JP5282597B2 - Clutch device for four-wheel drive vehicle and driving force distribution method for four-wheel drive vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clutch device for a four-wheel drive vehicle and a drive force distribution method for a four-wheel drive vehicle capable of properly suppressing judders generated by a slip of a wheel of the four-wheel drive vehicle and effectively accelerating the vehicle even under a circumstance where a front wheel and a rear wheel are caused to slip. <P>SOLUTION: The clutch device for the four-wheel drive vehicle is provided with a torque coupling 6 (solenoid clutch 15) provided between an engine 2 and the rear wheel 12r and capable of suppressing differential rotation of a propeller shaft 5 and a pinion shaft 7; and ECU 21 for controlling a torque transmission capacity (friction engagement force of solenoid clutch 15) based on the traveling state. Further, the ECU 21 reduces target torque when a speed difference &Delta;W of the front and rear wheels is vibrated so as to clamp zero and the amplitude is enlarged before and after a size relationship of a front wheel speed Vf of the front wheel 12f and a rear wheel speed Vr of the rear wheel 12r is reversed at acceleration in the four-wheel driving state that the torque transmission capacity is larger than "0". <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a clutch device and a driving force distribution method for distributing a driving force of a driving source of a four-wheel drive vehicle to a front wheel side and a rear wheel side.

  Conventionally, a drive source and an auxiliary drive wheel in a four-wheel drive vehicle having a main drive wheel to which the torque of the drive source is constantly transmitted and an auxiliary drive wheel to which the torque of the drive source is transmitted when necessary according to the state of the vehicle, There is a clutch device provided with a clutch (torque coupling) that is provided between the two and can change torque (torque transmission capacity) that can be transmitted to auxiliary driving wheels. Such a torque coupling includes a cylindrical first rotating member and a shaft-shaped second rotating member that is coaxially disposed in the first rotating member so as to be rotatable. The torque coupling is configured to connect the first rotating member and the second rotating member so that torque can be transmitted by a clutch mechanism provided between the first rotating member and the second rotating member ( For example, see Patent Document 1).

  By the way, in the four-wheel drive vehicle as described above, the torque from the engine is reduced due to the backlash of the gear and the twist of the propeller shaft in the driving force transmission system that transmits the engine torque to the front wheels and the rear wheels. The time until it is transmitted to the rear wheel is different from the time until it is transmitted to the rear wheel. For example, in a four-wheel drive vehicle based on a front-wheel drive vehicle having a front wheel as a main drive wheel and a rear wheel as an auxiliary drive wheel, the driving force transmission path from the engine to the front wheel is generally between the engine and the rear wheel. It is shorter than the driving force transmission path. Therefore, the torque from the engine is transmitted to the front wheels earlier than the rear wheels.

  Here, consider a case where the driver suddenly depresses the accelerator greatly in the four-wheel drive vehicle based on the front wheel drive vehicle. As described above, since the torque from the engine is transmitted to the front wheels quickly, the front wheel speed Vf indicated by the solid line in FIG. 5 increases faster than the rear wheel speed Vr indicated by the broken line in FIG. At this time, in a state where the front wheels are gripped on the road surface, torsion is accumulated in each driving force transmission member constituting the driving force transmission system as the torque to the front wheels increases.

  When the accelerator is depressed greatly, the torque of the front wheels becomes excessive, and the driving force of the front wheels (the force by which the front wheels move the vehicle) becomes larger than the friction force between the front wheels and the road surface. Slips. Due to the slip of the front wheel, the torsion of the driving force transmission system is released and vibration is generated.

  On the other hand, since torque is transmitted to the rear wheels later than the front wheels, the torque of the rear wheels tends to increase when the front wheels slip and the torque of the front wheels tends to decrease. At this time, as in the case of the front wheels, in the state where the rear wheels are gripped on the road surface, twist is accumulated in each driving force transmission member as the torque of the rear wheels increases. When the torque of the engine distributed to the front wheels is further reduced due to the increase in the torque of the rear wheels and the driving force of the front wheels becomes smaller than the frictional force between the front wheels and the road surface, the slip of the front wheels is settled and gripped. .

  However, when the front wheel torque starts to increase again, the rear wheel torque becomes excessive and the rear wheel slips. Due to the slip of the rear wheel, the twist of the driving force transmission member is released and vibration is generated. Then, when the rear wheel slip is settled and the rear wheel torque begins to increase again, the front wheel slips again.

  In this way, the front and rear wheel slips are repeated alternately with the fluctuations in the torque of the front and rear wheels, and the torsion stored in each driving force transmitting member is released by this slip, so-called judder occurs. End up.

  Therefore, in the driving force distribution control device described in Patent Document 2, these slips are detected based on the angular acceleration of the front wheels and the rear wheels, and when all the front wheels and the rear wheels are slipping, the electromagnetic force of the transfer clutch is detected. The torque applied to the rear wheel is cut off by setting the current applied to the coil to zero. Thus, by eliminating torque transmission to the rear wheel, the rear wheel is prevented from slipping and the judder is prevented.

Japanese Patent Laying-Open No. 2005-3167 JP 2002-293150 A (paragraph [0030] etc.)

  By the way, as in Patent Document 2, judder can be eliminated by interrupting torque transmission to the rear wheels when the front and rear wheels slip, but two-wheel drive in which driving force is transmitted only to the front wheels. Therefore, the traction necessary for acceleration (the frictional force for transmitting the driving force from the wheel tire surface to the road surface) cannot be sufficiently obtained. As a result, even if the judder is temporarily eliminated, the front wheel will idle, and if the transfer clutch is controlled to distribute the torque to the rear wheel in order to suppress this idling, the phenomenon that judder will occur again. Can happen. In such a case, there is a problem that it is difficult to accelerate the vehicle.

  The present invention has been made to solve the above-described problems, and its object is to appropriately suppress judder caused by slipping of wheels of a four-wheel drive vehicle, and to prevent front wheels and rear wheels from being generated. An object of the present invention is to provide a clutch device for a four-wheel drive vehicle and a distribution of driving force for the four-wheel drive vehicle that can effectively accelerate the vehicle even in a situation where the vehicle slips.

  In order to achieve the above object, the invention described in claim 1 is directed to a first driving wheel and a front wheel side which are a pair of left and right driving wheels on either the front wheel side or the rear wheel side. A first drive shaft that is disposed in a drive force transmission system of a four-wheel drive vehicle that is distributed to a second drive wheel that is a pair of left and right drive wheels on the other side of the rear wheel side, and that is coupled to the first drive wheel; A clutch for a four-wheel drive vehicle, comprising: a clutch capable of suppressing differential rotation with a second drive shaft coupled to the second drive wheel; and a control device that controls an engagement force of the clutch based on a running state. The control device is a front-rear wheel speed that is a difference between a wheel speed of the first drive wheel and a wheel speed of the second drive wheel during acceleration in a four-wheel drive state in which the clutch is engaged. The difference vibrates across zero, the amplitude is equal to or greater than a predetermined threshold, and the wheel speed of the first drive wheel When the magnitude relationship between the wheel speed of the second drive wheel is enlarged before and after inversion, the gist reducing the engaging force of the clutch.

  According to the above configuration, vibration is generated in the driving force transmission system, and for example, the resonance is generated by synchronizing the natural frequency of the driving force transmission member with the period in which the front wheel and the rear wheel slip, so that the vibration is generated. It is possible to reliably capture a large state and suppress judder that has a large influence on the vehicle. Even if the vibration becomes large at a certain point in time, for example, when the vibration is converging without expanding, vibration suppression control is not performed, and the engagement force of the clutch is maintained, so that the traction necessary for acceleration is reduced. Can be secured. Therefore, vibration suppression control is not performed more than necessary, and the vehicle can be effectively accelerated. Therefore, it is possible to appropriately suppress the judder caused by the slip of the wheels of the four-wheel drive vehicle, and to effectively accelerate the vehicle even in a situation where the front wheels and the rear wheels slip.

  According to a second aspect of the present invention, in the clutch device for a four-wheel drive vehicle according to the first aspect, the control device performs the first operation after the amplitude of the front-rear wheel speed difference becomes greater than a first predetermined threshold. The magnitude relationship between the wheel speed of one driving wheel and the wheel speed of the second driving wheel is reversed, and then the amplitude of the difference between the front and rear wheel speeds exceeds a second predetermined threshold value that is larger in absolute value than the first predetermined threshold value. The gist of the present invention is to reduce the engagement force of the clutch when the torque becomes large.

  According to the above configuration, when the magnitude relationship between the wheel speed of the first driving wheel and the wheel speed of the second driving wheel is reversed once, and the amplitude of the front and rear wheel speed difference is increased at that time, Since the engagement force is reduced, judder having a great influence on the vehicle can be quickly suppressed.

  According to a third aspect of the present invention, in the clutch device for a four-wheel drive vehicle according to the first aspect, the control device is configured such that the amplitude of the front-rear wheel speed difference is greater than or equal to the first predetermined threshold value. The gist is to reduce the engagement force of the clutch when the amplitude of the front-rear wheel speed difference becomes greater than or equal to the second predetermined threshold value within a predetermined time.

  According to the above configuration, since the time until the amplitude of the front and rear wheel speed difference becomes larger than the first predetermined threshold and becomes larger than the second predetermined threshold is added as a condition, it is caused by a delay in torque transmission. Thus, it is possible to reliably detect judder generated in the driving force transmission system and to avoid erroneous determination.

  According to a fourth aspect of the present invention, in the clutch device for a four-wheel drive vehicle according to the first aspect, the control device is configured such that the amplitude of the front-rear wheel speed difference is reversed before and after the magnitude relationship is reversed. The gist is to reduce the engagement force of the clutch when it is continuously expanded a plurality of times so that the absolute value is greater than or equal to the immediately-preceding threshold value which is larger than the immediately preceding threshold value.

  According to the above configuration, when the magnitude relationship between the wheel speed of the first driving wheel and the wheel speed of the second driving wheel is reversed a plurality of times and the amplitude of the front and rear wheel speed difference is continuously increased a plurality of times, In order to reduce the engagement force, it is possible to reliably detect only judder that has a great influence on the vehicle and to suppress the judder appropriately.

  According to a fifth aspect of the present invention, in the clutch device for a four-wheel drive vehicle according to the fourth aspect, the control device has an amplitude of the difference between the front and rear wheel speeds before and after the magnitude relationship is reversed a plurality of times. The gist is to reduce the engagement force of the clutch when it becomes greater than or equal to the immediately following threshold value within a predetermined time after becoming greater than or equal to the immediately preceding threshold value.

  According to the above configuration, since the time from when the amplitude of the front and rear wheel speed difference becomes greater than or equal to the immediately preceding threshold to when it becomes greater than or equal to the immediately following threshold is added as a condition, The generated judder can be reliably detected and erroneous determination can be avoided.

  According to the sixth aspect of the present invention, the driving force of the driving source of the vehicle is a first driving wheel which is a pair of left and right driving wheels on either the front wheel side or the rear wheel side, and the other one of the front wheel side and the rear wheel side. A driving force distribution method for a four-wheel drive vehicle that distributes to a second drive wheel that is a pair of left and right drive wheels, wherein the wheel speed of the first drive wheel and the second drive during acceleration in a four-wheel drive state The difference between the front and rear wheel speeds, which is the difference between the wheel speeds of the wheels, vibrates across zero, the amplitude thereof is greater than or equal to a predetermined threshold, and the wheel speeds of the first driving wheel and the second driving wheel are large or small. When the relationship is expanded before and after the relationship is reversed, the gist is to reduce the driving force distribution ratio to the first driving wheel or the second driving wheel.

  According to the above configuration, judder generated due to wheel slip of a four-wheel drive vehicle is appropriately suppressed, and the vehicle is effectively accelerated even in a situation where the front wheels and the rear wheels slip. Can do.

  According to the present invention, judder generated due to wheel slip of a four-wheel drive vehicle is appropriately suppressed, and the vehicle is effectively accelerated even in a situation where the front wheels and the rear wheels slip. It is possible to provide a clutch device for a four-wheel drive vehicle and a driving force distribution method for the four-wheel drive vehicle.

The schematic block diagram of the four-wheel drive vehicle provided with the driving force distribution control apparatus. The block diagram which shows schematic structure of ECU. The flowchart which shows the transfer process procedure of control mode of CPU. (A) Waveform diagram showing relationship between front wheel speed and rear wheel speed and time when judder occurs, (b) Waveform diagram showing relationship between front and rear wheel speed difference and time when judder occurs. The wave form diagram which shows the relationship between front wheel speed and rear-wheel wheel speed, and time when judder generate | occur | produces in the conventional four-wheel drive vehicle.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, the vehicle 1 is a four-wheel drive vehicle based on a front wheel drive vehicle. An engine 2 as a drive source is mounted on the front portion (left side in FIG. 1) of the vehicle 1, and a transaxle 3 is assembled to the engine 2. The transaxle 3 has a transmission, a front differential, a transfer, and the like. A pair of left and right front axles 4 and a propeller shaft 5 are connected to the transaxle 3. The propeller shaft 5 can be connected to a pinion shaft (drive pinion shaft) 7 via a torque coupling 6, and the pinion shaft 7 is connected to a pair of left and right rear axles 9 via a rear differential 8. The torque coupling 6 is housed in a differential carrier 11 that is fixed to a frame (not shown) of the vehicle 1 together with the rear differential 8.

  That is, the torque of the engine 2 is always transmitted to the front wheels 12 f via the transaxle 3 and the front axle 4. Further, when the propeller shaft 5 and the pinion shaft 7 are coupled by the torque coupling 6 so that torque can be transmitted, the torque of the engine 2 is transmitted via the propeller shaft 5, the pinion shaft 7, the rear differential 8 and the rear axle 9. It is transmitted to the wheel 12r.

  Therefore, in the present embodiment, the front wheels 12f are configured as main driving wheels to which driving force is always transmitted, and the rear wheels 12r are configured as auxiliary driving wheels to which driving force is transmitted when necessary. Also, the torque of the engine 2 is transmitted to the front wheels 12f and the rear wheels 12r by the driving force transmission members of the transaxle 3, the front axle 4, the propeller shaft 5, the torque coupling 6, the pinion shaft 7, the rear differential 8, and the rear axle 9. A driving force transmission system is configured. In the present embodiment, torque from the engine 2 is transmitted to the front wheel 12f earlier than the rear wheel 12r due to gear backlash in the driving force transmission system, torsion of the propeller shaft 5, and the like. ing.

  The torque coupling 6 includes an electromagnetic clutch 15. The electromagnetic clutch 15 changes the frictional engagement force between the respective clutch plates provided on the propeller shaft 5 side and the pinion shaft 7 side according to the amount of current supplied to the electromagnetic coil 16 provided in the electromagnetic clutch 15. The clutch mechanism is configured to transmit torque based on the frictional engagement force from the input-side propeller shaft 5 to the output-side pinion shaft 7. That is, the torque coupling 6 (electromagnetic clutch 15) adjusts the torque that can be transmitted to the rear wheel 12r, that is, the torque transmission capacity.

  Specifically, when the electromagnetic coil 16 is energized and the electromagnetic clutch 15 is operated, the differential rotation between the propeller shaft 5 and the pinion shaft 7 is suppressed by the frictional engagement force between the clutch plates. When the energizing current to the electromagnetic coil 16 increases and the frictional engagement force between the clutch plates of the electromagnetic clutch 15 becomes larger than the torque transmitted to the rear wheel 12r, the propeller shaft 5 and the pinion shaft 7 rotate integrally. Further, when the current applied to the electromagnetic coil 16 is reduced with respect to the torque of the engine 2 to reduce the frictional engagement force between the clutch plates, the torque transmitted to the pinion shaft 7 is reduced. As a result, the driving force distribution ratio to the front wheels 12f increases, while the driving force distribution ratio to the rear wheels 12r decreases. That is, by increasing or decreasing the energization current to the electromagnetic coil 16, it is possible to control the driving force distribution ratio to the front and rear wheels.

Next, an electrical configuration for controlling the torque coupling 6 provided in the vehicle 1 as described above will be described.
An ECU (electronic control device) 21 as a control device is connected to the torque coupling 6. As shown in FIG. 2, the ECU 21 is composed mainly of a microcomputer 22 and a drive circuit 23.

  The microcomputer 22 includes a CPU 25 that performs various calculations, a ROM 26 that stores control programs, a RAM 27 that functions as a work area for the CPU 25, and an input / output circuit (I / O) 28. The CPU 25, ROM 26, RAM 27 and input / output circuit 28 exchange data with each other via a bidirectional bus. The CPU 25 includes a timer 29. The timer 29 measures time based on a command from the CPU 25.

  The ECU 21 supplies a drive current to the electromagnetic coil 16 of the electromagnetic clutch 15 provided in the torque coupling 6 according to the running state of the vehicle 1 by the operation of the microcomputer 22 and the drive circuit 23, and torque is supplied through this current supply. The torque transmission capacity is changed by controlling the operation of the coupling 6 (engagement force of the electromagnetic clutch 15). That is, the torque coupling 6 and the ECU 21 constitute a clutch device for a four-wheel drive vehicle.

  Specifically, as shown in FIGS. 1 and 2, the CPU 25 is connected to the accelerator opening sensor 31 and the wheel speed sensors 32 a to 32 d via the input / output circuit 28. Information on the current accelerator opening degree Sa from the accelerator opening degree sensor 31 is input to the CPU 25, and the respective right front wheel speed Vfr, left front wheel speed Vfl, and right rear wheel speed Vrr are respectively input from the wheel speed sensors 32a to 32d. And information of the left rear wheel speed Vrl is input.

  The CPU 25 determines the front wheel speed Vf, the rear wheel speed Vr, the vehicle speed V, the front wheel 12f and the rear wheel 12r based on the wheel speeds Vfr, Vfl, Vrr, Vrl detected by the wheel speed sensors 32a to 32d, respectively. A front-rear wheel speed difference ΔW is calculated. In the present embodiment, the CPU 25 sets the average value of the right front wheel speed Vfr and the left front wheel speed Vfl as the front wheel speed Vf, and sets the average value of the right rear wheel speed Vrr and the left rear wheel speed Vrl as the rear wheel speed Vr.

  When the front wheel 12f is the first drive wheel of the present invention, the wheel speed of the first drive wheel is represented by the front wheel speed Vf, and the propeller shaft 5 is configured as the first drive shaft. In this case, the rear wheel 12r becomes the second drive wheel, the wheel speed of the second drive wheel is represented by the rear wheel speed Vr, and the pinion shaft 7 is configured as the second drive shaft. However, the present invention uses the front wheel 12f as the second drive wheel of the present invention, the propeller shaft 5 as the second drive shaft, the rear wheel 12r as the first drive wheel of the present invention, and the pinion shaft 7 as the first drive shaft. Can also be interpreted.

  Further, the CPU 25 sets the rear wheel speed Vr as the vehicle speed V, and sets the difference between the front wheel speed Vf and the rear wheel speed Vr as the front-rear wheel speed difference ΔW. The front-rear wheel speed difference ΔW is positive when the front wheel speed Vf is higher than the rear wheel speed Vr. Then, the CPU 25 calculates a control target value (target torque τp) of the torque transmission capacity based on the vehicle speed V, the front and rear wheel speed difference ΔW, and the accelerator opening degree Sa.

  Specifically, the CPU 25 refers to a predetermined torque map stored in the ROM 26 so that the first torque based on the vehicle speed V and the accelerator opening degree Sa and the absolute values of the vehicle speed V and the front-rear wheel speed difference ΔW are calculated. The second torque corresponding to the magnitude is calculated. Subsequently, the CPU 25 adds the first torque and the second torque to calculate a target torque τp corresponding to the vehicle speed V and accelerator opening degree Sa and the front-rear wheel speed difference ΔW. The torque map is set so that the first torque increases as the vehicle speed V decreases and the accelerator opening degree Sa increases, and the second torque increases as the vehicle speed V decreases and the front / rear wheel speed difference ΔW increases. It is set to become.

  Then, the CPU 25 supplies current to the electromagnetic coil 16 of the electromagnetic clutch 15 so as to generate a frictional engagement force corresponding to the determined target torque τp, thereby operating the torque coupling 6, that is, the front wheel 12f. The driving force distribution ratio with the rear wheel 12r is controlled.

Next, vibration suppression control that suppresses repeatedly generated vibration, so-called judder, by the front wheel 12f and the rear wheel 12r slipping alternately will be described.
In the CPU 25 of this embodiment, the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr is reversed, the amplitude (absolute value) of the front and rear wheel speed difference ΔW before and after the reversal is equal to or greater than a predetermined threshold, and before the reversal. It is determined whether or not the amplitude after inversion becomes larger than the amplitude of. That is, it is detected that the amplitude of the front-rear wheel speed difference ΔW is sequentially increasing beyond a predetermined threshold value, and it is determined that vibration has occurred when this phenomenon is detected. Then, when it is determined that vibration has occurred, the CPU 25 performs vibration suppression control for reducing the target torque τp. For this vibration suppression control, the control mode in which the target torque τp is determined based on the traveling state of the vehicle 1 (vehicle speed V, front and rear wheel speed difference ΔW, and accelerator opening degree Sa) is referred to as normal control.

  More specifically, during normal control, the CPU 25 determines that the amplitude of the front and rear wheel speed difference ΔW is greater than or equal to the immediately preceding threshold value, which is greater than the immediately preceding threshold value before the positive and negative reversal, before and after the sign of the front and rear wheel speed difference ΔW is reversed. In this way, it is determined whether or not judder is generated in the driving force transmission system by continuously enlarging a plurality of times.

  Specifically, the CPU 25 reverses the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr from a state in which the absolute value of the front and rear wheel speed difference ΔW is greater than the first predetermined threshold value W1, and the predetermined time (for example, 200 ms) is reversed. ), It is determined whether the absolute value is larger than the second predetermined threshold value W2 (immediate threshold value) greater than the first predetermined threshold value W1 (immediate threshold value). The predetermined time is, for example, a time substantially equal to the time from when the front wheel speed Vf is higher than the rear wheel speed Vr until it once decreases and becomes higher than the rear wheel speed Vr. It has been demanded. Subsequently, the CPU 25 reverses the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr from a state in which the absolute value of the front-rear wheel speed difference ΔW is greater than the second predetermined threshold value W2, and within a predetermined time, It is determined whether or not the absolute value is greater than a third predetermined threshold W3 (immediate threshold) that is greater than the predetermined threshold W2 (immediate threshold). When this condition is satisfied, the CPU 25 determines that judder having a large influence on the vehicle 1 has occurred due to, for example, resonance, and reduces the target torque τp to be equal to or less than the torque τth. It shifts to the vibration suppression control for suppressing judder.

  Here, the torque τth is a value lower than the time when it is determined that the front wheel 12f and the rear wheel 12r slip, and may be set to 15% of the maximum torque transmission capacity that can be transmitted by the torque coupling 6, for example. A value of 20% of the target torque τp at the time of the determination can also be used. The torque τth may be zero.

  During vibration suppression control, the CPU 25 determines whether or not the accelerator opening Sa is equal to or less than a predetermined accelerator opening Sath. The predetermined accelerator opening degree Sath is the accelerator opening degree when the accelerator pedal (not shown) is hardly depressed by the driver. Then, when the accelerator opening degree Sa is equal to or less than the predetermined accelerator opening degree Sath, the CPU 25 determines that the wheel slip is settled by reducing the output from the engine 2, and shifts to normal control. ing.

  Further, during the vibration suppression control, the CPU 25 determines whether or not the slip of the front wheel 12f and the rear wheel 12r is settled based on the wheel speeds Vfr, Vfl, Vrr, Vrl. Specifically, it is determined whether the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim. When the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim, the CPU 25 determines that the slip of the front wheel 12f and the rear wheel 12r has fallen, and shifts to normal control. It is supposed to be.

Next, the operation of the driving force distribution control apparatus according to the present embodiment will be described with reference to a flowchart showing a processing procedure of the CPU 25 provided in the ECU 21 shown in FIG.
Now, in a state where the vehicle 1 is traveling on a low μ road having a relatively small road friction coefficient μ by a driving operation by the driver, the processing of steps S1 to S8 shown in the flowchart of FIG. 3 is executed in a predetermined cycle. To repeat. Note that the case where the first predetermined threshold value W1 and the third predetermined threshold value W3 are positive values and the second predetermined threshold value W2 is a negative value is described.

  First, in step S1, the CPU 25 acquires various state quantities (accelerator opening Sa, wheel speeds Vfr, Vfl, Vrr, Vrl) from the accelerator opening sensor 31 and the wheel speed sensors 32a to 32d (step S1). . Next, the CPU 25 determines whether or not the state variable St indicating the state of vibration generation and vibration suppression control is “0” (step S2). The state variable St is initialized to “0” when the CPU 25 is activated.

  If the state variable St is “0” in step S2 (step S2: YES), the CPU 25 determines whether or not the front / rear wheel speed difference ΔW is greater than the first predetermined threshold value W1 (step S3). If the front-rear wheel speed difference ΔW is larger than the first predetermined threshold value W1 (step S3: YES), the state variable St is set to “1” (step S4), and the timer 29 is reset (step S5). Here, St = 1 is a state in which it is determined whether or not the front and rear wheel speed difference ΔW is smaller than the second predetermined threshold W2 within a predetermined time thereafter. If the front-rear wheel speed difference ΔW is equal to or smaller than the first predetermined threshold value W1 (step S3: NO), the state variable St remains “0” and the process returns to step S1.

  On the other hand, if the state variable St is not “0” in step S2 (step S2: NO), it is determined whether the state variable St is “1” (step S6). If it is St = 1 (step S6: YES), the CPU 25 executes the processing from step S7 to step S12. From step S7 to step S12, while the time variable t representing the elapsed time since the timer 29 was reset in step S5 is within a predetermined range (t1 ≦ t <t2), the front-rear wheel speed difference ΔW is a second predetermined value. This is a process for determining whether or not the threshold value is less than W2. Here, the time variable t is a variable incremented at a predetermined cycle. The first predetermined time t1 is substantially equal to the time until the front wheel speed Vf is larger than the rear wheel speed Vr until it temporarily decreases, and the second predetermined time t2 is, for example, the front wheel speed. This time is substantially equal to the time from when Vf is larger than the rear wheel speed Vr until it once decreases and then becomes larger than the rear wheel speed Vr again.

  Specifically, if St = 1 (step S6: YES), the CPU 25 determines whether or not the time variable t is equal to or longer than the first predetermined time t1 (step S7), and the time variable t is the first time variable t. If it is equal to or longer than the predetermined time t1 (step S7: YES), it is determined whether or not the time variable t is less than the second predetermined time t2 (step S8). If the time variable t is less than the first predetermined time t1 (step S7: NO), the CPU 25 returns to step S1.

  Subsequently, when the time variable t is less than the second predetermined time t2 (step S8: YES), the CPU 25 determines whether or not the front and rear wheel speed difference ΔW is less than the second predetermined threshold W2 (step S9). ). If the front-rear wheel speed difference ΔW is less than the second predetermined threshold W2 (step S9: YES), the CPU 25 sets the state variable St to “2” (step S10) and resets the timer 29 (step S11). . Here, St = 2 is a state in which it is determined whether or not the front and rear wheel speed difference ΔW is equal to or greater than a third predetermined threshold value W3 within a predetermined time period, and vibration suppression control is performed if the condition is satisfied.

  On the other hand, if the front and rear wheel speed difference ΔW does not become less than the second predetermined threshold W2 (step S9: NO), the CPU 25 returns to step 1. When the time variable t becomes equal to or greater than the second predetermined time t2 (step S8: NO), the CPU 25 determines that no vibration has occurred and sets the state variable St to “0” (step S12), thereby suppressing vibration. Does not transfer to control.

  On the other hand, if not St = 1 in step S6 (step S6: NO), the CPU 25 determines whether the state variable St is “2” (step S13). If it is St = 2 (step S13: YES), the CPU 25 executes the processes of steps S14 to S19. In steps S14 to S19, the front-rear wheel speed difference ΔW is set to the third predetermined threshold value W3 while the time variable t indicating the elapsed time since the timer 29 was reset in step S12 is within a predetermined range (t1 ≦ t <t2). This is a process for determining whether or not the value is larger.

  More specifically, if St = 2 (step S13: YES), the CPU 25 determines whether or not the time variable t is equal to or longer than the first predetermined time t1 (step S14), and the time variable t is the first time variable t. If it is equal to or longer than the predetermined time t1 (step S14: YES), it is determined whether or not the time variable t is smaller than the second predetermined time t2 (step S15). If the time variable t is smaller than the first predetermined time t1 (step S14: NO), the CPU 25 returns to step S1.

  Subsequently, when the time variable t is less than the second predetermined time t2 (step S15: YES), the CPU 25 determines whether or not the front / rear wheel speed difference ΔW is larger than a third predetermined threshold W3 (step S15). S16). If the front and rear wheel speed difference ΔW is larger than the third predetermined threshold W3 (step S16: YES), the CPU 25 sets the state variable St to “3” (step S17) and sets the flag F to 1 (step S18). ). Here, St = 3 is a state in which it is confirmed whether a condition for ending the vibration suppression control is satisfied, and normal control is performed if the condition is satisfied. The flag F is a flag for executing vibration suppression control. By turning this flag F on (F = 1), the CPU 25 changes the target torque τp to a value reduced.

  On the other hand, if the front and rear wheel speed difference ΔW does not become larger than the third predetermined threshold value W3 (step S16: NO), the CPU 25 returns to step 1. Then, when the time variable t becomes equal to or longer than the second predetermined time t2 (step S15: NO), the CPU 25 determines that no vibration has occurred, sets the state variable St to “0” (step S19), and suppresses vibration. Does not transfer to control.

  On the other hand, if it is determined in step S13 that St = 2 is not satisfied (step S13: NO), the CPU 25 executes the processes in steps S20 to S23. Steps S20 to S23 are processes for checking whether or not the condition for ending the vibration suppression control is satisfied, and initializing the state variable St and the flag F if they are satisfied.

  In step S20, it is determined whether or not the accelerator opening degree Sa is equal to or smaller than a predetermined accelerator opening degree Sath (step S20). Here, when the driver returns the accelerator pedal and the accelerator opening degree Sa becomes equal to or smaller than the predetermined accelerator opening degree Sath (step S20: YES), the state variable St and the flag F are initialized (step S22: St = 0, step S23: F = 0), the process is terminated.

  On the other hand, if the driver keeps stepping on the accelerator pedal (step S20: NO), the CPU 25 determines whether the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is equal to or less than the determination value Vlim. Determination is made (step S21). If the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is larger than the determination value Vlim (step S21: NO), the CPU 25 remains on (F = 1) and suppresses vibration. Control continues. On the other hand, if the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is equal to or less than the determination value Vlim (step S21: YES), the state variable St and the flag F are initialized (step S22, step S23), and processing Exit.

  Next, this series of processes will be described in association with waveforms representing temporal changes in the front wheel speed Vf and the rear wheel speed Vr shown in FIG. FIG. 4A is a waveform showing the front wheel speed Vf and the rear wheel speed Vr at the time of sudden start. In the figure, the solid line represents the front wheel speed Vf, and the broken line represents the rear wheel speed Vr. FIG. 4B is a waveform showing the result of calculating the front-rear wheel speed difference ΔW (= Vf−Vr) based on the waveform of FIG.

  In FIG. 4, the time “0” at which the left end of the time axis, which is the horizontal axis, starts sudden start is shown. Since both the front wheel speed Vf and the rear wheel speed Vr have increased from the time “0”, the torque from the engine 2 is transmitted to the front wheel 12f earlier than the rear wheel 12r as described above. The increasing speed of the wheel speed Vf is higher than the increasing speed of the rear wheel speed Vr. Thereafter, according to the principle described above, the front / rear wheel speed difference ΔW vibrates while the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr is reversed. For example, when the period in which the front wheel 12f and the rear wheel 12r slip is synchronized with the natural frequency of the driving force transmission member, resonance occurs, and when the amplitude of the front-rear wheel speed difference ΔW increases, judder is felt by the driver. It becomes like this.

  In the waveform of FIG. 4B, the front-rear wheel speed difference ΔW is larger than the first predetermined threshold value W1 at time ta. Therefore, the state variable St in the time zone before the time ta is “0”, and after the time ta, the state variable St becomes “1” in the process of step S4. Thereafter, the time difference t between the front and rear wheel speeds ΔW is increased by the processing of steps S7 to S10 while the time variable t is not less than the first predetermined time t1 and smaller than the second predetermined time t2 (t1 ≦ t <t2). It is determined whether it becomes smaller than the predetermined threshold W2. In the waveform of FIG. 4B, the front-rear wheel speed difference ΔW swings to the negative side at time tb, and the front-rear wheel speed difference ΔW is smaller than the second predetermined threshold value W2, which is a negative value. Since the time interval between the time ta and the time tb is not less than the first predetermined time t1 and less than the second predetermined time t2, YES is determined in step S9, the state variable St becomes “2” in step 10, and the step In S11, the timer 29 is reset.

  In the waveform of FIG. 4B, the front-rear wheel speed difference ΔW swings to the plus side at time tc, and the front-rear wheel speed difference ΔW is larger than the third predetermined threshold value W3. Since the time interval between the time tb and the time tc is not less than the first predetermined time t1 and less than the second predetermined time t2, it is determined YES in step S16, the state variable St becomes “3” in step 17, and the step In S18, the flag F is set to ON (F = 1). As a result, the target torque τp is changed to a reduced value, and the vibration suppression control is executed, whereby the front / rear wheel speed difference ΔW is reduced and vibration can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) A torque coupling 6 (electromagnetic clutch 15) provided between the engine 2 and the rear wheel 12r and capable of suppressing differential rotation between the propeller shaft 5 and the pinion shaft 7, and a torque transmission capacity based on the running state ECU21 (CPU25) which controls (the friction engagement force of the electromagnetic clutch 15) was provided. Then, the CPU 25 vibrates with the front-rear wheel speed difference ΔW oscillating between zero and a front wheel speed Vf of the front wheel 12f and the rear wheel 12r during acceleration in a four-wheel drive state where the torque transmission capacity is greater than “0”. The target torque τp is reduced when the magnitude relationship with the rear wheel speed Vr is enlarged before and after reversal. For this reason, vibration can be generated in the driving force transmission system, and for example, the state where the vibration is increased due to resonance or the like can be reliably captured, and judder having a large influence on the vehicle can be suppressed. Further, even if the vibration becomes large at a certain point in time, for example, when the vibration is converging without expanding, the vibration suppression control is not performed, and the operation of the torque coupling 6 is maintained and the four-wheel drive state is continued. Thus, the traction necessary for acceleration can be secured. Therefore, vibration suppression control is not performed more than necessary, and the vehicle 1 can be effectively accelerated.

  (2) The CPU 25 reverses the magnitude relationship between the front wheel speed Vf of the front wheel 12f and the rear wheel speed Vr of the rear wheel 12r a plurality of times, and the front-rear wheel speed difference ΔW has a first absolute value that increases in order with the inversion. When the predetermined threshold value W1, the second predetermined threshold value W2, and the third predetermined threshold value W3 are exceeded, the target torque τp is reduced. Therefore, it is possible to reliably detect only the judder whose vibration is increased and has a great influence on the vehicle 1, and to appropriately suppress the judder.

  (3) The CPU 25 increases the amplitude of the front / rear wheel speed difference ΔW within a predetermined time after the amplitude of the front / rear wheel speed difference ΔW becomes greater than or equal to the first predetermined threshold W1. When the value becomes larger than the third predetermined threshold value W3 within a predetermined time after becoming larger than the second predetermined threshold value W2, the target torque τp is reduced. As described above, the amplitude of the front-rear wheel speed difference ΔW increases from the first predetermined threshold W1 or the second predetermined threshold W2 to the second predetermined threshold W2 or the third predetermined threshold W3. Since time is added as a condition, judder generated in the driving force transmission system can be reliably detected.

  (4) The CPU 25 determines the occurrence of judder based on the front and rear wheel speed difference ΔW. In the present embodiment, the target torque τp of the torque coupling 6 is controlled based on the vehicle speed V, the front / rear wheel speed difference ΔW, and the accelerator opening degree Sa, so the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr is There is no need to separately provide components (sensors or the like) for determination, and an increase in cost can be prevented.

  (5) When the accelerator opening degree Sa is equal to or smaller than the predetermined accelerator opening degree Sath, the CPU 25 shifts to normal control. Accordingly, when the accelerator opening degree Sa becomes equal to or less than the predetermined accelerator opening degree Sath and the output from the engine 2 becomes small, so that the slip of the wheel is settled, the shift to the normal control is sufficient to shift to the normal control. Since the torque is distributed to the rear wheel 12r, the traction performance can be improved.

  (6) When the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim, the CPU 25 determines that the slip of the front wheel 12f and the rear wheel 12r has fallen, and shifts to normal control. I migrated. Therefore, when the target torque τp is reduced to a predetermined torque or less and the slip of the front wheels 12f and the rear wheels 12r is settled, a sufficient torque corresponding to the traveling state is distributed to the rear wheels 12r by shifting to the normal control. Therefore, the traction performance can be improved.

In addition, you may implement this embodiment in the following aspects.
In the above embodiment, the CPU 25 sequentially compares the front-rear wheel speed difference ΔW and the first to third predetermined threshold values W1, W2, W3, but is not limited thereto. For example, the front-rear wheel speed difference ΔW is compared with the first predetermined threshold value W1 and the second predetermined threshold value W2, and vibration suppression control is performed when the condition is satisfied. The comparison may be omitted. In this case, the processing from step S13 to step S18 in the flowchart shown in FIG. 3 can be omitted. As a result, when the magnitude relationship between the front wheel speed Vf and the rear wheel speed Vr is reversed once and the amplitude of the front and rear wheel speed difference ΔW is increased, the target torque τp is reduced to reduce the target torque τp. It is possible to quickly suppress judder having a great influence.

  Further, the comparison between the front-rear wheel speed difference ΔW and the first predetermined threshold value W1 and the third predetermined threshold value W3 is performed by omitting the comparison between the front-rear wheel speed difference ΔW and the second predetermined threshold value W2, which is a negative value. The vibration suppression control may be performed when the condition is satisfied. In this case, the processing from step S6 to step S12 in the flowchart shown in FIG. 3 can be omitted.

  In the above embodiment, the CPU 25 calculates the front / rear wheel speed difference ΔW based on the front wheel speed Vf and the rear wheel speed Vr to determine the occurrence of judder, but this is not restrictive. For example, the front-rear wheel speed difference ΔW may be calculated based on the rotational speed on the input side (propeller shaft 5) and the rotational speed on the output side (pinion shaft 7) of the torque coupling 6 to determine the occurrence of judder. Good. In addition to this, the front and rear wheel speed difference ΔW is calculated based on a parameter equivalent to the front wheel speed Vf (rotation speed) and a parameter equivalent to the rear wheel speed Vr (rotation speed) to determine the occurrence of judder. You may do it.

  In the above embodiment, during the vibration suppression control, the CPU 25 shifts to the normal control when the accelerator opening degree Sa is equal to or less than the predetermined accelerator opening degree Sath. When Sa becomes equal to or less than the predetermined accelerator opening degree Sath, it is not necessary to shift to the normal control.

  In the vibration suppression control, the CPU 25 shifts to the normal control when the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim. Not limited to the normal control, the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim.

Furthermore, at the time of vibration suppression control, the CPU 25 may shift to normal control due to requirements other than the above requirements.
In the above embodiment, during the vibration suppression control, the CPU 25 slips the front wheel 12f and the rear wheel 12r when the absolute value of the difference between the front wheel speed Vf and the rear wheel speed Vr is within the determination value ΔVlim. However, it is not limited to this. For example, when the difference between each wheel speed Vfr, Vfl, Vrr, Vrl and the vehicle speed V is within a predetermined value, the slip of the front wheel 12f and the rear wheel 12r may be detected by other methods.

  In the above embodiment, the clutch of the torque coupling 6 is the electromagnetic clutch 15 that is an electromagnetic friction clutch. However, the present invention is not limited to this, and the present invention may be applied to one using a hydraulic clutch or one using a clutch other than a friction clutch.

In the above embodiment, the present invention is applied to the vehicle 1 having the front wheels 12f as the main drive wheels. However, the present invention is not limited thereto, and may be applied to a vehicle having the rear wheels 12r as the main drive wheels.
In the above embodiment, the present invention is applied to the vehicle 1 having the front wheels 12f as the main drive wheels. However, the present invention is not limited to this, and the 1-input 2-output differential limitation that distributes the engine torque to the front wheels and the rear wheels. You may apply to the center differential apparatus with a function. In this case, the clutch may be disposed between the front wheel side drive shaft and the rear wheel side drive shaft, or may be disposed between the input rotation member and one of the front wheel side and rear wheel side drive shafts. . In such a center differential device, substantially equal torque is distributed to the front wheel side and the rear wheel side when the clutch is engaged, but torque to the front wheel side or the rear wheel side is reduced by reducing the clutch engagement force. Since the distribution ratio is low, vibration is suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 2 ... Engine, 4 ... Front axle, 5 ... Propeller shaft, 6 ... Torque coupling, 7 ... Pinion shaft, 8 ... Rear differential, 9 ... Rear axle, 12f ... Front wheel, 12r ... Rear wheel, 15 ... Electromagnetic Clutch, 21 ... ECU, Vfl ... front left wheel speed, Vfr ... front right wheel speed, Vrl ... left rear wheel speed, Vrr ... right rear wheel speed, Vf ... front wheel speed, Vr ... rear wheel speed, W1 ... first Predetermined threshold, W2... Second predetermined threshold, W3... Third predetermined threshold, ΔW.

Claims (6)

The driving force of the vehicle drive source is a first driving wheel which is a pair of left and right driving wheels on either the front wheel side or the rear wheel side, and a first driving wheel which is a pair of left and right driving wheels on the other side of the front wheel side or the rear wheel side. The difference between the first drive shaft connected to the first drive wheel and the second drive shaft connected to the second drive wheel is disposed in the drive force transmission system of the four-wheel drive vehicle distributed to the two drive wheels. A clutch device for a four-wheel drive vehicle, comprising: a clutch capable of suppressing dynamic rotation; and a control device that controls an engagement force of the clutch based on a running state,
The control device has a difference between the front and rear wheel speeds that is the difference between the wheel speed of the first drive wheel and the wheel speed of the second drive wheel during acceleration in a four-wheel drive state in which the clutch is engaged. And the amplitude of the clutch is greater than or equal to a predetermined threshold, and the engaging force of the clutch is increased when the magnitude relationship between the wheel speed of the first driving wheel and the wheel speed of the second driving wheel is reversed. A clutch device for a four-wheel drive vehicle, characterized in that it is reduced.   The control device reverses the magnitude relationship between the wheel speed of the first driving wheel and the wheel speed of the second driving wheel after the amplitude of the difference between the front and rear wheel speeds exceeds a first predetermined threshold, The engagement force of the clutch is reduced when the amplitude of the front-rear wheel speed difference becomes greater than or equal to a second predetermined threshold having an absolute value larger than the first predetermined threshold. The four-wheel drive vehicle clutch device.   In the control device, the amplitude of the front-rear wheel speed difference becomes greater than the second predetermined threshold within a predetermined time after the amplitude of the front-rear wheel speed difference becomes greater than the first predetermined threshold. The clutch device for a four-wheel drive vehicle according to claim 2, wherein the engagement force of the clutch is reduced.   The control device is continuously expanded a plurality of times so that the amplitude of the front and rear wheel speed difference before and after the reversal of the magnitude relationship is equal to or greater than the immediately following threshold value that is larger than the immediately preceding threshold value before the reversing of the magnitude relationship. The clutch device for a four-wheel drive vehicle according to claim 1, wherein the engagement force of the clutch is reduced.   The control device, when before and after the magnitude relationship is reversed a plurality of times, when the amplitude of the front and rear wheel speed difference becomes larger than the immediately preceding threshold within a predetermined time after the amplitude of the front and rear wheel speed becomes larger than the immediately preceding threshold 5. The clutch device for a four-wheel drive vehicle according to claim 4, wherein the engagement force of the clutch is reduced. The driving force of the vehicle drive source is a first driving wheel which is a pair of left and right driving wheels on either the front wheel side or the rear wheel side, and a first driving wheel which is a pair of left and right driving wheels on the other side of the front wheel side or the rear wheel side. A driving force distribution method for a four-wheel drive vehicle that distributes to two drive wheels,
When accelerating in a four-wheel drive state, the front-rear wheel speed difference, which is the difference between the wheel speed of the first drive wheel and the wheel speed of the second drive wheel, vibrates across zero, and the amplitude is not less than a predetermined threshold value. When the magnitude relationship between the wheel speed of the first driving wheel and the wheel speed of the second driving wheel is enlarged before and after reversing, the driving force distribution ratio to the first driving wheel or the second driving wheel is increased. A driving force distribution method for a four-wheel drive vehicle characterized by reducing the driving force.

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