JP3472988B2 - Vehicle differential limiter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential control system for a vehicle, and more particularly to a differential control system for a vehicle provided with differential systems between front, rear and front and rear wheel axles.

[0002]

2. Description of the Related Art A four-wheel drive vehicle has a center differential disposed between the front and rear wheel axles, a front differential disposed between the front wheels, and a front differential to compensate for the difference in the trajectories of the front and rear wheels when turning. , And rear differentials arranged between the rear wheels. The function of these differentials makes it possible to eliminate the so-called tight corner braking phenomenon and the like. However, in cars equipped with these differentials,
If any of the four wheels spins when starting or accelerating, the driving force is not sufficiently transmitted to the other wheels, making stable starting and accelerating difficult, resulting in poor steering stability, braking, and acceleration. There was a problem of doing.

In view of such a problem, Japanese Patent Laid-Open No. 62-16
Japanese Patent No. 6114 is provided with a differential limiting device that sets the operating states of a front differential, a rear differential, and a center differential, in which the operating states of the locked state and the unlocked state are set by hydraulic pressure according to the operating state, respectively. A wheel drive vehicle is disclosed. This differential limiting device inputs a wheel speed signal and a steering angle signal of each wheel to a control circuit, and makes a bad road determination, a straight traveling determination, an acceleration determination and a braking determination based on these values, and various running states. In response to this, the operation of the front differential, rear differential and center differential is controlled to improve steering stability, braking performance, acceleration performance, and the like.

[0004]

Problems to be Solved by the Invention JP-A-62-1661
In a device that controls a plurality of differentials such as the device disclosed in Japanese Patent Publication No. 14, each differential is independently controlled according to various parameters. However, in view of the overall drivability of the vehicle, it is desirable to detect each other's control state between the differentials and control based on the information, and if the control is performed independently, the drivability,
There is a possibility that traveling performance such as turning performance and traveling stability may deteriorate.

For example, when the center differential is locked, the front and rear differentials have the same driving force distribution ratio, and when the center is in a free state,
In a four-wheel drive vehicle that controls the distribution of the driving force of the front differential to be smaller than that of the rear differential, if one of the rear wheels slips during turning acceleration, when the center differential becomes free, Compared to the case where the drive force is uniformly distributed to the differential, the oversteer tends to be promoted more when the control that increases the drive force distribution to the rear differential is performed.

The reason for this is as follows. When the distribution ratio of the driving force changes, the driving force transmitted to the road surface by each wheel changes even with the same engine output. However, since the tires have the same capacity (friction circle), when the driving force on the rear side increases, the grip force against the lateral force decreases, and the tire tends to oversteer. Further, if the rear differential is locked, the grip force against the lateral force is further reduced, which may cause a sharp oversteering tendency.

Therefore, when changing the distribution ratio according to the differential limiting state of the differential, it is desirable to detect the control state of each differential between the differentials and control the differential limiting force of the differential. The present invention is configured in view of such a situation, and controls the differential limiting force of the inter-wheel differential in accordance with the change in the driving force distribution of the front and rear wheels, regardless of the change in the driving force distribution of the front and rear wheels. The purpose is to obtain desired running characteristics.

[0008]

In order to achieve the above object, the present invention provides a driving force distribution device which is provided between axles and is capable of continuously changing a driving force distribution ratio of front and rear wheels, and a left and right device. Between the wheels of the front wheels or the left and right rear wheels, a parameter setting means for detecting a running state of the vehicle and setting a predetermined parameter for controlling the inter-wheel differential, and based on the parameters. A differential limiting device having differential control means for controlling the differential limiting force of the inter-wheel differential, and a distribution ratio calculating means for calculating a driving force distribution ratio of front and rear wheels by the driving force distributing device, and the calculation And a changing unit that changes the differential limiting force based on the driving force distribution ratio of the front and rear wheels.

Preferably, the changing means relaxes the differential limiting force of the one wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. By allowing the differential between the left and right wheels, it is possible to mitigate the change in the steer characteristic during turning acceleration and improve the turning stability. This is because when the distribution ratio of the rear wheels becomes large, there is an oversteering tendency, and when the distribution ratio of the front wheels becomes large, there is an understeering tendency.

In another aspect, the changing means increases the differential limiting force of the one wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. By restricting the differential between the left and right wheels, it is possible to improve running performance when traveling straight on a road surface having a low friction coefficient. This is because, for example, when the distribution ratio on the rear wheel side increases, the rear wheel easily slips, but the slip tendency can be suppressed by controlling as described above.

Further, the changing means may increase the differential limiting force of the other wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. By restricting the differential between the wheels with the reduced distribution of the driving force, it is possible to improve the running stability during straight running. In other words, a wheel with reduced driving force distribution has a large lateral grip force, so even if a disturbance such as a lateral wind occurs on the vehicle body, lateral slip is eliminated, and due to the synergistic effect of regulating the differential, , Straight running stability can be improved.

On the contrary, when the driving force distribution ratio of one of the front and rear wheels increases, the differential limiting force of the other wheel differential may be relaxed. At the time of turning, the turning performance can be improved by allowing the differential between the wheels unlike the case of the straight running. That is, a wheel with a reduced distribution of driving force has a higher lateral grip force,
If the differential is restricted during turning, the grip force in the lateral direction is reduced and the turning performance is reduced. In order to prevent this, differential is allowed.

As the above-mentioned parameter, for example, the rotational speed difference between the left and right wheels can be used.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a vehicle controller according to an embodiment of the present invention. First, the power transmission system of the vehicle shown in FIG. 1 will be described. The automobile includes an engine 10, and a transmission 11 is connected to the engine 10. The center differential 12 is arranged on the output side of the transmission 11. Connected to the center differential 12 are a front propeller shaft 13 that transmits the output from the engine 10 to the front wheel side and a rear propeller shaft 14 that transmits the output to the rear wheel side.
A front wheel 16 is connected to the front propeller shaft 13 via a front axle 15. A rear wheel 18 is connected to the rear propeller shaft 14 via a rear axle 17. The front axle 15 is provided with a front differential 19 (hereinafter, referred to as front differential), and the rear axle 15 is provided with a rear differential 20 (hereinafter, referred to as rear differential).

The automobile of this example is equipped with an anti-skid brake device and a brake device control unit 21 (hereinafter referred to as ABS control unit) for controlling this device. Further, the automobile of this example includes a power train control unit 22 that controls the transmission 11 and the engine.

These control units 21, 22
Signals representing various traveling states are input to the. First,
A wheel speed sensor for detecting the wheel speed of each wheel is attached to each front wheel 16 and each rear wheel 18, and a signal from the wheel speed sensor is input to the ABS control unit 21. A brake switch 23 for detecting the operation state of the brake is provided, and a signal from this brake switch 23 is detected. A throttle sensor for detecting the throttle opening is provided in the intake system of the engine.

The control unit 22 includes a throttle opening from a throttle sensor and a yaw rate sensor 31.
The yaw rate of the running vehicle from the engine, the engine speed from the engine speed sensor, and the steering wheel 2
A signal from a steering angle sensor or the like for detecting the rotation of 4, that is, the steering angle is input. The control unit 22 outputs a throttle opening signal to the engine 10 to adjust the throttle opening and outputs a fuel injection signal to control the fuel injection valve. Further, an ignition signal is output to control the ignition timing.
In addition, a shift signal is output to the transmission 11 to control the shift. The powertrain control unit 22 is connected to the ABS control unit 21, and inputs a wheel speed signal and an estimated μ (estimated road surface friction coefficient) for each wheel via the control unit 21. The control unit 22 is the ABS control unit 2
On the other hand, in case of emergency or the like, the fail signal is output to cancel the differential lock.

The control units 21 and 22 include input / output sections 25 and 26 and CPUs 27 and 28, respectively.
And memories 29 and 30. All the above input / output signals are sent through the input / output section. In the differential control, the control unit 22 supplies the center diff current to the center diff 12, the front diff current to the front diff 19, and the rear diff current to the rear diff 20 based on the respective input values, and the center diff based on these current values. 12, the front differential 19 and the rear differential 20 are given an unlocked state, an intermediate locked state and a completely locked state. In the intermediate lock state, the differential torque continuously changes according to the amount of current.

FIG. 2 is a sectional view showing an electromagnetic multi-plate clutch provided on the center differential. The center differential 12, the front differential 19, and the rear differential 20 are each provided with an electromagnetic multi-plate clutch 50. With this electromagnetic multi-plate clutch 50, each center differential 12, the front differential 19, and the rear differential 2 are provided.
The differential state of 0 continuously changes from the unlocked state to the completely locked state. This electromagnetic multi-plate clutch 50
May be of any type as long as it can limit the differential between the front propeller shaft 13 and the rear propeller shaft 14. An example thereof is shown in FIG. In FIG. 2, an electromagnetic multi-plate clutch 50 includes a clutch plate 51 composed of a plurality of inner discs and an outer disc, and an actuator 5 for generating a pressing force on the clutch plate 51.
It consists of two. Further, 53 is a bearing, 54 is a transmission member that is transmission-connected to one propeller shaft, and 55 is a transmission member that is transmission-connected to the other propeller shaft. The actuator 52 is configured so that the armature 57 presses the clutch plate 51 by the magnetic force generated when a current flows through the solenoid 56. In the electromagnetic multi-plate clutch 50, the current flowing through the solenoid 56 and the pressing force for frictionally engaging the clutch plate 51, that is, the torque generated in the electromagnetic multi-plate clutch 50 are in a proportional relationship, so that the center differential 12, the front differential 19, and the Rear differential 2
The differential rotation speed of 1 can be continuously changed by increasing or decreasing the current.

FIGS. 3, 4 and 5 show flow charts of differential control of the differentials 12, 19 and 20 according to the present invention. The flow chart shown in FIG. 3 shows the contents of the main routine of the differential control of the differentials 12, 19 and 20. The control unit first determines the wheel speed of each wheel (left front wheel speed NFL, right front wheel speed).
NFR, left rear wheel speed NRL and right rear wheel speed NRR are calculated (step S1). Next, the differential rotations ΔNF, ΔNC, and ΔNR of the differentials 19, 12 and 20 are calculated based on these wheel speeds (step S2). Next, the control unit 22 calculates the lock force of each of the differentials 19, 12 and 20, that is, the differential limiting forces FF, FC and FR by the routine shown in the flowchart of FIG. 4 (step S3).
When the differential limiting force FF, FC and FR of each differential is obtained, each differential 1
The control current amounts IF, IC and IR to be supplied to the solenoid 56 for operating the electromagnetic multi-plate clutch 50 of 9, 12, and 20 are determined (step S4). In this case, each control current amount IF,
IC and IR are functions of differential limiting force FF, FC and FR IF = f (FF)
, IC = f (FC) and IR = f (FR). Therefore, the differential limiting forces FF, FC and
The current value can be calculated by FR. Further, the characteristics of the front differential 19 as shown in FIG. 5 may be set in advance for each differential and stored in the memory 29, and the current value may be obtained according to this characteristic.

Then, the control unit 22 obtains predetermined differential limiting forces FF, FC and FR by energizing the solenoid 56 of each differential with the obtained current value. Next, Figure 4
The procedure for calculating the differential limiting forces FF, FC and FR, which is the content of step S3 in FIG. 3, will be described with reference to FIG.
Since this procedure is common to each of the differentials 12, 19 and 20, the rear differential 20 will be described and the other differentials 19 will be described.
The description of 20 and 20 is omitted.

The control unit 22 includes a running performance weighting function kr1 (ΔNR) and a running stability weighting function kr2 (ΔN) for weighting the running performance and running stability of the vehicle.
R) based on the weights KR1 = kr1 (ΔNR) and KR2 = kr2 (ΔN
R) is calculated (step T1). The weight changes between 0.0 and 1.0 as shown in FIG. The running weighting function kr1 (ΔNR) changes from almost 0 to 1 when the differential rotation speed ΔNR increases above a predetermined value. On the contrary, the running stability weighting function kr2 (ΔNR) is 1 when the differential rotation speed ΔNR is equal to or lower than a predetermined value, and is almost 0 when the differential rotation speed ΔNR exceeds the predetermined value. The reason for this is that when the differential limiting force FR is reduced, the running performance is improved, and when the differential limiting force FR is increased, the running stability is improved.

In the configuration of this example, the control unit 2
2 calculates the distribution ratio S of the driving force to the rear differential 20 by the center differential 12, and the control unit 22 determines the correction amounts HR1 and HR2 of the differential limiting force FR based on the distribution ratio S ( Step T2). These correction amounts HR1 and HR2 are distribution ratio correction functions that emphasize running performance.
hr1 (S), distribution ratio correction function that emphasizes driving stability hr
It is decided based on 2 (S). That is, HR1 = hr1
(S), HR2 = hr2 (S).

The distribution ratio correction functions hr1 (S) and hr2 (
In this example, S) is given by the characteristics shown in FIG. That is, when the driving force distribution ratio to the rear differential 20 increases, the distribution ratio correction function hr1 (S) that emphasizes running performance is emphasized.
Gradually decreases from 2, and conversely, the distribution ratio correction function hr2 (S), which emphasizes traveling stability, gradually increases from 0. When the driving stability is important, the differential limiting force FR is increased to control the differential rotation of the left and right wheels, and when the running performance is important, the differential limiting force FR is decreased to reduce slip. Control to decrease.

Next, the control unit considers the distribution ratios HR1 and HR2 to the rear differential 20 and weights KR1.
And KR2 are updated (step T3). The differential limiting force FR is given based on the function of the differential rotation ΔHR of the rear differential 20, and the control function fr1 (ΔNR) that emphasizes traveling performance and the control function fr2 (ΔNR) that emphasizes traveling stability are described above. The weighting is performed according to the weights KR1 and KR2 obtained in the procedure. That is, the differential limiting force FR is FR = {KR1 × fr1 (ΔNR)
It is calculated by + KR2 × fr2 (ΔNR)} / (KR1 + KR2) (step T4).

Here, the differential limiting force control function with an emphasis on the running performance has the characteristics shown in FIG. That is, when the differential rotation ΔNR increases in a region where the differential rotation speed is small, the differential limiting force FR increases relatively rapidly, and even if the differential rotation ΔNR increases thereafter, the differential limiting force FR does not increase. Doesn't grow so big. The control function for limiting the differential force, which emphasizes running stability, has the characteristics shown in FIG. Differential rotation Δ
In the region where NR is relatively small, differential rotation ΔNR and differential limiting force
Although it is almost proportional to FR, the differential limiting force FR does not increase so much even if the differential rotation ΔNR increases. In a range in which the differential rotation ΔNR is relatively large, the increase range of the differential limiting force FR increases as the differential rotation ΔNR increases.

Differential limiting force FF for the front differential 19
Since the calculation procedure of FR and FR is the same as the above, its explanation is omitted. In this case, the characteristics of the weighting function used differ. For example, the weighting functions kc1 (ΔNF) and kc2 (ΔNF) of the front differential 19 are given the characteristics shown in FIG. Each front differential 19 and rear differential 20
Comparing the characteristics of the front differential 12 and the rear differential 20
In comparison with, the weighting of the stability characteristic tends to emphasize stability until the differential rotation ΔN increases. Differential rotation Δ
When increasing N, front differential 19 is rear differential 20
The weighting with emphasis on stability shifts to the weighting with emphasis on running performance later.

In another aspect, the distribution ratio correction function hr
1 (S) and hr2 (S) can be set to the characteristics shown in FIG. That is, the running stability weighting function kr2
The change of the value of (ΔNR) and the value of the running weighting function kr1 (ΔNR) with respect to the driving force distribution ratio to the rear differential 20 is set so as to be opposite to the characteristic of FIG. 7. In this way, running characteristics different from those of the previous example can be obtained.

[0029]

As described above, according to the present invention, the differential limiting force of the left and right wheels is controlled in accordance with the change of the front / rear driving force distribution, so that the front / rear wheel driving force distribution ratio is not affected. It is possible to maintain a desired running sensation. When the driving force distribution ratio of one of the front and rear wheels, for example, the rear wheel, is increased while the vehicle is running, if the differential limiting force of the rear wheel differential between the wheels is relaxed, the slip of the left and right wheels can be reduced. You can improve the running performance.

On the contrary, when the differential limiting force of the inter-wheel differential of the wheel with the increased distribution of the driving force is strengthened, the difference between the left and right rotational speeds is reduced and the running stability is improved. . Further, if the differential limiting force of the inter-wheel differential of the wheel that has not increased when the driving force distribution ratio of one of the front and rear wheels is increased, the resistance force to the lateral force is increased and the straight running stability is improved. be able to. On the contrary, if the differential limiting force is weakened, the turning performance can be improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an overall configuration of a vehicle control device to which a differential limiting device of the present invention is applied.

FIG. 2 is a sectional view showing an electromagnetic multi-plate clutch provided on a center differential.

FIG. 3 is a flowchart showing a main routine of differential differential control.

FIG. 4 is a flowchart of a routine for calculating a differential limiting force.

FIG. 5 is a graph showing the relationship between the differential limiting force and the control current to the solenoid.

FIG. 6 is a graph showing the relationship between the differential rotation amount of the rear differential and the weighting coefficient of the differential limiting force.

FIG. 7 is a graph showing a relationship with a correction coefficient of a differential limiting force based on a driving force distribution ratio to a rear differential.

FIG. 8 is a graph showing the relationship between the differential rotation of the rear differential and the differential limiting force with an emphasis on running performance.

FIG. 9 is a graph showing the relationship between the differential rotation of the rear differential and the differential limiting force that emphasizes running stability.

FIG. 10 is a graph showing the relationship between the differential rotation amount of the front differential and the weighting coefficient of the differential limiting force.

FIG. 11 is a graph showing a relationship with a correction coefficient of a differential limiting force based on a driving force distribution ratio to a rear differential according to another embodiment.

[Explanation of symbols]

12 Center differential (center differential) 19 front differential (rear differential) 20 Rear differential (Rear differential) 22 Control unit for differential 31 Yaw rate sensor 50 electromagnetic multi-plate clutch

Claims (6)

(57) [Claims] 1. A drive force distribution device provided between axles and capable of continuously changing a drive force distribution ratio of front and rear wheels, and a wheel-to-wheel differential provided between left and right front wheels or left and right rear wheels. A parameter setting means for detecting a traveling state of the vehicle and setting a predetermined parameter for controlling the inter-wheel differential, and a differential control means for controlling the differential limiting force of the inter-wheel differential based on the parameter. In a differential limiting device including: a distribution ratio calculating means for calculating a driving force distribution ratio of front and rear wheels by the driving force distributing device; and a differential limiting force changed based on the calculated driving force distribution ratio of the front and rear wheels. A differential limiting device for a vehicle, comprising: 2. The vehicle difference according to claim 1, wherein the changing means relaxes the differential limiting force of the one wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. Motion limiter. 3. The vehicle differential according to claim 1, wherein the changing means increases the differential limiting force of the one wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. Restriction device. 4. The differential limiting device for a vehicle according to claim 1, wherein when the driving force distribution ratio of one of the front and rear wheels is increased, the changing means enhances the differential limiting force of the other wheel differential. apparatus. 5. The vehicle differential according to claim 1, wherein the changing means reduces the differential limiting force of the other wheel differential when the driving force distribution ratio of one of the front and rear wheels increases. Restriction device. 6. The differential limiting device for a vehicle according to claim 1, wherein the parameter is a rotational speed difference between the left and right wheels.