JPH0626935B2 - Control method for continuously variable transmission for four-wheel drive vehicle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a control method for a continuously variable transmission for a four-wheel drive vehicle,
In particular, the present invention relates to a technique for suppressing a switching shock when switching from a two-wheel drive state to a four-wheel drive state.

2. Description of the Related Art A continuously variable transmission that continuously changes the output of an engine and transmits it to driving wheels, and a two-wheel drive state that transmits the rotational force output through the continuously variable transmission to a pair of left and right wheels. A four-wheel drive vehicle is known that includes a switching device that switches to a four-wheel drive state in which all four wheels are transmitted. In such a vehicle, when the drive wheels slip when starting or traveling in the two-wheel drive state, the switching device switches the drive wheels to the four-wheel drive state to improve the traveling performance.

Problems to be Solved by the Invention However, in such a conventional four-wheel drive vehicle, when the drive wheels slip, the switching device switches from the two-wheel drive state to the four-wheel drive state. When power is newly transmitted to the wheels, there is a disadvantage that an uncomfortable switching shock occurs due to the difference in rotation between the wheels.

Means for Solving Problems The present invention has been made against the above circumstances.
The gist of the point is that, when slippage of the drive wheels in the two-wheel drive state of the vehicle is detected, the gear ratio of the continuously variable transmission is decreased prior to switching to the four-wheel drive state. To change.

In this way, when the slip occurs, the gear ratio of the continuously variable transmission is changed in the decreasing direction prior to switching to the four-wheel drive state without changing the accelerator operation. As a result, the drive torque of the drive wheels is reduced to a value commensurate with the reduction of the friction coefficient of the road surface, slippage between the drive wheels and the road surface is suppressed, and the drive torque of the drive wheels is maintained at a required value to rotate the engine. Is lowered. Therefore, even when the two-wheel drive state is switched to the four-wheel drive state by the switching device, an uncomfortable switching shock due to the difference in rotation between the drive wheels up to that point and the wheel to which new power is transmitted is preferably suppressed. It is.

Examples Hereinafter, one application example of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows a four-wheel drive system used in a laterally mounted front engine front drive type vehicle. The output of the engine 10 is a fluid coupling 12 with a lock-up clutch, a belt type continuously variable transmission 14, and an auxiliary transmission 1.
6, the reduction gear device 18, and the differential gear device 20 are transmitted to the front wheels 21, and are transmitted to the rear wheels via the rear wheel power takeoff device 22. The rear wheel power take-off device 22 transmits the rotational force of the intermediate shaft of the reduction gear device 18 to the drive shaft 26 to the rear wheel 23 via the clutch 24.

The belt type continuously variable transmission 14 includes a pair of primary side variable pulleys 32 and secondary side variable pulleys 34 having variable effective diameters attached to the primary side rotary shaft 28 and the secondary side rotary shaft 30, respectively, and the primary side variable pulleys 34 and 34. The transmission belt 36 wound around the side variable pulley 32 and the secondary variable pulley 34, the V groove width of the primary variable pulley 32 and the secondary variable pulley 34, in other words, the effective diameter of the transmission belt 36 is changed. Primary side hydraulic cylinder 66 and secondary side hydraulic cylinder 6
The hydraulic oil in the primary side hydraulic cylinder 66 is supplied or the hydraulic oil is supplied from the inside of the primary side hydraulic cylinder 66 in response to the operation of the shift control valve 70 provided in the hydraulic device (not shown). By being discharged, the gear ratio γ
(= Rotational speed N _in of the primary side rotating shaft 28 / secondary side rotating shaft 3
The rotation speed N _{out of} 0) is changed.
The secondary side hydraulic cylinder 68 is supplied with the hydraulic pressure adjusted in relation to the output torque of the engine 10 and the actual gear ratio γ, so that the tension of the transmission belt 36 is controlled to be necessary and sufficient, The power loss is designed to be as small as possible.

Further, the sub transmission 16 establishes a Ravigneaux compound planetary gear device 40, a low speed brake 42 for establishing a low speed gear stage, a high speed clutch 44 for establishing a high speed gear stage, and a reverse gear stage. Reverse brake for 4
6 and the low speed brake 42, the high speed clutch 44 and the reverse brake 46 are selectively operated in response to the operation of a manual valve or a shift control valve 74 included in a hydraulic device (not shown) It can be selectively switched to a gear stage, a high speed gear stage, or a reverse gear stage.

The clutch 24 functions as a switching device and is a four-wheel drive switching valve 7 included in a hydraulic device (not shown).
Engagement control is performed in response to the operation of 2. When the clutch 24 is disengaged, the pair of left and right front wheels 21 is a driving wheel, and the clutch 24 is engaged, so that the front wheels 21 and the rear wheels 23 are driving wheels. It is in a four-wheel drive state.

As shown in FIG. 2, the control device 38 is provided with an operating position of a shift lever (not shown) that is operated to a reverse position, a neutral position, a low position, a drive position, etc. and drives the manual valve in accordance with this operation. Detecting shift lever position sensor 48, 2 wheel drive position and 4
A switching lever position sensor 49 that detects the operating position of a four-wheel drive switching lever (not shown) that is operated to the wheel drive position, a throttle sensor 50 that detects the throttle valve opening of the engine 10, and a rotation speed N of the primary side rotating shaft 28. Rotation speed N of the primary side rotation sensor 52 for detecting _in and the secondary side rotation shaft 30
Signals are respectively supplied from a secondary side rotation sensor 54 that detects _out , a front wheel rotation sensor 56 that detects the rotation speed of the front wheels 21, and a rear wheel rotation sensor 58 that detects the rotation speed of the rear wheels 23. The control device 38 includes a CPU 60 and a ROM
A so-called microcomputer including a RAM 62 and a RAM 64, and a ROM 62 using the storage function of the RAM 64
The input signal is processed in accordance with a program stored in advance, and a drive signal for operating the belt type continuously variable transmission 14, the auxiliary transmission 16 and the clutch 24 is output.

For example, the control device 38 calculates the rotation speed N _in of the primary rotation shaft 28 and the rotation speed _out of the secondary rotation shaft 30 based on the signals from the primary rotation sensor 52 and the secondary rotation sensor 54. , The speed ratio of the belt type continuously variable transmission 14 is calculated from them, and the rotary sensor 5
The rotation speed N _f of the front wheel 21 and the rotation speed N _r of the rear wheel 23 are calculated based on the signals from 6 and the rear wheel rotation sensor 58. Further, the control device 38 executes a gear ratio control for increasing fuel efficiency while maintaining drivability, and the engine 10
Determines a target rotational speed N ^* on the basis of the actual throttle valve opening and the vehicle speed from a relationship obtained in advance so as to operate substantially along the minimum fuel consumption rate curve.
The shift control valve 70 is operated to change the gear ratio γ of the continuously variable transmission 14 so that the rotation speed N _in of the continuously variable transmission matches the target rotation speed. Further, the control device 38 executes the automatic shift control, and determines the gear stage of the auxiliary transmission 16 based on the operation position of the shift lever, the actual throttle valve opening and the vehicle speed from the previously stored shift diagram. The shift control valve 74 is operated to switch the gear stage of the sub transmission 16 to the determined gear stage. Further, the control device 38 executes the four-wheel drive switching control for suppressing the switching shock, detects the slip of the driving wheels in the two-wheel drive state, and reduces the gear ratio γ of the belt type continuously variable transmission 14. Then, the four-wheel drive switching valve 72 is operated to switch to the four-wheel drive state.

The four-wheel drive switching control operation for suppressing the switching shock will be described in detail below.

FIG. 1 is a flowchart showing a part of a routine executed when the switching lever is operated to the four-wheel drive side, that is, when the four-wheel switching mode is set. First, by executing step S1, the slip state of the front wheels 21, which are the driving wheels at this time, is detected. In this slipping state, the rotation speed difference ΔN between the rotation speed N _f of the front wheels 21 and the rotation speed N _r of the rear wheels 23 is smaller than the predetermined constant rotation speed difference ΔN _o by performing step S2. It is judged by whether it is small or not. Rotational speed difference .DELTA.N _o of the constant, predetermined to allow switching of within the switching shock due to the difference in rotational speed between the rear wheels 23 and front wheels 21 is sufficiently small that the four-wheel drive mode It has been done.

When it is determined that the rotational speed difference ΔN is not smaller than the predetermined constant rotational speed difference ΔN _o , the front wheels 2
Since the slip of 1 is large, step S3 is executed and the actual gear ratio γ is decreased. For example, irrespective of the gear ratio control for improving fuel efficiency and drivability, the gear ratio control valve 70 for controlling the gear ratio changing direction is preferentially operated to the decreasing position where the gear ratio γ is reduced. While the determination in step S2 is negative, the series of steps S1, S2, and S3 are repeatedly executed to maintain the gear ratio control valve 70 at the position where the gear ratio γ decreases, so that the driving torque of the front wheels 21 is reduced. Even if the throttle valve opening remains constant, the throttle valve opening can be promptly decreased without waiting for the operation of decreasing the throttle valve opening.

In step S2, _if it is determined that the rotational speed difference ΔN between the rotational speed N _f of the front wheels 21 and the rotational speed N _r of the rear wheels 23 is less than a predetermined constant rotational speed difference ΔN _o , the front wheels Since the slip of 21 has become sufficiently small, step S4 is executed and the clutch 24
Are engaged. As a result, the power of the engine 10 is also transmitted to the rear wheels 23 and the vehicle is set to the four-wheel drive state.
Then, step S5 is executed to increase the gear ratio γ. For example, the shift control valve 7 that has been preferentially operated to the decreasing position for decreasing the gear ratio γ until then.
The maintenance of the operating position of 0 is eliminated. As a result, the gear ratio γ reaches a value controlled according to the normal gear ratio control, that is, an original value for matching the target rotation speed and the actual rotation speed N _in of the primary side rotating shaft 28. Can be increased.

Conventionally, when slippage of the front wheels 21 occurs, as shown in FIG. 4, the load of the engine 10 is reduced, the engine rotation speed is increased, and the slip is further increased. Therefore, the state is switched to the four-wheel drive state in this state. Sometimes the front wheels 21
And a shock due to the rotation difference between the rear wheel 23 and the rear wheel 23 occurred. However, according to the present embodiment, as described above, at the time of switching to the four-wheel drive, the slip of the front wheel 21 which is the driving wheel until then becomes a predetermined small slip state without changing the accelerator operation. If it has not reached, the gear ratio γ is reduced and the drive torque of the front wheels 21 is reduced. As a result, when the driving torque of the front wheels 21 is promptly reduced to the extent that the front wheels 21 do not slip due to the reduction of the frictional force on the road surface, the load of the engine 10 is increased and the rotation speed is reduced as the driving torque of the front wheels 21 is reduced. To be made. Then, with the slip of the drive wheels 21 almost eliminated, the engagement of the clutch 24, which has been waiting until then, is allowed and the four-wheel drive state is set. Therefore,
Even if the switching lever is switched from the two-wheel drive side position to the four-wheel drive side position while the front wheel 21 is slipping, the front wheel 21 that has been functioning as a drive wheel and the rear wheel 23 to which power is newly transmitted are An uncomfortable switching shock caused by the rotation difference is suitably suppressed.

The above description is merely an example of the present invention, and the present invention can be variously modified without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining the operation of the control circuit of FIG. FIG. 2 is a block diagram showing a control circuit of the apparatus shown in FIG. FIG. 3 is a skeleton view showing a power transmission device of a four-wheel drive vehicle to which the present invention is applied. FIG. 4 is a diagram showing the relationship between the engine rotation speed and the output torque when the throttle valve opening is constant in the slip state of the vehicle. 10: engine 14: belt type continuously variable transmission 21: front wheel (driving wheel) 23: rear wheel (driving wheel) 24: clutch (switching device)

Claims (1)

[Claims] 1. A continuously variable transmission that continuously changes the output of an engine and transmits it to driving wheels, and two wheels that transmit the rotational force output through the continuously variable transmission to a pair of left and right wheels. In a four-wheel drive vehicle provided with a switching device for switching between a drive state and a four-wheel drive state in which all four wheels are transmitted, a method for controlling a gear ratio of the continuously variable transmission, the two-wheel drive of the vehicle being provided. When a slip of the drive wheels in the state is detected, the gear ratio of the continuously variable transmission is changed in a decreasing direction prior to the switching to the four-wheel drive state. Control method of a gear transmission.