Vehicle drive control system

Abstract

The system will automatically determine whether or not tire chains are attached to the front or rear wheels. [Solution] The vehicle drive control device includes a wheel speed detection unit that detects the wheel speeds of the front and rear wheels in a four-wheel drive vehicle, and a tire chain installation determination calculation unit. The tire chain installation determination calculation unit includes a vehicle speed detection unit that detects the vehicle speed, a front wheel slip ratio calculation unit that calculates the front wheel slip ratio based on the front wheel speed and the vehicle speed, a rear wheel slip ratio calculation unit that calculates the rear wheel slip ratio based on the rear wheel speed and the vehicle speed at the same road surface position where the front wheel slip ratio was calculated, and a tire chain installation determination unit that determines that a tire chain is installed on the wheel with the lower slip ratio among the front and rear wheels if the difference between the front wheel slip ratio and the rear wheel slip ratio is greater than or equal to a first threshold.

Description

Technical Field

[0001] The present invention relates to a drive control device for a vehicle.

Background Art

[0002] In a four-wheel drive vehicle, when a tire chain is mounted on the front wheels or the rear wheels, a large difference in grip force occurs between the tire chain-mounted wheels and the non-mounted wheels. Therefore, it is preferable to appropriately change drive control such as front-rear drive force distribution control and vehicle stability control after the tire chain is mounted.

[0003] When attempting to automatically change the drive control after the tire chain is mounted, the control unit first needs to automatically detect the presence or absence of the tire chain.

[0004] For example, in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2019-113940), a technique is disclosed in which the frequency characteristics due to the vertical vibration generated in the vehicle are compared with the past frequency characteristics, and when the frequency characteristics are different, it is determined that the vehicle is equipped with a tire chain.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technique disclosed in Patent Document 1 only determines the presence or absence of the tire chain from the frequency characteristics of the vibration generated in the vehicle body. Therefore, with the technique disclosed in Patent Document 1, it is impossible to determine whether the tire chain is mounted on the front wheels or the rear wheels.

[0007] Therefore, the technology disclosed in Reference 1 cannot appropriately modify the drive control when tire chains are installed in a four-wheel drive vehicle.

[0008] The present invention aims to provide a vehicle drive control device that can automatically determine whether or not tire chains are attached to the wheels of a four-wheel drive vehicle, and can appropriately perform drive control such as drive force distribution control and vehicle stability control for drive wheels with and without tire chains. [Means for solving the problem]

[0009] The present invention relates to a drive control device for a vehicle having a wheel speed detection unit for detecting the wheel speeds of the front and rear wheels of a four-wheel drive vehicle, and a tire chain installation determination calculation unit, wherein the tire chain installation determination calculation unit comprises a vehicle speed detection unit for detecting the vehicle speed, a front wheel slip ratio calculation unit for calculating the front wheel slip ratio based on the wheel speed of the front wheels detected by the wheel speed detection unit and the vehicle speed detected by the vehicle speed detection unit, a rear wheel slip ratio calculation unit for calculating the rear wheel slip ratio based on the wheel speed of the rear wheels detected by the wheel speed detection unit and the vehicle speed detected by the vehicle speed detection unit at the same road surface position where the front wheel slip ratio was calculated, and a tire chain installation determination unit for determining that a tire chain is installed on the wheel with the lower slip ratio among the front and rear wheels if the difference between the front wheel slip ratio calculated by the front wheel slip ratio calculation unit and the rear wheel slip ratio calculated by the rear wheel slip ratio calculation unit is greater than or equal to a first threshold. [Effects of the Invention]

[0010] According to the present invention, the front wheel slip ratio is calculated based on the front wheel speed and vehicle speed, and the rear wheel slip ratio is calculated based on the rear wheel speed and vehicle speed at the same road surface position where the front wheel slip ratio was calculated. If the difference between the front wheel slip ratio and the rear wheel slip ratio is greater than or equal to a first threshold, it is determined that a tire chain is installed on the wheel with the lower slip ratio between the front and rear wheels. This allows for automatic determination of whether or not a tire chain is installed on the wheels of a four-wheel drive vehicle, and enables appropriate drive control, such as drive force distribution control and vehicle stability control, for wheels with and without tire chains. [Brief explanation of the drawing]

[0011] [Figure 1] Configuration diagram of a vehicle drive system according to the first embodiment [Figure 2A] A flowchart (part 1) showing the tire chain installation detection routine. [Figure 2B] The same, flowchart (part 2) showing the tire chain installation detection routine. [Figure 3A] This diagram illustrates the process of calculating the front wheel slip ratio at the low-friction surface detection point. [Figure 3B] This diagram illustrates the process of calculating the rear wheel slip ratio at the low-friction surface detection point. [Figure 4A] The same diagram illustrates the process of calculating the front wheel slip ratio at the judgment point on a road surface that changes from a high-μ surface to a low-μ surface. [Figure 4B] The same diagram illustrates the process of calculating the rear wheel slip ratio at the judgment point on a road surface that changes from a high-friction surface to a low-friction surface. [Figure 5A] The same diagram illustrates the process of calculating the front wheel slip ratio at the judgment point on a road surface that changes from a low-friction surface to a high-friction surface. [Figure 5B] The same diagram illustrates the process of calculating the rear wheel slip ratio at the judgment point on a road surface that changes from a low-friction surface to a high-friction surface. [Figure 6A] This diagram illustrates the process of calculating the front wheel slip ratio at the location where high-friction surfaces are detected. [Figure 6B]Explanatory drawing showing a state where the slip ratio of the rear wheels is calculated at the determination position of the same, high μ road [Figure 7] Conceptual diagram of the slip ratio determination threshold value table [Figure 8] Conceptual diagram of the tire chain mounting determination threshold value table [Figure 9] Conceptual diagram of the front and rear drive force distribution ratio map when a tire chain is mounted [Figure 10A] Flowchart (Part Ⅰ) showing the tire chain mounting determination routine according to the second embodiment [Figure 10B] Flowchart (Part Ⅱ) showing the tire chain mounting determination routine [Mode for Carrying Out the Invention]

[0012] Hereinafter, an embodiment of the present invention will be described based on the drawings. [First Embodiment]

[0013] The first embodiment of the present invention is shown in FIGS. 1 to 9. In FIG. 1, the host vehicle M is a four-wheel drive vehicle. A front and rear drive force distribution mechanism is provided in parallel with the center differential of the host vehicle M. This front and rear drive force distribution mechanism variably sets the distribution of the drive force (torque) from the drive source (engine or electric motor) to the front wheels Ft and the rear wheels Rt, which are the drive wheels, between 0 and 100 [%]. This front and rear drive force distribution mechanism operates according to a control signal from a front and rear drive force distribution control unit 21 described later.

[0014] Further, the drive force control device 1 mounted on the host vehicle M checks whether a tire chain is mounted on the front wheels Ft of the host vehicle M. When the drive force control device 1 determines that a tire chain is mounted on the front wheels Ft, it sets the ratio of the drive force distribution to the front wheels Ft to be larger than that to the rear wheels Rt. As the tire chain, a metal tire chain, a non-metal tire chain, a cloth tire chain, etc. are known.

[0015] The drive force control device 1 includes a tire chain installation determination calculation unit 11 and a front / rear drive force distribution control unit 21. The tire chain installation determination calculation unit 11 and the front / rear drive force distribution control unit 21 are connected via bidirectional communication. The tire chain installation determination calculation unit 11 and the front / rear drive force distribution control unit 21 are composed of a microcontroller. The microcontroller includes a CPU, RAM, ROM, rewritable non-volatile memory (flash memory or EEPROM), and peripheral devices. The ROM of the microcontroller stores programs and fixed data necessary for the CPU to execute various processes. The RAM is provided as the CPU's work area, and various data from the CPU are temporarily stored there. The CPU is also called an MPU (Microprocessor) or processor. Alternatively, a GPU (Graphics Processing Unit) or GSP (Graph Streaming Processor) may be used instead of the CPU. Alternatively, a selective combination of CPU, GPU, and GSP may be used.

[0016] The input side of the tire chain installation determination calculation unit 11 is connected to a GNSS (Global Navigation Satellite System) receiver 12, a wheel speed sensor 13 (which acts as a wheel speed detection unit), a front / rear acceleration sensor 14, and an accelerator pedal position sensor 15. A monitor 31 is connected to the output side of the tire chain installation determination calculation unit 11.

[0017] The GNSS receiver 12 acquires the position information (coordinates of latitude, longitude, and altitude) of the vehicle M based on position signals from GNSS satellites. Wheel speed sensors 13 are installed on each of the four wheels: the left and right front wheels Ft and the left and right rear wheels Rt. The wheel speed sensors 13 detect the wheel speeds of the left and right front wheels Ft and the left and right rear wheels Rt. The longitudinal acceleration sensor 14 detects the longitudinal acceleration of the vehicle M. The accelerator pedal position sensor 15 detects the amount the driver depresses the accelerator pedal. The monitor 31 is a multi-information display or center information display located on the combination meter.

[0018] The tire chain mounting determination calculation unit 11 calculates the slip ratio (front wheel slip ratio) λFt of the front wheel Ft and the slip ratio (rear wheel slip ratio) λRt of the rear wheel Rt at a predetermined cycle while the host vehicle M is running, and determines whether a tire chain is mounted on the front wheel Ft.

[0019] In addition, the front and rear drive force distribution control unit 21 sets the ratio of the drive force distribution between the front wheel Ft and the rear wheel Rt in normal running to an equal distribution of 50:50 [%]. Further, when the tire chain mounting determination calculation unit 11 determines that a tire chain is mounted on the front wheel Ft, it calculates the ratio of the drive force distribution between the front wheel Ft and the rear wheel Rt. The front and rear drive force distribution control unit 21 operates the front and rear drive force distribution mechanism according to the ratio of the drive force distribution between the front wheel Ft and the rear wheel Rt calculated by the tire chain mounting determination calculation unit 11, and variably sets the ratio of the drive force distribution for the front wheel Ft and the rear wheel Rt.

[0020] Specifically, the tire chain mounting determination calculation unit 11 determines whether a tire chain is mounted on the front wheel Ft according to the tire chain mounting determination routine shown in FIGS. 2A to 2B. This routine is executed at every predetermined calculation cycle after the system is started.

[0021] First, the tire chain mounting determination calculation unit 11 compares the vehicle speed (host vehicle speed) Vv of the host vehicle M with the traveling determination vehicle speed Vo to check whether the host vehicle M is running (step S1). The host vehicle speed Vv is obtained from, for example, the average value of the wheel speeds of the four wheels detected by the wheel speed sensor 13. The traveling determination vehicle speed Vo is an extremely low vehicle speed of about 1 [Km / h].

[0022] When Vv≥Vo (YES), the tire chain mounting determination calculation unit 11 determines that the vehicle is running and proceeds to step S2. When Vv<Vo (NO), the tire chain mounting determination calculation unit 11 exits the routine.

[0023] When the system proceeds to step S2, the tire chain installation determination calculation unit 11 reads the current front-to-rear drive force distribution ratio set by the front-to-rear drive force distribution control unit 21. The front-to-rear drive force distribution control unit 21 appropriately controls the drive force distribution between the front wheels Ft and the rear wheels Rt between 0 and 100% depending on the driving state of the vehicle M and the road surface conditions. The front-to-rear drive force distribution control unit 21 sets the ratio of drive force distribution between the front wheels Ft and the rear wheels Rt to an equal distribution of 50:50% during normal driving on a flat road. On the other hand, when driving uphill, the ground contact load on the rear wheels Rt increases. Therefore, the front-to-rear drive force distribution control unit 21 sets the torque distribution to be biased towards the rear wheels Rt when driving uphill. Also, when driving downhill, the ground contact load on the front wheels Ft increases. Therefore, the front-to-rear drive force distribution control unit 21 sets the torque distribution to be biased towards the front wheels Ft when driving downhill. Furthermore, the ratio of the driving force distribution between the front wheels Ft and the rear wheels Rt during normal driving on a flat road may be set to an unequal distribution such as 60:40[%].

[0024] Next, the tire chain installation determination calculation unit 11 reads the longitudinal gradient (uphill, downhill) of the road surface (step S3). The longitudinal gradient is calculated by the longitudinal drive force distribution control unit 21. The longitudinal drive force distribution control unit 21 calculates the longitudinal gradient by, for example, subtracting the vehicle acceleration from the longitudinal acceleration. The longitudinal acceleration is detected by the longitudinal acceleration sensor 14. The longitudinal drive force distribution control unit 21 also calculates the vehicle acceleration by determining the amount of vehicle movement per unit time based on the position information of the vehicle M obtained from the GNSS receiver 12, and then taking the second derivative of this amount of vehicle movement.

[0025] Subsequently, the tire chain installation determination calculation unit 11 compares the accelerator opening θacc detected by the accelerator opening sensor 15 with the accelerator depression determination threshold θo (step S4). This accelerator depression determination threshold θo is a value used to determine whether or not the driver has pressed the accelerator pedal. The slip ratios λFt and λRt of the front and rear wheels Ft and Rt must be detected while driving force is being transmitted to the front and rear wheels Ft and Rt.

[0026] Then, the tire chain installation determination calculation unit 11 determines that the driver has pressed the accelerator pedal if θacc ≥ θo (YES), and calculates the front wheel slip ratio λFt (step S5). Also, if θacc < θo (NO), the tire chain installation determination calculation unit 11 determines that the accelerator pedal is in the released state, and exits the routine. The processing in step S5 corresponds to the front wheel slip ratio calculation unit of the present invention.

[0027] The tire chain fitting determination calculation unit 11 calculates the front wheel slip ratio λFt from the following equation (1) based on, for example, the vehicle speed and the wheel speeds (average wheel speed) of the left and right front wheels Ft detected by the wheel speed sensor 13. λFt = ((vehicle speed - wheel speed) / wheel speed) · 100 [%] …(1)

[0028] The tire chain installation determination calculation unit 11 determines the vehicle speed based on the vehicle's movement per unit time, for example, using the position information of the vehicle M obtained from the GNSS receiver 12. Therefore, the tire chain installation determination calculation unit 11 is equipped with the function of a vehicle speed detection unit.

[0029] Next, the tire chain installation determination calculation unit 11 compares the front wheel slip ratio λFt with the slip ratio determination threshold λ1 (step S6). This slip ratio determination threshold λ1 is a value used to determine whether or not the front wheel Ft is slipping. If tire chains are installed on the front wheel Ft, the front wheel slip ratio λFt can be estimated to be small.

[0030] The tire chain installation determination calculation unit 11 sets the slip ratio determination threshold λ1 by referring to the slip ratio determination threshold table shown in Figure 7. This slip ratio determination threshold table stores the relationship between the longitudinal gradient of the road surface, the ratio of driving force distribution to the front wheels Ft, and the slip ratio determination threshold λ1, which has been determined in advance through experiments, etc. In the slip ratio determination threshold table, a higher slip ratio determination threshold λ1 is set as the longitudinal gradient of the road surface increases or the ratio of driving force distribution to the front wheels Ft increases.

[0031] For example, on an uphill road, if the front-to-rear gradient of the road surface is large, the proportion of ground contact load distribution to the front wheels Ft decreases. In such situations, the front wheels Ft are more prone to slipping, so the slip ratio determination threshold λ1 is set to a high value. Also, when driving on flat roads or other road surfaces with a small gradient, if the proportion of driving force distribution to the front wheels Ft is large, slipping is also more likely to occur. Therefore, in this case as well, the slip ratio determination threshold λ1 is set to a high value. As a result, it is possible to determine with high accuracy whether or not slipping is occurring on the front wheels Ft, even when driving on an uphill road or when the proportion of driving force distribution to the front wheels Ft is large.

[0032] Then, the tire chain installation determination calculation unit 11 determines that the front wheel Ft is slipping if λFt > λ1 (NO), and proceeds to step S7. In step S7, the tire chain installation determination calculation unit 11 determines that the tire chain is not installed, clears the front wheel slip determination flag FFt (FFt ← 0), and exits the routine. On the other hand, if λFt ≤ λ1 (YES), the tire chain installation determination calculation unit 11 determines that the front wheel Ft is not slipping, and branches to step S8.

[0033] Possible factors contributing to a low front wheel slip ratio λFt include the presence of tire chains on the front wheels Ft and the vehicle M traveling on a high-friction surface. In steps S8 to S15, the tire chain installation determination calculation unit 11 checks whether or not tire chains are installed on the front wheels Ft.

[0034] First, the tire chain installation determination calculation unit 11 checks whether the vehicle M has moved forward by the amount of its wheelbase (step S8). To determine whether the vehicle M has moved forward by the amount of its wheelbase, for example, the unit calculates the travel time for the wheelbase based on the vehicle speed Vv and the wheelbase, and checks whether the elapsed time has reached the travel time. Alternatively, the unit obtains the current position coordinates of the vehicle M from the GNSS receiver 12 and checks whether the vehicle M has moved to a position obtained by adding the wheelbase to these position coordinates.

[0035] The tire chain installation determination calculation unit 11 waits if it determines that the vehicle M has not moved forward by the amount of its wheelbase (NO). Then, if the tire chain installation determination calculation unit 11 determines that the vehicle M has moved forward by the amount of its wheelbase (YES), it calculates the rear wheel slip ratio λRt (step S9). Note that the processing in steps S8 and S9 corresponds to the rear wheel slip ratio calculation unit of the present invention.

[0036] As a result, the position for calculating the front wheel slip ratio λFt, as shown in Figures 3A to 6A, and the position for calculating the rear wheel slip ratio λRt, as shown in Figures 3B to 6B, are essentially the same. Therefore, the front wheel slip ratio λFt and the rear wheel slip ratio λRt can be calculated under the same road surface conditions.

[0037] The tire chain installation determination calculation unit 11 calculates the rear wheel slip ratio λRt from the following equation (2), for example, based on the average wheel speed of the left and right rear wheels Rt detected by the wheel speed sensor 13 and the vehicle speed. λRt = ((vehicle speed - average wheel speed) / average wheel speed) · 100 [%] …(2)

[0038] Subsequently, the tire chain installation determination calculation unit 11 compares the absolute value of the difference between the front wheel slip ratio λFt and the rear wheel slip ratio λRt (|λFt-λRt|) with the tire chain installation determination threshold λ2, which is the first threshold (step S10). The tire chain installation determination calculation unit 11 sets the tire chain installation determination threshold λ2 by referring to the tire chain installation determination threshold table shown in Figure 8. This tire chain installation determination threshold table stores the relationship between the front-to-rear gradient of the road surface, the ratio of front-to-rear driving force distribution, and the slip ratio difference threshold λ2, which has been determined in advance from experiments, etc. In the tire chain installation determination threshold table, a lower value for the tire chain installation determination threshold λ2 is set as the front-to-rear gradient of the road surface increases and the ratio of driving force distribution to the front wheel Ft increases.

[0039] For example, on an uphill road, if the front-to-rear gradient of the road surface is large, the proportion of the contact load distribution to the rear wheel Rt increases, making the rear wheel Rt less likely to slip. Therefore, in such situations, it can be estimated that the difference between the slip ratios λFt and λRt of the front and rear wheels will be small. Thus, the tire chain installation threshold λ2 is set to a low value. Also, when driving on flat roads or other roads with a small gradient, if the proportion of the driving force distribution to the front wheel Ft is large, the front wheel Ft is more likely to slip. Therefore, in such situations as well, the tire chain installation threshold λ2 is set to a low value. This allows for highly accurate determination of whether or not tire chains are installed on the front wheel Ft.

[0040] Then, the tire chain installation determination calculation unit 11 determines that if |λFt-λRt|≧λ2 (YES), the front wheel Ft is not slipping, but the rear wheel Rt is slipping, and jumps to step S13.

[0041] The state |λFt-λRt|≧λ2 can be considered in cases 1 and 2 below, for example. <Case 1>

[0042] As shown in Figures 3A and 3B, even when the front and rear wheels Ft and Rt are traveling on a uniformly low-friction surface, the front wheel Ft is fitted with a tire chain, and slippage of the rear wheel Rt is detected at the calculation position. Therefore, it can be inferred that the front wheel Ft is fitted with a tire chain. <Case 2>

[0043] As shown in Figures 4A and 4B, the position where the front wheel slip ratio λFt is calculated is on a low-μ surface, and at that time the rear wheel Rt is on a high-μ surface. However, when the rear wheel Rt reaches the calculation position, it is on a low-μ surface and is therefore slipping. In such a case, it can be inferred that tire chains are attached to the front wheel Ft.

[0044] Furthermore, the tire chain installation determination calculation unit 11 determines that neither the front wheel Ft nor the rear wheel Rt are slipping if |λFt-λRt|<λ2 (NO), and proceeds to step S11.

[0045] The state |λFt-λRt|<λ2 can be considered in cases 3 and 4 below, for example. <Case 3>

[0046] As shown in Figures 5A and 5B, the position where the front wheel slip ratio λFt is calculated is on a high-μ road, and at that time the rear wheel Rt is on a low-μ road. However, when the rear wheel Rt reaches the calculation position, it is on a high-μ road, so no slip is detected. Therefore, it is not possible to determine whether or not tire chains are attached to the front wheel Ft. <Case 4>

[0047] As shown in Figures 6A and 6B, the front and rear wheels Ft and Rt are traveling on a uniformly high-friction surface, and no slip is detected even when the rear wheel Rt reaches the calculation position. Therefore, it is not possible to determine whether or not a tire chain is attached to the front wheel Ft.

[0048] In steps S11 and S12, the tire chain installation determination calculation unit 11 determines whether or not tire chains are installed on the front wheel Ft.

[0049] The tire chain installation determination calculation unit 11 detects vibrations of the left and right front wheels Ft respectively (step S11). Various means can be considered for detecting vibrations of the front wheels Ft. In this embodiment, the change in acceleration (jerk) obtained from the wheel speeds of the left and right front wheels Ft detected by the wheel speed sensor 13 is detected as vibration of the front wheels Ft.

[0050] Next, the tire chain installation determination calculation unit 11 checks whether tire chains are installed on the front wheels Ft based on the vibration (jerk) of the left and right front wheels Ft (step S12). The contact portion of the tire chain is formed by the repetition of a certain unit pattern. The tire chain installation determination calculation unit 11 analyzes the vibration patterns of the left and right front wheels Ft respectively and determines whether tire chains are installed on the front wheels Ft. Then, if the vibration pattern of the front wheels Ft is repeated at a certain period, the tire chain installation determination calculation unit 11 determines that it is chain vibration.

[0051] If the tire chain installation determination calculation unit 11 determines that the vibration pattern of the front wheel Ft is chain vibration (step S12: YES), it proceeds to step S13. If the tire chain installation determination calculation unit 11 determines that the vibration pattern of the front wheel Ft is not chain vibration (step S12: NO), it returns to step S7.

[0052] When the process proceeds to step S13, the tire chain installation determination calculation unit 11 sets the front wheel slip determination flag FFt (FFt←1) and exits the routine. Furthermore, if the tire chain installation determination calculation unit 11 determines that a tire chain is installed on the front wheel Ft, it may display a message to that effect on the monitor 31, such as an image. Also, the processing in steps S6 to S13 corresponds to the tire chain installation determination unit of the present invention.

[0053] The front wheel slip detection flag FFt set in the tire chain installation detection calculation unit 11 is read by the front / rear drive force distribution control unit 21. The front / rear drive force distribution control unit 21 reads the value of the front wheel slip detection flag FFt, and if FFt=0, it appropriately adjusts the front / rear drive force distribution ratio from the initial ratio (for example, front wheel Ft: rear wheel Rt = 50:50 [%]) according to the state of the vehicle M.

[0054] On the other hand, if the value of the front wheel slip judgment flag FFt is FFt=1, the front-to-rear drive force distribution control unit 21 reads the front wheel slip ratio λFt and the rear wheel slip ratio λRt calculated by the tire chain mounting judgment calculation unit 11. Then, the front-to-rear drive force distribution control unit 21 refers to the front-to-rear drive force distribution ratio map shown in Figure 9. The front-to-rear drive force distribution ratio map shown in Figure 9 stores the relationship between the difference Δλ(λFt-λRt) between the front wheel slip ratio λFt and the rear wheel slip ratio λRt, and the ratios of front-to-rear drive force distribution and rear-to-rear drive force distribution, which has been determined in advance from experiments, etc.

[0055] In the front-to-rear torque distribution ratio map, the difference Δλ=0 is set as the median value (Ft:Rt=50:50[%] in the figure) A. In the front-to-rear torque distribution ratio map, a value is set that increases the ratio of front-wheel torque distribution as the relationship Δλ<0 (λFt<λRt) increases from the median value A. Furthermore, in the front-to-rear torque distribution ratio map, a value is set that increases the ratio of rear-wheel torque distribution as the relationship Δλ>0 (λFt>λRt) increases from the median value A.

[0056] Therefore, when a tire chain is attached to the front wheel Ft with FFt=1, the front-to-rear drive force distribution control unit 21 sets the ratio of front-to-rear drive force distribution to be biased towards the front wheel Ft. For example, compared to the difference Δλ (difference B) when winter tires are attached to all four wheels and a tire chain is attached to the front wheel Ft, the difference Δλ (difference C) when summer tires are attached to all four wheels and a tire chain is attached to the front wheel Ft will inevitably result in a higher proportion of drive force distribution to the front wheel Ft.

[0057] As described above, in this embodiment, the tire chain installation determination calculation unit 11 automatically determines whether or not a tire chain is installed on the front wheel Ft based on the difference between the front wheel slip ratio λFt and the rear wheel slip ratio λRt. As a result, the front and rear drive force distribution control unit 21 can appropriately control the ratio of drive force distribution to the front and rear wheels Ft and Rt based on the result determined by the tire chain installation determination calculation unit 11.

[0058] Furthermore, since the front wheel slip ratio λFt and the rear wheel slip ratio λRt are calculated under the same road surface conditions, it is possible to compare each slip ratio λFt and λRt with high accuracy. [Second Embodiment]

[0059] Figures 10A and 10B show a second embodiment of the present invention. In the first embodiment, it was checked whether or not a tire chain was attached to the front wheel Ft, but in this embodiment, it is checked whether or not a tire chain was attached to the rear wheel Rt.

[0060] Whether or not tire chains are attached to the rear wheel Rt is determined by the tire chain attachment determination calculation unit 11 shown in Figure 1. Specifically, the tire chain attachment determination calculation unit 11 determines whether or not tire chains are attached to the rear wheel Rt according to the tire chain attachment determination routine shown in Figures 10A to 10B. This routine is executed at predetermined calculation cycles after the system is started.

[0061] The tire chain installation determination calculation unit 11 performs the same processing as in steps S1 to S5 in Figure 2A in steps S21 to S25. Next, the tire chain installation determination calculation unit 11 checks whether the vehicle M has moved forward by the amount of its wheelbase (step S26). The determination of whether the vehicle M has moved forward by the amount of its wheelbase is performed by the same processing as in step S8 in Figure 2B, so the explanation is omitted.

[0062] The tire chain installation determination calculation unit 11 waits if it determines that the vehicle M has not moved forward by the amount of its wheelbase (NO). Then, if the tire chain installation determination calculation unit 11 determines that the vehicle M has moved forward by the amount of its wheelbase (YES), it calculates the rear wheel slip ratio λRt from equation (2) above (step S27). Note that the processing in steps S26 and S27 corresponds to the rear wheel slip ratio calculation unit of the present invention.

[0063] As a result, the position for calculating the front wheel slip ratio λFt, as shown in Figures 3A to 6A, and the position for calculating the rear wheel slip ratio λRt, as shown in Figures 3B to 6B, are the same. Therefore, the front wheel slip ratio λFt and the rear wheel slip ratio λRt can be calculated under the same road surface conditions.

[0064] Next, the tire chain installation determination calculation unit 11 compares the rear wheel slip ratio λRt with the slip ratio determination threshold λ1 (step S28). This slip ratio determination threshold λ1 is a value used to determine whether or not the rear wheel Rt is slipping. If tire chains are installed on the rear wheel Rt, the rear wheel slip ratio λRt can be estimated to be small.

[0065] The tire chain installation determination calculation unit 11 sets the slip ratio determination threshold λ1 by referring to the slip ratio determination threshold table shown in Figure 7. This slip ratio table stores the relationship between the longitudinal gradient of the road surface, the ratio of driving force distribution to the rear wheel Rt, and the slip ratio determination threshold λ1, which has been determined in advance through experiments, etc. In the slip ratio determination threshold table, a higher slip ratio determination threshold λ1 is set as the longitudinal gradient of the road surface decreases and the ratio of driving force distribution to the rear wheel Rt increases.

[0066] For example, on an uphill road, as the front-to-rear gradient of the road surface decreases, the proportion of the load distribution on the rear wheels Rt gradually decreases, and the relative load on the front wheels Ft increases. Therefore, the front wheels Ft become less likely to slip. Also, when driving on flat roads or other roads with a small gradient, if the proportion of the driving force distribution on the front wheels Ft is small, the front wheels Ft become less likely to slip.

[0067] The slip ratio determination threshold table stores slip ratio determination threshold values ​​λ1 that increase as the road gradient decreases and the proportion of driving force distributed to the rear wheels Rt increases. This allows for highly accurate determination of whether or not slip is occurring in the rear wheels Rt, even when the road gradient is small and the proportion of driving force distributed to the rear wheels Rt is large.

[0068] Then, if λRt > λ1 (step S28: NO), the tire chain installation determination calculation unit 11 determines that the rear wheel Rt is slipping and proceeds to step S29. In step S29, the tire chain installation determination calculation unit 11 determines that the tire chain is not installed, clears the rear wheel slip determination flag FRt (FRt ← 0), and exits the routine. On the other hand, if λRt ≤ λ1 (step S28: YES), the tire chain installation determination calculation unit 11 determines that the rear wheel Rt is not slipping and branches to step S30.

[0069] Possible factors contributing to a low rear wheel slip ratio λRt include the presence of tire chains on the rear wheels Rt and the vehicle M traveling on a high-friction surface. In steps S30 to S33, the tire chain installation determination calculation unit 11 checks whether or not tire chains are installed on the rear wheels Rt.

[0070] First, the tire chain installation determination calculation unit 11 compares the absolute value of the difference between the front wheel slip ratio λFt and the rear wheel slip ratio λRt (|λFt-λRt|) with the tire chain installation determination threshold λ2 (step S30). The tire chain installation determination calculation unit 11 sets the tire chain installation determination threshold λ2 by referring to the tire chain installation determination threshold table shown in Figure 8 above. In the tire chain installation determination threshold table, a lower tire chain installation determination threshold λ2 is set as the front-to-rear gradient of the road surface decreases and the proportion of the driving force distribution to the rear wheel Rt increases.

[0071] For example, when the front-to-rear gradient of the road surface is small, the proportion of the contact load distribution to the rear wheel Rt is lower compared to when the front-to-rear gradient is large, and the grip force of the front wheel Ft increases relatively, making the front wheel Ft less likely to slip. In such a situation, the difference between the slip ratios λFt and λRt of the front and rear wheels is considered to be small, so the tire chain installation detection threshold λ2 is set to a low value. Also, when driving on a flat road, if the proportion of the driving force distribution to the front wheel Ft is large, the front wheel Ft is less likely to slip. Therefore, in this situation as well, the tire chain installation detection threshold λ2 is set to a low value. This allows for highly accurate determination of whether or not tire chains are installed on the rear wheel Rt.

[0072] The tire chain installation determination calculation unit 11 then determines that if |λFt-λRt|≧λ2 (YES), the rear wheel Rt is not slipping, but the front wheel Ft is slipping, and jumps to step S33. Furthermore, if the tire chain installation determination calculation unit 11 determines that a tire chain is installed on the rear wheel Rt, it may display this information on the monitor 31 using an image or the like. Also, the processing in steps S28 to S33 corresponds to the tire chain installation determination unit of the present invention.

[0073] The state |λFt-λRt|≧λ2 can be considered, for example, in cases 1 and 2. <Case 1>

[0074] As shown in Figures 3A and 3B, even when the front and rear wheels Ft and Rt are traveling on a uniformly low-friction surface, a tire chain is attached to the rear wheel Rt, and slip is detected on the front wheel Ft at the calculated position. Therefore, it can be inferred that a tire chain is attached to the rear wheel Rt. <Case 2>

[0075] As shown in Figures 4A and 4B, the front wheel slip ratio λFt is calculated at a low-μ surface, so the front wheel Ft is slipping. However, no slip is detected when the rear wheel Rt reaches the calculation position. Therefore, it can be inferred that a tire chain is attached to the rear wheel Rt.

[0076] Furthermore, the tire chain installation determination calculation unit 11 determines that neither the front wheel Ft nor the rear wheel Rt are slipping if |λFt-λRt|<λ2 (NO), and proceeds to step S11.

[0077] The state |λFt-λRt|<λ2 can be considered in cases 3 and 4 below, for example. <Case 3>

[0078] As shown in Figures 5A and 5B, the position where the front wheel slip ratio λFt is calculated is on a high-μ surface, while the rear wheel Rt is on a low-μ surface at that time. However, when the rear wheel Rt reaches the calculation position, it is on a high-μ surface, so no slip is detected. Therefore, it is not possible to determine whether or not tire chains are attached to the rear wheel Rt. <Case 4>

[0079] As shown in Figures 6A and 6B, the front and rear wheels Ft and Rt are traveling on a uniformly high-friction surface, and no slip is detected even when the rear wheel Rt reaches the calculated position. Therefore, it is not possible to determine whether or not a tire chain is attached to the rear wheel Rt.

[0080] In steps S31 and S32, the tire chain installation determination calculation unit 11 determines whether or not tire chains are installed on the rear wheel Rt.

[0081] The tire chain installation determination calculation unit 11 detects vibrations of the left and right rear wheels Rt respectively (step S31). The tire chain installation determination calculation unit 11 calculates the jerk by taking the second derivative of the wheel speeds of the left and right rear wheels Rt detected by the wheel speed sensor 13, which acts as a wheel speed detection unit. The tire chain installation determination calculation unit 11 then sets this jerk as the vibration of the rear wheels Rt.

[0082] Next, the tire chain installation determination calculation unit 11 checks whether tire chains are installed on the rear wheels Rt based on the vibration (jerk) of the left and right rear wheels Rt (step S32). The tire chain installation determination calculation unit 11 analyzes the vibration patterns of the left and right front wheels Ft and determines whether tire chains are installed on the rear wheels Rt. Then, if the vibration pattern of the rear wheels Rt is repeated at a constant period, the tire chain installation determination calculation unit 11 determines that it is chain vibration.

[0083] If the tire chain installation determination calculation unit 11 determines that the vibration pattern of the rear wheel Rt is chain vibration (step S32: YES), it proceeds to step S33. If the tire chain installation determination calculation unit 11 determines that the vibration pattern of the rear wheel Rt is not chain vibration (step S32: NO), it returns to step S29.

[0084] When the process proceeds to step S33, the tire chain installation determination calculation unit 11 sets the rear wheel slip determination flag FRt (FRt←1) and exits the routine.

[0085] The rear wheel slip detection flag FRt, set in the tire chain installation detection calculation unit 11, is read by the front-to-rear drive force distribution control unit 21. The front-to-rear drive force distribution control unit 21 reads the value of the rear wheel slip detection flag FRt, and if FRt=0, it appropriately adjusts the front-to-rear drive force distribution ratio from the initial ratio (for example, front wheel Ft:rear wheel Rt=50:50[%]) according to the state of the vehicle M.

[0086] On the other hand, if the value of the rear wheel slip determination flag FRt is FRt=1, the front-to-rear drive force distribution control unit 21 reads the front wheel slip ratio λFt and the rear wheel slip ratio λRt calculated by the tire chain mounting determination calculation unit 11. Then, the front-to-rear drive force distribution control unit 21 refers to the front-to-rear drive force distribution ratio map shown in Figure 9 above.

[0087] The front-to-rear drive force distribution control unit 21 sets the ratio of front-to-rear drive force distribution to be biased towards the rear wheel Rt when a tire chain is attached to the rear wheel Rt with FRt=1. For example, compared to the difference Δλ (difference D) when winter tires are attached to all four wheels and a tire chain is attached to the rear wheel Rt, the difference Δλ (difference E) when summer tires are attached to all four wheels and a tire chain is attached to the rear wheel Rt will inevitably result in a higher ratio of drive force distribution to the rear wheel Rt.

[0088] As described above, in this embodiment, the tire chain installation determination calculation unit 11 automatically determines whether or not a tire chain is installed on the rear wheel Rt based on the difference between the front wheel slip ratio λFt and the rear wheel slip ratio λRt. As a result, the front and rear drive force distribution control unit 21 can appropriately control the ratio of drive force distribution to the front and rear wheels Ft and Rt based on the result determined by the tire chain installation determination calculation unit 11.

[0089] Furthermore, the present invention is not limited to the embodiments described above. For example, by combining the first and second embodiments, it is possible to determine whether or not tire chains are attached to the four wheels of the vehicle M. If it is determined that tire chains are attached to all four wheels, the front-to-rear drive force distribution control unit 21 may fix the ratio of drive force distribution between the front and rear wheels Ft and Rt to an initial value (for example, 50:50 [%]).

[0090] Furthermore, the values ​​of the slip detection flags FFt and FRt set in the tire chain installation detection calculation unit 11 may be read by other drive control systems, such as vehicle stability control, to perform control corresponding to the installation of tire chains. In addition, as a front-to-rear drive force distribution mechanism, for example, there is a torque vectoring mechanism that varies the torque between the front and rear wheels. [Explanation of symbols]

[0091] 1... Driving force control device, 11... Tire chain installation determination calculation unit, 12…GNSS receiver, 13...Wheel speed sensor, 14…Front and rear accelerometer, 15... Accelerator position sensor, 21... Front and rear drive force distribution control unit, 31... Monitor, A...median, FFt... Front wheel slip detection flag, FRt... Rear wheel slip detection flag, Ft...front wheel, M... Own vehicle, Rt...Rear wheel, Vo…Driving judgment vehicle speed, Vv…Vehicle speed, Δλ(A~E)...Difference, θacc...accelerator opening, θo...Accelerator pedal depression detection threshold, λ1...Slip ratio determination threshold, λ2…Tire chain installation detection threshold, λFt…Front wheel slip ratio, λRt…Rear wheel slip ratio

Claims

1. A wheel speed detection unit that detects the wheel speeds of the front and rear wheels in a four-wheel drive vehicle, Tire chain installation determination calculation unit and In a drive control device for a vehicle having, The tire chain installation determination calculation unit is: A vehicle speed detection unit that detects the vehicle speed, A front wheel slip ratio calculation unit calculates the front wheel slip ratio based on the wheel speed of the front wheel detected by the wheel speed detection unit and the vehicle speed detected by the vehicle speed detection unit. A rear wheel slip ratio calculation unit calculates the rear wheel slip ratio at the same road surface position from which the front wheel slip ratio was calculated, based on the wheel speed of the rear wheel detected by the wheel speed detection unit and the vehicle speed detected by the vehicle speed detection unit. A tire chain installation determination unit determines that if the difference between the front wheel slip ratio calculated by the front wheel slip ratio calculation unit and the rear wheel slip ratio calculated by the rear wheel slip ratio calculation unit is greater than or equal to a first threshold, then the tire chain is installed on the wheel with the lower slip ratio among the front wheel and the rear wheel. A vehicle drive control device characterized by comprising the following:

2. The system further includes a front-to-rear drive force distribution control unit that controls the distribution of drive force to the front wheel and the rear wheel. The front / rear drive force distribution control unit biases the drive force distribution towards the front wheel or rear wheel that the tire chain installation determination unit has determined to have the tire chain installed. The drive control device for a vehicle according to claim 1.

3. The tire chain installation determination unit determines that a tire chain is installed on the front wheel or rear wheel in which a slip rate of the second threshold or less was detected, if the front wheel slip rate calculated by the front wheel slip rate calculation unit is less than or equal to the second threshold, or the rear wheel slip rate calculated by the rear wheel slip rate calculation unit is less than or equal to the second threshold, and the absolute value of the difference between the front wheel slip rate and the rear wheel slip rate calculated by the rear wheel slip rate calculation unit is greater than or equal to the first threshold. The drive control device for a vehicle according to claim 1.

4. The tire chain installation determination unit determines that a tire chain is installed on the front wheel if the front wheel slip ratio calculated by the front wheel slip ratio calculation unit is less than or equal to the second threshold, the absolute value of the difference between the front wheel slip ratio and the rear wheel slip ratio calculated by the rear wheel slip ratio calculation unit is less than the first threshold, and the vibration of the front wheel is determined to be chain vibration. The drive control device for a vehicle according to claim 1.

5. The tire chain mounting determination unit determines that a tire chain is mounted on the rear wheel if the rear wheel slip ratio calculated by the rear wheel slip ratio calculation unit is less than or equal to the second threshold, the absolute value of the difference between the rear wheel slip ratio and the rear wheel slip ratio calculated by the front wheel slip ratio calculation unit is less than the first threshold, and the vibration of the rear wheel is determined to be chain vibration. The drive control device for a vehicle according to claim 1.

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