JPH0818503B2 - 4-wheel drive vehicle with front and rear wheel engagement mechanism - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a four-wheel drive vehicle capable of slip prevention control that detects slip from the rotation speed ratio of front wheels and rear wheels to control front and rear wheel engagement mechanisms.

[Conventional technology]

Generally, when driving a car, front-wheel drive has better straight-line stability than rear-wheel drive, but when cornering, the tires trying to return must apply force with the steering wheel, so front-wheel drive is less likely to bend. Tend. In that respect, the rear-wheel drive is more likely to bend, but if the driving force is too strong, it has the drawback of overturning. Therefore, it is ideal for driving the vehicle to drive the front wheels and the rear wheels with a force of about half and half, and in this respect, the four-wheel drive vehicle is extremely excellent.

By the way, since the turning radii of the left and right wheels of the automobile are different during cornering, this effect is absorbed, and in order to perform smooth cornering, the difference in rotational speed between the left and right wheels is absorbed according to the difference in turning radius. A mechanism, that is, a differential mechanism (front differential, rear differential) is provided. Since this difference in turning radius also occurs between the front wheels and the rear wheels, in a four-wheel drive vehicle, a mechanism that absorbs the difference in rotation speed between the front wheels and the rear wheels according to the difference in turning radius, that is, a center differential mechanism. The one with is proposed.

However, since this center differential mechanism has a function of distributing the torques of the front wheels and the rear wheels in an equal ratio, the driving force transmission limit should be balanced with the lower value of the driving force of the front wheels or the rear wheels. Becomes For example, if one of the front wheels runs idle, the driving energy escapes there, and the driving force of the rear wheels becomes extremely small. Therefore, a four-wheel drive vehicle with a center differential is
Compared with a wheel drive vehicle, the transmission drive force may be inferior when the road surface friction coefficient is low. This appears as a phenomenon such as a slip (idling) of the front wheels or the rear wheels when the driving force cannot be sufficiently transmitted to the road surface when a large driving force is generated such as during acceleration.

In order to prevent such an adverse effect, conventionally, a lock mechanism that directly connects the differential limitation between the front wheels and the rear wheels without using a center differential is provided, and a large driving force is required such as when accelerating or traveling on a rough road. In that case, the center differential mechanism was manually locked, and the lock was manually unlocked during normal running that does not require a large driving force.

FIG. 10 is a diagram for explaining a driving force transmission mechanism of a full-time four-wheel drive vehicle with a center differential in which an engine is mounted on the front side. In this drive force transmission mechanism, the power from the engine is transmitted to the torque converter 31, the main transmission 32, and the auxiliary transmission 33 arranged in the automatic transmission 30, and the output thereof is the drive gear 34 and then the drive gear. It is transmitted to the front wheel drive shaft 36 via 34, and the front wheels are driven. Here, the front differential mechanism 35 is a differential mechanism between the right wheel and the left wheel of the front wheels. On the other hand, the rear wheel drive propeller shaft 37 is connected via a bevel gear 38 to a center differential mechanism 39, which is a differential mechanism between the front and rear wheels.
Is coupled to the rear wheel transmission 40. Further, a center differential lock clutch is provided in parallel with the center differential mechanism 39.
41 are arranged. Therefore, the lock of the center differential is controlled by controlling the engagement state of the clutch 41 by the hydraulic circuit 42.

Generally, as a four-wheel drive vehicle, there is a part-time four-wheel drive vehicle in addition to the full-time four-wheel drive vehicle. This is a two-wheel drive system that does not have a center differential and normally drives either the front wheels or the rear wheels, and when the driving force is required on a snowy road, etc., the remaining wheels are directly connected to the drive shaft via a clutch etc. And four-wheel drive are switched intermittently.

By the way, conventionally, a proposal for avoiding a tight corner braking phenomenon or a slip is disclosed in, for example, Japanese Patent Laid-Open No. 57-
No. 134330 is published. This relates to a part-time four-wheel drive vehicle, in which slip is detected from the rotational speed difference between the front wheels and the rear wheels to control the on / off of a clutch that connects the front wheels and the rear wheels, thereby driving the front wheels and the four wheels. Is automatically switched. Specifically, the wheel rotation speeds of the front wheels and the rear wheels are detected, and when the rotation speed difference is larger than a preset value, the clutch connecting the front wheels and the rear wheels is operated to drive the front wheels. To switch from four-wheel drive to slip.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, the accuracy of the slip determination is poor, and rather, the slip cannot be detected even if the slip actually occurs, and conversely, the slip is detected even though the vehicle is not in the traveling state in which the slip occurs. There is a problem that erroneous decisions are made. That is, the rotational speed difference that does not cause slippage generally increases with the vehicle speed under the influence of the steering angle in a region where the vehicle speed is low, as shown by l in FIG. 9, and the centrifugal force is increased when the vehicle speed is around 20 km / h. There is a relation that it becomes large and decreases rapidly. For this reason, if the set value of the rotational speed difference is set to a fixed value, for example, the reference line L and the slip is determined as in the conventional technique described above, an erroneous determination is made in the shaded area.

The present invention solves the above-mentioned problems, and can detect a slip accurately from the rotation speed of the front wheels and the rotation speed of the rear wheels, and can effectively control the front and rear wheel engagement mechanism. An object of the present invention is to provide a four-wheel drive vehicle equipped with.

[Means for solving problems]

Therefore, the present invention provides a four-wheel drive vehicle including front and rear wheel engagement mechanisms in which the differential degree between the front wheels and the rear wheels can be controlled from direct connection to release through a slip region by controlling the degree of engagement. , An engaging means for driving the front and rear wheel engaging mechanism with a set degree of engagement, a detecting means for detecting a traveling state of the vehicle, and a slip limit value for setting a constant rotation speed ratio in a low vehicle speed range are preset and stored. And a control means for controlling the engagement means so as to increase the degree of engagement of the front and rear wheel engagement mechanism when the rotation speed ratio is obtained from the detection signal of the detection means and the rotation speed ratio is larger than the slip limit value. It is characterized by having.

[Operation and effect of the invention]

In the four-wheel drive vehicle equipped with the front and rear wheel engaging mechanism of the present invention, by paying attention to the fact that the slip limit value of the rotation speed ratio of the front and rear wheels becomes constant in the low vehicle speed range, the rotation speed becomes constant as the slip limit value. The speed ratio is set and stored, and when the rotation speed ratio is greater than the slip limit value, the degree of engagement of the front and rear wheel engagement mechanisms is increased.Therefore, in the low vehicle speed range, wheel slip prevention is performed while simplifying control. It can be done reliably.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a block configuration diagram for explaining one embodiment of a four-wheel drive vehicle equipped with front and rear wheel engagement mechanisms of the present invention, FIG. 2 is a diagram showing a rotational speed ratio at a slip occurrence limit, and FIG. Is a diagram showing the rotational speed ratio of the slip limit according to the steering angle,
The figure is a diagram showing the rotation speed ratio of the slip limit depending on the vehicle speed.

In FIG. 1, 1 is a steering sensor, 2 is a front wheel rotation sensor, 3 is a rear wheel rotation sensor, 4 is a vehicle speed sensor, 5-8 are interfaces, 9 is a control device (computer), 10 is a solenoid drive circuit, and 11 is The pressure regulating solenoid is shown. The interfaces 5 to 8 convert the output signal of each sensor into a signal that can be processed by the control device 9. For example, when the output signal of the sensor is an analog signal, A / D conversion processing is performed to output the sensor output. If the signal is a pulse signal, waveform shaping processing is performed. Control device 9
Is for controlling the solenoid drive circuit 10 by inputting the output signal of each sensor and performing arithmetic processing to make a slip determination. For example, a memory for storing a processing program and a table necessary for slip determination and an arithmetic operation. And a processing means.

Next, a slip determination process performed by the control device 9 will be described. In the control device of the present invention, as shown in FIG. 2, the rotation speed ratio r (N _f / N _r ) of the front and rear wheels is 1 <r <1 + α (where α <1) until the vehicle speed is about 20 km / h. When the vehicle speed further increases, slipping is determined if the vehicle speed deviates from the region (a) of 1 <r <curve a. The value of α is set based on the graph shown in FIG. 3, and the curve a is set based on the graph shown in FIG. That is, the steering angle is 0
The rotational speed ratio of the slip limit when changing from ゜ to 720 ゜ increases with the steering angle as shown in Fig. 3 because the difference in turning radius increases with increasing steering angle, and the vehicle speed is gradually increased. In this case, the slip limit rotation speed ratio becomes sharply smaller than the vehicle speed around 20 km / h as shown in FIG. 4 because the grip force at the wheels becomes smaller as the vehicle speed increases and the centrifugal force increases. As is clear from these figures, the slip limit rotation speed ratio greatly depends on the vehicle speed when the vehicle speed exceeds about 20 km / h, but depends on the steering angle at a lower vehicle speed. The value of α shown in FIG. 2 is determined by the steering angle, that is, FIG. 3, and indicates the slip limit region at the steering angle of 720 °. Therefore, for example, when the steering angle is 510 °, the value of α is 0.1, and when the steering angle is 360 °, the value of α is 0.05. In order to perform such slip determination processing, the control device 9 uses the third
The maps (tables) shown in FIGS. 4 and 5 are stored in the memory.

FIG. 5 is a block diagram showing a specific functional configuration of the control device, and FIG. 6 is a diagram showing an example of a processing flow by the control device.

In FIG. 5, 21 is a vehicle speed calculation unit, 22 is a steering angle calculation unit, 23 is a front wheel rotation speed calculation unit, 24 is a rear wheel rotation speed calculation unit, 25 is a vehicle speed rotation speed ratio setting unit, and 26 is a steering angle. A rotation speed ratio setting unit, 27 is a rotation speed ratio calculating unit, 28 is a slip region determining unit, and 29 is a hydraulic pressure setting unit. The vehicle speed rotation speed ratio setting unit 25 is a map (table) shown in FIG.
This is to obtain the rotation speed ratio corresponding to the vehicle speed from this map.
Is to obtain a rotation speed ratio corresponding to the steering angle from the map shown in FIG. 3 (set it to a large value that can be ignored when the vehicle speed is high). It is the slip area determination unit 28 that selects the one rotation speed ratio. Then, the oil pressure setting unit 29 compares the rotation speed ratio obtained by the slip area determination unit 28 with the actual rotation speed ratio of the front and rear wheels obtained by the rotation speed ratio calculation unit 27, and determines the actual rotation of the front and rear wheels. If the number ratio is in the slip range, increase the oil pressure of the clutch to lock the center differential,
When it is not in the slip range, the oil pressure of the clutch is reduced to unlock the center differential.

With the above configuration, when the rotation speed ratio of the front and rear wheels, the vehicle speed, and the steering angle are input, the maximum and minimum values of the rotation speed ratio, which are the limits determined by the steering angle and the vehicle speed, are retrieved from the memory and the rotation speed ratio of the front and rear wheels is calculated. Compare with. If the rotation speed ratio of the front and rear wheels does not fall between the maximum and minimum values of the limit rotation speed ratio, it is determined to be slip and the differential between the front and rear wheels is limited (center differential is locked). The maximum value of the limit rotation speed ratio is the smaller one of the maximum value by the steering angle and the maximum value by the vehicle speed.

FIG. 6 shows an example of processing when the above-described slip prevention control is performed by software by the control device. In this example, the rotation sensor is attached to the transmission and the rear wheels, and the output of the rotation sensor of the transmission is used as the rotation speed of the front wheels and the vehicle speed. The flow of processing will be described below step by step.

First, the rotation cycle of the transmission is measured to obtain the rotation speed N _f , and similarly, the rotation cycle of the rear wheels is measured to determine the rotation speed N _r.
Ask for. Then, the rotation speed ratio r = N _f / N _r is calculated (~
).

Next, it is checked whether the rotation speed N _f is larger than 60 km / h, and YE
In the case of S, the limit speed ratio r _max due to the steering angle
_{Let θ} be 2.0 (a value for ignoring the influence of the steering angle in subsequent processing), and in the case of NO, input the steering angle θ and set the limit rotation speed ratio r _{max θ} by the steering angle to the table f ₁ (θ ). Further, the limit rotation speed ratio r _{maxn depending} on the vehicle speed is read from the table f ₂ (N _f ) (
~).

Then, the limit rotation speed ratio r _{max θ depending on} the steering angle
And the limit speed ratio r _{maxn depending on} the vehicle speed are compared, and when the former is large, the limit speed ratio r _max for judging slip is determined.
Is the limit speed ratio r _{max θ} depending on the steering angle, and if the former is small, the limit speed ratio for slip determination
Let r _{max be the} limit speed ratio r _{maxn depending} on the vehicle speed. From the rotational speed ratio r _max that is the limit for determining slip, it is determined whether the actual rotational speed ratio r = N _f / N _r is within the slip determination limit, and if YES, the clutch hydraulic pressure is reduced. If NO, it is assumed that slip has been detected and the oil pressure of the clutch is increased (~). In this case, the values Δ1 and Δ2 in consideration of the measurement error may be adjusted with respect to the limit rotational speed ratios r _max and r _min shown in FIG.

FIG. 7 is a diagram showing an example of setting the hydraulic pressure when the differential is limited by the clutch according to the rotational speed ratio, and FIG. 8 is an example of setting the hydraulic pressure when the differential is limited by the clutch depending on the time. It is a figure.

When slip is detected, if the center differential, which has rapidly actuated the clutch, is locked, a sudden increase in driving force causes a pop-out phenomenon or blurring, which deteriorates riding comfort, running performance, and operability. Therefore, as shown in FIG. 7, the difference δ between the actual rotation speed ratio and the limit rotation speed ratios r _max and r _min (δ _{1 in} the case of point A shown in FIG. 2 and δ ₁ in the case of point B). δ ₂ ), that is, by controlling the hydraulic pressure P according to the depth of the slip occurrence region and gradually increasing the engagement of the clutch from the region where the slip begins to occur, it is possible to improve the riding comfort, running performance, and operability. . Further, as shown in FIG. 8, by increasing the hydraulic pressure P with time T and gradually strengthening the engagement of the clutch, it is possible to improve the riding comfort, running performance and operability. Hydraulic pressure P shown in FIG. 8 starts engagement from the vicinity of 1 kg / m ^2, there is shown an example of a clutch fully engaged around 4 kg / m ^2.

The present invention can be modified in various ways and is not limited to the above embodiments. For example, in the above-described embodiment, the front and rear wheel engagement mechanism is applied to the full-time type four-wheel drive vehicle with a center differential, but it is also applicable to a part-time type four-wheel drive vehicle. The front and rear wheel engagement mechanism in this case is a mechanism that can control the differential limitation between the front and rear wheels from direct connection to release through the slip area by controlling the degree of engagement. The latter is a center clutch that directly connects the front and rear wheels. Specifically, it is not limited to the hydraulic clutch, and any electromagnetic type or any other device that can control the degree of engagement may be used. In addition, a front wheel rotation sensor, a rear wheel rotation sensor, and a vehicle speed (T / M rotation) sensor are provided. Using any two of these, the vehicle speed and the front-rear wheel rotation speed ratio are obtained. You may do it. Therefore,
In this case, a speed sensor may be attached to the transmission and the propeller shaft, and a steering sensor may be attached to the steering. When the steering sensor is not attached, the steering angle may be maximized, that is, the slip determination may be performed using the map shown in FIG. 2, or in consideration of the situation that slip is likely to occur during operation of the brake. You may make it change a map according to the operating state of a brake.

Further, also in the control of the degree of engagement, the characteristics shown in FIG. 7 are replaced by P = kδ ² (k is a constant) or another function, and the front and rear wheel engagement is performed in accordance with the distance that the rotational speed ratio of the front and rear wheels deviates from the zone. It suffices to control the degree of engagement of the mechanism, and determine the hydraulic pressure at the time of slipping as a function of the time t from the time of starting to slip, or the hydraulic pressure P = k ₂ t ² + k ₁ t + k ₀ . The degree of engagement may be controlled according to time using a function of time or a table.

As is apparent from the above description, according to the present invention, as the speed sensor, in addition to the conventional vehicle speed (T / M rotation) sensor, only a front wheel or rear wheel sensor needs to be added, so that the structure is simple. Becomes In addition, since the rotation speed ratio is used as a criterion for slip, it is not affected by the vehicle speed,
The slip detection accuracy can be improved even at low speeds.
Furthermore, since the degree of engagement of the front and rear wheel engagement mechanism is controlled according to the degree of slippage and the time, it is possible to improve riding comfort, running performance, and operability.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining one embodiment of a four-wheel drive vehicle equipped with front and rear wheel engaging mechanisms of the present invention, FIG. 2 is a diagram showing a rotational speed ratio at a slip occurrence limit, and FIG. 6 is a diagram showing a slip limit rotation speed ratio according to a steering angle, FIG. 4 is a diagram showing a slip limit rotation speed ratio according to a vehicle speed, FIG. 5 is a block diagram showing a concrete functional configuration of a control device, FIG.
FIG. 7 is a diagram showing an example of the flow of processing by the control device, FIG. 7 is a diagram showing an example of hydraulic pressure setting when the differential is limited by the clutch according to the rotation speed ratio, and FIG. Diagram showing an example of hydraulic pressure setting when limiting the differential,
FIG. 9 is a diagram for explaining the rotational speed difference at the slip limit,
FIG. 10 is a diagram for explaining a driving force transmission mechanism of a full-time four-wheel drive vehicle with a center differential in which an engine is mounted on the front side. 1 ... Steering sensor, 2 ... Front wheel rotation sensor, 3 ... Rear wheel rotation sensor, 4 ... Vehicle speed sensor, 5
~ 8 ... Interface, 9 ... Control device (computer), 10 ... Solenoid drive circuit, 11 ... Pressure adjusting solenoid, 21 ... Vehicle speed calculation unit, 22 ... Steering angle calculation unit, 23 ... Front wheel speed Calculation unit, 24 ... Rear wheel rotation speed calculation unit, 25 ... Rotation speed ratio setting unit by vehicle speed, 26 ... Rotation speed ratio setting unit by steering angle, 27 ... Rotation speed ratio calculation unit,
28 …… Slip area determination unit, 29 …… Hydraulic pressure setting unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsugu Tatsuda 10 Takane, Fujii-cho, Anjo-shi, Aichi Aisin Warner Co., Ltd. (56) References JP-A-55-72420 (JP, A) -64029 (JP, U)

Claims (5)

[Claims] 1. A four-wheel drive vehicle equipped with front and rear wheel engaging mechanisms, wherein differential limitation between front wheels and rear wheels can be controlled from direct connection to release through a slip region by controlling the degree of engagement, Engagement means for driving the front and rear wheel engagement mechanism at a set degree of engagement, detection means for detecting the running state of the vehicle, and a slip limit value for maintaining a constant rotation speed ratio in the low vehicle speed range are preset and stored. Control means for controlling the engagement means so as to increase the degree of engagement of the front and rear wheel engagement mechanism when the rotation speed ratio is obtained from the detection signal of the detection means and the rotation speed ratio is larger than the slip limit value. A four-wheel drive vehicle equipped with front and rear wheel engaging mechanisms. 2. A front / rear wheel engaging mechanism according to claim 1, further comprising a center differential mechanism which absorbs a difference in turning radius between the front and rear wheels in parallel with the front / rear wheel engaging mechanism. 4-wheel drive vehicle. 3. The control means sets a slip limit value such that the value of the constant rotation speed ratio increases as the steering angle increases in a low vehicle speed range. A four-wheel drive vehicle including the front and rear wheel engaging mechanism according to any one of items 1 to 3. 4. The control means controls the front-rear direction according to the difference between the rotational speed ratios when the rotational speed ratio of the front and rear wheels obtained from the detection signal of the detection means becomes larger than the rotational speed ratio set as the slip limit value. The first aspect of the present invention is characterized in that the engagement means is controlled so as to increase the degree of engagement of the wheel engagement mechanism.
A four-wheel drive vehicle including the front and rear wheel engagement mechanism according to any one of items 1 to 3. 5. The front and rear wheel engagement mechanism according to the time after the rotation speed ratio of the front and rear wheels obtained from the detection signal of the detection means becomes larger than the rotation speed ratio set as the slip limit value. A four-wheel drive vehicle equipped with the front and rear wheel engagement mechanism according to any one of claims 1 to 4, wherein the engagement means is controlled so as to increase the degree of engagement.