JP2005083464A - Four-wheel drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve travelling stability at a low-medium speed region while improving power driving performance at starting. <P>SOLUTION: A clutch is provided between a transfer and a subsidiary driving wheel for changing over a driving system between two-wheel drive and four-wheel drive. A clutch control unit sets a torque fastening force Pt in accordance with input torque T (Step S2). When the input torque T is lower than a preset value At (Step S4) and a speed V is higher than a preset value Av (Step S5), the torque fastening force Pt is reset to be zero (Step S6). Thus, even when an acceleration pedal is released at a low-medium speed region during cornering travel, the control stability of a vehicle is improved without unnecessarily transmitting power to the subsidiary driving wheel. Still, when the vehicle is in an almost stopped condition, the power driving performance is improved in starting because the torque fastening force Pt is not reset to be zero. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a four-wheel drive device mounted on a vehicle.

  When driving at a constant speed, switching to front-wheel drive or rear-wheel drive to reduce fuel consumption, while driving on slippery road surfaces, etc., switch to four-wheel drive to improve driving performance and driving stability. Four-wheel drive systems have been developed. Engine power is transmitted directly from the transmission to the main drive wheels that are always driven, whereas engine power is distributed from the transmission via the transfer to the sub drive wheels that are driven during four-wheel drive. Yes. A clutch is provided between the transfer and the auxiliary drive wheel. When the clutch is engaged, the clutch is switched to four-wheel drive, and when the clutch is released, the clutch is switched to two-wheel drive.

  In such a four-wheel drive device, a viscous coupling or the like is incorporated as a clutch, and a rotational difference sensitive type in which torque is transmitted to the auxiliary drive wheel in accordance with the rotational difference between the front and rear wheels, or an electromagnetic control cup as the clutch. There is an electronic control type that incorporates a ring (hereinafter referred to as an electric control coupling), etc., and actively drives the auxiliary drive wheels to improve power performance and steering stability.

The electric control coupling incorporated in the electronically controlled four-wheel drive device includes a housing connected to the transfer and an inner shaft connected to the sub drive wheel. A main clutch for fastening the housing and the inner shaft is incorporated in the housing, and a pilot clutch as an electromagnetic clutch for controlling the main clutch is incorporated. A cam mechanism is provided between the main clutch and the pilot clutch, and the rotational force generated by the engagement of the pilot clutch can be converted into a pressing force for the main clutch via the cam mechanism. Since the pressure to the main clutch can be controlled according to the current value supplied to the pilot clutch, the torque distribution ratio to the front and rear wheels can be controlled by controlling the current value (see, for example, Patent Document 1). .
JP 2002-188656 A (page 3-4, FIG. 1)

  The fastening force of such an electric control coupling is often set based on the magnitude of the rotational difference between the front and rear wheels and the magnitude of the torque input to the electric control coupling. However, if the fastening force is set with an emphasis on the rotational difference between the front and rear wheels, the two-wheel drive is maintained until the main drive wheel is idled, so that the power performance is deteriorated on a slippery road surface or the like. Further, if the fastening force is set with an emphasis on the magnitude of the input torque in order to improve the power performance on a slippery road surface or the like, the driving stability of the vehicle may be affected depending on the traveling conditions.

  For example, in a four-wheel drive system that sets the fastening force with an emphasis on input torque, when the accelerator pedal is released during cornering in the low and medium speed range, the torque input from the engine to the electric control coupling is cut off. However, when the engine speed decreases, the input torque starts to increase and a small fastening force is set. At this time, since the electric coupling has a characteristic that the drag torque is smaller than that of other clutches, even if the electric coupling is controlled from a completely released state to a sliding state that transmits a minute torque, There may be a large drop in the transmission torque. For this reason, more torque than necessary is transmitted to the auxiliary drive wheels, which may affect the steering stability during cornering.

  An object of the present invention is to improve power performance at the time of starting and improve steering stability in a low and medium speed range.

  The four-wheel drive device of the present invention is a four-wheel drive device that drives main drive wheels with power output from a transmission, and drives auxiliary drive wheels with power output from the transmission via a transfer, A clutch that is provided between the transfer and the auxiliary drive wheel and is switched between an engagement state for transmitting power to the auxiliary drive wheel and a release state for blocking, and a torque engagement force based on a torque input to the clutch. And a clutch control means for engaging the clutch toward the torque engagement force. The clutch control means releases the clutch when the torque falls below a predetermined value and the vehicle speed exceeds a predetermined value. The torque fastening force is set to a value to be set.

  In the four-wheel drive device of the present invention, the clutch control means sets a rotational difference fastening force based on a rotational difference between the main drive wheel and the sub drive wheel, and the torque fastening force and the rotational difference fastening force The clutch is fastened to a fastening force obtained by adding.

  According to the present invention, when the torque is lower than the predetermined value, the torque engagement force is set to a value for releasing the clutch, so that the engagement of the clutch based on the minute torque engagement force can be avoided. As a result, even when the accelerator pedal is released during cornering traveling in the low and medium speed range, power is not unnecessarily transmitted to the auxiliary drive wheels, and the steering stability of the vehicle can be improved. .

  Even when the torque is below a predetermined value, when the vehicle speed is below the predetermined value, the torque fastening force is set based on the torque. It can be transmitted and the traction performance at the start can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a power transmission system of a vehicle equipped with a four-wheel drive device according to an embodiment of the present invention, and FIG. 2 is a skeleton diagram showing a part of the power transmission system of FIG.

  As shown in FIGS. 1 and 2, a transmission 11 is attached to an engine 10 disposed in front of the vehicle, and the engine 10 and the transmission 11 are disposed horizontally. A front differential mechanism 12 is incorporated in the transmission 11, and front wheels 14a and 14b as main drive wheels are connected to the front differential mechanism 12 via front wheel drive shafts 13a and 13b.

  Further, the transmission 11 is provided with a power distribution mechanism, that is, a transfer 15, and the rear differential mechanism 16 disposed at the rear of the vehicle is provided with an electromagnetic control coupling 17 (hereinafter referred to as an electric control coupling) as a clutch. It has been. The transfer 15 and the electric control coupling 17 are connected via a propulsion shaft 18, and the rear differential mechanism 16 is connected to rear wheels 20a and 20b as auxiliary drive wheels via rear wheel drive shafts 19a and 19b. ing.

  Thus, the illustrated vehicle is a four-wheel drive vehicle based on the front wheel drive, and the drive system is switched between the two-wheel drive and the four-wheel drive by switching the electric control coupling 17 between the fastening state and the release state. be able to. In addition, the rear wheel drive may be based on the rear wheel drive by arranging a vertically placed engine or transmission. In this case, the front wheel is driven as the auxiliary drive wheel, while the rear wheel is driven as the main drive wheel. become.

  Next, the electric coupling 17 that switches the vehicle drive method between two-wheel drive and four-wheel drive will be described. FIG. 3A is a schematic diagram showing the electronic control coupling 17 in the released state, and FIG. 3B is a schematic diagram showing the electronic control coupling 17 in the engaged state.

  As shown in FIGS. 3A and 3B, the electric control coupling 17 includes a housing 21 connected to the propulsion shaft 18. The housing 21 has a cylindrical drum 22 with a bottom and an opening end thereof. And a cover 23 that closes the cover. An inner shaft 24 is rotatably fitted in a through hole 23 a formed in the center of the cover 23, and the inner shaft 24 and the drive pinion shaft 25 of the rear differential mechanism 16 are connected.

  In the housing 21, a main clutch 26 that transmits the rotation of the drum 22 to the inner shaft 24 and a pilot clutch 27 that switches the main clutch 26 between an engaged state and a released state are provided. The main clutch 26 is provided between the drum 22 and the inner shaft 24. The outer plate 26a is mounted on the inner peripheral surface of the drum 22 so as to be movable in the axial direction via a spline, and the outer peripheral surface of the inner shaft 24. And an inner plate 26b that is movably mounted in the axial direction via a spline. A pilot clutch 27 is provided between a control cam 31 and a drum 22 which will be described later, and the pilot clutch 27 is an outer member that is mounted on the inner peripheral surface of the drum 22 so as to be movable in the axial direction via a spline. A plate 27a and an inner plate 27b mounted on the outer peripheral surface of the control cam 31 so as to be movable in the axial direction via a spline are provided.

  A cam mechanism 30 is provided between the main clutch 26 and the pilot clutch 27 to transmit the axial pressing force to the main clutch 26. The cam mechanism 30 includes a cylindrical control cam 31 that is rotatably provided on the outer peripheral side of the inner shaft 24, and a main cam 32 that faces the control cam 31. A plurality of cam grooves 31a and 32a are formed on the end surfaces of the control cam 31 and the main cam 32, respectively, and a ball member 33 is sandwiched between the cam grooves 31a and 32a facing each other.

  In order to fasten the pilot clutch 27, an electromagnet 34 in which an electromagnetic coil 34b is wound around an annular core 34a and an annular armature 35 attracted by the magnetic force of the electromagnet 34 are disposed on both sides of the pilot clutch 27. ing. The electromagnet 34 is accommodated in an annular groove 23b formed in the cover 23, and the armature 35 is mounted on the inner peripheral surface of the drum 22 via a spline so as to be movable in the axial direction.

  By supplying a current to the electromagnetic coil 34b, a magnetic flux is generated so as to surround the electromagnetic coil 34b, but an annular member 36 made of a non-magnetic material is embedded in the cover 23 formed using a magnetic material. Therefore, as shown in FIG. 3B, the magnetic flux passes through the circulating magnetic path L formed in the cover 23, the plates 27a and 27b, and the armature 35. The drum 22 is made of a non-magnetic material to avoid leakage of magnetic flux, and a notch is formed in each of the plates 27a and 27b to avoid magnetic flux short-circuiting, thereby efficiently generating magnetic force. Yes.

  By exciting such an electromagnet 34, the armature 35 can be attracted toward the electromagnet 34, and the plates 27a and 27b of the pilot clutch 27 can be pressed and fastened. When the pilot clutch 27 is engaged, a rotational force is transmitted from the drum 22 to the control cam 31 as shown in FIG. 3 (B), and this rotational force is converted into an axial pressing force via the ball member 33. Is transmitted to the main cam 32. When the drum 22 and the inner shaft 24 are fastened by the main cam 32 that moves in the axial direction, the power output from the transfer 15 is transmitted to the rear wheels 20a and 20b.

  By exciting the electromagnet 34 and switching the main clutch 26 to the engaged state, power can be transmitted to the rear wheels 20a and 20b, and the drive system can be switched to four-wheel drive. Moreover, since the fastening force of the main clutch 26 can be controlled according to the magnitude of the energization current to the electromagnetic coil 34b, the torque distribution ratio between the front and rear wheels is set to 100: 0 to 50:50 according to the traveling state of the vehicle. Can be controlled within the range. When the energization of the electromagnetic coil 34b is cut off, the main clutch 26 is switched to the released state, so that the drive system is switched to two-wheel drive.

  In order to switch the driving method in this way, as shown in FIG. 1, the clutch control unit 40 which is the clutch control means outputs a control signal to the electric control coupling 17. The clutch control unit 40 includes an engine control unit (not shown) that controls the drive of the engine 10, a transmission control unit (not shown) that controls the speed change of the transmission 11, and a control signal that changes according to the traveling state of the vehicle. An ABS control unit 41 that brakes each wheel is connected via a communication cable 42 so as to be able to communicate. That is, an in-vehicle LAN (Local Area Network) that connects the units is constructed, and CAN communication (Controller Area Network) is performed between the units to share various data. A wheel speed sensor 43 that detects the rotational speed of the wheel is connected to the in-vehicle LAN.

  Hereinafter, the fastening force setting control of the electric coupling 17 by the clutch control unit 40 will be described. FIG. 4 is a flowchart showing a procedure of fastening force setting control. As shown in FIG. 4, in step S1, the rotational speed Vt (wheel speed) of each wheel is detected based on the output signal from the wheel speed sensor 43, and the output signal from the engine control unit or transmission control unit is detected. Based on this, the input torque T of the transfer 15 is detected. When detecting the input torque T, the fuel injection amount, the intake air amount, the engine speed, the gear ratio, and the like are used as output signals.

  In step S2, the torque engagement force Pt of the electric control coupling 17 is calculated based on the input torque T detected in step S1. An arithmetic expression and a table are stored in the ROM in the clutch control unit 40, and a fastening force Pt that is substantially proportional to the magnitude of the input torque T is calculated using these arithmetic expressions and tables. When calculating the fastening force Pt in step S2, the fastening force Pt may be changed using the vehicle speed as a parameter, and the fastening force Pt is changed using a steering angle sensor (not shown) or a steering angle obtained from a wheel speed difference as a parameter. You may do it.

  In step S3, the rotational difference D between the front wheels 14a and 14b and the rear wheels 20a and 20b is calculated based on the wheel speed Vt detected in step S1. Next, the rotational difference fastening force Pd of the electric control coupling 17 is calculated based on the rotational difference D. An arithmetic expression and a table are stored in the ROM in the clutch control unit 40, and the fastening force Pd is calculated so as to converge the rotational difference between the front wheels 14a and 14b and the rear wheels 20a and 20b.

  Subsequently, in step S4, it is determined whether or not the input torque T exceeds a predetermined value At. At this time, the predetermined value At, which is a determination criterion, is set to the magnitude of the torque input to the transfer 15 during creep travel when the accelerator pedal is not depressed. In step S4, if the input torque T exceeds the predetermined value At, that is, if the accelerator pedal is depressed, the process proceeds to step S7, and the electric coupling 17 is engaged by adding the fastening forces Pt and Pd. The target fastening force P for performing is set.

  On the other hand, when the input torque T is lower than the predetermined value At in step S4, that is, when the accelerator pedal is not depressed, the routine proceeds to step S5, where it is determined whether or not the vehicle speed V is lower than the predetermined value Av. At this time, the predetermined value Av serving as a determination criterion is set to a vehicle speed (for example, 0 to 5 km / h) at which the vehicle is almost stopped. When the vehicle speed V is lower than the predetermined value Av in step S5, the process proceeds to step S7, where the target fastening force P is set by adding the fastening forces Pt and Pd, while when the vehicle speed V exceeds the predetermined value Av, Proceeding to step S6, the value of the fastening force Pt calculated at step S2 is reset to zero. That is, when the accelerator pedal is not depressed and the predetermined vehicle speed is maintained, in the subsequent step S7, the target fastening force P is set only by the fastening force Pd.

  As described above, when the input torque is less than the predetermined value At, the fastening force set based on the input torque is reset to 0, so that the electric coupling 17 is fastened based on the minute fastening force Pt. Control can be avoided and the handling stability of the vehicle can be improved. For example, if the accelerator pedal is released during cornering, the input torque once cut off will turn to a positive value as the engine speed decreases. Even in this case, the electric coupling 17 is fastened. Thus, since unnecessary power is not transmitted to the rear wheels 20a, 20b, the steering stability during cornering traveling can be improved.

  Even when the input torque is less than the predetermined value At, when the vehicle speed V is low and the vehicle is almost stopped, the process proceeds from step S5 to step S7, and therefore the fastening force Pt is reset to 0. Therefore, it is possible to reliably switch to four-wheel drive by depressing the accelerator pedal, and to improve the traction performance when starting the vehicle.

  Furthermore, it is not necessary to keep the electric coupling 17 in a light sliding state in order to eliminate the characteristic of the electric coupling 17 that the head of the transmission torque becomes large at the initial stage of fastening, and it is not necessary to maintain the electric coupling and the power. Consumption can be reduced.

  It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the clutch control unit 40 may be reduced by incorporating a function as a clutch control means in the transmission control unit.

  Further, when setting the torque fastening force Pt and the rotation difference fastening force Pd, a fastening force proportional to the magnitude of the input torque T and the rotation difference D may be set, and these are corrected in accordance with the traveling situation. Accordingly, a fastening force that is substantially proportional to the magnitude of the input torque T or the rotation difference D may be set.

  In step S6, the fastening force Pt is reset to 0. However, the resetting value is not limited to 0. If the value is to switch the electric coupling 17 to the released state, the fastening force Pt is very small. The fastening force Pt may be reset to the value.

  Furthermore, although CAN communication is performed between the control units by the in-vehicle LAN, another communication method may be used as the communication method.

  The speed change mechanism provided in the transmission 11 may be a belt drive type or traction drive type continuously variable transmission, a planetary gear type or a parallel shaft type automatic transmission, A parallel shaft type manual transmission may be used.

It is a block diagram which shows the power transmission system of the vehicle carrying the four-wheel drive device which is one embodiment of this invention. It is a skeleton figure which shows a part of power transmission system of FIG. (A) is the schematic which shows the electronic control coupling of a release state, (B) is the schematic which shows the electronic control coupling of a fastening state. It is a flowchart which shows the procedure of fastening force setting control.

Explanation of symbols

11 Transmission 14a, 14b Front wheel (main drive wheel)
15 Transfer 17 Electromagnetic control coupling (clutch)
20a, 20b Rear wheel (sub drive wheel)
40 Clutch control unit (clutch control means)
T Input torque (torque)
At Predetermined value V Vehicle speed Av Predetermined value D Rotational difference Pt Fastening force (torque fastening force)
Pd fastening force (rotational differential fastening force)

Claims (2)

A four-wheel drive device for driving main drive wheels with power output from a transmission and driving auxiliary drive wheels with power output from the transmission via a transfer;
A clutch that is provided between the transfer and the sub drive wheel, and that is switched between a fastening state for transmitting power to the sub drive wheel and a release state for blocking;
A clutch control means for setting a torque engagement force based on a torque input to the clutch and for engaging the clutch toward the torque engagement force;
The four-wheel drive device, wherein the clutch control means sets the torque engagement force to a value for releasing the clutch when the torque is below a predetermined value and the vehicle speed is above a predetermined value. 2. The four-wheel drive device according to claim 1, wherein the clutch control means sets a rotation difference fastening force based on a rotation difference between the main drive wheel and the sub drive wheel, and the torque fastening force and the rotation difference fastening. A four-wheel drive device for fastening the clutch toward a fastening force obtained by adding the force.

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