JPH0571407B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a part-time four-wheel drive vehicle capable of switching between two-wheel drive and four-wheel drive, in which the cornering force of the vehicle is adjusted during cornering during two-wheel drive driving. The present invention relates to an automatic switching device for a four-wheel drive vehicle to prevent a decrease in the number of wheels.

[Conventional technology]

Conventionally, in part-time 4-wheel drive vehicles that can be switched between front-wheel drive, rear-wheel drive, and 4-wheel drive, driving power is normally transmitted only to the front wheels or only to the rear wheels, but when driving on rough roads, connected roads, etc. It is now possible to switch to four-wheel drive and drive based on road conditions or driving conditions such as sudden acceleration or deceleration.

[Problem to be solved by the invention] However, in conventional part-time 4-wheel drive vehicles, when the vehicle is cornering and traveling in 4-wheel drive, each wheel distributes the driving force from the engine. Since the driving force from the engine that is handled by one wheel is smaller than that of a two-wheel drive, the cornering force that can be generated by the wheels is greater than that of a two-wheel drive, resulting in smoother cornering. However, when driving in two-wheel drive, the two drive wheels transmit the driving force from the engine to the road surface, so the cornering force that can be generated by the drive wheels is smaller than in four-wheel drive. When the driving force from the engine becomes excessive, the driving wheels cannot bear the centrifugal force caused by cornering and the driving force from the engine, causing the driving wheels to slip, resulting in a problem in which cornering performance deteriorates.

The present invention solves the above-mentioned problems and provides an automatic switching device for a four-wheel drive vehicle that automatically switches to four-wheel drive when cornering in two-wheel drive driving to improve limit performance during cornering. The purpose is to

[Means for solving problems]

To this end, the automatic switching device for a four-wheel drive vehicle of the present invention directly transmits power from the engine to either the front wheels or the rear wheels, and also uses a two-wheel to four-wheel switching clutch to transmit power to both the front and rear wheels. In an automatic switching device for a four-wheel drive vehicle that transmits the power, there is provided a determination means for determining whether the drive is two-wheel drive or four-wheel drive, and a drive force transmitted to the tires when the determination means determines that the drive is in two-wheel drive. An output torque calculation means that calculates a cornering force from the operating state of the engine, a cornering force calculation means that calculates a cornering force based on the running state of the vehicle including the steering wheel turning angle, and an output torque calculated from the output torque calculation means and the cornering force. a comparison means for comparing the calculated value (T _D ² +C _f ² ) obtained from the cornering force calculated by the force calculation means with a preset setting value (G ₂ ); The value ((T _D ² + C _f ² ) is the set value (G ₂ )
an arithmetic control unit (C) comprising a signal output means for outputting a four-wheel drive signal when the signal is larger than the current value; and a solenoid for switching the two-to-four wheel switching clutch to the four-wheel drive side based on the signal from the signal output means. (s).

[Operations and Effects of the Invention] The automatic switching device for a four-wheel drive vehicle of the present invention detects the two-wheel drive state and calculates the driving force transmitted to the tires at that time from the operating state of the engine. a torque calculation means, a cornering force calculation means that calculates a cornering force based on the running state of the vehicle including a steering wheel turning angle, and an output torque calculated from the output torque calculation means and the cornering force calculation means calculated from the cornering force calculation means. The calculation value obtained from the cornering force is compared with the preset setting value and the system automatically switches to four-wheel drive mode.
Depending on the operating state of the engine and the running state of the vehicle, the limits of the vehicle during cornering can be increased, and the stability of the vehicle can be ensured.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram of a control system to which the present invention is applied, FIGS. 2 and 3 are diagrams for explaining control flowcharts in each embodiment of the present invention, and FIG. 4 is a diagram showing the tire grip ability. Figure 5 is a diagram for explaining the engine performance curve, Figure 6 is a diagram showing the engine performance curve.
The figure shows a power transmission system of a part-time four-wheel drive vehicle. In the figure, C is an arithmetic control unit, S is a solenoid, A is an automatic transmission, 1 is a torque converter, 2 is a main transmission, 3 is a sub-transmission, 5 is a drive gear, 6 is a front differential, 7 is the front wheel drive shaft,
9 is a rear wheel drive propeller shaft, 10 is a bevel gear, 11 is a rear wheel output member, 12 is a rear wheel transmission device,
13 indicates a clutch for switching between two wheels and four wheels.

In general, this is an example of a part-time 4-wheel drive vehicle in which the engine is mounted on the front side in a part-time 4-wheel drive vehicle that is capable of 2-wheel drive using either the front or rear wheels or 4-wheel drive using both the front and rear wheels. As shown in FIG. 6, power from the engine is transmitted to a torque converter 1, a main transmission 2, and an auxiliary transmission 3 disposed in an automatic transmission A, and the output is transmitted to a drive gear 5, and then to the drive gear 5. The power is transmitted to the front wheel drive shaft 7 via a front actuating device 6 installed integrally with the gear 5, so that two-wheel drive is performed. On the other hand, the rear wheel drive propeller shaft 9 is connected to the bevel gear 10.
A rear wheel transmission device 12 connected to a rear wheel output member 11 via a rear wheel output member 11 and integrally installed on the rear wheel output member 11 and the drive gear 5 can be freely disconnected by a clutch 13 for switching between two wheels and four wheels. When the switching clutch 13 is operated, power is transmitted from the automatic transmission A to the propeller shaft 9 to drive the rear wheels, resulting in four-wheel drive. The driver then selects the clutch 13 for switching between two wheels and four wheels based on the road surface situation, driving conditions, etc.
2-wheel drive during normal driving,
Or, four-wheel drive driving is performed on frozen roads or during sudden acceleration and deceleration.

On the other hand, when cornering in two-wheel drive driving, the limit of the cornering force of the vehicle is calculated and the two-wheel-to-four-wheel switching clutch 13 is automatically operated to switch to four-wheel drive and change the cornering force of the vehicle. This increases the limit and improves cornering performance. To explain this point in more detail, as shown in Figure 4, the grip capacity G of a tire takes the driving force from the engine on the vertical axis and the cornering force to overcome the centrifugal force during cornering on the horizontal axis. It is represented by a certain circle, and if the driving force from the engine and cornering force are within the range of this circle, there will be no problem when cornering, but if it goes outside the range of the circle, the driving wheels will slip. . Now, when driving force b from the engine is transmitted during cornering in two-wheel drive driving,
Only the cornering force of b′ can be obtained, and
If the relationship G ² < b ² + b′ ² occurs, the driving wheels will slip, but in the case of four-wheel drive driving, the driving force of the engine is distributed among the four wheels, so the driving force handled by one wheel is c =b/2, and conversely, the cornering force c' increases, and slip of the driving wheels no longer occurs.

Next, we will introduce the first control method during cornering.
This will be explained with reference to FIGS. 2, 3, and 3.
First, the control system shown in Figure 1 will be explained.
Detection signals of accelerator opening θ, engine speed N _E , tire load F _t , steering wheel turning angle θ _st , and vehicle speed V are input to an arithmetic and control unit (computer) C, where the driving force from the engine and the cornering force are calculated. is calculated. When the cornering force reaches its limit, an output signal is sent to the solenoid S, and by energizing the solenoid S, the clutch 13 for switching between two wheels and four wheels, as explained in FIG. 6, is switched to the four-wheel drive side. It is something. Then the second
To explain the process flow using the flowchart shown in the figure, when the vehicle starts and runs, it is checked whether the solenoid that operates the clutch 13 for switching between two wheels and four wheels is OFF (two-wheel drive). (Judgment means)
If NO (4-wheel drive), repeat until YES; if YES, perform the next process.

Read the detection signals of accelerator opening θ and engine speed N _E and perform the following processing.

The engine driving force T _E is calculated from the accelerator opening degree θ and the engine rotation speed N _E. This calculation is performed by inputting the engine performance curve shown in FIG. 5 into a computer. Perform the following processing.

T/M output torque (calculates the driving force T _D transmitted to the tires from T _E , torque ratio, gear ratio, differential ratio, and number of gears. (Output torque calculation means) Driving force T _D is greater than constant G , if NO, process YES
In this case, perform the following processing. In addition, the constant G
is the limit value of cornering force set empirically.

Turn on the solenoid that operates the clutch 13 for switching between 2 wheels and 4 wheels to switch to 4 wheel drive. Return to next processing.

Next, the flow of processing will be explained using the embodiment shown in FIG. The processing of .

Tire load F _t , steering wheel turning angle θ _st , vehicle speed V
The detection signal is read and the next processing is performed.

Tire load F _t , steering wheel turning angle θ _st , vehicle speed V
The cornering force C _f is calculated from (cornering force calculation means), and the following processing is performed.

Check whether T _D ² + C _f ² > G ² . (Comparison method) If NO, process YES
In this case, perform the following processing. This results in 4
Switch to wheel drive.

As is clear from the above description, according to the present invention, the driving force from the engine is directly transmitted to one of the front wheels or the rear wheels, and the driving force is transmitted directly to one of the front wheels or the rear wheels by operating the clutch for switching between two wheels and four wheels. In a 4-wheel drive vehicle that also transmits power to the other side, when cornering in 2-wheel drive driving, the limit of cornering force is calculated and the system automatically switches to 4-wheel drive, thereby preventing the drive wheels from slipping and improving the Limit performance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control system to which the present invention is applied, FIGS. 2 and 3 are diagrams for explaining control flowcharts in each embodiment of the present invention, and FIG. 4 is a diagram showing the tire grip ability. Figure 5 is a diagram for explaining the engine performance curve, Figure 6 is a diagram showing the engine performance curve.
The figure shows a power transmission system of a part-time four-wheel drive vehicle. C... Arithmetic control unit, S... Solenoid, A...
...Automatic transmission, 1...Torque converter, 2...
Main transmission, 3... Sub-transmission, 5... Drive gear, 6
...Front differential gear, 7...Front wheel drive shaft, 9
... Propeller shaft for rear wheel drive, 10 ... Bevel gear, 11 ... Rear wheel output member, 12 ... Rear wheel transmission device, 13 ... 2-wheel to four-wheel switching clutch.

Claims (1)

[Claims] 1. A four-wheel drive vehicle that directly transmits power from an engine to either the front wheels or the rear wheels, and transmits power to both the front wheels and the rear wheels using a two-wheel to four-wheel switching clutch. In the automatic switching device, a determining means for determining whether the drive is two-wheel drive or four-wheel drive;
Output torque calculating means for calculating the driving force transmitted to the tires from the operating state of the engine when the determining means determines that the two-wheel drive state is in the two-wheel drive state, and calculating cornering force from the driving state of the vehicle including the steering wheel turning angle. a cornering force calculation means that calculates a cornering force, and compares a calculated value obtained from the output torque calculated from the output torque calculation means and the cornering force calculated from the cornering force calculation means with a preset setting value. an arithmetic control section comprising a comparison means and a signal output means for outputting a four-wheel drive signal when the calculated value is greater than the set value by the comparison means;
An automatic switching device for a four-wheel drive vehicle, comprising a solenoid for switching a wheel switching clutch to a four-wheel drive side.