JP2011218953A - Device for control of drive force - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for control of drive force that improves vehicle steering characteristics during traveling and prevents a driver from feeling discomfort.SOLUTION: The device for control of drive force controls a driving force of a driving wheel of a vehicle in order to attain target vehicle steering characteristics. The driving force controller includes: a first calculator (step S1) for calculating a driving force to be increased for relatively improving vehicle steering characteristics, with respect to a basic driving force of a driving wheel determined on the basis of an intention of a vehicle driver; a second calculator (step S2, S4 and S5) for calculating a plurality of upper limit values of the driving force to be increased, on the basis of a plurality of conditions; and a third calculator (step S6, S7) for calculating a final upper limit value of the increased driving force by limiting the increased driving force calculated in the first calculator by the lowest one of the upper limit values calculated in the second calculator.

Description

  The present invention relates to a driving force control apparatus that controls a steering characteristic during traveling of a vehicle by controlling a driving force of driving wheels.

  An example of a control system that stabilizes a vehicle body posture and characteristics by transmitting the power of a power source mounted on a vehicle to driving wheels to generate driving force and controlling the driving force of the driving wheels is disclosed in Patent Literature 1. The vehicle described in Patent Document 1 is a rear-wheel drive type two-wheel drive vehicle, and specifically, an axle torque corresponding to a basic required drive force required by a driver in the vehicle is obtained, and also according to a road gradient. Obtain the change in the ground load on the front and rear wheels, further determine the running resistance disturbance, estimate the virtual turning radius in the vehicle, and then based on parameters such as the change in ground load, turning radius, running resistance disturbance, etc. The control for correcting the axle torque so that the target value of the stability factor is obtained and the actual stability factor follows the target value is described. By performing such control, in the vehicle described in Patent Document 1, the stability factor is set so as to correspond to various surrounding environments that change from moment to moment and to have an ideal turning radius from time to time. It is said that it becomes possible to stabilize. A technique for stabilizing the running characteristics when the vehicle is turning is also described in Patent Document 2.

JP 2005-256636 A JP 2009-202621 A

  By the way, in the control system described in Patent Document 1, in correcting the axle torque corresponding to the basic required driving force required by the driver, parameters such as the ground load of the front wheels and the rear wheels, travel resistance disturbance, and the like are used. However, these parameters change depending on the road conditions, and it is difficult to say that the driver's intention is reflected.Therefore, if the axle torque is corrected by taking these parameters into account, the driver There was a possibility that the behavior of the vehicle was uncomfortable.

  The present invention has been made to solve the above problems, and in addition to being able to improve the steering characteristic when the vehicle is running, it is possible to suppress the driver from having a sense of incongruity in the steering characteristic. An object of the present invention is to provide a driving force control device.

  In order to achieve the above object, a first aspect of the present invention provides a driving force control apparatus for controlling a driving force generated in a driving wheel of the vehicle so that the steering characteristic of the vehicle becomes a target steering characteristic. First calculating means for obtaining an increase in driving force to improve the steering characteristics of the vehicle relative to the basic driving force of the driving wheel obtained based on the driver's intention; Second calculating means for obtaining a plurality of upper limit values of the driving force for the number of minutes based on a plurality of conditions determined in advance that the driver of the vehicle has a sense of incongruity in the change in steering characteristics, and the first calculating means A third calculating means for limiting the increased driving force by a smallest upper limit value among a plurality of upper limit values obtained by the second calculating means to obtain an upper limit value of the final driving force increase amount; Having It is an feature.

  According to a second aspect of the invention, in addition to the configuration of the first aspect, the plurality of conditions include a longitudinal acceleration of the vehicle, a road gradient on which the vehicle travels, and a lateral acceleration of the vehicle. A driving force control device characterized by the above.

  According to the first and second aspects of the invention, in increasing the driving force for relatively improving the steering characteristics of the vehicle relative to the basic driving force of the driving wheel obtained based on the intention of the driver of the vehicle. Then, the upper limit value of the driving force that is increased is obtained based on a condition that the driver has a feeling of strangeness in the steering characteristic. Therefore, in addition to relatively improving the steering characteristics of the vehicle, it is possible to suppress the driver from feeling uncomfortable with changes in the steering characteristics.

It is a flowchart which shows the example of control of this invention. It is a schematic diagram which shows the structure of the vehicle which can perform the example of control of this invention. It is a map used at the step of the flowchart of FIG. It is a map which shows the tendency of the increase amount of the control amount upper limit calculated | required with the flowchart of FIG. It is an example of the time chart which performs the flowchart of FIG. 1 and calculates | requires the control driving force after an upper limit process.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic diagram showing the configuration of the vehicle 1 capable of executing the control of the driving force control apparatus of the present invention. The vehicle 1 is a four-wheel drive vehicle that can generate driving force in both the front wheels 2 and the rear wheels 3. The configuration of the power train of the vehicle 1 will be described. An engine 4 is provided as a power source that generates power to be transmitted to the front wheels 2 and the rear wheels 3. The power of the engine 4 is transmitted to the transmission 5 and the power distribution device 6. It is configured to be distributed to the front wheel 2 and the rear wheel 3 via. The engine 4 is a power unit that generates power by burning fuel in the same manner as conventionally known, and controls output torque by controlling intake air amount, fuel injection amount, ignition timing, and the like. It is configured to be possible. The transmission 5 is a power transmission device that can change the ratio between the input rotation speed and the output rotation speed as is conventionally known. The transmission 5 is a stepped transmission or a continuously variable transmission. Either is acceptable.

  The power distribution device 6 is configured to be able to control the distribution ratio of power transmitted to the front wheels 2 and the rear wheels 3 in the same manner as conventionally known. As described above, for example, JP-A-5-278488, JP-A-6-72171, and JP2009 are power distribution devices capable of controlling the distribution ratio of power transmitted to the front wheels 2 and the rear wheels 3. Since it is well known as described in Japanese Patent No. -126457, the specific configuration and description of its operation are omitted. The power distribution device 6 has a front differential (not shown) interposed therebetween, and the front wheel 2 is connected to be able to transmit power, while the power distribution device 6 has a rear differential (not shown) interposed. The rear wheel 3 is connected so that power can be transmitted. Further, a braking device 7 that applies a braking force to the front wheel 2 and a braking device 8 that applies a braking force to the rear wheel 3 are provided. The braking devices 7 and 8 are configured to be able to control the braking force applied to each wheel according to the operation state of the brake pedal and other conditions in the same manner as conventionally known.

  Further, a power train control ECU (hereinafter referred to as an electronic control unit) 9 for controlling the engine 4, the transmission 5, the power distribution device 6 and the braking devices 7 and 8 is provided. The electronic control unit 9 controls the engine speed and engine torque, controls the transmission ratio of the transmission 5, and further controls the power transmitted to the front wheels 2 and the rear wheels 3 via the power distribution device 6. The distribution ratio is controlled, and further the braking force applied to the front wheels 2 and the rear wheels 3 is controlled. On the other hand, the vehicle 1 is provided with various sensors and a navigation system, and the signals of these sensors or the data of the navigation system are processed by the electronic control device 9, whereby the lateral acceleration (lateral G) of the vehicle 1, the vehicle 1 longitudinal acceleration (longitudinal G), yaw rate of the vehicle 1 in the horizontal plane, pitch angle of the vehicle 1 with respect to the horizontal plane, pitch rate, road surface gradient, vehicle speed, accelerator opening, steering angle of the steering wheel, road friction coefficient, wheel rotation speed, Parameters such as the ground load on the front wheel 2 and the rear wheel 3 and the amount of depression of the brake pedal can be detected or estimated. The engine speed and engine torque are controlled based on parameters detected or estimated by the electronic control unit 9 and maps, arithmetic expressions, data, etc. stored in advance in the electronic control unit 9, and the transmission 5 The transmission ratio of the power transmitted to the front wheels 2 and the rear wheels 3 via the power distribution device 6 is controlled, and the braking force applied to the front wheels 2 and the rear wheels 3 is further controlled. The

  In the vehicle 1 configured as described above, the total driving force in the vehicle 1 is obtained based on the vehicle speed and the accelerator opening, and the engine output and the gear ratio of the transmission 5 are controlled based on the total driving force. be able to. Further, when the vehicle 1 travels straight or turns at a corner, the target steer characteristic of the vehicle 1 is obtained based on the vehicle speed, the steering angle, the road surface friction coefficient, etc., and the actual steer characteristic of the vehicle 1 is determined as the target steer characteristic. Control close to characteristics can be performed.

  For example, oversteer can be targeted for relatively low vehicle speeds, neutral steer can be targeted for relatively medium vehicle speeds, and understeer can be targeted for relatively high vehicle speeds. Also, if the road surface has a relatively low friction coefficient, the target is understeer, if the road surface has a relatively intermediate friction coefficient, target the neutral steer, and if the road surface has a relatively high friction coefficient, oversteer. Can be targeted. Specifically, by controlling the yaw rate of the vehicle 1, the actual steering characteristic of the vehicle 1 can be brought close to the target steering characteristic. When the yaw rate of the vehicle 1 is controlled, the target yaw rate in the vehicle 1 is obtained based on the vehicle speed, the steering angle, the wheel base, etc., and the front wheel 2 and the rear wheel are set so that the actual yaw rate of the vehicle 1 approaches the target yaw rate. It is possible to control the power distribution ratio for 3.

  In this way, the target yaw rate is obtained, and the distribution ratio of the power transmitted to the front wheels 2 and the rear wheels 3 so as to bring the actual yaw rate in the vehicle 1 closer to the target yaw rate is, for example, disclosed in JP-A-5-278488. Since it is well-known as described in the gazette and the like, a specific description is omitted. Further, when the actual yaw rate is brought close to the target yaw rate, in addition to controlling the power distribution ratio by the power distribution device 6 or instead of controlling the power distribution ratio, the control given to the front wheel 2 or the rear wheel 3 is performed. The power may be controlled. Furthermore, when the actual yaw rate is brought close to the target yaw rate, the torque output from the engine 4 for transmission to the front wheels 2 or the rear wheels 3 can be controlled (increased or decreased). In the following description, the “driving force” includes the driving force generated when the power of the engine 4 is transmitted to the front wheels 2 or the rear wheels 3 and the braking force applied to the front wheels 2 and the rear wheels 3. I write.

  In controlling the steering characteristics when the vehicle 1 travels, if the driving force at the front wheels 2 and the rear wheels 3 is larger (larger) than the basic driving force of each wheel corresponding to the target steering characteristics, Responsiveness in which the steer characteristic changes is improved (increased). However, if a driving force that is relatively larger than the basic driving force for each wheel corresponding to the target steering characteristic is set in order to improve the responsiveness in which the steering characteristic of the vehicle 1 changes, the driver of the vehicle 1 May feel uncomfortable. Therefore, in order to improve the responsiveness in which the steering characteristic of the vehicle 1 changes, the vehicle 1 is set when a driving force relatively larger than the basic driving force for each wheel corresponding to the target steering characteristic is set. An example of control for suppressing the driver's uncomfortable feeling will be described based on the flowchart of FIG.

  In step S1 of FIG. 1, the control driving force (Fctrl) before the upper limit process is calculated (step S1). This “control driving force before the upper limit process” is a value obtained in order to improve the responsiveness in which the steering characteristic of the vehicle 1 changes, and is the basic for each front wheel 2 and rear wheel 3 corresponding to the target steering characteristic. It is relatively larger than the driving force. That is, it means a driving force that increases with respect to the basic driving force. The control driving force before the upper limit processing determines the actual steering characteristics when the vehicle 1 travels, changes the ground load of the front wheels 2 and the rear wheels 3, and sets the cutting angle (cornering stiffness) of the front wheels 2. By changing the value, the actual steer characteristic is adjusted, and a value obtained through an experiment or simulation is stored in the electronic control unit 9. In order to determine the actual steering characteristic of the vehicle 1, for example, a difference between the target yaw rate and the actual yaw rate or a “difference” between the target lateral acceleration and the actual lateral acceleration is obtained, and the “difference” is equal to or less than a predetermined value. Is judged as neutral steer, and if the "difference" exceeds a predetermined value and the product of the steering angle and "difference" is "positive", it is determined as oversteer, and the "difference" exceeds a predetermined value, If the product of the steering angle and the “difference” is “negative”, it can be determined that the vehicle is understeered.

  In step S2 of FIG. 1, a base control amount upper limit value (Fmax_base) is calculated. Here, the base control amount upper limit value is an upper limit value of the driving force that is increased to the basic driving force of each wheel, and is determined in order to suppress the driver from feeling uncomfortable. The map of FIG. 3 is used for the process of step S2. The map in FIG. 3 is obtained experimentally under the conditions of constant vehicle speed, straight traveling, and flat road traveling. This condition is a driving condition in which the driver is most uncomfortable when the behavior of the vehicle 1 changes. In the map of FIG. 3, the vehicle speed is shown on the horizontal axis and the control amount is shown on the vertical axis. As the vehicle speed is relatively higher, a relatively large value is obtained as the base control amount upper limit value.

  Further, in step S3 of FIG. 1, an increase amount (Fmax_gx) of the control amount upper limit value corresponding to the longitudinal acceleration of the vehicle 1 is calculated. Here, the reason why the longitudinal acceleration of the vehicle 1 is used as a parameter is that the longitudinal acceleration of the vehicle 1 is one factor of the stability factor, and the longitudinal acceleration originally changes during acceleration traveling compared to when the vehicle speed is constant. This is because even if the control for improving the steering characteristic of the vehicle 1 is executed, the driver does not feel uncomfortable. The increase amount (Fmax_gx) of the control amount upper limit value is a value obtained for the purpose of adding to the base control amount upper limit value (Fmax_base), and the increase amount (Fmax_gx) of the control amount upper limit value is (Equation 1). It can ask for.

  In this (Equation 1), Sgx is the longitudinal acceleration of the vehicle 1 corresponding to the basic driving force, Ngx is the longitudinal acceleration of the vehicle 1 when the base control amount upper limit value is added to the basic driving force, and Cgx is the vehicle 1 Is the ratio between the longitudinal acceleration Sgx of the vehicle and the longitudinal acceleration Ngx of the vehicle 1.

  Further, in step S4 of FIG. 1, an increase amount (Fmax_p) of the control amount upper limit value corresponding to the road surface gradient is calculated. The reason for using the road surface gradient as a parameter is one factor of stability factor, and steer characteristics change inevitably when traveling on an uphill or downhill compared to traveling on a flat road. This is because it is difficult for the driver to feel uncomfortable even when the control for improving the characteristics is performed. The increase amount (Fmax_p) of the control amount upper limit value is a value obtained for the purpose of adding to the base control amount upper limit value (Fmax_base), and the increase amount (Fmax_p) of the control amount upper limit value is (Expression 2) , (Equation 3), and (Equation 4).

  In the above (Equation 2), h is the vehicle height, L is the wheel base, Kf is the suspension spring constant of the front wheel 2, and Kr is the suspension spring constant of the rear wheel 3. In (Equation 3), Sp is the pitch angle of the vehicle 1 corresponding to the basic driving force, Np is the pitch angle of the vehicle 1 when the base control amount upper limit value is added to the basic driving force, and Cp is the vehicle 1. The pitch angle Sp of the vehicle 1 and the pitch angle Np of the vehicle 1 are ratios. From (Equation 2) and (Equation 3), the relationship between the increase amount (Fmax_p) of the control amount upper limit value and the pitch angle Sp of the vehicle 1 is expressed by (Equation 4).

  Further, in step S5 of FIG. 1, an increase amount (Fmax_gy) of the control amount upper limit value corresponding to the lateral acceleration of the vehicle 1 is calculated. The reason why this lateral acceleration is used as a parameter is one factor of the stability factor.The lateral acceleration is inevitably larger during turning than when traveling straight, and the driver feels uncomfortable with changes in steering characteristics. Because it is difficult to feel. The increase amount (Fmax_gy) of the control amount upper limit value is a value obtained for the purpose of adding to the base control amount upper limit value (Fmax_base), and the increase amount (Fmax_gy) of the control amount upper limit value is (Equation 5). , (Expression 6), and (Expression 7).

  In (Formula 5), A1 and A2 are design constants, V is a vehicle speed, δ is a steering angle, M is a vehicle body mass, and Gx is a longitudinal acceleration of the vehicle 1. In (Expression 6), Sgy is the lateral acceleration of the vehicle 1 corresponding to the basic driving force, Ngy is the lateral acceleration of the vehicle 1 when the base control amount upper limit value is added to the basic driving force, and Cgy. Is the ratio between the lateral acceleration Sgy of the vehicle 1 and the lateral acceleration Ngy of the vehicle 1. From (Equation 5) and (Equation 6), the relationship between the increase amount (Fmax_p) of the control amount upper limit value and the lateral acceleration Sgy of the vehicle 1 is expressed by (Equation 7).

  The processes in steps S3 to S5 may be performed all at the same time (in parallel), or each step may be performed sequentially. That is, the context of the timing of executing each step is not questioned. Further, an example of the above-described control amount upper limit increase amount (Fmax_gx), control amount upper limit increase amount (Fmax_p), and control amount upper limit increase amount (Fmax_gy) is shown in a comprehensive manner in the map of FIG. . In the map of FIG. 4, the longitudinal acceleration Sgx of the vehicle 1, the lateral acceleration Sgy of the vehicle 1, and the pitch angle Sp of the vehicle 1 are shown on the horizontal axis. In addition, the vertical axis indicates an increase amount (Fmax_gx) of the control amount upper limit value corresponding to the longitudinal acceleration Sgx, an increase amount Fmax_gy of the control amount upper limit value corresponding to the lateral acceleration Sgy of the vehicle 1, and a control amount corresponding to the pitch angle Sp. An increase amount Fmax_p of the upper limit value is shown. As shown in the map of FIG. 4, the amount of increase in each control amount upper limit value tends to be relatively large (large) as the parameter on the horizontal axis becomes relatively large (large). Note that the map of FIG. 4 is for showing the tendency of the increase amount of each control amount upper limit value, and does not represent the magnitude relationship between the increase amounts of each control amount upper limit value. For example, the increase amount Fmax_p of the control amount upper limit value is not always smaller than the increase amount Fmax_gx of the control amount upper limit value and the increase amount Fmax_p of the control amount upper limit value.

  Following the above steps S3 to S5, the control amount upper limit value is adjusted (step S6). In step S6, the control amount upper limit increase amount (Fmax_gx), the control amount upper limit increase amount (Fmax_p), or the control amount obtained in the processing in steps S3 to S5 is adjusted in accordance with the traveling conditions of the vehicle 1. Select the smallest value from the increase amount of the upper limit value (Fmax_gy), and add the increase amount of the selected control amount upper limit value to the base control amount upper limit value (Fmax_base) to obtain the final control amount upper limit value. This is control for obtaining Fmax, and is expressed by (Equation 8). When the amount of increase in any of the control amount upper limit values becomes “zero”, the base control amount upper limit value becomes the final control amount upper limit value.

  In the above (Formula 8), Min means the smallest value. Subsequent to the control in step S6, the control driving force Fctrl calculated in step S1 is limited by the final control amount upper limit value Fmax, and processing for obtaining the control driving force Fctrl_lim after the upper limit processing is performed (step S7). Return to start. The processing in step S7 is expressed by (Equation 9).

  In this way, the control driving force after the upper limit processing obtained by the processing in step S7 is a value obtained for each of the front wheels 2 and the rear wheels 3, and is based on the control driving force before the upper limit processing calculated in step S1. Is also a small (low) value.

  Next, an example of a time chart for obtaining the control driving force after the upper limit processing by executing the control example of FIG. 1 will be described based on FIG. Between Time0 and Time1, the vehicle travels straight on a flat road, the vehicle speed is constant, and the finally determined control driving force after the upper limit processing is the base control amount upper limit value. On the other hand, during Time 1 to Time 2, the vehicle is turning on a flat road at a constant vehicle speed. Since the vehicle is turning, the driver's sensitivity is low with respect to changes in lateral acceleration, but the driver is sensitive to changes in longitudinal acceleration because the vehicle speed is constant. Therefore, the control driving force after the upper limit process is maintained at the base control amount upper limit value.

  On the other hand, during Time 2 to Time 3, the vehicle is turning while accelerating the uphill path relatively small. In this case, the control driving force after the upper limit process is obtained by adding the increase amount Fmax_gx of the control amount upper limit value to the base control amount upper limit value. Furthermore, during Time 3 to Time 4, the vehicle is turning while relatively accelerating the uphill road. In this case, the control drive force after the upper limit process is obtained by adding the increase amount (Fmax_gy) of the control amount upper limit value to the base control amount upper limit value.

  As described above, in order to bring the actual steering characteristic of the vehicle 1 closer to the target steering characteristic, the driving force for each wheel can be relatively increased to improve the change response of the steering characteristic. The driving force to be increased for each wheel is selected according to the traveling state of the vehicle 1. This makes it possible to change the steer characteristic relatively large in situations where the driver does not feel uncomfortable, and to change the steer characteristic relatively small in situations where the driver tends to feel discomfort. It is possible to suppress the driver from feeling uncomfortable.

  Here, the correspondence between the functional means shown in FIG. 1 and the configuration of the present invention will be described. Step S1 corresponds to the first calculating means of the present invention, and steps S3, S4, and S5 are It corresponds to the second calculation means of the invention, and steps S6 and S7 correspond to the third calculation means of the invention. Further, the correspondence relationship between the configuration shown in FIG. 2 and the configuration of the present invention will be described. The front wheels 2 and the rear wheels 3 correspond to drive wheels of the present invention.

  In addition to the vehicle 1 shown in FIG. 2, the control example of FIG. 1 is also applied to a vehicle (hybrid vehicle) provided with an engine and an electric motor as a power source for generating power to be transmitted to the front wheels and the rear wheels. It is feasible. In this case, the target output of the engine and the target output of the electric motor are obtained based on the required driving force. Furthermore, the control example of FIG. 1 can also be executed in a vehicle provided with only an electric motor instead of the engine. In this case, the target output of the electric motor is obtained based on the required driving force.

  Furthermore, the control example of FIG. 1 can be executed also in a vehicle in which an electric motor is independently attached to each of the front wheels and the rear wheels, that is, a vehicle having an in-wheel motor type power train. The vehicle having the power train of the in-wheel motor type is not provided with the power distribution device 6 shown in FIG. 2, and is based on the required driving force, the target driving force on the front wheels, and the target driving force on the rear wheels. Thus, the output of the front wheel electric motor and the output of the rear wheel electric motor are controlled. Then, when bringing the actual steering characteristic of the vehicle closer to the target steering characteristic, the output of the electric motor for the front wheels so that the control driving force after the upper limit processing for each wheel becomes the value obtained in step S7. And the output of the electric motor for rear wheels is controlled. Furthermore, the control example shown in FIG. 1 can also be executed in a two-wheel drive vehicle configured such that the power of a power source such as an engine or an electric motor is transmitted to either the front wheels or the rear wheels. . That is, the control example of FIG. 1 can be executed if the vehicle can control the driving force generated at least one of the front wheels and the rear wheels in order to bring the actual yaw rate closer to the target yaw rate.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 2 ... Front wheel, 3 ... Rear wheel, 9 ... Electronic control apparatus.

Claims (2)

In the driving force control device that controls the driving force generated by the driving wheels of the vehicle so that the vehicle steering characteristic becomes the target steering characteristic,
First calculation means for obtaining an increase in driving force for relatively improving the steering characteristics of the vehicle relative to the basic driving force of the driving wheel obtained based on the intention of the driver of the vehicle;
Second calculating means for obtaining a plurality of upper limit values of the driving force for the increase based on a plurality of conditions that are predetermined as those for the driver of the vehicle to feel uncomfortable;
The drive force for the increase obtained by the first calculation means is limited by the smallest upper limit value among the plurality of upper limit values obtained by the second calculation means, so that the upper limit of the final increase in drive force is reached. A driving force control device comprising: third calculating means for obtaining a value.   The driving force control apparatus according to claim 1, wherein the plurality of conditions include a longitudinal acceleration of the vehicle, a gradient of a road surface on which the vehicle travels, and a lateral acceleration of the vehicle.

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