DE102016003628A1 - System and method for desensitizing the traction and brake slip control in electric vehicles with independent wheel drive - Google Patents

Abstract

The invention relates to the slip control in an electric vehicle with independent wheel drive. The corresponding control system is extended with the functions of the direct slip control, which improve the braking and drive efficiency even on uneven road conditions. The wheels (101-104) are individually controlled in the proposed system by the individual actuators. In braking mode, both the friction brakes (117-120) and the electric motors (109-112) act as actuators. In a drive mode, only electric motors (109-112) work as actuators. A slip control unit (204) defines the desired wheel slip and generates the reaction torques that govern the wheel slip for each respective wheel 101-104. The slip control unit (204) comprises a desensitization unit (206) which detects the unevenness of the road surface and uses a correction coefficient Kdesens_i for the calculation of the reaction torques in order to be able to ensure the required braking power and the handling behavior in the braking and drive mode. The information from the wheel speed sensors (203) is used in the desensitization unit (206) for the detection of the road bumps.

Description

The invention relates generally to the field of electric vehicles and to methods and apparatus for individually controlling the wheel torques in the drive and brake modes and the wheel slip when riding on an uneven road surface.

Most of the known slip control solutions in anti-lock braking systems (ABS) and traction control systems (ASR) are designed for operation on flat road surfaces. However, difficulties in slip control can occur while riding on bumpy roads. A corresponding correction of the control strategies in the ABS or ASR should then be carried out in order to achieve the required braking and drive power regardless of the road conditions. By detecting uneven road conditions, a corresponding control in braking mode can significantly reduce the braking distance and improve vehicle safety. In drive mode on uneven roads, the adapted traction control system can ensure the required driveability. The analysis of the relevant patents points to a number of methods for the detection of uneven road surfaces and the corresponding desensitization of the control processes in the braking and drive mode.

In the patent US 5,522,652 the vehicle is equipped with an ABS, which regulates the wheel acceleration or deceleration. Driving on uneven roads causes vibrations of the wheel deceleration. The system detects and stores the peak values of the wheel deceleration. With the help of this information, the control algorithm decides on the road conditions. If the road surface is detected as uneven, the ABS activation is blocked. This is achieved by shifting the wheel deceleration-related ABS control thresholds. As long as the wheel deceleration does not exceed any shifted control thresholds, the ABS will not be activated.

The one from the patent US 5,627,755 Known approach relates to an ABS with slip control. The wheel speed sensors are used in the ABS to derive the wheel acceleration or deceleration. The peak values of the wheel deceleration are stored for the calculation of a correction factor which is further used for desensitization of the slip control. To prevent false activation of the ABS, the slip control thresholds are shifted in consideration of the desensitization factor. The ABS is not activated on bumpy roads until the current wheel slip reaches a modified control threshold.

The patent US 6,952,637 suggests a road grade index as an index for the classification of road surfaces. The corresponding parameter is used to improve the ABS, ASR and yaw stability control functions by modifying the activation thresholds and control targets. In order to derive the road surface roughness index, the signal of the suspension travel in the suspension is basically required. The signal is filtered taking into account the typical jump frequency of 10 Hz and the filter passband is set to 10 ... 15 Hz. The road grade index is calculated by a peak detector. The slip reference values in the ASR and ABS are then updated taking into account the road grade index to achieve the required power in the braking or drive mode.

The patent US 7,591,170 describes the principles for the detection of road bumpiness in the case of a vehicle with an internal combustion engine. By using the crankshaft position signal, the normalized samples are compared to a certain threshold to determine if rough road conditions are occurring. A filter is used to remove the signal components that are outside the frequency corresponding to the rough road. The indication of rough road conditions is used to turn off an engine misfire detection system.

the patent US 7,739,019 describes a device for detecting the uneven road surface with a vertical acceleration sensor. For the different vehicle speeds certain thresholds of the vertical acceleration are defined. Achieving a vertical acceleration threshold is used as an indicator of rough road conditions. The indication of the rough road is then in a vibration-sensitive system such. As a continuously variable transmission (CVT), an automatic transmission, used in accelerator position sensors or in engine speed sensors. Special is in the patent US 7,739,019 the CVT is shown with the tension on a belt as operating parameter. Clamping pressure is increased on the CVT belt when the signal is transmitted from the threshold comparison module.

The patent application US 2009/0132120 A1 describes a harmonic analysis method which uses information from the wheel speed sensors to detect the uneven road conditions. In accordance with this method, the uneven road conditions may be identified by amplitude, phase and / or spectral energy of the particular harmonic. In particular, the amplitude of the predetermined frequency is compared with a predetermined amplitude range in a predetermined frequency range in order to detect the uneven road conditions.

The patent document US 2013/080014 A1 presents a method of distinguishing driving between road and off-road driving. The detection of the road conditions is realized with the help of a sensor system (the measuring principle was not described in detail in the document). Optionally, the off-road driving mode may be manually activated by an operator or driver of the vehicle through an input device connected to the brake control unit. In off-road mode, the brake slip control on the rear axle of the vehicle remains active until the condition that the brake slip on at least one wheel of the front axle is equal to or less than a predetermined brake slip limit.

Reduced slip thresholds in off-road driving mode are used in the system known from the patent application US 2005/140207 A1. The slip control is done individually for each wheel. The off-road driving mode is automatically deactivated when a predetermined vehicle speed is reached. Under off-road conditions, the ABS will operate at vehicle speeds in excess of 40 km / h during normal operation and will switch to a deep-cycle mode within the speed range of 40 to 15 km / h. The lock mode is activated when the vehicle speed is in the range of 15 to 0 km / h. The presented method of desensitization is characterized by a stepless transition between the normal ABS operation and the deep cycle mode. The deep cycle mode is characterized by longer brake pressure buildup phases with an increased slip threshold and pressure hold for an additional time of about 200 ms upon reaching the wheel lock.

The patent US 5,952,564 describes the braking on an uneven road surface and the occurrence of Bremsrubbeln. The detection of an uneven road surface or vibrations occurring due to brake rubbing is performed by various methods. In particular, the periods of the wheel vibrations, the corrected acceleration, the torque oscillations and the phase measurements and / or the amplitude ratio between wheel acceleration and torque are analyzed and compared with specific threshold values. This information is used to toggle between the ABS operating modes. In particular, the ABS reduces the brake hydraulic pressure in the rough-road mode or selectively increases the brake hydraulic pressure on at least one of the drive wheels.

Only solutions are known from the prior art, with which the robust ABS control can be realized on uneven road surface for an electric vehicle, in each case the actual control algorithm is not fully disclosed.

Object of the present invention is therefore to overcome the disadvantages of the prior art and to provide a system and associated method for desensitizing the drive and brake slip control in electric vehicles with independent wheel drive, with which the required braking and driving power regardless of the road conditions can be realized.

According to the invention, the solution of this problem succeeds with the features of the first and fifth patent claims. Advantageous embodiments of the solution according to the invention are specified in the subclaims.

Details and advantages of the invention will become apparent from the following description part, in which the invention with reference to the accompanying drawings is explained in more detail. It shows:

1 - The basic structure of a drive and brake system of an electric vehicle with independent wheel drive

2 - A block diagram of the unit for controlling the drive and brake slip

3 A block diagram of the desensitization unit

4 An example of processing a wheel acceleration signal to determine the bump index in the desensitization algorithm

5 An example of the unevenness index and the control thresholds for determining an uneven road in the desensitization algorithm

In 1 the basic structure according to the invention of a drive and brake system with an electric brake system and a friction brake system for an electric vehicle with single-wheel drive is shown. It comprises in particular a unit for regulating the drive and brake slip ( 125 ) with the desensitizing function for the normal and uneven roadway. The unit for controlling the drive and brake slip ( 125 ) realizes the functions of determining the required torques at the wheels ( 101 to 104 ) and the corresponding slip control.

Each wheel to be driven ( 101 - 104 ) is with one of the electric motors ( 109 - 112 ) via drive train elements ( 113 - 116 ) connected. The system further includes a friction brake for each wheel ( 117 to 120 ), each having a friction braking torque on the relevant wheel ( 101 to 104 ) generated. The unit for controlling the drive and brake slip ( 125 ) realized in the drive mode of the vehicle movement, the function of the drive control and sends to each electric motor ( 109 to 112 ) Signals for generating a drive torque at the respective wheels ( 101 to 104 ). In the braking mode of the vehicle movement, the unit for controlling the drive and brake slip ( 125 ) the function of the brake control and sends each electric motor ( 109 to 112 ) Signals for generating a combined braking torque at the respective wheels ( 101 to 104 ).

In braking mode, the electric motors ( 109 to 112 ) as generators that store the memory ( 131 ) during the generation of a braking torque on one of the wheels ( 101 to 104 ) provide with renewable electrical energy. An engine control unit ( 123 ) and a brake control unit ( 124 ) define the required demand _torques T _{em_dem_i} and T _{fric_dem_i generated} by the respective electric motors ( 109 to 112 ) and the friction brakes ( 117 to 120 ) will be realized.

Electric motors ( 109 to 112 ) are connected to the memory unit ( 131 ) electrically connected. Depending on the operating mode of the vehicle (drive or braking), the electrical power is either from the memory unit ( 131 ) to the electric motors ( 109 to 112 ) or of the electric motors ( 109 - 112 ) to the storage unit ( 131 ) transferred accordingly. The memory sensor ( 121 ) detects the state of charge of the memory unit ( 131 ). The detected parameters are the charge and discharge current, the temperature of the storage unit, the voltage and other available storage data. The information from the memory sensor ( 121 ) are controlled by the drive and brake slip control unit ( 125 ) as a residual charge of the storage unit ( 131 ) and for limiting the demand _torque T _{em_dem_i of} the electric motors ( 109 to 112 ) used.

On every bike ( 101 to 104 ) are sensors for detecting the rotational speeds of the individual wheels ( 105 to 108 ) assembled. Each sensor ( 105 to 108 ) generated for the unit for controlling the drive and brake slip ( 125 ) in each case a signal of the rotational speed of the corresponding wheel ( 101 to 104 ). The unit for controlling the drive and brake slip ( 125 ) uses this information for the limitation of the demand _torques T _{em_dem_i of} the electric motors ( 109 to 112 ), for the procedure of driving state estimation and for the definition of the desensitization functions of the slip control.

The sensors ( 129 and 127 ) for detecting the position of the driving or brake pedal ( 130 and 128 ) measure the position of the driving or brake pedal ( 130 and 128 ) of the vehicle and create for the unit for controlling the drive and brake slip ( 125 ) each have a signal corresponding to the actual travel or brake pedal travel.

The acceleration sensor ( 126 ) generated for the unit for controlling the drive and brake slip ( 125 ) a signal of the acceleration of the vehicle body ( 122 ) in the direction of travel of the vehicle movement. The information about the acceleration of the vehicle body is in the unit for controlling the drive and brake slip ( 125 ) is used for the driving state estimation.

The following is based on the 2 and 3 the structure of the unit for controlling the drive and brake slip ( 125 ) and the slip control method according to the invention.

2 shows the block diagram of the unit for controlling the drive and brake slip ( 125 ), which realizes the functions of generating the demand torque in the drive and brake modes, the slip control with the desensitization, the driving state estimation, the signal routing and the distribution of the control actions.

In the braking mode of the vehicle movement is in the unit for generating the braking torques ( 214 ) is detected when the driver depresses the brake pedal ( 128 ). In this case, the brake pedal sensor transmits ( 127 ) the information about the brake pedal way. Depending on the brake pedal travel and a number of rules, the unit for generating the braking torques ( 214 ) a total braking _{requirement torque} T _{brk_dem} : T _{brk_dem} = f ₁ (s _brk ) (Equation 1)

The total braking requirement torque is determined as a function of the product of the predetermined vehicle mass m _a and the gravitational acceleration g as follows:

In the drive mode of the vehicle movement is in the unit for generating the drive torque ( 205 ) detected when the driver the accelerator pedal ( 130 ). In this case, the accelerator pedal sensor ( 129 ) the information about the accelerator pedal way. Depending on the accelerator pedal travel and a number of rules, the unit for generating the drive torques ( 205 ) a total _{drive demand torque} T _{drv_dem} : T _{drv_dem} = f ₂ (s _drv ) (Equation 3)

The total drive demand torque is determined as _a function of the product of the given vehicle mass m _a and the gravitational acceleration g as follows:

The signals of the total braking and total _{driving demand torques} T _{brk_dem} and T _{drv_dem} become the mode selector ( 210 ) Delivered which a total demand torque T _{tot_dem} generated therefrom, whereby the total torque demand is defined with a priority for the braking control when both the vehicle and the brake pedal are actuated simultaneously at random by the driver:

The total _{demand torque} T _{tot_dem} is displayed after the mode selector ( 210 ) in the moment distribution unit ( 211 ), which determines the total _{requirement torque} T _{tot_dem} between the wheels ( 101 to 104 ) and the allocated moments T _{allc_i} generated. The torque _limits T _{lim_i} that are generated by the memory unit ( 131 ) and the electric motors ( 109 to 112 ) are determined in the unit for energy management ( 213 ) and continue in the moment distribution unit ( 211 ) used.

The slip control unit ( 204 ) realized in the unit for controlling the drive and brake slip ( 125 ) the ASR and ABS functions by an individual slip control for each wheel ( 101 to 104 ). The slip control unit ( 204 ) comprises a unit for generating a reference _slip s _{ref_i} ( 209 ), the desired slip _value s _{ref_i} , for each wheel ( 101 to 104 ) at given road conditions. For this purpose, the estimated adhesion coefficient μ _{x_i} between the wheel and the roadway in the direction of travel and the estimated value of the normal force F _{z_i} on the wheel is used. Desensitization unit ( 206 ) identifies an uneven road and desensitizes the control in the reaction momentum control unit ( 208 ) to achieve the desired braking or drive efficiency. The reaction torque T _{react_i} is desensitized by the desensitization _factor K _{desens_i} as follows: T _{desens_i} = T _{react_i} K _{desens_i} , where K _{desens_i} ε [0; 1] (Equation 6)

The resulting desensitized reaction _{torque Tdesens_i} is added to the assigned to the respective wheels moments T _{allc_i} taking into account the signs. The result T _{dem_i} is continued in the unit for brake blending ( 212 ) processed. The unit for brake blending ( 212 ) uses a set of rules and the limited moment T _{lim_i} of the unit for energy management ( 213 ) in order to determine the respective demand _torques T _{em_dem_i} and T _{fric_dem_i} for the engine control unit ( 123 ) and the brake control unit ( 124 ) to generate.

The estimated coefficient of adhesion μ _{x_i} , between a wheel and the roadway in the direction of travel, the estimated value of the normal force F _{z_i} to a wheel and the vehicle _speed V _x are determined using an indirect estimation method in the driving state estimator ( 207 ) derived. For this, the current i _{act_i of} the electric motors of the drive train ( 201 ), the actual brake pressure P _{act_i} in the wheel brakes of the friction brake system ( 202 ), the wheel speeds ω _{whl_i} from the sensors ( 105 to 108 ) for detecting the rotational speeds of the wheels and the acceleration of the vehicle body a _{x_act} from the acceleration _sensor ( 126 ) used.

The unit for energy management ( 213 ) uses the signals from the sensors ( 105 to 108 ) for detecting the rotational speeds of the wheels and the storage unit ( 131 ). The output _{limiting torque} T _{lim_i} defines the torque generated by the electric motors ( 109 - 112 ) can possibly be realized.

3 shows a block diagram of the desensitization unit ( 206 ), with the unevenness of the road surface is determined and a correction factor K _{desens_i is} generated, which is for the desensitization of the control in the unit for controlling the reaction torque ( 208 ) is used.

Desensitization unit ( 206 ) receives the signals of the wheel speeds ω _{whl_i} from the sensors ( 105 - 108 ) for detecting the rotational speeds of the wheels. The block ( 301 ) calculates the wheel accelerations by deriving the signals of the wheel speeds ω _{whl_i} . The signal of the wheel accelerations is transmitted directly to the generator of the unevenness index ( 303 ) Via a filter ( 302 ) Posted. The passband of the filter ( 302 ) is determined taking into account the operating frequency of the slip control and the typical road bumps and can be varied in most cases between 15 and 20 Hz.

The generator of the roughness index ( 303 ) uses a set of rules and computes the variable I _{r_i} which determines the road grade for each wheel ( 101 - 104 ). With the aid of the unevenness index I _{r_i} , the classifier of the road surface ( 304 ) about the roadway type and generates the desensitization _factor K _{desens_i} . The desensitization _factor K _{desens_i} and the reaction torque T _{react_i} is used according to the equation 6 for the calculation of the desensitized reaction torque T _{desens_i} .

In 4 the calculation of the unevenness index is shown in the desensitization algorithm. The lower ( 404 ) and upper ( 403 Deadband thresholds become the filtered signal of the wheel acceleration ( 402 ) was added. It is further examined in which area the unfiltered wheel acceleration signal ( 401 ) lies. Is the unfiltered signal ( 401 ) outside the deadband area ( 405 ) between the thresholds ( 404 ) and ( 403 ), the bump index is incremented. The unevenness index is decremented when it is in the deadband area 405 located. The increment I _ins and the decrement I _dec as well as the lower t _low and upper t _up thresholds are specified in the controller. The unevenness index I _{r_i} can then be calculated as follows:

Additional rules and conditions may be used for the increment I _ins and the decrement I _dec . For example, the unevenness index I _{r_i} can only be incremented if the unfiltered wheel acceleration ( 401 ) a transition from the lower ( 404 ) to the upper ( 403 ) Threshold of the dead band area ( 405 ) he follows.

The unevenness starting index is determined by the lower I _low and upper I _up saturation limits:

5 shows an example of a roughness index I _{r_i} and the control thresholds for determining an uneven road in the desensitization algorithm.

The unevenness index I _{r_i} ( 505 ) varies between the lower ( 504 ) and upper ( 503 ) Saturation limits. Various methods can be used for the determination of desensitization factor. In the simplest case, the desensitization _factor K _{desens_i has} two states that correspond to a flat and uneven road surface. Is the bump index I _{r_i} below the threshold ( 505 ), the desensitization is inactive and the desensitization _factor K _{desens_i} equals 1. If the unevenness index I _{r_i reaches} the threshold ( 505 ), the desensitization _factor K _{desens_i is} equal to a predetermined value K _{desens_act} in the controller. Once the threshold ( 505 ) corresponds to a variable t _{h desens} in the controller, the control law can be defined as follows:

Optionally, the desensitization _factor K _{desens_i} may be _calculated as a function of the _bump index I _{r_i} : Kdesens_i = ζ (I _{r_i} ) (Equation 10)

This desensitization process is characterized by several smooth transients of reaction momentum on an uneven road surface.

LIST OF REFERENCE NUMBERS

101-104

wheel

105-108

Sensor for detecting the rotational speeds of the wheels

109-112

electric motors

113-116

Powertrain elements

117-120

friction brakes

121

Sensor for detecting the state of the storage unit

122

vehicle body

123

Engine control unit

124

Brake control unit

125

Unit for controlling drive and brake slip

126

Sensor for detecting the acceleration of the vehicle body

127

Sensor for detecting the position of the brake pedal

128

brake pedal

129

Sensor for detecting the position of the accelerator pedal

130

accelerator

131

storage unit

201

_Current i _{act_i of} the electric motors of the drive _trains

202

p _{act_i}

203

Wheel rotation speed ω _{whl_i}

204

Slip control unit

205

Unit for generating drive torque

206

Desensibilisierungseinheit

207

Driving state estimator

208

Unit for controlling the reaction torque

209

Unit for generating a reference slip

210

mode selector

211

Unit for moment distribution

212

Unit for brake blending

213

Unit for energy management

214

Unit for generating the braking torques

301

Block for calculating the wheel accelerations

302

filter

303

Generator of Rub Index

304

Classifier of the road surface

401

unfiltered signal of the wheel acceleration

402

filtered signal of the wheel acceleration

403

upper dead band threshold

404

lower deadband threshold

405

deadband

501

??

502

??

503

upper saturation limit of the unevenness index I _{r_i}

504

lower saturation limit of the unevenness index I _{r_i}

505

Rub Index I _{r_i}

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

• US 5522652 [0003]
• US 5627755 [0004]
• US 6952637 [0005]
• US 7591170 [0006]
• US 7739019 [0007, 0007]
• US 2013/080014 A1 [0009]
• US 5952564 [0011]

Claims (8)

System for desensitizing traction and brake slip control in electric single-wheel drive vehicles comprising: 131 ) for loading or unloading with electrical energy, • for each wheel to be driven ( 101 - 104 ) each have an electric motor ( 109 - 112 ) for generating an electrical drive or braking torque and a friction brake ( 117 - 120 ) for generating a Reibbremsmomentes, • sensor units for detecting the state of the memory unit ( 121 ), the position of a brake pedal ( 127 ), the rotational speeds of the individual wheels ( 105 - 108 ) and the acceleration of the vehicle body ( 126 ) in the direction of travel and • a brake control unit ( 124 ) for determining the friction braking torque and the electric braking torque to the respective wheel ( 101 - 104 ), characterized in that the system comprises a unit for controlling the drive and brake slip ( 125 ) for each individual wheel ( 101 - 104 ), with which: • the generation of required torques in the drive and braking modes, • the desensitization of the slip control taking into account uneven roads, • the driving state estimation, • the signal routing and • the distribution of the control actions are feasible. System according to claim 1, characterized in that the unit for controlling the drive and brake slip ( 125 ) a vehicle condition determination unit ( 207 ), a unit for energy management ( 213 ), one unit each for generating drive and braking torques ( 205 ) 214 ), a unit for selecting the operating mode ( 210 ), a slipper control unit ( 204 ), a moment distribution unit ( 211 ) and a unit for generating a combined braking torque ( 212 ) having. System according to claim 2, characterized in that the control unit for slippage ( 204 ) a unit for generating a reference slip ( 209 ), a unit for controlling the reaction torque ( 208 ) and a Desensitization Unit ( 206 ) having. System according to claim 3, characterized in that the unit for desensitization ( 206 ) a road surface classification unit ( 304 ) and a unit for generating a roughness index I _{r_i} ( 303 ). Method for desensitizing the traction and brake slip control in electric single-wheel drive vehicles with a system according to one of claims 1 to 4, comprising the steps of: detecting the drive and brake demand _torques T _{drv_dem} and T _{brk_dem generated} by the electric motors ( 109 - 112 ) and the friction brakes ( 117 - 120 ) on each wheel ( 101 - 104 ) are to be generated; • determination of the total _{demand torque} T _{tot_dem} ; • Distribution of the total _{requirement torque} T _{tot_dem} on the individual wheels ( 101 - 104 ); • Calculation of the reference _slip s _{ref_i} for each wheel ( 101 - 104 ) taking into account an estimated adhesion coefficient μ _xi between the respective wheel and the roadway in the road direction and an estimated normal force F _zi on the respective wheel; Determination of the current wheel slip s _{act_i} for each wheel ( 101 - 104 ) from the acceleration of the vehicle body a _{x_act} , the current brake pressure P _{act_i} , the current strength of the electric motors i _{act_i} and the wheel speeds ω _{whl_i} ; • calculation of the reaction torque T _{react_i} for each wheel from the reference slip s _{ref_i,} the current wheel slip s _{act_i} and the vehicle speed V _x; • calculation of the desensitization _factor K _{desens_i} as a function of the road surface unevenness; • Calculation of the desensitized reaction _moments T _{desens_i} for each wheel ( 101 - 104 ) by multiplication of the respective reaction torque T _{react_i} with the respective desensitization _factor K _{desens_i} ; • calculation of the demand _torques T _{dem_i} for each wheel ( 101 - 104 ) by adding the reaction torque T _{react_i} and the _shared demand _torques T _{allc_i} , taking into account the respective signs; and • division of the generated demand _torque T _{dem_i} for each wheel ( 101 - 104 ) between the electric motors ( 109 - 112 ) and the friction brakes ( 117 - 120 ). A method according to claim 5, characterized in that in the case of a simultaneous actuation of the driving and brake pedal, the total _{demand torque} T _{tot_dem is defined} with a priority for the brake control. Method according to one of claims 5 or 6, characterized in that the desensitization _factor K _{desens_i is adjusted} according to predefined control _laws , wherein an estimated _bump index is used. Method according to one of claims 5 or 6, characterized in that the desensitization _factor K _{desens_i is calculated} as a function of the unevenness index I _{r_i} .

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