JPH05155264A - Front and rear drive force distribution controller for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To improve the control responsibility and the stability of the behavior of a vehicle by temporarily making an electromagnetic clutch as a clutch used for controlling the front and rear wheel drive force distribution of a four wheel drive vehicle keep in a neutral state of ON and OFF in ON and OFF switching. CONSTITUTION:In a four wheel drive vehicle, exciting current of the solenoid 5a of a electromagnetic clutch 5 for controlling front and rear drive force distribution is controlled by a controller 6 based on wheel revolution VFL, VFR, VRL, and VRR sent from wheel revolution sensors 15 to 18, and when a clutch is turned ON from OFF, the exciting current is kept in the neutral state of ON and OFF by switching a clutch OFF current map to a clutch ON current map.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the responsiveness of front-rear driving force distribution control by switching between 2WD / 4WD by using an electromagnetic clutch as a clutch for front-rear driving force distribution control of a four-wheel drive vehicle. The present invention relates to a front-rear driving force distribution control device for a four-wheel drive vehicle.

[0002]

2. Description of the Related Art Conventionally, in a front-rear driving force distribution control device for a four-wheel drive vehicle, a ratio of distributing the driving force from the engine to the front and rear wheels is controlled by a clutch. A hydraulically controlled multi-disc clutch as disclosed in JP 61-155027 A is used. The multi-disc clutch is controlled to be turned on (engaged) when the difference in wheel speed between the front and rear wheels exceeds a set value, and the multi-disc clutch is turned on to bring the vehicle into a four-wheel drive state. At this time, the ratio of the front-rear driving force distribution is controlled as 100: 0 to 70:30 to 60:40 to 50:50 in the case of an FF vehicle-based four-wheel drive vehicle, for example.

[0003]

In the four-wheel drive vehicle using the above-described multi-disc clutch, the control characteristic of the multi-disc clutch, for example, the response of the control is emphasized, and the clutch is turned off.
If the setting is made so that the torque rises abruptly when turning from ON to ON, hunting may occur and the vehicle behavior may become unstable. Conversely, with emphasis on vehicle behavior stability, the torque rise may be moderate. When set to, the clutch is OF
There is a large time lag when shifting from F to ON, and there is a delay in the control response, and the ABS device (anti-skid)
If a brake device is installed, there is a risk that it will interfere with ABS control.

According to the present invention, an electromagnetic clutch as a clutch used for front-rear driving force distribution control is temporarily set to an intermediate state between ON and OFF at the time of ON-OFF switching.
The object is to solve the above-mentioned problems.

[0005]

To this end, a front-rear drive force distribution control device for a four-wheel drive vehicle according to the present invention is a four-wheel drive vehicle having a clutch for front-rear drive force distribution, wherein an electromagnetic clutch is used as the clutch. Is used to switch the electromagnetic clutch from OFF to ON or from ON to OFF.
The present invention is characterized in that a control means is provided for performing current control so as to switch between an intermediate state between N and OFF.

[0006]

According to the present invention, the electromagnetic clutch as the clutch for distributing the front-rear driving force is turned on and off without the exciting current being completely reduced to 0 by the current control by the control means when switching from off to on. Because the current value is maintained at the current value corresponding to the intermediate state of (when switching from ON to OFF, the excitation current does not rise to the maximum value and is maintained at the current value corresponding to the intermediate state of ON and OFF) , The time lag when the clutch turns from OFF to ON (or when turning from ON to OFF) is reduced, the control response is improved, the torque fluctuation width is reduced, and the vehicle behavior stability is improved by preventing hunting. Further, when the ABS device is mounted, compatibility with the ABS control can be easily realized.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of a first embodiment of a front-rear driving force distribution control device for a four-wheel drive vehicle according to the present invention.
The wheel drive vehicle is configured as an FF vehicle-based four-wheel drive vehicle (it goes without saying that the front-rear driving force distribution control device for the four-wheel drive vehicle of this example can be applied to an FR vehicle-based four-wheel drive vehicle). I). In FIG. 1, 1L and 1R are left and right front wheels, 2L and 2R are left and right rear wheels, 3 is an engine, 4 is an automatic transmission, 5 is an electromagnetic clutch, and 6 is a controller. The driving force generated by the engine 3 is input to the automatic transmission 4 and transmitted from its output shaft 4a to the front wheel drive shaft 10 via the joint 7, the shaft 8 and the joint 9, and when the front wheel drive shaft 10 is driven, the left and right sides are driven. Front wheels 1L and 1R are constantly driven. Further, the driving force transmitted from the output shaft 4a to the joint 7 is also transmitted to the electromagnetic clutch 5 via the shaft 11. When the electromagnetic clutch 5 is ON (when engaged), the driving force from the shaft 11 is transmitted to the shaft 12, It is transmitted to the rear wheel drive shaft 14 via the joint 13, and the left and right rear wheels 2L and 2R are driven by the drive of the rear wheel drive shaft, so that the vehicle enters the four-wheel drive state (4WD). When the electromagnetic clutch 5 is OFF (released), the driving force is not transmitted to the rear wheels 2L and 2R, and the vehicle is in the two-wheel drive state (2WD).

ON / OFF of the electromagnetic clutch 5 is controlled by a controller 6 as a control means. For ON-OFF control of this electromagnetic clutch, each wheel 1L, 1R, 2L,
Wheel rotation speed sensors 15, 16, 17, 18 for detecting wheel rotation speeds VFL, VFR, VRL, VRR of 2R are provided (note that
In this example, the wheel rotation speed sensor is provided for each wheel, but one wheel rotation speed sensor is provided in the vicinity of the front wheel drive shaft 10 and the rear wheel drive shaft 14 to measure the average rotation speed of the left and right front wheels and the left and right rear wheels. May be detected). The controller 6 includes wheel speeds VFL, VFR, VR detected by these sensors.
Input L and VRR. The controller 6 executes the control program of FIG. 2 based on these input signals to control the current of the solenoid 5a of the electromagnetic clutch 5.

That is, in the control program of FIG. 2 which is repeatedly executed by the periodic interrupt every predetermined period, first, in step 101, which is executed only for the first time of the current control period,
The clutch ON duration Ton set in the previous control cycle is reset (Ton = 0), and the state of the controller 6 is checked in step 102. If the controller 6 is determined to have failed in this check, step 103
After resetting the controller 6 in step 104, Ton is reset in step 104 and then the control is returned to step 102. On the other hand, if the CPU is determined to be normal in the check in step 102, the presence or absence of ABS operation is determined in the next step 105, and during ABS operation, the ABS current map as illustrated in FIG. 3 is looked up in step 106. After it has been up, reset Ton in step 107 and then control.
Returning to 102, control proceeds to step 108 when ABS is not operating.

In step 108, each wheel rotation speed sensor 15
The wheel speeds VFL, VFR, VRL, and VRR are read from .about.18, and the vehicle speed V and the front-rear differential speed .DELTA.N are calculated based on these wheel speeds in the next step 109. In addition,
In this calculation, for example, V = (VRL + VRR) / 2 is used to obtain the average rotational speed of the left and right rear wheels, which are driven wheels, and
ΔN = (VFL + VFR) / 2- (VRL + VRR) /
It is calculated by subtracting the average driven wheel rotational speed from the driven wheel average rotational speed by 2. V, ΔN obtained in this way
In step 110, the clutch ON-OFF judgment map as illustrated in FIG. 4 is looked up by using the above, and the clutch ON-OFF judgment is performed in the next step 111. This clutch ON-OFF determination is, for example, in the clutch ON region when ΔN in the map of FIG. 4 is equal to or greater than the set value (curve shown in the figure) set according to the vehicle speed V (for example, when the drive wheels are slipping). If it is less than the set value, it is determined to be in the clutch OFF region. If the clutch is OFF, the control proceeds to step 112. If the clutch is ON, the control proceeds to step 113. As a result, in the low speed region of the vehicle speed of FIG. 4, the ON region of the clutch is expanded so as to cope with the slip at the time of starting, and the boundary between the ON and OFF regions is changed in consideration of the lock prevention during turning.

In the control of this example, the clutch is turned off.
Since the main purpose is to reduce the time lag when shifting from ON to ON, the clutch OF
It is premised that the F command is issued. Therefore, in step 112 corresponding to the clutch OFF, the clutch OFF current map as illustrated in FIG.
The current of the solenoid 5a of the electromagnetic clutch 5 is controlled so that the current value becomes the current value. That is, the clutch current Ioff is gradually reduced according to the map illustrated in FIG.
It is stored in 114. The clutch current Ioff stored in this step 114 finally turns the clutch from OFF to ON.
The value at the moment of switching to. When the clutch OFF state continues for a predetermined time Tmax or more, the clutch current Ioff is held at the lower limit value Imin as shown in FIG.

When it is judged that the clutch is ON in the judgment of step 111, step 113 selects step 113, and in step 113, the state of the electromagnetic clutch 5 is checked depending on whether Ton = 0 or not. The clutch is open here.
At the moment of switching from F to ON, YES at Ton = 0, so step 113 selects step 115, and in step 115 the lookup start current is set to Ioff. In the next step 116, Ioff set with the clutch ON current map as illustrated in FIG. 6 is set in step 105.
Then, the current of the solenoid 5a of the electromagnetic clutch 5 is controlled so as to obtain the current value. The vehicle is brought into the four-wheel drive state (4WD state) by the current control after the map switching. After performing this step 116, step 117
The clutch current Ion is stored with, and the clutch ON duration timer Ton is incremented (To
n = Ton + 1). Thereafter, when the control advances from NO-105 to NO-108-109-110-111-113 in step 102, step 113 becomes NO and step 119 is selected, where the clutch ON duration Ton is set to the clutch O.
It is determined whether the N set time T ₀ or more has been reached.

In this judgment, until the count value of the clutch ON duration timer Ton reaches the clutch ON set time T ₀ , the control is NO-116 to 118 of step 119.
The NO-119 loop of -102 to 113 is repeated, while the clutch current Ion gradually increases along the map shown in FIG. It should be noted that when the clutch is on for a predetermined time Tmax (=
When it continues for more than T ₀ ), the clutch current Ion is held at the upper limit value Imax as shown in FIG.

When the count value of the timer Ton reaches the clutch ON set time T ₀ , the step 119 selects the step 120, and resets the Ton (Ton = 0) there, and then in the step 121, the lookup start current Ion is set. Set to. After execution of step 121, control proceeds to step 112 where the map is switched back to the clutch off current map. Note that the control of FIG. 2 is always executed while the vehicle is running, and for example, when the vehicle is stopped, the ignition key is turned off.
Finish by pressing F.

The operation of the above control will be described in detail with reference to FIGS. Generally, when the front-rear driving force distribution control is performed in a four-wheel drive vehicle, the front and rear wheel differential rotation speeds are calculated based on the wheel rotation speeds from the respective wheel rotation speed sensors 15 to 18, which is shown in FIG.
When it exceeds the predetermined value shown in, the clutch for front-rear driving force distribution control (electromagnetic clutch 5 in this example) is turned on.
The basic control is to switch from the 2WD state to the 4WD state. At that time, in the 4WD state, the front and rear wheels are directly connected (for example, rigid 4WD; front and rear wheel drive force distribution = 50:50) and the front and rear wheel differential rotation speed cannot be detected, so the clutch is in the ON state (that is, the 4WD state). Time to continue
ON is set in advance, and when the set time (constant value, for example, 1 second) elapses, the front-rear differential rotation speed ΔN can be detected by forcibly switching to the clutch OFF region. The clutch ON-OFF control is judged.

Before explaining the control of this example,
For comparison, turn on air conditioners that are generally installed in vehicles.
A case where an electromagnetic clutch is used for the -OFF control will be described (note that the configuration in which the electromagnetic clutch is used for the front-rear driving force distribution control is the object of the present invention). For example, in a system in which only the ON / OFF of the clutch is controlled by an electromagnetic clutch, a method of shortening the torque rise time by voltage control such as rapid excitation (applying a voltage higher than the rating) is generally adopted to improve control accuracy. In that case, the rise time of the torque can be shortened, but hunting or the like may occur and the vehicle behavior may become unstable. Therefore, as a countermeasure against this, if the rise and fall of the exciting current of the electromagnetic clutch is slowed down and the rise time of the torque is lengthened, the clutch is switched from OFF to ON as shown in FIGS. 10 (a) and 10 (b). The time lag of time becomes large.

On the other hand, in the control of this example, the vehicle speed V and the front-rear differential rotation speed Δ obtained by executing step 109 in FIG.
Clutch ON-OFF in steps 110 and 111 based on N
Therefore, for example, when switching the clutch from OFF to ON at the instant t ₁₁ in FIG.
By executing 112, the clutch OFF current map of FIG. 5 is selected and the clutch current Ioff gradually decreases.
It is stored as the current value I _{1 at} the instant t _{11 in} (a), and the value is set to the lookup start current of the clutch ON current map of FIG. 6 by executing step 115. Therefore, by executing step 116, the clutch current Ion, which is looked up at the instant t _{11 of} map switching, is maintained at the current value I ₁ corresponding to the intermediate state of clutch ON-OFF as shown in FIG. 7B. It starts to increase from that state. When switching the clutch from ON to OFF, the clutch current Ion stored by executing step 117 is set to the lookup start current of the clutch OFF current map of FIG. 5 by executing step 121. The clutch current Ioff, which is looked up at the time of map switching by executing 117, becomes a current value corresponding to the intermediate state of the clutch ON-OFF similarly to the above.

As described above, when the clutch current of the electromagnetic clutch 5 changes via the current value (I _{1 in the} above case) corresponding to the intermediate state of the clutch ON-OFF, the vehicle behavior stability and the control response are remarkably increased. improves. That is, in the control example shown in FIGS. 7 (a) and 7 (b), a simple ON-O is performed without passing through the current value corresponding to the intermediate state of ON-OFF.
When the FF control is performed, the time t ₁ until the clutch current Ion further decreases from I ₁ and reaches the lower limit value Imin in FIG.
Also, the time t ₂ required for the torque to increase from the lower limit value to reach I ₁ is required, but the control of the present example does not require these times, and the time lag when the clutch is switched from OFF to ON is shown in FIG. As shown in FIG. 8, the control response is improved by shortening the time corresponding to (t ₁ + t ₂ ), and the vehicle behavior is changed unnecessarily because the current value is held at I ₁ during map switching. There is no. Further, as shown in FIG. 9, the fluctuation range of the torque is significantly compressed as compared with the case of the simple ON-OFF control. As a result, hunting is prevented and the vehicle behavior stability is improved.

Note that the determination in step 105 of FIG. 2 is YES.
When the ABS is operated, the map is unconditionally set to the clutch OFF current by maintaining the current value I ₁ at the time of map switching by executing step 106 regardless of whether the electromagnetic clutch 5 is ON or OFF. Map or clutch ON
By switching from the current map to the ABS current map of FIG. 3, the ABS control is immediately transferred, so that the vehicle behavior does not change unnecessarily. When the ABS is in the clutch OFF state (2WD) (the ABS does not operate in the 4WD state because the front and rear wheels do not rotate differentially),
The clutch is faster to turn off than the map in FIG.
Since the map is selected, it is possible to achieve both the control of this example and the ABS control. Further, since the front-rear driving force distribution control device of the present embodiment uses the electromagnetic clutch, compared to a system using a hydraulically controlled clutch (for example, a multi-plate clutch), a hydraulic pump, piping, etc. are unnecessary, and the cost is reduced. Get down.

[0020]

As described above, the front-rear driving force distribution control device for a four-wheel drive vehicle according to the present invention temporarily turns ON and OFF the electromagnetic clutch as a clutch used for the front-rear driving force distribution control at the time of ON-OFF switching. I'm going to be in an intermediate state,
Due to the current control by the control means, the exciting current is not completely reduced to 0 and is maintained at the current value corresponding to the intermediate state between ON and OFF (when switching from ON to OFF, the exciting current reaches the maximum value). ON and OF without rising
The current value corresponding to the intermediate state of F is maintained), and the time lag when the clutch turns from OFF to ON (or when it turns from ON to OFF) is reduced, and the control response is improved. The torque fluctuation width is reduced, hunting is prevented, vehicle behavior stability is improved, and when an ABS device is installed, compatibility with ABS control can be easily realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a front-rear driving force distribution control device for a four-wheel drive vehicle according to the present invention.

FIG. 2 is a flowchart showing a control program for current control of a solenoid of an electromagnetic clutch by a controller in the same example.

FIG. 3 is a diagram illustrating an ABS current map in the same example.

FIG. 4 is a diagram illustrating a clutch ON-OFF determination map in the same example.

FIG. 5 is a diagram illustrating a clutch OFF current map in the same example.

FIG. 6 is a diagram illustrating a clutch ON current map in the same example.

7A and 7B are diagrams for explaining the operation of the same example.

FIG. 8 is a diagram for explaining the operation of the same example.

FIG. 9 is a diagram for explaining the operation of the same example.

10A and 10B are views for explaining the operation of the conventional example.

[Explanation of symbols]

 1L Front wheel 1R Front wheel 2L Rear wheel 2R Rear wheel 3 Engine 4 Automatic transmission 5 Electromagnetic clutch 5a Solenoid 6 Controller 15 Wheel speed sensor 16 Wheel speed sensor 17 Wheel speed sensor 18 Wheel speed sensor

Claims (1)

[Claims] 1. A clutch having a clutch for distributing front-rear driving force.
In a wheel drive vehicle, an electromagnetic clutch is used as the clutch, and the electromagnetic clutch is turned from OFF to ON or from ON to OFF.
A front-rear driving force distribution control device for a four-wheel drive vehicle, characterized in that a control means is provided for performing current control so as to switch through an intermediate state between ON and OFF when switching to.