JP3579962B2 - Four-wheel drive - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a so-called torque split type four-wheel drive device capable of variably distributing a driving force from an engine to front and rear wheels.
[0002]
[Prior art]
As a four-wheel drive device applied to a four-wheel drive vehicle, a so-called torque split type that has an electronically controlled clutch and can variably distribute driving force or torque to front and rear wheels has been put to practical use. According to this, the torque distribution can be optimized according to the driving situation, and the four wheels can always be driven optimally, so that the driving performance is remarkably improved, and unnecessary slips are prevented to improve safety. Can also be increased.
[0003]
[Problems to be solved by the invention]
By the way, in such a device, when considering a part-time system capable of switching to two-wheel drive, it is easy to stop and disconnect the clutch control at the time of two-wheel drive, and a switch that can be operated from the driver's seat It is also conceivable that the switching is performed electrically by providing such a method.
[0004]
However, in such a case, if a failure of a switch or the like, an abnormality of a harness (a disconnection, a short circuit, or the like), or an erroneous operation by an occupant or the like occurs, the switching is performed without permission of the driver. In particular, it is extremely difficult to discriminate such a failure or the like from switching by a normal operation, and it is very difficult to deal with the structure.
[0005]
On the other hand, in a conventional rear-wheel drive-based device in particular, the front wheels are separated from the drive system when switching from four-wheel drive to two-wheel drive, and the drive system is prevented from being reversely driven by the front wheels that rotate while traveling. Some of them aim to improve fuel efficiency, reduce vibration noise, and the like. An intermittent mechanism (a so-called freewheel hub or the like) for intermittently connecting the front wheel and the drive system is generally operated manually. It is also conceivable to perform automatic control in synchronization.
[0006]
However, also in this case, if the aforementioned harness abnormality or the like occurs, the intermittent mechanism is interrupted, and the intermittent mechanism is disconnected during traveling with four-wheel drive, and the driving force to the front wheels is suddenly removed. If it is deviated, the steering characteristics may suddenly change from the understeer tendency to the oversteer tendency, and the steering stability is reduced.
[0007]
Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a four-wheel drive device capable of preventing a sudden change in steering characteristics when switching from four-wheel drive to two-wheel drive. is there.
[0008]
[Means for Solving the Problems]
To achieve the above object, a four-wheel drive device according to the present invention controls a clutch for distributing a driving force from an engine to front and rear wheels, and controls a clutch engagement force based on a speed difference between front and rear wheels. A controller that switches between four-wheel drive and two-wheel drive by switching on and off the clutch, and a disconnection mechanism that connects the four wheels to the drive system during four-wheel drive and disconnects the front wheels from the drive system during two-wheel drive; An arithmetic processing unit is provided for controlling the connection and disconnection of the connection / disconnection mechanism, and for maintaining the connection state of the connection / disconnection mechanism until the vehicle speed falls below a predetermined speed when switching from four-wheel drive to two-wheel drive.
[0009]
[Action]
In the above configuration, the intermittent mechanism is maintained in the connected state until the vehicle speed becomes equal to or lower than the predetermined speed, and conversely, it is disconnected only when the vehicle speed is equal to or lower than the predetermined speed. Therefore, if the vehicle speed at which the division is performed is set to a sufficiently safe low speed, the division during the normal traveling can be prevented.
[0010]
【Example】
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0011]
FIG. 1 is a configuration diagram showing a four-wheel drive device according to the present invention. 1 is a front wheel on the left side of the drawing and 2 is a rear wheel on the right side. In this case, the rear wheel 2 is always directly driven by the driving force from the engine 3. That is, the four-wheel drive device 5 is based on rear-wheel drive (FR). Note that FIG. 2 illustrates the configuration of FIG. 1 more specifically and should be referred to as appropriate.
[0012]
The four-wheel drive device 5 has a transfer 6 for inputting a driving force or torque from the engine 3 and outputting the driving force or torque to the front and rear wheels 1 and 2 respectively. A transmission (transmission) 4 is interposed between the engine 3 and the transfer 6. The transfer 6 has a switching mechanism 8 for switching between a high-speed gear (hereinafter referred to as high mode) and a low-speed gear (hereinafter referred to as low mode) by manual operation of the selector lever 7, and for substantially distributing an input from the switching mechanism 8. Mainly composed of the clutch 9.
[0013]
The switching mechanism 8 includes an input spline 11 and an input gear 12 provided coaxially with the input shaft 10, a planetary gear 14 that meshes with an input gear 12 and a fixed gear 13 as a sun gear, and a rotation of the planetary gear 14. And a cylindrical gear 15 that rotates around the input shaft 10. The input spline 11 or the spline attached to the cylindrical gear 15 is selectively connected to the drive spline 16 a at the input end of the rear wheel drive shaft 16 via the slidable shift sleeve 18 by operating the selector lever 7. It is supposed to be. In the illustrated example, the four-wheel drive high mode 4H is selected assuming normal four-wheel drive. In this case, the shift sleeve 18 connects the input spline 11 and the drive spline 16a to connect the input shaft 10 It is directly connected to the rear wheel drive shaft 16. When the 4WD low mode 4L is selected, the shift sleeve 18 connects the spline attached to the cylindrical gear 15 and the drive spline 16a, and causes the rear wheel drive shaft 16 to rotate at a reduced speed. The four-wheel drive high mode 4H is selected under normal road conditions such as snowy roads and muddy areas, and the four-wheel drive low mode 4L is selected under conditions requiring relatively high driving force such as steep slopes, extremely rough roads, and towing.
[0014]
An output end of the rear wheel drive shaft 16 is provided with a small gear 16b which forms a part of the final reduction gear 17, and the small gear 16b drives a large gear 20 provided integrally with the differential case 19. The large gear 20 drives the rear wheel 2 via the left and right differential small gears 21 and the rear wheel axle 22, respectively. As shown in FIG. 2, a portion of the rear wheel drive shaft 16 extending from the transfer 6 is formed by a rear wheel side propeller shaft 16c.
[0015]
The clutch 9 has a wet multi-plate structure, that is, a frictional connection between a plurality of inner plates 23 arranged in a row on the rear wheel drive shaft 16 and an outer plate 24 arranged between the inner plates 23. The driving force is distributed. The inner plate 23 and the outer plate 24 are spline-fitted to the rear wheel drive shaft 16 and the clutch housing 25, respectively, so that they can slide in the axial direction but cannot move in the rotational direction. The clutch housing 25 is rotatable around the rear wheel drive shaft 16. Then, the inner plate 23 and the outer plate 24 are slid to perform pressure bonding by using an electromagnetic force generated by an actuator, that is, an electromagnetic solenoid 26 fixed in the vicinity thereof. Therefore, in this clutch 9, by controlling the electromagnetic solenoid 26, the state of contact or contact between the inner plate 23 and the outer plate 24 is controlled, and the torque distributed to the front and rear wheels 1, 2 according to the running state of the vehicle. Control mechanism. By controlling the engagement force of the clutch 9 in this way, a distributed torque of 0: 100 to 50:50 (front wheel: rear wheel) can always be continuously obtained from the clutch 9.
[0016]
Further, splines 27 and 28 for direct connection are provided on the clutch housing 25 and the rear wheel drive shaft 16, respectively. These direct connection splines 27 and 28 are connected to each other by a slidable connection sleeve 29 when the 4WD low mode 4L is selected. In this case, the clutch housing 25 is directly connected to the rear wheel drive shaft 16, and the mechanical lock is achieved, so that the distribution torque control by the clutch 9 is not performed. As described above, the direct connection splines 27 and 28 and the connection sleeve 29 form a direct connection mechanism 9a for directly connecting the front wheel drive side of the clutch 9 to the rear wheel drive system.
[0017]
FIG. 3 shows a state when the selector lever 7 is viewed from the passenger compartment. The selector lever 7 is movable along a crank-shaped gate 55. In the gate 55, in addition to the four-wheel low mode 4L and the four-wheel high mode 4H, the positions of a neutral mode N and a two-wheel high mode 2H described later are set. Each is given. Therefore, the driver moves the selector lever 7 along the gate 55 to select each mode. As shown in FIGS. 1 and 2, the transfer 6 is provided with two switches SW1 and SW2 that are turned on / off by the position of the selector lever 7. The ON / OFF combinations of the switches SW1 and SW2 are as shown in FIG.
[0018]
Returning to FIG. 1, a sprocket 30 is provided in the clutch housing 25, and a front wheel driving force is transmitted from the sprocket 30 to a front wheel driving shaft 33 via a chain 31 and a driving sprocket 32. As described above, a small gear 35 which is a part of the final reduction gear 34 is provided at the output end of the front wheel drive shaft 33. The small gear 35 is composed of a large gear 36, a differential case 37, a small differential gear 38, and a front wheel axle 39. , The front wheels 1 are respectively driven. As shown in FIG. 2, a portion of the front wheel drive shaft 33 extending from the transfer 6 is formed by a front wheel side propeller shaft 33a.
[0019]
Further, in the transfer 6, the rear wheel drive shaft 16 and the front wheel drive shaft 33 are provided with projection disks 41 and 42 for speed detection, respectively. The disks with projections 41 and 42 have a plurality of projections at equal intervals on the periphery. In the vicinity of the protruding disks 41, 42, non-contact proximity type speed sensors 43, 44 using a Hall element are provided, and the speed sensors 43, 44 are provided each time the protrusions of the rotating disks 41, 42 pass. To output a pulse signal.
[0020]
These speed sensors 43 and 44 are electrically connected to a computer controller 45 (for example, an ECU) for mainly performing electronic control of the clutch 9. The controller 45 includes an input unit 46 that inputs signals from the speed sensors 43 and 44 and other signals, an arithmetic processing unit 47 that performs arithmetic processing based on the input signal from the input unit 46, and an arithmetic processing unit 47. And an output section 48 for outputting an output signal or an operating current based on the output value or the like. Here, the operating current output from the output unit 48 to the electromagnetic solenoid 26 is specifically increased or decreased by a change in the duty ratio due to the pulse current. Then, electronic control of the clutch 9 is achieved by increasing or decreasing the operating current. The controller 45 also receives an ON / OFF signal from the switches SW1 and SW2 indicating the position of the selector lever 7, a signal indicating the connection state of the intermittent mechanism 40 described later, and the like, and collectively operates the four-wheel drive device 5. Control.
[0021]
In the normal control in the 4WD high mode 4H, the arithmetic processing unit 47 reads the pulse signals from the speed sensors 43 and 44, and corrects the rotational speeds of the shafts 16 and 33 and the rotational speeds from the rotational phase per time. Then, the rear wheel speed Vr and the front wheel speed Vf are calculated. In this embodiment, the front wheel speed Vf is assumed to be equal to the speed of the vehicle itself, that is, the vehicle speed. When there is a speed difference between them, for example, when Vr> Vf in starting acceleration or the like, the torque is distributed to the front wheels 1 so as to cancel the speed difference. Specifically, the operating current applied to the electromagnetic solenoid 26 is increased, and the pressing between the inner plate 23 and the outer plate 24 is increased. On the other hand, when Vr ■ Vf, the pressing of the plates 23 and 24 is weakened. In this way, the controller 45 controls the clutch 9 by increasing or decreasing the pressure between the inner plate 23 and the outer plate 24 every time a pulse signal is sent from the speed sensors 43 and 44.
[0022]
On the other hand, as described above, in the four-wheel drive device 5, the two-wheel drive high mode 2H, that is, the high-speed two-wheel drive mode can be selected. In this case, the positions of the shift sleeve 18 and the connection sleeve 29 are equal to those in the case of the four-wheel drive high mode 4H, and the clutch 9 is disconnected and no control is performed.
[0023]
In the two-wheel drive high mode 2H, one of the front wheel axles 39, that is, the left front axle 39, is disconnected by an intermittent mechanism 40 for connecting and disconnecting the axle 39. Specifically, the front wheel axle 39 is composed of divided axles 39a and 39b, and the divided axles 39a and 39b are provided with intermittent splines 56a and 56b, and these intermittent splines 56a and 56b are connected when in the 4WD high mode 4H. While the connection is made via the sleeve 40a, in the two-wheel drive high mode 2H, the connection is broken by the sliding movement of the connection sleeve 40a. Here, the movement of the connection sleeve 40a is automatically performed by air pressure control by the actuator 40b in synchronization with the operation of the selector lever 7.
[0024]
FIG. 2 shows the configuration of the actuator 40b in detail. According to this, a vacuum pump 50 is connected to the intermittent mechanism 40, and the vacuum pressure generated by the vacuum pump 50 is stored in a vacuum tank 51, and the vacuum By selectively supplying the pressure to the intermittent mechanism 40 by switching the solenoid valve 52, the connecting sleeve 40a is reciprocated and the automatic switching of the intermittent mechanism 40 is achieved. Reference numeral 53 denotes a check valve.
[0025]
Here, the arithmetic processing unit 47 supplies the operating current from the output unit 48 to the solenoid valve 52 to execute the above-described control. Then, the arithmetic processing unit 47 can detect the position of the connection sleeve 40a by using the switch SW3 provided in the connection / disconnection mechanism 40 to confirm the connection / disconnection. The connection / disconnection mechanism 40 is configured to be connected when the switch SW3 is ON and disconnected when the switch SW3 is OFF, and the combination of ON / OFF and each mode is as shown in FIG. According to this, it can be seen that it is ON (connected) in the case of four-wheel drive, and OFF (disconnected) in other cases.
[0026]
Thus, when the front wheel axle 39 is separated, the left and right front wheels 1 are separated from the front wheel drive system, and can freely rotate during traveling. Since the front wheel drive system from the front wheel drive shaft 33 to the clutch housing 25 is not reversely driven by the rotation during traveling, they can be kept stationary even during traveling, resulting in deterioration of fuel efficiency, vibration noise, etc. Can be prevented.
[0027]
Next, the neutral mode N will be described. As described above, in the case of the 4WD low mode 4L, the cylindrical gear 15 and the drive spline 16a are provided in the switching mechanism 8, and the direct connection splines 27 and 28 are provided in the direct connection mechanism 9a. Connected mechanically. When switching from the four-wheel drive high mode 4H to the four-wheel drive low mode 4L is considered, there is a speed difference between the respective gears, so that it is necessary to adjust the speed. In this embodiment, however, there is no mechanism for adjusting the speed. Therefore, connection of each gear can be performed only at the time of stop. Therefore, on the way, the neutral mode N is entered once, each gear is completely cut off, the shift sleeve 18 and the connecting sleeve 29 are set to an intermediate position where only one of them meshes, and then the connection is made so that the connection is smooth. . Further, by providing the neutral mode N, it is possible to prevent direct switching from the 4WD high mode 4H to the 4WD low mode 4L, thereby preventing damage to the mechanisms 8, 9a. Here, in the neutral mode N, the driving force from the engine 3 is not transmitted to any of the front and rear wheels 1 and 2, and the control of the clutch 9 is not performed.
[0028]
Thus, the four-wheel drive device 5 is of a variable distribution type and of a part-time type.
[0029]
By the way, especially when the vehicle is running in the 4WD low mode 4L, the combination of ON / OFF shown in FIG. 4 changes due to failure of the switches SW1 and SW2 or abnormality of the harness connecting the switches SW1 and SW2 and the controller 45. In some cases, the mode switching signal is input to the controller 45, and the two-wheel drive high mode 2H or the neutral mode N is unexpectedly selected. In this case, the control of the intermittent mechanism 40 as described above is executed, and the intermittent mechanism 40 is in a disconnected state, and is substantially in a two-wheel drive or neutral state, so that the steering stability may be reduced.
[0030]
Therefore, in the present embodiment, the following control is executed to solve such a problem.
[0031]
FIG. 5 shows a flowchart of control of the intermittent mechanism 40 by the arithmetic processing unit 47 of the controller 45. When a mode switching signal to the 2WD high mode 2H or the neutral mode N is input due to a harness abnormality or the like while driving in the 4WD low mode 4L, the front wheel speed Vf is first read from the signal of the front wheel speed sensor 44. The Vf predetermined speed V ₀ or less, i.e., sufficient or a determines if an slower or less, proceed to the next step if so, reads the rear wheel speed Vr from the signal of the rear-wheel-side speed sensor 43. And also Vr is determined whether a V ₀ or less, the process proceeds to the next step if so, to divide the intermittent mechanism 40 by supplying the operating current to the solenoid valve 52. Whereas in this, after the input of the mode switching signal, as long as none of the rear wheel speed Vr and wheel speed Vf (equivalent to vehicle speed) does not fall to V ₀ below, the connection is intermittent mechanism 40 is maintained.
[0032]
According to this, even if the switching is suddenly performed during traveling in the 4WD low mode 4L, the intermittent mechanism 40 is kept connected, so that the front wheel 1 is disengaged from the driving system and is switched to a complete two-wheel drive or neutral state. This can prevent sudden changes in steering characteristics and maintain steering stability. Here, since the vehicle speed at which the interrupting mechanism 40 splits is set to a sufficiently low speed, the splitting can be performed at a safe speed. Alternatively, the speed V ₀ is set to substantially stop the same speed, in the present embodiment, it can be said to perform the first split in a state close stop or to it. Note that the above-described control is limited to the case of switching from the four-wheel drive low mode 4L. In the case of switching from the four-wheel drive high mode 4H, another control is performed in accordance with the driving situation and the like. The determination that switching from the 4WD low mode 4L has been performed is performed by the arithmetic processing unit 47 monitoring the mode before switching. In the above description, the case where the harness is abnormal has been described. However, exactly the same control is performed in the case of switching by the normal operation, that is, this control also has a fail-safe function.
[0033]
Note that the present invention is not limited to the above-described embodiment, and various modified embodiments are possible, for example, providing an intermittent mechanism at a place other than the front wheel axle.
[0034]
【The invention's effect】
The present invention exhibits the following excellent effects.
[0035]
(1) Even if a failure occurs in the drive mode detection switch system during four-wheel drive traveling, a sudden change in steering characteristics can be prevented, and steering stability can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of a four-wheel drive device according to the present invention.
FIG. 2 is a configuration diagram more specifically depicting the four-wheel drive device of FIG. 1;
FIG. 3 is a plan view showing a selector lever and a gate.
FIG. 4 is a table showing ON / OFF combinations of switches in each mode.
FIG. 5 is a flowchart illustrating control by an arithmetic processing unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 3 Engine 5 Four-wheel drive 9 Clutch 40 Intermittent mechanism 45 Controller 47 Operation processing part

Claims (1)

A clutch for distributing the driving force from the engine to the front and rear wheels, a controller for controlling the engagement force of the clutch based on the speed difference between the front and rear wheels, and intermittently switching the clutch to switch between four-wheel drive and two-wheel drive; An intermittent mechanism that connects the four wheels to the drive system during four-wheel drive, and disconnects the front wheels from the drive system during two-wheel drive. The controller controls the intermittent operation of the intermittent mechanism and switches from four-wheel drive to two-wheel drive. A four-wheel drive device provided with an arithmetic processing unit for maintaining the connection state of the intermittent mechanism until the vehicle speed becomes equal to or lower than a predetermined speed at the time of switching.

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