JP7224721B2 - Distribution status display device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distribution display device for use in a vehicle equipped with an electronically controlled coupling that distributes torque for running to main drive wheels and sub-drive wheels.

2. Description of the Related Art Conventionally, an active torque split 4WD system is widely known as a 4WD (four-wheel-drive) system for vehicles such as four-wheeled vehicles. In one example of an active torque split 4WD system, torque for driving the vehicle is normally transmitted to the main drive wheels (eg, front left and right wheels). If tire slip occurs while the vehicle is running, the road surface friction coefficient is estimated, and based on the estimated road surface friction coefficient, torque is applied to the main and auxiliary drive wheels by an electronically controlled coupling to prevent tire slip. are actively allocated to

A vehicle equipped with this active torque split 4WD system is provided with a display device that displays the state of torque distribution to the main drive wheels and the auxiliary drive wheels (see, for example, Patent Document 1). In one example of a conventional display device, on the screen of a liquid crystal display, five segments are arranged in a row corresponding to each of the four wheels of left and right main driving wheels and auxiliary driving wheels. The magnitude of the torque distributed to the wheels is indicated by the number of lit segments.

JP 2018-122857 A

In such a display device, when the number of segments corresponding to the sub-driving wheels exceeds the number of segments corresponding to the main driving wheels, the driver of the vehicle feels uncomfortable because it does not match the driving style of the vehicle. there is a possibility.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a torque distribution display device that can prevent a driver from feeling uncomfortable due to a display that does not match the driving style of a vehicle.

In order to achieve the above object, a torque distribution display device according to the present invention provides a torque distribution display device for use in a vehicle equipped with an electronically controlled coupling that distributes torque for running to main drive wheels and auxiliary drive wheels. a level display unit provided corresponding to each of the main driving wheels and the sub-driving wheels and displaying the distribution of driving torque to the main driving wheels and the sub-driving wheels in a plurality of levels; Depending on the total driving force of the wheels and auxiliary drive wheels, the level displayed on the level display corresponding to the main drive wheels is increased or decreased within the range not exceeding the level displayed on the level display corresponding to the main drive wheels. , and a control unit for increasing or decreasing the level displayed on the level display unit corresponding to the auxiliary driving wheel in accordance with the drive torque distributed to the auxiliary driving wheel.

According to this configuration, the level display portions are provided corresponding to the main driving wheels and the sub-driving wheels, respectively. The distribution of torque to the main driving wheels and sub-driving wheels is displayed according to the level displayed on each level display. Therefore, the driver of the vehicle can visually recognize the state of torque distribution to the main driving wheels and the auxiliary driving wheels.

The level display portion corresponding to the main driving wheels displays the level corresponding to the total driving force of the main driving wheels and the auxiliary driving wheels. On the other hand, the level display portion corresponding to the auxiliary driving wheels displays the level corresponding to the drive torque distributed to the auxiliary driving wheels.

The total driving force of the main drive wheels and auxiliary drive wheels is obtained by multiplying the torque output by the drive source (e.g., engine) by the total gear ratio (total reduction ratio) of the vehicle, and then multiplying the resulting product by the power of the main drive wheels and auxiliary drive wheels. Calculated by dividing by the tire radius. Therefore, depending on the driving conditions of the vehicle, such as sudden braking in high gear, the total driving force of the main drive wheels and the auxiliary drive wheels may be small, so the level displayed on the level display corresponding to the auxiliary drive wheels may be the main level. If the level displayed on the level display section corresponding to the drive wheels is exceeded, the display of the torque distribution state may not match the driving style of the vehicle, which may give the driver a sense of discomfort.

Therefore, the level displayed on the level display portion corresponding to the sub-driving wheels is increased or decreased within a range not exceeding the level displayed on the level display portion corresponding to the main driving wheels. As a result, it is possible to prevent the display of the state of torque distribution to the main drive wheels and the auxiliary drive wheels from being displayed in a manner that does not match the drive system of the vehicle. can be suppressed.

The level display section may have a plurality of segments, and may display the level by the number of lighting of the segments, or may display the level numerically.

In addition, since the magnitude of the drive torque distributed to the auxiliary drive wheels has a correlation with the current supplied to the electronically controlled coupling, the torque corresponding to the auxiliary drive wheels is adjusted according to the magnitude of the current. The level displayed on the level display section may be increased or decreased.

A threshold corresponding to each level in a plurality of stages is set, and the level displayed on the level display section corresponding to the auxiliary drive wheel is raised or lowered based on the relationship between the current supplied to the electronically controlled coupling and each threshold. Based on the relationship, if the level displayed in the level display section corresponding to the auxiliary drive wheels exceeds the level displayed in the level display section corresponding to the main drive wheels, the auxiliary drive wheels It is preferable that the threshold value corresponding to at least one level is changed so that the level displayed on the level display section corresponding to is limited to the level displayed on the level display section corresponding to the main driving wheels or less.

According to the present invention, it is possible to prevent the display of the state of distribution of torque to the main drive wheels and the auxiliary drive wheels from being displayed in a manner that does not match the drive type of the vehicle. You can restrain yourself from giving.

1 is a plan view of a vehicle equipped with a torque distribution display device according to an embodiment of the present invention; FIG. It is a figure which shows an example of a torque distribution condition display screen. 4 is a flow chart showing the contents of display control of a torque distribution status display screen; FIG. 4 is a diagram showing an example of a lighting number map (first lighting number map); 4 is a flow chart showing the contents of display control of a torque distribution status display screen; It is a figure which shows an example of a 2nd lighting number map.

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Vehicle configuration>
FIG. 1 is a plan view of a vehicle 1 equipped with a torque distribution display device according to one embodiment of the present invention.

The vehicle 1 employs an active torque split 4WD system. Vehicle 1 includes engine 2 , transmission 3 , front differential gear 4 , transfer 5 , propeller shaft 6 and rear differential gear 7 .

The engine 2 is laterally mounted (mounted) on the front portion of the vehicle 1 so that the crankshaft is oriented laterally with respect to the longitudinal direction of the vehicle 1, that is, so that the crankshaft extends in the vehicle width direction.

The transmission 3 may be, for example, a stepped automatic transmission (AT) equipped with a Ravigneau-type planetary gear mechanism, or a belt-type continuously variable transmission (CVT). may

A ring gear 12 is fixed to a differential case 11 of the front differential gear 4 . The rotation of the engine 2 is changed by the transmission 3 and input to the ring gear 12 . The rotation input to the ring gear 12 causes the differential case 11 to rotate integrally with the ring gear 12 . The rotation of the differential case 11 is converted into rotation of the side gears 14 via the pinion gear 13, and the left and right front drive shafts 15L and 15R rotate together with the side gears. It is transmitted to the front wheels 16L and 16R, which are drive wheels.

The transfer 5 includes, for example, a first bevel gear 17 that rotates integrally with the differential case 11 of the front differential gear 4 and a second bevel gear 18 that meshes with the first bevel gear 17 . A front end of a propeller shaft 6 extending in the longitudinal direction of the vehicle 1 is connected to the center of the second bevel gear 18 .

The propeller shaft 6 is divided into a front side portion 6F and a rear side portion 6R, and an electronically controlled coupling 21 is interposed between the front side portion 6F and the rear side portion 6R. . The electronically controlled coupling 21 includes a main clutch consisting of a multi-plate friction clutch that transmits torque, and an electromagnet that controls the torque capacity of the main clutch. ), the torque capacity of the main clutch increases in proportion to the torque capacity.

A rear end of the propeller shaft 6 is connected to a drive pinion shaft of a rear differential gear 7 . Torque transmitted from the propeller shaft 6 to the rear differential gear 7 rotates the rear drive shafts 22L, 22R, and the rotation of the rear drive shafts 22L, 22R is transmitted to the rear wheels 23L, 23R, which are auxiliary drive wheels, respectively.

The vehicle 1 also includes an ECU (Electronic Control Unit) 31 including a microcomputer (microcontroller unit).

A tire rotation sensor 32 is provided for each of the front wheels 16L, 16R and the rear wheels 23L, 23R for outputting a pulse signal synchronized with the rotation of each tire as a detection signal. Each tire rotation sensor 32 is connected to the ECU 31 . The ECU 31 also receives an engine rotation sensor 33 that outputs a pulse signal synchronized with the rotation of the engine 2 (rotation of the crankshaft) as a detection signal, and a detection signal corresponding to the operation amount of the accelerator pedal provided in the vehicle 1. An accelerator sensor 34 for output is connected.

The ECU 31 obtains the tire rotation speeds of the front wheels 16L, 16R and the rear wheels 23L, 23R from the detection signals of the tire rotation sensors 32, respectively. The ECU 31 obtains the engine rotation speed, which is the rotation speed of the engine 2 , from the detection signal of the engine rotation sensor 33 , and obtains the accelerator opening from the detection signal of the accelerator sensor 34 . The accelerator opening is the amount of operation of the accelerator pedal, and is a percentage of 100%, for example, when the accelerator pedal is fully depressed. The ECU 31 controls the electronically controlled coupling 21 based on numerical values obtained from detection signals input from various sensors.

Although only one ECU 31 is shown in FIG. 1, the vehicle 1 is equipped with a plurality of ECUs having the same configuration as the ECU 31 in order to control each part. A plurality of ECUs including the ECU 31 are connected so as to be capable of two-way communication by CAN (Controller Area Network) communication protocol. Moreover, only a part of various sensors required for control by the ECU 31 are shown in FIG.

The vehicle 1 is also provided with a meter unit 41 . In the passenger compartment of the vehicle 1, an instrument panel (dashboard) is provided in front of the front seats (the frontmost part in the passenger compartment), and the meter unit 41 is attached to the instrument panel. The meter unit 41 includes a display 42 that displays various information. The display 42 may be, for example, a liquid crystal display or an organic EL (electroluminescence) display. The display on the display 42 may be controlled by the ECU 31 or may be controlled by a meter unit control ECU separate from the ECU 31 .

<Torque distribution status display>
FIG. 2 is a diagram showing an example of a torque distribution status display screen displayed on the display 42. As shown in FIG.

In the vehicle 1, during normal running, torque for running the vehicle 1, that is, engine torque from the engine 2 is transmitted to the left and right front wheels 16L, 16R. For example, when a tire slip occurs while the vehicle 1 is running, the ECU 31 estimates the road friction coefficient, and supplies the estimated road friction coefficient to the electronically controlled coupling 21 so that the tire slip does not occur. A coupling current value is controlled to actively distribute torque to the front wheels 16L, 16R and the rear wheels 23L, 23R.

The display 42 displays a torque distribution status display screen that displays the distribution status of the torque. In the torque distribution status display screen, an image simulating the driving system of the vehicle 1 is arranged in the center. The images include wheel images 51FL, 51FR, 51RL, and 51RR imitating the front wheels 16L, 16R and the rear wheels 23L, 23R, respectively. Level indicators 52FL and 52RL are arranged on the left sides of the wheel images 51FL and 51RL, respectively. Level indicators 52FR and 52RR are arranged on the right sides of the wheel images 51FR and 51RR, respectively.

Level indicators 52FL, 52FR, 52RL and 52RR include five segments Sg1, Sg2, Sg3, Sg4 and Sg5. Each of the segments Sg1 to Sg5 is an area capable of displaying a lit state and an extinguished state. The segments Sg1, Sg2, Sg3, Sg4 and Sg5 are arranged vertically in this order from bottom to top.

The state of torque distribution to the front wheels 16L, 16R and the rear wheels 23L, 23R is indicated by the number of lighting states of the segments Sg1 to Sg5 (hereinafter simply referred to as "number of lighting") in each level indicator 52FL, 52FR, 52RL, 52RR. Is displayed. In the display of the torque distribution state, the difference in torque between the left and right front wheels 16L and 16R is not taken into consideration, and the lighting numbers of the segments Sg1 to Sg5 of the level indicators 52FL and 52FR are the same. Similarly, for the left and right rear wheels 23L, 23R, the torque difference between them is not taken into consideration, and the lighting numbers of the segments Sg1 to Sg5 of the level indicators 52FL, 52FR are the same.

<Level indicator lighting control>
FIG. 3 is a flow chart showing the content of display control of the torque distribution status display screen.

In order to control the lighting states of the segments Sg1 to Sg5 of the level indicators 52FL, 52FR, 52RL and 52RR on the torque distribution status display screen, the ECU 31 executes the following processing.

First, the total driving force of the front wheels 16L, 16R and the rear wheels 23L, 23R, that is, the total driving force is calculated (step S1). The total driving force can be calculated by multiplying the engine torque output by the engine 2 by the total gear ratio of the vehicle 1 and dividing the product by the tire radii of the front wheels 16L, 16R and the rear wheels 23L, 23R.

Next, the lighting number of the segments Sg1 to Sg5 of the level indicators 52FL and 52FR (hereinafter referred to as "main drive wheel segment lighting number") corresponding to the total driving force is determined (step S2). For example, first to fourth thresholds are set, and when the total driving force is less than the first threshold (greater than 0), the lighting number of segments Sg1 to Sg5 is determined to be one. When the total driving force is greater than or equal to the first threshold and less than the second threshold, the lighting number of the segments Sg1 to Sg5 is determined to be 2. When the total driving force is greater than or equal to the second threshold and less than the third threshold, , the lighting number of the segments Sg1 to Sg5 is determined to be 3, and the total driving force is equal to or greater than the third threshold and less than the fourth threshold, the lighting number of the segments Sg1 to Sg5 is determined to be 4, and the total driving force is If it is equal to or greater than the fourth threshold, the lighting number of segments Sg1 to Sg5 is determined to be five. When the total driving force is 0, the lighting number of segments Sg1 to Sg5 is determined to be 0.

Further, the lighting number map is referenced to determine the lighting number of the segments Sg1 to Sg5 of the level indicators 52RL and 52RR (hereinafter referred to as "sub-drive wheel segment lighting number") corresponding to the coupling current value (step S3). The contents of the lighting number map are shown in FIG. In the lighting number map, the range of possible values of the coupling current value (hereinafter referred to as "coupling current value range") is divided into six ranges, and the boundary values of each range are the first to It is set as the fifth threshold. According to the lighting number map, when the coupling current value is less than the first threshold, the lighting number of the segments Sg1 to Sg5 is determined to be 0, and when the coupling current value is greater than or equal to the first threshold and less than the second threshold. , the lighting number of the segments Sg1 to Sg5 is determined to be 1, and when the coupling current value is equal to or greater than the second threshold value and less than the third threshold value, the lighting number of the segments Sg1 to Sg5 is determined to be 2, and the cup When the ring current value is greater than or equal to the third threshold and less than the fourth threshold, the number of lighting segments Sg1 to Sg5 is determined to be 3. When the coupling current value is greater than or equal to the fourth threshold and less than the fifth threshold, , the lighting number of the segments Sg1 to Sg5 is determined to be 4, and when the coupling current value is equal to or greater than the fifth threshold value, the lighting number of the segments Sg1 to Sg5 is determined to be 5.

After that, the main drive wheel segment lighting number and the sub-driving wheel segment lighting number are compared in magnitude, and it is determined whether or not the main driving wheel segment lighting number is greater than or equal to the sub-driving wheel segment lighting number (step S4). .

If the main driving wheel segment lighting number is greater than or equal to the auxiliary driving wheel segment lighting number (YES in step S4), the segments Sg1 to Sg5 of the level indicators 52FL and 52FR are turned on according to the main driving wheel segment lighting number ( step S5). The segments Sg1 to Sg5 to be lit are determined in order from the lowest segment Sg1 in accordance with the number of main driving wheel segments to be lit. That is, when the main driving wheel segment lighting number is 1, only the segment Sg1 is lit, and when the main driving wheel segment lighting number is 2, the segments Sg1 and Sg2 are lit, and the main driving wheel segments are lit. When the number is 3, the segments Sg1 to Sg3 are lit, when the main drive wheel segment lighting number is 4, the segments Sg1 to Sg4 are lit, and when the main driving wheel segment lighting number is 5 , the segments Sg1 to Sg5 are lit.

Also, the segments Sg1 to Sg5 of the level indicators 52RL and 52RR are turned on according to the number of auxiliary drive wheel segments to be lit (step S5). The segments Sg1 to Sg5 to be turned on are determined in order from the lowest segment Sg1 according to the number of auxiliary driving wheel segments to be turned on. That is, when the auxiliary driving wheel segment lighting number is 1, only the segment Sg1 is lit, and when the auxiliary driving wheel segment lighting number is 2, the segments Sg1 and Sg2 are lit, and the auxiliary driving wheel segment is lighting. When the number is 3, the segments Sg1 to Sg3 are lit, when the number of lighting auxiliary drive wheel segments is 4, the segments Sg1 to Sg4 are lit, and when the number of lighting auxiliary driving wheel segments is 5 , the segments Sg1 to Sg5 are lit.

On the other hand, if the auxiliary driving wheel segment lighting number exceeds the main driving wheel segment lighting number (NO in step S4), the auxiliary driving wheel segment lighting number is limited to the same number as the main driving wheel segment lighting number (step S6). .

For example, if the main driving wheel segment lighting number is 3, even if the auxiliary driving wheel segment lighting number determined according to the lighting number map exceeds 3 (that is, even if it is 4 or more), the auxiliary driving wheel segment The number of lights is re-determined to be the same number as 3, which is the number of lights of the main driving wheel segments.

After that, the segments Sg1 to Sg5 of the level indicators 52FL and 52FR are lit according to the lighting number of the main driving wheel segments, and the lighting number of the auxiliary driving wheel segments Sg1 to Sg5 of the level indicators 52RL and 52RR are re-determined by the limit. is turned on (step S5).

<Effect>
As described above, on the torque distribution status display screen, the level indicators 52FL, 52FR, 52RL and 52RR are provided corresponding to the front wheels 16L and 16R as the main drive wheels and the rear wheels 23L and 23R as the auxiliary drive wheels, respectively. ing. The distribution of torque to the front wheels 16L, 16R and the rear wheels 23L, 23R is displayed according to the level represented by the number of lights of the segments Sg1 to Sg5 in the level indicators 52FL, 52FR, 52RL, 52RR. Therefore, the driver of the vehicle 1 can visually recognize the distribution of torque to the front wheels 16L, 16R and the rear wheels 23L, 23R.

Level indicators 52FL, 52FR, 52RL and 52RR corresponding to the front wheels 16L and 16R display levels corresponding to the total driving force of the front wheels 16L and 16R and the rear wheels 23L and 23R. On the other hand, the level indicators 52FL, 52FR, 52RL and 52RR corresponding to the rear wheels 23L and 23R display levels corresponding to the driving torque distributed to the rear wheels 23L and 23R.

The total driving force of the front wheels 16L, 16R and the rear wheels 23L, 23R is obtained by multiplying the engine torque output by the engine 2 by the total gear ratio of the vehicle 1, and the multiplied value is the tire radius of the front wheels 16L, 16R and the rear wheels 23L, 23R. It is calculated by dividing by Therefore, depending on the driving conditions of the vehicle 1, such as sudden braking in a high gear state, the total driving force of the front wheels 16L, 16R and the rear wheels 23L, 23R may be small. The number of lighting of segments Sg1 to Sg5 in 52RR exceeds the number of lighting of segments Sg1 to Sg5 in level indicators 52FL and 52FR corresponding to front wheels 16L and 16R, and the display of torque distribution does not match the drive system of vehicle 1. This may cause the driver to feel uncomfortable.

Therefore, the lighting number of the segments Sg1 to Sg5 in the level indicators 52RL and 52RR corresponding to the rear wheels 23L and 23R should be within a range not exceeding the lighting number of the segments Sg1 to Sg5 in the level indicators 52FL and 52FR corresponding to the front wheels 16L and 16R. be done. As a result, it is possible to prevent the display of the distribution of torque to the front wheels 16L, 16R and the rear wheels 23L, 23R from being inconsistent with the drive system of the vehicle 1, thereby reducing discomfort caused by the display inconsistent with the drive system of the vehicle 1. You can control what you give to the driver.

<Other embodiments>
The display control of the torque distribution status display screen described below may be performed instead of the display control of the torque distribution status display screen (lighting control of the level indicator) in the above-described embodiment.

FIG. 5 is a flow chart showing the contents of another display control of the torque distribution status display screen.

In the display control shown in FIG. 5, the ECU 31 first calculates the total driving force by the same method as in step S1 of FIG. 3 (step S11).

Next, the number of main driving wheel segment lighting is determined based on the total driving force by the same method as step S2 in FIG. 3 (step S12).

Also, the first lighting number map is referenced to determine the auxiliary driving wheel segment lighting number (step S13). The contents of the first lighting number map are the same as the contents of the lighting number map shown in FIG. Therefore, the method for determining the lighting number of the auxiliary driving wheel segment according to the first lighting number map is the same as the method for determining the lighting number of the auxiliary driving wheel segment in step S3 of FIG.

After that, the main drive wheel segment lighting number and the sub-driving wheel segment lighting number are compared in magnitude, and it is determined whether or not the main driving wheel segment lighting number is equal to or greater than the sub-driving wheel segment lighting number (step S14). .

If the main driving wheel segment lighting number is greater than or equal to the auxiliary driving wheel segment lighting number (YES in step S14), the segments Sg1 to Sg5 of the level indicators 52FL and 52FR are lit according to the main driving wheel segment lighting number ( step S5). Also, the segments Sg1 to Sg5 of the level indicators 52RL and 52RR are turned on according to the number of auxiliary drive wheel segments to be lit (step S5).

On the other hand, if the auxiliary driving wheel segment lighting number exceeds the main driving wheel segment lighting number (NO in step S14), the second lighting number map is referred to, and the auxiliary driving wheel segment lighting number is re-determined (step S16). The second lighting number map is prepared with the upper limit of the auxiliary driving wheel segment lighting number set to 1 to 4, respectively. A second lighting number map with the same upper limit number is used. In each second lighting number map, the same coupling current value range as in the first lighting number map is set according to the upper limit so that the lighting number of each sub-driving wheel segment below the upper limit is determined according to the coupling current value. , and the boundary value of each range is set as a threshold.

For example, if the main driving wheel segment lighting number is 3, the second lighting number map shown in FIG. 6 is used to redetermine the auxiliary driving wheel segment lighting number. First to third threshold values are set in the second lighting number map shown in FIG. According to the second lighting number map, when the coupling current value is less than the first threshold, the lighting number of the segments Sg1 to Sg5 is determined to be 0, and when the coupling current value is equal to or greater than the first threshold and less than the second threshold, In some cases, the lighting number of the segments Sg1 to Sg5 is determined to be 2, and when the coupling current value is equal to or greater than the third threshold, the lighting number of the segments Sg1 to Sg5 is determined to be 3. As a result, the re-determined auxiliary driving wheel segment lighting number becomes equal to or less than the main driving wheel segment lighting number.

After that, the segments Sg1 to Sg5 of the level indicators 52FL and 52FR are lit according to the number of main drive wheel segments lit, and the segments Sg1 to Sg5 of the level indicators 52RL and 52RR are lit according to the number of the auxiliary drive wheel segments lit. (step S15).
This display control of the torque distribution status display screen can also provide the same advantages as those of the above-described embodiment.

<Modification>
Although two embodiments of the present invention have been described above, the present invention can also be implemented in other forms.

For example, in the above-described embodiment, the front wheels 16L and 16R are the main drive wheels to which power is transmitted when power is not distributed. It can also be used in a vehicle having a configuration in which the main driving wheels to which the power is transmitted are the rear wheels 23L and 23R.

The transmission 3 may be a power split type continuously variable transmission. A power split type continuously variable transmission, for example, is equipped with a belt-type continuously variable transmission mechanism that changes the power steplessly by changing the gear ratio, and divides the power into two paths between the input shaft and the output shaft. It is a transmission that can be transmitted by

In addition, various design changes can be made to the above configuration within the scope of the matters described in the claims.

1: Vehicle 16L, 16R: Front wheel 21: Electronic control coupling 23L, 23R: Rear wheel 31: ECU (control unit)
42: Display (torque distribution status display device)
52FL, 52FR, 52RL, 52RR: Level indicators (level display units)
Sg1 to Sg5: Segment (level display part)

Claims (1)

A torque distribution status display device used in a vehicle equipped with an electronically controlled coupling that distributes torque for running to main drive wheels and auxiliary drive wheels,
a level display unit provided corresponding to each of the main driving wheels and the sub-driving wheels and displaying a distribution of driving torque to the main driving wheels and the sub-driving wheels in a plurality of levels;
The level displayed on the level display unit corresponding to the main driving wheels is determined by comparing the total driving force of the main driving wheels and the auxiliary driving wheels with a preset threshold value , and corresponding to the auxiliary driving wheels. is determined according to the drive torque distributed to the auxiliary drive wheels within a range not exceeding the level displayed on the level display unit corresponding to the main drive wheels; and a control section for displaying the determined levels on the level display section corresponding to the driving wheel and the level display section corresponding to the sub-driving wheel.

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