Controller of four-wheel drive vehicle

Abstract

To provide a controller of a four-wheel drive vehicle which can improve switching performance into a release state of an engagement type clutch when a two-wheel driving state is selected.SOLUTION: A controller of a four-wheel drive vehicle is given in which: when a two-wheel driving state is selected and the controller is activated to switch an engagement device and an engagement type clutch into release states, the engagement device is determined to be switched into the release state, the engagement type clutch is determined to be in an engagement state, and either stopping determination condition or acceleration prediction determination condition is determined to be satisfied, the engagement device is temporarily switched into the engagement state. Thereby, when vehicle start or acceleration is performed in a looseness filling state where backlash is formed between teeth of the engagement type clutch in a sub-driving wheel side and teeth in a sub-drive force transmission shaft side, the looseness filling state is resolved and the engagement type clutch is switched into the release state. When the two-wheel driving state is selected, switching performance of the engagement type clutch into the release state can be improved.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a control device for a four-wheel drive vehicle having a disconnection mechanism on each of the main driving force transmission shaft side and the auxiliary drive wheel side of an auxiliary driving force transmission shaft. [Background technology]

[0002] A control device for a four-wheel drive vehicle is well known, which includes a power source, a main driving force transmission shaft that transmits the power of the power source to a main driving wheel, a driving force distribution device that distributes a part of the power of the power source distributed by the driving force distribution device to the auxiliary driving wheel, an auxiliary driving force transmission shaft that transmits a part of the power of the power source distributed by the driving force distribution device to the auxiliary driving wheel, an engagement device that connects and disconnects a power transmission path between the main driving force transmission shaft and the auxiliary driving force transmission shaft, and a mesh clutch that connects and disconnects the power transmission path between the auxiliary driving force transmission shaft and the auxiliary driving wheel. For example, a control device for a four-wheel drive vehicle described in Patent Document 1 is such a control device. Patent Document 1 discloses that a two-wheel drive state in which the power of the power source is transmitted to the main driving wheel by disengaging both the engagement device and the mesh clutch, and a four-wheel drive state in which the power of the power source is transmitted to the main driving wheel and the auxiliary driving wheel by engaging both the engagement device and the mesh clutch can be selectively switched. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-131814 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, when switching from the four-wheel drive state to the two-wheel drive state is selected, both the engagement device and the meshing clutch are operated to switch to the release state. At this time, for example, due to the difference in tire diameter between the front and rear wheels, the rotation speed of the auxiliary drive wheels may be higher than the rotation speed of the main drive wheels. In this case, the teeth on the auxiliary drive wheel side, i.e., the driven side, of the meshing teeth of the meshing clutch are in a state where the teeth on the auxiliary drive force transmission shaft side, i.e., the driving side are compressed (pushed) to reduce backlash. In this case, for example, due to the influence of the retaining taper on the meshing teeth of the meshing clutch, or insufficient load when switching the meshing clutch to the release state, the meshing clutch may not be switched to the release state, and the auxiliary drive force transmission shaft may continue to rotate. In other words, even if the two-wheel drive state is selected, the auxiliary drive wheels may rotate the auxiliary drive force transmission shaft.

[0005] The present invention has been made against the background of the above circumstances, and its object is to provide a control device for a four-wheel drive vehicle that can improve the performance of switching a mesh clutch to a released state when a two-wheel drive state is selected. [Means for solving the problem]

[0006] The gist of a first aspect of the present invention is a vehicle equipped with: (a) a power source, a main driving force transmission shaft that transmits the power of the power source to main driving wheels, a driving force distribution device that distributes a portion of the power of the power source to auxiliary driving wheels, a secondary driving force transmission shaft that transmits a portion of the power of the power source distributed by the driving force distribution device to the auxiliary driving wheels, an engagement device that connects and disconnects a power transmission path between the main driving force transmission shaft and the secondary driving force transmission shaft, and a mesh clutch that connects and disconnects the power transmission path between the secondary driving force transmission shaft and the auxiliary driving wheels, wherein the engagement device and the mesh clutch are both in a released state to transmit the power of the power source to the main driving wheels, and the engagement device and the mesh clutch are both in an engaged state to transmit the power of the power source to the main driving wheels. A control device for a four-wheel drive vehicle in which a four-wheel drive state in which power is transmitted to the main drive wheels and the auxiliary drive wheels can be selectively switched between the two-wheel drive state and a four-wheel drive state, and (b) when the control device operates to switch both the engagement device and the mesh clutch to a released state due to a selection of switching from the four-wheel drive state to the two-wheel drive state, if the control device determines that the engagement device has been switched to the released state, determines that the mesh clutch is in an engaged state without being switched to the released state, and determines that any one of a stop determination condition in which the vehicle speed is less than a predetermined vehicle speed, and an acceleration prediction determination condition in which future acceleration based on the driver's acceleration request amount is equal to or greater than a predetermined acceleration is satisfied, the control device temporarily switches the engagement device to an engaged state. Effect of the Invention

[0007] According to the first invention, when the engagement device and the mesh clutch are both operated to be switched to the released state due to the selection of switching from the four-wheel drive state to the two-wheel drive state, if it is determined that the engagement device has been switched to the released state, the mesh clutch is determined to be in the engaged state, and it is determined that any one of the stop determination condition and the acceleration prediction determination condition is satisfied, the engagement device is temporarily switched to the engaged state. As a result, when starting or accelerating is performed in a backlash-reduced state in which the teeth of the auxiliary drive wheel side (driven side) of the mesh clutch are packed with the teeth of the auxiliary drive force transmission shaft side (driving side), torque is input to the driving side of the mesh clutch to eliminate the backlash-reduced state. Then, the mesh clutch is switched to the released state by the switching operation to the released state of the mesh clutch that has already been performed. Therefore, when the two-wheel drive state is selected, the switching performance of the mesh clutch to the released state can be improved. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of a schematic configuration of a vehicle to which the present invention is applied; [Diagram 2] FIG. 2 is a schematic diagram for explaining the general configuration of a transfer case. [Diagram 3] 4 is a flowchart illustrating a main portion of the control operation of the electronic control device, and is a flowchart illustrating the control operation for improving the switching performance of the EDD to the released state when the 2WD state is selected. [Figure 4] FIG. 4 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 3 is executed, and is a diagram illustrating the control for temporarily setting the vehicle in a 4WD state, which is executed when the vehicle starts moving. [Diagram 5] 4A and 4B are diagrams showing examples of time charts when the control operation shown in the flowchart of FIG. 3 is executed, in which (a) illustrates the suspension of the control for temporarily switching to 4WD mode, which is performed when starting off, and (b) illustrates the control for temporarily switching to 4WD mode, which is performed when accelerating. 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 a schematic configuration of a vehicle 10 to which the present invention is applied. In FIG. 1, the vehicle 10 is equipped with an engine 12 as a power source, front wheels 14 (14L, 14R), rear wheels 16 (16L, 16R), a power transmission device 18 for transmitting the power of the engine 12 to the front wheels 14 and the rear wheels 16, respectively. The rear wheels 16 are main drive wheels that serve as drive wheels both during two-wheel drive (2WD) running and during four-wheel drive (4WD) running. The front wheels 14 are auxiliary drive wheels that serve as driven wheels during 2WD running and as drive wheels during 4WD running. The vehicle 10 is a 4WD vehicle based on a front-mounted engine, rear-wheel drive (FR) system.

[0011] The power transmission device 18 includes a transmission 20 connected to the engine 12, a transfer 22 connected to the transmission 20, a front propeller shaft 24 and a rear propeller shaft 26 each connected to the transfer 22, a front differential 28 connected to the front propeller shaft 24, a rear differential 30 connected to the rear propeller shaft 26, front drive shafts 32 (32L, 32R) connected to the front differential 28, and rear drive shafts 34 (34L, 34R) connected to the rear differential 30. The transfer 22 is a driving force distribution device that distributes a portion of the power of the engine 12 to the front wheels 14.

[0012] The front differential 28 includes a differential ring gear 28a, a differential case 28b, a differential side gear 28c, a differential pinion 28d, a pinion shaft 28e, an EDD 36, and the like.

[0013] The EDD 36 is an internal differential power disconnect / connect mechanism, and is a dog clutch (i.e., a meshing clutch) that selectively connects or disconnects the power transmission path between the differential case 28b and the pinion support member 28f (i.e., between the front propeller shaft 24 and the front wheels 14).

[0014] The EDD 36 includes a plurality of output side meshing teeth 36o (see FIG. 4 described later) formed on the pinion support member 28f, a movable sleeve 36s on which a plurality of input side meshing teeth 36i (see FIG. 4 described later) capable of meshing with the output side meshing teeth 36o are formed, and an actuator 38 that moves the movable sleeve 36s in the axial direction of the front drive shaft 32 to a meshed position (an engaged state of the EDD 36) and a non-meshed position (a released state of the EDD 36). The input side meshing teeth 36i are meshed teeth on the front propeller shaft 24 side, i.e., the driving side. The output side meshing teeth 36o are meshed teeth on the front wheels 14 side, i.e., the driven side.

[0015] The actuator 38 includes a magnetic plunger (not shown), an electromagnetic coil 38c, and a disc spring 38s (see FIG. 4 described later). When a driving current is supplied from an electronic control device 80 (described later), the electromagnetic coil 38c generates a predetermined amount of thrust in the magnetic plunger. The actuator 38 is a device that uses the thrust to move the movable sleeve 36s to the meshing position of the EDD 36. The disc spring 38s is a return spring that constantly urges the movable sleeve 36s to return to the non-meshing position of the EDD 36.

[0016] FIG. 2 is a schematic diagram for explaining the schematic configuration of the transfer 22. In FIG. 2, the transfer 22 includes a transfer case 40. The transfer 22 includes an input shaft 42, a rear-wheel output shaft 44, a drive gear 46, a high / low switching mechanism 48 that changes the speed of the rotation of the input shaft 42 and transmits it to the rear-wheel output shaft 44, and a front-wheel drive clutch 50, all of which are arranged around a common axis C1 within the transfer case 40. The transfer 22 also includes a front-wheel output shaft 52 and a driven gear 54 that is integral with the front-wheel output shaft 52, all of which are arranged around a common axis C2 within the transfer case 40. The transfer 22 also includes a front-wheel drive chain 56 that connects the drive gear 46 and the driven gear 54, and a differential lock mechanism 58 that connects the rear-wheel output shaft 44 and the drive gear 46 together.

[0017] The input shaft 42 is connected to the transmission 20. The rear-wheel output shaft 44 is a main driving force transmission shaft connected to the rear propeller shaft 26, which transmits the power of the engine 12 to the rear wheels 16. The drive gear 46 is provided so as to be rotatable relatively around the rear-wheel output shaft 44. The front-wheel output shaft 52 is an auxiliary driving force transmission shaft connected to the front propeller shaft 24, which transmits a portion of the power of the engine 12 distributed by the transfer 22 to the front wheels 14. The front propeller shaft 24 also functions as an auxiliary driving force transmission shaft.

[0018] The differential lock mechanism 58 has lock teeth 60 fixed to the inner peripheral surface of the drive gear 46, and a lock sleeve 62 having outer peripheral teeth 62a fixed to its outer peripheral surface that mesh with the lock teeth 60 by moving in a direction parallel to the axis C1. When the differential lock mechanism 58 is in an engaged state in which the outer peripheral teeth 62a mesh with the lock teeth 60, the rear wheel side output shaft 44 and the drive gear 46 of the transfer 22 are rotated integrally, creating a so-called center differential lock state.

[0019] The front-wheel drive clutch 50 is equipped with a friction engagement element 64, a piston 66 that presses the friction engagement element 64, and the like, and is a multiple-plate friction clutch that adjusts the transmission torque (torque capacity) transmitted from the rear-wheel output shaft 44 to the drive gear 46. The front-wheel drive clutch 50 is in a released state when the piston 66 is not in contact with the friction engagement element 64. On the other hand, when the piston 66 is in contact with the friction engagement element 64, the front-wheel drive clutch 50 has the transmission torque adjusted depending on the amount of movement of the piston 66, and is in a released state, a slip state, or an engaged state.

[0020] The transfer 22 is equipped with a motor 68, a screw mechanism 70 that converts the rotational motion of the motor 68 into linear motion, a transmission mechanism 72 that transmits the linear force of the screw mechanism 70 to the high-low switching mechanism 48, the front-wheel drive clutch 50, and the differential lock mechanism 58, respectively, a worm gear 74, and a gear position holding mechanism 76, as devices for operating the high-low switching mechanism 48, the front-wheel drive clutch 50, and the differential lock mechanism 58.

[0021] When the front-wheel drive clutch 50 is in a disengaged state and the differential lock mechanism 58 is in a disengaged state, the power transmission path between the rear-wheel output shaft 44 and the drive gear 46 is interrupted, and the transfer 22 transmits the power transmitted from the transmission 20 only to the rear wheels 16. When the front-wheel drive clutch 50 is in a slipping state or an engaged state, or when the differential lock mechanism 58 is in an engaged state, the transfer 22 distributes the power transmitted from the transmission 20 to each of the front wheels 14 and the rear wheels 16. When the front-wheel drive clutch 50 is in a slipping state, the transfer 22 establishes a non-center differential lock state. When the front-wheel drive clutch 50 is in an engaged state, or when the differential lock mechanism 58 is in an engaged state, the transfer 22 establishes a center differential lock state.

[0022] The front-wheel drive clutch 50 and the differential lock mechanism 58 are engagement devices that connect and disconnect the power transmission path between the rear-wheel output shaft 44 and the front-wheel output shaft 52 (i.e., the front propeller shaft 24). The vehicle 10 can be selectively switched between a 2WD state in which the power of the engine 12 is transmitted to the rear wheels 16 by disengaging the front-wheel drive clutch 50, the differential lock mechanism 58, and the EDD 36, and a 4WD state in which the power of the engine 12 is transmitted to the rear wheels 16 and the front wheels 14 by engaging the front-wheel drive clutch 50 (or the differential lock mechanism 58) and the EDD 36 (including the front-wheel drive clutch 50 in a slip state).

[0023] 1, the vehicle 10 is provided with an electronic control device 80 as a control device that performs control for switching between the 2WD state and the 4WD state, etc. The electronic control device 80 includes a so-called microcomputer equipped with, for example, a CPU, a RAM, a ROM, an input / output interface, etc.

[0024] The electronic control device 80 receives various signals based on detection values ​​from various sensors (e.g., each wheel speed sensor 82, an accelerator opening sensor 84, a G sensor 86, a steering sensor 88, a vehicle weight sensor 90, a transfer position switch 92, an EDD position switch 94, a 4WD selection switch 96, etc.) provided in the vehicle 10. The electronic control device 80 receives various signals (e.g., front wheel speed Nwf (wheel speeds Nwfl, Nwfr of the front wheels 14L, 14R), rear wheel speed Nwr (wheel speeds Nwrl, Nwrr of the rear wheels 16L, 16R), a driver (=driver) and a vehicle speed sensor (=vehicle speed sensor). The vehicle 10 is supplied with the accelerator opening θacc corresponding to an acceleration request amount representing the magnitude of the acceleration operation of the driver, the longitudinal acceleration G of the vehicle 10, the steering angle θsw which is the steering angle of the steering wheel, the vehicle weight WTv which is the weight of the vehicle 10, the transfer position T / F_P / SW which is a signal indicating the state of the front wheel drive clutch 50, the EDD position EDD_P / SW which is a signal indicating the state of the EDD 36, the 4WD request 4WDon which is a signal indicating that the 4WD state has been selected by the driver, etc. The front wheel speed Nwf is, for example, an average value of the wheel speeds Nwfl, Nwfr. The rear wheel speed Nwr is, for example, an average value of the wheel speeds Nwrl, Nwrr, and corresponds to the vehicle speed V.

[0025] When the front wheel drive clutch 50 is in a released position, the transfer position T / F_P / SW indicates a 2WD state, whereas when the front wheel drive clutch 50 is in a slip or engaged position, the transfer position T / F_P / SW indicates a 4WD state. When the EDD 36 is in a released position, the EDD position EDD_P / SW indicates a 2WD state, whereas when the EDD 36 is in an engaged position, the EDD position EDD_P / SW indicates a 4WD state.

[0026] The electronic control device 80 outputs various command signals (e.g., EDD operation command signal (current) Sd for switching the state of the EDD 36, motor drive command signal (current) Sm for controlling the amount of rotation of the motor 68, etc.) to each device (e.g., actuator 38 (electromagnetic coil 38c), motor 68, etc.) provided in the vehicle 10.

[0027] Incidentally, when switching to the 2WD state, there is a possibility that the output side meshing teeth 36o of the EDD 36 may be in a state where the input side meshing teeth 36i are packed together to eliminate backlash (see the EDD connection state at time t1 in FIG. 4 described later). In this case, for example, due to insufficient load on the disconnection side of the disc spring 38s, the EDD 36 may not be switched to the released state, and the front wheels 14 may rotate the front propeller shaft 24, the drive gear 46, etc. As a result, for example, in 2WD driving, the running resistance may not be reduced, which may lead to a deterioration in fuel efficiency.

[0028] Therefore, when starting or accelerating, such as when the rear wheels 16 turn first, the electronic control unit 80 temporarily engages the front-wheel drive clutch 50 or the differential lock mechanism 58 (hereinafter, the front-wheel drive clutch 50 also includes a slipping state), thereby inputting torque to the input side engaging tooth 36i, eliminating the backlash-relieving state, and disengaging the EDD 36. In other words, when the electronic control unit 80 operates to switch both the front-wheel drive clutch 50 (or differential lock mechanism 58) and the EDD 36 to the released state due to the selection of switching from the 4WD state to the 2WD state, if the electronic control unit 80 determines that the front-wheel drive clutch 50 (or differential lock mechanism 58) has been switched to the released state, determines that the EDD 36 has not been switched to the released state and is in an engaged state, and determines that either of the following conditions is satisfied: a stop determination condition where the vehicle speed V is less than a predetermined vehicle speed Vf, and an acceleration prediction determination condition where the future acceleration GF based on the accelerator opening θacc is equal to or greater than a predetermined acceleration GFf, the electronic control unit 80 temporarily switches the front-wheel drive clutch 50 (or differential lock mechanism 58) to the engaged state.

[0029] The predetermined vehicle speed Vf is, for example, a predetermined threshold value for determining that the vehicle will stop or that it has stopped. The stopping determination condition is a condition for determining that the vehicle will stop, and is also a condition for determining that a start will be made thereafter. The electronic control device 80 calculates a future acceleration GF, which is the longitudinal acceleration G predicted thereafter, based on, for example, the longitudinal acceleration G, the vehicle speed V, the accelerator opening θacc, and the vehicle weight WTv. The predetermined acceleration GFf is, for example, a predetermined threshold value for determining that acceleration will be made. The acceleration prediction determination condition is a condition for determining that acceleration will be made thereafter.

[0030] FIG. 3 is a flowchart explaining the main parts of the control operation of the electronic control device 80, and is a flowchart explaining the control operation for improving the switching performance of the EDD 36 to the released state (i.e., the disconnection ability of the EDD 36) when the 2WD state is selected. For example, when the front-wheel drive clutch 50 is in a slipping state or an engaged state and the 4WD request 4WDon is released in response to the operation of the 4WD selection switch 96, the control operation is repeatedly executed when switching to the 2WD state.

[0031] In FIG. 3, first, in step (hereinafter, step will be omitted) S10, the display of the 4WD indicator (not shown) is switched. Next, in S20, the actuator 38 switches the EDD 36 to the released state. Also, the motor 68 switches the front wheel drive clutch 50 to the released state. Next, in S30, it is determined whether the transfer position T / F_P / SW is in the 2WD state or not, or whether the EDD position EDD_P / SW is in the 2WD state or not. If the determination in S30 is negative, this S30 is repeatedly executed. If the determination in S30 is positive, in S40, the display of the 4WD indicator is switched to "2WD". Next, in S50, it is determined whether the EDD position EDD_P / SW is in the 4WD state or not. If the determination in S50 is negative, this routine is terminated. If the determination in S50 is positive, then in S60, it is determined whether the vehicle speed V is less than a predetermined vehicle speed Vf or whether the future acceleration GF is equal to or greater than a predetermined acceleration GFf. If the determination in S60 is negative, then in S60, it is determined whether the steering angle θsw is less than a predetermined steering angle θswf. When the control for temporarily setting the vehicle in the 4WD state is performed, the driver is assumed to be in the 2WD state, so that the driver may feel uncomfortable due to a phenomenon specific to the 4WD state (slip, steering force change). The predetermined steering angle θswf is, for example, a predetermined threshold value for determining that such discomfort may be felt. If the determination in S70 is negative, then the above S60 is executed. If the determination in S70 is positive, then in S80, the diff-lock mechanism 58, which is a T / F synchronization mechanism, is engaged, that is, connected. Next, in S90, it is determined whether the vehicle speed V is equal to or greater than a predetermined vehicle speed Vf, or whether the longitudinal acceleration G, which is the actual acceleration, is equal to or greater than a predetermined actual acceleration Gf, or whether the steering angle θsw is equal to or greater than a predetermined steering angle θswf. The predetermined actual acceleration Gf is, for example, a predetermined threshold value for determining that acceleration has occurred. If the determination in S90 is negative, S90 is repeatedly executed. If the determination in S90 is positive, the differential lock mechanism 58 is released, that is, disengaged, in S100.In this way, when the steering angle θsw is equal to or greater than the predetermined steering angle θswf, the electronic control unit 80 temporarily stops the control for the 4WD state. This makes it possible to improve the disconnection of the EDD 36 and eliminate the discomfort described above. In addition, the electronic control unit 80 releases the connection of the diff-lock mechanism 58 after starting or accelerating. This makes it possible to improve the disconnection of the EDD 36. Next, in S110, it is determined whether the EDD position EDD_P / SW is in the 2WD state. If the determination in S110 is positive, this routine is terminated. In this way, when the EDD 36 is disconnected, the electronic control unit 80 temporarily stops or terminates the control for the 4WD state. This makes it possible to improve the disconnection of the EDD 36 and eliminate the discomfort described above. It is possible to avoid unnecessary control and reduce the probability of causing discomfort to the driver. On the other hand, if the determination in S110 is negative, in S120, the predetermined acceleration GFf, which is the threshold value of the future acceleration GF, is updated by learning. The electronic control device 80 learns the longitudinal acceleration G required for disconnection using the success / failure of disconnection of the EDD 36 and the longitudinal acceleration G during acceleration, and corrects the predetermined acceleration GFf. This makes it possible to improve the disconnection performance of the EDD 36 and eliminate the discomfort described above. It is possible to avoid unnecessary control and reduce the probability of causing discomfort to the driver. Next, the above-mentioned S60 is executed.

[0032] FIG. 4 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 3 is executed, and is a diagram explaining the control to temporarily set the state to 4WD state, which is executed when starting. In FIG. 4, at time t1, when switching from 4WD state to 2WD state with the operation of the 4WD selection switch 96, the front wheel drive clutch 50 is switched to the released state, but the EDD 36 is in a state in which the output side meshing teeth 36o are closed against the input side meshing teeth 36i, and cannot be switched to the released state. At time t2, in the 4WD state with the EDD position EDD_P / SW, the vehicle speed V is made less than a predetermined vehicle speed Vf, so that the differential lock mechanism 58, which is the T / F_2-4WD switching mechanism, is engaged, and the state is temporarily switched to 4WD state. At time t3, it is shown that the play-reduced state in the EDD 36 is eliminated, that is, the meshing is released, as starting is started. At time t4, the EDD 36 is disengaged and the EDD position EDD_P / SW is set to the 2WD state. At time t5, the vehicle speed V is equal to or higher than the predetermined vehicle speed Vf, so that the differential lock mechanism 58 is disengaged and the vehicle is returned to the 2WD state.

[0033] FIG. 5 is a diagram showing an example of a time chart when the control operation shown in the flowchart of FIG. 3 is executed, where (a) is a diagram explaining the suspension of the control to temporarily switch to 4WD state, which is performed when starting off, and (b) is a diagram explaining the control to temporarily switch to 4WD state, which is performed when accelerating.

[0034] 5A, time t1a indicates that in the 4WD state with the EDD position EDD_P / SW, the vehicle speed V becomes less than a predetermined vehicle speed Vf, so the differential lock mechanism 58 is engaged and the vehicle is temporarily switched to the 4WD state. Time t2a indicates that the steering angle θsw becomes equal to or greater than a predetermined steering angle θswf, so the differential lock mechanism 58 is disengaged and the control to temporarily switch to the 4WD state is stopped.

[0035] In Fig. 5B, at time t1b, in the 4WD state with the EDD position EDD_P / SW, the future acceleration GF becomes equal to or greater than a predetermined acceleration GFf, so that the differential lock mechanism 58 is engaged and the state is temporarily switched to the 4WD state. At time t2b, the EDD 36 is disengaged and the EDD position EDD_P / SW is in the 2WD state. At time t3b, the longitudinal acceleration G becomes equal to or greater than a predetermined actual acceleration Gf, so that the differential lock mechanism 58 is disengaged and the state is returned to the 2WD state.

[0036] As described above, according to this embodiment, when starting or accelerating is performed in a state where the output side meshing teeth 36o are close to the input side meshing teeth 36i, torque is input to the drive side of the EDD 36 to eliminate the backlash-reduced state. Then, the EDD 36 is switched to the released state by the switching operation to the released state of the EDD 36 that has already been performed. Therefore, when the 2WD state is selected, the switching performance of the EDD 36 to the released state can be improved.

[0037] 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.

[0038] For example, in the above-mentioned embodiment, the electronic control device 80 may temporarily stop the control for the 4WD state when the front and rear wheel speed difference is equal to or greater than a predetermined value. The present invention may also be applied to a 4WD vehicle based on a front-mounted engine, front-wheel drive (FF) system. The front-wheel drive clutch 50 may be of a wet or dry type, and may be replaced with an electromagnetic clutch, an electronically controlled coupling, a dog clutch with a synchronizer ring, or the like. The meshing clutch that disconnects the power transmission path between the front propeller shaft 24 and the front wheels 14 may be an external differential power disconnection / connection mechanism (ADD) instead of the EDD 36. The actuator 38 may not include the disc spring 38s, and may be configured with a thrust generating mechanism for pulling out of the meshing state by a motor or an electromagnetic clutch.

[0039] 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]

[0040] 10: vehicle (four-wheel drive vehicle) 12: engine (power source) 14 (14L, 14R): front wheels (auxiliary drive wheels) 16 (16L, 16R): rear wheels (main drive wheels) 22: transfer (driving force distribution device) 24: front propeller shaft (auxiliary drive force transmission shaft) 36: EDD (mesh clutch) 44: rear wheel side output shaft (main drive force transmission shaft) 50: front wheel drive clutch (engagement device) 52: front wheel side output shaft (auxiliary drive force transmission shaft) 58: differential lock mechanism (engagement device) 80: electronic control device (control device)

Claims

[Claim 1] a main driving force transmission shaft that transmits power of the power source to main driving wheels; a driving force distribution device that distributes a portion of the power of the power source to auxiliary driving wheels; an auxiliary driving force transmission shaft that transmits a portion of the power of the power source distributed by the driving force distribution device to the auxiliary driving wheels; an engagement device that connects and disconnects a power transmission path between the main driving force transmission shaft and the auxiliary driving force transmission shaft; and a mesh clutch that connects and disconnects the power transmission path between the auxiliary driving force transmission shaft and the auxiliary driving wheels, wherein the control device for a four-wheel drive vehicle is capable of selectively switching between a two-wheel drive state in which the power of the power source is transmitted to the main driving wheels by bringing both the engagement device and the mesh clutch into a released state, and a four-wheel drive state in which the power of the power source is transmitted to the main driving wheels and the auxiliary driving wheels by bringing both the engagement device and the mesh clutch into an engaged state, When the engagement device and the dog clutch are both operated to be switched to a released state due to selection of switching from the four-wheel drive state to the two-wheel drive state, determining that the engagement device has been switched to a released state; Furthermore, it is determined that the dog clutch is in an engaged state without being switched to a released state, In addition, when it is determined that either one of the following conditions is satisfied: a stop determination condition that the vehicle speed is less than a predetermined vehicle speed, and an acceleration prediction determination condition that the future acceleration based on the driver's acceleration request amount is equal to or greater than a predetermined acceleration. A control device for a four-wheel drive vehicle, comprising: a control unit for controlling a vehicle in which the engagement device is temporarily switched to an engaged state.

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