drive control device

Abstract

The drive control device of the present application can quickly switch from two-wheel drive to four-wheel drive according to the situation. The drive control device includes: an estimated front-rear acceleration acquisition section that acquires an estimated front-rear acceleration of the vehicle based on an estimated driving force of the vehicle and a wheel speed of a main drive wheel of the vehicle; an estimated lateral acceleration acquisition section that acquires an estimated lateral acceleration of the vehicle; an estimated tire load calculation section that calculates an estimated tire load of the main drive wheel based on the estimated front-rear acceleration and the estimated lateral acceleration; and a drive mode selection section that selects either a two-wheel drive mode in which the vehicle is driven by only the main drive wheel or a four-wheel drive mode in which the vehicle is driven by both the main drive wheel and a sub drive wheel. The drive mode selection section selects the two-wheel drive mode in the vehicle when the estimated tire load calculated by the estimated tire load calculation section is lower than a two-wheel drive threshold.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a drive control device. BACKGROUND

[0002] There is known a device that switches between two-wheel drive and four-wheel drive by adjusting the distribution of driving force to the front wheels and the rear wheels of a vehicle. For example, Patent Literature 1 discloses a device that calculates the tire load of the front wheels in accordance with the estimated driving force of the vehicle and the steering angle, selects two-wheel drive in the case where the calculated tire load is relatively low, and selects four-wheel drive in the case where the tire load is relatively high.

[0003] [Patent Literature]

[0004] [Patent Literature]

[0005] [Patent Literature 1] Japanese Patent Application Publication No. 2014-189253 SUMMARY

[0006] [Problems to be Solved by the Invention]

[0007] In addition, under a condition where the load is large, such as during traction running, the fuel efficiency is likely to deteriorate, and in addition, the temperature of each part of the vehicle is likely to rise. Therefore, in order to suppress the deterioration of the fuel efficiency or the rise in the temperature of each part of the vehicle, there is a tendency to expand the region in which two-wheel drive is selected. On the other hand, from the viewpoint of improving the passability and the handling stability of the vehicle, there is a demand to select four-wheel drive as much as possible. Thus, it is desirable to quickly switch to four-wheel drive according to the situation while ensuring a wide region in which two-wheel drive is selected.

[0008] Therefore, an object of the drive control device of the present disclosure is to make it possible to quickly switch from two-wheel drive to four-wheel drive according to the situation.

[0009] [Means of Solving the Problems]

[0010] The drive control device 1 of one embodiment of the present disclosure includes: an estimated front-rear acceleration acquisition section 10 that acquires an estimated front-rear acceleration of a vehicle on the basis of an estimated driving force of the vehicle and a wheel speed of a main drive wheel of the vehicle; an estimated lateral acceleration acquisition section 11 that acquires an estimated lateral acceleration of the vehicle; an estimated tire load calculation section 12 that calculates an estimated tire load of the main drive wheel on the basis of the estimated front-rear acceleration acquired by the estimated front-rear acceleration acquisition section 10 and the estimated lateral acceleration acquired by the estimated lateral acceleration acquisition section 11; and a drive mode selection section 13 that selects either a two-wheel drive mode in which the vehicle is driven by only the main drive wheel or a four-wheel drive mode in which the vehicle is driven by both the main drive wheel and a sub drive wheel, in the vehicle, and the drive mode selection section 13 selects the two-wheel drive mode in the vehicle in a case where the estimated tire load calculated by the estimated tire load calculation section 12 is lower than a two-wheel drive threshold.

[0011] According to the drive control device 1, the estimated front-rear acceleration of the vehicle is acquired on the basis of not only the estimated driving force of the vehicle but also the wheel speed of the main drive wheel. Further, in a case where the estimated tire load of the main drive wheel acquired by synthesizing the estimated front-rear acceleration and the estimated lateral acceleration is lower than the two-wheel drive threshold, the two-wheel drive is selected. That is, in a case where the estimated driving force of the vehicle is relatively small and the condition such as the main drive wheel is idling is not present, the two-wheel drive is selected. In other words, even if the estimated driving force of the vehicle is relatively small, in a case where the condition such as the main drive wheel is idling is present, the four-wheel drive is selected. Thus, it is possible to determine whether the condition in which the two-wheel drive should be selected or the condition in which the four-wheel drive should be selected with high accuracy. As a result, it is possible to switch from the two-wheel drive to the four-wheel drive quickly according to the condition.

[0012] In the drive control device 1 of one embodiment of the present disclosure, the drive mode selection section 13 can select the four-wheel drive mode in the vehicle in a case where the estimated tire load calculated by the estimated tire load calculation section 12 is higher than a four-wheel drive threshold. Thus, even if the estimated driving force of the vehicle is relatively small, in a case where the condition such as the main drive wheel is idling is present, the four-wheel drive is selected. Thus, it is possible to appropriately exert the effects of the drive control device 1.

[0013] In the drive control device 1 of one embodiment of the present disclosure, the two-wheel drive threshold and the four-wheel drive threshold each can constitute a friction circle. Thus, it is possible to specifically realize the drive control device 1 that exerts the effects.

[0014] In the drive control device 1 of one embodiment of the present disclosure, the estimated front-rear acceleration acquisition unit 10 can also acquire, as the estimated front-rear acceleration, any one of the front-rear accelerations of the vehicle calculated from the estimated driving force and the wheel speed, respectively, which is larger. Thus, even if the estimated driving force of the vehicle is relatively small, four-wheel drive can be selected more reliably in a situation such as free running of the main drive wheels.

[0015] The drive control device 1 of one embodiment of the present disclosure can also include an abrupt acceleration determination unit 14 that determines whether the vehicle is about to undergo abrupt acceleration on the basis of the estimated driving force, and the drive mode selection unit 13 is prohibited from selecting the two-wheel drive mode in the vehicle in a case where the vehicle is determined by the abrupt acceleration determination unit 14 to be about to undergo abrupt acceleration. Thus, four-wheel drive can be selected more reliably at the time of abrupt acceleration, which is a situation in which higher passability and steering stability are required.

[0016] In the drive control device 1 of one embodiment of the present disclosure, the abrupt acceleration determination unit 14 can determine whether the vehicle is about to undergo abrupt acceleration on the basis of a differential value of the front-rear acceleration of the vehicle calculated from the estimated driving force. Thus, whether the vehicle is about to undergo abrupt acceleration can be determined with high accuracy.

[0017] The drive control device 1 of one embodiment of the present disclosure can also include a characteristic mode selection unit 15 that selects, in the vehicle, either a normal mode in which normal travel characteristics are achieved or a non-normal mode in which travel characteristics different from the travel characteristics of the normal mode are achieved, and the drive mode selection unit 13 is prohibited from selecting the two-wheel drive mode in the vehicle in a case where the non-normal mode is selected by the characteristic mode selection unit 15. Thus, four-wheel drive can be selected more reliably in a case where travel characteristics different from the normal travel characteristics are used.

[0018] The drive control device 1 of one embodiment of the present disclosure can also include a front-rear limited slip differential (LSD) operation determination unit 16 that determines whether a front-rear LSD 4 is operating in the vehicle, and the drive mode selection unit 13 is prohibited from selecting the two-wheel drive mode in the vehicle in a case where the front-rear LSD 4 is determined by the front-rear LSD operation determination unit 16 to be operating. Thus, four-wheel drive can be selected more reliably at the time of operation of the front-rear LSD 4, which is a situation in which higher passability and steering stability are required.

[0019] In the drive control device 1 of one embodiment of the present disclosure, the torque allocated to the sub drive wheels among the main drive wheels and the sub drive wheels in the four-wheel drive mode can be equal to or higher than a predetermined minimum torque. Thus, in a case where the four-wheel drive mode is selected, sufficient passability and steering stability can be easily maintained.

[0020] In the drive control device 1 of one embodiment of the present disclosure, the main drive wheels can also be front wheels, and the sub drive wheels can also be rear wheels. Thus, in a vehicle that achieves four-wheel drive based on two-wheel drive by the front wheels and also drives the rear wheels, the drive control device 1 that exhibits the effects described above can be specifically achieved.

[0021] Further, the symbols in parentheses are symbols of structural elements in the embodiments described later, and are shown as examples of the present disclosure, and do not limit the present disclosure to the modes of the embodiments.

[0022] [Effects of Invention]

[0023] Thus, the drive control device of the present disclosure can achieve rapid switching from two-wheel drive to four-wheel drive according to the situation. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A block diagram of the drive control device of the present embodiment is shown.

[0025] Figure 2 A graph for explaining the drive control logic is shown.

[0026] Figure 3 A graph showing the friction circle and the estimated tire load is shown.

[0027] Figure 4 A time chart showing the change in the estimated resultant acceleration at the time of turning is shown.

[0028] Figure 5 A time chart showing the change in the estimated resultant acceleration at the time of sudden acceleration is shown.

[0029] Figure 6 A flowchart of the drive control is shown.

[0030] Figure 7 A graph showing the relationship between the vehicle speed and the two-wheel drive threshold and the four-wheel drive threshold in the comparative example at the time of cruising is shown.

[0031] Figure 8 A graph showing the friction circle and the estimated tire load in the comparative example at the time of cruising is shown.

[0032] Figure 9 A graph showing the relationship between the vehicle speed and the two-wheel drive threshold and the four-wheel drive threshold in the comparative example at the time of heavy load is shown.

[0033] Figure 10 A graph showing the friction circle and the estimated tire load in the comparative example at the time of heavy load is shown.

[0034] Figure 11A time chart showing the change in the estimated resultant acceleration at the time of turning in the comparative example.

[0035] Figure 12 A time chart showing the change in the estimated resultant acceleration at the time of sudden acceleration in the comparative example.

[0036] [Explanation of symbols]

[0037] 1: Drive control device

[0038] 2: Internal sensor

[0039] 3: Characteristic mode input device

[0040] 4: Front-rear LSD

[0041] 10: Estimated front-rear acceleration acquisition section

[0042] 11: Estimated lateral acceleration acquisition section

[0043] 12: Estimated tire load calculation section

[0044] 13: Drive mode selection section

[0045] 14: Sudden acceleration determination section

[0046] 15: Characteristic mode selection section

[0047] 16: Front-rear LSD operation determination section

[0048] 20: Accelerator pedal opening sensor

[0049] 21: Wheel speed sensor

[0050] 22: Vehicle speed sensor

[0051] 23: Steering angle sensor DETAILED DESCRIPTION

[0052] Hereinafter, exemplary embodiments will be described with reference to the drawings. Like or equivalent parts are denoted by like symbols throughout the drawings and repetitive description is omitted.

[0053] [Overall structure]

[0054] Figure 1 A block diagram of the drive control device 1 of the present embodiment is shown. Figure 2 A diagram for explaining the drive control logic. As Figure 1 and Figure 2As shown, the drive control device 1 is a device mounted in a vehicle, which switches between two-wheel drive and four-wheel drive by adjusting the distribution of driving force to the main drive wheels and the sub drive wheels of the vehicle. In particular, under a condition where the load is large, such as during traction running, the drive control device 1 can also quickly switch to four-wheel drive according to the situation to improve the passability and handling stability of the vehicle while ensuring a wide range of selection of two-wheel drive to suppress deterioration of fuel efficiency or temperature rise of each part of the vehicle.

[0055] The "main drive wheels" are wheels among the front wheels and the rear wheels that are driven when two-wheel drive is performed. The main drive wheels are also driven when four-wheel drive is performed. The "sub drive wheels" are wheels among the front wheels and the rear wheels that are not driven when two-wheel drive is performed and are driven when four-wheel drive is performed. Here, the main drive wheels are the front wheels, and the sub drive wheels are the rear wheels. That is, the vehicle exemplified here realizes four-wheel drive by driving the rear wheels in addition to two-wheel drive with the front wheels driven. For example, the two-wheel drive (2WD) can be a state in which all of the driving force is distributed to the main drive wheels, and the four-wheel drive (4WD) can be a state in which the driving force is distributed according to a front-rear weighting distribution ratio.

[0056] The drive control device 1 communicates with the internal sensors 2 and the characteristic pattern input device 3 mounted in the vehicle and receives and transmits various information. In addition, the drive control device 1 acquires information related to the operating conditions of the front-rear LSD 4.

[0057] The drive control device 1 is configured as a computer that includes a control arithmetic device, a storage device, and an input-output device in terms of physical structure. The control arithmetic device is, for example, an electronic control unit (ECU) including a controller such as a central processing unit (CPU), which performs control of the storage device and the input-output device while performing arithmetic processing. The storage device has, for example, a main storage device and an auxiliary storage device. The main storage device includes, for example, a random access memory (RAM). In addition, the auxiliary storage device includes, for example, a read only memory (ROM). The input-output device has an input device that, for example, inputs data from the outside to the storage device and an output device that, for example, outputs an arithmetic result calculated by the control arithmetic unit and stored in the storage device to the outside.

[0058] The drive control device 1 reads, for example, a program stored in the ROM into the RAM, and the CPU executes the program read into the RAM, thereby performing the processing of the drive control described later. Furthermore, the drive control device 1 can include a structure that is physically different from the structure.

[0059] The internal sensor 2 is a detection device that detects various internal information at the time of running of the vehicle. The internal sensor 2 includes an accelerator pedal opening degree sensor 20, a wheel speed sensor 21, a vehicle speed sensor 22, and a steering angle sensor 23.

[0060] The accelerator pedal opening degree sensor 20 is a device that detects the depression amount (accelerator pedal opening degree) of the accelerator pedal. The accelerator pedal opening degree sensor 20 is provided on the accelerator pedal, and transmits information related to the detected depression amount to the drive control device 1. The wheel speed sensor 21 is a device that detects the rotational speed (angular velocity) of the wheel. The wheel speed sensor 21 is provided on a rotating portion in the drive system of the vehicle, and transmits information related to the detected rotational speed to the drive control device 1. The vehicle speed sensor 22 is a device that detects the vehicle speed of the vehicle. Further, the wheel speed sensor 21 can also function as the vehicle speed sensor 22. That is, the drive control device 1 can also calculate the vehicle speed from the rotational speed of the wheel detected by the wheel speed sensor 21. In addition, the drive control device 1 can also infer the vehicle speed from the value of the yaw rate sensor in addition to the rotational speed of the wheel. The steering angle sensor 23 is a device that detects the steering amount (steering angle) of the steering wheel by the driver. The steering angle sensor 23 is provided on the steering shaft of the vehicle, and transmits information related to the detected steering amount to the drive control device 1.

[0061] The characteristic mode input device 3 is an input device for the driver to select the running characteristic of the vehicle. The characteristic mode input device 3 can be, for example, a switch or a dial provided around the driver's seat. The "running characteristic" can include, for example, the output characteristic or response characteristic of the engine or drive motor of the vehicle with respect to the accelerator pedal opening degree, or the shift pattern of the transmission, or the like. The characteristic mode input device 3 can be able to select a normal mode that realizes the usual running characteristic of the vehicle, and a non-normal mode that realizes a running characteristic different from the running characteristic of the normal mode. The "normal mode" can be, for example, a mode (NORMAL mode) that sets the initial state at the time when the ignition of the vehicle is turned on. The "non-normal mode" can be another mode changed from the normal mode, and can include, for example, at least any one of a mode (SNOW mode) suitable for snow road running, a mode (SAND mode) suitable for sand road running, a mode (MUD mode) suitable for muddy road running, a mode (TRAIL mode) suitable for poor road running, a mode (TOW mode) suitable for towing running, and the like.

[0062] The front-rear LSD 4 is a so-called limited slip differential that limits the differential of the front wheels and the rear wheels of the vehicle. The front-rear LSD 4 controls the driving force distributed to the front wheels and the rear wheels in such a manner that the rotational speed of the front wheels and the rotational speed of the rear wheels become the same degree. For example, in a case where either one of the front wheels and the rear wheels is idling, the front-rear LSD 4 transmits the driving force to the other wheel. Information related to whether or not the front-rear LSD 4 is operating is acquired by a sensor provided on the front-rear LSD 4 or a controller that controls the front-rear LSD 4, and the acquired information is transmitted to the drive control device 1.

[0063] Next, the functional structure of the drive control device 1 will be described. The drive control device 1 includes an estimated front-rear acceleration acquisition section 10, an estimated lateral acceleration acquisition section 11, an estimated tire load calculation section 12, a drive mode selection section 13, a sudden acceleration determination section 14, a characteristic mode selection section 15, and a front-rear LSD operation determination section 16.

[0064] The estimated front-rear acceleration acquisition section 10 acquires an estimated front-rear acceleration of the vehicle on the basis of an estimated driving force of the vehicle and a wheel speed of a main driving wheel of the vehicle. The so-called "estimated front-rear acceleration" is an estimated value of the front-rear acceleration of the vehicle for the drive control performed by the drive control device 1. In more detail, the estimated front-rear acceleration acquisition section 10 acquires either one of the front-rear accelerations of the vehicle calculated on the basis of the estimated driving force and the wheel speed as a high select value, as the estimated front-rear acceleration.

[0065] In calculating the front-rear acceleration of the vehicle on the basis of the estimated driving force, the estimated front-rear acceleration acquisition section 10 can acquire the estimated driving force of the vehicle on the basis of the accelerator pedal opening degree acquired by the accelerator pedal opening degree sensor 20, for example, and divide the acquired estimated driving force by the vehicle weight, thereby calculating the front-rear acceleration. In this case, the estimated front-rear acceleration acquisition section 10 can acquire the estimated driving force of the vehicle by combining the total driving force of the vehicle (for example, the output torque of the engine or the driving motor) assumed on the basis of the accelerator pedal opening degree with the gear ratio of the transmission, and the like.

[0066] In addition, when the front-rear acceleration of the vehicle is calculated from the wheel speed, the estimated front-rear acceleration acquisition unit 10 can calculate the angular acceleration by time-differentiating the angular speed of the wheel (main drive wheel) acquired by the wheel speed sensor 21, for example, and calculate the front-rear acceleration as the acceleration of the vehicle corresponding to the calculated angular acceleration. In this case, the estimated front-rear acceleration acquisition unit 10 can acquire, as the front-rear acceleration, the acceleration of the vehicle calculated on the assumption that the wheels are gripping the road surface (not spinning) with respect to each of the calculated accelerations of the wheels. Thus, in the case where the wheels (main drive wheels) are spinning, the value of the front-rear acceleration of the vehicle calculated from the wheel speed is sometimes larger than the actual front-rear acceleration actually generated by the vehicle.

[0067] The estimated lateral acceleration acquisition unit 11 acquires the estimated lateral acceleration of the vehicle. The "estimated lateral acceleration" is an estimated value of the lateral acceleration of the vehicle used for the drive control performed by the drive control device 1. The estimated lateral acceleration acquisition unit 11 can calculate the estimated lateral acceleration from the vehicle speed acquired by the vehicle speed sensor 22 and the steering angle of the steering wheel acquired by the steering angle sensor 23, for example. In this case, the estimated lateral acceleration acquisition unit 11 can use a two-wheel model of the vehicle to calculate the estimated lateral acceleration.

[0068] The estimated tire load calculation unit 12 calculates the estimated tire load of the main drive wheel. The "estimated tire load" is an estimated load resulting from the front-rear force applied to the tire and the load resulting from the lateral force. The estimated tire load can be an estimated value of the frictional force between the tire and the road surface, for example. The estimated tire load calculation unit 12 calculates the estimated tire load of the main drive wheel from the estimated front-rear acceleration acquired by the estimated front-rear acceleration acquisition unit 10 and the estimated lateral acceleration acquired by the estimated lateral acceleration acquisition unit 11. More specifically, the estimated tire load calculation unit 12 combines the estimated front-rear acceleration and the estimated lateral acceleration to calculate an estimated combined acceleration, and calculates the estimated tire load from the calculated estimated combined acceleration. As described later, the drive control device 1 compares the magnitude relationship between the estimated tire load and the radius of the friction circle (two-wheel drive threshold or four-wheel drive threshold), and switches between two-wheel drive and four-wheel drive in accordance with the comparison result. Therefore, the estimated tire load is also referred to as a two-wheel drive control amount.

[0069] The drive mode selection unit 13 selects either a two-wheel drive mode or a four-wheel drive mode for the vehicle. The so-called "two-wheel drive mode" is a mode in which the vehicle is driven only by the main drive wheels. Selecting the two-wheel drive mode results in a two-wheel drive vehicle. The so-called "four-wheel drive mode" is a mode in which the vehicle is driven by both the main drive wheels and the auxiliary drive wheels. Selecting the four-wheel drive mode results in a four-wheel drive vehicle. In the four-wheel drive mode, the torque allocated to the auxiliary drive wheels is greater than a predetermined minimum torque. In other words, when the four-wheel drive mode is selected, the driving force is distributed between the main drive wheels and the auxiliary drive wheels in such a way that the auxiliary drive wheels are always driven at a torque greater than the minimum torque.

[0070] Figure 3 is a diagram showing the friction circle and the inferred tire load. Figure 3 As shown, the drive mode selection unit 13 pre-stores a two-wheel drive threshold TH2 and a four-wheel drive threshold TH4 that constitute the friction circle. The estimated tire load G0 is expressed as a vector formed by synthesizing the vehicle's tire load G1 in the longitudinal direction based on the estimated longitudinal acceleration and the vehicle's tire load G2 in the lateral direction based on the estimated lateral acceleration. The drive mode selection unit 13 compares the estimated tire load G0 calculated by the estimated tire load calculation unit 12 with the radius of the pre-set friction circle (the two-wheel drive threshold TH2 or the four-wheel drive threshold TH4), and selects either the two-wheel drive mode or the four-wheel drive mode based on the comparison result. Furthermore, the lateral diameter of the friction circle is smaller than the diameter in the straight-ahead direction. Therefore, when turning, the estimated lateral acceleration is more likely to exceed the four-wheel drive threshold TH4, making it easier to switch from two-wheel drive to four-wheel drive.

[0071] Here, the "two-wheel drive threshold" is the threshold at which the drive mode selection unit 13 selects the two-wheel drive mode when the estimated tire load G0 calculated by the estimated tire load calculation unit 12 is lower than the specified value. In other words, when the estimated tire load G0 calculated by the estimated tire load calculation unit 12 is lower than the two-wheel drive threshold TH2, the drive mode selection unit 13 selects the two-wheel drive mode for the vehicle. The two-wheel drive threshold TH2 constitutes a friction circle (friction ellipse).

[0072] Further, the so-called "four-wheel drive threshold value" is a threshold value for the drive mode selection section 13 to select the four-wheel drive mode in a case where the estimated tire load G0 calculated by the estimated tire load calculation section 12 is higher than the value. In other words, in a case where the estimated tire load G0 calculated by the estimated tire load calculation section 12 is higher than the four-wheel drive threshold value TH4, the drive mode selection section 13 selects the four-wheel drive mode in the vehicle. The four-wheel drive threshold value TH4 constitutes a friction circle (friction ellipse). The four-wheel drive threshold value TH4 is a value larger than the two-wheel drive threshold value TH2, and the diameter of the friction circle including the four-wheel drive threshold value TH4 is larger than the friction circle including the two-wheel drive threshold value TH2. That is, the friction circle including the four-wheel drive threshold value TH4 encloses the friction circle including the two-wheel drive threshold value TH2. Thereby, the case where the drive mode selection section 13 frequently switches the two-wheel drive mode and the four-wheel drive mode is suppressed.

[0073] Further, as shown in FIG. 6, the friction circle can not be reduced in the lateral direction, but the estimated lateral acceleration can be multiplied by a gain larger than one. Figure 4 Figure 4 A time chart showing the change in the estimated resultant acceleration at the time of turning. Figure 4 In FIG. 6, the total driving force of the vehicle, the steering angle, the 4WD threshold value G, the 2WD threshold value G, the resultant G, the 2WD control gain, and the driving force distribution to the main drive wheels and the sub drive wheels are shown from the top. The total driving force of the vehicle is fixed, and the acceleration corresponding to the two-wheel drive threshold value (2WD threshold value G) and the acceleration corresponding to the four-wheel drive threshold value (4WD threshold value G) are set in advance. Further, the resultant G corresponds to the estimated resultant acceleration.

[0074] Figure 4 In FIG. 6, when the steering is started, the estimated lateral acceleration starts to increase, and thereby the estimated resultant acceleration starts to increase. Here, since the estimated lateral acceleration is multiplied by a gain larger than one, the estimated resultant acceleration also easily increases, and thereby the four-wheel drive threshold value is easily exceeded. As a result, the driving force distribution to the sub drive wheels easily increases. Here, the 2WD control gain related to the driving force distribution ratio to the sub drive wheels starts to increase from the time point at which the estimated resultant acceleration exceeds the two-wheel drive threshold value (i.e., the transition state from the two-wheel drive to the four-wheel drive is entered), and is completely switched to the four-wheel drive at the time point at which the four-wheel drive threshold value is exceeded.

[0075] ​The drive mode selection section 13 is prohibited from selecting the two-wheel drive mode (i.e., selects the four-wheel drive mode) in a case where the vehicle is in a prescribed condition (a condition that satisfies a prohibition condition for two-wheel drive conversion). For example, in a case where the vehicle is determined to be about to perform a sudden acceleration by the sudden acceleration determination section 14 described later, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle. In addition, in a case where the non-ordinary mode is selected by the characteristic mode selection section 15 described later, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle. In addition, in a case where the front-rear LSD 4 is determined to be operating by the front-rear LSD operation determination section 16 described later, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle.

[0076] The sudden acceleration determination section 14 determines whether or not the vehicle is about to perform a sudden acceleration on the basis of the estimated driving force. For example, the sudden acceleration determination section 14 determines whether or not the vehicle is about to perform a sudden acceleration on the basis of the estimated driving force of the vehicle acquired by the estimated front-rear acceleration acquisition section 10. Specifically, the sudden acceleration determination section 14 determines whether or not the vehicle is about to perform a sudden acceleration on the basis of a differential value of the front-rear acceleration of the vehicle calculated on the basis of the estimated driving force. More specifically, the sudden acceleration determination section 14 compares the differential value of the front-rear acceleration of the vehicle with a prescribed threshold value, thereby determining whether or not the vehicle is about to perform a sudden acceleration.

[0077] Figure 5 A time chart showing a change in the estimated resultant acceleration at the time of a sudden acceleration. Figure 5 From the top, there are displayed an accelerator pedal opening degree (Accelerator Pedal (AP)), a total driving force of the vehicle, a 4WD threshold value G, a 2WD threshold value G, a resultant G, a differential value of the front-rear acceleration of the vehicle (front-rear jerk), a 2WD control gain, and a driving force distribution between the main drive wheels and the sub drive wheels. As shown in Figure 5 When the differential value of the front-rear acceleration of the vehicle exceeds a prescribed value (an acceleration determination ON threshold value) in the Figure 5 , a full (forcibly) transition to the four-wheel drive is made.

[0078] The characteristic mode selection section 15 selects a characteristic mode of a travel characteristic in the vehicle. More specifically, the characteristic mode selection section 15 selects either one of an ordinary mode and a non-ordinary mode in the vehicle. Specifically, the characteristic mode selection section 15 selects a characteristic mode (ordinary mode or non-ordinary mode) corresponding to a travel characteristic input by the driver into the characteristic mode input device 3.

[0079] The front-rear LSD operation determination unit 16 determines whether or not the front-rear LSD 4 is operating in the vehicle. Specifically, information related to whether or not the front-rear LSD 4 is operating is acquired by a sensor provided on the front-rear LSD 4 or a controller that controls the front-rear LSD 4, and the acquired information is transmitted to the front-rear LSD operation determination unit 16.

[0080] With the above structure, the drive control device 1 realizes the following drive control logic. As shown in (1) of Figure 2 The estimated front-rear acceleration (Acceleration G) of the vehicle is acquired based on the estimated driving force of the vehicle (Driving force) and the estimated front wheel acceleration (Fr wheel G) calculated from the wheel speed of the main driving wheel of the vehicle. In addition, the estimated lateral acceleration (Lateral G) of the vehicle is calculated using a two-wheel model (Standard model) of the vehicle. Then, the square root of the sum of the squares of these estimated front-rear acceleration and estimated lateral acceleration (resultant value) is acquired as the estimated resultant acceleration (estimated tire load) (Total G).

[0081] Then, as shown in (2) of Figure 2 The values of the two-wheel drive threshold (2WD) and the four-wheel drive threshold (4WD) are determined based on the acquired vehicle speed (Estimated vehicle speed). Then, the 2WD control gain (Rear torque gain) is determined by comparing the two-wheel drive threshold and the four-wheel drive threshold (friction circle) with the estimated resultant acceleration (estimated tire load) (Total G). Thereafter, the driving torque of the sub driving wheel (Base rear torque) is determined in the form of the value obtained by multiplying the driving torque of the sub driving wheel required from the viewpoint of the performance (vehicle requirement torque by RT based on the rear torque (Rear Torque, RT)) by the 2WD control gain (Rear torque gain).

[0082] Then, as shown in (3) of Figure 2As shown in (3), the estimated driving force of the vehicle is differentiated to calculate the differential value of the vehicle's longitudinal acceleration (jerk) (the jerk of the drive torque at the driveshaft (DTD)). The jerk is then used to determine whether the vehicle is about to accelerate rapidly (acceleration judgment).

[0083] Then, if Figure 2 As shown in (4), it is determined whether the situation has met the prohibition conditions for two-wheel drive. Specifically, it is determined whether at least one of the following conditions has been met (OR operation): whether the vehicle is about to perform rapid acceleration (Acceleration judgment), whether the characteristic mode of the driving characteristics is a non-normal mode (Intelligent Traction Management (ITM) / Integrated Dynamic System (IDS) mode (ITM / IDS mode)), whether the front and rear LSD 4 are operating (Front / Back, F / B LSD active), and whether the rear drive unit (RDU) oil temperature is lower than a specified value (Rear Drive Unit state (RDU condition)). Then, if none of the conditions are met, the drive torque of the auxiliary drive wheel (Base Rear Torque) is used. If at least one of the conditions is met, the port switch (Switch (SW)) is controlled to prohibit two-wheel drive.

[0084] Then, if Figure 2The minimum value of the lower limit value in the distribution ratio dimension (minimum rear (Rr) bias by speed (Min Rr Bias by speed)), the lower limit value in the torque dimension (minimum rear (Rr) torque by speed (Min Rr Torque by speed)), and the maximum value of the output value from the port switch (SW) is acquired. Thus, the sub drive wheels reach above the minimum torque in the four-wheel drive mode. Then, the minimum value of the maximum value and the drive torque of the sub drive wheels required from the viewpoint of the running performance (torque (TRQ) by base bias (TRQ by Base Bias), i.e., vehicle requirement torque by RT) is acquired. Further, a rate limit for suppressing a phenomenon in which an impact is generated due to a sudden change in the control output value is applied to the minimum value. Through the above process, the drive torque distributed to the sub drive wheels in the four-wheel drive mode is determined.

[0085] [Drive control]

[0086] The drive control performed by the drive control device 1 will be described. Figure 6 A flowchart of the drive control. Figure 6 The drive control illustrated in the drawing is control for switching between two-wheel drive and four-wheel drive by adjusting the distribution of the drive forces of the main drive wheels and the sub drive wheels of the vehicle. The drive control is particularly control that enables a quick switch to four-wheel drive according to the situation while ensuring a wide range of selection of two-wheel drive.

[0087] In step S10, the estimated front-rear acceleration acquisition section 10 of the drive control device 1 acquires the estimated front-rear acceleration of the vehicle on the basis of the estimated drive force of the vehicle and the wheel speed of the main drive wheels of the vehicle. More specifically, the estimated front-rear acceleration acquisition section 10 acquires the larger value (i.e., the high selection value) of the front-rear acceleration of the vehicle calculated on the basis of the estimated drive force and the wheel speed as the estimated front-rear acceleration. In calculating the front-rear acceleration of the vehicle on the basis of the estimated drive force, the estimated front-rear acceleration acquisition section 10, for example, acquires the estimated drive force of the vehicle on the basis of the accelerator pedal opening degree acquired by the accelerator pedal opening degree sensor 20 and divides the acquired estimated drive force by the vehicle weight, thereby calculating the front-rear acceleration. In addition, in calculating the front-rear acceleration of the vehicle on the basis of the wheel speed, the estimated front-rear acceleration acquisition section 10, for example, calculates the angular acceleration by time-differentiating the angular speed of the wheel (main drive wheel) acquired by the wheel speed sensor 21 and calculates the front-rear acceleration in the form of the acceleration of the vehicle corresponding to the calculated angular acceleration. Thereafter, the drive control proceeds to step S12.

[0088] In step S12, the estimated lateral acceleration acquisition section 11 of the drive control device 1 acquires the estimated lateral acceleration of the vehicle. More specifically, the estimated lateral acceleration acquisition section 11 calculates the estimated lateral acceleration, for example, from the vehicle speed acquired by the vehicle speed sensor 22 and the steering angle of the steering wheel acquired by the steering angle sensor 23. Here, the estimated lateral acceleration acquisition section 11 uses a two-wheel model of the vehicle to calculate the estimated lateral acceleration. Thereafter, the drive control shifts to step S14.

[0089] In step S14, the estimated tire load calculation section 12 of the drive control device 1 calculates the estimated tire load of the main drive wheels. More specifically, the estimated tire load calculation section 12 calculates an estimated combined acceleration by combining the estimated front-rear acceleration and the estimated lateral acceleration, and calculates the estimated tire load from the calculated estimated combined acceleration. Thereafter, the drive control shifts to step S16.

[0090] In step S16, the drive mode selection section 13 of the drive control device 1 determines whether or not the vehicle is in a prescribed condition (a condition in which the prohibition condition for two-wheel drive conversion is satisfied). The prohibition condition for two-wheel drive conversion is, for example, a case where the vehicle is about to undergo rapid acceleration as determined by the rapid acceleration determination section 14, a case where the non-ordinary mode is selected by the characteristic mode selection section 15, or a case where the front-rear LSD 4 is operating as determined by the front-rear LSD operation determination section 16. Thereafter, the drive control shifts to step S18.

[0091] In step S18, the drive mode selection section 13 of the drive control device 1 selects either the two-wheel drive mode or the four-wheel drive mode in the vehicle. In a case where it is determined in step S16 that the vehicle is in a condition in which the prohibition condition for two-wheel drive conversion is satisfied, the drive mode selection section 13 selects the four-wheel drive mode. On the other hand, in a case where it is not determined in step S16 that the vehicle is in a condition in which the prohibition condition for two-wheel drive conversion is satisfied, the drive mode selection section 13 compares the magnitude relationship between the estimated tire load calculated by the estimated tire load calculation section 12 and the radius of the friction circle (the two-wheel drive conversion threshold or the four-wheel drive conversion threshold) that is set in advance, and selects either the two-wheel drive mode or the four-wheel drive mode in accordance with the comparison result. Thereafter, the drive control shifts to step S20.

[0092] In step S20, the drive mode selection section 13 of the drive control device 1 determines the distribution of the drive torque (the distributed torque) to the main drive wheels and the auxiliary drive wheels individually. Specifically, the drive mode selection section 13 determines the distribution of the drive torque in such a manner that the torque distribution becomes in accordance with the 2WD control gain. At this time, in the four-wheel drive mode, the drive mode selection section 13 sets the torque distributed to the auxiliary drive wheels to be equal to or greater than the minimum torque set in advance. Through the above process, the drive control ends.

[0093] [Function and Effect]

[0094] Here, refer to Figures 7-12 , a conventional drive control device is described as a comparative example. Figure 7 Graph showing the relationship between the vehicle speed during cruising, the two-wheel drive threshold, and the four-wheel drive threshold in a comparative example. Figure 8 Graph showing the friction circle and estimated tire load during cruising in a comparative example. Figure 9 Graph showing the relationship between the vehicle speed, the two-wheel drive threshold, and the four-wheel drive threshold under heavy load conditions in a comparative example. Figure 10 Graph showing the friction circle and estimated tire load under heavy load conditions in a comparative example. Figure 11 1 is a time chart showing changes in the estimated combined acceleration during cornering in the comparative example. Figure 12 1 is a time chart showing changes in the estimated combined acceleration during rapid acceleration in a comparative example.

[0095] In the comparative example, Figure 7 and Figure 8 As shown, in the cruising range, it is easy to set the relationship between the estimated tire load G0 and the radius of the friction circle (two-wheel drive threshold TH2 or four-wheel drive threshold TH4) relatively appropriately, and it is possible to switch between two-wheel drive and four-wheel drive at a relatively appropriate time. Figure 9 and Figure 10 As shown, under heavy load conditions such as towing, a wide range of two-wheel drive selection is necessary to minimize degradation in fuel efficiency and temperature increases in various vehicle components. Therefore, it is difficult for the estimated tire load G0 to exceed the four-wheel drive threshold TH4, potentially leading to a switch to four-wheel drive at an inappropriate time.

[0096] according to Figure 11 In the comparative example, as in the drive control device 1, when steering begins, the estimated lateral acceleration also begins to increase, and thus the estimated resultant acceleration begins to increase. However, in the comparative example, the estimated lateral acceleration is not multiplied by a gain, so the estimated resultant acceleration cannot be easily increased, and it is difficult to exceed the four-wheel drive threshold. As a result, it is difficult to increase the driving force distribution to the auxiliary drive wheels. In addition, according to Figure 12 Since the control of fully switching to four-wheel drive when the differential value of the vehicle's longitudinal acceleration (fore-and-aft jerk) exceeds the specified value is not performed, there is a risk that the four-wheel drive may not be switched at the appropriate time during sudden acceleration of the vehicle.

[0097] In this regard, the drive control device 1 includes: an estimated front-rear acceleration acquisition section 10 that acquires an estimated front-rear acceleration of the vehicle on the basis of an estimated driving force of the vehicle and a wheel speed of a main drive wheel of the vehicle; an estimated lateral acceleration acquisition section 11 that acquires an estimated lateral acceleration of the vehicle; an estimated tire load calculation section 12 that calculates an estimated tire load of the main drive wheel on the basis of the estimated front-rear acceleration acquired by the estimated front-rear acceleration acquisition section 10 and the estimated lateral acceleration acquired by the estimated lateral acceleration acquisition section 11; and a drive mode selection section 13 that selects either a two-wheel drive mode in which the vehicle is driven by only the main drive wheel or a four-wheel drive mode in which the vehicle is driven by both the main drive wheel and a sub drive wheel, the drive mode selection section 13 selecting the two-wheel drive mode in the vehicle in a case where the estimated tire load calculated by the estimated tire load calculation section 12 is lower than a two-wheel drive threshold.

[0098] According to the drive control device 1, the estimated front-rear acceleration of the vehicle is acquired on the basis of not only the estimated driving force of the vehicle but also the wheel speed of the main drive wheel. Also, in a case where the estimated tire load of the main drive wheel acquired by synthesizing the estimated front-rear acceleration and the estimated lateral acceleration is lower than the two-wheel drive threshold, the two-wheel drive is selected. That is, in a case where the estimated driving force of the vehicle is relatively small and a condition such as a main drive wheel idling does not exist, the two-wheel drive is selected. In other words, even if the estimated driving force of the vehicle is relatively small, in a condition such as a main drive wheel idling, the four-wheel drive is selected. Thus, it is possible to determine with high accuracy whether a condition in which the two-wheel drive should be selected or a condition in which the four-wheel drive should be selected. As a result, it is possible to switch from the two-wheel drive to the four-wheel drive promptly according to the condition.

[0099] In the drive control device 1, in a case where the estimated tire load calculated by the estimated tire load calculation section 12 is higher than a four-wheel drive threshold, the drive mode selection section 13 selects the four-wheel drive mode in the vehicle. Thus, even if the estimated driving force of the vehicle is relatively small, in a condition such as a main drive wheel idling, the four-wheel drive is selected. Thus, it is possible to appropriately exert the effects and advantages of the drive control device 1.

[0100] In the drive control device 1, the two-wheel drive threshold and the four-wheel drive threshold each constitute a friction circle. Thus, it is possible to specifically realize the drive control device 1 that exerts the effects and advantages.

[0101] In the drive control device 1, the estimated front-rear acceleration acquisition section 10 acquires either a larger one of the front-rear accelerations of the vehicle calculated on the basis of the estimated driving force and the wheel speed as the estimated front-rear acceleration. Thus, even if the estimated driving force of the vehicle is relatively small, in a condition such as a main drive wheel idling, the four-wheel drive is more reliably selected.

[0102] The drive control device 1 includes an abrupt acceleration determination section 14 that determines whether the vehicle is about to undergo abrupt acceleration on the basis of the estimated driving force, and in a case where the abrupt acceleration determination section 14 determines that the vehicle is about to undergo abrupt acceleration, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle. Thus, in the case of abrupt acceleration as a condition in which higher passability and steering stability are required, four-wheel drive can be selected more reliably.

[0103] In the drive control device 1, the abrupt acceleration determination section 14 determines whether the vehicle is about to undergo abrupt acceleration on the basis of a differential value of the front-rear acceleration of the vehicle calculated on the basis of the estimated driving force. Thus, whether the vehicle is about to undergo abrupt acceleration can be determined with high precision.

[0104] The drive control device 1 includes a characteristic mode selection section 15 that selects either a normal mode in which normal running characteristics are realized or a non-normal mode in which running characteristics different from the running characteristics of the normal mode are realized in the vehicle, and in a case where the characteristic mode selection section 15 selects the non-normal mode, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle. Thus, in the case where running characteristics different from normal running characteristics are used, four-wheel drive can be selected more reliably.

[0105] The drive control device 1 includes a front-rear LSD operation determination section 16 that determines whether the front-rear LSD 4 is operating in the vehicle, and in a case where the front-rear LSD operation determination section 16 determines that the front-rear LSD 4 is operating, the drive mode selection section 13 is prohibited from selecting the two-wheel drive mode in the vehicle. Thus, in the case of operation of the front-rear LSD 4 as a condition in which higher passability and steering stability are required, four-wheel drive can be selected more reliably.

[0106] In the drive control device 1, in the four-wheel drive mode, the torque allocated to the sub drive wheels among the main drive wheels and the sub drive wheels is equal to or higher than a preset minimum torque. Thus, in the case where four-wheel drive is selected, sufficient passability and steering stability are easily maintained.

[0107] In the drive control device 1, the main drive wheels are front wheels, and the sub drive wheels are rear wheels. Thus, in a vehicle in which four-wheel drive is realized by driving the rear wheels on the basis of two-wheel drive by the front wheels, the drive control device 1 that exerts the effects and the advantages described above and below can be concretely realized.

[0108] [Modified Aspects]

[0109] The embodiments described above and below can be implemented in various aspects in accordance with the knowledge of those skilled in the art.

[0110] For example, in the embodiment, the main drive wheels are front wheels, and the sub drive wheels are rear wheels. However, the main drive wheels can be rear wheels, and the sub drive wheels can be front wheels. That is, the vehicle can also realize four-wheel drive based on two-wheel drive with rear-wheel drive and drive the front wheels as well.

Claims

1. A drive control device comprising: an estimated longitudinal acceleration acquisition unit that acquires a larger value of the longitudinal acceleration of the vehicle calculated based on the estimated driving force of the vehicle and the wheel speed of the main drive wheel of the vehicle as the estimated longitudinal acceleration of the vehicle; an estimated lateral acceleration acquiring unit configured to acquire an estimated lateral acceleration of the vehicle; an estimated tire load calculation unit that calculates an estimated tire load of the main drive wheel based on the estimated longitudinal acceleration acquired by the estimated longitudinal acceleration acquisition unit and the estimated lateral acceleration acquired by the estimated lateral acceleration acquisition unit; and a drive mode selection unit for selecting, in the vehicle, either a two-wheel drive mode in which the vehicle is driven only by the main drive wheels or a four-wheel drive mode in which the vehicle is driven by both the main drive wheels and the auxiliary drive wheels; The drive mode selection unit selects the two-wheel drive mode in the vehicle when the estimated tire load calculated by the estimated tire load calculation unit is lower than a two-wheel drive threshold value.

2. The drive control device according to claim 1, wherein: The drive mode selection unit selects the four-wheel drive mode in the vehicle when the estimated tire load calculated by the estimated tire load calculation unit is higher than a four-wheel drive threshold value.

3. The drive control device according to claim 2, wherein: The two-wheel drive threshold and the four-wheel drive threshold each constitute a friction circle.

4. The drive control device according to any one of claims 1 to 3, comprising a sudden acceleration determination unit for determining whether the vehicle is about to undergo sudden acceleration based on the estimated driving force, When the rapid acceleration determination unit determines that the vehicle is about to undergo rapid acceleration, the drive mode selection unit is prohibited from selecting the two-wheel drive mode in the vehicle.

5. The drive control device according to claim 4, wherein: The sudden acceleration determination unit determines whether the vehicle is about to accelerate suddenly based on a differential value of the longitudinal acceleration of the vehicle calculated based on the estimated driving force.

6. The drive control device according to any one of claims 1 to 3, including a characteristic mode selection unit configured to select, in the vehicle, either a normal mode for achieving normal driving characteristics or a non-normal mode for achieving driving characteristics different from those in the normal mode, When the non-normal mode is selected by the characteristic mode selection unit, the drive mode selection unit is prohibited from selecting the two-wheel drive mode in the vehicle.

7. The drive control device according to any one of claims 1 to 3, The invention comprises a front and rear limited slip differential operation determination unit, wherein the front and rear limited slip differential operation determination unit determines whether the front and rear limited slip differentials are operating in the vehicle. When the front and rear limited slip differential operation determination unit determines that the front and rear limited slip differential is operating, the drive mode selection unit is prohibited from selecting the two-wheel drive mode in the vehicle.

8. The drive control device according to any one of claims 1 to 3, wherein: In the four-wheel drive mode, the torque distributed to the auxiliary drive wheels among the main drive wheels and the auxiliary drive wheels is equal to or greater than a predetermined minimum torque.

9. The drive control device according to any one of claims 1 to 3, wherein: The main driving wheel is the front wheel, The auxiliary driving wheel is a rear wheel.

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