Electric vehicle control device

Abstract

To provide a controller of an electric vehicle in which a high / low switching device can be properly switched into a low gear when a high / low selection device selects the low gear at the time of executing creeping-cut.SOLUTION: When a low gear Lo is selected while executing creeping-cut (YES at determination of S2), the creeping-cut is aborted (S3) to control an electric motor MG so as to generate creeping torque Tcreep. When a high / low switching device is switched from a high gear Hi to a low gear Lo by a high / low switching clutch D1 in association with selection of the low gear Lo, the high / low switching clutch D1 assumes a neutral state, a low gear side engagement tooth is turned by the creeping torque Tcreep so that an HL switching sleeve is surely engaged with the low gear side engagement tooth, and the high / low switching device is appropriately switched to the low gear Lo.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a control device for an electric vehicle that controls an electric motor to generate creep torque. [Background technology]

[0002] Patent Document 1 (a) relates to an electric vehicle equipped with an electric motor as a power source, and (b) describes a control device for an electric vehicle equipped with a creep control unit that performs creep control to control the electric motor to generate creep torque while the vehicle is stopped and performs creep cut to stop the creep control under certain predetermined conditions. In Patent Document 1, if the vehicle speed falls below a predetermined creep cut prohibition speed while creep control is being performed, creep cut is prohibited regardless of whether a creep cut permission condition is met. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-16168 Summary of the Invention [Problem to be solved by the invention]

[0004] There is known an electric vehicle that includes: (a) a high / low switching device that uses a mesh clutch to change the rotation output from the power source between two stages, high gear and low gear; (b) a center differential that transmits the rotation output from the high / low switching device to the front and rear wheels in a manner that allows differential rotation; (c) a differential locking device that limits the differential rotation of the center differential; (d) a high / low selection device that can select whether the high / low switching device is in the high gear or the low gear; and (e) a differential state selection device that can select whether the center differential is in a free state, in which the differential rotation is not limited, or in a differential lock state, in which the differential rotation is limited by the differential locking device. In such electric vehicles, the vehicle can be switched between the following modes: H4F mode, in which the high / low switching device is in high gear and the center differential is free; H4L mode, in which the high / low switching device is in high gear and the center differential is diff-locked; L4F mode, in which the high / low switching device is in low gear and the center differential is free; and L4L mode, in which the high / low switching device is in low gear and the center differential is diff-locked. In this case, although not yet publicly known, creep cut is permitted in the H4F mode to reduce power loss and improve fuel economy, while the H4L mode, L4F mode, and L4L mode are often selected to improve drivability on poor road conditions, so it is conceivable that creep cut will be prohibited to prioritize power performance over fuel economy.

[0005] However, when low gear is selected by the high / low selector in H4F ​​mode with creep cut, and an attempt is made to switch from high gear to low gear using the mesh clutch, even if the mesh clutch is in neutral, the input side is stopped from rotating due to creep cut, and the output side is stopped from rotating due to the vehicle being stopped. As a result, the mesh clutch cannot engage with the mesh teeth on the low gear side, and the high / low switching device may not be able to switch to low gear.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to enable a high / low switching device to properly switch to a low gear when a low gear is selected by a high / low selecting device while creep cut is being performed. [Means for solving the problem]

[0007] The first invention relates to an electric vehicle having (a) a power source having an electric motor, (b) a high / low switching device that changes the rotation output from the power source in two stages, high gear and low gear, using a dog clutch, (c) a center differential that transmits the rotation output from the high / low switching device to front and rear wheels so as to be able to rotate differentially, and (d) a high / low selection device that can select whether the high / low switching device is in the high gear or the low gear, and (e) a creep control unit that performs creep control to control the electric motor to generate creep torque while the vehicle is stopped, and performs creep cut to stop the creep control under certain predetermined conditions, in a control device for an electric vehicle, (f) the creep control unit stops the creep cut when the high / low selection device selects the low gear while the creep cut is being performed. (g) the electric vehicle is equipped with (g-1) a differential locking device that limits differential rotation of the center differential, and (g-2) a differential state selection device that can select whether the center differential is in a free state where the differential rotation is not limited, or in a differential lock state where the differential rotation is limited by the differential locking device, while (h) the control device has a driving mode switching control unit that switches between four driving modes in accordance with the selection by the high / low selection device and the selection by the differential state selection device: an H4F ​​mode where the high / low selection device is in the high gear and the center differential is in the free state, an H4L mode where the high / low selection device is in the high gear and the center differential is in the differential lock state, an L4F mode where the high / low selection device is in the low gear and the center differential is in the free state, and an L4L mode where the high / low selection device is in the low gear and the center differential is in the differential lock state; and (i) the creep control unit permits the creep cut in the H4F mode, prohibits the creep cut in the H4L mode, the L4F mode, and the L4L mode, and prohibits the creep cut when the low gear is selected by the high / low selection device in the H4F mode. It is characterized by:

[0008] A second invention is a control device for an electric vehicle according to the first invention, characterized in that (a) the electric vehicle is a hybrid electric vehicle that has an engine in addition to the electric motor as the power source, and a torque converter is provided between the power source and the high / low switching device, and (b) the creep control unit generates the creep torque using the torque converter by rotating the electric motor at a predetermined rotational speed, and performs the creep cut by stopping the rotation of the electric motor.

[0010] No. 3 The invention is 1st invention or 2ndIn the control device for an electric vehicle of the invention, the creep control unit prohibits the creep cut when at least one of the following conditions is met: when high / low switching control is in progress in which the high / low switching device switches between the high gear and the low gear in accordance with the selection by the high / low selection device; when the high / low switching device is in the low gear; and when the center differential is in the differential lock. [Effects of the Invention]

[0011] In such an electric vehicle control device, if low gear is selected by the high / low selection device while creep cut is in progress, creep cut is canceled and the electric motor is controlled to generate creep torque. Therefore, when the high / low switching device is switched from high gear to low gear by the mesh clutch in response to low gear selection, if the mesh clutch is in a neutral state, the mesh teeth on the input side, i.e., the low gear side, are rotated by the creep torque, so that the mesh clutch is reliably engaged with the mesh teeth on the low gear side, and the high / low switching device is appropriately switched to low gear. In addition, creep cut is permitted in H4F ​​mode, improving fuel economy, while creep cut is prohibited in H4L, L4F, and L4L modes, allowing for superior power performance through creep torque and improving drivability on poor road conditions such as muddy roads. Furthermore, when low gear is selected by the high / low selection device in H4F ​​mode, where creep cut is permitted, creep cut is prohibited, and the electric motor is controlled to generate creep torque, ensuring that the mesh clutch engages with the mesh teeth on the low gear side, allowing the high / low switching device to appropriately switch to low gear.

[0012] The second invention is a vehicle that has an engine in addition to an electric motor as a power source, and a torque converter is provided between the power source and the high / low switching device, and creep torque can be generated by the torque converter by rotating the electric motor at a predetermined rotational speed.

[0014] No. 3 In the present invention, creep cut is prohibited when at least one of the following conditions is met: when the high-low switching device is in high-low switching control, when the high-low switching device is in low gear, and when the center differential is in differential lock. 1st invention or 2nd The effects of the invention can be obtained appropriately. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating a schematic configuration of a drive system of a front-wheel drive electric vehicle to which the present invention is applied, and also shows essential parts of control functions. [Figure 2] FIG. 2 is a schematic diagram illustrating a specific example of the HV transmission device of FIG. 1. [Figure 3] FIG. 2 is a schematic diagram illustrating a specific example of the transfer of FIG. 1. [Figure 4] FIG. 2 is a diagram illustrating a plurality of driving modes of the electric vehicle of FIG. [Figure 5] 5 is a diagram illustrating a switching pattern of a plurality of driving modes in FIG. 4. FIG. [Figure 6] 2 is a flowchart illustrating signal processing executed by the creep control unit of FIG. 1. [Figure 7] 7 is an example of a time chart showing changes in the operating state of each part when creep cut is prohibited according to the flowchart of FIG. 6. [Figure 8] 10 is a flowchart illustrating another embodiment of the creep control unit of FIG. [Figure 9] 9 is an example of a time chart showing changes in the operating state of each part when determining whether or not creep cut is possible according to the flowchart of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention is applicable to electric vehicles equipped with only an electric motor as a power source, as well as hybrid electric vehicles equipped with both an electric motor and an internal combustion engine (ICE). A motor-generator that also functions as a generator is suitable for the electric motor, but an electric motor without generator functionality can also be used. The high-low switching device and center differential are typically single-pinion or double-pinion planetary gear units, but parallel-axis high-low switching devices or bevel-gear center differentials can also be used. The high-low switching device is equipped with a mesh clutch, which preferably has a synchronizing mechanism, but does not necessarily have to have a synchronizing mechanism. The differential lock can also be a mesh clutch with a synchronizing mechanism, but a mesh clutch without a synchronizing mechanism or a friction-engagement clutch can also be used. When a fluid transmission such as a torque converter is provided between the electric motor and the high-low switching device, creep torque can be generated by rotating the electric motor at a predetermined rotational speed. However, when no fluid transmission is provided, creep torque can be generated by the torque of the electric motor.

[0017] The driving mode switching control unit is configured to establish, for example, four driving modes, H4F mode, H4L mode, L4F mode, and L4L mode, in accordance with the selection by the high / low selection device and the selection by the differential state selection device. However, it may also be possible to switch to only three driving modes, H4F mode, L4F mode, and L4L mode, or to only three driving modes, H4F mode, H4L mode, and L4L mode. The creep control unit is configured, for example, to permit creep cut in H4F ​​mode but prohibit creep cut in H4L mode, L4F mode, and L4L mode. However, it may also be configured to permit creep cut in H4F ​​mode and H4L mode but prohibit creep cut in L4F mode and L4L mode. In this case, when switching from H4L mode to L4L mode, for example, creep cut can be stopped when a low gear is selected by the high / low selection device. [Example]

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating the drive system of an electric vehicle 10 to which the present invention is applied, and also shows the main parts of the control functions for various controls in the electric vehicle 10. The electric vehicle 10 is a front-to-rear (four-wheel drive) hybrid electric vehicle based on a front-engine, rear-wheel drive (FR) system. The electric vehicle 10 includes an engine 12, a pair of left and right front wheels 14, a pair of left and right rear wheels 16, and a power transmission 18. The power transmission 18 includes an HV transmission 20 connected to the engine 12 and a transfer 22 connected to the HV transmission 20. Driving force transmitted from the engine 12 and the HV transmission 20 to the transfer 22 is distributed to a front propeller shaft 24 and a rear propeller shaft 26. From the front propeller shaft 24, power is transmitted to the left and right front wheels 14 via a differential 28, while from the rear propeller shaft 26, power is transmitted to the left and right rear wheels 16 via a differential 30. The engine 12 is an internal combustion engine such as a gasoline engine, and is used as a power source for traveling. The torque of the engine 12, that is, an engine torque Te, is controlled by an engine control signal Se output from an electronic control unit 150.

[0019] 2 is a schematic diagram illustrating a specific example of HV transmission 20. HV transmission 20 includes an electric motor MG, a motor connecting shaft 42, a torque converter 44, and an automatic transmission 46, which are arranged on a common first axis CL1 inside a case 40, which is a non-rotating member. The electric motor MG and the torque converter 44 are configured substantially symmetrically with respect to the first axis CL1, and the lower half of the first axis CL1 is omitted from FIG. 2.

[0020] An engine connecting / disconnecting clutch K0 is provided between the engine 12 and the motor connecting shaft 42. An electric motor MG, which is used together with the engine 12 as a power source for traveling, is connected to the motor connecting / disconnecting clutch K2 via a motor connecting / disconnecting clutch K2. The engine connecting / disconnecting clutch K0 and the motor connecting / disconnecting clutch K2 are hydraulic friction engagement devices, and the engagement oil pressure supplied from a hydraulic control circuit 52 (see FIG. 1) is controlled by a K0 switching signal Sk0 and a K2 switching signal Sk2 output from an electronic control device 150, respectively, so that the engagement / disconnecting states of the engine and motor connecting / disconnecting clutches K0 and K2 are individually switched between engagement / disconnecting states. The hydraulic control circuit 52 includes an electromagnetic switching valve, an electromagnetic pressure regulating valve, and an electric oil pump, so that a predetermined oil pressure can be output even when the electric vehicle 10 is stopped. The electric motor MG is a motor generator that functions as a generator and is connected to an electricity storage device via an inverter (not shown), and the torque of the electric motor MG, i.e., MG torque Tmg, is controlled by an MG control signal Smg output from the electronic control device 150.

[0021] The torque converter 44 includes a pump wheel 44a connected to the motor connecting shaft 42 and a turbine wheel 44b connected to the transmission input shaft 48. The torque converter 44 is a fluid transmission device that transmits power from the engine 12 and / or electric motor MG, which are power sources, to the transmission input shaft 48 via fluid. The torque converter 44 includes a lock-up clutch LU that connects the pump wheel 44a and the turbine wheel 44b. The lock-up clutch LU is a hydraulic friction engagement device, and its engagement and disengagement states are switched by controlling the engagement oil pressure supplied from the hydraulic control circuit 52 by an LU control signal Slu output from the electronic control device 150.

[0022] The automatic transmission 46 is a known planetary gear automatic transmission equipped with, for example, one or more planetary gear devices and multiple engagement devices CB. The engagement devices CB are hydraulic friction engagement devices, and their disengagement states are switched by controlling the engagement oil pressure supplied from the hydraulic control circuit 52 by a CB control signal Scb output from the electronic control device 150. The automatic transmission 46 is a stepped transmission that can form multiple gears with different speed ratios γ (=AT input rotation speed Ni / AT output rotation speed No) depending on the engagement and disengagement states of the multiple engagement devices CB. The AT input rotation speed Ni is the rotation speed of the transmission input shaft 48 and is equal to the turbine rotation speed Nt, which is the output rotation speed of the torque converter 44. The AT output rotation speed No is the rotation speed of the transmission output shaft 50.

[0023] 3 is a schematic diagram illustrating a specific example of the transfer case 22. The transfer case 22 includes a TF input shaft 62 connected to the transmission output shaft 50, a high / low switching device 64, a center differential 66, a rear-wheel output shaft 68, and a sprocket-like drive gear 70 that outputs driving force to the front wheels 14, all of which are located on a first axis CL1 that is the same axis as the HV powertrain 20. Driving force is transmitted from the rear-wheel output shaft 68 to the rear propeller shaft 26. The transfer case 22 also includes a front-wheel output shaft 72 and a sprocket-like driven gear 74 that is integral with the front-wheel output shaft 72, all of which are located on a second axis CL2 that is parallel to the first axis CL1. A chain 76 is wound between the drive gear 70 and the driven gear 74, and driving force is transmitted from the center differential 66 to the front wheel output shaft 72 via the drive gear 70, chain 76, and driven gear 74. Driving force is transmitted from the front wheel output shaft 72 to the front propeller shaft 24.

[0024] The high / low switching device 64 is configured to include a single-pinion planetary gear set having a sun gear S1, a carrier C1, and a ring gear R1, and a high / low switching clutch D1, with the sun gear S1 connected to the TF input shaft 62 and the ring gear R1 fixed to the case 40. The high / low switching clutch D1 is a meshing clutch with a synchronization mechanism, and includes high-gear side meshing teeth 80 provided on the TF input shaft 62, low-gear side meshing teeth 82 provided on the carrier C1, and an HL switching sleeve 86 that is disposed on the HL output member 84 so as to be non-rotatable relative to the HL output member 84 but movable in the axial direction, and is provided with meshing teeth that selectively mesh with the meshing teeth 80, 82. The HL switching sleeve 86 is reciprocated in the axial direction by a hydraulic actuator, thereby switching between a high gear Hi that meshes with the high gear side meshing teeth 80 to connect the TF input shaft 62 and the HL output member 84, and a low gear Lo that meshes with the low gear side meshing teeth 82 to connect the carrier C1 and the HL output member 84. The HL switching sleeve 86 is moved in the axial direction by controlling the hydraulic pressure supplied from the hydraulic control circuit 52 by a D1 switching signal Sd1 output from the electronic control device 150, and the high / low switching device 64 is switched between the high gear Hi and the low gear Lo. Between the high gear Hi and the low gear Lo, the HL switching sleeve 86 does not mesh with either the meshing teeth 80, 82, resulting in a neutral state in which power transmission is interrupted.

[0025] The center differential 66 is configured with a single-pinion planetary gear device having a sun gear S2, a carrier C2, and a ring gear R2, and the carrier C2 is connected to and rotated by the HL output member 84. The ring gear R2 is connected to the rear wheel side output shaft 68, and the sun gear S2 is connected to the drive gear 70, so that the rotation of the HL output member 84 is transmitted to the front wheels 14 and the rear wheels 16 so as to be able to rotate differentially.

[0026] A differential lock clutch D2 is provided between the sun gear S2 and carrier C2 of the center differential 66 as a differential lock device that limits differential rotation. The differential lock clutch D2 is a meshing clutch without a synchronization mechanism, and includes meshing teeth 90 provided on the sun gear S2, meshing teeth 92 provided on the carrier C2, and a differential lock sleeve 94 that is disposed so as to be movable in the axial direction and has meshing teeth that mesh with the meshing teeth 90, 92. The differential lock sleeve 94 is always meshed with one of the meshing teeth 90, and is reciprocated in the axial direction by a hydraulic actuator to mesh with the other of the meshing teeth 92, thereby connecting the sun gear S2 and carrier C2 so that they cannot rotate relative to each other, or a free state, in which meshing with the other of the meshing teeth 92 is released and relative rotation between the sun gear S2 and carrier C2, i.e., differential rotation of the center differential 66, is permitted. The differential lock sleeve 94 is moved axially by controlling the hydraulic pressure supplied from the hydraulic control circuit 52 by the D2 switching signal Sd2 output from the electronic control unit 150, and the center differential 66 is switched between free and differential lock.

[0027] Such an electric vehicle 10 is equipped with an electronic control device 150 as a control device for controlling the operation of each part, such as the engine 12, the HV transmission 20, and the transfer case 22. The electronic control device 150 is configured to include a so-called microcomputer equipped with a CPU, RAM, ROM, an input / output interface, etc., and executes various controls by processing signals in accordance with programs stored in advance in the ROM.

[0028] The electronic control unit 150 receives various information required for control from various sensors provided on the electric vehicle 10. For example, from the engine rotation speed sensor 112, MG rotation speed sensor 114, AT input rotation speed sensor 116, AT output rotation speed sensor 118, accelerator opening sensor 120, throttle valve opening sensor 122, braking force sensor 124, wheel speed sensor 126, high / low state detection sensor 128, differential state detection sensor 130, etc., the following information is obtained: engine rotation speed Ne which is the rotation speed of the engine 12, MG rotation speed Nmg which is the rotation speed of the electric motor MG, AT input rotation speed Ni, AT output rotation speed No, accelerator opening θacc corresponding to the amount of depression of the accelerator pedal, throttle valve opening θth which is the opening of the electronic throttle valve of the engine 12, braking force Fbr corresponding to the depression force of the brake pedal, wheel speeds Nwfl, Nwfr, Nwrl, Nwrr of the front wheels 14 and the rear wheels 16, whether the high / low switching device 64 is in high gear Hi or low gear Lo, Signals indicating the high / low state Phl, which indicates whether the center differential 66 is free or locked, and the differential state Pdiff, which indicates whether the center differential 66 is free or locked, are supplied. The vehicle speed V can be calculated based on the wheel speeds Nwfl, Nwfr, Nwrl, and Nwrr.

[0029] The electronic control unit 150 also receives a selection range signal Srang, a high / low selection signal Shl, and a differential state selection signal Sdiff from a range selector 140, a high / low selection device 142 that selects whether the high / low switching device 64 is in high gear (Hi) or low gear (Lo), and a differential state selector 144 that selects whether the center differential 66 is in free or differential lock. The range selector 140, high / low selection device 142, and differential state selector 144 are all located near the driver's seat and operated by the driver. The range selector 140 can be, for example, a shift lever or the like, and can select a D range for forward travel, an R range for reverse travel, a P range for parking, or the like. The high / low selection device 142 is, for example, a low gear selection switch operated to select low gear (Lo), and when not operated, high gear (Hi) is selected. The differential state selector 144 is, for example, a differential lock selection switch operated to select differential lock, and when not operated, the free selection is selected. The high / low selector device 142 and the differential state selector device 144 are operated to shift the high / low switching device 64 to low gear Lo or to put the center differential 66 into differential lock, for example, when improving the vehicle's drivability on poor road conditions such as muddy roads.

[0030] The electronic control device 150 calculates the required drive torque etc. based on the accelerator opening θacc, the vehicle speed V etc., and controls the engine torque Te and the MG torque Tmg so as to obtain the required drive torque etc., and performs shift control of the automatic transmission 46 in accordance with a predetermined shift map. In addition, the electronic control device 150 is functionally equipped with a drive mode switching control unit 152 that switches between multiple drive modes with different operating states of the transfer case 22, and a creep control unit 154 that generates creep torque when the vehicle is traveling at a low speed below a predetermined speed, including while the vehicle is stopped.

[0031] 4 by changing the operating states of the high / low switching device 64 and the differential-lock clutch D2 in accordance with the selection made by the high / low selection device 142 and the selection made by the differential state selection device 144. Specifically, the mode is switched between an H4F ​​mode in which the high / low switching device 64 is in high gear Hi and the center differential 66 is free, an H4L mode in which the high / low switching device 64 is in high gear Hi and the center differential 66 is differential-locked, an L4F mode in which the high / low switching device 64 is in low gear Lo and the center differential 66 is free, and an L4L mode in which the high / low switching device 64 is in low gear Lo and the center differential 66 is differential-locked. As shown in FIG. 5, in these H4F mode, H4L mode, L4F mode, and L4L mode, the high-low switching device 64 and the differential-lock clutch D2 are switched separately in accordance with the selection operation of the high-low selection device 142 and the differential state selection device 144, and the high-low switching device 64 and the differential-lock clutch D2 are not switched simultaneously.

[0032] The creep control unit 154 executes creep control, controlling the electric motor MG to generate a predetermined creep torque Tcreep that allows the electric vehicle 10 to creep on flat roads when the vehicle is traveling at a low speed below a predetermined vehicle speed, including when the vehicle is stopped. In this embodiment, the torque converter 44 is disposed between the electric motor MG and the transfer case 22, and the electric motor MG is rotated at a predetermined creep rotation speed Nmgc to generate the creep torque Tcreep. When a predetermined creep cut condition is met, such as when the vehicle is stopped and the braking force Fbr is equal to or greater than a predetermined value, indicating that the driver has no intention of starting the electric vehicle 10, the creep control unit 154 executes creep cut, which halts creep control to reduce energy consumption due to the creep torque Tcreep. In this embodiment, creep cut can be performed by stopping the rotation of the electric motor MG.

[0033] On the other hand, when creep cut is performed in this manner, power performance such as driving force responsiveness decreases. For this reason, creep cut is prohibited when a certain power performance is required. In this embodiment, whether or not creep cut is performed is set according to the driving mode as shown in FIG. 4. In H4F ​​mode, high power performance is not considered necessary, so creep cut is permitted with priority given to energy efficiency (fuel economy). On the other hand, in H4L mode, L4F mode, and L4L mode, creep cut is prohibited with priority given to power performance over energy efficiency.

[0034] Here, because creep cut is permitted in H4F ​​mode, it is assumed that low gear Lo is selected by the high / low selection device 142 in H4F ​​mode with creep cut, and the high / low switching device 64 is switched from high gear Hi to low gear Lo by the high / low changeover clutch D1. In this case, even if the HL changeover sleeve 86 disengages from the high gear side meshing teeth 80 and enters the neutral state, the input side of the high / low changeover clutch D1 is stopped from rotating due to creep cut, and the output side is also stopped from rotating due to the vehicle being stopped, so the HL changeover sleeve 86 cannot mesh with the low gear side meshing teeth 82, and it is possible that the high / low changeover device 64 cannot be switched to low gear Lo.

[0035] In contrast, the creep control unit 154 of this embodiment executes signal processing in accordance with steps S1 to S4 of the flowchart in Fig. 6 (hereinafter, the steps will be omitted and simply referred to as S1 to S4. The same applies to other flowcharts), and inhibits creep cut under certain conditions. In the flowchart in Fig. 6, YES in the decision steps indicated by diamonds means affirmative, and NO means negative.

[0036] In S1 of Figure 6, it is determined whether creep cut is being performed, and if creep cut is not being performed, the process ends. However, if creep cut is being performed, S2 is executed. Since creep cut is permitted only in H4F ​​mode, S2 is executed when creep cut is being performed in H4F ​​mode. In S2, it is determined based on the high-low selection signal Shl whether L4 mode has been selected, specifically whether low gear Lo has been selected by the high-low selection device 142, and if low gear Lo has been selected, S3 is executed. In other words, L4 mode essentially means L4F mode, and when switching from H4F mode to L4F mode, the determination in S2 becomes YES, and S3 and subsequent steps are executed.

[0037] In S3, creep cut is prohibited, and in S4, the HL switching sleeve 86 of the high / low changeover clutch D1 meshes with the low gear side meshing teeth 82, and it is determined whether low gear Lo has been established in the high / low changeover device 64. Specifically, it is determined whether low gear Lo has been established based on a signal indicating the high / low state Phl supplied from the high / low state detection sensor 128, and if low gear Lo is established and the determination in S4 is YES, the series of controls related to creep control during the transition to L4 mode changeover is terminated. In this case, since creep cut is prohibited in S3, creep control is executed and the electric motor MG is rotated at the creep rotational speed Nmgc, causing creep torque Tcreep to act on the input side of the high / low changeover clutch D1. Therefore, when the HL switching sleeve 86 disengages from the high gear side meshing teeth 80 and enters a neutral state, the low gear side meshing teeth 82 are rotated based on the creep torque Tcreep, and the HL switching sleeve 86 is properly meshed with the low gear side meshing teeth 82, thereby establishing low gear Lo.

[0038] Figure 7 is an example of a time chart showing the changes in the operating state of each part when creep cut is prohibited and the mode is switched to L4 according to the flowchart of Figure 6. Time t1 is the time when low gear Lo is selected by the high / low selection device 142 during creep cut, the determination in S2 becomes YES, and execution of S3 and subsequent steps begins. Time t2 is the time when the HL switching sleeve 86 meshes with the low gear side meshing teeth 82 to establish low gear Lo, and it is detected that the gear has been switched to low gear Lo based on the signal indicating the high / low state Phl.

[0039] As described above, according to the creep control unit 154 of the electric vehicle 10 of this embodiment, if low gear Lo is selected by the high / low selection device 142 while creep cut is being performed (determination in S2 is YES), creep cut is canceled (S3), and the electric motor MG is controlled to generate creep torque Tcreep. Therefore, when the high / low switching device 64 is switched from high gear Hi to low gear Lo by the high / low switching clutch D1 in response to the selection of low gear Lo, if the high / low switching clutch D1 is in the neutral state, the low gear side meshing teeth 82 are rotated by the creep torque Tcreep, and the HL switching sleeve 86 is reliably brought into mesh with the low gear side meshing teeth 82, and the high / low switching device 64 is appropriately switched to low gear Lo.

[0040] Furthermore, a torque converter 44 is provided between the electric motor MG and the high / low switching device 64, and by rotating the electric motor MG at a creep rotation speed Nmgc, the torque converter 44 can generate a creep torque Tcreep.

[0041] Furthermore, while creep cut is permitted in H4F ​​mode, improving fuel economy, creep cut is prohibited in H4L mode, L4F mode, and L4L mode, allowing excellent power performance to be obtained by creep torque Tcreep, improving drivability on poor road conditions such as muddy roads. Also, since creep cut is prohibited when low gear Lo is selected by high / low selection device 142 in H4F ​​mode, where creep cut is permitted (S3), electric motor MG is controlled to generate creep torque Tcreep, thereby reliably engaging HL switching sleeve 86 of high / low switching clutch D1 with low gear side meshing teeth 82, and thereby appropriately switching high / low switching device 64 to low gear Lo.

[0042] In the above embodiment, creep cut is prohibited if low gear Lo is selected while creep cut is being performed, but it is also possible to set a creep cut prohibition condition in advance, under which creep cut should be prohibited, and determine whether creep cut is permitted or not depending on whether the creep cut prohibition condition is met, as shown in the flowchart of Figure 8. That is, it is determined in SS1 whether the creep cut prohibition condition is met, and if it is met (established), creep cut is prohibited in SS2, while if it is not met, creep cut is permitted in SS3.

[0043] The creep cut prohibition condition is preset to satisfy at least one of the following conditions: high-low switching control is in progress, in which the high-low switching device 64 is switched between high gear Hi and low gear Lo in accordance with the selection operation by the high-low selection device 142; the high-low switching device 64 is in low gear Lo; and the center differential 66 is in differential lock. Whether the high-low switching device 64 is in low gear Lo can be determined based on a signal indicating the high-low state Phl, and whether the center differential 66 is in differential lock can be determined based on a signal indicating the differential state Pdiff. Whether the high-low switching device 64 is under high-low switching control can be determined, for example, by providing a high-low switching in-progress flag Fhl that is turned on when high-low switching control is in progress, and the flag is switched on and off based on the high-low switching control executed by the driving mode switching control unit 152.

[0044] FIG. 9 is an example of a time chart showing changes in the operating state of each component when switching between multiple driving modes (H4F mode, H4L mode, L4F mode, L4L mode) while performing creep control by determining whether or not creep cut is enabled according to the flowchart of FIG. 8. In this case, too, when low gear Lo is selected by the high / low selection device 142 in H4F ​​mode, in which creep cut is enabled, the driving mode switching control unit 152 executes high / low switching control, turning on the high / low switching in progress flag Fhl and prohibiting creep cut (time t1). Accordingly, when the electric motor MG is controlled to generate creep torque Tcreep, the HL switching sleeve 86 of the high / low switching clutch D1 is reliably engaged with the low gear side meshing teeth 82, and the high / low switching device 64 is appropriately switched to low gear Lo, enabling switching to L4F mode (time t2). In other words, substantially the same effects as those of the above-described embodiment can be achieved.

[0045] Although the embodiments of the present invention have been described in detail above with reference to the drawings, these are merely embodiments and the present invention can be embodied in various forms with various modifications and improvements. [Explanation of symbols]

[0046] 10: Electric vehicle 12: Engine 14: Front wheels 16: Rear wheels 44: Torque converter 64: High / low switching device 66: Center differential 142: High / low selection device 144: Differential state selection device 150: Electronic control unit (control unit) 152: Driving mode switching control unit 154: Creep control unit MG: Electric motor D1: High / low switching clutch (meshing clutch) D2: Differential lock clutch (differential lock device)

Claims

1. An electric vehicle includes a power source having an electric motor, a high / low switching device that changes the speed of the rotation output from the power source in two stages, high gear and low gear, using a meshing clutch, a center differential that transmits the rotation output from the high / low switching device to front wheels and rear wheels so as to be able to rotate differentially, and a high / low selection device that can select whether the high / low switching device is in the high gear or the low gear, A control device for an electric vehicle, comprising: a creep control unit that performs creep control to control the electric motor so as to generate creep torque while the vehicle is stopped, and a creep cut that stops the creep control under a predetermined condition, the creep control unit stops the creep cut when the low gear is selected by the high / low selection device while the creep cut is being performed, The electric vehicle includes: a differential lock device that limits differential rotation of the center differential; a differential state selection device that selects whether the center differential is in a free state in which the differential rotation is not restricted, or in a differential lock state in which the differential rotation is restricted by the differential lock device; While it has the control device has a driving mode switching control unit that switches between four driving modes, in accordance with the selection by the high / low selection device and the selection by the differential state selection device, an H4F ​​mode in which the high / low switching device is in the high gear and the center differential is free, an H4L mode in which the high / low switching device is in the high gear and the center differential is the differential lock, an L4F mode in which the high / low switching device is in the low gear and the center differential is free, and an L4L mode in which the high / low switching device is in the low gear and the center differential is the differential lock, The creep control unit permits the creep cut in the H4F mode, and prohibits the creep cut in the H4L mode, the L4F mode, and the L4L mode, while prohibiting the creep cut when the low gear is selected by the high / low selection device in the H4F mode. A control device for an electric vehicle.

2. the electric vehicle is a hybrid electric vehicle that includes an engine in addition to the electric motor as the power source, and a torque converter is provided between the power source and the high / low switching device, The creep control unit generates the creep torque by the torque converter by rotating the electric motor at a predetermined rotation speed, and performs the creep cut by stopping the rotation of the electric motor. The control device for an electric vehicle according to claim 1 .

3. The creep control unit prohibits the creep cut when at least one of the following conditions is satisfied: during high-low switching control in which the high gear and the low gear of the high-low switching device are switched in accordance with the selection by the high-low selection device, when the high-low switching device is in the low gear, and when the center differential is in the differential lock.

3. The control device for an electric vehicle according to claim 1 or 2.

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