JP3430495B2 - 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 control device for a four-wheel drive vehicle, and more particularly to a front wheel differential device, a rear wheel differential device and a differential limiting torque between these two differential devices. The present invention relates to a control device for a four-wheel drive vehicle having differential limiting clutch means that changes according to a driving state.

[0002]

2. Description of the Related Art Conventionally, a four-wheel drive vehicle is provided with a transfer device that distributes a driving force to front wheels and rear wheels, and this transfer device normally has a differential gear that does not have a differential limiting function. A mechanism is provided, but recently, in order to make it possible to control the distribution of the driving force to the four wheels, a differential limiting device including an electromagnetic multi-plate clutch is provided together with or instead of the differential gear. Some have been proposed. On the other hand, Japanese Patent Application Laid-Open No. 63-251327 discloses a vehicle equipped with a center differential device for absorbing a rotational speed difference between front wheels and rear wheels and a differential limiting device for locking the center differential device. A four-wheel drive vehicle in which this sender differential device is locked by a differential limiting device at the time of starting to equalize the power distribution of the engine transmitted to the front wheels and the rear wheels at the time of starting the vehicle so that the vehicle can start smoothly. Is disclosed.

[0003]

Here, in normal traveling, for example, front wheel drive is used to drive only one wheel, which is the front wheel. In a traveling state where differential limitation is required, the other wheel, which is the rear wheel, is also driven. When the above conventional technique is applied to a so-called part-time four-wheel drive vehicle, the following problems occur. That is, in a four-wheel drive vehicle in which an electromagnetic multi-plate clutch is provided between the front wheel differential device and the rear wheel differential device,
In order to enable a smooth start, it is necessary to energize the electromagnetic multi-plate clutch to transmit equal drive torque to the front wheels and the rear wheels when the vehicle starts. Therefore, when the deviation between the rotation speed of the front wheels and the rotation speed of the rear wheels increases, it is necessary to increase the differential limiting torque in order to reduce the deviation to zero. However, if the differential limiting torque is increased without limit, the electromagnetic multi-plate clutch will suffer seizure damage, or excessive drive torque will act on the rear wheel differential gear that becomes the driven wheel during normal driving. May be damaged by
Further, there arises a problem that it is difficult to make the device compact. Although such a phenomenon occurs not only at the time of starting the vehicle, it is most likely to occur at the time of starting the vehicle.

Therefore, the present invention has been made in order to solve the problems of the prior art, and prevents seizure damage to the differential limiting clutch means and also provides a differential device for a wheel on the side which becomes a driven wheel during normal traveling. It is an object of the present invention to provide a control device for a four-wheel drive vehicle, which prevents damage and is compact.

[0005]

In order to achieve the above object, the present invention provides a front wheel differential device, a rear wheel differential device, and a differential limiting torque between these two differential devices to determine a vehicle operating condition. In a control device for a four-wheel drive vehicle having differential limiting clutch means for changing the differential limiting clutch means so as to increase the differential limiting torque as the deviation between the rotational speed of the front wheels and the rotational speed of the rear wheels increases. And the control means for controlling the means, and the differential limiting torque by the differential limiting clutch means when the speed of the transmission is the lowest speed and the deviation between the rotational speed of the front wheels and the rotational speed of the rear wheels is a predetermined value or more. And a correction means for correcting to the decreasing side. In the present invention thus configured, normally, by the control means,
The differential limiting clutch means is controlled so that the differential limiting torque is increased as the deviation between the rotational speed of the front wheels and the rotational speed of the rear wheels increases. However, the gear stage of the transmission is the lowest gear stage and the front wheel is When the difference between the rotation speed of the above and the rotation speed of the rear wheels is equal to or greater than a predetermined value, the correction means corrects the differential limiting torque by the differential limiting clutch means to the decreasing side. As a result, excessive differential limiting torque does not act on the differential limiting clutch means, and seizure damage is prevented. At the same time, excessive drive torque does not act on the wheel differential that is the driven wheel (for example, the rear wheel) at the time of normal traveling, so damage can be prevented and the size can be reduced.

Further, in the present invention, preferably, the correcting means reduces the differential limiting torque by the differential limiting clutch means when the vehicle starts. Further, the present invention preferably has a road surface friction coefficient estimating means for estimating the road surface friction coefficient, and the correcting means further reduces the differential limiting torque by the differential limiting clutch means as the road surface friction coefficient increases. to correct.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. This embodiment is an example in which the present invention is applied to a four-wheel drive vehicle of a type in which the front wheels are driven during normal traveling and the rear wheels are also driven in a traveling state where differential limitation is required. First, a schematic overall configuration of a four-wheel drive vehicle to which the present invention is applied will be described with reference to FIG. As shown in FIG.
In a wheel drive vehicle, the left front wheel axle 5 is located between the left and right front wheels 1, 2.
And a right front wheel axle 6 are provided, a left rear wheel axle 8 and a right rear wheel axle 9 are provided between the left and right rear wheels 3, 4, and the left front wheel axle 5 and the right front wheel axle 6 are left and right. The front wheel differential 8 for permitting the differential between the front wheels 1 and 2 is interlocked and coupled, and the left rear wheel axle 8 and the right rear wheel axle 9 are the differentials for the rear wheel that permit the differential between the left and right rear wheels 3, 4. It is interlockingly connected by the moving device 10. A power unit 11 including an engine and an automatic transmission connected to the engine is disposed in the front-rear direction in the center of the front part of the vehicle body. The output shaft 12 of the power unit 11 is connected to the front wheel differential device 7. A front wheel driving force transmission system 13 for transmitting driving force,
From the output shaft 12 of the power unit 11 to the rear wheel differential 1
A rear wheel driving force transmission system 14 for transmitting the driving force to 0 is provided.

The front wheel drive force transmission system 13 transmits the drive force from the gear 15 fixed to the output shaft 12 to the gear 16, and the drive force of the gear 16 is transmitted via the front wheel drive shaft 17 to the front wheel differential device. 7 is configured to be transmitted. The rear wheel drive force transmission system 14 includes a rear wheel drive shaft 18 that is interlocked with the rear wheel differential device 10 and an electromagnetic clutch 19 provided between the output shaft 12 and the rear wheel drive shaft 18. An electromagnetic clutch 19 (differential limiting clutch means) capable of limiting the dynamic limiting torque is provided. The electromagnetic clutch 19 includes an output shaft 12
And a plurality of clutch plates 21 disposed in the case 20 and integrally rotating with the case 20.
And a plurality of clutch discs 22 disposed in the case 20 and rotating integrally with the rear wheel drive shaft 18, and electromagnets (which are the coil 23 and the magnetic disc) that act on the clutch plates 21 and the clutch discs 22. (Including a path forming member), and is composed of an electromagnet or the like fixed to the vehicle body. When the coil 23 of the electromagnetic clutch 19 is not energized, the electromagnetic clutch 19 is disengaged,
Although only the left and right front wheels 1 and 2 are driven and the driving force is not transmitted to the rear wheel drive shaft 18, when the coil 23 is energized, a drive torque equal to the fastening torque proportional to the magnitude of the coil current is applied to the rear wheel drive shaft. 18 is transmitted to the four-wheel drive state.

Next, the control system will be described. A power unit control device 30 for controlling the power unit 11, an ABS control device 31 (control device for anti-skid control) for controlling a braking device (not shown), and an electromagnetic clutch 19
And a clutch control device 23 for controlling the.
Further, as sensors, the rotation speed N1 of the left front wheel 1 is
A front left wheel speed sensor 34 that detects through a disk 33 that rotates integrally with the front left wheel axle 5, and a rotation speed N of the front right wheel 2.
2 through the disk 35 that rotates integrally with the right front wheel axle 6 and the right front wheel speed sensor 36, and the rotational speed N3 of the left rear wheel 3 through the disk 37 fixed to the left rear wheel axle 8. A left rear wheel wheel speed sensor 38 for detecting, a right rear wheel wheel speed sensor 40 for detecting the rotational speed N4 of the right rear wheel 4 via a disc 39 that rotates integrally with the right rear wheel axle 9, and a brake switch 41. , A steering angle sensor 43 for detecting the steering angle θh of the steering wheel 42, a neutral / inhibitor switch 44, a yaw rate sensor 45 for detecting a yaw rate ψv acting on the vehicle body, an idle switch 46 and a throttle opening sensor provided in the engine. 47, a crank angle sensor 48, and the like are provided.

The wheel speed sensors 34, 36, 38, 40
The wheel speed signals N1, N2, N3, N4 are input to the ABS control device 31, and from the ABS control device 31, the ABS signal and the wheel speed signals N1, N2, N3, N4 which are turned on during execution of the anti-skid control. Are supplied to the clutch control device 32. Further, the ABS control device 31 determines that the wheel speed signal N
The road surface friction coefficient μ is estimated based on 1, N2, N3, N4, and is supplied to the clutch control device 32. The switch signal BR from the brake switch 41 and the steering angle sensor 4
The steering angle signal θh from 3 and the yaw rate signal ψv from the yaw rate sensor 45 are directly input to the clutch control device 32. The switch signal NI from the neutral / inhibitor switch 44 and the idle switch 4
Switch signal ID from 6 and throttle opening sensor 4
The throttle opening signal TVO from 7 and the crank angle signal CA from the crank angle sensor 45 are supplied to the clutch control device 32 via the power unit control device 30. The clutch control device 32 is configured to be able to output a coil current Iout to the coil 23 of the electromagnetic clutch 19, and the clutch control device 32 is connected to a power source when the ignition switch is ON, and also the ignition switch is turned on. Is off, power is supplied from the backup battery 49, and the clutch control device 32
Is basically configured to operate when the ignition signal IG that is input when the ignition switch is ON is being input, but during the tailing process, the ignition switch signal IG is OF
Works with F.

The clutch control device 32 includes an A / D converter for A / D converting the detection signal as needed, a waveform shaping circuit for shaping the detection signal as necessary, an input / output interface, a CPU and a ROM. It is composed of a microcomputer including a RAM, a coil drive circuit that outputs a coil electromagnetic Iout to the coil 23, and the like. In the ROM of the microcomputer, as will be described later, a control program for driving force distribution control for controlling the fastening torque according to the running state of the four-wheel drive vehicle to control the driving force distribution to the four wheels 1 to 4. , A plurality of maps associated with the control program are input and stored in advance, and the RAM is
Various memories necessary for the arithmetic processing of the control are provided. Here, the outline of the control for the electromagnetic clutch 19 will be briefly described. As shown in FIG. 2, as the physical quantity (physical parameter) related to the running state and behavior of the four-wheel drive vehicle, mainly the differential rotation speed ΔN of the front and rear wheels,
The yaw rate ψv and the vehicle speed V are used. First, the detected differential rotation speed ΔN is applied to the map M1 to obtain the fastening torque Tn, and the fastening torque Tn is calculated using the map M1.
Gain G1n obtained from the gain characteristic of No. 2 and map M3
The gain is changed with the gain G2n obtained from the gain characteristic of the differential torque, and the fastening torque Tn at the time of the gain change is subjected to a holding process as necessary to perform the differential rotation speed reflecting fastening torque Tn.
Ask for 1.

In parallel with the above, the detected yaw rate ψv
The estimated lateral acceleration α obtained from the vehicle speed V and the vehicle speed V (the speed of the four-wheel drive vehicle) is applied to the map M4 to obtain the engagement torque Tψ.
The engagement torque Tψ is changed by the gain G1ψ obtained from the gain characteristic of the map M5 to obtain the yaw rate reflected engagement torque T2. In parallel with the above, the detected vehicle speed V
Is applied to the map M6 to obtain the engagement torque Tv and the vehicle speed reflected engagement torque T3. Next, the total fastening torque Tt obtained by adding the fastening torques T1, T2, and T3 is calculated by the map M
7 is applied to convert the coil current I into a coil current I, and then the coil current Iout is multiplied by a gain Ga by an ABS corresponding process and a gain Gt by a tailing process to obtain an output coil current Iout. The coil current Iout is set and output to the coil 23. Here, each of the maps M1, M4, M6 corresponds to a torque characteristic in which the characteristic of the fastening torque is set, and the maps M2, M4.
Each of M3 and M5 corresponds to a gain characteristic in which the characteristic of the gain multiplied by the engagement torque is set. Next, the structure of these maps M1 to M7 will be described. Map M
As shown in FIG. 3, 1 is a characteristic of the fastening torque Tn set with the differential rotation speed ΔN as a parameter, and the differential rotation speed ΔN is the maximum wheel speed and the minimum wheel speed of the detected four wheels. And the difference is determined by the following equation.

ΔN = Max [N1, N2, N3, N4] -min
[N1, N2, N3, N4] In the map M1, the solid line shows the torque characteristic during acceleration, the broken line shows the torque characteristic during deceleration, and a = 80 to 12
The values are 0, b = 40 to 80, c = 400 to 500. Although a slight slip is allowed during acceleration, it is desirable to prevent the wheels from locking during deceleration so that as many wheels as possible share the braking force, so a> b is set. Thereby, braking performance can be improved. As shown in FIG. 4, the map M2 shows the vehicle speed V and the yaw rate ψv.
Is set as a parameter, and the vehicle speed V is determined by the following equation by multiplying the detected minimum wheel speed by a constant. V = min [N1, N2, N3, N4] ・ 2π ・ rt ・ 60/10
00 where rt is the dynamic load radius of the tire. Since the lowest wheel speed is generated from the wheels gripping the road surface, the vehicle speed V is determined from the lowest wheel speed. In the map M2, in the area A1, the gain G1n = 1.0 is set to ensure straight running stability, and in the area A3, the gain G1n = 1.0 is set to prevent spin during a sharp turn. In the area A4, the gain G1n = 1.0 is ensured in order to secure the traveling performance during turning and enable the power drift traveling.
Is set to. Incidentally, d = 25 to 35, e = 70 to 10
0, f = 25 to 30, g = 40 to 60, and speed values.

Further, in the area A2, the gain G1n = 0 is set in order to improve the turning performance of turning a tight corner. Further, when turning, the ground load of the front and rear wheels changes due to the load movement due to acceleration, and the steering characteristics change. Therefore, in the region A5, it is necessary to switch to the torque characteristic based on the estimated lateral acceleration α in order to correct the change in the steering characteristic due to the movement of the load. Therefore, the gain G1n = 0 is set. The boundary line L1 is 0.
4G (where G is the gravitational acceleration) is a line corresponding to the lateral acceleration, and the boundary lines L2 and L3 decrease the yaw rate ψv as the vehicle speed V increases. Torque can be distributed to ~ 4. As shown in FIG. 5, the map M3 sets the characteristics of the gain G2n using the vehicle speed V and the differential rotation speed ΔN as parameters. The boundary line L4 is a line of the differential rotation speed ΔN corresponding to the case where the tire dynamic radius is reduced by 10% due to the decrease of the tire air pressure or the temper tire device, and the region B
In No. 1, in order to ignore the influence of the decrease in tire air pressure and the differential rotation speed ΔN due to the temper tire device, the gain G
2n = 0 is set, and in the region B2, the gain G2n = 1.0 is set to correspond to the differential rotation speed ΔN substantially generated.
Is set to. Note that h = 7, i = 70 to 100, j =
The value of h = 7 is about 30 to 50, and the value of h = 7 is the minimum vehicle speed that can be detected from the detection signals of the wheel speed sensors 34, 36, 38, 40.

As shown in FIG. 6, the hold process is a control for holding the fastening torque Tn for a predetermined time in order to prevent hunting, and the fastening torque Tn ≧ the set torque Tno (this is 95% of the maximum fastening torque). Is a value). In this hold processing, Tn ≧ Tn
When it is o, the fastening torque Tn is held for a predetermined hold time th while counting by the counter, and after the predetermined time th elapses, the hold process is released and the fastening torque Tn is decreased at a predetermined reduction rate. However, if the fastening torque Tn ≧ the set torque Tno is reached within the predetermined time tf after the release of the hold process, the next hold process is executed for the hold time 2th that is twice the previous hold time th, and the hold time After the elapse of 2th, the fastening torque Tn is reduced at a predetermined reduction rate as described above. As shown in FIG. 7, the map M4 sets the characteristic of the fastening torque Tψ using the estimated lateral acceleration α as a parameter. The estimated lateral acceleration α is determined by the following equation using the yaw rate ψv and the vehicle speed V as parameters. α = (V · 1000/3600) · (ψv · π / 10
0) In this map M4, when the estimated lateral acceleration α is equal to or more than a certain value, the estimated lateral acceleration α increases as shown in the line L5 in order to improve the running performance of the winding traveling and enable the power drift traveling. Tightening torque Tψ
Is increased to a certain value.

Near the turning limit (position of estimated lateral acceleration α = m), since the front and rear wheels are directly connected to each other, there is a tendency to spin out. Therefore, the grip force of the rear wheels 3 and 4 is increased, and the front wheels 1 and 2 are also increased. In order to reduce the grip force and eliminate this spin-out tendency, a characteristic is set such that the fastening torque Tψ gradually decreases along the line L6 near the turning limit. As described above, when the turning degree is near the turning limit, the fastening torque Tψ gradually decreases along the line L6. Therefore, the fastening torque Tψ is not suddenly released and the front and rear wheels 1 to 4 are not released. Since the grip force of the vehicle does not change suddenly, it is possible to secure the steering stability in the limit turning traveling. In addition, k = 5.5 to 6.0, m
= 6.5 to 7.0, n = 440 to 460, which are values.
As shown in FIG. 8, the map M5 sets the characteristic of the gain G1ψ using the differential rotation speed ΔN as a parameter, and this map M5 shows the responsiveness when the differential rotation occurs during turning travel. It is for raising. Incidentally, p = 30
.About.40, q = 60 to 80, and values of the order. Map M6
Indicates that the characteristic of the engagement torque Tv is set with the vehicle speed V as a parameter, and this map M6 is for ensuring straight running stability during high-speed traveling. Incidentally, r = 60,
The values are s = 70 to 90, t = 100, and so on.

The map M7 is a map in which the relationship between the total engagement torque Tt and the coil current I is set. In consideration of the influence of the hysteresis of the coil 23, when the total engagement torque Tt increases, the map M7 is drawn by the broken line L7. When the current I is determined and the total engagement torque Tt decreases, the broken line L
The coil current I is determined by 8. The ABS corresponding process is a device for releasing the engagement torque of the electromagnetic clutch 19 in order to prevent the wheels from being locked by the ABS control device 31 while the ABS control is being executed, and the ABS signal is ON.
If the brake switch signal BR is ON, the gain Ga is set to 0, and otherwise the gain Ga is set to 1.0. Map M8 is
The characteristic of the gain Gt by the tailing process for preventing the shock due to the sudden change of the fastening torque when the running state is changed to the stopped state is set, and the fastening torque is gradually reduced over 3 seconds. It is set to various characteristics. The tailing processing conditions are ignition switch signal IG = OFF and crank angle signal CA = 0 (rp
m), vehicle speed V = 0, neutral / inhibitor signal NI
This is executed when the conditions of = ON are satisfied.

Next, referring to FIG. 12 to FIG. 14, the clutch control executed by the clutch control device 32 is performed, and the driving force for appropriately setting the distribution of the driving force to the four wheels in accordance with the traveling state. The contents of distribution control will be described. 12 to 14, the symbol S indicates each step. First, in S1, control is started when the ignition switch signal IG is turned ON, and first,
Various detection signals (N1 to N4, BR, ABS, TVO, C
(A, NI, θh, μ, etc.) are read. Next, in S2, using the detection signal read in S1,
The differential rotation speed ΔN, the yaw rate ψv, the vehicle speed V, and the estimated lateral acceleration α are calculated as described above. Next, in S3, the differential rotation speed ΔN is applied to the map M1 to calculate the engagement torque Tn, and then in S4, the vehicle speed V and the yaw rate ψv are applied to the map M2 to calculate the gain G1n, Next, in S5, the vehicle speed V and the differential rotation speed ΔN are applied to the map M3 to calculate the gain G2n. Next, in S6, it is determined whether the hold process is necessary,
When the determination result is No, the fastening torque Tn is held unchanged (S7). When the determination result in S6 is Yes, the fastening torque Tn is corrected by the hold process (S8). Since this hold processing is as described above, its explanation is omitted.

Next, in S9, the differential rotation speed reflecting fastening torque T1 is calculated by the following equation. T1 = Tn × G1n × G2n Next, in S10, the estimated lateral acceleration α is applied to the map M4 to calculate the fastening torque T1ψ, and then, in S11, the differential rotation speed ΔN is applied to the map M5 to obtain the gain. G
1ψ is calculated, and then, in S12, the yaw rate reflected fastening torque T2 is calculated by the following equation. T2 = Tψ × G1ψ Next, in S13, the vehicle speed V is applied to the map M6 to calculate the engagement torque Tv, and then in S14, the vehicle speed reflected engagement torque T3 is calculated by the following equation. T3 = Tv Next, in S15, the total engagement torque Tt, which is the sum of the torques T1, T2, and T3, is calculated by the following equation. Tt = T1 + T2 + T3 Next, in S16, it is determined whether or not it is the first speed, and in S17, it is determined whether or not the steering angle θh is a predetermined value, that is, whether or not the steering angle θh is in a substantially straight traveling state. By these S16 and S17, it is determined whether or not the vehicle is in the start state. When it is determined that the vehicle is in the starting state, the process proceeds to S18, and it is determined whether the deviation ΔNA between the average rotational speed of the left and right front wheels and the average rotational speed of the left and right rear wheels is larger than a predetermined value ΔNA ₁ .

Next, when the deviation ΔAN is larger than the predetermined value ΔNA _{1, the} routine proceeds to S19, where the road surface friction coefficient μ is judged. Here, it is determined whether the road surface is a high μ road, a medium μ road, or a low μ road. Next, in S20, the coefficient K1 is set as follows. FIG. 16 shows the coefficient K1, the deviation ΔNA, and the road surface friction coefficient μ (B1, B2,
It is a map showing the relationship of B3). In FIG. 16, B1 shows the case of the high μ road, B2 shows the case of the medium μ road, and B3 shows the case of the low μ road. That is, the deviation ΔN between the average rotational speed of the left and right front wheels and the average rotational speed of the left and right rear wheels.
When A is larger than the predetermined value ΔNA ₁ , the higher μ road,
The coefficient K1 is set to be smaller than the deviation ΔNA. Next, in S21, the value of the total engagement torque Tt obtained in S15 is added to the coefficient K1 obtained in S20.
And the value is replaced as a new total engagement torque Tt. Here, a more specific description will be given with reference to FIG. When the deviation ΔNA is larger than the predetermined value ΔNA ₁ , the value of the total engagement torque Tt obtained in S15 is
This is an increased value as indicated by A1 in FIG. However, the value of the total engagement torque Tt shown by A1 is
Coefficient K corresponding to each road surface friction coefficient (B1, B2, B3)
As a result, the value of the total engagement torque Tt is corrected to the decreasing side (in the case of A2) or decreases, as represented by A2 or A3 in FIG. (A3) is corrected. As a result, even if the deviation ΔAN between the average rotational speeds of the left and right front wheels and the average rotational speeds of the left and right rear wheels increases more than the predetermined value ΔNA ₁ , the total engagement torque does not greatly exceed the predetermined value Tt ₀ shown in FIG. Absent.

Next, the process proceeds to S23. In addition, when the deviation ΔNA between the average rotational speeds of the left and right front wheels and the average rotational speeds of the left and right rear wheels is smaller than the predetermined value ΔNA ₁ even when the vehicle is not started,
Similarly, the process proceeds to S23. In S23, the total fastening torque Tt is applied to the map M7 to calculate the coil current I. When the total fastening torque Tt increases, the map M is increased.
7 is calculated based on the line L7, and when the total engagement torque Tt is decreased, calculation is performed based on the line L8 of the map M7. Next, at S24, the ABS signal becomes O.
If the ABS control is being executed at N, the brake switch signal BR is ON, and the brake is operating, the gain Ga is set to Ga = 1.0 when the determination result is No (S25). If the determination result of S24 is Yes, the gain Ga is set to Ga = 0 (S2
6). Next, in S27, it is determined whether the tailing process is necessary. This determination is made by ignition switch signal IG = OFF, crank angle signal CA = 0 (rpm),
Vehicle speed V = 0, neutral / inhibitor signal NI = O
When the conditions of N are satisfied, the determination is Yes, and when the conditions are not satisfied, the determination is No. When the determination result is No, the gain Gt is set to Gt = 1.0 (S28). When the determination result is Yes, the gain Gt is the counter clock time and the map M.
It is calculated based on 8 etc. (S29).

Next, in S30, the output coil current Iout output to the coil 23 is calculated by the following equation. Iout = I × Ga × Gt Next, in S31, the output coil current Iout is output to the coil 23, and then the process returns to S1 to S31.
However, it is repeatedly executed every predetermined minute time. In this four-wheel drive vehicle, there are an auto mode in which the drive force distribution control is automatically executed, an FF mode in which only the front wheels are always driven, and a 4WD mode in which four electromagnetic wheels are always connected to drive the four wheels. Is configured to be selectively set, and the high μ road traveling mode and the low μ road traveling mode can be selectively set. The present invention is also applied to a four-wheel drive vehicle in which the rear wheels are always driven, the front wheels are driven wheels in a normal traveling state, and the rear wheels are driven only when four-wheel drive is required. it can. The torque characteristics and the gain characteristics are characteristics premised on a high μ road. Except for S16 to S21, the auto mode and the high μ are used.
This is related to the case of the road driving mode.

The characteristics similar to the torque characteristic and the gain characteristic are applied in the low μ road traveling mode, but the values of the various values (a to k, m, n, p to t) are applied. But,
If necessary, the slip suppression direction will be changed accordingly.
Regarding the characteristics of the map M4, the line L5 itself is changed to the left. As described above, according to the embodiment of the present invention, when the deviation ΔNA between the average rotational speeds of the left and right front wheels and the average rotational speeds of the left and right rear wheels becomes larger than the predetermined value ΔNA ₁ when the vehicle starts, Originally, it is necessary to increase the total engagement torque Tt as the deviation ΔNA increases. However, the total engagement torque Tt is corrected to a decreasing side or a decreasing direction without increasing. As a result, it is possible to prevent seizure damage to the electromagnetic clutch 19 without exerting an excessive torque on the electromagnetic clutch 19. At the same time, since an excessive driving torque does not act on the rear wheel differential device, the rear wheel differential device can be prevented from being damaged and can be made compact. In addition, as the deviation μNA increases, the value of the total engagement torque Tt tends to increase and the seizure damage of the electromagnetic clutch 19 tends to occur on a higher μ road. Therefore, in the embodiment of the present invention, when the deviation ΔNA between the average rotational speeds of the left and right front wheels and the average rotational speeds of the left and right rear wheels becomes larger than the predetermined value ΔNA ₁ , the total engagement torque of the electromagnetic clutch becomes higher on the higher μ road. Since it is corrected to the side where it is further reduced, it is effective on high μ roads.

Further, as described above, in the driving force distribution control (differential limit control) executed by the clutch control device 32 of the present embodiment, the engagement torque Tn corresponding to the differential rotation speed ΔN, The engagement torque Tψ according to the estimated lateral acceleration α and the engagement torque Tv according to the vehicle speed V are obtained from the respective torque characteristic maps, and the differential limiting torque of the electromagnetic clutch 19 is controlled based on the total torque. Therefore, ideally, the driving force distribution according to the differential rotational speed ΔN during slope traveling or turning traveling, the driving force distribution according to the yaw rate ψv during turning traveling, and the driving force distribution according to the vehicle speed V are ideal. I can do it. Moreover, since the engagement torque Tn is changed with the gain G1n obtained from the map M2 based on the vehicle speed V and the yaw rate ψv, the engagement is performed by comprehensively considering the differential rotation speed ΔN, the vehicle speed V, and the yaw rate ψv. The torque Tn can be set appropriately. In particular, in the map M2, the lines L2 and L3 are set to have a characteristic that ψv decreases with an increase in the vehicle speed V, so that the torque distribution according to the increase in the lateral acceleration α is the tire lateral force. It becomes possible to distribute the torque in consideration of the limit of, and it is possible to prevent the sudden change of the tire lateral force and the steep characteristic of the steer characteristic during the turning traveling, and to improve the turning performance remarkably.

Particularly, on the map M2, the predetermined vehicle speed d
Regarding the following areas, by setting the gain G1n = 1.0 in the yaw rate small area A1, it is possible to improve the straight running stability, and in the yaw rate intermediate area A2, the gain G is increased.
By setting 1n = 0, it is possible to improve the turning performance when turning in a tight corner, and by setting the gain G1n = 1.0 in the excessive yaw rate region A3, spin prevention is achieved and steering stability is improved. Can be increased. Moreover, in the map M2, the lines L2 and L3 are set to have a characteristic that ψv decreases with an increase in the vehicle speed V, so that the torque distribution corresponds to an increase in the lateral acceleration α,
It becomes possible to distribute torque considering the limit of tire lateral force,
It is possible to prevent a sudden change in the tire lateral force and a steep change in the steer characteristic during turning and to improve the turning performance remarkably. In particular, in the map M3, the line L4 that separates the region B1 and the region B2 is a line that indicates the differential rotation speed ΔN corresponding to the case where the tire dynamic radius is reduced by 10%, and the differential rotation speed ΔN is the line L4. In the following region, the gain G2n is G2
Since n is set to 0, the tire pressure drops,
Since the fastening torque Tn is not controlled to increase due to the erroneous differential rotation speed ΔN that occurs when a temper tire having a small radius is mounted, the accuracy and reliability of the differential limiting control can be improved.

Further, since the engagement torque Tn is changed by the gain G2n obtained from the vehicle speed V and the differential rotation speed ΔN, the engagement torque is taken into consideration in consideration of the correlation between the differential rotation speed ΔN and the vehicle speed V. Tn can be set appropriately. Moreover, map M1
Indicates that the torque characteristics at the time of acceleration shown by the solid line and the torque characteristics at the time of deceleration shown by the broken line are set to different characteristics.The torque characteristics at the time of deceleration have more differential limiting action than the torque characteristics at the time of acceleration. Since the height is increased, the differential limitation can be performed with appropriate characteristics at the time of acceleration and deceleration, so that it is possible to ensure both driveability during acceleration and braking performance during deceleration. Also,
Gain G obtained from the engagement torque T ψ from the differential rotation speed ΔN
Since the gain is changed with 1n, the yaw rate ψ and the vehicle speed V
And the differential rotation speed ΔN are comprehensively taken into consideration, and the fastening torque T
ψ can be set appropriately. Also, the fastening torque T
Since the gain of ψ is changed by the gain G1n obtained from the differential rotation speed ΔN, the yaw rate ψ, the vehicle speed V, and the differential rotation speed ΔN are comprehensively taken into consideration to appropriately set the engagement torque Tψ. be able to. In particular, as shown in the map M4 shown in FIG. 7, the lateral acceleration α is a predetermined lateral acceleration (position where α = m).
In the above case, since the fastening torque Tψ is gradually reduced along the line L6, the grip force of the front and rear wheels 1 to 4 (tire lateral force of the tire) is increased in a severe turning traveling state near the turning limit. ) Does not suddenly change, and the effective driving force does not suddenly change, so that the stability of turning traveling can be secured.

Further, in order to determine the coil current I based on the map M7 in which the hysteresis of the coil 23 is added,
The coil current I can be set with high accuracy. In addition to the above, hold processing can suppress hunting,
Further, the tailing process can prevent a shock when the vehicle is stopped. In the embodiment, the three torque characteristics are preset in the maps M1, M4, M6, but some or all of the torque characteristics are preset in the table or the arithmetic expression. May be. Similarly, the three gain characteristics are represented by maps M2, M3, and M.
Although it is preset to 5, some or all of these gain characteristics may be preset to a table or an arithmetic expression. Further, regarding the map M4, the actual lateral acceleration acting on the vehicle body may be applied as a parameter of the horizontal axis. In that case, the actual lateral acceleration detected by the lateral acceleration detection sensor is applied to the map M4. Then, the fastening torque Tψ is obtained. The total fastening torque Tt may be calculated without using the vehicle speed reflecting fastening torque T3 as necessary, and the total fastening torque Tt may use the yaw rate reflecting fastening torque T2 as necessary. It may be configured so as to obtain without using.

[0028]

As described above, according to the control device for a four-wheel drive vehicle of the present invention, seizure damage to the differential limiting clutch means is prevented and the differential device for the wheel which is the driven wheel during normal traveling. It is possible to prevent damage and to make it compact.

[Brief description of drawings]

FIG. 1 is a block diagram of a control device for a four-wheel drive vehicle according to the present invention;
Overall configuration diagram showing a wheel drive vehicle

FIG. 2 is an explanatory diagram showing the content of driving force distribution control of a four-wheel drive vehicle.

FIG. 3 is a map M1 showing the torque characteristics of the engagement torque Tn.

FIG. 4 is a map M2 showing a gain characteristic of a gain G1n.

FIG. 5 is a map M3 showing a gain characteristic of a gain G2n.

FIG. 6 is a diagram showing a hold process.

FIG. 7 is a map M4 showing torque characteristics of the fastening torque Tψ.

FIG. 8 is a map M5 showing torque characteristics of a gain G1ψ.

FIG. 9 is a map M6 showing torque characteristics of the engagement torque Tv.

FIG. 10 is a map M7 for converting the total engagement torque Tt into a coil current.

FIG. 11 is a map M8 showing the gain characteristic of the gain Gt in the tailing process.

FIG. 12 is a first half of a flowchart showing driving force distribution control.

FIG. 13 is an intermediate part of a flowchart showing driving force distribution control.

FIG. 14 is a second half of a flowchart showing driving force distribution control.

FIG. 15 is a map showing a total engagement torque Tt and a deviation ΔNA between the rotational speeds of the front wheels and the rear wheels.

FIG. 16 is a coefficient K1, a deviation ΔN between the rotational speeds of the front wheels and the rear wheels.
A map showing the relationship between A and the road surface friction coefficient μ (B1, B2, B3)

[Explanation of symbols]

1 front wheel 2 front wheels 3 rear wheels 4 rear wheels 7 Front wheel differential 10 Rear wheel differential 19 Electromagnetic clutch 23 coils 31 ABS control device 32 clutch control device 38 Left rear wheel speed sensor 40 Right rear wheel speed sensor 43 Rudder angle sensor 44 Neutral / Inhibitor switch

Claims (3)

(57) [Claims] 1. A four-wheel drive having a front-wheel differential device, a rear-wheel differential device, and a differential limiting clutch means for changing a differential limiting torque between these differential devices according to a driving state of a vehicle. In a vehicle control device, a control means for controlling the differential limiting clutch means so as to increase the differential limiting torque as the deviation between the rotational speeds of the front wheels and the rear wheels increases, and a gear stage of the transmission. Correction means for correcting the differential limiting torque by the differential limiting clutch means to a decreasing side when the difference between the rotational speed of the front wheels and the rotational speed of the rear wheels is equal to or more than a predetermined value at the lowest speed. A characteristic control device for a four-wheel drive vehicle. 2. The control device for a four-wheel drive vehicle according to claim 1, wherein the correction means reduces the differential limiting torque by the differential limiting clutch means when the vehicle starts. 3. A road surface friction coefficient estimating means for estimating a road surface friction coefficient is provided, and the correcting means further reduces the differential limiting torque by the differential limiting clutch means as the road surface friction coefficient increases. The control device for a four-wheel drive vehicle according to claim 2, wherein the correction is performed.