Vehicle control device

Abstract

To provide a vehicle control device capable of eliminating a backlash and ensuring responsiveness during acceleration while avoiding a deterioration in energy efficiency.SOLUTION: A rising gradient of torque in an auxiliary drive wheel used upon switching from a two-wheel drive state to a four-wheel drive state is set to a rapid change rising gradient having a greater value than a gradual change rising gradient for suppressing a shock caused by backlash elimination. As a result, a backlash is eliminated during acceleration, so that it is not necessary to eliminate the backlash in advance before acceleration. In addition, torque of a second power source is quickly raised upon switching to the four-wheel drive state, so that acceleration is inhibited from being performed in two steps. Thus, it is possible to eliminate the backlash and ensure responsiveness during acceleration while avoiding a deterioration in energy efficiency.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a vehicle control device capable of independently controlling the amount of change in drive torque of front and rear wheels. [Background technology]

[0002] There is a well-known control device for a vehicle that includes a first power source, a main drive wheel that is 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 wheel, a second power source, an auxiliary drive wheel that is driven only in the four-wheel drive state, and a second power transmission device that transmits power from the second power source to the auxiliary drive wheel. For example, a vehicle driving force control device is described in Patent Document 1. Patent Document 1 discloses that when it is determined that there is a possibility of transitioning from a two-wheel drive state to a four-wheel drive state, backlash elimination control is performed to control a motor (second power source) to a small torque generating state, thereby suppressing the occurrence of shocks due to backlash. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-98718 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the technology described in Patent Document 1 generates torque for removing backlash in advance in the two-wheel drive state, that is, before the driver's intention to accelerate (for example, depressing the accelerator pedal) intervenes, which may lead to a deterioration in energy efficiency. On the other hand, a method can be considered in which, when accelerating again from a driven state to a driving state, the amount of change in torque at the driving wheels is temporarily limited in a region where the direction in which the backlash between the components constituting the power transmission device is removed is reversed, thereby suppressing the backlash removal shock caused by teeth striking when the direction in which the backlash is removed is reversed. If this method is applied when shifting from a two-wheel drive state to a four-wheel drive state and the amount of change in torque at the auxiliary driving wheels is suppressed, the vehicle will accelerate due to the increase in torque of the first power source, and then accelerate due to the increase in torque of the second power source with a delay, which may result in two-stage acceleration.

[0005] The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a vehicle control device that can eliminate backlash during acceleration and ensure responsiveness while avoiding a deterioration in energy efficiency. [Means for solving the problem]

[0006] The gist of a first invention is a control device for a vehicle including: (a) a first power source, a main drive wheel that is 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 wheel, a second power source, an auxiliary drive wheel that is driven only in the four-wheel drive state, and a second power transmission device that transmits power from the second power source to the auxiliary drive wheel, and (b) a sudden change upward gradient of torque at the auxiliary drive wheel used when switching from the two-wheel drive state to the four-wheel drive state is set to a value greater than a slow change upward gradient that suppresses backlash elimination shock caused by teeth striking when the direction in which backlash is eliminated between components that constitute the second power transmission device is reversed as the power transmission state of the second power transmission device is switched from a driven state to a driving state. Effect of the Invention

[0007] According to the first aspect of the present invention, the torque increase gradient at the auxiliary drive wheels used when switching from the two-wheel drive state to the four-wheel drive state is set to a steep increase gradient that is greater than the gradual increase gradient that suppresses backlash elimination shock. As a result, backlash is eliminated during acceleration, so there is no need to eliminate backlash before acceleration. In addition, the torque of the second power source rises quickly when switching to the four-wheel drive state, so two-stage acceleration is suppressed. Therefore, backlash elimination during acceleration and responsiveness can be achieved while avoiding deterioration of energy efficiency. [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] 1 is a flowchart illustrating the main control operations of an electronic control device, and is a flowchart illustrating the control operations for eliminating backlash during acceleration and ensuring responsiveness while avoiding deterioration of energy efficiency. [Diagram 3] 3 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 2 is executed. 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 for explaining the schematic configuration of a vehicle 10 to which the present invention is applied, as well as a diagram for explaining the main parts of the control functions and control system for various controls in the vehicle 10. In Fig. 1(a), the vehicle 10 is equipped with left and right front wheels 12, a front-wheel drive unit 20 that drives the front wheels 12, left and right rear wheels 14, and a rear-wheel drive unit 30 that drives the rear wheels 14, which are separated from each other. The vehicle 10 is also equipped with a battery 40 which is a chargeable and dischargeable DC power source, etc. Note that the above "left and right" refers to the left and right with respect to the forward direction of the vehicle 10.

[0011] The vehicle 10 is an all-wheel drive vehicle capable of adjusting the distribution of drive torque between the front wheels 12 and the rear wheels 14. The vehicle 10 is also a four-wheel drive vehicle since it has four wheels, that is, two front wheels 12 and two rear wheels 14. In this embodiment, all-wheel drive (=AWD) and four-wheel drive (=4WD) are synonymous. In addition to running under 4WD control (also synonymous with 4WD state) in which drive torque is distributed to the four wheels, the vehicle 10 can also run under two-wheel drive (=2WD) control (also synonymous with 2WD state) in which drive torque is distributed to only one of the front wheels 12 and the rear wheels 14.

[0012] The front-wheel drive device 20 includes a front motor MGF as a power source, a front-wheel power transmission device 22 that transmits power from the front motor MGF to the front wheels 12, a front-wheel PCU (Power Control Unit) 24 that controls the front motor MGF, and a front case 26 that is attached to the vehicle body. The front motor MGF is a known rotating electric machine, a so-called motor generator, and is connected to a battery 40 via the front-wheel PCU 24. The front motor MGF is provided in the front case 26. The front-wheel PCU 24 includes, for example, an inverter, and converts DC power from the battery 40 into AC power and supplies it to the front motor MGF, and converts AC power generated by the front motor MGF by regenerative braking into DC power and supplies it to the battery 40. The front-wheel PCU 24 is a power control device that controls the power exchanged between the battery 40 and the front motor MGF. The front-wheel PCU 24 may be provided in the front case 26.

[0013] The front-wheel power transmission device 22 includes a drive gear 50, a driven gear 52, a driven shaft 54, a final gear 56, a differential gear 58, and the like, in the front case 26. The front-wheel power transmission device 22 also includes a pair of front drive shafts 60 connected to the differential gear 58, and the like. The drive gear 50 is connected to a rotor shaft of the front motor MGF, and the front motor MGF is connected to the drive gear 50 so as to be capable of transmitting power. The driven gear 52 has a larger diameter than the drive gear 50 and is meshed with the drive gear 50. The driven shaft 54 ​​fixes the driven gear 52 and the final gear 56 so that they cannot rotate relative to each other. The final gear 56 has a smaller diameter than the driven gear 52 and is meshed with a differential ring gear 58a of the differential gear 58. The differential ring gear 58a has a larger diameter than the final gear 56. In the front wheel power transmission device 22, a reduction gear mechanism is configured in the power transmission path between the rotor shaft of the front motor MGF and the front drive shaft 60.

[0014] The rear-wheel drive device 30 includes a rear motor MGR as a power source, a rear-wheel power transmission device 32 that transmits power from the rear motor MGR to the rear wheels 14, a rear-wheel PCU 34 that controls the rear motor MGR, and a rear case 36 that is attached to the vehicle body. The rear motor MGR, the rear-wheel power transmission device 32, and the rear-wheel PCU 34 have the same functions as the front motor MGF, the front-wheel power transmission device 22, and the front-wheel PCU 24, respectively, and therefore their description will be omitted.

[0015] The vehicle 10 is a vehicle in which the amount of change in torque of the front and rear wheels can be controlled independently, and is a front and rear wheel independent drive type electric vehicle, that is, a BEV (Battery Electric Vehicle).

[0016] When the front wheels 12 are driven in the 2WD state and the 4WD state, and the rear wheels 14 are driven only in the 4WD state, the front wheels 12 are main drive wheels and the rear wheels 14 are auxiliary drive wheels. In this case, the front motor MGF functions as a first power source, the front wheel power transmission device 22 functions as a first power transmission device, the rear motor MGR functions as a second power source, and the rear wheel power transmission device 32 functions as a second power transmission device. Alternatively, the rear wheels 14 can be driven in the 2WD state and the 4WD state, and the front wheels 12 can be driven only in the 4WD state. In this case, the rear wheels 14 are main drive wheels, the front wheels 12 are auxiliary drive wheels, the rear motor MGR is the first power source, the rear wheel power transmission device 32 is the first power transmission device, the front motor MGF is the second power source, and the front wheel power transmission device 22 is the second power transmission device.

[0017] The vehicle 10 is equipped with an electronic control unit 70 (see "ECU" in the figure) including a control device for the vehicle 10 related to various controls such as torque distribution control between the front and rear wheels. The electronic control unit 70 is configured to include a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc.

[0018] 1(b), the electronic control device 70 is supplied with various signals (e.g., MGF rotation speed Nmgf, MGR rotation speed Nmgr, left and right front wheel rotation speeds Nwfl, Nwfr, left and right rear wheel rotation speeds Nwrl, Nwrr, accelerator opening θacc, longitudinal acceleration Gx, lateral acceleration Gy, yaw rate Ryuw, etc.) based on detection values ​​by various sensors (MGF rotation sensor 80, MGR rotation sensor 82, each wheel speed sensor 84, accelerator opening sensor 86, G sensor 88, yaw rate sensor 90, etc.) provided on the vehicle 10. The electronic control device 70 acquires the vehicle speed V based on the front wheel rotation speeds Nwfl, Nwfr and the rear wheel rotation speeds Nwrl, Nwrr.

[0019] 1(a), various command signals (e.g., MGF control command signal Smgf, MGR control command signal Smgr, etc.) are output from an electronic control device 70 to each device (e.g., front wheel PCU 24, rear wheel PCU 34, etc.) provided in a vehicle 10. The MGF control command signal Smgf is a torque command value for controlling the MGF torque Tmgf, and the MGR control command signal Smgr is a torque command value for controlling the MGR torque Tmgr.

[0020] The electronic control device 70 calculates the amount of drive required by the driver for the vehicle 10, for example, by applying the accelerator opening θacc and the vehicle speed V to a predetermined drive demand map. For example, the required drive torque Twdem [Nm] and the required drive force Fwdem [N] at the wheels (front wheels 12, rear wheels 14) are used as this drive demand. The required drive torque Twdem is a sum of a required front torque Twfdem as a required value of the front torque Twf, which is the torque at the front wheels 12, and a required rear torque Twrdem as a required value of the rear torque Twr, which is the torque at the rear wheels 14.

[0021] The electronic control unit 70 sets the torque distribution ratio γfr of the front and rear wheels by applying a plurality of driving force related values, such as the accelerator opening θacc, the vehicle speed V, the longitudinal acceleration Gx, and the yaw rate Ryaw, to a predetermined torque distribution ratio map. The electronic control unit 70 calculates the required front torque Twfdem and the required rear torque Twrdem, for example, based on the required driving torque Twdem and the torque distribution ratio γfr. The electronic control unit 70 outputs an MGF control command signal Smgf for controlling the front motor MGF to realize the required front torque Twfdem. The electronic control unit 70 also outputs an MGR control command signal Smgr for controlling the rear motor MGR to realize the required rear torque Twrdem.

[0022] Here, the region where the power transmission state of each of the front-wheel power transmission device 22 and the rear-wheel power transmission device 32 is switched from the driven state to the driving state is a torque region where teeth strike when the direction of eliminating the backlash between the components constituting the power transmission device is reversed, that is, the backlash elimination region. In the backlash elimination region, there is a risk of backlash elimination shock, which is a shock caused by teeth strike. In response to this, the electronic control device 70 suppresses the backlash elimination shock when passing through the backlash elimination region, for example, by setting a gentle change upward gradient that makes the change in torque at the driving wheels gentle. The driving state is a state in which the driving wheels are rotated by the torque output from the power source. The driven state is a state in which the rotating members of the power transmission device are rotated by the torque input from the driving wheels.

[0023] Incidentally, if the torque distribution ratio γfr is set to 100[%] (including close to 100[%]) on the front wheels 12 (or rear wheels 14) due to requirements for energy efficiency or the like, the torque of the rear motor MGR (or front motor MGF), which was in a non-driven state with the torque distribution ratio γfr being 0[%] (including close to 0[%]), is restored during re-acceleration. At this time, since the backlash elimination region is passed through, if a gradual change upward gradient is set that limits the amount of change in the rear torque Twr (or front torque Twf) so as to suppress the backlash elimination shock, there is a possibility that acceleration will occur in two stages (see the comparative example shown by the dashed line in FIG. 3 described later).

[0024] Therefore, in this embodiment, when the torque of the rear motor MGR (or the front motor MGF) returns from the torque distribution ratio γfr of 100[%] on the front wheels 12 side (or the rear wheels 14), a dedicated torque increase gradient (torque rate) is set that prioritizes eliminating backlash in the rear wheel power transmission device 32 (front wheel power transmission device 22). The electronic control device 70 increases the torque rate at the rear wheels 14 (or the front wheels 12) at the timing of switching from the 2WD state to the 4WD state.

[0025] The electronic control device 70 sets the torque increase gradient at the auxiliary drive wheels used when switching from the 2WD state to the 4WD state to a predetermined rapid change increase gradient that is greater than the gradual change increase gradient. This gradual change increase gradient is a predetermined torque increase gradient at the auxiliary drive wheels for suppressing backlash reduction shock caused by teeth striking when the direction in which backlash is reduced between the components constituting the second power transmission device is reversed as the power transmission state in the second power transmission device is switched from the driven state to the driving state.

[0026] Fig. 2 is a flow chart for explaining the main part of the control operation of the electronic control device 70, which is a flow chart for explaining the control operation for realizing the elimination of backlash during acceleration and ensuring responsiveness while avoiding the deterioration of energy efficiency, and which is executed repeatedly, for example. Fig. 2 shows an example used when the torque of the rear motor MGR is restored from the torque distribution ratio γfr of 100[%] on the front wheel 12 side, for example.

[0027] In FIG. 2, each step of the flowchart corresponds to a function of the electronic control device 70. In step (hereinafter, step will be omitted) S10, it is determined whether or not the torque distribution ratio γfr of the front torque Twf exceeds 90[%]. If the determination in S10 is positive, it is determined in S20 whether or not the rear torque Twr is less than a predetermined torque. This predetermined torque is, for example, a predetermined threshold value for determining, in conjunction with the determination in S10, that the vehicle is in a 2WD state with the front wheels 12 driven. If the determination in S10 is negative or the determination in S20 is negative, this routine is terminated. If the determination in S20 is positive, the rear torque rate, which is the rising gradient of the rear torque Twr, is switched to a sudden rising gradient in S30.

[0028] FIG. 3 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 2 is executed. FIG. 3 shows an example of a case where, for example, an accelerator full-open acceleration request is made during steady running at a low speed in a 2WD state with a torque distribution ratio γfr of 100[%] on the front wheel 12 side. In FIG. 3, time t1 indicates the time when it is determined that the accelerator pedal depression operation has started. This determines the switching from the 2WD state of the front wheel drive to the 4WD state. In the comparative example shown by the broken line, the rising gradient (rising rate) of the rear torque Twr is set to a gently changing rising gradient (normal torque rate). Therefore, in the comparative example, the MGR torque Tmgr rises with a delay from the rise of the MGF torque Tmgf, and two-stage acceleration is performed. In contrast, in the present embodiment shown by the solid line, the rising rate of the rear torque Twr is set to a rapidly changing rising gradient (fast torque rate), so that the MGR torque Tmgr rises in accordance with the rise of the MGF torque Tmgf, and the two-stage acceleration is eliminated or suppressed.

[0029] As described above, according to this embodiment, the torque increase gradient at the auxiliary drive wheels used when switching from the 2WD state to the 4WD state is set to a steep increase gradient that is greater than the gradual increase gradient that suppresses backlash elimination shock. As a result, backlash is eliminated during acceleration, so there is no need to eliminate backlash before acceleration. In addition, the torque of the second power source rises quickly when switching to the 4WD state, so two-stage acceleration is suppressed. Therefore, backlash elimination during acceleration and responsiveness can be achieved while avoiding deterioration of energy efficiency.

[0030] Although the embodiment of the present invention has been described in detail above with reference to the drawings, the present invention can be applied to other embodiments.

[0031] For example, in the above-described embodiment, the present invention can be applied even if one of the front wheel drive device 20 and the rear wheel drive device 30 is a hybrid vehicle equipped with a known internal combustion engine (engine) in addition to a motor (electric motor) as a power source.

[0032] It should be noted that the above 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]

[0033] 10: vehicle 12: front wheels (main drive wheels / auxiliary drive wheels) 14: rear wheels (auxiliary drive wheels / main drive wheels) 22: power transmission device for front wheels (first power transmission device / second power transmission device) 32: power transmission device for rear wheels (second power transmission device / first power transmission device) 70: electronic control device (control device) MGF: front motor (first power source / second power source) MGR: rear motor (second power source / first power source)

Claims

[Claim 1] A control device for a 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, auxiliary drive wheels that are driven only in the four-wheel drive state, and a second power transmission device that transmits power from the second power source to the auxiliary drive wheels, a torque increase gradient at the auxiliary drive wheels used when switching from the two-wheel drive state to the four-wheel drive state is set to a sudden-change increase gradient that is greater than a slow-change increase gradient that suppresses backlash-eliminating shock caused by teeth striking when a direction in which backlash is eliminated between components constituting the second power transmission device is reversed as the power transmission state in the second power transmission device is switched from a driven state to a driving state.

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