Control device for four-wheel drive vehicle

Abstract

To provide a control device for a 4WD vehicle, capable of maintaining 4WD traveling and stabilizing vehicle behavior even when an abnormality occurs in a wheel speed sensor for detecting a wheel rotational speed.SOLUTION: While a vehicle is traveling in a 4WD state, when an abnormality occurs in a wheel speed sensor 86, and when a high-friction road determination unit 74 determines that the vehicle is traveling on a high-friction road, and an automatic driving control unit 76 is performing automatic driving control, a drive control unit 72 performs torque distribution control without using a wheel speed Nw output from the wheel speed sensor 86. As a result, it is possible to provide a control device 70 for a 4WD vehicle, capable of maintaining 4WD traveling and stabilizing vehicle behavior even when there occurs the abnormality in the wheel speed sensor 86, making it impossible to detect a slip, in a case where the vehicle is traveling on the high-friction road unlikely to cause the slip and is being automatically driven such that an occurrence frequency of requests for sudden acceleration / deceleration is low.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control device for a four-wheel drive vehicle. [Background technology]

[0002] Four-wheel drive (hereinafter referred to as 4WD) vehicles equipped with an automatic driving function are available. Compared to two-wheel drive (hereinafter referred to as 2WD) driving, 4WD driving is less affected by road surface conditions and allows for stable driving. 4WD, along with the automatic driving function, is a function and equipment that improves driving comfort and safety. Meanwhile, the automatic driving function is implemented by control and processing based on various sensor information, and technologies such as determining whether automatic driving can be continued based on the sensor information and controlling the driving force of the 4WD by estimating the friction coefficient of the road surface being driven are disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-157836 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a 4WD vehicle, if an abnormality occurs in the wheel speed sensor that detects the rotation speed of each wheel, making it impossible to detect the rotation speed of each wheel, slip detection becomes impossible, so 4WD control is stopped and the vehicle is switched to 2WD control using only the main drive wheels. However, switching from 4WD to 2WD reduces driving stability, so in situations where an abnormality in the wheel speed sensor will not have an impact, such as when the vehicle is traveling on a high friction road where slip is unlikely to occur and during automatic driving where sudden acceleration and deceleration requests are rare, it is necessary to maintain 4WD driving and stabilize the vehicle behavior.

[0005] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a control device for a 4WD vehicle that can maintain 4WD driving and stabilize vehicle behavior even if an abnormality occurs in the wheel speed sensor that makes it impossible to detect slip, when the vehicle is traveling on a high friction road where slip is unlikely to occur and when the vehicle is in automatic driving mode where sudden acceleration / deceleration requests are rare. [Means for solving the problem]

[0006] The gist of a first invention is a control device for a four-wheel drive vehicle including: (a) a first power source; main drive wheels that are driven in a two-wheel drive state and a four-wheel drive state; a first power transmission device that transmits power from the first power source to the main drive wheels; a second power source that is either a torque distribution device that distributes drive torque of the first power source or a power source other than the first power source; auxiliary drive wheels that are driven only in the four-wheel drive state; a second power transmission device that transmits power from the second power source to the auxiliary drive wheels; and a wheel speed sensor that detects the rotational speeds of the main drive wheels and the auxiliary drive wheels; The vehicle includes a drive control unit that performs torque distribution control between the drive torque of the main drive wheel and the drive torque of the auxiliary drive wheel, including switching between the two-wheel drive state and the four-wheel drive state, a high-friction road judgment unit that determines whether the road surface on which the vehicle is traveling is a high-friction road, and an automatic driving control unit that performs automatic driving control of the vehicle, and (c) when an abnormality occurs in the wheel speed sensor while the vehicle is traveling in the four-wheel drive state, the high-friction road judgment unit judges that the vehicle is traveling on a high-friction road, and the automatic driving control unit is performing automatic driving control, the drive control unit performs the torque distribution control without using the rotational speed from the wheel speed sensor. Effect of the Invention

[0007] According to the first invention, when an abnormality occurs in the wheel speed sensor while traveling in the four-wheel drive state, the high friction road determination unit determines that the vehicle is traveling on a high friction road, and the automatic driving control unit is in automatic driving control, the drive control unit performs the torque distribution control without using the rotation speed from the wheel speed sensor. This makes it possible to provide a control device for a 4WD vehicle that can maintain 4WD traveling and stabilize vehicle behavior, even if an abnormality occurs in the wheel speed sensor that makes it impossible to detect slip, when the vehicle is traveling on a high friction road where slip is unlikely to occur, and when the vehicle is in automatic driving mode with a low frequency of sudden acceleration / deceleration requests. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of a vehicle to which the present invention is applied, and is also a diagram illustrating main parts of control functions and a control system for various controls in the vehicle. [Diagram 2] 4 is a flowchart illustrating the main control operations of the electronic control device, and is a flowchart illustrating the control operations for maintaining 4WD driving when an abnormality occurs in a wheel speed sensor of a wheel. [Diagram 3] FIG. 2 is a view showing another embodiment of a vehicle to which the present invention is applied, and corresponds to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0010] FIG. 1 is a diagram illustrating a schematic configuration of a vehicle 10 to which the present invention is applied, and is also a diagram illustrating main parts of control functions and a control system for various controls in the vehicle 10. As shown in FIG.

[0011] In Fig. 1, a vehicle 10 is an electronically controlled torque split type 4WD vehicle based on a front engine, front drive (FF) type main wheel drive vehicle equipped with an engine 12 as a power source, front wheels 14 including left and right front wheels 14L, 14R, and rear wheels 16 including left and right rear wheels 16L, 16R. 2WD driving is driving under 2WD control in which driving torque from the engine 12 is distributed only to the front wheels 14. 4WD driving is driving under 4WD control in which driving torque from the engine 12 is distributed to both the front wheels 14 and the rear wheels 16.

[0012] The vehicle 10 includes a first power transmission path PT1 that transmits the power of the engine 12 to front wheels 14 and a second power transmission path PT2 that transmits the power of the engine 12 to rear wheels 16.

[0013] The engine 12 has an engine torque Te, which is the output torque of the engine 12, controlled by an engine control device 40, which includes a throttle actuator, a fuel injection device, an ignition device, etc., provided on the vehicle 10, controlled by an electronic control device 70, which will be described later.

[0014] The first power transmission path PT1 includes a transmission 18, a front differential 20, a front drive shaft 22 including left and right front drive shafts 22L, 22R, etc. The second power transmission path PT2 includes a transmission 18, a transfer 24, a propeller shaft 26, a coupling 28, a rear differential 30, a rear drive shaft 32 including left and right rear drive shafts 32L, 32R, etc.

[0015] The transfer 24 is a front / rear wheel power distribution device that distributes a portion of the power of the engine 12 to the rear wheels 16 via a propeller shaft 26. The coupling 28 is an electronically controlled drive torque distribution coupling disposed in series with the propeller shaft 26, and is a torque distribution device that is controlled to distribute the drive torque from the transfer 24 to the rear wheels 16.

[0016] The transmission 18 constitutes a part of a common power transmission path of the first power transmission path PT1 and the second power transmission path PT2, and transmits the power of the engine 12 to the front wheels 14 and the rear wheels 16. The transmission 18 is, for example, a known planetary gear type multi-speed transmission that selectively establishes a plurality of speed stages (also called gear stages) having different gear ratios.

[0017] The coupling 28 transmits torque between the propeller shaft 26 and the rear differential 30. The coupling 28 is electrically controlled by an electronic control device 70, and is therefore capable of continuously changing the torque distribution between the front and rear wheels, for example, between 100:0 and 50:50. Note that the coupling 28 is a known technology, and therefore a detailed description of its structure and operation will be omitted.

[0018] The electronic control device 70 includes, for example, a so-called microcomputer. The electronic control device 70 is supplied with various signals based on detection values ​​by various sensors provided on the vehicle 10 (e.g., a vehicle speed sensor 84, a wheel speed sensor 86, an accelerator opening sensor 88, a throttle valve opening sensor 90, a G sensor 92, a yaw rate sensor 94, a road surface detection sensor 96, an automatic driving assistance sensor 98, etc.) (e.g., signals such as the vehicle speed V, front wheel rotational speeds Nwfl, Nwfr which are the rotational speeds of the left and right front wheels 14L, 14R, rear wheel rotational speeds Nwrl, Nwrr which are the rotational speeds of the left and right rear wheels 16L, 16R, accelerator opening θacc which is the amount of accelerator operation representing the magnitude of the driver's acceleration operation, throttle valve opening θth which is the opening of the electronic throttle valve, the longitudinal acceleration Gx and lateral acceleration Gy of the vehicle 10, the yaw rate Ryaw which is the rotational angular velocity of the vehicle 10 around the vertical axis, various information Iard for detecting the road surface, and various information Adr for automatic driving assistance).

[0019] The wheel speed sensor 86 includes a main drive wheel rotation speed sensor that detects the front wheel rotation speeds Nwfl, Nwfr and outputs signals of the front wheel rotation speeds Nwfl, Nwfr, and an auxiliary drive wheel rotation speed sensor that detects the rear wheel rotation speeds Nwrl, Nwrr and outputs signals of the rear wheel rotation speeds Nwrl, Nwrr. The front wheel rotation speeds Nwfl, Nwfr and the rear wheel rotation speeds Nwrl, Nwrr are each the wheel speed Nw.

[0020] The road surface detection sensor 96 is a sensor used to detect road surface conditions while the vehicle 10 is traveling, and various information Iard for detecting the road surface is supplied from, for example, a camera, a temperature sensor (outside air temperature sensor, road surface temperature sensor), a near-infrared sensor, a millimeter wave radar, a laser radar, etc.

[0021] The automatic driving assistance sensor 98 is a sensor used when the vehicle 10 performs automatic driving, and various information Adr for automatic driving assistance is supplied from, for example, a position sensor (GPS), a camera, a millimeter wave radar, a laser radar, etc. Note that the traveling road surface detection sensor 96 and the automatic driving assistance sensor 98 may be partly or entirely configured in common.

[0022] The electronic control unit 70 outputs an engine control command signal Se to the engine control unit 40 for controlling the engine 12, and outputs a coupling control command signal Sc to the coupling 28, i.e., a signal for controlling the torque distribution to the rear wheels 16.

[0023] The electronic control device 70 functionally comprises a drive control unit 72 that controls the drive of the vehicle 10, a high friction road determination unit 74 that determines whether the road surface on which the vehicle is traveling is a high friction road or not, and an automatic driving control unit 76 that controls the automatic driving of the vehicle 10.

[0024] The drive control unit 72 calculates the drive demand amount of the vehicle 10 by the driver, for example, by applying the accelerator opening θacc and the vehicle speed V to a predetermined drive demand amount map. For example, the required drive torque Twdem [Nm] and the required drive force Fwdem [N] at the wheels (front wheels 14, rear wheels 16) are used as this drive demand amount. The required drive torque Twdem is a combined value of the required front torque Twfdem to the front wheels 14 and the required rear torque Twrdem to the rear wheels 16.

[0025] The drive control unit 72 sets the torque distribution ratio γfr (front distribution ratio Fr: rear distribution ratio Rr) for the front and rear wheels by applying multiple driving force related values ​​such as the accelerator opening θacc, vehicle speed V, longitudinal acceleration Gx, and yaw rate Ryaw to a predetermined torque distribution ratio map, and also calculates the required rear torque Twrdem (=required driving torque Twdem x rear distribution ratio Rr) based on the required driving torque Twdem and the torque distribution ratio γfr.

[0026] The drive control section 72 outputs an engine control command signal Se to the engine control device 40 so as to realize the required drive torque Twfdem, and outputs a coupling control command signal Sc to the coupling 28 so as to realize the required rear torque Twrdem, thereby controlling the torque distribution. In this way, the torque distribution between the required front torque Twfdem to the front wheels 14 and the required rear torque Twrdem to the rear wheels 16 is performed.

[0027] Furthermore, the drive control unit 72 performs slip feedback to correct the torque distribution ratio γfr based on the slip of the front wheels 14 or the rear wheels 16. This slip feedback is a correction to stop the wheel slip. For example, when the front wheels 14 slip, the drive control unit 72 increases the rear distribution ratio Rr. Slip detection of the front wheels 14 or the rear wheels 16 is performed in a suitable manner, for example, by comparing the wheel speeds Nw (Nwfl, Nwfr, Nwrl, Nwrr) of each wheel from the wheel speed sensor 86 with the vehicle speed V, or by fluctuations in the wheel speeds Nw (Nwfl, Nwfr, Nwrl, Nwrr) of each wheel.

[0028] The high friction road determination unit 74 determines whether the road surface on which the vehicle is traveling is a high friction road or not based on various information Iard for detecting the road surface from the road surface detection sensor 96. When determining the road surface, for example, a method described in JP 2020-157836 A may be adopted.

[0029] The automatic driving control unit 76 controls automatic driving of the vehicle 10 based on various information Adr of automatic driving assistance from the automatic driving assistance sensor 98. During automatic driving, the automatic driving control unit 76 performs control equivalent to driving operations such as the accelerator opening θacc and steering of a steering wheel (not shown).

[0030] In a conventional 4WD vehicle, if an abnormality occurs in the wheel speed sensor 86 and the wheel speed Nw (Nwfl, Nwfr, Nwrl, Nwrr) of even one of the wheels cannot be detected, slip detection becomes impossible, so 4WD control is stopped and the vehicle is switched to 2WD control using only the main drive wheels. However, switching from 4WD to 2WD reduces driving stability, so in situations where an abnormality in the wheel speed sensor 86 will not have an effect, such as when the vehicle is traveling on a high friction road where slip is unlikely to occur and during automatic driving where sudden acceleration and deceleration requests are rare, it is necessary to maintain 4WD driving and stabilize the vehicle behavior.

[0031] Therefore, the electronic control unit 70 of this embodiment maintains 4WD driving by a control operation that will be described later with reference to Fig. 2. Fig. 2 is a flowchart that explains the control operation when an abnormality occurs in the wheel speed sensor 86.

[0032] First, in step (hereinafter, step will be omitted) S10, the drive control unit 72 judges whether an abnormality has occurred in the wheel speed sensor 86, that is, whether any of the wheel speeds Nw (Nwfl, Nwfr, Nwrl, Nwrr) of the wheels cannot be detected. If the judgment in S10 is negative, this routine is ended.

[0033] If the determination in S10 is positive, then in S20, which corresponds to the high friction road determination unit 74, it is determined whether or not the road surface on which the vehicle is traveling is a high friction road on which slipping is unlikely to occur. If the determination in S20 is negative, then in S50, which corresponds to the drive control unit 72, the 4WD control is stopped and switched to 2WD control for the main drive wheels only, and this routine is terminated.

[0034] If the determination in S20 is positive, then in S30 corresponding to the automatic driving control unit 76, it is determined whether or not automatic driving control is in progress. If the determination in S30 is negative, then the process also transitions to S50, where the control is switched from 4WD control to 2WD control, and this routine is terminated.

[0035] If the determination in S30 is positive, in S40 corresponding to the drive control unit 72, the control is switched to temporary 4WD control with the implementation of slip feedback stopped, and this routine is ended. By stopping the implementation of slip feedback, the 4WD control and 4WD driving are maintained without using the wheel speeds Nw (Nwfl, Nwfr, Nwrl, Nwrr) of each wheel from the wheel speed sensor 86.

[0036] As described above, according to this embodiment, if an abnormality occurs in the wheel speed sensor 86 while traveling in 4WD state, the high friction road determination unit 74 determines that the vehicle is traveling on a high friction road, and the automatic driving control unit 76 is performing automatic driving control, the drive control unit 72 performs torque distribution control without using the wheel speed Nw from the wheel speed sensor 86. As a result, even if an abnormality occurs in the wheel speed sensor 86 that makes it impossible to detect slip, if the vehicle is traveling on a high friction road where slip is unlikely to occur and the vehicle is in automatic driving mode where sudden acceleration and deceleration requests are unlikely to occur, 4WD traveling is maintained, so that a control device 70 for a 4WD vehicle that can stabilize the behavior of the vehicle can be provided.

[0037] Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments are given the same reference numerals and the description thereof will be omitted. EXAMPLES

[0038] In Fig. 3, vehicle 48 is an example in which the configuration of the power source is changed from vehicle 10 of the first embodiment to a 4WD vehicle based on a hybrid vehicle. The first power source is a hybrid power source 50 consisting of an engine 12 and a trunk axle 52 incorporating electric motors (MG1, MG2), and constitutes a first power transmission path PT1 that drives front wheels 14 via a front drive shaft 22. The second power source is an e-axle 64 incorporating electric motor MG3, and constitutes a second power transmission path PT2 that drives rear wheels 16 via a rear drive shaft 32. Vehicle 48 also includes a battery 62 as a power source for operating electric motors MG1, MG2, and MG3, and is connected to inverters 56, 58, and 60, which will be described later.

[0039] The trunk axle 52 includes a power split mechanism 54, electric motors MG1 and MG2, inverters 56 and 58, the front differential 20, a group of connecting gears, and the like, and is a unit that constitutes a known hybrid vehicle.

[0040] The electric motor MG1 is a so-called motor generator. The inverter 56 performs control such as converting DC power from the battery 62 into AC power and supplying it to the electric motor MG1, and converting AC power generated by the electric motor MG1 into DC power and supplying it to the battery 62. The electric motor MG2 and the inverter 58 have the same functions as the electric motor MG1 and the inverter 56, respectively, and their description will be omitted. An MG1 control command signal Smg1 for controlling the torque of the electric motor MG1 and an MG2 control command signal Smg2 for controlling the torque of the electric motor MG2 are output from the electronic control device 70 to the inverter 56 and the inverter 58, respectively. The power (driving torque) from the engine 12, the electric motor MG1, and the electric motor MG2 is transmitted to the front wheels 14 via the front differential 20.

[0041] The e-axle 64 includes an electric motor MG3, an inverter 60, a reduction gear mechanism 66, a rear differential 30, etc. The electric motor MG3 and the inverter 60 have the same functions as the electric motor MG1 and the inverter 56, respectively, and their description will be omitted. For example, an MG3 control command signal Smg3 that controls the torque of the electric motor MG3 is output to the inverter 60 from the electronic control device 70. Power (driving torque) from the electric motor MG3 is transmitted to the rear wheels 16 via the reduction gear mechanism 66 and the rear differential 30.

[0042] The control functions and control system of the electronic control device 70 differ from those of the first embodiment only in the control system for the distribution of drive torque in the drive control unit 72. Hereinafter, only the differences will be described, and descriptions of contents common to the first embodiment will be omitted.

[0043] The drive control unit 72 calculates the required front torque Twfdem (=required driving torque Twdem × front distribution ratio Fr) and the required rear torque Twrdem (=required driving torque Twdem × rear distribution ratio Rr) based on the required driving torque Twdem and the torque distribution ratio γfr calculated in the same manner as in Example 1.

[0044] The drive control unit 72 outputs an engine control command signal Se to the engine control device 40, an MG1 control command signal Smg1 to the inverter 56, and an MG2 control command signal Smg2 to the inverter 56 so that the combined drive torque of the engine 12, the electric motor MG1, and the electric motor MG2 realizes the required front torque Twfdem. Also, the drive control unit 72 outputs an MG3 control command signal Smg3 to the inverter 58 so as to realize the required rear torque Twrdem, thereby controlling the torque distribution. As a result, the torque distribution between the required front torque Twfdem to the front wheels 14 and the required rear torque Twrdem to the rear wheels 16 is performed.

[0045] Other than the above, the present embodiment is the same as the first embodiment, and therefore the description thereof will be omitted. The control operation of the flowchart in Fig. 2 is also commonly applied to this embodiment. Therefore, according to this embodiment, the same effects as those of the first embodiment can be obtained.

[0046] Although the embodiment of the present invention has been described in detail above with reference to the drawings, this is merely one embodiment, and the present invention can be embodied in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of symbols]

[0047] 10, 48: vehicle 12: engine (first power source) 14 (14L, 14R): front wheels (main drive wheels) 16 (16L, 16R): rear wheels (auxiliary drive wheels) 28: coupling (torque distribution device) 70: electronic control device (control device) 72: drive control unit 74: high friction road determination unit 76: automatic driving control unit 86: wheel speed sensor MG1: electric motor MG2: electric motor MG3: electric motor

Claims

[Claim 1] A control device for a four-wheel drive vehicle including a first power source, main drive wheels that are driven in a two-wheel drive state and a four-wheel drive state, a first power transmission device that transmits power from the first power source to the main drive wheels, a second power source that is either a torque distribution device that distributes drive torque of the first power source or a power source other than the first power source, auxiliary drive wheels that are driven only in the four-wheel drive state, a second power transmission device that transmits power from the second power source to the auxiliary drive wheels, and a wheel speed sensor that detects rotational speeds of the main drive wheels and the auxiliary drive wheels, a drive control unit that performs torque distribution control between the drive torque of the main drive wheels and the drive torque of the auxiliary drive wheels, including switching between the two-wheel drive state and the four-wheel drive state, a high-friction road determination unit that determines whether the road surface on which the vehicle is traveling is a high-friction road, and an automatic driving control unit that performs automatic driving control of the vehicle, A control device for a four-wheel drive vehicle, characterized in that when an abnormality occurs in the wheel speed sensor while driving in the four-wheel drive state, the high friction road judgment unit judges that the vehicle is driving on a high friction road, and the automatic driving control unit is performing automatic driving control, the drive control unit performs the torque distribution control without using the rotational speed from the wheel speed sensor.

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