JP2005207953A - Road surface friction coefficient detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a road surface friction coefficient detector capable of detecting a road surface friction coefficient during vehicle stoppage before traveling. <P>SOLUTION: The road surface friction coefficient detector 1 is provided with electric motors 11FR-11RL individually driving each wheel 10FR-10RL provided on a vehicle V, a driving force control part 20A controlling the electric motors 11FR-11RL such that the right front wheel 10FR and left front wheel 10FL are driven forward, and the right rear wheel 10RR and left rear wheel 10RL are driven rearward, current sensors 15FR-15RL detecting current values supplied to the electric motors 11FR-11RL, and a friction coefficient calculating part 20B calculating the road surface friction coefficient μ on the basis of a value of a current supplied to an electric motor driving a wheel at a point of time when one of the wheels start to slip. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a road surface friction coefficient detection device.

  A regenerative braking device that applies a regenerative braking torque to a wheel by regenerative braking of an electric motor, and a friction braking device that frictionally engages a friction member with a brake rotating body that rotates together with the wheel to apply a friction braking torque to the wheel. Japanese Patent Application Laid-Open Publication No. 2004-259542 discloses a technique for controlling a regenerative braking torque to a magnitude based on a friction coefficient between a wheel and a road surface (road surface friction coefficient) during antilock control in a vehicle braking device.

According to this vehicle braking device, the road surface friction coefficient is based on the braking torque including the total braking torque, that is, the regenerative braking torque and the friction braking torque when the braking slip amount of the wheel becomes equal to or greater than the predetermined slip amount during braking. Detected. Then, an upper limit value of the regenerative braking torque is determined according to the detected road surface friction coefficient, and a regenerative braking torque target value is determined based on the upper limit value. Then, in a state where the regenerative braking torque is maintained so as to match the target value, the anti-lock control is performed by increasing / decreasing the friction braking torque.
Japanese Patent Laid-Open No. 10-322803 (page 6-16, FIG. 1)

  In the above technique, the road surface friction coefficient is detected based on the total braking torque when the braking slip amount becomes a predetermined value or more during braking. Therefore, the road surface friction coefficient cannot be detected when the vehicle is stopped. . Accordingly, since the road surface friction coefficient cannot be known in advance before traveling or before starting braking, there is a delay from when braking is started until the regenerative braking torque is adjusted to an appropriate value.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a road surface friction coefficient detection device capable of detecting a road surface friction coefficient when the vehicle is stopped before traveling.

  A road surface friction coefficient detecting device according to the present invention includes a driving unit that independently drives each of a plurality of wheels provided in a vehicle, and a driving unit that causes the wheels to slip while maintaining the vehicle in a stopped state. A driving force control means for adjusting the output driving torque, a driving torque detection means for detecting the driving torque of each of the plurality of wheels, and a road surface based on the driving torque of the wheels when any of the wheels starts to slip. Friction coefficient calculation means for calculating a friction coefficient is provided.

  According to the road surface friction coefficient detecting device according to the present invention, the driving torque of each of the plurality of wheels is adjusted so that the vehicle can maintain the stopped state, and the slip state is caused between the wheels and the road surface while the vehicle is stopped. Is made. Since the road surface friction coefficient is calculated based on the wheel driving torque at the start of slip detected by the driving torque detecting means, it is possible to detect the road surface friction coefficient when the vehicle is stopped.

  The friction coefficient calculating means preferably calculates the road surface friction coefficient based on the driving torque at the start of the slip, the wheel radius, and the wheel load.

  In the road surface friction coefficient detecting device according to the present invention, the driving force control means is output from the driving means so that the wheels arranged opposite to the front and rear with respect to the traveling direction of the vehicle are driven in opposite directions. It is preferable to adjust the driving torque. In this way, the driving torque of both wheels is canceled out, so that the vehicle can be maintained in a stopped state.

  The road surface friction coefficient detecting device according to the present invention preferably includes a braking unit that independently applies a braking force to each of the plurality of wheels, and the braking unit applies the braking force to a wheel to which no driving torque is output. In this way, the vehicle can be stably stopped even when the wheels are slipping.

  In the road surface friction coefficient detecting device according to the present invention, it is preferable that the driving force control means selects a wheel driven by the driving means so that a yawing moment acting on the vehicle becomes zero. In this way, since the total rotational force acting on the vehicle becomes zero, the vehicle can be maintained in a stable stopped state.

  According to the present invention, the driving torque of each of the plurality of wheels is adjusted so that the vehicle can maintain the stopped state, and the slip state is created between the wheels and the road surface while the vehicle is stopped. The road surface friction coefficient can be detected when the vehicle is stopped before traveling.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the figure, the same reference numerals are used for the same or corresponding parts.

  First, the configuration of the road surface friction coefficient detection device 1 according to the embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing a main configuration of a vehicle V equipped with a road surface friction coefficient detection device 1. FIG. 2 is a diagram illustrating a brake system of the vehicle V. In this specification, the forward direction when the vehicle is moving forward is defined as “front”, and terms such as “front”, “rear”, “left”, and “right” are used.

  Wheels 10FR, 10FL, 10RR, and 10RL are attached to the vehicle V. Here, the wheel 10FR indicates the right front wheel, the wheel 10FL indicates the left front wheel, the wheel 10RR indicates the right rear wheel, and the wheel 10RL indicates the left rear wheel.

  Wheel speed sensors 12FR, 12FL, 12RR, and 12RL that detect the rotational speed of the wheels are attached to the wheels 10FR, 10FL, 10RR, and 10RL. Each wheel speed sensor 12FR to 12RL is connected to an electronic control unit (hereinafter referred to as “ECU”) 20 which will be described later. A slip state of each wheel is detected based on detection signals from the wheel speed sensors 12FR to 12RL.

  As shown in FIG. 2, a brake disk 3 is attached to each wheel 10FR, 10FL, 10RR, 10RL. A brake caliper 6 incorporating a brake pad 4 and a wheel cylinder 5 is attached to each brake disk 3. Each wheel cylinder 5 is connected to a brake actuator 8 via a brake pipe 7.

  The brake actuator 8 has a hydraulic pump, an electromagnetic valve, and the like. At the time of brake braking, the brake oil in the master cylinder 9 is sent to the wheel cylinder 5 through the brake pipe 7 by the hydraulic pump of the brake actuator 8, thereby increasing the hydraulic pressure in the wheel cylinder 5 and causing the wheels 10 FR to 10 RL to move. Brake. Specifically, by increasing the hydraulic pressure in the wheel cylinder 5, the brake pad 4 is pressed against the brake disc 3, and the wheels 10FR to 10RL connected to the brake disc 3 are braked by the frictional force. That is, the brake disc 3, brake pad 4, wheel cylinder 5, brake caliper 6, brake pipe 7, and brake actuator 8 function as braking means.

  The brake actuator 8 individually adjusts the braking force of each wheel 10FR to 10RL by adjusting the hydraulic pressure in the wheel cylinder 5 by opening and closing the electromagnetic valve. The brake system used in this embodiment is a disc brake system, but may be a drum brake system or the like.

  The brake actuator 8 is connected to an electronic control device (hereinafter referred to as a brake ECU) 18 that controls the braking force acting on the wheels 10FR to 10RL, and a hydraulic pump, an electromagnetic valve, and the like that the brake actuator 8 has are driven by the brake ECU 18. Is done. The brake ECU 18 and the ECU 20 are connected via a communication line 19, and are configured to be able to exchange data with each other.

  Returning to FIG. 1, the description will be continued. Electric motors 11FR, 11FL, 11RR, 11RL are incorporated inside the wheels 10FR, 10FL, 10RR, 10RL. That is, each of the electric motors 11FR to 11RL is an in-wheel motor, and drives each of the wheels 10FR to 10RL independently. That is, these electric motors 11FR to 11RL function as drive means. In addition, the electric motor may not be an in-wheel motor as long as it is attached so that each wheel can be driven independently. For example, an electric motor may be attached to the vehicle body side, and the electric motor and wheels may be coupled by a drive shaft or the like.

  Electric motors 11FR, 11FL, 11RR, and 11RL are AC synchronous motors and are driven by AC power output from inverter 13. Further, the electric motors 11FR, 11FL, 11RR, and 11RL can generate electric power (regenerative power generation) by using the rotation of the wheels 10FR, 10FL, 10RR, and 10RL.

  The inverter 13 converts electric power stored in the high voltage battery 14 from direct current to three-phase alternating current based on a control signal from the ECU 20 and supplies it to the electric motors 11FR, 11FL, 11RR, 11RL. Further, the inverter 13 converts the electric power regenerated by the electric motors 11FR to 11RL from AC to DC and stores it in the high voltage battery 14.

  The inverter 13 includes current sensors 15FR, 15FL, 15RR, and 15RL that detect phase currents flowing through the three-phase lines 16FR, 16FL, 16RR, and 16RL that connect the electric motors 11FR, 11FL, 11RR, and 11RL to the inverter 13. ing. The actual current values Ifr, Ifl, Irr and Irl supplied to the electric motors 11FR to 1RL are obtained from the phase current values detected by the current sensors 15FR to 15RL. The obtained actual current values Ifr to Irl are transmitted from the inverter 13 to the ECU 20 via the communication line 17.

  In the present embodiment, the output torque of the electric motors 11FR to 11FL, that is, the driving torque of the wheels 10FR to 10FL is obtained based on the actual current values Ifr to Irl. That is, the current sensors 15FR to 15FL function as drive torque detection means. For detection of the drive torque, for example, a torque sensor using a strain gauge for detecting the strain amount of the axle shaft may be used.

  The steering 21 is provided with a steering angle sensor 22 composed of a rotary encoder or the like. The steering angle sensor 22 outputs a signal corresponding to the direction and magnitude of the steering angle input by the driver. The steering angle sensor 22 functions as a traveling state detection unit. A signal output from the steering angle sensor 22 is input to the ECU 20.

  In addition to the wheel speed sensors 12FR, 12FL, 12RR, 12RL and the steering angle sensor 22, the ECU 20 includes an accelerator opening sensor 23 that detects the opening of the accelerator pedal, a yaw rate sensor 24 that detects the yaw rate of the vehicle, and the left and right sides of the vehicle V. A left / right acceleration sensor 25 that detects the acceleration in the direction and a longitudinal acceleration sensor 26 that detects the acceleration in the longitudinal direction of the vehicle V are connected.

  The ECU 20 includes a microprocessor for performing calculations, a ROM for storing a program for causing the microprocessor to execute each process, a RAM for storing various data such as calculation results, and a 12V battery (not shown). A backup RAM or the like is held.

  A driving force control unit that adjusts the driving torque of the electric motors 11FR to 11RL so that the wheels 10FR to 10RL slip while maintaining the vehicle V in the ECU 20 by the microprocessor or the like. 20A and a friction coefficient calculation unit 20B that calculates a road surface friction coefficient based on the driving torque of the wheel at the time when one of the wheels starts slipping is constructed. That is, the driving force control unit 20A functions as a driving force control unit, and the friction coefficient calculation unit 20B functions as a friction coefficient calculation unit.

  Next, the operation of the road surface friction coefficient detection device 1 will be described with reference to FIG. FIG. 3 is a flowchart showing a processing procedure of road surface friction coefficient detection processing by the road surface friction coefficient detection device 1. This process is repeatedly executed every predetermined time.

  In step 100, it is determined whether or not the execution flag F for identifying whether or not the road surface friction coefficient detection process is being executed is set, specifically, whether or not the execution flag F is 1. Is done. If the execution flag F is 1, that is, if the road surface friction coefficient detection process is being executed, the process proceeds to step S106. On the other hand, when the execution flag is 0, that is, when the road surface friction coefficient detection process is not executed, the process proceeds to step S102.

  In step S102, it is determined whether or not an execution start condition for the road surface friction coefficient detection process is satisfied, specifically, whether or not the vehicle V is in a stopped state. When the speeds of the wheels 10FR to 10RL detected by the wheel speed sensors 12FR to 12RL are zero, it is determined that the vehicle V is in a stopped state. Here, when it is determined that the vehicle V is in a stopped state, it is determined that the condition for starting the road surface friction coefficient detection process is satisfied, and after the execution flag F is set in step S104, the process proceeds to step S106. Will migrate. On the other hand, when it is determined that the vehicle V is not in the stopped state, the execution start condition is not satisfied, and the process is temporarily exited. It should be noted that the determination as to whether or not the road surface friction coefficient detection process can be performed may be made on the condition that, for example, the steering angle of the steering is equal to or less than a predetermined value in addition to the vehicle being stopped. Good.

  In step S106, first, selection of a wheel driven by the electric motors 11FR to 11RL and determination of a driving direction of the driving wheel are performed. In this embodiment, as shown in FIG. 4A, all four wheels 10FR to 10RL provided in the vehicle V are selected as drive wheels, the right front wheel 10FR and the left front wheel 10FL are driven forward, and the right Electric motors 11FR to 11RL are controlled such that rear wheel 10RR and left rear wheel 10RL are driven rearward.

  By controlling the electric motors 11FR to 11RL so that the front wheels 10FR, 10FL and the rear wheels 10RR, 10RL are driven in opposite directions, the driving torque of the front wheels 10FR, 10FL and the driving torque of the rear wheels 10RR, 10RL are increased. Since they cancel each other, the vehicle can be maintained in a stopped state.

  The driving wheel and its driving direction are not limited to the above embodiment, and various modifications are possible. 4B to 4D show other examples of driving patterns of the wheels 10FR to 10RL. In the example of FIG. 4B, the electric motors 11FR to 11RL are controlled such that the right front wheel 10FR and the left front wheel 10FL are driven rearward, and the right rear wheel 10RR and the left rear wheel 10RL are driven forward. In the example of FIG. 4C, the electric motors 11FR to 11RL are controlled so that the right front wheel 10FR and the left rear wheel 10RL are driven forward, and the right rear wheel 10RR and the left front wheel 10FL are driven rearward. In the example of FIG. 4D, the electric motors 11FR to 11RL are controlled so that the right front wheel 10FR and the left rear wheel 10RL are driven rearward, and the right rear wheel 10RR and the left front wheel 10FL are driven forward. .

  The selection of wheels driven by the electric motors 11FR to 11RL and the drive torque of each drive wheel are set so that the yawing moment acting on the vehicle V becomes zero. By setting in this way, the total rotational force acting on the vehicle V becomes zero, so that the vehicle V can be maintained in a stable stopped state.

  As yet another pattern, the electric motors 11FR and 11RR are controlled such that the right front wheel 10FR is driven forward and the right rear wheel 10RR is driven rearward, and the braking force is applied to the left front wheel 10FL and left rear wheel 10RL that are not driven. It is also possible to control the brake actuator 8 so that is added. Further, the electric motors 11FR and 11RR are controlled so that the right front wheel 10FR is driven rearward and the right rear wheel 10RR is driven forward, and braking force is applied to the left front wheel 10FL and left rear wheel 10RL that are not driven. The brake actuator 8 may be controlled as described above. Further, the electric motors 11FL and 11RL are controlled so that the left front wheel 10FL is driven forward and the left rear wheel 10RL is driven rearward, and braking force is applied to the right front wheel 10FR and right rear wheel 10RR that are not driven. The brake actuator 8 may be controlled as described above. The electric motors 11FL and 11RL are controlled so that the left front wheel 10FL is driven rearward and the left rear wheel 10RL is driven forward, and braking force is applied to the undriven right front wheel 10FR and right rear wheel 10RR. The brake actuator 8 may be controlled.

  Thus, if braking force is applied to the wheels that are not driven, the vehicle V can be stably stopped even when the drive wheels are in a slip state.

  Next, the command value of the current supplied to the electric motors 11FR to 11RL is set according to the target drive torque of the electric motors 11FR to 11FL. The current command value is gradually increased with a predetermined slope. Therefore, the driving torque is gradually increased with the passage of time until one of the driving wheels starts to slip.

  FIG. 5A shows temporal changes in the current command values of the electric motors 11FR and 11FL that drive the right front wheel 10FR and the left front wheel 10FL, and FIG. 5B shows the electric motor 11RR that drives the right rear wheel 10RR and the left rear wheel 10RL. , 11RL shows the time change of the current command value. As shown in FIG. 5, the current command values supplied to the electric motors 11FR to 11RL are such that the drive torques of the left and right front wheels 10FR, 10FL and the left and right rear wheels 10RR, 10RL are equal and the drive directions are reversed. Is set.

  Then, inverter 13 is controlled such that the current command value matches the actual current value supplied to electric motors 11FR to 11RL.

  In step S108, a determination is made as to whether any wheel is slipping. Specifically, it is determined whether or not slip has occurred depending on whether or not the speeds of the wheels 10FR to 10RL detected by the wheel speed sensors 12FR to 12RL are zero (or less than a predetermined value). A wheel whose wheel speed is not zero (or less than a predetermined value) is determined to be slipping. On the other hand, it is determined that a wheel having a wheel speed of zero (or less than a predetermined value) does not slip.

  Here, if it is determined that any of the wheels is slipping, the process proceeds to step S110. On the other hand, when it is determined that none of the wheels is slipping, the process is temporarily exited.

  In step S110, the command current value at the time of the start of slipping of the electric motor disposed on the wheel in which the slip has occurred is read. Instead of the command current value, actual current values detected by the current sensors 15FR to 15RL may be used.

  Subsequently, in step S112, based on the current value read in step S110, the driving torque of the electric motor at the start of slip, that is, the driving torque of the wheels is obtained. Based on this drive torque, the road surface friction coefficient μ is calculated by the following equation.

Road surface friction coefficient μ = Ti / (r × Wi) (1)
Here, Ti is a drive torque [N · m], r is a tire moving radius (wheel moving radius) [m], and Wi is a wheel load [N]. The tire moving radius r and the wheel load Wi are predetermined constants, and are stored in advance in the ROM of the ECU 20 as data. The wheel load Wi may be obtained by correcting the stored wheel load data according to the longitudinal acceleration detected by the longitudinal acceleration sensor 26 and the lateral acceleration detected by the lateral acceleration sensor 25. Good.

  After the road surface friction coefficient μ is calculated, the execution flag F is reset to 0 in step S114. Thereafter, the process is exited.

  In the present embodiment, the right front wheel 10FR and the left front wheel 10FL are driven forward, the right rear wheel 10RR and the left rear wheel 10RL are driven rearward, and the vehicle V is stopped between the wheels and the road surface. A slip condition is created. Then, the road surface friction coefficient μ is calculated based on the current value supplied to the electric motor at the start of slip detected by the current sensors 15FR to 15RL. This makes it possible to detect the road surface friction coefficient μ when the vehicle is stopped before traveling.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in this embodiment, the electric motor is mounted on the front, rear, left, and right four wheels as the driving force source. However, as long as the four wheels can be driven independently, the driving force source is single or plural. The internal combustion engine may be used.

It is a figure which shows the main structures of the vehicle carrying the road surface friction coefficient detection apparatus which concerns on embodiment. It is a figure showing a brake system of vehicles carrying a road surface friction coefficient detecting device concerning an embodiment. It is a flowchart which shows the process sequence of the road surface friction coefficient detection process by the road surface friction coefficient detection apparatus which concerns on embodiment. (A)-(d) is a figure which shows the example of the drive pattern of the wheel in a road surface friction coefficient detection process. (A) is a figure which shows the example of the time change of the front wheel electric current command value in a road surface friction coefficient detection process. (B) is a figure which shows the example of the time change of the rear-wheel electric current command value in a road surface friction coefficient detection process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Road surface friction coefficient detection apparatus, 3 ... Brake disc, 4 ... Brake pad, 5 ... Wheel cylinder, 6 ... Brake caliper, 7 ... Brake piping, 8 ... Brake actuator, 9 ... Master cylinder, 18 ... Brake ECU, 10FR, 10FL, 10RR, 10RL ... Wheel, 11FR, 11FL, 11RR, 11RL ... Electric motor, 12FR, 12FL, 12RR, 12RL ... Wheel speed sensor, 13 ... Inverter, 14 ... High voltage battery, 15FR, 15FL, 15RR, 15RL ... Current Sensor: 20 ... ECU, 21 ... Steering, 22 ... Steering angle sensor, 23 ... Accelerator opening sensor, 24 ... Yaw rate sensor, 25 ... Left / right acceleration sensor, 26 ... Longitudinal acceleration sensor, 20A ... Driving force control unit, 20B ... Friction Coefficient calculator, V ... vehicle.

Claims (5)

Drive means for independently driving each of the plurality of wheels provided in the vehicle;
Driving force control means for adjusting a driving torque output from the driving means so that the wheels slip while maintaining the vehicle in a stopped state;
Drive torque detection means for detecting the drive torque of each of the plurality of wheels;
A road surface friction coefficient detecting device comprising: friction coefficient calculating means for calculating a road surface friction coefficient based on a driving torque of one of the wheels at the start of slipping.   2. The road surface friction coefficient detection device according to claim 1, wherein the friction coefficient calculation unit calculates a road surface friction coefficient based on a driving torque at a slip start time, a wheel radius, and a wheel load.   The driving force control means adjusts a driving torque output from the driving means so that wheels disposed opposite to the front and rear of the traveling direction of the vehicle are driven in opposite directions. The road surface friction coefficient detecting device according to claim 1 or 2. A braking means for independently applying a braking force to each of the plurality of wheels;
The road friction coefficient detecting device according to any one of claims 1 to 3, wherein the braking means applies a braking force to a wheel to which no driving torque is output.   The said driving force control means selects the wheel driven by the said driving means so that the yawing moment which acts on the said vehicle may become zero, The any one of Claims 1-4 characterized by the above-mentioned. Road friction coefficient detection device.

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