle traction and the remaining lateral force potential already from a standstill, but also with dynamic wheel load shifts.

This increased tendency to slip is counteracted individually by a precontrol of a starting and / or adjusting torque on each driven wheel. For this purpose, a simplified vehicle model is used in the pre-control, which describes a kinematics of a respective vehicle, in this case of the passenger car K. The model is extended by the elastokinematics, supplemented by the properties of the respective tires, for example, at least with a distinction at least in summer or winter tires, but also taking into account possible differences in tire pressure.

Furthermore, so-called predictable influences are mapped in the model. Under this term u. a. a motor torque available at startup, a current accelerator pedal position, a transmission behavior of a drive train in an automatic drive, a position of a clutch in a vehicle with a manual transmission and further vehicle-specific parameters summarized.

Finally, current external factors are considered, such. B. a current vehicle position with respect to a normal plane. A position according to 1 may be a common rule, but also a start on a steep ramp or a significant slope is to be mastered by the proposed feedforward under significant reduction in a tendency to slip of all wheels. To this end, a modeling of the caused by a current deviation of a vehicle position of the positioning on a normal plane and already static acting shifts of the wheel loads.

Dynamically occurring directly at startup shifts according to the example 2 can be superimposed on these effects in the form of a prediction of a respective wheel load displacement and also be considered for each driven wheel on the vehicle. In this sense, a steering wheel angle can also be taken into consideration proactively in the model as driver input.

Preferably, a wheel-specific, model-based determination of the optimal conditions of maximum deductible wheel torques or forces also includes a possibly necessary therefor locking torque. To optimize the start-up behavior, wheels that could slip are precautionarily braked while stationary. As a result, the friction between the wheel and the road surface or the "grip" of the wheel in question is fictitiously increased. This slippage of the wheel in question is prevented, at the same time a full maximum force can be brought via another drive wheel on the road. Thus, despite the braking intervention, more power is transferred to the road altogether. The model-based calculation of a fictitious optimal situation is carried out in an exemplary embodiment not illustrated further using a current friction value prevailing at a current location of the vehicle, whereby this friction value for each driven and thus slipping wheel results from a stored short-term history of an immediately preceding one Abbremsung in the state or briefly previous approach and deceleration determined and used for the feedforward control to determine a fictitious optimal situation.

In which with reference to the drawing of 2 explained case of turning with Steering Impact already in the state was already on the background and the need for an available actuating torque for braking a driven, inner curve wheel on a motor vehicle received.

The described controlled restriction of a respective drive torque when starting is advantageously implemented on the basis of the total torque balance of the driven wheels. Here then compensation of a braking or actuating torque of at least one otherwise slip-endangered wheel can then be calculated. Overall, this results in terms of traction, dynamics and directional stability compared to known control approaches significantly improved result.

From all the above not conclusively specified influencing variables, a model is created for a respective present motor vehicle, on which the forces which can be put on the road in a best case or under otherwise optimal conditions are calculated. Practically, under the never-optimal conditions of reality, only a lesser force can be deducted, leaving one based on the model determined force can be used as an upper limit for an engine torque when starting in the state.

An egg. d. R. Wheel slip-based control present in a modern vehicle with the functionality of a lateral lock (EDS) and known possibilities for the controlled reduction of engine torque works with standardized starting values. Since this is a wheel slip-based control, the vehicle must already be in motion for this control to take effect and only be able to bring about an improvement when real slip occurs. A model-based precontrol described above can determine as starting function from its internal model under cover all predictable influences with mapping of an optimal situation current operating points from the state of the vehicle out. Directly with a start of the vehicle, an entire control torque of the vehicle is thus composed of a control torque of the pilot control and a control torque of the control. These current operating points determined by the precontrol are i. d. R. better than start values of a known Radschlupfbasierten scheme. If these current operating points are thus handed over to a wheel slip-based control, then they become more or less capable of learning and can work better in a particular situation. The combination of feedforward control and known control can increase the overall dynamics of the system. This makes it possible to improve the functional goals despite the same model design. The pre-control allows comfort-oriented, d. H. in the low torque range, slower actuators are used.

This shows 3 a course of an available braking torque in a motor vehicle, showing a possible influence of a pilot control according to the invention. A hydraulic brake system of a passenger car usually has a limited capacity, since it has to build up pressure via an electrically driven hydraulic pump. Such a system basically has some system inertia. Thus, each ASR system is inert because it reacts only in response to a first real slip with the switching of the hydraulic pump and the relatively slow construction of a control torque. The graph of 3 For this purpose, a constant torque buildup, ie a progressively stronger actuating or braking torque over the duty cycle of the hydraulic pump, is achieved with a constant increase of the delivery volume of hydraulic oil.

By a pre-control described above, however, a possible need for actuating torque is already known before starting. Thus, by the pilot control, an operating point A _{o of} the hydraulic brake system at a time t = 0 to an operating point A 'quasi shifted, so that the actual ASR control at a time t' from the state out already has a control torque M _s , Thus, a low-dynamic range of the pilot control, a higher dynamic range for the ASR control is used.

Because of the temporally forward-looking regulation and avoidance of unstable states while limiting the rotational energy in the drive train and in the wheel, fewer ASR interventions are required by using a method according to the invention. This results in a significantly more comfortable operation of the startup process. The described functionalities are not limited to specific powertrain configurations and not to specific brake system designs. For example, these approaches are also represented with active differentials (superposition gear) or controllable transverse locks. Also, a combination with mechanically active, z. B. torque or differential speed sensing, locking differentials possible.

LIST OF REFERENCE NUMBERS

• K

  Passenger car

  G

  weight force

  V

  Wheels of a front axle

  H

  Wheels of a rear axle

  a

  starting acceleration

  a _x

  Starting acceleration in vehicle longitudinal direction x

  a _y

  Acceleration in vehicle transverse direction y

  V _l

  left front wheel

  V _r

  right front wheel

  F _l

  force acting on the left front wheel

  F _r

  force acting on the right front wheel

  A _o

  working

  A '

  shifted operating point

  M _s

  righting moment

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

• DE 19634203 A1 [0003]
• EP 0554838 A1 [0004]
• US 5406486 A1 [0005]

Claims (11)

A method for improving the traction of vehicles by controlling the drive torque, characterized in that a model-based feedforward control of the drive torque taking into account various parameters of a motor vehicle for calculating the deductible in an optimal situation forces is used. Method according to the preceding claim, characterized in that the model-based precontrol takes place on the basis of a simplified vehicle model. Method according to one of the preceding claims, characterized in that for the calculation of a respective kinematics, Elastokinematik and tire properties in the simplified vehicle model considered who the. Method according to one of the preceding claims, characterized in that the calculation is carried out individually for each driven wheel of a respective motor vehicle. Method according to one of the preceding claims, characterized in that a prediction for a Radlastverlagerungen z. B. on the basis of a current steering angle and / or a road position in this feedforward control is taken into account. Method according to one of the preceding claims, characterized in that in the model-based feedforward control a respective current driver input is taken into account, as z. B. is given by steering wheel angle or accelerator pedal position, etc. Method according to one of the preceding claims, characterized in that the method under cover all foreseeable influences z. B. in the form of an available engine torque, a transmission behavior of a drive train in automatic transmission, a position of a clutch in manual transmission, and other vehicle-specific characteristics in internal mapping of the optimal situation between the wheel and road surface in the model is performed. Method according to one of the preceding claims, characterized in that the model-based calculation of a fictitious optimal situation is performed using a current or prevailing at a current location of the vehicle coefficient of friction, from a stored short-term history with previous deceleration in the state or shortly preceding Approach and deceleration determined and used for the feedforward control to determine a fictitious optimal situation. Method according to one of the preceding claims, characterized in that the structure of a locking torque already takes place during a standstill of the vehicle by a controlled brake pressure build-up in the context of precontrol. Method according to one of the two preceding claims, characterized in that the drive torque is limited based on a total torque balance by this type of feedforward control and an adjusting or braking torque is compensated. Method according to one of the preceding claims, characterized in that the operating points determined by the precontrol are transmitted as start values of a known wheel slip-based control.

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