JPH0419231A - Driving force distribution switching type four-wheel drive automobile - Google Patents

Abstract

PURPOSE:To improve reliability in control by controlling the driving torque transmitting state according to the difference between front wheel speed and rear wheel speed. CONSTITUTION:The rotating speed difference computing part 48a of a control means 48 computes the difference of the rotating speed of wheels 16, 18, 24, 26 detected by front wheel speed detecting means 40, 42 and rear wheel speed detecting means 44, 46. The computed rotating speed difference is compared with the preset threshold value by a comparing/judging part 48b, and when the rotating speed difference is smaller than the threshold value, a control signal output part 48c outputs such a control signal to a driving force distribution control means 56 as not to limit the differential transmission of a center differential gear 12. When the rotating speed difference is larger than the threshold value, the control signal output part 48c outputs such a control signal to the driving force distribution control means 56 as to limit the differential transmission of the center differential gear 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a four-wheel drive vehicle capable of switching the distribution of driving force, and in particular, to a motor vehicle capable of changing the distribution of driving force, and in particular, it is used to suppress wheel slip and adjust the yaw angular acceleration to a suitable value. The present invention relates to an active power distribution switching type 4611 motor vehicle equipped with means for switching the distribution of driving force based on the following.

[Prior Art] In a four-wheel drive vehicle, a driving force transmission device has conventionally been configured to control the ratio of torque transmitted to the front wheels and torque transmitted to the rear wheels according to driving conditions. Various types are known.

For example, a driving force transmission device in which a differential limiting device such as a VCU (viscous coupling unit) is attached to the center differential to appropriately regulate the difference in rotation speed of the center differential, a hydraulic multi-disc clutch, etc. A driving force transmission device has been developed in which the power transmission state can be adjusted according to the control oil pressure.

It is conceivable that such a driving force transmission device performs various controls depending on the driving state of the vehicle and the like.

[Problems to be Solved by the Invention] By the way, if the center differential allows differential movement between the front and rear wheels, one of the front and rear wheels may slip. In this case, the driving force is transmitted to the slipping wheel, and the output torque of the engine is not transmitted to the road surface, making it difficult to accelerate the vehicle.

Therefore, when a wheel slips, it is conceivable to immediately restrict the differential of the center differential by a differential limiting device to suppress the wheel slip.

The present invention was devised in view of the above-mentioned problem, and while normally allowing the differential between the front and rear wheels to obtain a predetermined drive force distribution, when the wheels start spinning, the present invention reduces the differential between the front and rear wheels. It is an object of the present invention to provide a four-wheel drive vehicle with a switching driving force distribution type that can quickly regulate and reliably suppress wheel slip.

[Means for Solving the Problems] Therefore, the driving force distribution switching type four-wheel drive vehicle of the present invention is a four-wheel drive vehicle that can actively drive the vehicle by transmitting the output torque of the engine to the front wheels and the rear wheels. , a driving force distribution control means capable of controlling the distribution of the output torque between the front wheels and the rear wheels; a front wheel speed detection means detecting the rotational speed of the front wheels;
Rear wheel speed detection means for detecting the rotational speed of the rear wheels, and control for outputting a control signal for controlling the state of distribution of driving force to the front wheels and the rear wheels based on information from these detection means. The driving force distribution control means includes a center differential that differentially operates between the front wheels and the rear wheels, and a differential limiting mechanism that limits the differential movement of the center differential, and the control means includes a rotational speed difference calculation section that calculates the difference in rotational speed of each wheel detected by the front wheel speed detection means and the rear wheel speed detection means; a comparison/judgment unit that compares and makes a decision with a threshold; and the comparison/judgment unit outputs a control signal to the driving force distribution control means so as not to limit the differential of the center differential when the rotational speed difference is smaller than the threshold; and a control signal output section that outputs a control signal to the active force distribution control means so as to limit the differential of the center differential when the rotational speed difference is larger than the threshold value. There is.

[Function] In the active power distribution switching type four-wheel drive vehicle of the present invention described above,
The rotational speed difference calculation section of the control means calculates the difference between the rotational speeds of each wheel detected by the front wheel speed detection means and the rear wheel speed detection means, and the comparison determination section sets the calculated rotational speed difference in advance. If the rotational speed difference is smaller than the threshold, a control signal is output from the control signal output section to the driving force distribution control means so as not to limit the differential of the center differential; When the rotational speed difference is larger than the threshold value, a control signal is output from the control signal output section to the driving force distribution control means so as to limit the differential movement of the center differential. This results in
Normally, a vehicle is driven by four wheels with a predetermined drive force distribution, with differential differential between the front and rear wheels allowed within a certain range, and if any wheel slips, the differential is immediately limited. Wheel slip is suppressed.

[Embodiment] A four-wheel drive vehicle with active power distribution switching as an embodiment of the present invention will be explained below with reference to the drawings. Fig. 1 is a schematic configuration diagram of the active system, and Fig. 2 shows its control contents. FIG. 3 is a graph showing the characteristics of the yaw angular velocity according to the control.

In FIG. 1 showing the overall configuration, reference numeral 2 denotes an engine, and the output of the engine 2 is transmitted to an output shaft 8 via a torque converter 4 and an automatic transmission 6. The output of the output shaft 8 is transmitted to a planetary gear type differential device (center differential) 12 via an intermediate gear 10.

The output of this planetary gear type differential 12 is transmitted on the one hand to a reduction gear mechanism 19. The transmission is transmitted from the axles 17L, 17R to the left and right front wheels 16.18 via the front wheel differential gear mechanism 14, and the bevel gear mechanism 15. Propeller shaft 20 and bevel gear mechanism 21. Differential gear device 2 for rear wheels
2 from the axles 25L and 25R to the left and right rear wheels 24.2
6. The planetary gear type differential device 112 includes a sun gear 12a, a planetary gear 12b disposed outside the sun gear 12a, and a ring gear 12c disposed outside the planetary gear 12b, as in the conventionally known one. A carrier 12d that supports the planetary gear 12b.
The output of the output shaft 8 of the automatic transmission 6 is inputted to the , the sun gear 12a is interlocked with a front wheel differential gearing 14, and the ring gear 12c is interlocked with a propeller shaft 20.

Further, a hydraulic multi-disc clutch 28 whose frictional force changes depending on the pressure applied to its own hydraulic chamber is interposed between the ring gear 12c and the carrier 12d as driving force distribution control means.

The planetary gear type differential device 12 appropriately controls the hydraulic multi-disc clutch 28 from a completely free state to a locked state, thereby controlling the torque transmitted to the front wheels and the rear wheels.
Front 1m: Fixed ratio when the rear wheels are completely free (for example, about 33:
67) to a fixed ratio when locked (here, 50:5)
(approximately 0). In other words, the pressure in the hydraulic chamber of the hydraulic multi-disc clutch 28 is in the minimum pressure state (Mi
n) That is, when it is zero and in a completely free state, the front a:rear transport is about 33:67 (it varies depending on the load balance between the front wheel system and the rear wheel system, etc., but it is generally around this value). ), when the pressure in the hydraulic chamber is at the maximum pressure state (Max), that is, the set pressure (for example, 9 kg/ci), the hydraulic multi-disc clutch 28 is in the locked state, and the differential restriction becomes substantially zero. Front wheel:Rear wheel set constant ratio 50:
50, resulting in a direct connection state.

Further, reference numeral 30 denotes a steering sensor that detects the rotation angle of the steering wheel 32 from the neutral position, that is, the steering angle θ;
34a is a front lateral acceleration sensor (front lateral acceleration means) for detecting lateral acceleration G□ acting on the front of the vehicle body;
b is a rear lateral acceleration detection sensor (rear lateral acceleration detection means) that detects lateral acceleration G2 acting on the rear of the vehicle body;
36 is a longitudinal acceleration sensor that detects longitudinal acceleration Gx acting on the vehicle body; 38 is a throttle sensor that detects the throttle opening of engine 2; 39 is an engine key switch of engine 2; 40.42.44.46 are the front left wheel 16, the front right wheel 18, and the rear left wheel 26, respectively. Right rear wheel 28
The vehicle speed is also calculated based on the detected values of these wheel speed sensors 16, 18, 26, and 28. Further, 41 is an engine rotation speed sensor.

The outputs of these switches and each sensor are input to a controller (control means) 48. The controller 48 controls each hydraulic multi-disc clutch 2 based on the detected values of these sensors.
8 connection states are controlled.

Reference numeral 50 indicates an anti-lock brake device, and this anti-lock brake device 50 operates in conjunction with a brake switch (not shown). That is, when the brake switch is turned on when the brake pedal is depressed, an anti-lock brake activation signal is output in conjunction with this, and the anti-lock brake device 50 is activated. When the anti-lock brake activation signal is output, a signal indicating the state thereof is simultaneously input to the controller 48. Further, 52 is a warning light that lights up based on a control signal from the controller 48.

Note that the controller 48 is a computer equipped with a CPU, ROM, RAM, interface, etc. necessary for control, which will be described later, although not shown.

Reference numeral 54 indicates a hydraulic power source, and 56 indicates a pressure control valve interposed between the hydraulic power source 54 and the hydraulic chamber of the hydraulic multi-disc clutch 28, and this pressure control valve 56 is controlled by a control signal from the controller 48. It has become so.

By the way, the controller 48 includes a control signal output section 48c that outputs a control signal to the pressure control valve 56 as described above in order to control the state of distribution of driving force to the front wheels 16.18 and the rear wheels 24.26. However, the controller 4
8 further includes each wheel speed sensor 16 for the front wheel and the rear wheel.
, 18, 26° 28; a rotational speed difference calculation unit 48a that calculates the difference 1ωf−ω4I between the rotational speed ωf of the front wheel and the rotational speed ω of the rear wheel detected at 28;
The rotational speed difference 1ωf-ωrl calculated by is a preset threshold value ω. A comparison/determination section 48b is provided for comparing and determining.

Note that the rotational speed ωf of the front wheels is determined by each wheel speed sensor 1 of the front wheels.
The average value of the detected values ωfffitωfr of 6 and 18, that is, ω, = (ωf! 10ωfr)/2, and the rotational speed ω1 of the rear wheel is the detected value ω of each wheel speed sensor 26°28 of the rear wheel.
The average value of rL, ωrr, that is, ω1=(ωr4+ωr
r)/2.

The four-wheel drive vehicle with switching drive force distribution according to the present invention is constructed as described above, and the operation of its drive system will now be described in accordance with the flowchart shown in FIG.

First, the wheel speed sensor 40, 42, 44, 46 reads the rotational speed ωf of the front wheel and the rotational speed ω1 of the rear wheel (step 51). The comparison and determination section 48b calculates the difference 1ωf-ωr1 between the rotational speed ω1 and the rotational speed difference 1ωf-ωr.
I is the threshold ω. It is determined whether it is larger than (step s2).

Then, the rotational speed difference 1ωf−ωr1 is the threshold value ω. If it is not greater than , the process proceeds to step S4, where a control signal is output from the control signal output section 48c to the pressure control valve 56 to minimize the oil pressure. As a result, the pressure in the hydraulic chamber of the hydraulic multi-disc clutch 28 is set to zero, the hydraulic multi-disc clutch 28 becomes completely free, and a center differential free state is established in which the center differential operates, thereby distributing torque to the front wheels and rear wheels. The ratio is about 33:67.

On the other hand, the rotational speed difference 1ωf-ωr1 is the threshold value ω. If it is not larger than
A control signal is output from 8c to the pressure control valve 56 to maximize the oil pressure.

As a result, the pressure in the hydraulic chamber of the hydraulic multi-disc clutch 28 is set to the set pressure (for example, 9 kg/d), the hydraulic multi-disc clutch 28 is locked, and the center differential is directly connected (center differential lock state), and the front wheels and Drive torque is reliably transmitted to each wheel at a predetermined torque distribution ratio to the rear wheels (here, 50:50).

In this way, by controlling the transmission state of drive torque according to the difference 1ωf - ωr1 between the wheel speed ωf of the front wheels and the wheel speed ω of the rear wheels, a differential between the front wheels and the rear wheels is allowed during normal driving. While driving in 4-wheel drive mode, which mainly drives the rear wheels, you can enjoy so-called sports driving while enjoying maneuverability, and if one of the wheels starts to slip while driving, the differential The vehicle is switched to a direct-coupled four-wheel drive mode in which the wheels are limited, preventing the wheels from slipping, ensuring that the driving force is transmitted to each wheel, and, in particular, ensuring the acceleration of the vehicle.

Note that FIG. 3 is a graph showing temporal changes in longitudinal G of the vehicle body when the vehicle accelerates, where the song @Qa is the center differential free characteristic, and the curve b1 is the threshold value ω. The characteristic curve b2 is the threshold value ω when performing slip suppression control with a small speed (60 rpm). The curve b3 is the threshold value ω when slip suppression control is performed with the speed set to medium (120 rpm). Large (24O
Characteristics when slip suppression control is performed at (rpm).

Curve C shows the characteristics of the center differential lock in a directly connected state.

As shown in Figure 3, in each of the curves a, bl, b2 and b3, there is a sudden drop in longitudinal G after the start of acceleration, but this indicates a drop in driving force transmission due to wheel slip, and slip suppression When control is performed, each threshold value ω. The longitudinal G increases accordingly. In particular, the threshold value ω as shown in curve b2. It can be seen that when the speed is set to medium, the acceleration force is significantly improved compared to the case where direct four-wheel vehicle movement is performed from the beginning (see curve C). In this way, the rotational speed difference threshold ω.

needs to be set optimally.

Further, in this embodiment, the threshold value ω of the rotational speed difference.

is set to a constant value, and this threshold value ω. may be changed in accordance with the vehicle speed. For example, the threshold value ω at low speed.

is a large value, the threshold ω at high speed. By changing to a small value, it is possible to perform control at high speeds with high sensitivity while reducing the frequency of control at low speeds. Also, the threshold ω
. Define ω as a function of vehicle speed and find the optimal threshold ω depending on the vehicle speed. may be set appropriately.

Furthermore, the torque distribution ratio between the front wheels and the rear wheels is not limited to the above-mentioned values, and the driving condition when normal center differential differential restriction is not performed is a four-wheel drive motor that mainly drives the rear wheels. Instead, a drive mode in which torque is distributed almost equally between the front and rear wheels may also be considered.

Furthermore, the torque distribution in direct-coupled four-wheel immediate driving by limiting the differential is not limited to 50:50.

That is, in general, the final reduction ratio of the front wheels ρf, the dynamic load radius of the front wheels rf+the final reduction ratio of the rear wheels ρ1. Rear wheel dynamic load radius rr
and transfer ratio ρt, (pt/rf)=(
Set so that the relationship ρ1・ρt/rr) holds,
The front wheel:rear wheel torque distribution ratio in direct connection is 50:5.
0, but in all running conditions, (ρr/rf)<(ρr'ρ,/rr)...(1)
It is conceivable to set the relationship so that the following relationship holds true.

Note that the final reduction ratio ρf of the front wheels relates to, for example, the reduction gear mechanism 19, and the final reduction ratio ρ1 of the rear wheels relates to, for example, the bevel gear mechanism 21.
Regarding the transfer ratio ρ, it is a value related to the bevel gear mechanism 15, for example.

With this setting, if both the front wheels and the rear wheels are not slipping, the rotational speed of the rear wheels of the clutch disk of the hydraulic multi-disc clutch 28 will be faster than the rotational speed of the front wheels. For this reason, the hydraulic multi-plate clutch 28
When the pressure in the hydraulic chamber is increased and the clutch is connected, torque is transferred from the rear wheels to the front axle according to this difference in rotation between the rear wheel side clutch disk and the rear wheel side clutch disk. Communication takes place.

As a result, the torque distribution to the front wheels can be made much larger than that to the rear wheels, and the torque distribution ratio at which the torque to the front wheels is maximum is determined by the value of (ρf/rf) and (
By setting the value of ρ,・ρt/rr), the torque distribution to the front wheels can be significantly increased. For example, the torque distribution ratio between the front and rear wheels, that is, the front wheel:rear wheel is set to 100:0. It is also possible to set it to 120 knees or higher (for example, 120 knees to 20 knees).

Therefore, the value of (ρt/rt) and (ρ, ·ρ.

By appropriately setting the value of /rr), you can freely set the torque distribution ratio (front wheels: rear wheels) when direct-coupled 4-wheel drive is active, and the torque distribution ratio during direct-coupling 4-wheel drive can be changed from the torque distribution ratio when the center differential is activated. Even the distribution ratio can be adjusted within an extremely wide range.

[Effects of the Invention] As detailed above, according to the four-wheel drive vehicle with switching drive force distribution of the present invention, the transmission state of drive torque can be adjusted according to the difference between the wheel speeds of the front wheels and the wheel speeds of the rear wheels. By controlling
During normal driving, for example, it runs in a four-wheel drive mode that primarily drives the rear wheels while allowing differential movement between the front and rear wheels.
You can drive while enjoying the maneuverability that is called sports driving, and if one of the wheels starts to slip while driving, it switches to direct-coupled 4@drive mode, which limits the differential, to prevent wheel slippage. , the driving force can be reliably transmitted to each wheel, and in particular, the vehicle can be accelerated more reliably. In addition, since the control is directly based on the wheel speed difference, the reliability of the control is improved, and since the wheel speed detection means used for other controls can also be used, it contributes to the simplification of the device and cost reduction. sell.

[Brief explanation of drawings]

Figures 1 to 3 show a four-wheel drive vehicle with variable power distribution as an embodiment of the present invention. Figure 1 is a schematic diagram of its active system, and Figure 2 shows its control details. The flowchart shown in FIG. 3 is a graph showing the characteristics of the yaw angular velocity according to the control. 2-engine, 4-torque converter, 6-automatic transmission, 8-output shaft, 10-intermediate gear, 12-planetary gear differential! (center differential), 12a-sun gear, 12b-planetary gear, 12cm ring gear, 12d-carrier, 14--differential gear device for front wheels, 15-bevel gear mechanism, 16--front axle, 17L, 17R-axle, 18-Front wheel, 19-Reduction gear fi411.20-Flopeller shaft, 21-Bevel gear mechanism, 22-Differential gear device, 24
... Rear wheel, 25L, 25R - axle, 28 - hydraulic multi-plate clutch, 30 - steering sensor, 32 - steering wheel, 34a, 34b - lateral acceleration sensor, 36 - longitudinal acceleration sensor, 38 - throttle Sensor, 39 - Engine key switch, 41 - Engine speed sensor, 4
0.42--Wheel speed sensor as front axle speed detection means, 44.46--Wheel speed sensor as rear axle speed detection means, 48-Controller (control means), 48a-Rotational speed difference calculation unit, 48b-comparison/judgment section, 48c-control signal output section, 5o-antilock brake device, 51-brake pedal, 52-warning light, 54-hydraulic power source, 56-pressure control valve.

Claims (1)

[Claims] In a four-wheel drive vehicle capable of transmitting engine output torque to front wheels and rear wheels to drive the vehicle, a driving force distribution control means capable of distributing and controlling the output torque between the front wheels and the rear wheels; front wheel speed detection means for detecting the rotational speed of the
Rear wheel speed detection means for detecting the rotational speed of the rear wheels, and a control signal for controlling the state of distribution of driving force to the front wheels and the rear wheels based on information from these detection means. the driving force distribution control means comprises a center differential that differentially operates between the front wheels and the rear wheels; and a differential limiting mechanism that limits the differential movement of the center differential; is a rotational speed difference calculation section that calculates the difference in rotational speed of each wheel detected by the front wheel speed detection means and the rear wheel speed detection means, and a rotational speed difference calculation section that calculates the rotational speed difference calculated by the rotational speed difference calculation section in advance. a comparison/judgment section that makes a comparison decision with a set threshold; and the drive force distribution control so as not to limit the differential of the center differential if the rotational speed difference is smaller than the threshold in the comparison/judgment section. a control signal output section that outputs a control signal to the drive force distribution control means to limit the differential of the center differential when the rotational speed difference is larger than the threshold; A four-wheel drive vehicle with a switchable driving force distribution system.