Control device for all-wheel drive vehicle

Abstract

This disclosure relates to a control device for all-wheel-drive vehicles. While ensuring power performance in a differential limiting state of the power distribution device, it suppresses a decrease in the durability of the power transmission path on the front wheels. When the power distribution device is set to a differential limiting state and wheel braking torque is applied to both the front and rear wheels, torque limiting control is performed, setting the upper limit of the power source torque to a smaller value when the wheel braking torque is high compared to when the wheel braking torque is low. Therefore, for example, when a large accelerator and a large brake operation are performed in the differential limiting state of the power distribution device, it is easier to limit the torque of the power source, so it is less likely to transmit high torque to the power transmission path on the front wheels. Furthermore, for example, when the braking operation gradually decreases while the accelerator operation gradually increases in the differential limiting state of the power distribution device, the torque limitation of the power source is gradually released, so the torque of the power source increases when the rear wheels are less prone to slight slippage.

Description

Technical Field

[0001] This invention relates to a control device for distributing power from a power source to the front and rear wheels of an all-wheel drive vehicle. Background Technology

[0002] A control device for an all-wheel-drive vehicle is known, comprising: a power source; a power distribution device that distributes power from the power source to the front and rear wheels; a differential limiting mechanism that restricts rotational differential between the front and rear wheels; and a braking device that applies braking torque to the front and rear wheels respectively. For example, Patent Document 1 describes a four-wheel-drive vehicle, which is an all-wheel-drive vehicle. Patent Document 1 discloses that, under predetermined conditions, the power distribution device is set to a differential limiting state.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-47877 Summary of the Invention

[0006] However, vehicles sometimes experience situations where all wheels are prone to spinning or the rear wheels are prone to slipping, depending on road conditions such as poor road surfaces. On the other hand, vehicles generally have brake characteristics set so that the braking torque of the front wheels is greater than that of the rear wheels. Therefore, when applying wheel braking torque to the wheels under the aforementioned conditions and in the differential limiting state of the power distribution device, and transmitting drive torque provided by the power source to the wheels, the drive torque is set to be greater than the wheel braking torque, and the rear wheels sometimes slip slightly. Consequently, under the differential limiting state of the power distribution device, the power transmission path on the front wheel side, where the wheel braking torque has stopped rotating, is transmitted with high torque, potentially leading to reduced durability. Consider limiting, for example, the torque of the power source to address this phenomenon. However, uniformly limiting the torque of the power source would reduce the power performance under the differential limiting state of the power distribution device, potentially making it impossible to ensure suitable drive torque during driving under conditions such as those described above, or when climbing hills.

[0007] The present invention was made against the background of the above situation, and its purpose is to provide a control device for an all-wheel drive vehicle that can ensure power performance while suppressing the reduction of durability of the power transmission path on the front wheel side under the differential limitation state of the power distribution device.

[0008] The essence of the first invention is (a) a control device for an all-wheel drive vehicle, the all-wheel drive vehicle comprising: a power source; a power distribution device for distributing power from the power source to the front wheels and the rear wheels; a differential limiting mechanism for setting the state of the power distribution device to a differential limiting state in which rotational differential between the front wheels and the rear wheels is limited; and a braking device for applying wheel braking torque to the front wheels and the rear wheels respectively, wherein (b) when the state of the power distribution device is set to the differential limiting state and the wheel braking torque is applied to the front wheels and the rear wheels respectively, torque limiting control is performed to set the upper limit value of the torque of the power source to a smaller value when the wheel braking torque is large compared to when the wheel braking torque is small.

[0009] According to the first invention, when the power distribution device is set to a differential limiting state and wheel braking torque is applied to both the front and rear wheels, torque limiting control is performed to set the upper limit of the power source torque to a smaller value when the wheel braking torque is large compared to when the wheel braking torque is small. Therefore, for example, when a large accelerator and brake operation are performed in the differential limiting state of the power distribution device, it is easy to limit the torque of the power source, so it is less likely to transmit high torque to the power transmission path on the front wheel side. Furthermore, for example, when the braking operation gradually decreases while the accelerator operation gradually increases in the differential limiting state of the power distribution device, the torque limitation of the power source is gradually released, so the torque of the power source increases when the rear wheels are less likely to slip slightly. Therefore, in the differential limiting state of the power distribution device, it is possible to ensure power performance while suppressing the reduction in durability of the power transmission path on the front wheel side. Attached Figure Description

[0010] Figure 1 This is a diagram illustrating the general structure of a vehicle to which the present invention is applied, and also a diagram illustrating the control functions for various controls in the vehicle and the main parts of the control system.

[0011] Figure 2 yes Figure 1 A diagram showing the key features of the transfer case in the vehicle.

[0012] Figure 3 This is a diagram illustrating an example of the upper limit of engine torque determined in advance based on the hydraulic pressure of the master cylinder.

[0013] Figure 4 It is a flowchart illustrating the main parts of the control operation of the electronic control device, and also a flowchart illustrating the control operation used to ensure power performance while suppressing the degradation of the durability of the power transmission path on the front wheel side under the differential limiting state of the transfer case.

[0014] (Symbol Explanation)

[0015] 10: Vehicle (all-wheel drive vehicle); 12: Engine (power source); 14 (14L, 14R): Front wheels; 16 (16L, 16R): Rear wheels; 22: Automatic transmission (transmission, power transmission device); 24: Transfer case (power distribution device); 44: Sub-transmission (stepped transmission); 52: Transmission locking mechanism (differential limiting mechanism); 90: Electronic control unit (control device); 122: Shift lever (shifting operation device); 132: Wheel braking device (braking device). Detailed Implementation

[0016] In embodiments of the present invention, the stepped transmission and the gear ratio (gear ratio also has the same meaning) in the transmission are defined as "the rotational speed of the input rotating component / the rotational speed of the output rotating component". The low-speed gear ratio is the gear ratio on the low-speed side where the gear ratio increases. For example, the lowest-speed gear ratio is the lowest-speed side gear ratio that becomes the lowest-speed side. The low gear of the stepped transmission is the low-speed side gear among multiple gears (gear stages also have the same meaning) where the gear ratio becomes the low-speed side gear ratio. For example, the lowest gear of the stepped transmission is the gear among multiple gears where the gear ratio becomes the lowest-speed gear ratio.

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0018]

Example

[0019] Figure 1 This is a diagram illustrating the general structure of the vehicle 10 to which the present invention is applied, and also a diagram illustrating the control functions for various controls and the main parts of the control system in the vehicle 10. Figure 1 In this vehicle 10, the vehicle is an all-wheel drive vehicle equipped with an engine 12 as a power source, front wheels 14 including left and right front wheels 14L and 14R, and rear wheels 16 including left and right rear wheels 16L and 16R. The vehicle 10 is equipped with a power transmission device 18 that transmits power from the engine 12 to the front wheels 14 and the rear wheels 16 respectively.

[0020] Engine 12 is a known internal combustion engine, controlled by an electronic control device 90 described later, which controls the engine torque Te, which is the torque of engine 12.

[0021] The power transmission device 18 includes a torque converter 20, an automatic transmission 22, a transfer case 24, a front drive shaft 26, a rear drive shaft 28, a front differential 30, a rear differential 32, a front drive shaft 34, and a rear drive shaft 36.

[0022] Automatic transmission 22 is, for example, a known planetary gear type automatic transmission. Automatic transmission 22 is a transmission located between engine 12 and transfer case 24. Automatic transmission 22 forms gears under the control of electronic control unit 90 (described later). The gears of automatic transmission 22 include multiple gears with different gear ratios γat. The gears of automatic transmission 22 include forward gears and reverse gears Rev. Forward gears are gears where the gear ratio γat is set to a forward gear ratio. For example, the lowest forward gear, i.e., first gear 1st, is a gear among the multiple forward gears where the gear ratio γat is set to the lowest forward gear ratio. Reverse gear Rev is a gear where the gear ratio γat is set to a reverse gear ratio.

[0023] The transfer case 24 is connected to the output side of the automatic transmission 22. The transfer case 24 is a power distribution device that distributes power from the engine 12 to the front wheels 14 and the rear wheels 16.

[0024] Figure 2 This is a key diagram of the transfer case 24. Figure 2 In this configuration, the transfer case 24 is located in the transmission housing 38 of the automatic transmission 22 (see reference). Figure 1 The transfer case 40 is a non-rotating component connected to the rear side of the vehicle. The transfer case 24 includes an input shaft 42, a secondary transmission 44, a first output shaft 46, a second output shaft 48, a center differential 50, and a transmission locking mechanism 52 within the transfer case 40.

[0025] Input shaft 42 is connected to output shaft 54 ​​of automatic transmission 22 and is driven by rotation through power input from engine 12 via automatic transmission 22. First output shaft 46 is connected to rear drive shaft 28. Second output shaft 48 is connected to front drive shaft 26.

[0026] The auxiliary transmission 44 has a single pinion type planetary gear unit 56 and a meshing clutch mechanism 58 that selectively engages either the low gear L or the high gear H.

[0027] The planetary gear unit 56 has a sun gear S1 connected to the input shaft 42, a ring gear R1 connected to the transfer case 40, and a gear carrier CA1 that rotates and revolves, supporting multiple pinions P1 that mesh with the sun gear S1 and the ring gear R1. A synchronizing engagement mechanism 60 in the engagement clutch mechanism 58, which participates in the establishment of high gear H, is connected to the sun gear S1. A clutch gear 62 in the engagement clutch mechanism 58, which participates in the establishment of low gear L, is connected to the gear carrier CA1.

[0028] The engagement clutch mechanism 58 includes a synchronous engagement mechanism 60 for engaging high gear H and an engagement clutch 64 for engaging low gear L. The engagement clutch 64 includes a cylindrical sleeve 68 that is rotatable relative to the differential housing 66 provided in the central differential 50 about the axis of the first output shaft 46 and is movable relative to the axis of the first output shaft 46. Furthermore, the engagement clutch 64 includes a clutch gear 62 that engages with the outer peripheral teeth 70 provided on the outer periphery of the sleeve 68.

[0029] Regarding the auxiliary transmission 44, the high gear H is engaged by the inner circumferential teeth of the sleeve 68 engaging with the synchronous engagement mechanism 60 through the sliding of the sleeve 68 in the axial direction of the first output shaft 46 within the engagement clutch mechanism 58. Furthermore, regarding the auxiliary transmission 44, the low gear L is engaged by the outer circumferential teeth 70 of the sleeve 68 engaging with the clutch gear 62 through the sliding of the sleeve 68 in the axial direction of the first output shaft 46 within the engagement clutch mechanism 58. The auxiliary transmission 44 is a stepped transmission located in the transfer case 24 that transmits power from the engine 12 to the front wheels 14 and the rear wheels 16 by changing the rotational speed of the engine 12.

[0030] The center differential 50 is a central differential device that distributes power to the first output shaft 46 and the second output shaft 48 while allowing rotational differential between them. The center differential 50 is a well-known torque-sensing type differential gear limiting device. The center differential 50 includes a differential housing 66, a ring gear R2, a sun gear S2, and a gear carrier CA2. The differential housing 66 is supported by the first output shaft 46 in a manner rotatable about the axis of the first output shaft 46. The ring gear R2 is connected to the first output shaft 46. The sun gear S2 is supported in a manner rotatable relative to the first output shaft 46. The gear carrier CA2 supports a plurality of pinions P2 that mesh with the sun gear S2 and the ring gear R2 in a rotational and revolution-oriented manner, and is connected to the differential housing 66.

[0031] The transfer case 24 includes a drive toothed reel 72, a driven toothed reel 74, and a chain 76. The drive toothed reel 72 is rotatably supported relative to the first output shaft 46 and connected to the sun gear S2. The driven toothed reel 74 is non-rotatably connected relative to the second output shaft 48. The chain 76 is wound around both the drive toothed reel 72 and the driven toothed reel 74. Rotation of the drive toothed reel 72 is transmitted to the driven toothed reel 74 via the chain 76.

[0032] When vehicle 10 is traveling straight, the torque transmitted from planetary gear assembly 56 to differential housing 66 is transmitted through central differential 50 via ring gear R2 to first output shaft 46 and via sun gear S2 to second output shaft 48. Furthermore, when vehicle 10 is turning, and the front wheels 14 rotate at high speeds, a differential limiting force occurs in central differential 50 due to the speed difference between sun gear S2 and ring gear R2. Therefore, for example, when vehicle 10 accelerates while turning, the torque distribution to the front wheels 14 is smaller compared to the torque distribution when traveling straight.

[0033] The transmission locking mechanism 52 puts the transfer case 24 into a central transmission locked state where the rotational differential between the first output shaft 46 and the second output shaft 48 is restricted. That is, the transmission locking mechanism 52 is a differential limiting mechanism that puts the transfer case 24 into a differential limiting state where the rotational differential between the front wheel 14 and the rear wheel 16 is restricted.

[0034] The transmission locking mechanism 52 includes a sleeve 78 and a clutch gear 80. The sleeve 78 is rotatable relative to the differential housing 66 about the axis of the first output shaft 46 and is movable relative to the axis of the first output shaft 46. The clutch gear 80 has outer teeth that mesh with the inner teeth of the sleeve 78, and is disposed between the drive toothed reel 72 and the differential housing 66, and is connected to the drive toothed reel 72. The transmission locking mechanism 52 engages with the differential housing 66 simultaneously with the sleeve 78 and the clutch gear 80, thereby putting the transfer case 24 into a central transmission locking state where the differential of the central differential 50 is restricted.

[0035] The transfer case 24 includes a shift actuator 82. The engagement clutch mechanism 58 and the transmission locking mechanism 52 are engaged by the electronic control unit 90 (described later) via the shift actuator 82. In the engagement clutch mechanism 58, the first output component 84 of the shift actuator 82 moves toward the axis of the first output shaft 46, and the sleeve 68 moves toward its axis, selectively engaging either low gear (L) or high gear (H). In the transmission locking mechanism 52, the second output component 86 of the shift actuator 82 moves toward the axis of the first output shaft 46, and the sleeve 78 moves toward its axis, switching between engagement and disengagement. The transfer case 24 is in a central transmission locked state due to the engagement of the transmission locking mechanism 52, and the central transmission lock is set to ON. The transfer case 24 is in a central transmission unlocked state due to the release of the transmission locking mechanism 52, and the central transmission lock is set to OFF, with the differential of the central differential 50 unrestricted.

[0036] Transfer drive 24 changes the rotational speed of input shaft 42 and transmits it to first output shaft 46 and second output shaft 48 in a differential or direct connection state.

[0037] Vehicle 10 is a full-time all-wheel drive vehicle capable of always operating in an all-wheel drive state, transmitting power from engine 12 to the rear wheels 16 and front wheels 14 via transfer case 24. Vehicle 10 has four wheels, with two front wheels 14 and two rear wheels 16, and is therefore also a four-wheel drive vehicle. In this embodiment, all-wheel drive (AWD) and four-wheel drive (4WD) have the same meaning. Furthermore, vehicle 10 is an AWD vehicle capable of operating in a non-differential state, i.e., a locked state, where the rotational differential between the front wheels 14 and rear wheels 16 is limited, by engaging the transmission locking mechanism 52 using shift actuator 82.

[0038] Return to Figure 1 The vehicle 10 also includes an electronic control unit 90, which serves as a controller for vehicle 10 control devices associated with the control of the engine 12. The electronic control unit 90 is configured as a so-called microcomputer, including, for example, a CPU, RAM, ROM, input / output interfaces, etc.

[0039] The electronic control unit 90 is supplied with various signals based on the detection values ​​detected by various sensors installed on the vehicle 10 (e.g., engine speed Ne, output speed No, front wheel speeds Nwfl, Nwfr, rear wheel speeds Nwrl, Nwrr, brake on signal Bon, brake operation amount Bra, master cylinder hydraulic pressure PRmc, operating position POSop, accelerator opening θacc, transmission lock signal Slock, transmission lock selection signal DLon, high / low shift operation signal OPhl, etc.).

[0040] Engine speed Ne is the rotational speed of engine 12. Output speed No is the rotational speed of rear drive shaft 28 and is a signal corresponding to vehicle speed V. Front wheel speeds Nwfl and Nwfr are the rotational speeds of front wheels 14 (14L, 14R), respectively. Rear wheel speeds Nwrl and Nwrr are the rotational speeds of rear wheels 16 (16L, 16R), respectively. Brake engagement signal Bon is a signal indicating the state of the brake pedal 120 located on vehicle 10 operated by the driver. Brake operation amount Bra is a signal indicating the magnitude of the brake operation performed by the driver. Master cylinder hydraulic pressure PRmc is hydraulic pressure generated from a master cylinder (not shown) provided in the wheel brake device 128 described later. Operating position POSop is a signal indicating the operating position of shift lever 122 located on vehicle 10. Accelerator opening θacc is a signal indicating the magnitude of the acceleration operation performed by the driver using accelerator pedal 124 located on vehicle 10, and is the driver's accelerator operation amount. The transmission lock signal Slock indicates that the transmission lock mechanism 52 has completed its engagement and that the transfer case 24 is in the central transmission lock state. The transmission lock selection signal DLon indicates that the central transmission lock switch 116 has been activated and that the transfer case 24 has been switched to the central transmission lock state. The high / low shift operation signal OPhl indicates that the shift lever 126 located on the vehicle 10 has been activated.

[0041] The shift lever 122 is a shifting operation device operated by the driver to one of a plurality of operating positions POSOP. The operating positions POSOP include, for example, P, R, N, and D operating positions corresponding to the P, R, N, and D positions, respectively, which are the plurality of shift positions of the automatic transmission 22. The shift position of the automatic transmission 22 indicates the power transmission state in the automatic transmission 22. The shift lever 122 is a shifting operation device that selects the power transmission state of the power transmission device, such as the automatic transmission 22, located between the engine 12 and the transfer case 24.

[0042] The central transmission lock switch 116 is, for example, a latched push-button switch manually operated by the driver, and is used to select the differential and non-differential states of the central differential 50. For example, when the central transmission lock switch 116 is engaged and held in the pushed-in state, it outputs a transmission lock selection signal DLon. When the transmission lock selection signal DLon is output, the electronic control unit 90 engages the transmission lock mechanism 52, thereby locking the central differential 50 from the unlocked state.

[0043] The gear shift dial 126 is, for example, a dial-type switch manually operated by the driver, and has two dial positions: a High position for selecting to shift to high gear H and a Low position for selecting to shift to low gear L. The high / low shift operation signal OPhl is a signal indicating the position of the gear shift dial 126 provided on the vehicle 10. For example, when the gear shift dial 126 is in the High position, it outputs the high / low shift operation signal OPhl corresponding to the High position. When the high / low shift operation signal OPhl corresponding to the High position is output, the electronic control unit 90 engages the synchronizing engagement mechanism 60, causing the sub-transmission 44 to shift to high gear H. On the other hand, when the gear shift dial 126 is in the Low position, it outputs the high / low shift operation signal OPhl corresponding to the Low position. When the high / low shift operation signal OPhl corresponding to the Low position is output, the electronic control unit 90 engages the engagement clutch 64, causing the sub-transmission 44 to shift to low gear L.

[0044] Vehicle 10 can select four driving modes—H4F, H4L, L4F, and L4L—by operating the gear shift dial 126 and the central transmission lock switch 116. H4F driving mode allows operation with the central transmission unlocked in AWD mode (high gear H). H4L driving mode allows operation with the central transmission locked in AWD mode (high gear H). L4F driving mode allows operation with the central transmission unlocked in AWD mode (low gear L). L4L driving mode allows operation with the central transmission locked in AWD mode (low gear L).

[0045] The electronic control unit 90 outputs various command signals to the various devices installed in the vehicle 10 (such as engine 12, automatic transmission 22, shift actuator 82, wheel brake device 128, etc.). These signals include engine control command signal Se for controlling engine 12, AT control command signal Sat for controlling automatic transmission 22, high / low shift control command signal Shl for switching the gear shift of auxiliary transmission 44, unlocking shift control command signal Sfl for switching the state of central differential 50, and brake control command signal Sbra for controlling wheel brake 130.

[0046] The wheel brake device 128 includes a master cylinder (not shown) for generating brake hydraulic pressure and a cylinder actuator. Each wheel, including the front wheel 14 and the rear wheel 16, is equipped with a wheel brake 130. The wheel brake device 128 supplies brake hydraulic pressure to wheel cylinders (not shown) respectively disposed in the wheel brakes 130. The wheel brake device 128 is a braking device that imparts a wheel braking torque TBw, which is the braking torque provided by the wheel brake 130, to each wheel. Under normal conditions, the wheel brake device 128 supplies master cylinder hydraulic pressure PRmc, corresponding to the brake operation amount Bra, as brake hydraulic pressure to the wheel cylinders. In the wheel brake device 128, the brake characteristics under normal conditions are set such that the wheel braking torque TBw of the front wheel 14 is greater than the wheel braking torque TBw of the rear wheel 16.

[0047] In order to realize various controls in the vehicle 10, the electronic control device 90 includes a power source control unit, namely the power source control unit 92, a transmission control unit, namely the transmission control unit 94, and a driving mode switching control unit, namely the driving mode switching control unit 96.

[0048] The power source control unit 92 calculates the driver's driving demand for the vehicle 10 by mapping, for example, a predetermined driving demand to an accelerator opening θacc and a vehicle speed V. This driving demand includes, for example, the required driving torque Trdem [Nm] and the required driving force Frdem [N] in the wheels. The power source control unit 92 outputs an engine control command signal Se for controlling the engine 12 in a manner that achieves the required driving torque Trdem.

[0049] The transmission control unit 94 uses, for example, a predetermined shift mapping to determine the shift of the automatic transmission 22, and outputs an AT control command signal Sat to perform shift control of the automatic transmission 22 based on the result of the shift determination.

[0050] The driving mode switching control unit 96 controls the switching of driving modes based on the high / low switching operation signal OPhl of the gear shift dial 126 and the transmission lock selection signal DLon of the central transmission lock switch 116.

[0051] When the high / low shift operation signal Ophl corresponds to the High position, the driving mode switching control unit 96 outputs a high / low shift control command signal Shl to switch the sub-transmission 44 to a high gear H. Conversely, when the high / low shift operation signal Ophl corresponds to the Low position, the driving mode switching control unit 96 outputs a high / low shift control command signal Shl to switch the sub-transmission 44 to a low gear L.

[0052] Furthermore, when the driving mode switching control unit 96 receives the transmission lock selection signal DLon, it outputs an unlocking switching control command signal Sfl to switch the center differential 50 to the locked state. On the other hand, when the driving mode switching control unit 96 does not receive the transmission lock selection signal DLon, it outputs an unlocking switching control command signal Sfl to switch the center differential 50 to the unlocked state.

[0053] However, when driving uphill on a steep slope, for example, if the accelerator pedal is not engaged, the vehicle 10 will roll backward. Similarly, when restarting from a stop on an uphill slope using only the right foot, if the brake pedal 120 is released and the accelerator pedal 124 is pressed, the vehicle 10 is prone to rolling backward. Therefore, when restarting from a stop on an uphill slope, consider pressing the accelerator pedal 124 while the brake pedal 120 is engaged with the left foot. In this case, both the brake pedal 120 and the accelerator pedal 124 are pressed simultaneously. In this situation, if the transfer case 24 is locked and the road surface is prone to wheel slippage, or if the rear wheel 16 is prone to slippage, the rear wheel 16 may slip slightly due to the drive torque Tr exceeding the wheel braking torque TBw. Therefore, transfer case 24 is locked in the central transmission state, so there is a possibility that the power transmission path on the front wheel 14 side may receive higher torque than the power transmission path on the rear wheel 16 side, resulting in reduced durability. This phenomenon is significant in L4L driving mode with high drive torque Tr, and it also occurs when driving on rough roads. In contrast, if the engine torque Te is consistently limited in L4L driving mode, there is a possibility that the drive torque Tr required for driving on uphill or rough roads cannot be guaranteed.

[0054] Therefore, the electronic control unit 90 performs torque limiting control CTtl, which limits the engine torque Te to an upper limit of the driving torque Tr that prevents the rear wheel 16 from slipping, relative to the wheel braking torque TBw. Thus, when restarting, for example, on an uphill road, as the brake pedal 120 is gradually released and the accelerator pedal 124 is gradually depressed from a simultaneously depressed position, the limitation on the engine torque Te is gradually released in accordance with the decrease in wheel braking torque TBw. Therefore, it is easy to eliminate both the possibility of reduced durability of the power transmission path on the front wheel 14 side and the possibility of not being able to ensure the driving torque Tr.

[0055] In order to realize torque limiting control CTtl, the electronic control device 90 also includes a state determination unit, namely a state determination section 98.

[0056] The status determination unit 98 determines whether the transfer case 24 is in a differential limiting state, i.e., whether the transfer case 24 is in a central transmission lock state. For example, the status determination unit 98 determines whether the transfer case 24 is in a central transmission lock state based on whether a transmission lock selection signal DLon is output. The meaning of whether the transmission lock selection signal DLon is output is the same as whether the central transmission lock is set to ON.

[0057] The state determination unit 98 determines whether wheel braking torque TBw has been applied to the front wheel 14 and the rear wheel 16 respectively. For example, the state determination unit 98 determines whether wheel braking torque TBw has been applied to the front wheel 14 and the rear wheel 16 respectively based on whether a brake activation signal Bon has been output. The meaning of whether a brake activation signal Bon has been output is the same as whether the brake pedal 120 has been activated.

[0058] When the state determination unit 98 determines that the transfer case 24 is in a differential limiting state and applies wheel braking torque TBw to the front wheel 14 and the rear wheel 16 respectively, the power source control unit 92 performs torque limiting control CTtl.

[0059] In the power source control unit 92, as a torque limiting control CTtl, the engine torque upper limit value Teul is set to a smaller value when the wheel braking torque TBw is large compared to when the wheel braking torque TBw is small. The engine torque upper limit value Teul is the upper limit value of the engine torque Te. The power source control unit 92 uses the master cylinder hydraulic pressure PRmc as a signal to indicate the wheel braking torque TBw.

[0060] Figure 3 This is a diagram illustrating an example of the engine torque ceiling value Teul, predetermined based on the master cylinder hydraulic PRmc. Figure 3In the range where the master cylinder hydraulic pressure PRmc is below the first master cylinder hydraulic pressure PRmc1, the engine torque upper limit value Teul is set as the first engine torque upper limit value Teul1. The first engine torque upper limit value Teul1 is, for example, an engine torque upper limit value Teul set under necessary conditions different from the torque limit control CTtl. That is, in the range where the master cylinder hydraulic pressure PRmc is below the first master cylinder hydraulic pressure PRmc1, the engine torque Teul is not substantially limited. In the region where the master cylinder hydraulic pressure PRmc gradually increases from the first master cylinder hydraulic pressure PRmc1, the engine torque upper limit value Teul gradually decreases from the first engine torque upper limit value Teul1. That is, in the range where the master cylinder hydraulic pressure PRmc is greater than the first master cylinder hydraulic pressure PRmc1, the engine torque Teul is limited. For example, the engine torque upper limit value Teul is set in such a way that it becomes the driving torque Tr that is relative to the wheel braking torque TBw of the rear wheel 16 without the rear wheel 16 slipping. Within the range where the master cylinder hydraulic pressure PRmc is greater than or equal to the second master cylinder hydraulic pressure PRmc2, the engine torque upper limit value Teul is set as the second engine torque upper limit value Teul2. For example, the second master cylinder hydraulic pressure PRmc2 is set considering that the increase in the wheel braking torque TBw of the rear wheel 16 is mitigated relative to the increase in the master cylinder hydraulic pressure PRmc. For example, the second engine torque upper limit value Teul2 is set considering the value of the engine torque Te that ensures the durability of the power transmission path on the front wheel 14 side, and the value of the drive torque Tr used to move the vehicle 10.

[0061] The status determination unit 98 determines whether the gear shift of the auxiliary transmission 44 is the lowest gear, i.e., low gear L. The status determination unit 98 determines whether the gear shift of the auxiliary transmission 44 is low gear L, for example, based on the high / low shift control command signal Shl. The meaning of whether the gear shift of the auxiliary transmission 44 is low gear L is the same as the L4 state, which indicates the AWD state in low gear L, for the transfer case 24.

[0062] When the state determination unit 98 determines that the transfer case 24 is in a differential limiting state, and applies wheel braking torque TBw to the front wheel 14 and the rear wheel 16 respectively, and determines that the auxiliary transmission 44 is in a low gear L, the power source control unit 92 performs torque limiting control CTtl.

[0063] The state determination unit 98 determines whether the vehicle speed V is below a predetermined vehicle speed Vf. The predetermined vehicle speed Vf is, for example, a pre-determined threshold used to determine whether the vehicle is stopped or traveling at a low speed. Traveling at a low speed is, for example, traveling at a vehicle speed V at the level of a person walking. Alternatively, a predetermined vehicle speed Vf can be set that takes into account the vehicle speed V under conditions such as wheel spin on a poor road.

[0064] When the state determination unit 98 determines that the transfer case 24 is in a differential limiting state, and applies wheel braking torque TBw to the front wheel 14 and the rear wheel 16 respectively, and determines that the vehicle speed V is below the predetermined vehicle speed Vf, the power source control unit 92 performs torque limiting control CTtl.

[0065] The state determination unit 98 determines whether the operation position POSop is either the D operation position or the R operation position. The D operation position is a forward driving operation position that selects the D position of the automatic transmission 22. The D position is a forward driving position that enables the vehicle 10 to move forward. That is, the D operation position is an operation position that selects a power transmission state that enables the vehicle 10 to move forward. The R operation position is a reverse driving operation position that selects the R position of the automatic transmission 22. The R position is a reverse driving position that enables the vehicle 10 to move backward. That is, the R operation position is an operation position that selects a power transmission state that enables the vehicle 10 to move backward.

[0066] When the state determination unit 98 determines that the transfer case 24 is in a differential limiting state, and applies wheel braking torque TBw to the front wheel 14 and the rear wheel 16 respectively, and determines that the operating position POSop is either the D operating position or the R operating position, the power source control unit 92 performs torque limiting control CTtl.

[0067] The status determination unit 98 determines whether the gear ratio γat of the automatic transmission 22 is the lowest gear ratio for forward or the gear ratio for reverse. When the automatic transmission 22 is a stepped transmission, the meaning of whether the gear ratio γat of the automatic transmission 22 is the lowest gear ratio for forward or the gear ratio for reverse is the same as whether the gear shift of the automatic transmission 22 is the first gear shift 1st or the reverse gear shift Rev.

[0068] When the state determination unit 98 determines that the transfer case 24 is in a differential limiting state, and applies wheel braking torque TBw to the front wheel 14 and the rear wheel 16 respectively, and determines that the gear ratio γat of the automatic transmission 22 is the lowest speed gear ratio for forward or the gear ratio for reverse, the power source control unit 92 performs torque limiting control CTtl.

[0069] Figure 4 It is a flowchart illustrating the main part of the control operation of the electronic control device 90, and also a flowchart illustrating the control operation for ensuring power performance while suppressing the reduction of durability of the power transmission path on the front wheel 14 side under the differential limiting state of the transfer case 24, for example, repeated execution.

[0070] exist Figure 4First, in step S10 (steps omitted below) corresponding to the function of the state determination unit 98, it is determined whether the central transmission lock is set to ON. If the determination in S10 is affirmative, in step S20 (corresponding to the function of the state determination unit 98), it is determined whether the transfer case 24 is in the L4 state. If the determination in S20 is affirmative, in step S30 (corresponding to the function of the state determination unit 98), it is determined whether the brake pedal 120 is set to ON. If the determination in S30 is affirmative, in step S40 (corresponding to the function of the state determination unit 98), it is determined whether the vehicle speed V is below the predetermined vehicle speed Vf. If the determination in S40 is affirmative, in step S50 (corresponding to the function of the state determination unit 98), it is determined whether the operating position POSop is the D operating position or the R operating position. If the determination in S50 is affirmative, in step S60 (corresponding to the function of the state determination unit 98), it is determined whether the automatic transmission 22 is in the first gear (1st) or the reverse gear (Rev). If the determination in S60 is affirmative, in S70, corresponding to the function of the power source control unit 92, the execution flag of the torque limit control CTtl is set to ON. Next, in S80, corresponding to the function of the power source control unit 92, the master cylinder hydraulic pressure PRmc is obtained. Next, in S90, corresponding to the function of the power source control unit 92, the engine torque upper limit value Teul is calculated based on the master cylinder hydraulic pressure PRmc (refer to...). Figure 3 If the judgment in S10, S20, S30, S40, S50, or S60 above is negative, this routine ends.

[0071] As described above, according to this embodiment, when the transfer case 24 is in a differential limiting state and wheel braking torque TBw is applied to both the front wheel 14 and the rear wheel 16, torque limiting control CTtl is performed. Therefore, when, for example, a large accelerator and brake operation are performed in the differential limiting state of the transfer case 24, the engine torque Te is easily limited, making it difficult to transmit high torque to the power transmission path on the front wheel 14 side. Furthermore, when, for example, the brake operation gradually decreases while the accelerator operation gradually increases in the differential limiting state of the transfer case 24, the limitation on engine torque Te is gradually released, so the engine torque Te increases when the rear wheel 16 is less prone to slight slippage. Therefore, in the differential limiting state of the transfer case 24, it is possible to ensure power performance while suppressing the reduction in durability of the power transmission path on the front wheel 14 side.

[0072] Furthermore, according to this embodiment, torque limiting control CTtl is performed when the sub-transmission 44 is in low gear L. Additionally, torque limiting control CTtl is performed when the vehicle speed V is below a predetermined vehicle speed Vf. Furthermore, torque limiting control CTtl is performed when the operating position POSop is in the D or R operating position. Additionally, torque limiting control CTtl is performed when the automatic transmission 22 is in first gear 1st or reverse gear Rev. Therefore, torque limiting control CTtl is performed in situations where the durability of the power transmission path on the front wheel 14 side is prone to decrease. Thus, the decrease in durability of the power transmission path on the front wheel 14 side can be suppressed.

[0073] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention can also be applied in other ways.

[0074] For example, in the above embodiments, the automatic transmission 22 may be, in addition to a planetary gear type automatic transmission, a synchronous meshing type parallel 2-shaft automatic transmission including a known DCT (Dual Clutch Transmission), a known belt-type continuously variable transmission, etc.

[0075] In addition, in the above embodiments, the power source of vehicle 10 may be an electric motor, or a combination of an engine and an electric motor, in addition to the engine 12.

[0076] Furthermore, in the above embodiments, in the torque limiting control CTtl, the engine torque Te can be limited either by controlling the command value of the engine torque Te, or by controlling the command value of the input torque of the automatic transmission 22 or the output torque of the torque converter 20.

[0077] In short, it is sufficient to limit the driving torque Tr.

[0078] Furthermore, in the above embodiment, the engine torque upper limit value Teul is set according to the master cylinder hydraulic PRmc, but it is not limited to this method. The setting of the engine torque upper limit value Teul requires a value representing the magnitude of the wheel braking torque TBw, so only the master cylinder hydraulic PRmc is used. However, any value representing the magnitude of the wheel braking torque TBw can be a value other than the master cylinder hydraulic PRmc.

[0079] Furthermore, in the above embodiments, the AWD vehicle can be either a full-time AWD vehicle or an AWD vehicle capable of switching between AWD and front-wheel drive or rear-wheel drive. In short, any AWD vehicle that can operate in AWD mode with the central transmission locked can be used with this invention.

[0080] Furthermore, the above is only one embodiment, and the present invention can be implemented in various ways with modifications and improvements based on the knowledge of those skilled in the art.

Claims

1. A control device (90) for an all-wheel drive vehicle (10), the all-wheel drive vehicle (10) comprising: The system comprises: a power source (12); a power distribution device (24) for distributing power from the power source (12) to the front wheel (14) and the rear wheel (16); a differential limiting mechanism (52) for setting the power distribution device (24) in a differential limiting state where rotational differential between the front wheel (14) and the rear wheel (16) is limited; and a braking device (132) for applying wheel braking torque to the front wheel (14) and the rear wheel (16) respectively. When the state of the power distribution device (24) is set to the differential limit state and the front wheel (14) and the rear wheel (16) are respectively given the wheel braking torque, torque limit control is performed to set the upper limit value of the torque of the power source (12) to a smaller value when the wheel braking torque is large compared to when the wheel braking torque is small.

2. The control device (90) for an all-wheel drive vehicle (10) according to claim 1, characterized in that, The torque limiting control is performed when the gear of the stepped transmission (44) provided in the power distribution device (24) that transmits power from the power source (12) to the front wheel (14) and the rear wheel (16) by changing the rotation speed of the power source (12) is in the lowest gear.

3. The control device (90) for an all-wheel drive vehicle (10) according to claim 1, characterized in that, The torque limiting control is performed when the vehicle speed is below the predetermined speed for determining whether to stop or drive at a low speed.

4. The control device (90) for an all-wheel drive vehicle (10) according to claim 1, characterized in that, The torque limiting control is performed when the operating position of the shifting device (122) of the all-wheel drive vehicle (10) is either the operating position for selecting the power transmission state of the power transmission device (22) between the power source (12) and the power distribution device (24) or the operating position for selecting the power transmission state ...

5. The control device (90) for an all-wheel drive vehicle (10) according to claim 1, characterized in that, The torque limiting control is performed when the gear ratio of the transmission (22) located between the power source (12) and the power distribution device (24) is the lowest speed gear ratio for forward movement or the gear ratio for reverse movement.

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