DRIVING ASSISTANCE SYSTEM FOR VEHICLE

An object of the invention is to provide a technology that can provide driving assistance matching the sense of the driver in a system for assisting avoidance of a collision of a vehicle. To achieve the object, a system for assisting avoidance of a collision of a vehicle according to the invention predicts a range of paths extending from a start point at the position at which the self-vehicle will arrive after free running for a predetermined period of time from the present time along which the self-vehicle can travel by possible driving operations that the driver can normally perform. The system does not perform driving assistance if a path along which a solid object can be avoided exists in the predicted range of paths, and performs driving assistance if a path along which a solid object can be avoided does not exist in the predicted range of paths.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

In the following, specific embodiments of the present invention will be described with reference to the drawings. Here, an exemplary case in which the present invention is applied to a system that determines a travel path of a self-vehicle and/or an obstacle and performs driving assistance for preventing deviation from the determined travel path and/or avoiding a collision with the obstacle. The “driving assistance” mentioned here refers to a process executed at a timing that enables the self-vehicle to avoid a solid object, and the process is executed at a time earlier than the execution of a process for reducing collision damage, which is executed in the case where a collision of the vehicle with the obstacle is unavoidable. The constructions of the embodiments described in the following are illustrative modes of the present invention and not intended to limit the present invention.

First Embodiment

A first embodiment of the present invention will be described firstly with reference toFIGS. 1 to 9.FIG. 1is a block diagram showing, on a function-by-function basis, the configuration of a driving assistance system for a vehicle to which the present invention is applied. As shown inFIG. 1, the vehicle is equipped with a control unit (ECU)1for driving assistance.

The ECU1is an electronic control unit having a CPU, a ROM, a RAM, a backup RAM, and I/O interface etc. The ECU1is electrically connected with various sensors such as a surrounding sensing device2, a yaw rate sensor3, a wheel speed sensor4, an acceleration sensor5, a brake sensor6, an accelerator sensor7, a steering angle sensor8, and a steering torque sensor9. Signals output from these sensors are input to the ECU1.

The surrounding sensing device2includes, for example, at least one measurement device selected from among an LIDAR (Laser Imaging Detection And Ranging), an LRF (Laser Range Finder), a millimeter wave radar, and a stereo camera. The surrounding sensing device2acquires, by detection, information about a relative position (e.g. relative distance and/or relative angle) of the self-vehicle and a solid object existing in the surrounding of the vehicle.

The yaw rate sensor3is mounted, for example, on the body of the self-vehicle and outputs an electrical signal correlating with the yaw rate of the self-vehicle. The wheel speed sensor4is attached to a wheel of the vehicle and outputs an electrical signal correlating with the running speed of the vehicle (vehicle speed). The acceleration sensor5outputs electrical signals correlating with the acceleration of the self-vehicle in the front-rear direction (longitudinal acceleration) and the acceleration of the self-vehicle in the left-right direction (lateral acceleration).

The brake sensor6is attached, for example, to a brake pedal provided in the cabin and outputs an electrical signal correlating with the operation torque of (or depression force acting on) the brake pedal. The accelerator sensor7is attached, for example, to an accelerator pedal provided in the cabin and outputs an electrical signal correlating with the operation torque of (or depression force acting on) the accelerator pedal. The steering angle sensor8is attached, for example, to a steering rod connected with a steering wheel provided in the cabin and outputs an electrical signal correlating with the rotational angle of the steering wheel (steering angle) relative to a neutral position. The steering torque sensor9is attached to the steering rod and outputs an electrical signal correlating with the toque (steering torque) exerted on the steering wheel.

The ECU1is also connected with various devices such as a buzzer10, a display device11, an electric power steering (EPS)12, and an electronically controlled brake (ECB)13. These devices are electrically controlled by the ECU1.

The buzzer10is provided, for example, in the cabin to provide warning sound or the like. The display device11is provided, for example, in the cabin to display various messages and warning light. The electric power steering (EPS)12is a device that assists the steering torque of the steering wheel utilizing torque generated by an electric motor. The electronically controlled brake (ECB)13is a device that electrically adjusts the operation oil pressure (brake oil pressure) of friction brakes provided for the respective wheels.

To control the various devices using signals output from the above-described various sensors, the ECU1has the following functions. Specifically, the ECU1has a travel path recognition part100, a travel range prediction part101, an assistance determination part102, a warning determination part103, a control determination part104, and a control amount calculation part105.

The travel path recognition part100generates information about the road (travel path) on which the self-vehicle will travel, on the basis of information output from the surrounding sensing device2. For example, the travel path recognition part100generates information about the positions of solid objects that can be obstacles to the self-vehicle and indexes indicating lane boundaries (e.g. road markings such as white or yellow lines indicating lane boundaries and solid objects such as curbstones, guard rails, grooves, walls, and poles existing along and on the side of the lane) in a coordinate system having an origin at the position of the self-vehicle and information about the posture of the self-vehicle relative to such solid objects and lane boundaries (e.g. the distances and yaw angle relative to them). The travel path recognition part100corresponds to the recognition means according to the present invention.

The travel range prediction part101determines a path along which the self-vehicle is predicted to travel in the coordinate system generated by the travel path recognition part100. In this process, the travel range prediction part101predicts a range (travel range) of paths along which the self-vehicle can travel in the future by possible operations that the driver can normally perform.

Specifically, the travel range prediction part101calculates the present lateral acceleration Gy0 of the self-vehicle A form a signal output from the acceleration sensor5and determines a path a along which the self-vehicle A is predicted to travel if the self-vehicle A runs with the present lateral acceleration Gy0 being unchanged.

Then, the travel range prediction part101determines a path b1 along which the self-vehicle A is predicted to travel if a normal change ΔGy is added to the present lateral acceleration Gy0 of the self-vehicle A and determines a path b2 along which the self-vehicle A is predicted to travel if a normal change ΔGy is subtracted from the present lateral acceleration Gy0 of the self-vehicle A.

In this process, the travel range prediction part101may calculate the turning radius R of the self-vehicle from the value obtained by adding/subtracting the normal change ΔGy to/from the present lateral acceleration Gy0 and determine the path b1, b2 on the basis of the turning radius R thus calculated and the width of the self-vehicle. The turning radius R can be calculated by dividing the vehicle speed V by the yaw rate γ (R=V/γ), where the yaw rate γ can be calculated by dividing the lateral acceleration Gy by the vehicle speed V (γ=Gy/V). Then, the travel range prediction part101determines paths b0 associated with regular-step variations in the steering angle or the lateral acceleration in the range (travel range) from the aforementioned path b1 to path b2.

The aforementioned normal change ΔGy is an amount equal to the maximum change in the lateral acceleration caused by driving operations that the driver can normally perform. This amount is determined in advance by experiments. The normal change ΔGy may be corrected in relation to the vehicle speed. For example, the normal change ΔGy may be corrected to be larger when the vehicle speed is low than when it is high. This can lead to a decrease in the frequency of the occurrence of driving assistance performed against the driver's will while the self-vehicle are running at a low speed and can delay the timing of execution of driving assistance as much as possible. Moreover, this can prevent the timing of execution of driving assistance from becoming unduly late.

If the self-vehicle A is already in a turning state at the present time (|Gy0|>0), the absolute value (|Gy0±ΔGy|) of the value obtained by adding/subtracting the normal change ΔGy to/from present lateral acceleration Gy0 can be larger than the maximum lateral acceleration (in the range of, for example, 0.2 G to 0.3 G) that can be generated by normal driving operations performed by the driver. In view of this, the value of the normal change ΔGy may be limited so that the absolute value (|Gy0±ΔGy|) of the value obtained by adding/subtracting the normal change ΔGy to/from present lateral acceleration Gy0 will not exceed the aforementioned maximum lateral acceleration.

In determining the travel range, the travel range prediction part101may set paths along which the self-vehicle is predicted to travel if the vehicle runs at the aforementioned maximum lateral acceleration as path b1 and path b2. For example, as shown inFIG. 3, the travel range prediction part101may set a path along which the self-vehicle is predicted to travel if the vehicle runs while turning to the right at the maximum lateral acceleration as path b1 and set a path along which the self-vehicle is predicted to travel if the vehicle runs while turning to the left at the maximum lateral acceleration as path b2.

Then, the assistance determination part102determines whether or not driving assistance is to be performed, on the basis of the information generated by the travel path recognition part100and the travel range predicted by the travel range prediction part101. Specifically, the assistance determination part102disables driving assistance, if there is (are) a path(s) (avoidance line(s)) E along which a solid object B can be avoided in the aforementioned travel range as shown inFIG. 4. On the other hand, the assistance determination part102enables driving assistance, if there are no avoidance lines in the aforementioned travel range as shown inFIG. 5.

The warning determination part103warns the driver by buzzing of the buzzer10and/or display of a warning message or warning light on the display device11, when driving assistance is enabled by the assistance determination part102. For example, the warning determination part103may cause the buzzer10to buzz and/or cause the display device11to display the warning message or warning light immediately at the time when driving assistance is enabled by the assistance determination part102(at the time when avoidance lines cease to exist in the aforementioned travel range).

The warning determination part103may be configured to cause the buzzer10to buzz and/or to cause the display device11to display the warning message or warning light at the time when the distance between a solid object and the self-vehicle traveling along the path in which the distance between the self-vehicle and the solid object is largest among the paths included in the aforementioned travel range becomes equal to or smaller than a predetermined distance. Moreover, the warning determination part103may be configured to calculate the time taken for the self-vehicle A to travel along the path in which the distance between the self-vehicle and the solid object is largest to reach the solid object B, and to cause the buzzer10to buzz and/or to cause the display device11to display the warning message or warning light at the time when the result of the calculation becomes equal to or shorter than a predetermined time. If the timing of buzzing of the buzzer10and/or display of the warning message or warning light by the display device11is determined with respect to the path in which the distance between the self-vehicle and the solid object is largest as described above, the timing can be retarded as much as possible. Consequently, driving assistance can be performed without bothering the driver.

The predetermined distance and the predetermined time mentioned above may be varied responsive to the signals output from the yaw rate sensor3and the vehicle speed sensor4. For example, the predetermined distance or the predetermined time may be set longer when the vehicle speed is high than when it is low. The predetermined distance or the predetermined time may be set longer when the yaw rate is high than when it is low.

The aforementioned predetermined distance may be set to be equal to the length of each of the paths included in the travel range, and the warning determination part103may be configured to cause the buzzer10to buzz and/or cause the display device11to display the warning message or warning light at the time when all the paths included in the travel range interfere with the solid object. The way of warning the driver is not limited to buzzing of the buzzer10or display of a warning message or warning light on the display device11, but other methods such as intermittently changing the fastening torque of the sheet belt may be adopted.

When driving assistance is enabled by the assistance determination part102, the control determination part104determines the timing for automatically performing a driving operation needed to avoid a collision of the self-vehicle with the solid object. (This operation will be hereinafter referred to as “avoidance operation”.)

Specifically, the control determination part104may be configured to synchronize the time at which the avoidance operation is to be performed with the time when the distance between a solid object and the self-vehicle traveling along the path in which the distance between the self-vehicle and the solid object is largest among the paths included in the aforementioned travel range becomes equal to or smaller than a predetermined distance. The control determination part104may be configured to calculate the time taken for the self-vehicle to travel along the path in which the distance between the self-vehicle and the solid object is largest among the paths included in the aforementioned travel range to reach the solid object, and to synchronize the time at which the avoidance operation is to be performed with the time when the result of the calculation becomes equal to or shorter than a predetermined time. The aforementioned predetermined distance may be set to be equal to the length of each of the paths included in the travel range, and the control determination part104may be configured to synchronize the time at which the avoidance operation is to be performed with the time when all the paths included in the travel range interfere with the solid object.

If the timing for performing driving assistance is determined with respect to the path in which the distance between the self-vehicle and the solid object is largest as described above, the timing can be retarded as much as possible. Consequently, driving assistance can be performed without bothering the driver. The avoidance operation mentioned here includes an operation of changing the steering angle of wheels using the electric power steering (EPS)12and an operation of changing the braking force acting on wheels using the electronically controlled brake (EBC)13.

The predetermined distance and the predetermined time referred to by the control determination part104may be varied in relation to the vehicle speed and the yaw rate, as with the predetermined distance and the predetermined time referred to by the warning determination part103described above. The predetermined distance and the predetermined time referred to by the control determination part104should be set to be equal to or shorter than the predetermined distance and the predetermined time referred to by the warning determination part103described above.

When the timing for performing the avoidance operation is determined by the control determination part104, the control amount calculation part105calculates control amounts for the electric power steering (EPS)12and the electronically controlled brake (ECB)13and controls the electric power steering (EPS)12and the electronically controlled brake (ECB)13in accordance with the control amounts thus calculated and the timing for performing the avoidance operation determined by the control determination part104.

Specifically, the control amount calculation part105determines an avoidance line along which a collision of the self-vehicle with the solid object can be avoided and calculates a target yaw rate needed to cause the self-vehicle to travel along the avoidance line thus determined. Then, the control amount calculation part105sets a control amount (steering torque) for the electric power steering (EPS)12and a control amount (brake oil pressure) for the electronically controlled brake (ECB)13so as to make the yaw rate of the self-vehicle (a signal output from the yaw rate sensor3) equal to the target yaw rate. In connection with this, the relationship between the target yaw rate and the steering torque and the relationship between the target yaw rate and the brake oil pressure may be prepared in advance as maps.

The method of decelerating the vehicle is not limited to operating the friction brake by the electronically controlled brake (EBC)13, but other methods such as converting the kinetic energy of the vehicle into electrical energy (regeneration) and increasing the engine brake by changing the change gear ratio of the change gear may be employed. The method of changing the yaw rate of the vehicle is not limited to changing the steering angle by the electric power steering (EPS)12, but other methods such as applying different brake oil pressures to the right and left wheels of the vehicle may be employed.

The travel range prediction part101, the assistance determination part102, the warning determination part103, the control determination part104, and the control amount calculation part105described in the foregoing constitute the assistance means according to the present invention.

The ECU1configured as described above prevents driving assistance from being performed when there is an avoidance line (or avoidance lines) in the travel range predicted by the travel range prediction part101, that is, when it is possible for the driver to avoid a collision of the self-vehicle with the solid object by performing normal driving operations. In consequence, a situation in which driving assistance is performed in spite of the driver's intention of performing normal driving operations can be prevented from occurring.

There is a possibility that the driver may not perform driving operations as usual, while driving assistance is not performed. For example, when the level of alertness of the driver is low (e.g. when the driver is looking aside or falling asleep), there is a possibility that the driver may not perform normal driving operations. While the driver does not perform normal driving operations, the number of available avoidance lines decreases as the self-vehicle comes closer to the solid object. Then, driving assistance such as warning and/or avoiding operation is performed at the time when avoidance lines cease to exist in the travel range. In other words, even in the case where the driver does not perform normal driving operations, driving assistance is performed at the time when avoidance lines cease to exist in the travel range.

There is a reaction delay from the time at which the driver is warned to the time at which the driver starts a driving operation. For example, in the case shown inFIG. 6in which a travel range (the travel range Ra1 indicated by solid lines inFIG. 6) extending from a start point at the position of the self-vehicle A at the present time is determined by prediction, an avoidance line Le along which the self-vehicle A can avoid the solid object B is included in the travel range. Therefore, the above-described driving assistance is not performed in this case.

However, if warning is issued to the driver at the present time, it takes some time (reaction delay) for the driver thus warned to start a driving operation for avoiding the solid object B. It is considered that during the reaction delay period, the self-vehicle A will continue free running with a momentum substantially equal to the momentum at the present time. Therefore, the momentum of the self-vehicle A will start to change after the free running. At that time, the avoidance line (or avoidance lines) Le′ may deviate from the range (travel range Ra2 inFIG. 6) within which the self-vehicle A can travel by normal operations performed by the driver.

Therefore, if the travel range is determined by prediction as a range extending from a start point at the position of the self-vehicle at the present time, there is a possibility that the timing of warning may be unduly late or that the avoidance line (or avoidance lines) along which the solid object can be actually avoided may differ from the predicted avoidance line.

There also is a response delay from the time at which the control amount calculation section105starts an avoidance operation to the time at which the yaw rate starts to change actually. For example, in the case shown inFIG. 7in which there is no avoidance line in the travel range Ra predicted as a range extending from a start point at the position of the self-vehicle at the present time, the control amount calculation part105determines an avoidance line Le along which the solid object B can be avoided and controls the electric power steering (EPS)12and the electronically controlled brake (ECB)13on the basis of the travel path L thus determined.

However, it takes some time (response delay) since the control amount calculation part105starts to control the electric power steering (EPS)12and the electronically controlled brake (ECB)13until the steering angle of the wheels and the brake oil pressure start to change. It is considered that during the response delay period, the self-vehicle A will continue free running with a momentum substantially equal to the momentum at the present time. Consequently, the momentum of the self-vehicle A will start to change after the free running. This means that the self-vehicle A will travel along a path Le′ having a shape same as the aforementioned avoidance line Le, after the free running.

Therefore, if the travel range is determined by prediction as a range extending from a start point at the position of the self-vehicle at the present time, there is a possibility that the timing of performing an avoidance operation may be unduly late or that the avoidance line along which the solid object can be actually avoided may differ from the avoidance line determined by the control amount calculation part105.

In view of this, in the driving assistance system for a vehicle according to this embodiment as shown inFIG. 8, the travel range prediction part101predicts a travel range Ra extending from a start point at the position P1 at which the self-vehicle A will arrive after free running for a predetermined period of time from the position P0 of the self-vehicle A at the present time.

The time length of the reaction delay of the driver and the time length of the response delay of the system are different from each other. Therefore, it is desirable that the length of the aforementioned predetermined period of time set in determining the timing of performing warning and the length of the aforementioned predetermined period of time set in determining the timing of performing an avoidance operation be different from each other.

Therefore, the travel range prediction part101predicts a travel range based on the reaction delay of the driver (which will be hereinafter referred to as the “first travel range”) and a travel range based on the response delay of the system (which will be hereinafter referred to as the “second travel range”) individually.

The time length of the reaction delay of the driver is determined in advance by a statistical method. The time length of the reaction delay thus obtained may be corrected in accordance with the level of alertness of the driver. For example, the travel range prediction part101may determine the level of alertness (whether or not the driver is looking aside or feeling sleepy) using a camera imaging the face of the driver and correct the time length of the reaction delay in such a way as to make the time length longer when the level of alertness is low than when the level of alertness is high. The travel range prediction part101may determine whether or not the driver is operating the air conditioner or navigation system using signals output from operation switches of these devices and correct the time length of the reaction delay in such a way as to make the time length longer when the driver is operating the aforementioned devices than when the driver is not operating the aforementioned devices.

The time length of the response delay of the system is determined in advance by, for example, an adaptation process based on experiments. The time length of the response delay thus obtained may be corrected in accordance with the communication load of an in-vehicle network interconnecting the ECU1and various devices. For example, the travel range prediction part101may correct the time length of the response delay in such a way as to make the time length longer when the communication load of the in-vehicle network is high than when it is low.

As described above, if the travel range is predicted taking into account a free running period necessitated by a reaction delay of the driver or a response delay of the system, a situation in which the timing of performing driving assistance is unduly late can be prevented from occurring and the difference between a path along which a solid object can be actually avoided and a predicted avoidance line can be reduced. In consequence, effective driving assistance can be provided even if there is a reaction delay of the driver or a response delay of the system.

In the following, a process of performing driving assistance in this embodiment will be described with reference toFIG. 9.FIG. 9is a flow chart of a processing routine, which is stored in, for example, the ROM of the ECU1and executed repeatedly by the ECU1.

In the processing routine shown inFIG. 9, first in step S101, the ECU1generates information (travel path information) about a travel path along which the self-vehicle will travel in the future, on the basis of a signal output from the surrounding sensing device2. Specifically, the ECU1generates information about the coordinates of the positions of a solid object that can be an obstacle to the self-vehicle and indexes indicating lane boundaries in a coordinate system having an origin at the position of the self-vehicle, information about the sizes of them, and information about the posture of the self-vehicle relative to the solid object and lane boundaries.

In step S102, the ECU1determines, based on the travel path information generated in step S101, whether or not there is a solid object that can be obstacle on the course of the self-vehicle. The “course” mentioned here is a travel path along which the self-vehicle is predicted to travel if the vehicle will continue to run while maintaining the present lateral acceleration Gy0. If the determination in step S102is negative, the ECU1once terminates the execution of this routine. On the other hand, if the determination in step S102is affirmative, the ECU1proceeds to step S103.

In step S103, the ECU1calculates the time length T1 of the reaction delay of the driver and the time length T2 of the response delay of the system. Specifically, the ECU1reads the time length T1 base of the reaction delay and the time length T2base of the response delay stored in advance in, for example, the ROM and corrects the values thereof using a correction factor F1 according to the level of alertness of the driver and a correction factor F2 according to the communication load of the in-vehicle network (T1=T1 base×F1, T2=T2base×F2). The correction factor F1 is set to be larger when the level of alertness of the driver is low than when the level of alertness of the driver is high. The correction factor F2 is set to be larger when the communication load of the in-vehicle network is high than when the level of alertness of the driver is low. The relationship between the level of alertness of the driver and the correction factor F1 and the relationship between the communication load of the in-vehicle network and the correction factor F2 may be prepared in advance as maps.

In step S104, the ECU1read various data including a signal output from the yaw rate sensor3(yaw rate γ), a signal output from the wheel speed sensor4(vehicle speed V), and a signal output from the acceleration sensor5(lateral acceleration Gy0).

In step S105, the ECU1calculates positions (arrival points) P1, P2 at which the self-vehicle will arrive after free running for the time length of reaction delay and for the time length of response delay. Specifically, the ECU1calculates the turning radius R (=V/γ) of the self-vehicle at the present time using the yaw rate γ and the vehicle speed V read in step S104as parameters. The ECU1calculates the distance L1 (which will be hereinafter referred to as the “first free running distance) through which the self-vehicle will travel by free running during the reaction delay period using the time length T1 of the reaction delay calculated in the above-described step S103and the vehicle speed V read in the above-described step S104as parameters (L1=T1×V). The ECU1calculates the coordinates of the arrival point P1 in the coordinate system generated in the above-described step S101using the aforementioned turning radius R and the first free running distance L1 as parameters. Furthermore, the ECU1calculates the distance L2 (which will be hereinafter referred to as the “second free running distance) through which the self-vehicle will travel by free running during the reaction delay period using the time length T2 of the response delay calculated in the above-described step S103and the vehicle speed V read in the above-described step S104as parameters (L2=T2×V). The ECU1calculates the coordinates of the arrival point P2 in the coordinate system generated in the above-described step S101using the aforementioned turning radius R and the second free running distance L2 as parameters.

In step S106, the ECU1calculates the coordinates of the first travel range and the second travel range extending from the start points at the coordinates of the arrival points P1 and P2 calculated in the above-described step S105. Specifically, the ECU1determines paths b1 and b2 extending from the arrival points P1 and P2 by adding and subtracting the normal change ΔGy to and from the lateral acceleration Gy0 read in the above-described step S104(i.e. the lateral acceleration of the self-vehicle at the present time). Then, the ECU1determines paths b0 associated with regular-step variations in the steering angle or the lateral acceleration in the range (travel range) from the aforementioned path b1 to path b2.

In step S107, the ECU1compares the position of the solid object in the coordinate system generated in the above-described step S101and the second travel range predicted in the above-described step S106to determine whether or not there is an avoidance line (or avoidance lines) along which the self-vehicle can avoid the solid object in the aforementioned second travel range.

If the determination in the above step S107is affirmative, the ECU1proceeds to step S108without performing driving assistance by an avoiding operation. In step S108, the ECU1compares the coordinates of the position of the solid object generated in the above-described step S101and the first travel range predicted in the above-described step106to determine whether or not there is an avoidance line (or avoidance lines) along which the self-vehicle can avoid the solid object in the aforementioned first travel range.

If the determination in the above step S108is affirmative, the ECU1terminates the execution of this routine without performing driving assistance by warning.

If the determination in step S107is negative, the ECU1proceeds to step S109, where the ECU1performs an avoidance operation using the electric power steering (EPS)12and/or the electronically controlled brake (ECB)13. Specifically, the ECU1determines a travel path (avoidance line) Le starting from the arrival point P2 along which the self-vehicle can avoid the solid object and calculates a target yaw rate needed to cause the self-vehicle to travel along the avoidance line Le thus determined. Then, the ECU1controls the electric power steering (EPS)12and/or the electronically controlled brake (ECB)13in such a way as to make the actual yaw rate of the self-vehicle equal to the target yaw rate.

During this process, the self-vehicle may move from its position at the present time to the arrival point P2 by free running. However, a collision of the self-vehicle with the solid object can be prevented with improved reliability, because the avoidance line Le is determined as a line starting from the arrival point P2. Moreover, the lateral acceleration of the self-vehicle in traveling along the avoidance line Le can be made low.

If the determination in the above step S108is negative, the ECU1proceeds to step S110, where the ECU1performs warning using the buzzer10or the display device11. In this case, there may be a reaction delay until the driver thus warned starts a driving operation for avoiding the solid object, and the self-vehicle may move to the arrival point P1 by free running during the reaction delay period. However, a situation in which the timing of performing the warning is unduly late or a situation in which the avoidance line along which the solid object can be actually avoided is different from the predicted avoidance line can be prevented from occurring, because the first travel range is determined as a range extending from the start point at the arrival point P1.

In the driving assistance system according to the embodiment described in the foregoing, driving assistance is not performed if the situation allows the driver to avoid a collision of the self-vehicle with the solid object by normal driving operations. In consequence, a situation in which driving assistance is performed in spite of the driver's intention of performing normal driving operations can be prevented from occurring.

Furthermore, in the driving assistance system according to the embodiment, since a travel range is predicted taking into consideration a free running period necessitated by a reaction delay of the driver or a response delay of the system, a situation in which the timing of performing driving assistance is unduly late can be prevented from occurring, and the difference between the path along which the solid object can be avoided and the predicted avoidance line can be made small. In consequence, effective driving assistance can be provided even if there is a reaction delay of the driver or a response delay of the system.

While in this embodiment, the lateral acceleration is used as a parameter representing the momentum of the self-vehicle, other parameters such as the yaw rate, lateral G-force, and cornering force may be used. It is preferred that the use be made of a parameter correlating with the yaw rate and the vehicle speed like the lateral acceleration and the lateral G-force.

The lateral acceleration and the lateral G-force increase with increase in the yaw rate and increases in the vehicle speed. Therefore, in the case where the lateral acceleration or the lateral G-force is used as a parameter representing the momentum of the self-vehicle, the travel range predicted by the travel range prediction part101is smaller when the vehicle speed is high than when the vehicle speed is low. Consequently, the time at which avoidance lines cease to exist in the travel range (that is, when driving assistance is performed) is earlier when the vehicle speed is high than when the vehicle speed is low. Therefore, even when the running speed of the self-vehicle is high, a collision of the self-vehicle with a solid object can be avoided with improved reliability.

Second Embodiment

A second embodiment of the present invention will be described with reference toFIG. 10. In the following, features different from those in the above-described first embodiment will be described, and the same features will not be described.

A difference between this embodiment and the above-described first embodiment resides in that an arrival point is determined taking into consideration wobbling of the self-vehicle. In this embodiment, the travel range prediction part101determines an arrival point on the assumption that the self-vehicle will wobble to the left or right while the self-vehicle is in free running.

The vehicle may sometimes wobble to the left or right during free running due to play of the steering mechanism, cant of the road surface, slip angle of wheels, or other causes. When such wobbling occurs, the arrival point determined by the method described in the first embodiment may be different from the actual arrival point.

In this embodiment, as shown inFIG. 10, the travel range prediction part101may determine a plurality of arrival points P on the assumption that the self-vehicle will wobble to the left or right during free running. In connection with this, the amount of wobbling to the left or right may be obtained in advance by an adaptation process based on, for example, experiments.

In the case where a plurality of arrival points P are determined as described above, the travel range prediction part101may predict the first travel range or the second travel range for each of the plurality of arrival points P. Alternatively, the travel range prediction part101may predict to which of the left and right sides the self-vehicle will wobble from the yaw rate at the present time and predicts the first travel range or the second travel range only for the arrival points P on the predicted side. The travel range prediction part101may predict from the yaw rate at the present time not only the direction of wobbling but also the amount of wobbling and predict the first travel range or the second travel range only for the arrival point P specified by the wobbling direction and the wobbling amount.

In the case where the travel range prediction part101predicts the first travel range or the second travel range for each of the plurality of arrival points P, the assistance determination part102may enable driving assistance by warning on condition that there is no avoidance line in any of the first travel ranges and enable driving assistance by an avoiding operation on condition that there is no avoidance line in any of the second travel ranges.

As described above, if wobbling during free running is taken into consideration in determining an arrival point(s) and/or in predicting the travel range, a situation in which the timing of performing driving assistance is unduly late can be prevented from occurring with improved reliability, and the difference between the path along which a solid object can be actually avoided and the predicted avoidance line can be further reduced.

DESCRIPTION OF THE REFERENCE SIGNS

1: ECU2: surrounding sensing device3: yaw rate sensor4: wheel speed sensor5: acceleration sensor6: brake sensor7: accelerator sensor8: steering angle sensor9: steering torque sensor10: buzzer11: display device12: electric power steering (EPS)13: electronically controlled brake (ECB)100: travel path recognition part101: travel range prediction part102: assistance determination part103: warning determination part104: control determination part105: control amount calculation part