Patent Application
20070038340
1. Field of the Invention
The present invention relates to a running controller and an electric running control system for an electric vehicle, such as an electric car or a hybrid car, in which at least one of wheels of the vehicle is driven by a motor for running of the vehicle.
2. Description of the Related Art
In one example of known electric vehicles, such as electric cars or hybrid cars, each of which employs a motor as a driving source, a motor output and a regenerative braking force are controlled depending on the difference in rotation speed between a drive wheel and a driven wheel, thereby eliminating a wheel slip in a motor driving mode and a regenerative braking mode, as disclosed in JP-UA-5-2501.
With the motor braking/driving control as disclosed in JP-UA-5-2501, however, the following problem occurs because the motor output and the regenerative braking force are controlled depending on the difference in rotation speed between the drive wheel and the driven wheel.
A tire braking/driving force F is expressed by the following formula (1);
F=μ×W (1)
where μ is the coefficient of road friction, and W is the load of tire contact.
Further, in the relationship between the coefficient μ of road friction and the tire slip rate, a slip rate providing a maximum value μmax of the coefficient of road friction varies depending on road conditions. In order to always maximize the acceleration/deceleration performance, the driving/braking force is preferably controlled such that the coefficient μ of road friction has a maximum value. With the motor braking/driving control as disclosed in JP,U 5-2501, however, because the motor control is performed depending on the difference in rotation speed between the drive wheel and the driven wheel, it is impossible to perform the control in such a manner as always providing the maximum coefficient μ of road friction in all of the road conditions.
An object of the present invention is to provide a running controller and an electric running control system for an electric vehicle, in which when a tire slip occurs during running of the vehicle, such as under driving, braking and turning, a motor output is controlled to always maximize the coefficient μ of road friction, thereby obtaining a maximum tire driving force and a maximum tire braking force.
(1) To achieve the above object, the present invention provides a running controller for an electric vehicle in which a wheel is driven and braked through control of an electric driving apparatus including a motor, wherein the running controller includes a control unit for executing powering and regenerative control of the motor to change, depending on road conditions, a target value to which a slip rate is to be converged, when slipping of the wheel is detected.
With that feature, when a tire slip occurs during running of the vehicle, a maximum tire driving force and a maximum tire braking force can be obtained.
(2) In above (1), preferably, the control unit calculates the coefficient μ of road friction based on a motor current and executes the powering and regenerative control of the motor such that the calculated coefficient μ of road friction is maintained in the vicinity of a maximum value thereof.
(3) In above (2), preferably, the control unit performs regenerative braking of the motor of the electric driving apparatus when slipping of the wheel is detected in a state of the electric vehicle being driven by the motor of the electric driving apparatus; the control unit performs powering control of the motor of the electric driving apparatus when a reversal of a value of the coefficient μ of road friction from an increase to a decrease is detected during the regenerative braking; and the control unit performs regenerative braking of the motor of the electric driving apparatus again when a reversal of a value of the coefficient μ of road friction from an increase to a decrease is detected during the powering control.
(4) In above (3), preferably, the electric vehicle drives a wheel by an engine having an electronic throttle valve; and when slipping of the wheel driven by the engine is detected, the control unit controls the electronic throttle valve in a valve closing direction until the slipping of the wheel is suppressed, thereby reducing an output of the engine, and the control unit executes the powering and regenerative control of the motor such that the coefficient μ of road friction is maintained in the vicinity of the maximum value thereof.
(5) In above (4), preferably, when the electronic throttle valve is substantially fully closed as a result of controlling the electronic throttle valve in the valve closing direction until the slipping of the wheel is suppressed, the control unit stops the engine and drives the wheel for running of the electric vehicle by the motor of the electric driving apparatus.
(6) In above (3), preferably, the electric vehicle includes a steering angle sensor for detecting a steering angle applied from a driver; the electric driving apparatus drives a pair of left and right wheels independently of each other; the control unit executes the powering and regenerative control of the motor of the electric driving apparatus such that the calculated coefficient μ of road friction is maintained in the vicinity of the maximum value thereof, when slipping of any one of the pair of left and right wheels is detected; and the control unit sets motor torque for driving non-slipping one of the pair of left and right wheels to be substantially equal to motor torque for driving the other wheel when straightforward running of the electric vehicle is detected based on a signal from the steering angle sensor.
(7) In above (2), preferably, the control unit weakens a regenerative braking force of the motor of the electric driving apparatus when slipping of the wheel is detected in a state of the electric vehicle being braked by motor regenerative braking in the electric driving apparatus; the control unit strengthens the regenerative braking force of the motor of the electric driving apparatus when a reversal of a value of the coefficient μ of road friction from an increase to a decrease is detected after weakening the regenerative braking force; and the control unit weakens the motor regenerative braking force again when a reversal of a value of the coefficient μ of road friction from an increase to a decrease is detected after strengthening the motor regenerative braking force.
(8) In above (7), preferably, the electric vehicle includes a steering angle sensor for detecting a steering angle applied from a driver; the electric driving apparatus drives a pair of left and right wheels independently of each other; the control unit executes the regenerative control of the motor of the electric driving apparatus such that the calculated coefficient μ of road friction is maintained in the vicinity of the maximum value thereof, when slipping of any one of the pair of left and right wheels is detected; and the control unit sets motor regenerative torque in the electric driving apparatus for braking non-slipping one of the pair of left and right wheels to be substantially equal to motor regenerative torque for braking the other wheel when straightforward running of the electric vehicle is detected based on a signal from the steering angle sensor.
(9) In above (3) or (7), preferably, when turning of the electric vehicle is detected based on the signal from the steering angle sensor, the control unit gives a difference in motor driving torque or regenerative torque between left and right electric driving apparatuss to generate a vehicle turn moment due to the torque difference, thereby assisting the electric vehicle to turn; and when the control unit controls, upon detection of slipping of any one of the pair of left and right wheels, the motor torque generated by the motor of each of the electric driving apparatuss such that the calculated coefficient μ of road friction is maintained in the vicinity of the maximum value thereof, the control unit modifies the motor torque of the other non-slipping wheel such that a target turn moment set depending on the steering angle is obtained.
(10) Also, to achieve the above object, the present invention provides an electric running control system for an electric vehicle in which a wheel is driven and braked through control of an electric driving apparatus including a motor, the electric running control system comprising the electric driving apparatus; a motor control unit for controlling electric power supplied to the electric driving apparatus; and a running controller for controlling the motor control unit, the running controller including a control unit for executing powering and regenerative control of the motor to change, depending on road conditions, a target value to which a slip rate is to be converged, when slipping of the wheel is detected.
With those features, when a tire slip occurs during running of the vehicle, a maximum tire driving force and a maximum tire braking force can be obtained.
According to the present invention, when a tire slip occurs during running of the vehicle, the motor output is controlled to always maximize the coefficient μ of road friction, thereby obtaining the maximum tire driving force and the maximum tire braking force.
The construction and operation of a running controller and an electric running control system for an electric vehicle according to one embodiment of the present invention will be described below with reference to
The internal combustion engine is a motive power source for outputting motive power with burning of fuel and is, for example, a gasoline engine, a diesel engine, or a gas engine gaseous fuel, such as hydrogen gas. In the following description, the internal combustion engine is referred to simply as the engine.
First, the construction of the electric vehicle equipped with the running controller and the electric running control system for the electric vehicle according to one embodiment will be described below with reference to
The electric vehicle shown in
An output from the engine 1 and the motor 2 coupled to an engine crankshaft is increased or decreased in speed by a transmission 3 and drives the pair of front wheels 4 and 5 through a differential mechanism disposed inside the transmission 3. The electric driving apparatuss 8 and 9 are coupled to the left and right rear wheels 6, 7 and drive the left and right rear wheels 6, 7, respectively.
The rotation speed of the engine 1 is controlled by an engine control unit (E-CU) 26. The engine control unit (E-CU) 26 controls the engine 1 in accordance with an accelerator opening signal detected by an accelerator opening sensor 22, a signal from an electronic throttle valve position sensor disposed in an electronic throttle body (ETB) (or valve) 14, an engine rotation speed signal, and an engine cooling water temperature signal. The engine control unit (E-CU) 26 controls the electronic throttle body (ETB) 14 to change the opening of a throttle valve, thereby controlling the amount of air taken into the engine 1. The engine control unit (E-CU) 26 also controls a fuel injection valve (INJ) 15, thereby controlling the fuel injection amount supplied to the engine 1.
A transmission control unit (TM-CU) 27 controls a gear ratio of the transmission 3 depending on the vehicle running state.
An inverter (INV) 30 comprises three motor control units (M-CU) 28 and three semiconductor switching devices in the form of IGBTs (Insulated Gate Bipolar Transistors) 29. The three motor control units (M-CU) 28 control respectively the three semiconductor switching devices in the form of IGBTs (Insulated Gate Bipolar Transistors) 29. DC power of a battery (BAT) 32 is converted to AC power that is supplied to the motor 2 and the respective motors inside the electric driving apparatuss 8 and 9, thereby controlling output torques of those motors. Each of the motors is, for example, a 3-phase synchronous motor. During regenerative braking, output power of each motor is converted to DC power that is accumulated in the battery 32.
An engine-stability-control control unit (ESC-CU) 31 detects wheel locked states based on respective wheel speeds detected by wheel speed sensors 17, 18, 19 and 20 which are disposed in association with the wheels 4, 5, 6 and 7. In the event of a slip, an engine-stability-control actuator (ESC-Act) 16 controls brakes 10, 11, 12 and 13 disposed in association with the wheels 4, 5, 6 and 7. Namely, the engine-stability-control control unit (ESC-CU) 31 serves as the so-called anti-brake system (ABC) to control the brakes.
Further, the engine-stability-control control unit (ESC-CU) 31 detects wheel slip states during running of the vehicle, such as under driving, braking and turning, based on the respective wheel speeds detected by the wheel speed sensors 17, 18, 19 and 20, and then executes driving control or regenerative braking control of the motor 2 and the motors inside the electric driving apparatuss 8 and 9. In other words, the engine-stability-control control unit (ESC-CU) 31 corresponds to the running controller for the electric vehicle according to the embodiment. Also, the engine-stability-control control unit (ESC-CU) 31, the inverter 30, and the electric driving apparatuss 8 and 9 constitute the electric running control system for the electric vehicle according to the embodiment.
When the engine-stability-control control unit (ESC-CU) 31 controls the engine 1, it outputs a control command to the engine control unit (E-CU) 26, whereupon the engine control unit (E-CU) 26 controls the engine 1 in accordance with the control command. Also, when the engine-stability-control control unit (ESC-CU) 31 controls each motor, it outputs a control command to the corresponding motor control units (M-CU) 28, whereupon the motor control units (M-CU) 28 controls the motor in accordance with the control command. Details of running control by the engine-stability-control control unit (ESC-CU) 31 will be described later with reference to
The engine-stability-control control unit (ESC-CU) 31 determines based on a signal from a brake depressing force sensor 23 whether a brake pedal is depressed and how degree the brake pedal is depressed, thereby determining, for example, whether the vehicle is under braking. Also, the engine-stability-control control unit (ESC-CU) 31 determines based on a signal from a steering angle sensor 21 whether the vehicle runs straightforward or turns. In addition, the engine-stability-control control unit (ESC-CU) 31 detects the vehicle speed from an output of an acceleration/-deceleration sensor 24.
The engine control unit (E-CU) 26, the transmission control unit (TM-CU) 27, the motor control units (M-CU) 28, and the engine-stability-control control unit (ESC-CU) 31 are controlled by a higher-level hybrid electric vehicle control unit (HEV-VU) 25 in an integrated manner.
When the vehicle is driven, the rotation speed of the engine 1 and the motor 2 coupled to the engine crankshaft is increased or decreased by the transmission 3, and the pair of front wheels 4 and 5 are driven through the differential mechanism disposed inside the transmission 3. The electric driving apparatuss 8 and 9 are coupled to the left and right rear wheels 6, 7, whereby the left and right rear wheels 6, 7 are driven by the electric driving apparatuss 8 and 9, respectively.
When the vehicle is braked, the pair of front wheels 4 and 5 are braked by a resultant force generated from the hydraulic brakes 10 and 11 associated with the left and right front wheels 4, 5 and the regenerative braking of the motor 1 coupled to the engine crankshaft. Also, the pair of rear wheels 6 and 7 are braked primarily by the regenerative braking of the motors constituting the pair of electric driving apparatuss 8 and 9 associated with the left and right rear wheels 6, 7, respectively, and additionally by the hydraulic brakes 12 and 13.
One construction of the electric driving apparatus 8 used in the electric running control system for the electric vehicle according to the embodiment will be described below with reference to
The electric driving apparatus 8 comprises a motor 101 and a reduction gearing 102. The reduction gearing 102 is constituted by a planetary gearing made up of a sun gear 103, a ring gear 104, a plurality of pinion gears 105 meshing with the sun gear 103 and the ring gear 104, and a carrier 106 supporting the plurality of pinion gears 105 in such a manner that each pinion gear is able to rotate about its own axis and to revolve around the sun gear 103.
A motor shaft 107 is coupled to the sun gear 103, and the ring gear 104 is coupled to a reduction gearing case 108 to be fixed in an un-rotatable manner. The carrier 106 is coupled to a drive shaft 109. With such an arrangement, rotation of the motor 101 drives a tire 6 through the drive shaft 109 while the rotation speed is reduced.
While in the illustrated example the reduction gearing is constituted by one set of planetary gearing, the number of sets of planetary gearing is not limited to one. The reduction gearing may be constituted by a plurality of planetary gearings to provide a larger reduction ratio of the reduction gearing. Also, while the sun gear 103, the ring gear 104, and the carrier 106 are coupled respectively to the motor shaft 107, the case 108, and the drive shaft 109, an arrangement is not limited to such a combination and can be modified to other suitable combination so long as the rotation speed of the motor shaft is reduced. Further, while the illustrated electric driving apparatus is constituted as a single-pinion planetary gearing, it may be a double-pinion planetary gearing.
Another construction of the electric driving apparatus used in the electric running control system for the electric vehicle according to the embodiment will be described below with reference to
An electric driving apparatus 8A shown in
The motor shaft 107 is coupled to the carrier 116 through the sun gear 113 and a clutch 119. The ring gear 114 is coupled to a case 121 of the electric driving apparatus through a bi-directional brake 120. The carrier 116 is coupled to the drive shaft 109. The clutch 119 can be, e.g., an electromagnetic clutch or a hydraulic clutch. The bi-directional brake 120 is, e.g., an electromagnetic brake.
In the transmission 112 having the above-described arrangement, a first-speed gear stage (first shift stage) and a second-speed gear stage (second shift stage) are selectively established by controlling engagement and disengagement of the clutch 119 and engagement and disengagement of the bi-directional brake 120. A specific speed change ratio γ (=input shaft rotation speed Nin/output shaft rotation speed Nout) is assigned to each gear stage. For example, the first-speed gear stage (first shift stage) is established by disengaging the clutch 119 and engaging the bi-directional brake 120 so as to prevent the ring gear 114 from rotating in the reversed direction with the rotation of the motor 101 coupled to the sun gear 113. The second-speed gear stage (second shift stage) is established by engaging the clutch 119 such that the planetary gearing 112 is integrally rotated and the bi-directional brake 120 is automatically disengaged.
The vehicle is driven in reverse by rotating the motor 101 in the reversed direction. During the backing-up, because the vehicle speed is low, the vehicle can be driven only in the first-speed gear stage (first shift stage) with the clutch 119 disengaged. Incidentally, the arrangement of the transmission 112 is not limited to the above-described one.
Still another construction of the electric driving apparatus used in the electric running control system for the electric vehicle according to the embodiment will be described below with reference to
While the motor 101 of the electric driving apparatus 8 shown in
Still another construction of the electric driving apparatus used in the electric running control system for the electric vehicle according to the embodiment will be described below with reference to
While the motor 101 of the electric driving apparatus 8 shown in
The following description is made of (1) control of the engine and the motor in the event of a tire slip when the vehicle is driven, (2) control of the motor in the event of a tire slip when the vehicle is braked, and (3) control of the motor in the event of a tire slip when the vehicle is turned, which are executed by the running controller in the system shown in
First, the contents of control of the engine and the motor in the event of a tire slip when the vehicle is driven, the control being executed by the running controller for the electric vehicle according to the embodiment, will be described below with reference to
With reference to
The control process of
First, in step S001, the ESC-CU 31 reads various signals representing (1) the engine driving force and the motor driving force calculated by the HEV-CU 25, (2) the motor rotation speeds detected by motor rotation speed sensors disposed in the electric driving apparatuss 8 and 9, (3) the motor currents detected by motor current sensors disposed in the electric driving apparatuss 8 and 9, and (4) the wheel speeds detected by the wheel speed sensors 17, 18, 19 and 20.
The engine driving force and the motor driving force in above (1) are calculated by the HEV-CU 25 as follows. By using the map of the accelerator opening versus the demanded driving torque shown in
Then, in step S002, the ESC-CU 31 calculates the coefficient μ of road friction in accordance with the following formula (2);
μ=|(Tmotor−I×α)/(r×W)| (2)
where Tmotor is the motor torque, I is the inertial moment between a motor rotor and a tire, α is the angular acceleration of the motor rotation, r is the radius of the tire, and W is the wheel load.
The motor torque Tmotor is calculated from the motor current read in step S001. The angular acceleration a of the motor rotation is calculated from the rotation speed that is detected by a motor rotation sensor and is read in step S001. The inertial moment I between the motor rotor and the tire, the radius r of the tire, and the wheel load W are stored in ROM inside CPU of the HEV-CU 25. The wheel load can be obtained with a sensor for detecting the road contact load that acts on each of the left and right front wheels and left and right rear wheels.
Then, in step S003, the ESC-CU 31 determines whether any drive wheel is slipped. In the case of a four-wheel-drive vehicle, a wheel slip is determined by calculating the vehicle speed VSP from the longitudinal acceleration sensor 24, and comparing the calculated vehicle speed VSP with the wheel speeds detected by the wheel speed sensors 17, 18, 19 and 20 associated with the respective drive wheels. When any of the wheel speeds is higher than the vehicle speed VSP, this condition is regarded as meaning that the relevant wheel is slipped.
If it is determined that the drive wheel is slipped, a HEV-TCS (Hybrid-Electric-Vehicle Traction Control) subroutine is executed in step S004, and a MOTOR-TCS (Motor Traction Control) subroutine is executed in step S005. Thereafter, the end of slip control is determined in step S006. In the HEV-TCS subroutine, when the slip state is determined, the engine 1 is controlled so as to suppress the slip. Details of the HEV-TCS subroutine will be described later with reference to
In step S006, the motor demand torque Tdemand read in step S001 is compared with driving torque Tdrive obtained through MOTOR-TCS control (described later), and the end of the slip control is determined when Tdemand=Tdrive is confirmed. Additionally, if it is determined in step S003 that no slip occurs, the main routine of
With reference to
First, in step S101, the E-CU 26 reads various signals, such as the accelerator position sensor signal, the electronic throttle valve position sensor signal, the engine rotation speed sensor signal, and the engine cooling water temperature signal. The accelerator position sensor signal is obtained from the accelerator opening sensor 22. The electronic throttle valve position sensor signal is obtained from the position sensor disposed in the electronic throttle body (ETB) (or valve) 14. The engine rotation speed signal is obtained from the engine rotation speed sensor disposed in association with the engine 1. The temperature of engine cooling water signal is obtained from the engine cooling water temperature sensor disposed in association with the engine 1.
Then, in step S102, the E-CU 26 determines based on the engine rotation speed sensor signal, for example, whether the engine is started. If the engine is started, the control flow proceeds to step S103.
In step S103, the E-CU 26 determines whether any of the pair of left and right wheels driven by the engine driving force is slipped. In the case of the system shown in
If the wheel slip is determined in step S103, the control flow proceeds to step S104 in which the E-CU 26 controls the electronic throttle valve 14 in the closing direction until the wheel slip is suppressed. In other words, by closing the electronic throttle valve 14, the intake air amount is reduced and so is the output torque of the engine 1. As a result, the driving torque of the front wheel is reduced to lower the front wheel speed, thereby suppressing the slip.
In step S105, the E-CU 26 determines whether the electronic throttle valve 14 is fully closed. If the electronic throttle valve 14 is fully closed, the control flow proceeds to step S106 in which the E-CU 26 determines the warm-up state of the engine. If the temperature of the engine cooling water is higher than a setting value, this condition means the completion of engine warm-up, and therefore the control flow proceeds to step S107. In step S107, the E-CU 26 determines whether the motor is generating power at that time. If the motor is not generating power, the control flow proceeds to step S108 in which the engine 1 is stopped. Stated another way, when the engine is not in any state of vehicle driving, warm-up and power generation, the engine is stopped to prevent wasteful consumption of fuel by the engine. With the stop of the engine 1, the output torque of the engine 1 becomes 0 and the rotations of the front wheels 4 and 5 are stopped. As a result, the slips of the front wheels can be avoided.
On the other hand, if it is determined in step S103 that both of the pair of left and right wheels driven by the engine driving force are not slipped, or if it is determined in step S105 that the electronic throttle valve 14 is not fully closed, or if it is determined in step S106 that the temperature of the engine cooling water is lower than the setting value, or if it is determined in step S107 that the motor is generating power, the engine is not stopped.
Then, in step S109, the E-CU 26 refers to the result of the determination in step S006. If the end of slip control is determined, the E-CU 26 reads the results of the control for the engine and motor driving forces executed by the HEV-CU 25 via CAN (Controlled Area Network) 33 in step S110. In accordance with those control results, the E-CU 26 controls the engine in step S111. Thereafter, the HEV-TCS subroutine is brought to an end. Stated another way, if the end of slip control is determined in step S006, this means that the slip has been suppressed. Hence the E-CU 26 controls the engine in an ordinary manner in the same condition as that before the occurrence of the slip in step S111.
Further, even if it is determined in step S109 that the slip control is not yet completed, the HEV-TCS subroutine is brought into an end.
With reference to
First, in step S201, the M-CU 28 determines whether any of the wheels driven by the motors, i.e., any of the rear wheels 6 and 7, is slipped. In the case of the system shown in
If any of the rear wheels is slipped, the control flow proceeds to step S202 in which the M-CU 28 performs motor regenerative braking control to suppress the wheel slip. Regenerative braking torque applied at that time is given as torque obtained by subtracting a setting value from the driving torque detected at the time of occurrence of the slip. In step S203, the M-CU 28 sets a regenerative braking flag Re-Flag to be on.
Then, in step S204, the M-CU 28 determines whether the regenerative braking flag Re-Flag is set to be on or off. Because the regenerative braking flag Re-Flag=ON is set in step S203, the control flow proceeds to step S205 after the determination in step S204 in the first cycle.
Then, in step S205, the M-CU 28 differentiates the coefficient μ of road friction calculated in step S002 (to obtain a derivative value Δμ), and determines whether the derivative value is positive or negative. If Δμ≧0 is determined, i.e., if it is determined that the coefficient μ of road friction is increasing or remains maintained, the M-CU 28 refers, in step S206, to the determination result in step S006 of
When the coefficient μ of road friction exceeds a maximum value and starts to reduce, the M-CU 28 determines Δμ<0 in step S205, followed by proceeding to step S207.
In step S207, the M-CU 28 executes driving force ramp control expressed by the following formula (3);
Trdrive=Trmin+Tlamp×t (3)
where Trdrive is the driving torque, Trmin is the initial torque during powering in the TCS control, Tlamp is the torque increase amount, and t is the lapsed time. The initial torque Trmin during powering is calculated from the motor torque immediately before the detection of the slip.
Then, in step S208, the M-CU 28 sets the Re-Flag to be off. Thereafter, in step S206, the M-CU 28 refers to the determination result in step S006 of
Because the motor is now under the driving force ramp control in step S207, the driving torque is gradually increased and the wheel slip is also gradually increased. In step S209, the M-CU 28 determines whether the derivative value of μ is positive or negative. If Δμ≧0 is determined, the control flow proceeds to step S206 in which the motor driving force ramp control is continued. If the driving force is increased and the slip rate is increased correspondingly with the continued control, the coefficient μ of road friction is reduced while changing from a region (1) to (2) in
Then, the M-CU 28 sets Re-Flag=ON in step S211 and refers, in step S206, to the determination result in step S006 of
As described above, by repeating the motor regenerative braking control and the motor driving force ramp control until the end of the slip control is determined in step S006, the motor driving/regenerative force control is executed such that the coefficient μ of road friction varies in the vicinity of its maximum value. Consequently, the vehicle is always able to run with the driving force in the vicinity of its maximum value.
The relationship between the slip rate and the coefficient μ of road friction depending on differences in the road condition will be described below with reference to
In the graph of
Although the coefficient μ of road friction is maximized at the slip rate in the range of 10 to 20%, the slip rate at which the coefficient μ of road friction is maximized differs depending on the road conditions A-E. For example, under the road condition A of a smooth icy surface, the slip rate at which the coefficient μ of road friction is maximized is about 7%, while under the road condition E of a dried asphalt surface, it is about 22%.
In the embodiment, as described above with reference to
Further, in the embodiment, when only one of the rear wheels in the system of
Moreover, when the motor driving force is controlled to drive the pair of front wheels in the system shown in
With reference to
The control process of
First, in step S301, the ESC-CU 31 reads various signals representing each motor rotation speed, each motor current, and each wheel-speed brake SW. The motor rotation speed is detected by the motor rotation speed sensor associated with each of the electric driving apparatuss 8 and 9. The motor current is detected by the motor current sensor associated with each of the electric driving apparatuss 8 and 9. The on/off-state of each wheel-speed brake SW is detected by the brake depressing force sensor 23.
Then, in step S302, the ESC-CU 31 determines whether the brake SW is turned on or off. If the brake SW is turned off, this main routine is brought to an end. If the brake SW is turned on, the control flow proceeds to step S303 in which the motor is subjected to the regenerative braking control to obtain demanded braking torque Tddemand that is required to produce a braking force depending on the brake depressing force.
Then, in step S304, the ESC-CU 31 calculates the coefficient μ of road friction in accordance with the following formula (4);
μ=|(Trmotor−I×α)/(r×W)| (4)
where Trmotor is the motor regenerative braking torque, I is the inertial moment between the motor rotor and the tire, α is the angular acceleration of the motor rotation, r is the radius of the tire, and W is the wheel load.
The motor regenerative braking torque Trmotor is calculated from the motor current detected by the current sensor. The angular acceleration α of the motor rotation is calculated from the rotation speed detected by the motor rotation sensor. The inertial moment I between the motor rotor and the tire, the radius r of the tire, and the wheel load W are stored in the ROM inside the CPU of the HEV-CU 25. The wheel load can be obtained with the sensor for detecting the road contact load that acts on each of the left and right front wheels and left and right rear wheels.
Then, in step S305, the ESC-CU 31 determines whether any wheel (tire) is slipped. A wheel slip is determined by calculating the vehicle speed VSP from the longitudinal acceleration sensor 24, and comparing the calculated vehicle speed VSP with the wheel speeds detected by the wheel speed sensors 17, 18, 19 and 20 associated with the respective wheels.
If it is determined that the wheel is slipped, a MOTOR-ABS (Motor Anti-lock Brake System) subroutine is executed in step S306, and the end of slip control is determined in step S307. Details of the MOTOR-ABS subroutine will be described later with reference to
The principal control contents of the MOTOR-ABS subroutine will be described below with reference to FIG. 14. The MOTOR-ABS subroutine is executed by the M-CU 28 for controlling each of the motors in the electric driving apparatuss 8 and 9.
First, in step S401, the M-CU 28 determines whether any of the rear wheels 6 and 7 is slipped. If both of the rear wheels are not slipped, this subroutine is brought to an end. If any of the rear wheels is slipped, the control flow proceeds to step S402.
In step S402, the M-CU 28 reduces the motor regenerative braking torque (force) to a setting value stored in ROM inside the M-CU 28. The setting value is set depending on the coefficient μ of road friction at the time of detection of the slip. The smaller the coefficient μ of road friction at the time of detection of the slip, the smaller is the setting value. Because the motor regenerative braking torque is reduced, the wheel slip is suppressed.
Then, in step S403, the M-CU 28 sets a motor regenerative braking torque down-flag Dn-Flag to be on. Thereafter, in step S404, the M-CU 28 determines whether the motor regenerative braking torque down-flag Dn-Flag is set to be on or off. Because the motor regenerative braking torque down-flag Dn-Flag=ON is set in step S403, the control flow proceeds to step S405 after the determination in step S404 in the first cycle.
Then, in step S405, the M-CU 28 differentiates the coefficient μ of road friction and determines whether the derivative value Δμ is positive or negative. If Δμ≧0 is determined, i.e., if it is determined that the coefficient μ of road friction is increasing or remains maintained, the M-CU 28 refers, in step S406, to the determination result in step S307 of
In this case, the Dn-Flag is still kept on, and therefore the control flow proceeds to step S405. Because the motor regenerative braking torque is in a reduced state at that time, the slip in braking the wheel is suppressed and the slip rate is varied toward 0. In other words, the coefficient μ of road friction is changed from the region (3) to (4) in
When the coefficient μ of road friction exceeds a maximum value and starts to reduce, the M-CU 28 determines Δμ<0 in step S405, followed by proceeding to step S407.
In step S407, the M-CU 28 restores the regenerative torque so that the motor regenerative braking torque is equal to the demanded braking torque Tddemand. In step S408, the M-CU 28 sets the Dn-Flag to be off. Thereafter, in step S406, the M-CU 28 refers to the determination result in step S307 of
Because the regenerative torque is gradually increased, the wheel slip is also gradually increased. In step S409, the M-CU 28 determines whether the derivative value of the coefficient μ of road friction is positive or negative. If Δμ≧0 is determined, the control flow proceeds to step S406 in which the motor braking force ramp control is continued. If the braking force is increased and the slip rate is increased correspondingly with the continued ramp control, the coefficient μ of road friction is reduced while changing from the region (1) to (2) in
Then, the M-CU 28 sets Dn-Flag=ON in step S411 and refers, in step S406, to the determination result in step S307 of
As described above, by repeating the motor regenerative braking-force reduction control and the motor regenerative braking-force ramp control until the end of the slip control is determined in step S307, the motor regenerative torque control is executed such that the coefficient μ of road friction varies in the vicinity of its maximum value. In other words, taking into account the various road conditions shown in
When only one of the rear wheels in the system of
Further, when the motor regenerative braking torque is controlled to brake the pair of front wheels in the system shown in
With reference to
The control process of
First, in step S501, the ESC-CU 31 reads various signals representing the steering angle, the accelerator opening, the on/off-state of each wheel-speed brake SW, and the brake depressing force. The steering angle is detected by the steering angle sensor 21. The accelerator opening is detected by the accelerator opening sensor 22. The on/off-state of each wheel-speed brake SW and the brake depressing force are detected by the brake depressing force sensor 23.
Then, in step S502, the ESC-CU 31 determines the presence or absence of steering operation based on the steering angle. If the absence of steering operation is determined, this means that the vehicle runs straightforward, and the main routine is brought to an end. If the presence of steering operation is determined, this is regarded as meaning the vehicle runs while turning, and the control flow proceeds to step S503 in which the on/off-state of the brake SW is determined in step S503.
If the brake SW is not turned off, i.e., if brake SW =ON is determined, this condition means that the vehicle is in the operating state where the vehicle runs while turning under deceleration. Therefore, the ESC-CU 31 controls the motors for the left and right wheels in step S507 according to procedures A), B) and C) as follows.
In step S507, A) the ESC-CU 31 first obtains the demanded braking torque from the brake depressing force based on the map, shown in
By thus giving the difference in motor regenerative braking torque between the inner and outer wheels in turning, it is possible to generate a turn moment in the vehicle and to improve the turning performance of the vehicle.
On the other hand, if brake SW=OFF is determined in step S503, the ESC-CU 31 determines in step S504 whether the accelerator opening is over 0 (i.e., opened) or 0 (i.e., fully closed). If the accelerator opening is over 0, this condition means that vehicle runs while turning under acceleration or coasting at a constant speed. Therefore, the ESC-CU 31 controls the motors for the left and right wheels in step S505 according to procedures A), B) and C) as follows. A) The ESC-CU 31 first obtains the demanded driving torque from the accelerator opening based on the map, shown in
By thus giving the difference in driving torque between the inner and outer wheels in turning, it is possible to generate a turn moment in the vehicle and to improve the turning performance of the vehicle.
Further, if it is determined in step S504 that the accelerator opening is fully closed, this means that the vehicle runs while turning under coasting. Therefore, the ESC-CU 31 obtains the motor driving torque of the outer wheel in turning and the motor regenerative braking torque of the inner wheel in turning from the steering angle based on the map, shown in
Each of steps S505, S506 and S507 represents a series of processes given below. A driving or regenerative-braking command is outputted from the ESC-CU 31 to the HEV-CU 25, and the HEV-CU 25 calculates a driving torque value or a regenerative braking torque value. The M-CU 28 reads the driving torque value or the regenerative braking torque value and executes the control of the motor.
Then, in step S508, the ESC-CU 31 determines whether any wheel (tire) is slipped. If a wheel slip is determined, it is determined in step S509 whether the tire slip is caused during the driving or braking.
In the case of the driving, the MOTOR-TCS control shown in
Then, the M-CU 28 executes driving/regenerative control for the non-slipping wheel in step S512, and then determines the end of the slip control in step S513. Details of the driving/regenerative control for the non-slipping wheel will be described later with reference to
The motor driving/regenerative control for the non-slipping wheel will be described below with reference to
First, in step S601, the M-CU 28 reads, from the HEV-CU 25, a target value of the driving or regenerative torque difference between the left and right wheels based on the steering angle, the on/off-state of each wheel-speed brake SW, and the accelerator opening. More specifically, that target value is obtained from
Then, in step S602, the M-CU 28 reads the driving torque or the regenerative torque of the slipped wheel from the M-CU that controls the motor for the slipped wheel.
Then, in step S603, the M-CU 28 calculates, based on the driving torque or the regenerative torque of the slipped wheel, the driving torque or the regenerative torque of the non-slipping wheel and executes the control of the motor so that the driving or regenerative torque difference obtained in step S601 is produced. Stated another way, when any of the inner and outer wheels in turning is slipped in the state of the vehicle running while turning, the driving torque or the regenerative torque of the non-slipping wheel is controlled based on the driving torque or the braking torque of the slipped wheel so as to realize the torque difference between the inner and outer wheels in turning, which is obtained from the steering angle. As a result, a turn moment can be generated depending on the steering angle, and the turning performance of the vehicle is stabilized even in the occurrence of the tire slip.
Other constructions of the electric vehicle equipped with the running controller and the electric running control system for the electric vehicle according to the embodiment of the present invention will be described below with reference to
In any of the electric vehicles shown in
Thus, according to the embodiment, in the event of a tire slip during driving or braking of the vehicle, the motor driving force and the motor regenerative force are controlled such that the coefficient μ of road friction of each tire is always maintained in the vicinity of its maximum value. It is therefore possible to prevent unstable vehicle behaviors caused by a tire slip. Also, since the vehicle is always able to run over roads under any of various conditions with the tire driving torque and the tire braking torque held at maximum values, maximum driving and braking performance can be realized. In other words, since maximum acceleration is obtained, the vehicle is able to run over bad muddy roads without being stuck, or the vehicle can be positively moved out of the stuck state. Additionally, in the case of braking, the vehicle can be stopped with a minimum braking distance.
Further, in match with the motor control for slipped one of paired wheels, motor torque for the other non-slipping wheel is modified depending on the running state, such as straightforward running and turning. Therefore, vehicle behaviors can be obtained as per the driver's estimation, and satisfactory driving performance and safety performance can be realized.
Moreover, when the wheel driven by the engine is slipped, the engine is stopped and that wheel is driven by the motor such that the coefficient μ of road friction is always maintained in the vicinity of its maximum value. Hence wasteful fuel consumption can be suppressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-231862 | Aug 2005 | JP | national |
