Driving force control device

Abstract

Provided is a driving force control device (1), wherein if it is determined that the behavior of a preceding vehicle is unstable, the driving force control device (1) sets the inter-vehicle distance to a predetermined value or greater while executing suppression control for suppressing the control of a driving source so as to enter a second state in which a driving wheel drives the driving source via a power transmission mechanism. With this configuration, even if the behavior of the preceding vehicle is unstable during the inter-vehicle distance control, it is possible to obtain a driving sensation without causing discomfort a to the driver.

Description

Driving force control device

[0001] The present invention relates to a driving force control device.

[0002] As a driving force control device that controls the inter-vehicle distance to a preceding vehicle traveling ahead of the host vehicle, there is known a device that adjusts the throttle opening of the engine of the host vehicle by following the acceleration and deceleration of the preceding vehicle. For example, Patent Document 1 discloses a driving force control device that stabilizes the host vehicle by suppressing fluctuations in the throttle opening of the host vehicle when the preceding vehicle accelerates or decelerates abruptly.

[0003] Japanese Unexamined Patent Publication No. Hei 7-17297

[0004] In the above-described conventional driving force control device, when the behavior of the preceding vehicle is unstable, controlling the throttle opening of the engine of the host vehicle following the acceleration and deceleration of the preceding vehicle results in frequent switching between a state where engine braking is generated (deceleration state) and a state where the engine drives the drive wheels (acceleration state). Such frequent switching of power transmission causes discomfort to the driver in driving feel. In particular, when the power transmission mechanism of the host vehicle is a dog-type transmission, shocks occurring when switching the dog clutch occur frequently.

[0005] An object of the present invention is to solve the above-described problems and provide a driving force control device capable of providing a driving feel without discomfort for the driver even when the behavior of the preceding vehicle is unstable during inter-vehicle distance control.

[0006] To solve the aforementioned problems, the present invention provides a drive force control device comprising: a control unit that controls the drive source of the vehicle based on the distance between the vehicle and a preceding vehicle; and a preceding vehicle behavior determination unit that determines the behavior of the preceding vehicle. The vehicle is configured such that drive force is transmitted between the drive source and the drive wheels via a power transmission mechanism. The control unit can control the drive source to be in one of three states: a first state in which the drive source drives the drive wheels via the power transmission mechanism; a second state in which the drive wheels drive the drive source via the power transmission mechanism; or a third state between the first and second states. Furthermore, if the preceding vehicle behavior determination unit determines that the behavior of the preceding vehicle is unstable, the control unit performs suppression control to prevent the control of the drive source from being moved to the second state, while simultaneously setting the distance between the vehicles to a predetermined value or greater.

[0007] In the drive force control device of the present invention, even when the behavior of the preceding vehicle is unstable during inter-vehicle distance control, the shock caused by the switching of drive transmission by the power transmission mechanism can be suppressed, thus providing a driving feel that is natural for the driver.

[0008] This is a configuration diagram showing a drive force control device according to an embodiment of the present invention. This is a graph showing the relationship between throttle opening and engine speed in a drive force control device according to an embodiment of the present invention. This is a diagram showing the state of the dog clutch in inter-vehicle distance control by a drive force control device according to an embodiment of the present invention. This is a time chart showing engine brake suppression control by a drive force control device according to an embodiment of the present invention. This is a time chart showing engine brake suppression control by a drive force control device according to an embodiment of the present invention. This is a flowchart showing the inter-vehicle distance control method by a drive force control device according to an embodiment of the present invention.

[0009] Embodiments of the present invention will be described in detail with reference to the drawings as appropriate. The drive force control device 1 shown in Figure 1 is mounted on a vehicle that transmits engine drive force to the drive wheels via a dog-type transmission.

[0010] In this embodiment, a drive force control device 1 mounted on a motorcycle, which is a saddle-type vehicle having front and rear wheels, will be described as an example. In this embodiment, the motorcycle transmits the driving force from the engine (internal combustion engine), which is the drive source, to the rear wheel, which is the drive wheel, via a dog-type transmission, which is the power transmission mechanism. Note that the drive force control device 1 in this embodiment can also be applied to various vehicles such as saddle-type vehicles such as motorcycle tricycles and four-wheeled vehicles.

[0011] Vehicles equipped with a dog-type transmission have three states: a first state in which the engine drives the drive wheels via the transmission; a second state in which the drive wheels drive the engine via the transmission; and a third state other than the first and second states (a state between the first and second states, i.e., a state in which the engagement between the dog claw and the dog hole is released).

[0012] The first state, as shown in Figure 3, is when the engine's driving force is transmitted to the drive wheels via the transmission. That is, the dog holes of the drive gear are engaged with the dog pawls of the dog clutch in the direction of rotation of the drive gear.

[0013] The second state is when the drive wheels are driving the engine via the transmission, and engine braking is occurring. In other words, the dog holes of the drive gear are engaged with the dog pawls of the dog clutch in the opposite direction to the rotation of the drive gear.

[0014] The third state is an intermediate state between the first and second states (i.e., the dog pawl and dog hole are disengaged). In the third state, the dog hole of the drive gear is not engaged with the dog pawl of the dog clutch, which is a neutral state, and the engine's driving force is not transmitted to the drive wheels via the transmission, nor does engine braking occur.

[0015] The drive force control device 1 shown in Figure 1 is an electronic control device such as an ECU (Electronic Control Unit) that performs automatic cruise control to control the vehicle's speed. Automatic cruise control includes vehicle speed control to maintain the vehicle speed at a predetermined speed and distance control to adjust the distance to the preceding vehicle. The drive force control device 1 consists of a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and the CPU executes programs stored in the memory unit 20 such as the ROM to perform the work of each part.

[0016] The drive force control device 1 includes a control unit 10 that controls the engine based on the distance between the vehicle and the preceding vehicle, a storage unit 20 that stores various data, and a preceding vehicle behavior determination unit 30 that determines the behavior of the preceding vehicle.

[0017] The preceding vehicle behavior determination unit 30 determines whether the behavior of the preceding vehicle is stable or unstable by analyzing images of the preceding vehicle taken by a camera 2 installed on the vehicle. Various known determination methods can be used to determine whether the behavior of the preceding vehicle is stable or not.

[0018] For example, the preceding vehicle behavior determination unit 30 determines the behavior of the preceding vehicle based on the positional relationship between the preceding vehicle and the lane. Specifically, it detects fluctuations in the distance between the preceding vehicle and the lane from the image of the camera 2, and if the degree of fluctuation per unit time exceeds a predetermined value, it determines that the behavior of the preceding vehicle is unstable (the preceding vehicle is driving erratically).

[0019] Furthermore, the preceding vehicle behavior determination unit 30 determines the behavior of the preceding vehicle, for example, based on the frequency of the preceding vehicle's brake operation. Specifically, it detects the flashing of the preceding vehicle's brake lights from the image of the camera 2, and if the flashing of the preceding vehicle's brake lights is frequent, it determines that the preceding vehicle's behavior is unstable (the preceding vehicle is frequently applying the brakes).

[0020] Furthermore, the preceding vehicle behavior determination unit 30 determines the behavior of the preceding vehicle, for example, based on the relative speed between the self-vehicle and the preceding vehicle. Specifically, it detects the relative speed between the self-vehicle and the preceding vehicle from the image of the camera 2, and if the fluctuation in relative speed is greater than the fluctuation in the self-vehicle's speed, it determines that the behavior of the preceding vehicle is unstable (the preceding vehicle is repeatedly accelerating and decelerating rapidly). In other words, the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is unstable when the frequency of repeated increases and decreases in the relative speed of the preceding vehicle with respect to the self-vehicle is above a threshold.

[0021] The memory unit 20 stores data or a relational expression that shows the relationship between the throttle opening and the engine speed. Figure 2 is a graph showing the relationship between the throttle opening and the engine speed.

[0022] In this embodiment, the throttle opening for the first state (a state in which the drive wheels are driven via the transmission), the throttle opening for the second state (a state in which the drive wheels drive the engine via the transmission), and the throttle opening for the third state (a state between the first and second states) are defined. Referring to the graph in Figure 2, the third state can be represented by a function that increases as the engine speed increases (hereinafter referred to as the "no-load line"). When the throttle opening is adjusted to a value on the no-load line, the transmission enters the third state. When the throttle opening is adjusted to exceed the throttle opening for the third state (no-load line), the system transitions to the first state, and when the throttle opening is adjusted to fall below the throttle opening for the third state (no-load line), the system transitions to the second state.

[0023] The control unit 10 is connected to the throttle drive unit 4, which varies the throttle opening, and increases or decreases the engine's throttle opening through feedback control. The control unit 10 also sets the magnitude of the gain when performing feedback control of the engine. Based on the engine speed input from the rotation speed meter, the control unit 10 refers to information about the third state (no-load line) stored in the memory unit 20 (for example, a map showing NLL opening information) and calculates the throttle opening that corresponds to the third state (the throttle opening that becomes the no-load line) corresponding to the engine speed. The control unit 10 can also detect the distance between its vehicle and the vehicle ahead using a camera 2 or radar 3 installed on the vehicle.

[0024] The control unit 10 controls the throttle opening of the vehicle's engine and the brake control device 5 so that the distance between the vehicle and the preceding vehicle becomes the target distance. The default value of the target distance set when executing auto cruise control (hereinafter referred to as the "first distance") may be a value specified by the driver when executing auto cruise control, or it may be a fixed value. If the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is stable, the control unit 10 sets the target distance to the first distance.

[0025] If the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is unstable, the control unit 10 sets the target following distance to a distance (second following distance that is greater than the first following distance) which is the default value (first following distance) plus a correction value. In this way, if the behavior of the preceding vehicle is unstable, the control unit 10 controls the throttle opening and brakes so that the following distance between the vehicle and the preceding vehicle is greater than the first following distance. The correction value may be a fixed value set in advance or a value specified by the driver, or a different value may be selected depending on the size of the first following distance specified by the driver.

[0026] When the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is unstable and the second following distance is set to the target following distance, if the actual following distance becomes greater than or equal to the target following distance (greater than or equal to a predetermined value), the control unit 10 executes control (engine brake suppression control) that suppresses the control of the throttle opening so that the vehicle enters the second state (a state in which engine braking occurs).

[0027] In the engine brake suppression control of this embodiment, the throttle opening is controlled to maintain the dog clutch in the first state (the state in which the engine's driving force is transmitted to the drive wheels). Furthermore, in the engine brake suppression control of this embodiment, after reducing the engine's throttle opening while maintaining the dog clutch in the first state, the throttle opening is maintained at the lower limit of the first state (a value that does not fall below the no-load line), thereby preventing the dog clutch from entering the third and second states.

[0028] Furthermore, in the engine braking suppression control of this embodiment, it is preferable to make the behavior of the vehicle gentler by making the feedback gain for controlling the engine smaller than the feedback gain set when the distance between vehicles falls below the first distance between vehicles.

[0029] Furthermore, when the control unit 10 drives the brake control device 5 to perform brake control during engine brake suppression control, it activates only the rear brakes and applies braking force only to the rear wheels. In addition, the control unit 10 performs brake control such that the braking force is weaker than when the distance between vehicles is less than the first distance between vehicles.

[0030] Next, the method for controlling the distance between vehicles by the drive force control device 1 will be described. In the following description, the timetables in Figures 4 and 5 and the flowchart in Figure 6 will be referred to as appropriate. In the process of step S1, the control unit 10 determines whether or not to perform distance control. If the camera 2 or radar 3 recognizes a preceding vehicle during auto cruise control and distance control is performed (YES in step S1), the process proceeds to step S2.

[0031] In step S2, the control unit 10 sets the first inter-vehicle distance to the target inter-vehicle distance and controls the engine throttle opening to achieve that target inter-vehicle distance (from t0 to t1 in Figure 4). In step S3, the preceding vehicle behavior determination unit 30 starts determining the behavior of the preceding vehicle. If the behavior of the preceding vehicle is stable (from t0 to t1 in Figure 4), the deviation from the target inter-vehicle distance (target inter-vehicle distance - actual inter-vehicle distance) will be small.

[0032] At t1 in Figure 4, if the behavior of the preceding vehicle becomes unstable, the amplitude of the deviation from the target inter-vehicle distance increases, and the amplitude of the target acceleration (operation request) required to maintain the target inter-vehicle distance also increases. If this condition continues and the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is unstable (t2 in Figure 4), the control unit 10, in the processing of step S4, sets the target inter-vehicle distance to a second inter-vehicle distance (a distance greater than the first inter-vehicle distance) which is the first inter-vehicle distance plus a correction value.

[0033] The control unit 10 controls the engine throttle opening to achieve the newly set target distance between vehicles. Note that when the target distance between vehicles is set to the second distance at t2 in Figure 4, the deviation from the target distance will temporarily increase. If the feedback gain is set to the normal gain (default value during distance control), the deceleration will also temporarily increase, which may cause discomfort to the driver. Therefore, it is preferable to change the feedback gain for controlling the throttle opening to a smaller feedback gain (medium gain in Figure 4) than the normal gain when the second distance between vehicles is set to the target distance. As a result, the behavior of the vehicle becomes gentler than under normal control, and the vehicle can gradually decelerate without excessively following the unstable movements of the preceding vehicle (for example, repeated acceleration and deceleration), bringing the distance between the vehicle and the preceding vehicle closer to the second distance.

[0034] In step S5, based on the detection results of camera 2 or radar 3, it is determined whether the absolute value of the deviation between the target inter-vehicle distance (second inter-vehicle distance) and the actual inter-vehicle distance is less than or equal to a specified value. If the absolute value of the deviation between the target inter-vehicle distance and the actual inter-vehicle distance is less than or equal to the specified value (YES in step S5), in step S6, the control unit 10 executes engine brake suppression control and controls the throttle opening so that the dog clutch enters the first state. At this time, the control unit 10 sets the throttle opening to the lower limit of the first state (a value that does not fall below the no-load line). As a result, the control unit 10 sufficiently reduces the throttle opening and adjusts the inter-vehicle distance by decelerating its own vehicle to the target inter-vehicle distance while slightly transmitting the driving force of the drive source to the drive wheels (t2 to t3 in Figure 4).

[0035] Furthermore, if the answer to step S5 is YES, the control unit 10 preferably changes the feedback gain for controlling the throttle opening to a feedback gain smaller than the medium gain (low gain in Figure 4) (t3 in Figure 4). That is, it is preferable that the feedback gain after the actual distance between vehicles becomes equal to or greater than the target distance (second distance between vehicles) is smaller than the feedback gain set when the distance between vehicles is less than the first distance between vehicles. This allows the target distance between vehicles to be maintained while suppressing changes in the vehicle's speed (i.e., while making the vehicle's behavior smoother) (from t3 onwards in Figure 4). After the feedback gain is set to the low gain, engine brake suppression control is performed until the actual distance between vehicles falls outside a predetermined range centered on the target distance (second distance between vehicles) (for example, target distance ± correction value).

[0036] Furthermore, as shown from t4 to t5 in Figure 5, when the throttle opening is set to the lower limit in the first state, resulting in insufficient deceleration of the vehicle and a situation where it is desirable to return the actual distance to the vehicle to the target distance (second distance), the control unit 10 executes brake control of the rear brakes. It is preferable to limit the braking force applied to the rear brakes to be weaker than the braking force applied when the distance to the vehicle is less than the first distance. By applying a weak braking force only to the rear wheels in this way, the stability of the vehicle when the braking control force acts on the vehicle can be improved.

[0037] As described above, if the behavior of the preceding vehicle is unstable, the control unit 10 controls the throttle opening to maintain the first state and increases the target distance between vehicles to a distance greater than or equal to the first distance between vehicles, thereby moving the vehicle away from the preceding vehicle with unstable behavior.

[0038] The control unit 10 detects the difference between the actual distance between vehicles and the target distance at predetermined intervals. At t5 in Figure 5, if the difference between the actual distance between vehicles and the target distance becomes smaller than a threshold (YES in step S7), the engine brake suppression control is terminated. When the engine brake suppression control is released because the vehicle approaches the preceding vehicle, the control unit 10 changes the feedback gain for controlling the throttle opening from low gain to medium gain and applies braking force to the front and rear wheels to increase the distance between the vehicle and the preceding vehicle (t5 to t6 in Figure 5).

[0039] Furthermore, in the process of step S8, if the cruise control is deactivated, such as when the driver operates the accelerator pedal or brake pedal or operates the cruise control OFF switch, the control unit 10 terminates the distance control and switches to normal driving control.

[0040] Furthermore, if the actual distance between vehicles decreases further after the feedback gain has been changed from low to medium gain (t6 in Figure 5), the control unit 10 applies braking force to the front and rear wheels while changing the gain for controlling the throttle opening from medium gain to normal gain (t6 to t7 in Figure 5). As a result, when the distance between vehicles begins to increase, the control unit 10 applies braking force to the front and rear wheels while changing the gain for controlling the throttle opening from normal gain to medium gain (t7 to t8 in Figure 5).

[0041] Furthermore, if the preceding vehicle behavior determination unit 30 determines that the behavior of the preceding vehicle is unstable, the control unit 10 executes engine brake suppression control again (t8 in Figure 5). From t8 onward in Figure 5, while applying braking force only to the rear wheels, the gain for controlling the throttle opening is changed from a medium gain to a low gain, thereby suppressing the acceleration of the own vehicle while approaching the target distance between vehicles.

[0042] With the drive force control device 1 described above, even when the behavior of the preceding vehicle is unstable during distance control, the shock caused by the switching of drive transmission by the dog clutch of the power transmission mechanism can be suppressed. This suppresses disturbances in the driver's riding posture and provides a driving feeling that is natural for the driver.

[0043] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be modified as appropriate without departing from its spirit. In this embodiment, the control unit 10 prohibits controlling the engine (throttle opening) so that the dog clutch enters the second state in engine brake suppression control, but it is also possible to suppress controlling the engine to enter the second state in engine brake suppression control. In other words, in the present invention, when predetermined conditions are met, the control unit 10 does not exclude controlling the engine to enter the second state in engine brake suppression control.

[0044] In this embodiment, the control unit 10 maintains the first state in engine brake suppression control, but it may also be configured to maintain both the first and third states.

[0045] In the suppression control of the present embodiment, the control unit 10 applies braking force by the brake only to the rear wheels, but may also apply braking force by the brake to the front wheels and the rear wheels. In this case, by executing brake control such that the braking force of the rear wheels is greater than that of the front wheels, the stability of the host vehicle can be improved when the braking force of the brake acts on the host vehicle.

[0046] In the present embodiment, the driving force control device 1 mounted on a vehicle having an engine (internal combustion engine) as a driving source is described, but the driving source of a vehicle to which the driving force control device of the present invention is applicable is not limited. For example, the present invention is also applicable to vehicles having an electric motor as a driving source. Note that the suppression control when an electric motor is used as the driving source is regenerative brake suppression control.

[0047] Furthermore, in the present embodiment, the driving force control device 1 mounted on a vehicle having a dog clutch as a power transmission mechanism is described, but the power transmission mechanism of a vehicle to which the driving force control device of the present invention is applicable is not limited. For example, the present invention is also applicable to vehicles having an electromagnetic clutch as a power transmission mechanism.

[0048] 1: Driving force control device, 2: Camera, 3: Radar, 4: Throttle drive unit, 5: Brake control device, 10: Control unit, 20: Storage unit, 30: Preceding vehicle behavior determination unit

Claims

1. A drive force control device comprising: a control unit that controls the drive source of the vehicle based on the distance between the vehicle and a preceding vehicle; and a preceding vehicle behavior determination unit that determines the behavior of the preceding vehicle, wherein the vehicle is configured such that drive force is transmitted between the drive source and the drive wheels via a power transmission mechanism, and the control unit is capable of controlling the drive source to be in one of three states: a first state in which the drive source drives the drive wheels via the power transmission mechanism; a second state in which the drive wheels drive the drive source via the power transmission mechanism; and a third state between the first and second states, and when the preceding vehicle behavior determination unit determines that the behavior of the preceding vehicle is unstable, the control unit is characterized by performing suppression control to suppress the control of the drive source to be in the second state, while maintaining the distance between the vehicles at or above a predetermined value.

2. A drive force control device according to claim 1, wherein the control unit maintains the first state or the third state in the suppression control.

3. A drive force control device according to claim 1, wherein the control unit maintains the first state in the suppression control.

4. A drive force control device according to claim 3, wherein the drive source is an engine, and the control unit, in the suppression control, reduces the throttle opening of the drive source while maintaining the first state, and then sets the throttle opening to the lower limit value in the first state.

5. A drive force control device according to claim 1, wherein the control unit executes the suppression control when the preceding vehicle behavior determination unit determines that the behavior of the preceding vehicle is unstable and the distance between vehicles is greater than or equal to a predetermined value.

6. A drive force control device according to claim 5, wherein the control unit reduces the feedback gain for controlling the drive source when the inter-vehicle distance is greater than or equal to a predetermined value, compared to when the inter-vehicle distance is less than a predetermined value.

7. A drive force control device according to claim 5, wherein the vehicle comprises front wheels and rear wheels which are drive wheels, and the control unit performs brake control such that the braking force of the rear wheels is greater than that of the front wheels when the distance between vehicles is greater than or equal to a predetermined value.

8. A drive force control device according to claim 5, wherein the vehicle comprises front wheels and rear wheels which are drive wheels, and the control unit performs brake control to limit the braking force more than when the distance between vehicles is greater than or equal to a predetermined value.

9. A drive force control device according to claim 1, wherein the preceding vehicle behavior determination unit determines the behavior of the preceding vehicle based on the frequency of braking of the preceding vehicle.

10. A drive force control device according to claim 1, characterized in that the power transmission mechanism is a dog-type transmission.

11. A drive force control device according to claim 1, wherein the control unit prohibits controlling the drive source in the suppression control to reach the second state.

Images