Vehicle Control Systems

Abstract

To prevent abrupt acceleration of a vehicle even when a driver excessively steps on an accelerator pedal in a state where the vehicle is traveling on a bad road having a downward gradient.SOLUTION: As a control system of a vehicle, a controller 22: acquires a road surface gradient along a longitudinal direction of the vehicle on the basis of acceleration detected through an acceleration sensor SN2; determines an idling rotation speed of an engine 2; and controls the engine 2 so that the rotation speed of the engine 2 corresponds to the idling rotation speed while the engine is idling. When the road surface gradient in a travel direction of a vehicle 1 is a downward gradient larger than a predetermined value and an off-road mode is selected through a travel mode selection switch SN1, the idling rotation speed is set lower than the same when a normal mode is selected or the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a control system for a vehicle having an engine that provides power to drive drive wheels. [Background technology]

[0002] Conventionally, in order to improve fuel efficiency during creeping, a technique has been proposed for controlling the engine speed and the engine power transmission rate according to the gradient of the road surface.For example, Patent Document 1 discloses a technique for controlling the engine speed to a lower value according to the gradient when the road surface is downward and the brake is released while the vehicle is idling or stopped idling, compared to when the vehicle is flat. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-43424 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when driving on a rough road with a highly uneven road surface, such as an unpaved road, the driver tends to depress the accelerator pedal more than when driving on a paved road. However, the coefficient of friction of a highly uneven road surface is generally small, so the driving wheels are more likely to spin. That is, even though the driving wheels are more likely to spin when driving on a rough road than usual, the driver depresses the accelerator pedal more than usual, so the driving torque transmitted to the driving wheels becomes excessive, making the driving wheels more likely to spin. In particular, when the vehicle is on a downward slope facing forward, gravity acceleration is also added, and combined with excessive depression of the accelerator pedal and wheel slip due to a low road friction coefficient, the vehicle is likely to jump forward with an acceleration greater than the driver intends when starting the vehicle. However, the technology described in the above-mentioned Patent Document 1 does not determine the engine speed taking into account excessive depression of the accelerator pedal when driving on a rough road or unevenness of the road surface.

[0005] The present invention has been made to solve the problems of the conventional technology described above, and has an object to provide a vehicle control system that can suppress sudden acceleration of the vehicle even if the driver excessively depresses the accelerator pedal when traveling on a rough road with a downward slope. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides an engine for supplying power for driving a driving wheel. a torque converter provided with a lock-up clutch on a power transmission path of the engine; a vehicle control system having: gradient measurement means for measuring a road surface gradient along a longitudinal direction of the vehicle; driving mode selection means for selecting one driving mode from a plurality of driving modes including a first driving mode for normal driving and a second driving mode for driving on rough roads in response to an operation by a driver of the vehicle; and engine control means for determining an idle speed of the engine and controlling the engine so that the engine speed during idling is the idle speed, wherein when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second driving mode has been selected by the driving mode selection means, the engine control means sets the idle speed lower than when the first driving mode is selected or when the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value. death , The vehicle control system has a lock-up clutch control means for controlling the lock-up clutch so as to engage the lock-up clutch in a first driving range of the vehicle and release the lock-up clutch in a second driving range of the vehicle, and when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second driving mode is selected by the driving mode selection means, the lock-up clutch control means expands the first driving range more than when the first driving mode is selected and the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value. It is characterized by: According to the present invention configured as described above, in a situation where the driver recognizes that the vehicle is traveling on a bad road and is likely to depress the accelerator pedal heavily, and further in a situation where the vehicle is likely to accelerate suddenly, such as a slope with a downward gradient of a predetermined value or more, the engine control means sets the idle speed low. This makes it possible to reduce the driving torque from the engine during idling, so that even if the driver depresses the accelerator pedal heavily or the wheels slip due to a low road friction coefficient, the vehicle is prevented from lurching forward at an acceleration greater than the driver's intention when starting the vehicle. Therefore, even if the driver depresses the accelerator pedal excessively, sudden acceleration of the vehicle can be suppressed. In addition, in a situation where the driver is aware that the vehicle is traveling on a rough road and is likely to depress the accelerator pedal heavily, and further where the vehicle is traveling on a slope with a downward gradient greater than a predetermined value, where sudden acceleration of the vehicle is more likely to occur, the lock-up clutch is more likely to be engaged. This reduces transmission loss between the drive wheels and the engine, thereby increasing the braking force provided by the engine brake and suppressing sudden acceleration of the vehicle even if the driver depresses the accelerator pedal excessively.

[0007] In the present invention, preferably, when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the vehicle travel direction and the second travel mode is selected by the travel mode selection means, the engine control means reduces the idle speed when the downward gradient is large compared to when the downward gradient is small. According to the present invention thus configured, in a situation where the vehicle is more likely to accelerate suddenly due to a steep downhill gradient, the engine control means sets the idle speed even lower, so that the driving torque from the engine during idling can be made appropriate according to the road gradient, and sudden acceleration of the vehicle can be suppressed even if the driver depresses the accelerator pedal excessively on various road gradients.

[0008] In the present invention, preferably, the vehicle is a four-wheel drive vehicle in which torque generated by the engine is distributed to front wheels which are drive wheels and rear wheels which are auxiliary drive wheels, and has a torque distribution control means for controlling the torque distributed to the front and rear wheels, and when the road surface gradient measured by the gradient measurement means is an upward gradient greater than a predetermined value in the direction of travel of the vehicle and the second driving mode is selected by the driving mode selection means, the torque distribution control means distributes a larger torque to the rear wheels than when the first driving mode is selected or the road surface gradient is a downward gradient or an upward gradient equal to or less than a predetermined value, and when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the direction of travel of the vehicle and the second driving mode is selected by the driving mode selection means, the torque distribution control means distributes a smaller torque to the rear wheels than when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the direction of travel of the vehicle and the second driving mode is selected. According to the present invention thus configured, in a situation where the driver recognizes that the vehicle is traveling on a rough road and is likely to depress the accelerator pedal heavily, and further in a situation where the vehicle is more likely to accelerate suddenly, such as on a slope with a downward gradient greater than a predetermined value, the torque distribution control means sets the torque distribution to the rear wheels to be smaller than in the case of an upward gradient, thereby reducing the propulsive force of the vehicle on the rough road and suppressing sudden acceleration of the vehicle even if the driver depresses the accelerator pedal excessively.

[0010] In another aspect, the present invention provides an engine for providing power to drive drive wheels. a torque converter provided with a lock-up clutch on a power transmission path of the engine; a driving mode selection switch that receives an operation for selecting one of a plurality of driving modes including a first driving mode for normal driving and a second driving mode for driving on rough roads; a memory that stores a program; and a processor that executes the program, wherein the processor obtains a road gradient along a longitudinal direction of the vehicle based on the acceleration detected by the acceleration sensor, determines an idle speed of the engine, and controls the engine so that the engine speed becomes the idle speed when idling, and when the road gradient is a downward gradient greater than a predetermined value toward the traveling direction of the vehicle and the second driving mode is selected by the driving mode selection switch, the idle speed is set to a higher value than when the first driving mode is selected or when the road gradient is an upward gradient or a downward gradient equal to or less than the predetermined value. The lock-up clutch is controlled so as to lower the lock-up clutch, engage the lock-up clutch in a first driving range of the vehicle, and release the lock-up clutch in a second driving range of the vehicle, and when the road surface gradient is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second driving mode is selected by the traveling mode selection switch, the first driving range is expanded compared to when the first traveling mode is selected and the road surface gradient is an upward gradient or a downward gradient equal to or less than a predetermined value. The present invention is characterized in that it is configured to According to the present invention configured as described above, in a situation where the driver recognizes that the vehicle is traveling on a bad road and is likely to depress the accelerator pedal heavily, and further, where the vehicle is likely to accelerate suddenly, such as on a slope with a downward gradient of a predetermined value or more, the processor sets the idle speed low. This makes it possible to reduce the driving torque from the engine during idling, so that even if the driver depresses the accelerator pedal heavily or the wheels slip due to a low road friction coefficient, the vehicle is prevented from lurching forward at an acceleration greater than the driver's intention when starting the vehicle. Therefore, even if the driver depresses the accelerator pedal excessively, sudden acceleration of the vehicle can be suppressed. In addition, in a situation where the driver is aware that the vehicle is traveling on a rough road and is likely to depress the accelerator pedal heavily, and further where the vehicle is traveling on a slope with a downward gradient greater than a predetermined value, where sudden acceleration of the vehicle is more likely to occur, the lock-up clutch is more likely to be engaged. This reduces transmission loss between the drive wheels and the engine, thereby increasing the braking force provided by the engine brake and suppressing sudden acceleration of the vehicle even if the driver depresses the accelerator pedal excessively. Effect of the Invention

[0011] According to the vehicle control system of the present invention, when the vehicle is traveling on a rough road with a downward gradient, sudden acceleration of the vehicle can be suppressed even if the driver depresses the accelerator pedal excessively. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a vehicle to which a vehicle control system according to an embodiment of the present invention is applied. [Diagram 2] 1 is a block diagram showing an electrical configuration of a vehicle control system according to an embodiment of the present invention. [Diagram 3] FIG. 4 is an explanatory diagram showing an example of a control condition for a lock-up clutch. [Figure 4] 4 is a flowchart of a vehicle control process according to an embodiment of the present invention. [Diagram 5] FIG. 4 is an explanatory diagram showing the relationship between a road surface gradient and a corrected engine revolution speed. [Figure 6] FIG. 4 is an explanatory diagram showing the relationship between a road surface gradient and a corrected rear wheel torque distribution of the engine. [Figure 7] 4 shows an example of a time chart when vehicle control according to the embodiment of the present invention is executed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control device for a hybrid vehicle according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0014] <Device configuration> First, the overall configuration of a vehicle to which a vehicle control system according to an embodiment of the present invention is applied will be described with reference to Fig. 1. Fig. 1 is a schematic configuration diagram of a vehicle to which a vehicle control system according to an embodiment of the present invention is applied.

[0015] As shown in FIG. 1, the vehicle 1 mainly has an engine 2, a transmission 4, a transfer 6, a front drive shaft 8, a pair of left and right front wheels 10, a pair of left and right rear wheels 12, a propeller shaft 14, an electromagnetic coupling 16, a rear differential gear 18, a rear drive shaft 20, a controller 22, a driving mode selection switch SN1, a wheel speed sensor SN2, an acceleration sensor SN3, a steering angle sensor SN4, and a shift position sensor SN5.

[0016] The vehicle 1 is a four-wheel drive vehicle based on a front engine / front drive system (FF system). Specifically, the vehicle 1 does not implement a full-time four-wheel drive system, but is configured to be able to switch between a two-wheel drive state (a state in which only the front wheels 10 are driven) and a four-wheel drive state (a state in which both the front wheels 10 and the rear wheels 12 are driven) as appropriate. That is, in the vehicle 1, which is a four-wheel drive vehicle based on the FF system, the front wheels 10 function as drive wheels, and the rear wheels 12 function as auxiliary drive wheels. In addition, the vehicle 1 is configured to steer the front wheels 10 in response to the operation of a steering wheel (not shown). Note that at least a part of the present invention is not limited to application to the drive system of a four-wheel drive vehicle as shown in FIG. 1, but can also be applied to various drive systems (for example, two-wheel drive vehicles such as FF system and front engine / rear drive system (FR system), and four-wheel drive vehicles based on the FR system, etc.).

[0017] The engine 2 burns a mixture of fuel and air to generate a driving torque (engine torque) as a propulsive force for the vehicle 1, and transmits the driving torque to the transmission 4. The transmission 4 includes a torque converter 4a and an automatic transmission 4b, and transmits the driving torque from the engine 2 at a set gear ratio. The torque converter 4a includes a torus 4c that transmits the driving torque of the engine 2 to the automatic transmission 4b by fluid, and a lock-up clutch 4d that mechanically connects the engine 2 and the automatic transmission 4b directly. The automatic transmission 4b is a multi-speed gear mechanism that converts the rotation speed and torque by a combination of gears. Gears are switched using hydraulic pressure supplied from an oil pump (not shown). The automatic transmission 4b transmits the driving torque transmitted from the engine 2 via the torque converter 4a to the front wheels 10 via the front drive shaft 8, and also to the transfer 6. The transfer 6 transmits the driving torque from the automatic transmission 4b to the propeller shaft 14, and the propeller shaft 14 transmits the driving torque from the transfer 6 to an electromagnetic coupling 16. The electromagnetic coupling 16 then transmits the driving torque from the propeller shaft 14 to a rear differential gear 18, and the rear differential gear 18 transmits the driving torque transmitted from the electromagnetic coupling 16 to the rear wheels 12 via a rear drive shaft 20.

[0018] In detail, the electromagnetic coupling 16 is a coupling that connects the propeller shaft 14 and a shaft connected to the rear differential gear 18, and has an electromagnetic coil, a cam mechanism, a clutch, and the like (not shown). The electromagnetic coupling 16 is configured to vary the fastening torque in the electromagnetic coupling 16 according to the current supplied to the internal electromagnetic coil under the control of the controller 22. By changing the fastening torque in this manner, the electromagnetic coupling 16 is configured to change the maximum transmission torque, which is the maximum value of the driving torque transmitted to the rear differential gear 18 (i.e., the driving torque transmitted to the rear wheels 12) among the driving torque from the propeller shaft 14. In this case, the electromagnetic coupling 16 functions such that the maximum transmission torque is set under the control of the controller 22, and the electromagnetic coupling 16 transmits the driving torque corresponding to this maximum transmission torque to the rear differential gear 18.

[0019] Specifically, for driving torque transmitted from the propeller shaft 14 that is equal to or less than the maximum transmission torque, the electromagnetic coupling 16 transmits the driving torque as is to the rear differential gear 18. On the other hand, for driving torque transmitted from the propeller shaft 14 that exceeds the maximum transmission torque, the electromagnetic coupling 16 does not transmit all of the transmitted driving torque to the rear differential gear 18, but transmits only the driving torque corresponding to the maximum transmission torque to the rear differential gear 18. Note that the electromagnetic coupling 16 can be configured as described in, for example, JP 2013-32060 A or JP 2020-85045 A.

[0020] The driving mode selection switch SN1 is a switch for selecting one of the driving modes, a normal mode (first driving mode) for normal driving on a smooth road surface such as a paved road, and an off-road mode (second driving mode) for driving on a rough road surface with severe bumps such as an unpaved road, and is disposed in a position where the driver of the vehicle 1 can operate it (typically on the center console or dashboard in the vehicle cabin). The driving mode selection switch SN1 may be capable of selecting other driving modes (e.g., sports mode, snow mode, etc.) in addition to the normal mode and the off-road mode. The wheel speed sensor SN2 detects the wheel speed. Typically, the wheel speed sensor SN2 is provided on each of the left and right front wheels 10 and the left and right rear wheels 12, and detects the speed of each wheel. The acceleration sensor SN3 is typically a three-axis acceleration sensor capable of measuring the acceleration of the vehicle 1 in three axes, namely, the front-rear direction, the left-right direction, and the up-down direction. The steering angle sensor SN4 detects the steering angle of the vehicle 1. For example, the steering angle sensor SN4 detects the steering angle based on the rotation angle of a steering shaft (not shown). The shift position sensor SN5 detects a shift position (e.g., P range, R range, D range, etc.) selected by a shift lever or paddle switch (not shown). The driving mode selection switch SN1, the wheel speed sensor SN2, the acceleration sensor SN3, the steering angle sensor SN4, and the shift position sensor SN5 output detection signals corresponding to the detected driving mode, wheel speed, acceleration, steering angle, and shift position, respectively, to the controller 22.

[0021] Next, FIG. 2 is a block diagram showing the electrical configuration of the vehicle control system according to the embodiment of the present invention.

[0022] As shown in FIG. 2, the controller 22 receives as input a signal from a driving mode selection switch SN1, a signal from a wheel speed sensor SN2, a signal from an acceleration sensor SN3, a signal from a steering angle sensor SN4, and a signal from a shift position sensor SN5.

[0023] The controller 22 is configured by a computer having one or more processors 22a (typically a CPU), various programs (including basic control programs such as an OS and application programs that are started on the OS and realize specific functions) interpreted and executed on the processor, and a memory 22b such as a ROM or RAM for storing the programs and various data. The controller 22 functions as the "gradient measurement means", "driving mode selection means", "engine control means", "torque distribution control means" and "lock-up clutch control means" of the "vehicle control system" of the present invention.

[0024] Specifically, the controller 22 mainly outputs control signals to the engine 2, the automatic transmission 4b, the lockup clutch 4d, and the electromagnetic coupling 16 based on detection signals from the above-mentioned driving mode selection switch SN1, the wheel speed sensor SN2, the acceleration sensor SN3, the steering angle sensor SN4, and the shift position sensor SN5, and controls them. For example, the controller 22 performs control to adjust the ignition timing, fuel injection timing, and fuel injection amount of the engine 2, control to switch the gear stage of the automatic transmission 4b, control to switch the lockup clutch 4d between a plurality of states including an engaged state and a released state, and control to adjust the engagement torque of the electromagnetic coupling 16. More specifically, for example, the controller 22 controls the ignition plug, fuel injection valve, throttle valve, etc. of the engine 2, controls the oil pump and hydraulic control valve, etc. that supply hydraulic pressure to the clutch and brake of the automatic transmission 4b, controls the oil pump and hydraulic control valve, etc. that supply hydraulic pressure to the lockup clutch 4d, and controls the electromagnetic coil, cam mechanism, clutch, etc. of the electromagnetic coupling 16.

[0025] <Vehicle Control> Next, in the embodiment of the present invention, a description will be given of the control contents performed by the controller 22. In this embodiment, the controller 22 executes a vehicle control process that determines the idle speed of the engine 2 and the torque to be distributed to the rear wheels 12, and sets the control conditions of the lock-up clutch 4d.

[0026] First, the basic control of the lock-up clutch 4d will be described. The controller 22 appropriately switches the state of the lock-up clutch 4d between a plurality of states including an engaged state, a released state, and a slip state by controlling an oil pump and a hydraulic control valve that supply hydraulic pressure to the lock-up clutch 4d. The controller 22 controls the lock-up clutch 4d to be in an engaged state when the driving state of the vehicle 1 is within a predetermined lock-up region (first driving region) that is set in advance, and to be in a released state when the driving state is within a predetermined non-lock-up region (second driving region). For example, FIG. 3 shows an example of a control map in which the lock-up region and the non-lock-up region are set with the vehicle speed as a condition. In the example of FIG. 3, the lock-up region in the normal mode described later is set as a driving region where the vehicle speed is V2 or more, and the non-lock-up region is set as a driving region where the vehicle speed is less than V2. Moreover, the lock-up region in the expanded mode described later is set as a driving region where the vehicle speed is V1 or more, which is less than V2, and the non-lock-up region is set as a driving region where the vehicle speed is less than V1. That is, in the expanded mode, the lock-up region is expanded compared to the normal mode, making it easier for the lock-up clutch 4d to be engaged. In the example of Fig. 3, the lock-up region and the non-lock-up region are set based only on the vehicle speed, but they may be set based on other driving conditions in addition to the vehicle speed (for example, the accelerator opening), or may be set based on something other than the vehicle speed.

[0027] Next, the vehicle control process according to the embodiment of the present invention will be specifically described with reference to Fig. 4 to Fig. 6. Fig. 4 is a flowchart of the vehicle control process according to the embodiment of the present invention, Fig. 5 is an explanatory diagram showing the relationship between the road surface gradient and the corrected engine revolution speed, and Fig. 6 is an explanatory diagram showing the relationship between the road surface gradient and the corrected rear wheel torque distribution of the engine. The vehicle control process is started when the ignition of the vehicle 1 is turned on and the power is supplied to the vehicle system, and is repeatedly executed by the controller 22 at a predetermined cycle.

[0028] 4 is started, in step S11, the controller 22 acquires various information about the vehicle 1, including information corresponding to detection signals from the driving mode selection switch SN1, the wheel speed sensor SN2, the acceleration sensor SN3, the steering angle sensor SN4, and the shift position sensor SN5. Then, the controller 22 proceeds to step S12.

[0029] In step S12, the controller 22 calculates the normal idle speed Rs based on the information acquired in step S11. The normal idle speed Rs is the idle speed in a normal situation where the controller 22 does not correct the idle speed based on the driving mode or road surface gradient in the vehicle control process. Specifically, the controller 22 refers to an idle speed map (created in advance and stored in the memory 22b or the like) that defines the relationship between the idle speed and the coolant temperature of the engine 2, the operating state of the air conditioner compressor of the vehicle 1, the power usage state of the vehicle 1, etc., and calculates the normal idle speed Rs that corresponds to various current states of the vehicle 1 based on the information acquired in step S11. For example, the normal idle speed Rs is about 800 rpm.

[0030] Next, in step S13, the controller 22 judges whether or not the off-road mode is selected as the traveling mode based on the detection signal from the traveling mode selection switch SN1. Specifically, if the driver operates the traveling mode selection switch SN1 to select the off-road mode, it is judged that the off-road mode is selected (step S13: Yes), and if the driver selects a traveling mode other than the off-road mode (e.g., the normal mode), it is judged that the off-road mode is not selected (step S13: No).

[0031] In step S13, if it is determined that the off-road mode is selected (step S13: Yes), the process proceeds to step S14, where the controller 22 acquires a corrected rotation speed and a corrected rear wheel torque distribution. The corrected rotation speed is a correction value for correcting the idle rotation speed when the off-road mode is selected. For example, the controller 22 obtains an angle between a gravity vector and a longitudinal axis of the vehicle 1 based on signals input from the wheel speed sensor SN2 and the acceleration sensor SN3, and calculates a road surface gradient along the longitudinal direction of the vehicle 1 from this angle. Furthermore, the controller 22 identifies the traveling direction of the vehicle 1 (forward direction in the case of D range, backward direction in the case of R range, etc.) based on a signal input from the shift position sensor SN5. This makes it possible to identify whether the road surface gradient along the longitudinal direction of the vehicle 1 is an upward gradient or a downward gradient toward the traveling direction of the vehicle 1. Then, the controller 22 refers to a map (created in advance and stored in a memory, etc.) that specifies the relationship between the road surface gradient in the traveling direction of the vehicle 1 and the corrected rotation speed, as shown in FIG. 5, and acquires a corrected rotation speed corresponding to the road surface gradient calculated as above.

[0032] The horizontal axis in the map of FIG. 5 indicates the road surface gradient [%] in the traveling direction of the vehicle 1, and is a positive value when the gradient is upward in the traveling direction of the vehicle 1 (forward when moving forward, backward when moving backward), and is a negative value when the gradient is downward. In the following description, "a large downward gradient" means "a large absolute value of the downward gradient." The vertical axis indicates the corrected rotation speed [rpm]. As shown in FIG. 5, when the road surface gradient is upward, the corrected rotation speed is a positive value, and until the road surface gradient reaches the threshold value m1, the larger the road surface gradient, the larger the corrected rotation speed becomes. In other words, when the upward gradient in the traveling direction of the vehicle 1 is large, the corrected rotation speed is larger than when the upward gradient is small. Furthermore, when the road surface gradient is m1 or more, the corrected rotation speed is a maximum value Rc max The maximum value of this correction speed Rc maxcan be set according to the reliability of the engine 2 and the requirements for NVH performance, and is, for example, 700 rpm. Furthermore, the road surface gradient threshold m1 can be set according to, for example, the torque characteristics of the engine 2, the weight of the vehicle 1, the tire grip force, and the like, and, for example, m1 is 30%. Furthermore, when the road surface gradient is a downward gradient, the corrected rotation speed is a negative value, and until the road surface gradient reaches the threshold m2, the larger the road surface gradient (i.e., the larger the absolute value of the road surface gradient), the smaller the corrected rotation speed becomes. In other words, when the downward gradient in the traveling direction of the vehicle 1 is large, the corrected rotation speed is smaller than when the downward gradient is small. Furthermore, when the road surface gradient is m2 or more, the corrected rotation speed is set to a minimum value Rc min The minimum value of this correction speed Rc min can be set according to the misfire limit and torque characteristics of the engine 2 and the weight of the vehicle 1, and is, for example, -300 rpm. Furthermore, the road surface gradient threshold m2 can be set according to, for example, the torque characteristics of the engine 2, the weight of the vehicle 1, the tire grip force, and the like, and is, for example, -15%. Note that in the map of FIG. 5, the correction speed is set to a positive value on an upward gradient and a negative value on a downward gradient, but the correction speed may be set to 0 on an upward gradient and a downward gradient where the absolute value of the road surface gradient is equal to or less than a predetermined value (for example, 5%). In other words, when the absolute value of the road surface gradient is equal to or less than a predetermined value, the controller 22 may not control the correction of the idle speed.

[0033] The corrected rear wheel torque distribution is a correction value for correcting the rear wheel torque distribution when the off-road mode is selected. For example, the controller 22 calculates the road surface gradient along the longitudinal direction of the vehicle 1 in the same manner as in step S14 of FIG. 3. Then, the controller 22 refers to a map (created in advance and stored in a memory or the like) that defines the relationship between the road surface gradient in the longitudinal direction of the vehicle 1 and the corrected rear wheel torque distribution, as shown in FIG. 6, and obtains the corrected rear wheel torque distribution corresponding to the road surface gradient calculated as described above. The horizontal axis in the map of FIG. 6 indicates the road surface gradient [%] in the longitudinal direction of the vehicle 1, and is a positive value when the road surface gradient is an upward gradient toward the traveling direction of the vehicle 1 and is a negative value when the road surface gradient is a downward gradient. The vertical axis indicates the corrected rear wheel torque distribution [%]. As shown in FIG. 6, when the road surface gradient in the longitudinal direction of the vehicle 1 is an upward gradient toward the traveling direction, the corresponding corrected rear wheel torque distribution is Tc1. On the other hand, when the road surface gradient in the longitudinal direction of the vehicle 1 is a downward gradient toward the traveling direction, the corresponding corrected rear wheel torque distribution is Tc2. This corrected rear wheel torque distribution Tc2 is smaller than the corrected rear wheel torque distribution Tc1. Note that, in the map of Fig. 6, the corrected rear wheel torque distribution is set to Tc1 on an upward gradient and to Tc2 on a downward gradient, but the corrected rear wheel torque distribution may be set to 0 on an upward gradient or downward gradient where the absolute value of the road surface gradient is a predetermined value (e.g., 5%) or less. In other words, when the absolute value of the road surface gradient is a predetermined value or less, the correction of the rear wheel torque distribution may not be performed.

[0034] 4, after step S14, the process proceeds to step S15, where the controller 22 determines whether the road surface gradient in the longitudinal direction of the vehicle 1 is a downward gradient of a predetermined value ms or more in the traveling direction. The predetermined value ms is set to 0% in this embodiment, but may be set to, for example, 5% or 10%.

[0035] If the result of the determination in step S15 is that the road surface gradient is a downward gradient of the predetermined value ms or more (step S15: Yes), the process proceeds to step S16, where the controller 22 expands the lock-up region in which the lock-up clutch 4d is engaged. Specifically, the controller 22 sets the control condition of the lock-up clutch 4d illustrated in Fig. 3 to an expanded mode, thereby performing control so that the lock-up clutch 4d is engaged in a driving region where the vehicle speed is V1 or more.

[0036] If it is determined in step S13 that the off-road mode is not selected (step S13: No), if the road surface gradient is not a downward gradient of the predetermined value ms or more in step S15, or after step S16, the process proceeds to step S17, where the controller 22 determines the required idle speed and the required rear wheel torque distribution. The required idle speed is the engine speed that the engine 2 should maintain during idling, and the required rear wheel torque distribution is the rear wheel torque distribution that should be transmitted from the electromagnetic coupling 16 to the rear wheels 12. Specifically, if it is determined in step S13 that the off-road mode is not selected (step S13: No), the controller 22 sets the normal idle speed and the normal rear wheel torque distribution calculated in step S12 as the required idle speed and the required rear wheel torque distribution as they are. In other words, if the normal idle speed is 800 rpm, the required idle speed is also 800 rpm, and if the normal rear wheel torque distribution is 0%, the required rear wheel torque distribution is also 0%. On the other hand, when the corrected rotation speed and corrected rear wheel torque distribution are acquired in step S14, the normal idle rotation speed calculated in step S12 plus the corrected rotation speed is set as the required idle rotation speed, and the normal rear wheel torque distribution calculated in step S12 plus the corrected rear wheel torque distribution is set as the required rear wheel torque distribution. For example, if the normal idle rotation speed is 800 rpm and the corrected rotation speed is 300 rpm, the required idle rotation speed is 800 + 300 = 1100 rpm. Also, if the normal rear wheel torque distribution is 0% and the corrected rear wheel torque distribution is 10%, the required rear wheel torque distribution is 0 + 10 = 10%. At this time, the maximum value T of the required rear wheel torque distribution max(For example, 30%) is preset, and the sum of the normal rear wheel torque distribution and the corrected rear wheel torque distribution is this maximum value T max If the torque distribution exceeds the maximum value T max After step S17, the controller 22 ends the idle speed determination process.

[0037] When the engine 2 is made to idle, the controller 22 controls the engine 2 so that the rotation speed of the engine 2 becomes the required idle rotation speed determined in the latest vehicle control process. For example, if the required idle rotation speed while the vehicle 1 is stopped is 800 rpm, and then the required idle rotation speed becomes 1100 rpm after the vehicle 1 starts running, and then the vehicle 1 is stopped again, the controller 22 controls the engine 2 so that the idle rotation speed is maintained at 1100 rpm after it has dropped to 1100 rpm. In other words, the controller 22 does not control the idle rotation speed to be once lowered to 800 rpm and then raised to 1100 rpm. In addition, the controller 22 controls the electromagnetic coupling 16 so that the distribution ratio of the drive torque of the rear wheels 12 to the drive torque of the front wheels 10 becomes the required rear wheel torque distribution determined in the latest rear wheel torque distribution determination process.

[0038] <Action and effect> Next, the operation and effects of the vehicle control system according to the embodiment of the present invention will be described.

[0039] Fig. 7 shows an example of a time chart when vehicle control according to an embodiment of the present invention is executed. The time chart in Fig. 7 shows, from the top, the driving mode selected by the driving mode selection switch SN1 (normal mode / off-road mode), the road surface gradient [%] in the longitudinal direction of the vehicle 1, the required idle speed [rpm], the required rear wheel torque distribution [%], and the control conditions of the lock-up clutch 4d (normal mode / expanded mode).

[0040] In the example shown in Fig. 7, the normal idle speed is S1 [rpm] and the normal rear wheel torque distribution is 0% throughout the entire period. However, the normal idle speed and the normal rear wheel torque distribution may be values ​​different from those in the example shown in Fig. 7 and may change over time.

[0041] First, in the period up to time t1 in Fig. 7, the normal mode is selected as the driving mode, and the road surface gradient in the longitudinal direction of the vehicle 1 is 0%. Therefore, the controller 22 sets the normal idle speed Rs as the required idle speed, sets the normal rear wheel torque distribution of 0% as the required rear wheel torque distribution, and sets the control condition of the lock-up clutch 4d to the normal mode. In this case, the controller 22 performs control so that the lock-up clutch 4d is in the engaged state in a driving region where the vehicle speed is equal to or higher than V2.

[0042] After time t1, the upward gradient starts to increase. This means, for example, that the vehicle 1 approaches an uphill road and the upward gradient starts to increase in the traveling direction. However, since the driving mode remains in the normal mode, the controller 22 does not obtain the corrected rotation speed or corrected rear wheel torque distribution, and sets the normal idle rotation speed Rs as the requested idle rotation speed and 0%, which is the normal rear wheel torque distribution, as the requested rear wheel torque distribution. In addition, the control condition of the lock-up clutch 4d also remains in the normal mode.

[0043] At time t2, the driver operates the driving mode selection switch, and the driving mode is switched from the normal mode to the off-road mode. At this time, the road gradient is an upward gradient. That is, since the road gradient is an upward gradient and the off-road mode is selected, the controller 22 obtains a positive corrected rotation speed, and sets the value obtained by adding the corrected rotation speed to the normal idle rotation speed Rs as the requested idle rotation speed. That is, the requested idle rotation speed is made higher than that before time t2 when the normal mode was selected. In addition, the controller 22 obtains a corrected rear wheel torque distribution Tc1 for the upward gradient, and sets the value Tc1 obtained by adding the corrected rear wheel torque distribution Tc1 to the normal rear wheel torque distribution of 0% as the requested rear wheel torque distribution. That is, the requested rear wheel torque distribution is made higher than that before time t2 when the normal mode was selected.

[0044] After that, between time t2 and t3, the road gradient is an upward gradient and increases to m1. As the upward gradient increases, the corrected rotation speed also increases. Therefore, the controller 22 increases the required idle rotation speed as the road gradient increases. Meanwhile, since the corrected rear wheel torque distribution is constant at Tc1, the required rear wheel torque distribution also remains constant at Tc1. In addition, the control condition of the lock-up clutch 4d remains at the normal mode.

[0045] Between times t3 and t4, the driving mode is the off-road mode, and the road gradient is an uphill gradient equal to or greater than the threshold m1. Therefore, between times t3 and t4, the correction rotation speed is set to the maximum value Rc max In this case, the controller 22 is set to a value equal to the normal idle speed Rs+the correction speed Rc max is the required idle speed. The corrected rear wheel torque distribution is constant at Tc1, and the required rear wheel torque distribution is normal rear wheel torque distribution 0% + corrected rear wheel torque distribution Tc1. The control condition of the lock-up clutch 4d remains in the normal mode.

[0046] Thereafter, the upward gradient decreases between time t4 and t5, and the road gradient becomes 0% (i.e., a flat road surface with no gradient) at time t5. As the upward gradient decreases, the corrected rotation speed also decreases, and the corrected rotation speed becomes 0 at time t5. Therefore, the smaller the road gradient, the smaller the requested idle rotation speed becomes, and at time t5 the requested idle rotation speed becomes the same as the normal idle rotation speed Rs. Meanwhile, since the corrected rear wheel torque distribution is constant at Tc1, the requested rear wheel torque distribution also remains constant at Tc1 until time t5. In addition, the control condition of the lock-up clutch 4d remains in the normal mode.

[0047] After time t5, the downward gradient starts to increase. This means, for example, that the vehicle 1 approaches a downhill road and the downward gradient starts to increase in the traveling direction. The road surface gradient becomes a downward gradient, so the corrected rotation speed becomes a negative value, and the larger the downward gradient, the smaller the corrected rotation speed becomes. In other words, since the road surface gradient is a downward gradient and the off-road mode is selected, the controller 22 obtains the negative corrected rotation speed and adds the negative corrected rotation speed to the normal idle rotation speed Rs to set the requested idle rotation speed. In other words, the requested idle rotation speed is made lower than before time t2 when the normal mode was selected and between times t2 and t5 when the road surface gradient was an upward gradient. In addition, the controller 22 obtains the corrected rear wheel torque distribution Tc2 for the downward gradient, and sets the value Tc2 obtained by adding the corrected rear wheel torque distribution Tc2 to the normal rear wheel torque distribution of 0% to set the requested rear wheel torque distribution. In other words, the requested rear wheel torque distribution is made larger than before time t2 when the normal mode was selected and smaller than between times t2 and t5 when the road surface gradient was an upward gradient. Furthermore, because the road surface gradient is a downward gradient and the off-road mode is selected, the controller 22 sets the control condition of the lock-up clutch 4d to the enlarged mode. In this case, the controller 22 controls the lock-up clutch 4d to be in an engaged state in a driving region where the vehicle speed is equal to or greater than V1, which is lower than V2, so that the lock-up clutch 4d is more likely to be engaged. In other words, the controller 22 enlarges the lock-up region in which the lock-up clutch 4d is in an engaged state compared to before time t2 when the normal mode was selected and between times t2 and t5 when the road surface gradient was an upward gradient.

[0048] After that, after time t6, the driving mode is the off-road mode, and the downward gradient is equal to or smaller than the threshold value m2. Therefore, after time t6, the correction speed is set to the minimum value Rc min In this case, the controller 22 is set to a value equal to the normal idle speed Rs+the correction speed Rc min (negative value) is set as the required idle speed. The corrected rear wheel torque distribution is constant at Tc2, and the required rear wheel torque distribution is normal rear wheel torque distribution 0% + corrected rear wheel torque distribution Tc2. The control condition of the lock-up clutch 4d remains in the expansion mode.

[0049] As described above, in this embodiment, when the road surface gradient is a downward gradient greater than a predetermined value (0%) toward the traveling direction of the vehicle 1 and the off-road mode is selected by the traveling mode selection switch SN1, the controller 22 sets the required idle speed lower than when the normal mode is selected or when the road surface gradient is an upward gradient or a downward gradient equal to or less than a predetermined value. In other words, in a situation where the driver recognizes that the vehicle is traveling on a bad road and is likely to depress the accelerator pedal heavily, and further, in a situation where the vehicle is likely to accelerate suddenly, such as a slope with a downward gradient of a predetermined value or more, the controller 22 sets the required idle speed low. This makes it possible to reduce the driving torque from the engine 2 during idling, so that even if the driver depresses the accelerator pedal heavily or the wheels slip due to a low road friction coefficient, the vehicle 1 can be prevented from jumping forward with an acceleration greater than the driver's intention when the vehicle 1 starts moving. Therefore, even if the driver depresses the accelerator pedal excessively, sudden acceleration of the vehicle can be prevented.

[0050] Furthermore, according to this embodiment, when the downward gradient is steep, the controller 22 sets the required idle speed lower than when the downward gradient is shallow. In other words, in a situation where the vehicle 1 is more likely to accelerate suddenly due to a steep downward gradient, the controller 22 sets the required idle speed even lower. Therefore, the driving torque from the engine 2 during idling can be made appropriate according to the road gradient, and sudden acceleration of the vehicle can be suppressed even if the driver excessively depresses the accelerator pedal on various road gradients.

[0051] This embodiment is also applied to a four-wheel drive vehicle in which the torque generated by the engine 2 is distributed to the front wheels 10, which are driving wheels, and the rear wheels 12, which are auxiliary driving wheels. When the road surface gradient is a downward gradient greater than a predetermined value (0%) toward the traveling direction of the vehicle 1 and the off-road mode is selected by the traveling mode selection switch SN1, the controller 22 reduces the requested rear wheel torque distribution compared to when the road surface gradient is an upward gradient greater than a predetermined value (0%) and the off-road mode is selected by the traveling mode selection switch SN1. In other words, in a situation in which the driver recognizes that the vehicle is traveling on a bad road and is likely to greatly depress the accelerator pedal, and further in a situation in which the vehicle 1 is more likely to accelerate suddenly, such as a slope with a downward gradient greater than a predetermined value, the controller 22 sets the torque distribution of the rear wheels 12 to be smaller than in the case of an upward gradient. This makes it possible to reduce the propulsive force of the vehicle 1 on a bad road, and to suppress sudden acceleration of the vehicle even if the driver depresses the accelerator pedal excessively.

[0052] This embodiment is also applied to a vehicle 1 having a torque converter 4a equipped with a lock-up clutch 4d provided on a power transmission path of the engine 2. When the road surface gradient is a downward gradient greater than a predetermined value (0%) toward the traveling direction of the vehicle 1 and the off-road mode is selected by the traveling mode selection switch SN1, the controller 22 enlarges the lock-up region more than when the normal mode is selected by the traveling mode selection switch SN1 or when the road surface gradient is an upward gradient or a downward gradient equal to or less than a predetermined value. In other words, in a situation where the driver recognizes that the vehicle is traveling on a bad road and is likely to greatly depress the accelerator pedal, and further, in a situation where the vehicle 1 is more likely to accelerate suddenly, such as a slope with a downward gradient greater than a predetermined value, the lock-up clutch 4d is more likely to be engaged. This reduces the transmission loss between the drive wheels and the engine 2, thereby increasing the braking force by the engine brake and suppressing sudden acceleration of the vehicle even if the driver depresses the accelerator pedal excessively. [Explanation of symbols]

[0053] 1 vehicle 2 Engine 4a torque converter 4d Lock-up clutch 10 Front wheels (drive wheels) 12 Rear wheels (auxiliary drive wheels) 16 Electromagnetic Coupling 22 Controller 22a Processor 22b Memory SN1 Driving mode selection switch SN2 Wheel Speed ​​Sensor SN3 Accelerometer SN4 Steering Angle Sensor SN5 Shift position sensor

Claims

1. A control system for a vehicle having an engine that supplies power for driving drive wheels, and a torque converter equipped with a lock-up clutch provided on a power transmission path of the engine, A gradient measuring means for measuring a road gradient along a front-rear direction of the vehicle; a driving mode selection means for selecting one driving mode from a plurality of driving modes including a first driving mode for normal driving and a second driving mode for driving on rough roads in response to an operation by a driver of the vehicle; and an engine control means for determining an idle speed of the engine and controlling the engine so that the engine speed becomes the idle speed during idling. when the road surface gradient measured by the gradient measuring means is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection means, the engine control means reduces the idle rotation speed compared to when the first traveling mode is selected or the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value; the control system for the vehicle includes a lock-up clutch control means for controlling the lock-up clutch so as to bring the lock-up clutch into an engaged state in a first operating range of the vehicle and bring the lock-up clutch into a released state in a second operating range of the vehicle; the lock-up clutch control means, when the road surface gradient measured by the gradient measurement means is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection means, expands the first driving range more than when the first traveling mode is selected and the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value. A vehicle control system comprising:

2. 2. The vehicle control system according to claim 1, wherein, when the road surface gradient measured by the gradient measurement means is a downward gradient greater than the predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection means, when the downward gradient is large, the engine control means reduces the idle speed more than when the downward gradient is small.

3. the vehicle is a four-wheel drive vehicle in which torque generated by the engine is distributed to front wheels, which are drive wheels, and rear wheels, which are auxiliary drive wheels; a torque distribution control means for controlling a torque to be distributed to the front wheels and the rear wheels, The torque distribution control means when the road surface gradient measured by the gradient measuring means is an upward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection means, the torque distributed to the rear wheels is made larger than when the first traveling mode is selected or when the road surface gradient is a downward gradient or an upward gradient equal to or less than the predetermined value; When the road surface gradient measured by the gradient measuring means is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection means, the torque distributed to the rear wheels is made smaller than when the road surface gradient is an upward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected.

3. A vehicle control system according to claim 1 or 2.

4. A control system for a vehicle having an engine that supplies power for driving drive wheels, and a torque converter equipped with a lock-up clutch provided on a power transmission path of the engine, an acceleration sensor for measuring the acceleration of the vehicle; a driving mode selection switch that accepts an operation for selecting one driving mode from a plurality of driving modes including a first driving mode for normal driving and a second driving mode for driving on rough roads; A memory for storing programs; A processor for executing the program, The processor, A road surface gradient along a front-rear direction of the vehicle is obtained based on the acceleration detected by the acceleration sensor. determining an idle speed of the engine, and controlling the engine so that the engine speed becomes the idle speed during idling; When the road surface gradient is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection switch, the idle speed is made lower than when the first traveling mode is selected or when the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value, controlling the lock-up clutch so as to engage the lock-up clutch in a first operating range of the vehicle and release the lock-up clutch in a second operating range of the vehicle; When the road surface gradient is a downward gradient greater than a predetermined value in the traveling direction of the vehicle and the second traveling mode is selected by the traveling mode selection switch, the first driving range is enlarged compared to when the first traveling mode is selected and the road surface gradient is an upward gradient or a downward gradient equal to or less than the predetermined value. A vehicle control system comprising:

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