JP2007045205A - Control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a vehicle capable of preventing reduction of traveling performance by road surface condition. <P>SOLUTION: In the vehicle 10, ECU 100 executes assist torque control processing. In the assist torque control processing, a slip ratio SL is calculated on the basis of an output value of wheel speed sensors provided on left and right front wheels. When a driver operates a steering 11 to steer the vehicle, in the case where the slip ratio becomes an increase characteristic relative to a steering direction, the ECU 100 controls EPS 500 to reduce assist torque TA so as to assist steering torque. Whereas, when the slip ratio becomes a reduction characteristic relative to the steering direction, the ECU 100 controls the EPS 500 to increase the assist torque TA. As a result, the vehicle 10 is guided so that a gripping degree of the wheel is increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the technical field of vehicle control devices.

  As this type of device, for example, a device that controls the vehicle speed has been proposed (see, for example, Patent Document 1). According to the creep travel control device disclosed in Patent Document 1 (hereinafter referred to as “conventional technology”), it is easy to start on a slope by causing the vehicle to travel at a low speed on the slope of the slope. It is possible to make it.

Japanese Patent Laid-Open No. 2004-90679

  For example, when a vehicle travels on a road surface with a low coefficient of friction or a rough road such as a rocky mountain, the ground contact state between the wheel and the road surface tends to be unstable. Therefore, it is difficult to maintain the vehicle speed under such traveling conditions due to wheel slip or the like. That is, the conventional technique has a technical problem that the running performance on a rough road is likely to be significantly reduced. Furthermore, when the ground contact state is unstable, there is a technical problem that there is a concern that not only the vehicle speed is maintained, but also that the basic running performance is deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a vehicle control device that can prevent a decrease in traveling performance due to road surface conditions.

  In order to solve the above-described problems, a vehicle control apparatus according to the present invention is a vehicle control apparatus that controls a vehicle including a steering torque assisting unit that applies an assisting torque for assisting a steering torque to the steering unit. A grip degree specifying means for specifying a grip degree of a wheel in the vehicle, a steering direction specifying means for specifying a steering direction of the vehicle, and the specified steering direction based on the specified grip degree. A change characteristic specifying means for specifying a change characteristic of a grip degree of a wheel; a first control for controlling the steering torque auxiliary means so that the auxiliary torque is increased when the specified change characteristic is an increase characteristic; and If the specified change characteristic is a decrease characteristic, at least of the second control for controlling the steering torque auxiliary means so that the auxiliary torque decreases. Characterized by comprising an auxiliary torque control means for executing one.

  The “steering means” according to the present invention is a concept including a mechanism, a device, a system, and the like for steering a vehicle. Accordingly, the steering means may include at least a part of, for example, a steering wheel (hereinafter referred to as “handle” as appropriate), a steering shaft, and a gear mechanism.

  The auxiliary torque applied to the steering means is a torque for assisting the steering torque applied to the steering means by the driver of the vehicle, and is typically the same direction as the steering torque (that is, the same rotational direction). ). The mode of the steering torque assisting means for applying the assist torque (also referred to as assist torque) is not limited as long as the steering torque is finally assisted. However, it is preferable that the auxiliary torque is applied via an electric torque generating means such as a motor because the auxiliary torque can be applied regardless of the engine output of the vehicle. Such steering torque assisting means preferably takes the form of an EPS (Electronic Power Steering) device or the like. The steering torque assisting unit may be configured as a part of the steering unit or may be configured separately from each other.

  According to the vehicle control apparatus of the present invention, the grip degree of the wheel in the vehicle is specified by the grip degree specifying means during the operation.

  Here, the “grip degree of the wheel” is a concept that includes an index value that defines the grip state between the wheel and the road surface, and as the value increases, the grip state improves (that is, shifts to the gripping side). ) Is defined as a value that worsens the grip state (ie, shifts to a non-grip side) as it decreases. The grip degree may be any value as long as the concept is secured. For example, the grip state of the wheel is influenced by the ground load applied to the wheel. That is, when the ground load is insufficient (that is, the ground load is missing), the grip state is relatively deteriorated. Therefore, the grip degree may be represented by the value of the ground load itself or a value derived from the ground load value according to some rule or algorithm. Further, the grip degree may be a value derived based on the self-aligning torque and lateral force of the vehicle. Alternatively, the grip degree may be a value determined in advance so that the grip state can be defined experimentally, empirically, or based on simulation.

  In the present invention, “specify” means not only physical, electrical, mechanical, mechanical, or chemical detection of a specific target value, but also physical, electrical, mechanical, or mechanical. Alternatively, the concept includes estimation or estimation according to some rule or algorithm based on a chemically detected value having some correspondence with a value of a specific target. Alternatively, “specify” may have a form in which a measurement result is received as an electrical signal from a means for measuring a value to be specified, for example, various sensor devices.

  The wheel for which the grip degree is specified is not limited as long as it is a wheel provided in the vehicle, but preferably refers to at least one of steering wheels, for example, left and right front wheels. When the vehicle travels on a rough road, the grip state is often greatly different between the left and right front wheels. Therefore, the grip degree is preferably specified by the left and right front wheels. In this case, the specified grip degree may be an average value of the left and right front wheels, or may be determined based on a corresponding weight given to the left and right front wheels. Or you may utilize separately as a grip degree of a right-and-left front wheel, respectively.

  On the other hand, according to the vehicle control apparatus of the present invention, the steering direction of the vehicle is specified by the steering direction specifying means. Here, the “steering direction of the vehicle” is a direction in which steering torque is generated, and indicates a direction in which the steering angle of the wheel is changed. Therefore, the concept is irrelevant to whether the wheel is facing right or left at that time. The steering angle of the wheel may be acquired based on the output of some steering angle detection means such as a steering angle sensor or a handle angle sensor.

  Furthermore, according to the vehicle control apparatus of the present invention, the change characteristic specifying means specifies the change characteristic of the grip degree with respect to the steering direction.

  Here, the aspect of specifying the change characteristic of the grip degree relative to the steering direction is a change characteristic of the grip degree when the wheel is steered in the steering direction specified by the steering direction specifying means, for example, whether the grip degree is increased. There is no limitation as long as it is possible to specify the characteristics of whether to decrease or not change. For example, the change characteristic can be identified relatively easily by storing the grip degree in association with the steering angle of the vehicle. Alternatively, it may be estimated how the grip degree changes for a small steering angle region including the current steering angle without storing the grip degree in association with the steering angle.

  The identification of such change characteristics may be performed in real time as the wheels are actually steered, and it has been known in advance how the degree of grip changes with respect to the steering direction. When it is possible to estimate, it may be performed before the steering operation.

  Here, in the vehicle control apparatus according to the present invention, the auxiliary torque control means (i) controls the steering torque auxiliary means to increase the auxiliary torque when the change characteristic is an increase characteristic, and (Ii) When the change characteristic is a decrease characteristic, at least one of the second controls for controlling the steering torque assisting unit is executed so that the assist torque is decreased.

  When the first control is executed, the steering torque assisting means is controlled so that the assist torque is increased, so that the driver can easily perform the steering operation in the steering direction in which the grip degree increases. That is, the steering operation is invited in the direction in which the grip degree increases, and as a result, the vehicle can be guided to a road surface with a relatively high grip degree.

  In addition, when the second control is executed, the steering torque assisting means is controlled so that the assist torque is decreased, so that it is difficult for the driver to perform the steering operation in the steering direction in which the grip degree decreases. That is, the steering operation in the direction in which the grip degree decreases is hindered, and as a result, the vehicle can be guided to a road surface with a relatively high grip degree.

  As described above, when either the first control or the second control is preferably executed, the vehicle is invited to a road surface with a high grip. That is, it is possible to effectively prevent a decrease in running performance due to road surface conditions such as low μ roads and rocky mountains.

  Note that “in the case of an increase characteristic” and “in the case of a decrease characteristic” are not necessarily all in the case of an increase characteristic or a decrease characteristic. For example, a certain threshold value may be set to a value that defines a change characteristic such as an increase rate in the increase characteristic and a decrease rate in the decrease characteristic. That is, the first or second control may be executed only when the grip ratio changes relatively large.

  The amount of increase and decrease of the auxiliary torque is not limited as long as it can prevent such a decrease in the running performance of the vehicle. For example, since the auxiliary torque is a torque applied to the steering direction, in other words, the direction of the steering torque, “the auxiliary torque is reduced” means that the steering direction is opposite to the steering direction. It is a concept that includes the application of torque in a direction that cancels the torque. However, from the viewpoint of executing vehicle control that reflects the driver's steering intention, the auxiliary torque is preferably a torque that is applied only in the steering direction. Therefore, the lower limit value of the auxiliary torque is zero or a value that is small enough to be regarded as zero, or the minimum level necessary for the driver to steer the vehicle (that is, as the driver's sense, the steering torque is sufficiently high). It is preferable that the torque is set to a large value. On the other hand, from the viewpoint of respecting the driver's steering intention, the upper limit value of the auxiliary torque is preferably set to a value that does not cause the vehicle to be steered only by the auxiliary torque. Further, the increase amount and decrease amount of the auxiliary torque may be set in advance so as to effectively prevent a decrease in running performance experimentally, empirically, or based on simulation.

  In one aspect of the vehicle control device according to the present invention, the vehicle further includes a braking device for braking the vehicle and a drive device for driving the vehicle, and the vehicle control device includes The vehicle further includes vehicle speed control means for controlling the braking device and the drive device so that the vehicle speed is maintained at a predetermined value, and the auxiliary torque control means is configured to maintain the vehicle speed at the predetermined value. At least one of the above.

  The braking means provided in the vehicle is a concept including a mechanism, a device, and a system for braking the vehicle, and refers to, for example, a brake device or a brake system. Further, at least a part of the function of the braking means may be controlled in cooperation with various devices for stabilizing the vehicle such as an ABS (Antilock Braking System) or a VSC (Vehicle Stability Control) device. Good. Or you may be comprised integrally as a part of these various apparatuses.

  On the other hand, the drive means is a concept that encompasses a mechanism, a device, and a system for driving a vehicle. For example, an engine, a throttle valve for supplying air to the engine, or a throttle valve motor that drives the throttle valve And so on.

  According to this aspect, the braking device and the driving device are maintained by the vehicle speed control means so that the vehicle speed (hereinafter referred to as “vehicle speed” as appropriate) is maintained at a predetermined value (hereinafter referred to as “predetermined vehicle speed” as appropriate). Is controlled.

The predetermined vehicle speed at the time of maintaining the vehicle speed is not necessarily a fixed value, but includes a constant or indefinite vehicle speed range defined by a preset upper limit value and lower limit value. That is,
The state where the vehicle speed is within such a vehicle speed region is also a category of “the vehicle speed is maintained” according to the present invention.

  The control mode of the braking device and the driving device is not limited as long as the vehicle can be maintained at a predetermined vehicle speed. Further, the maintenance of the vehicle speed may be performed on a flat road or on a slope. When the vehicle speed is maintained on a slope (mainly descending road), for example, when the vehicle speed exceeds a target value, the oil pressure of the wheel cylinder provided to each wheel is controlled independently of the driver's brake pedal operation, thereby controlling the predetermined vehicle speed. May be maintained. When the vehicle speed is maintained on a flat road, for example, the vehicle speed may be maintained by cooperatively controlling the open / close state of the throttle valve and the hydraulic pressure of the wheel cylinder.

  Further, the auxiliary torque control means executes at least one of the first control and the second control when the vehicle speed is maintained at a predetermined value by the vehicle speed control means. In order to maintain the vehicle speed, the wheels need to maintain a grip state that can be regarded as normal. Therefore, for example, it is difficult to maintain the vehicle speed remarkably on a rough road. According to this aspect, when the vehicle speed is maintained at a predetermined value, at least one of the first and second controls is executed, so that the vehicle speed is preferably maintained.

  Note that “when the vehicle speed is maintained at a predetermined value” does not necessarily represent only the period during which the actual vehicle speed is maintained at the predetermined value. For example, an input to maintain the vehicle speed is made, and the vehicle speed This is a concept including a period in which a control mode for maintaining the power is activated. That is, even if the braking means and the driving means are controlled to maintain the vehicle speed, the vehicle frequently stops depending on the road surface condition, for example, particularly when driving on a rocky mountain. In such a case as well, control is performed to maintain the vehicle speed, which is a category of “when the vehicle speed is maintained at a predetermined value”.

  In another aspect of the vehicle control apparatus according to the present invention, the grip degree specifying means specifies the wheel slip degree that decreases and increases in accordance with the increase and decrease in the grip degree of the wheel, respectively. Specify the grip level.

  According to this aspect, the grip degree is specified based on the slip degree. The slip degree according to the present invention is a concept that includes values that define the slip state of a wheel. When the ground contact load of the wheel decreases, the grip degree decreases. At this time, the wheel starts to slip as the ground load decreases. That is, the slip degree is a concept contrary to the grip degree, in which the decrease and increase correspond to the increase and decrease of the grip degree, respectively.

  Therefore, it is possible to indirectly specify the grip degree based on the slip degree. If the correspondence between the slip degree and the grip degree, or the correspondence between the slip degree and the increase or decrease in the auxiliary torque is defined in advance, the grip degree is indirectly determined by specifying the slip degree. Since the degree is specified, it is not always necessary to specify the grip degree when actually increasing or decreasing the auxiliary torque. Note that the slip phenomenon is a phenomenon that occurs secondaryly due to a lack of the grip degree. However, since the slip degree can be specified more simply than the grip degree, the first or second control can be suitably executed. It becomes possible.

  Note that the grip degree and the slip degree do not necessarily correspond to each other one to one. For example, in a state where the wheel is gripping the road surface to some extent (that is, a state where the grip degree is a predetermined value or more), the wheel does not slip, and the slip degree does not change, for example, to zero. However, in view of the purpose of ensuring the running performance of the vehicle, it is not necessary to control the auxiliary torque in a region where no slip occurs, and the problem arises when slip occurs and the running performance deteriorates. That is, when the grip degree is specified by specifying the slip degree, the vehicle can be controlled efficiently.

  In this aspect, the grip degree specifying means may specify the slip degree of the wheel based on the wheel speed of the vehicle.

  In this case, since the slip degree is specified based on the wheel speed, it is efficient. The aspect which specifies a slip degree based on wheel speed is not limited at all. For example, a slip ratio defined as a ratio between the vehicle speed obtained based on the wheel speed with respect to the target vehicle speed (the dimension of the speed) and the target vehicle speed may be specified as one form of the slip degree. In this case, the slip degree can be specified relatively accurately. At this time, the wheel speed may be specified based on an output value of a wheel speed detecting means such as a wheel speed sensor provided in each wheel of the vehicle.

  In another aspect of the vehicle control apparatus according to the present invention, the auxiliary torque control means determines an increase or decrease amount of the auxiliary torque in the first or second control in accordance with the specified grip degree. .

  For example, when the grip degree is extremely small, there is a high possibility that the running performance of the vehicle will be relatively greatly reduced at such a steering position. Therefore, steering in a steering direction in which the grip degree tends to increase due to a relatively large auxiliary torque. It is preferable to prompt the operation. On the other hand, in the steering direction in which the grip degree decreases, it is preferable to inhibit the steering operation by reducing the auxiliary torque relatively large from the viewpoint of preventing further deterioration in running performance. According to this aspect, since the amount of increase or decrease in the auxiliary torque is determined according to the grip degree, it is possible to efficiently and effectively prevent a decrease in the running performance of the vehicle.

  In another aspect of the vehicle control apparatus according to the present invention, the auxiliary torque control means determines an increase or decrease amount of the auxiliary torque in the first or second control according to a value defining the change characteristic. To do.

  According to this aspect, instead of the grip degree described above or in addition to the grip degree, a value that defines the change characteristic of the grip degree, for example, the slope of the profile (characteristic curve) representing the change characteristic, that is, the change rate of the grip degree, etc. Accordingly, the amount of increase or decrease in the auxiliary torque is determined, so that the auxiliary torque can be controlled in view of the overall change characteristic of the grip degree. Note that the setting mode of the increase or decrease amount according to the value defining the change characteristic may be determined in advance experimentally, empirically, or based on simulation.

  Such an operation and other advantages of the present invention will become apparent from the embodiments described below.

<Embodiment>
Preferred embodiments of the present invention will be described below with reference to the drawings as appropriate.

<Configuration of Embodiment>
First, the configuration of a vehicle according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of the vehicle 10. Here, the configuration of the vehicle 10 will be described with a part of its operation.

  In FIG. 1, a vehicle 10 is a vehicle that includes a left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR, and travels by the power of an engine (not shown).

  The vehicle 10 includes a handle 11, a shaft 12, and a steering device 13.

  The handle 11 is a device for transmitting a steering operation (hereinafter referred to as “handle operation” as appropriate) by a driver (not shown) to the shaft 12. The handle operation by the driver is transmitted to the shaft 12 as rotational power. Is done. The rotational power received by the shaft 12 is transmitted to the steering device 13.

  The steering device 13 is a rack-and-pinion type steering device, and the reciprocating motion of the rack (not shown) meshed with the pinion gear in the left-right direction shown in the figure is caused by the rotational motion of the pinion gear (not shown) provided at the tip of the shaft 12. Thus, the steering angles of the left front wheel FL and the right front wheel FR, which are drive wheels, are controlled in accordance with the driver's steering operation. The handle 11, the shaft 12, and the steering device 13 constitute an example of “steering means” according to the present invention.

  In FIG. 1, the vehicle 10 further includes an ECU 100, a throttle valve motor 200, a start switch 300, a brake actuator 400, an EPS 500, a handle angle sensor 600, braking devices 700FL, 700FR, 700RL and 700RR, wheel cylinders 710FL, 710FR, 710RL and 710RR. And wheel speed sensors 800FL and 800FR.

  The ECU 100 includes an unillustrated ROM (Read Only Memory), RAM (Random Access Memory), and the like, and is an electronic control unit that controls the entire operation of the vehicle 10, and is an example of the “vehicle control device” according to the present invention. It is. The ECU 100 is configured to execute an assist torque control process, which will be described later, according to a program stored in the ROM, and temporarily stores various data generated in the execution process of the assist torque control process in the RAM. Is configured to be possible.

  The throttle valve motor 200 is a motor that drives a throttle valve (not shown) for supplying air sucked through an intake system to an engine (not shown), and is an example of a “drive device” according to the present invention. is there. The throttle valve motor 200 is superordinately controlled by the ECU 100 by being electrically connected to the ECU 100.

  The activation switch 300 is an input device that is installed at a predetermined location (for example, a console panel) in the vehicle interior of the vehicle 10 and is operated by a driver or the like, and is electrically connected to the ECU 100. In this embodiment, when the start switch 300 is operated, a start input signal that prompts the ECU 100 to execute the vehicle speed maintenance control is output. Here, the vehicle speed maintenance control is a control for maintaining the vehicle speed of the vehicle 10 at a preset value or range. In the present embodiment, an assist torque control process, which will be described later, is executed according to the activation input signal, that is, in accordance with the execution of the vehicle speed maintenance control.

  The brake actuator 400 is an example of the “braking means” according to the present invention that is electrically connected to the ECU 100 and configured to be able to control the hydraulic pressure of each wheel cylinder according to the upper control by the ECU 100.

  The EPS 500 is an electronically controlled power steering device, and is an example of the “steering torque assisting means” according to the present invention. The EPS 500 includes a motor (not shown), and a pinion gear (substantially the pinion gear is fixed to the pinion gear) of the steering device 13 by an assist torque TA (that is, an example of the “auxiliary torque” according to the present invention) by the motor. ) To assist the steering torque TS applied to the shaft 12 via the handle 11. The EPS 500 is electrically connected to the ECU 100 and is superordinately controlled by the ECU 100. The EPS 500 includes a steering torque sensor (not shown) that detects the steering torque TS by detecting the twist of the shaft 12.

  The handle angle sensor 600 is a sensor that detects the rotation angle (that is, the handle angle) of the handle 11. The detected handle angle is output to the ECU 100 electrically connected to the handle angle sensor 600 as an electric signal representing the handle angle. The ECU 100 is configured to be able to acquire the steering angles DS of the wheels FL and FR, which are the steering wheels, based on the detected steering wheel angle and the steering gear ratio in the steering device 13.

  The braking device 700FL is a disc brake device that is provided on the left front wheel FL and brakes the left front wheel FL by a brake pad (not shown) pressing a disk (not shown) according to the hydraulic pressure of the wheel cylinder 710FL. Similarly, the braking devices 700FR, 700RL, and 700RR are disc brake devices that brake the right front wheel FR, the left rear wheel RL, and the right rear wheel RR in cooperation with the wheel cylinders 710FR, 710RL, and 710RR, respectively.

  Each wheel cylinder is configured to transmit the hydraulic pressure of the brake oil via a master cylinder (not shown) and the brake actuator 400. Usually, when a brake pedal (not shown) is depressed by the driver, the hydraulic pressure corresponding to the depression amount is transmitted to each wheel cylinder via the master cylinder. On the other hand, the ECU 100 can also control the hydraulic pressure of each wheel cylinder by controlling the brake actuator 400 regardless of the driver's brake pedal operation. Each braking device and each wheel cylinder together with the brake actuator 400 constitute an example of the “braking means” according to the present invention.

  Wheel speed sensors 800FL and 800FR are sensors that detect the rotational speeds of wheels FL and FR, respectively. Each wheel speed sensor is electrically connected to the ECU 100, and the detected wheel speed is output to the ECU 100. The ECU 100 is configured to be able to acquire a slip rate SL described later of the vehicle 10 based on the wheel speed.

<Operation of Embodiment>
Next, with reference to FIG. 2, the details of the assist torque control process executed by the ECU 100 will be described as the operation of the present embodiment. FIG. 2 is a flowchart of the assist torque control process.

  As already described, the assist torque control process is a process executed as the vehicle speed maintenance control is executed. The vehicle speed maintenance control is executed in response to an activation input signal generated by operating the activation switch 300. For example, when the activation switch 300 is operated by the driver, the ECU 100 controls the throttle valve motor 200 and the brake actuator 400 so that the target vehicle speed (for example, about 3 to 4 km / h) is maintained.

  Specifically, the ECU 100 controls the driving force of the vehicle 10 by controlling the opening and closing of the throttle valve by driving the throttle valve motor 200 on the one hand, and the brake pedal by the driver via the brake actuator 400 on the other hand. Regardless of the operation, the vehicle 10 is braked by controlling the hydraulic pressure of each wheel cylinder, and the target vehicle speed is maintained.

  Such vehicle speed maintenance control is effective in rough road conditions where it is difficult to secure the grip of each wheel such as a dirt road or a rocky mountain, that is, a relatively high driving skill is required. On the other hand, under such a rough road condition, particularly under a rough road surface condition such as a rocky mountain, unless the travel route of the vehicle 10 is appropriately selected, the traveling performance is likely to deteriorate due to slipping of the wheels and the like. Therefore, in the present embodiment, assist torque control processing is executed during vehicle speed maintenance control, and a decrease in travel performance is prevented.

  In FIG. 2, the ECU 100 calculates a wheel slip rate SL (step A10). In the present embodiment, the slip ratio SL is calculated based on the vehicle speed obtained from the target vehicle speed and the wheel speed. Note that the vehicle speed obtained from the wheel speed refers to the vehicle speed calculated based on the output value of each wheel speed sensor, unlike the actual vehicle speed of the vehicle 10. When the target vehicle speed is 4 km / h and the vehicle speed obtained from the wheel speed as the output value of each wheel speed sensor is 8 km / h, the vehicle speed obtained from the wheel speed is twice the target vehicle speed, and the slip ratio Is 100%. The slip ratio is an example of the “slip degree” according to the present invention. In view of the fact that the wheel speed sensor is provided on the left and right front wheels, the slip ratio SL is a value obtained for each of the left and right front wheels. In this embodiment, the average value of the slip ratio SL of the left and right front wheels is the final slip. It shall be used as rate SL.

  During execution of the assist torque control process, the ECU 100 calculates the slip ratio SL for each period based on a predetermined clock. The calculated slip rate SL is buffered by a predetermined amount in the ECU 100 RAM.

  At a timing synchronized with the calculation of the slip ratio SL, the ECU 100 determines whether or not the driver has operated the steering wheel (step A11). When there is no steering wheel operation (step A11: NO), the ECU 100 repeats step A11. On the other hand, when there is a steering wheel operation (step A11: YES), the ECU 100 determines whether or not the latest slip ratio SL is larger than a preset threshold SLth of the slip ratio SL (step A12). .

  Here, the threshold value SLth is set in advance to a value that can be estimated to cause no decrease in running performance without taking any measures, experimentally, empirically, or based on simulation. .

  When the slip ratio SL is equal to or less than the threshold value SLth (step A12: NO), the ECU 100 returns the process to step A11 and sets the assist torque TA of the EPS 500 based on normal assist characteristics. Here, a normal assist characteristic will be described with reference to FIG. FIG. 3 is a schematic diagram showing normal assist characteristics of the EPS 500.

  In FIG. 3, the EPS 500 assists the steering torque TS by applying an assist torque TA to the steering device 13 based on the illustrated assist profile. For example, the assist torque TA0 corresponds to the steering torque TS0, and the EPS 500 has a motor so that the assist torque TA becomes TA0 when the steering torque TS detected by the steering torque sensor is TS0. Control the output. In FIG. 3, the assist profile has a contrasting shape with respect to the point at which the steering torque TS becomes zero. This is because the direction in which the steering torque TS and the assist torque TA corresponding to the steering torque TS act is steering. It shows that the opposite is true depending on the direction.

  Returning to FIG. 2, when the slip ratio SL is larger than the threshold value SLth (step A12: YES), the ECU 100 determines whether or not the slip ratio SL has an increasing characteristic with respect to the steering direction (step A13). When the slip ratio SL does not have an increase characteristic with respect to the steering direction (step A13: NO), the ECU 100 determines whether or not the slip ratio SL has a decrease characteristic with respect to the steering direction (step A15). ).

  Here, the change characteristic of the slip ratio SL will be described with reference to FIG. FIG. 4 is a schematic diagram showing the change characteristic of the slip ratio SL.

  In FIG. 4, the vertical axis and the horizontal axis represent the slip ratio SL and the steering angle DS, respectively. In the steering angle DS, the steering angle corresponding to the neutral position of the steering device 13 is the reference angle (that is, zero). The reference angle may be set to any steering angle. In FIG. 4, as the handle 11 is turned to the left, that is, the wheel is steered to the left, the steering angle DS becomes larger in the left direction in the figure, and as the handle 11 is turned to the right, that is, the wheel is steered to the right. This indicates that the steering angle DS increases in the right direction in the figure.

  In FIG. 4, the slip ratio (white circle in the figure) when the steering angle DS is zero is shown. In this steering position, when the steering direction is the left steering direction (the direction of the arrow A in the figure), the slip ratio SL increases. Further, when the steering direction is the right steering direction (the arrow B direction in the figure), the slip ratio SL decreases. That is, in FIG. 4, at the steering position where the steering angle DS is zero, if the steering direction is left, the slip ratio SL is an increase characteristic, and if the steering direction is right, the slip ratio SL is a decrease characteristic.

  In the processing according to step A13 and step A15 in FIG. 2, the ECU 100 monitors the value of the slip ratio SL calculated at regular intervals, and the value of the slip ratio SL is buffered in the RAM. Based on whether the value has increased or decreased from the value, it is determined what change characteristic the steering direction has. The steering direction is the direction in which the steering angle DS changes, and is easily specified based on the output value of the steering wheel angle sensor 600.

  The change characteristic of the slip ratio SL illustrated in FIG. 4 represents the slip ratio SL for a relatively wide range of steering angles for the sake of simplicity of explanation. Actually, it is rare that the ECU 100 can acquire a wide range of change characteristics in the process of buffering the slip rate SL in the RAM, and it is preferable that the change characteristics are discriminated in real time for the steering operation as described above. It is. However, if the change characteristic as shown in FIG. 4 can be obtained in advance, or if the change characteristic of the slip ratio SL can be estimated, of course, the change characteristic of the slip ratio is obtained before the actual steering operation. It may be specified.

  Returning to FIG. 2, when the slip ratio SL has an increasing characteristic with respect to the steering direction (step A13: YES), the ECU 100 controls the EPS 500 to decrease the assist torque TA (step A14). On the other hand, when the slip ratio SL is a decreasing characteristic with respect to the steering direction (step A15: YES), the ECU 100 controls the EPS 500 to increase the assist torque TA (step A16). When the slip ratio SL is not a decrease characteristic with respect to the steering direction (step A15: NO), the ECU 100 determines the assist torque TA based on the assist profile shown in FIG. 3 without performing increase / decrease control.

  Whether the slip rate SL is an increase characteristic or a decrease characteristic with respect to the steering direction is determined by whether the change rate of the slip rate SL (the change gradient of the slip rate SL with respect to the steering angle DS) is equal to or greater than a threshold stored in the ROM in advance. It is determined by whether or not there is. That is, if it is within the range of the threshold value (set to both positive and negative), it is determined that the slip ratio SL is neither an increase characteristic nor a decrease characteristic.

  When the assist torque TA is increased by the process related to step A16, the driver feels that the steering wheel has become relatively light, and thus the steering wheel operation in the steering direction is facilitated. On the other hand, when the assist torque TA is reduced by the processing related to step A14, the driver feels that the steering wheel is relatively heavy, and thus steering of the steering wheel in the steering direction is hindered. Therefore, as a result, the vehicle 10 is invited in a direction in which the slip rate decreases, that is, in a direction in which the grip degree increases, and the vehicle speed maintenance control is effectively executed. That is, a decrease in the running performance of the vehicle is effectively prevented.

  Note that the mode of increasing or decreasing the assist torque TA may be freely determined as long as the effect according to the present invention is ensured. Here, with reference to FIG.5 and FIG.6, the determination aspect of the increase / decrease amount of the assist torque TA is demonstrated. FIG. 5 is an example of a correction coefficient map for correcting the assist torque TA, and FIG. 6 is another example of the correction coefficient map.

  In FIG. 5, a correction coefficient map 900A stored in the ROM of the ECU 100 is shown. In the correction coefficient map 900A, the vertical axis and the horizontal axis represent the correction coefficient P and the slip ratio SL, respectively. Here, the correction coefficient P is a coefficient by which the assist torque TA determined based on the assist profile shown in FIG. 3 is multiplied, that is, when the correction coefficient is “1”, It means that no correction is made.

  In the correction coefficient map 900A, the range where the slip ratio SL is equal to or less than the above-mentioned SLth is set to the dead zone, the correction coefficient P is set to 1, and no correction is made to the assist torque TA. That is, the assist torque TA is determined according to the assist profile. On the other hand, in the region where the slip ratio SL is larger than the threshold value SLth, two types of assist torque correction profiles are defined. That is, the profiles Pri0 (shown by a solid line) and Prd0 (shown by a chain line).

  The profile Pri0 is a profile that increases the correction coefficient P as the slip ratio SL increases. Therefore, in step A16 in FIG. 2, this profile Pri0 is selected. In this case, if the slip ratio SL is relatively large, the assist torque TA is set relatively large.

  The profile Prd0 is a profile that decreases the correction coefficient P as the slip ratio SL increases. Therefore, in step A14 in FIG. 2, this profile Prd0 is selected. In this case, if the slip ratio SL is relatively large, the assist torque TA is set relatively small.

  For example, at a certain slip ratio SL0 (SL0> SLth), if the slip ratio SL is a decrease characteristic with respect to the steering direction, the correction coefficient P1 (P1> 1) according to the profile Pri0, and the slip ratio SL is an increase characteristic with respect to the steering direction. If so, the correction coefficient P2 (P2 <1) is set as the correction coefficient according to the profile Prd0.

  On the other hand, FIG. 6 shows a correction coefficient map 900B stored in the ROM. In the correction coefficient map 900B, the vertical axis and the horizontal axis represent the absolute values of the above-described correction coefficient P and slip ratio change gradient GSL, respectively. Here, the slip ratio change gradient GSL is an inclination when the slip ratio SL changes, and is a value that can be defined in either positive or negative direction. That is, the slip rate SL changes rapidly as it goes to the right in the figure. A dead zone is set in the correction coefficient map 900B as in the correction coefficient map 900A. The dead zone in the correction coefficient map 900B is a range in which the absolute value of the slip rate change gradient GSL is within | GSLth |. Note that the change gradient belonging to the dead zone is equivalent to the change gradient determined to be neither an increase characteristic nor a decrease characteristic with respect to the steering direction in FIG. In the correction coefficient map 900B, two types of assist torque correction profiles are defined in a region beyond the dead zone. That is, the profile Pri1 and the profile Prd1.

  The profile Pri1 is a profile when the slip ratio SL has a decreasing characteristic with respect to the steering direction, and is a profile that increases the correction coefficient P as the absolute value of the slip ratio change gradient GSL increases. Therefore, in step A16 in FIG. 2, for example, this profile Pri1 is selected. In this case, if the change gradient of the slip ratio SL is relatively large, the assist torque TA is set relatively large.

  The profile Prd1 is a profile when the slip ratio SL has an increasing characteristic with respect to the steering direction, and is a profile that decreases the correction coefficient P as the absolute value of the slip ratio change gradient GSL increases. Therefore, in step A14 in FIG. 2, for example, this profile Prd1 is selected. In this case, if the change gradient GSL of the slip ratio SL is relatively large, the assist torque TA is set relatively small.

  For example, in the absolute value | GSL0 | (| GSL0 |> | GSLth |) of a certain slip ratio change gradient, if the slip ratio SL is a decreasing characteristic with respect to the steering direction, the correction coefficient P3 (P3> 1) is set according to the profile Pri1. If the slip ratio SL is an increase characteristic with respect to the steering direction, the correction coefficient P4 (P4 <1) is set as the correction coefficient according to the profile Prd1.

  Returning to FIG. 2, when the processing according to step A14 or step A16 is executed, or when it is determined in step A15 that the slip ratio SL is not a decreasing characteristic with respect to the steering direction, the ECU 100 proceeds to step A11. Then, a series of processing is repeated until the speed maintenance control is completed.

  The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. Is also included in the technical scope of the present invention.

1 is a schematic configuration diagram of a vehicle according to an embodiment of the present invention. 2 is a flowchart of an assist torque control process executed by an ECU in the vehicle of FIG. FIG. 2 is a schematic diagram illustrating normal assist characteristics of EPS provided in the vehicle of FIG. 1. It is a schematic diagram showing the change characteristic of the slip ratio of the wheel in the vehicle of FIG. It is a schematic diagram of the correction coefficient map referred in the assist torque control process of FIG. It is another schematic diagram of the correction coefficient map referred in the assist torque control process of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Vehicle, 100 ... ECU, 200 ... Throttle valve motor, 300 ... Start switch, 400 ... Brake actuator, 500 ... EPS, 600 ... Steering angle sensor, FL700, 700FR, 700RL, 700RR ... Braking device, 710FL, 710FR, 710RL , 710RR ... wheel cylinder, 800FL, 800FR ... wheel speed sensor.

Claims (6)

A vehicle control apparatus for controlling a vehicle including a steering torque assisting means for applying an assisting torque for assisting a steering torque to the steering means,
Grip degree specifying means for specifying the grip degree of the wheel in the vehicle;
Steering direction specifying means for specifying the steering direction of the vehicle;
A change characteristic specifying means for specifying a change characteristic of the grip degree of the wheel with respect to the specified steering direction based on the specified grip degree;
The first control for controlling the steering torque assisting means so that the auxiliary torque increases when the specified change characteristic is an increase characteristic, and the auxiliary torque when the specified change characteristic is a decrease characteristic. An auxiliary torque control means for executing at least one of the second controls for controlling the steering torque auxiliary means so as to decrease. The vehicle further includes a braking device for braking the vehicle and a driving device for driving the vehicle,
The vehicle control device further includes vehicle speed control means for controlling the braking device and the driving device so that the speed of the vehicle is maintained at a predetermined value.
2. The vehicle control device according to claim 1, wherein the auxiliary torque control unit executes the at least one when the speed of the vehicle is maintained at the predetermined value. 3. The grip degree specifying means specifies the grip degree of the wheel by specifying the slip degree of the wheel that decreases and increases in accordance with the increase and decrease of the grip degree of the wheel, respectively. Or the control apparatus of the vehicle of 2. The vehicle control device according to claim 3, wherein the grip degree specifying unit specifies a slip degree of the wheel based on a wheel speed of the vehicle. The auxiliary torque control means determines an increase or decrease amount of the auxiliary torque in the first or second control according to the specified grip degree. The vehicle control device according to Item. The said auxiliary torque control means determines the increase or decrease amount of the said auxiliary torque in said 1st or 2nd control according to the value which prescribes | regulates the said change characteristic. The vehicle control device according to one item.

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