JP3140845B2 - Torque distribution control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque distribution control device for variably controlling the torque distribution of front and rear wheels in a four-wheel drive vehicle having a center differential device.
The present invention relates to correction for a road surface state in a rear wheel biased unequal torque distribution system.

[0002]

2. Description of the Related Art In a full-time type four-wheel drive vehicle equipped with a center differential device, turning performance and maneuverability are improved by setting the rear wheel biased unequal torque distribution by the center differential device. Also, in the case of a slip, the method of variably controlling the torque distribution of the front and rear wheels by the differential limiting torque of the hydraulic clutch in a range from the rear wheel biased state to the directly connected front wheel biased state,
It has already been proposed by the applicant. As a future subject, it is desired that such a torque distribution control system be electronically controlled so as to sufficiently exhibit its advantages.

[0003] Conventionally, with respect to the torque distribution control of the four-wheel drive vehicle, for example, there is a prior art disclosed in Japanese Patent Application Laid-Open No. 3-86636. Here, in the unequal torque distribution control system, slip control and traction control are performed, and in the slip control, the slip ratio of the rear wheel that always slips first is calculated, and the differential limiting torque is determined according to the slip ratio to distribute the torque. It is shown to control.

[0004]

By the way, in the above-mentioned prior art, in the method of unequal torque distribution of rear wheel bias, it is possible to determine the slip state optimally and control the torque distribution. Since the road surface condition is not taken into consideration, there are the following problems. In other words, in this kind of unequal torque distribution of rear wheel bias, the rear wheel tends to slip during acceleration, and therefore, in order to secure stability on low μ roads, the differential limiting torque should be set large during acceleration. It is desired to perform torque distribution control close to direct connection. However, if the torque distribution control is performed in a direct connection manner during acceleration on a high μ road, the tendency of understeer becomes strong, and the turning property, that is, the characteristic of unequal torque distribution due to rear wheel imbalance cannot be exhibited. Therefore, it is necessary to accurately determine the road surface condition and correct the road surface condition so that both the turning performance of the high μ road and the stability of the low μ road are compatible.

The present invention has been made in view of the above points, and in a torque distribution control system based on unequal torque distribution due to rear wheel bias, turning characteristics and stability during turning acceleration according to road surface conditions are improved. The purpose is to improve both.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a center differential device for setting unequal torque distribution for rear wheel bias, and a differential between the center differential device for limiting torque of front and rear wheels. In a four-wheel drive vehicle with a center differential device having a differential limiting device for controlling distribution, a differential limiting torque setting unit that sets a differential limiting torque of the differential limiting device according to an operating state; A correction coefficient setting unit for setting a correction coefficient for correcting the torque in a weakening direction; and a differential limiting torque set by the differential limiting torque setting unit is corrected by a correction coefficient set by the correction coefficient setting unit. The correction coefficient set by the correction coefficient setting section is set to a smaller value as the lateral acceleration is larger, and is set to the smallest value in a middle to low speed range. Is set so as to be lower when the vehicle speed is lower on the low speed side than the middle and low speed range, and is set to be higher when the vehicle speed is higher on the high speed side than the middle and low speed range. The differential limiting torque is set so as to decrease as the value decreases.

[0007]

Based on the above structure, the road surface condition is determined based on the lateral acceleration during four-wheel drive traveling. In turning acceleration on a high μ road with a large lateral acceleration, the differential limiting torque is corrected to be reduced by the correction coefficient, and the understeer tendency is reduced. The turning property is improved. Also, in turning acceleration on a low μ road with a small lateral acceleration, the differential limiting torque remains increased in accordance with the rear wheel slip in this case, and stability and the like are improved.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 2, the outline of the drive system of a full-time four-wheel drive vehicle equipped with a center differential device will be described. Reference numeral 1 denotes an engine, 2 denotes a clutch, 3 denotes a transmission, and the transmission output shaft 4 is a center differential. It is input to the device 20. The front drive shaft 5 is output forward from the center differential device 20 and the rear drive shaft 6 is output rearward.
Are connected to left and right front wheels 9L and 9R via a front differential device 7 and an axle 8. Rear drive shaft 6
Is a propeller shaft 10, a rear differential device 1
1. The transmission is constructed by being connected to the left and right rear wheels 13L, 13R via the axle 12.

The center differential device 20 is of a compound planetary gear type, and includes a first sun gear 21 integrated with the transmission output shaft 4, a second sun gear 22 integrated with the rear drive shaft 6, and the periphery of these sun gears 21 and 22. The first pinion gear 23 a of the pinion 23 meshes with the first sun gear 21, and the second pinion gear 23 b meshes with the second sun gear 22. A reduction drive gear 25 is rotatably provided on the transmission output shaft 4, and a pinion 23 is supported by a carrier 24 integrated with the drive gear 25. The drive gear 25 is a driven gear integrated with the front drive shaft 5. 26. On the other hand, the center differential device 20 is provided with a hydraulic clutch 27 as a differential limiting device. The hydraulic clutch 27 is arranged coaxially with the drum 27a connected to the carrier 24 and the hub 27b connected to the rear drive shaft 6, for example, immediately after the center differential device 20.

This center differential device 20
With the configuration described above, the shifting power input to the first sun gear 21 is transmitted to the carrier 24 and the second sun gear 22 separately with a predetermined reference torque distribution. In addition, the difference in rotation between the front and rear wheels at the time of turning is absorbed by the planetary rotation of the pinion 23. Here, the reference torque distribution is two sun gears 2
Since the four gear meshing pitch radii of the first and second 22 and the two pinion gears 23a and 23b are freely set, the reference torque distribution of the front and rear wheels can be sufficiently set to the rear wheel biased. When the front engine is mounted, the static weight distribution of the front wheel weight and the rear wheel weight of the vehicle is the front wheel bias, and in the case of the direct connection due to the differential limitation of the hydraulic clutch 27, the front wheel weight is reduced in accordance with this weight distribution. The torque is distributed. Therefore, by controlling the differential limiting torque of the hydraulic clutch 27, it is possible to control the torque distribution of the front and rear wheels in a wide range from the reference torque distribution of rear wheel bias to the weight distribution of front wheel bias.

Next, the hydraulic control system of the hydraulic clutch 27 will be described. First, when the transmission is an automatic transmission, the transmission is configured using a line pressure obtained by adjusting a hydraulic pressure of an oil pump 30 of a hydraulic control system by a regulator valve 31. Therefore, in the hydraulic control unit 32, the line pressure oil passage 33 communicates with the hydraulic clutch 27 via the clutch control valve 34 and the oil passage 35. A line pressure oil passage 33 is connected to a solenoid valve 40 by an oil passage 38 having a pilot valve 36 and an orifice 37.
, The duty pressure of the solenoid valve 40 acts on the control side of the clutch control valve 34 via the oil passage 39.
When a duty signal corresponding to each traveling condition is input from the control unit 50, the solenoid valve 40 drains the hydraulic pressure to generate a duty pressure, and operates the clutch control valve 34 according to the duty pressure. hand,
The differential limiting torque Tc of the hydraulic clutch 27 is variably controlled.

Referring to FIG. 1, the electronic control system of the control unit 50 will be described. First, an engine speed sensor 47 for detecting the engine speed Ne, a throttle sensor 41 for detecting the throttle opening θ, a front wheel speed sensor 42 for detecting the front wheel speed Nf, and a rear wheel speed sensor 43 for detecting the rear wheel speed Nr. , An inhibitor switch 44 for detecting a range position, and a lateral G sensor 45 for detecting a road surface state based on the lateral acceleration Gs of the vehicle. These sensor and switch signals are input to the control unit 50.

The control unit 50 controls the engine speed N
e, a throttle opening θ, and a differential limiting torque setting unit 51 to which a range signal is input. The operating state is determined based on the engine speed Ne and the throttle opening θ, and the traveling mode is determined based on the range signal. For example, for the engine speed Ne and the throttle opening θ, the differential limiting torque Tc is set in an increasing function according to the map of FIG.
Further, it has a rear wheel slip detector 52 to which the front wheel speed Nf and the rear wheel speed Nr are input, and calculates a slip ratio S of the rear wheel that always slips first, for example, based on the angular velocities of the front and rear wheels. The front wheel rotation speed Nf and the rear wheel rotation speed Nr are also input to the vehicle speed detection unit 53, and the vehicle speed V is detected based on, for example, the smaller rotation speed.

The vehicle speed V and the rear wheel slip ratio S are input to a differential limiting torque setting section 51 to avoid a braking phenomenon at an extremely low speed with respect to the vehicle speed V and to prevent deterioration of fuel efficiency at a high speed. In any case, the differential limiting torque Tc is corrected to decrease. For the rear wheel slip ratio S, the differential limiting torque Tc is corrected in an increasing function. Then, the differential limiting torque Tc is input to the duty ratio converting unit 54, converted into a duty ratio D according to the differential limiting torque Tc, and this duty signal is output to the solenoid valve 40.

The correction control system corresponding to the road surface condition will be described. The correction control system includes a correction coefficient setting unit 56 to which the lateral acceleration Gs of the lateral G sensor 45 is input. Here, when turning on a dry high μ road surface state, the lateral acceleration Gs becomes larger than when turning on a low μ road surface state. Therefore, the road surface state can be generally determined using such characteristics. That is, when the lateral acceleration Gs is, for example, 0.3 or less, it can be determined as a low μ road, when it is 0.7 or more, a high μ road, and when the lateral acceleration Gs is 0.5 between the two, it can be determined as a middle μ road. Therefore, in the correction coefficient setting unit 56, the lateral acceleration Gs and the vehicle speed V
The correction coefficient K is set according to the map shown in FIG. 3B according to, and the duty ratio D is multiplied and corrected by the correction coefficient K in the correction section 57 on the output side of the duty ratio conversion section 54.

According to the map shown in FIG. 3 (b), the correction coefficient K is set to a smaller value as the lateral acceleration Gs is larger, that is, the higher the road, the lower the differential limiting torque Tc. It has become. Further, the correction coefficient K is set to the smallest value in the low to middle speed range, and is set to a larger value as the vehicle speed V is lower on the lower side and higher as the vehicle speed V is higher on the higher side.

Next, the operation of this embodiment will be described. First, when the vehicle is running, the power of the engine 1 is input to the transmission 3 via the clutch 2, and the power for shifting is input to the first sun gear 21 of the center differential device 20. Here, since the reference torque distribution is set to the rear wheel biased by each gear specification of the center differential device 20, the carrier 24 and the second sun gear 22
And power is output.

At this time, the control unit 50 of the electronic control system determines the operating state based on the engine speed Ne and the throttle opening θ, and detects the vehicle speed V based on the front and rear wheel speeds Nr, Nr. And when starting the accelerator,
The differential limiting torque setting section 51 sets the differential limiting torque Tc to a large value. However, since the differential limiting torque is extremely low, the reduction is corrected and the duty signal corresponding thereto is output to the solenoid valve 40. Therefore, in the hydraulic control system, a low duty pressure by the solenoid valve 40 acts on the clutch control valve 34,
Accordingly, the amount of oil supplied to the hydraulic clutch 27 is reduced, and a low differential limiting torque Tc is generated.

Therefore, based on the substantially reference torque distribution of the center differential device 20, the carrier 2
4 to gears 25 and 26, front wheels 9L and 9R after the front drive shaft 5, and rear wheels 13L and 9L after the rear drive shaft 6.
Power is transmitted to each of the wheels 13R and 13R, and the vehicle is driven in a four-wheel drive mode with rear-wheel bias. In this torque distribution, the torque distribution becomes FR, and the turning property and the maneuverability are improved. Also, since the center differential device 20 is substantially free, it becomes possible to freely turn while absorbing the rotation difference between the front and rear wheels when turning,
The braking phenomenon is also avoided.

Next, during normal running, the differential limiting torque Tc is set in accordance with the driving condition, and particularly under a high load such as during acceleration, the differential limiting torque Tc is controlled to increase. For this reason, the front and rear wheels tend to be directly connected, and the running performance and the like are sufficiently exhibited.

The rear wheel slip detecting unit 52 detects rear wheel slip. When a slip occurs on a low μ road, the rear wheel 13L or 13R always slips first due to unequal torque distribution due to rear wheel bias. Thus, four-wheel slip is avoided. At the time of this rear wheel slip, the differential limiting torque Tc of the hydraulic clutch 27 is controlled to be high according to the slip ratio S, whereby the center differential device 20
Differential is limited. In addition, the power is bypassed and transmitted from the second sun gear 22 to the carrier 24 in accordance with the differential limiting torque Tc, and the load shifts from rear wheel bias to torque distribution closer to the front wheel or is directly connected, thus causing slip. Is prevented.

Further, when a large lateral acceleration Gs is generated, the correction coefficient setting unit 56 regards the turning on a high μ road as a correction coefficient K,
Is set to a small value (zero in a low-medium speed range), and the correction unit 57
Reduces the duty ratio D. Therefore, in the hydraulic control system, the differential limiting torque Tc of the hydraulic clutch 27 is also reduced, and the rear wheel biased torque distribution is performed based on the reference torque distribution of the center differential device 20. For this reason, as shown in FIG. 4, the yaw rate tends to increase, the understeer is reduced, and the turning performance is improved. On the other hand, when the lateral acceleration Gs is small, it is considered that the vehicle is turning on a low μ road, and the correction using the correction coefficient K is not performed, and the differential limiting torque Tc can be controlled to a substantially directly-coupled torque distribution according to the rear wheel slip state. Stability is ensured.

Although the embodiment of the present invention has been described above, the present invention is not limited to this.

[0024]

As described above, according to the present invention, in a four-wheel drive vehicle equipped with a center differential device set for unequal torque distribution of rear wheel imbalance, torque distribution of front and rear wheels by differential limiting torque. Is controlled, the road surface condition is detected based on the lateral acceleration, and the differential limiting torque in the low to medium speed range is corrected in accordance with the road surface condition, so that the torque distribution during turning acceleration can be optimally controlled.

At the time of turning acceleration on a high μ road, the differential limiting torque is corrected to decrease, so that the advantage of the reference torque distribution of the center differential device can be sufficiently exhibited and the turning performance can be improved. Also, at the time of turning acceleration on a low μ road, the differential limiting torque is increased and corrected according to the slip state, so that safety and the like can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control system of an embodiment of a torque distribution control device for a four-wheel drive vehicle of the present invention.

FIG. 2 is a configuration diagram showing the overall configuration of a four-wheel drive vehicle with a center differential device to which the present invention is applied.

FIG. 3 is a diagram showing a map of a differential limiting torque and a correction coefficient.

FIG. 4 is a diagram showing a state of a high μ road at the time of turning acceleration.

[Explanation of symbols]

 Reference Signs List 20 center differential device 27 differential limiting hydraulic clutch 45 lateral G sensor 50 control unit 55 road μ detection unit 56 correction coefficient setting unit 57 correction unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60K 17/28-17/36 B60K 23/00-23/08

Claims (1)

(57) [Claims] 1. A center differential device having a center differential device for setting unequal torque distribution of rear wheel bias, and a differential limiting device for limiting the differential of the center differential device and controlling the torque distribution of front and rear wheels. in four-wheel drive vehicle, the correction to set the differential limiting torque setting unit for setting a differential limiting torque of the differential limiting apparatus according to operating conditions, a correction factor for correcting the direction of weakening the differential limiting torque A coefficient setting unit, and a correction unit that corrects the differential limiting torque set by the differential limiting torque setting unit with a correction coefficient set by the correction coefficient setting unit.
The correction coefficient is set to a smaller value as the lateral acceleration increases.
And the smallest value in the middle and low speed range
Set, and the lower the vehicle speed at lower speeds than the middle / low speed range,
Larger value, higher at higher vehicle speeds than mid-low speed range
The correction unit sets the correction coefficient
It is set so that the differential limiting torque decreases as the value decreases.
And four-wheel drive vehicle torque distribution control apparatus, characterized in that are.