JPH03148336A - Differential controller of four-wheel drive car - Google Patents

Abstract

PURPOSE:To constantly obtain good responsibility and stability of differential control in a simple structure, irrespective of the condition of road surface by estimating a condition of a frictional coefficient of the road surface based on the value of a torque capacity of a differential control clutch, and by changing feedback gain according to the result thereof. CONSTITUTION:In a four-wheel drive car, an output of an automatic change gear 4 connected with an engine 3 is transmitted to each differential gear 5, 6 for front and back wheels, 1L, 2L, while differential conditions of front and back wheels are controlled by means of changing the quantity of torque transmission of front wheel side by a differential control clutch 7, which is feedback- controlled by an actuator 8, in order to make slip or differential rotation of front and back wheels an aimed slip ratio or an aimed differential rotation. The torque capacity actually employed by the differential control clutch 7 is detected, and the feedback control gain is changed by a control gain determining means 18, according to the detected torque capacity.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a differential control device for a four-wheel drive vehicle, and particularly to a differential control device for a four-wheel drive vehicle that is designed to achieve both responsiveness and stability when controlling the differential between front and rear wheels. 81111
Regarding equipment.

[Conventional technology]

Equipped with a differential control clutch for feeding back the differential state of the front and rear wheels so that the slip ratio (or differential rotation speed) between the front wheels and the rear wheels becomes the target slip ratio (or target differential rotation speed). A four-wheel drive vehicle is known (Japanese Unexamined Patent Publication No. 132421/1983). This technology is based on the following technical philosophy. In other words, when a large driving force is required when starting, etc., only two wheels can be used with a low power of 11! When attempting to drive a vehicle on a road surface with a high coefficient of friction, only the drive wheels slip significantly and the power transmitted from the engine is not fully utilized as power to drive the vehicle. However, even if the four wheels are directly connected, when starting on a road surface with a friction coefficient of H, such as a dry concrete road surface, the amount of slip between the front and rear wheels is mutually regulated. The problem was that sufficient driving force could not be exerted. In other words, as shown in Figure 7, in order to make the most of the power transmitted from the engine as driving force for the vehicle, there is an optimal slip ratio for the front and rear wheels, and the actual slip ratio does not match this optimal slip ratio. If the slip ratio deviates in either direction, the power transmitted from the engine cannot be utilized to its maximum as driving force for the vehicle. Therefore, if feedback control is performed so that the slip ratio of the front and rear wheels is always at this optimal slip ratio, the power transmitted from the engine can always be maximized. Based on this technical idea, the above feedback technology feedbacks the differential state of the front and rear wheels so that the slip ratio between the front wheels and the rear wheels becomes the target slip ratio.
, it is something that is. Note that this technical idea can be considered to be almost synonymous with the technical idea of ``feedback control of the differential state of the front and rear wheels so that the differential rotation speed between the front wheels and the rear wheels becomes the target differential rotation speed.''

[Problem to be Solved by the Invention 1] However, in general, on low μ roads, slips with the road surface are likely to occur, so differential motion between the front and rear wheels is likely to occur, resulting in slight changes in the torque capacity of the differential clutch. On the other hand, on high-μ roads, it is difficult to generate a differential between the front and rear wheels, and the differential state does not change much even if the torque capacity of the differential control clutch is slightly changed. be. Therefore, if the feedback gain K is fixed at a constant value when performing the feedback III described above, if the gain K is tuned to match a high μ road, the gain will be too large on a low μ road and the slip ratio will increase. Hunting (or differential rotation speed) occurs, and conversely, low μ
If the vehicle is tuned to suit the road, a problem arises in that target tracking performance deteriorates on high μ roads. The present invention has been made in view of these problems, and is designed to maintain the responsiveness and stability of the differential side control at all times, even when driving on a low μ road or while driving on a ^μ road. An object of the present invention is to provide a differential control device for a four-wheel drive vehicle that can perform optimal matching. [Means for Solving the Problems] As the gist of the present invention is shown in FIG. In a differential control device for a four-wheel drive vehicle equipped with a differential III clutch for feedback controlling a differential state between front and rear wheels, the differential clutch
The above object is achieved by comprising means for detecting the torque capacity currently handled by the clutch II, and means for changing the gain of the feedback IIIg in accordance with the torque capacity currently handled by the differential control clutch. This has been achieved.

[Effect]

The present invention is basically based on the technical concept of increasing the feedback gain K on an 8μ road and decreasing it on a low μ road. however,
The friction coefficient of the road surface constantly changes, and it is extremely difficult to accurately detect it in real time. Therefore, in the present invention, we have focused on the fact that the torque capacity of the differential ISM clutch during feedback control is small on low μ roads, and conversely, the torque capacity of the differential control clutch is large on high μ roads. The torque capacity currently handled by the differential 11111 clutch is detected, and the feedback control gain is changed accordingly. The torque capacity that the differential lilIW clutch is actually responsible for can be easily determined by detecting the value of the oil pressure that controls the differential w4M clutch, or the current value of a solenoid valve that controls this oil pressure value. It is possible to grasp the According to the present invention, when slipping is likely to occur on a low μ road, and therefore the driving force of the front and rear wheels is small, and therefore the differential control clutch is responsible for only a small torque capacity, it is possible to reduce the gain to prevent hunting; On the μ road, the driving force between the front and rear wheels is large, and there is a difference! When the lIliIIIll clutch is in charge of a large torque capacity, the gain can be increased to improve responsiveness.

【Example】

Embodiments of the present invention will be described in detail below based on the drawings. FIG. 2 shows a schematic configuration of a differential control device for a four-wheel drive vehicle according to an embodiment of the present invention. In the figure, 1L11R is the front wheel, 2L12R is the rear wheel, 3
is the engine, 4 is the automatic transmission, 5.6 is the differential device for the front and rear wheels, 7 is the differential control clutch that controls the differential between the front and rear wheels by increasing or decreasing the amount of torque transmitted to the front wheels, and -8 is the differential control clutch for the front and rear wheels. This is an actuator (electromagnetic proportional valve) that controls the differential control clutch 7. This four-wheel drive vehicle uses 2L of output from the automatic transmission for the rear wheels.
, 2R is transmitted as is, and front wheels 1L and 1R are differentially transmitted.
The transmission is performed via a third clutch 7. When the differential control clutch 7 is fully engaged, rigid four-wheel drive with no differential between the front and rear wheels is achieved, and when the differential control clutch 7 is completely released, the rear wheels (two wheels) are
Drive is realized. In Fig. 2, 10 is a sensor that detects the front wheel rotation speed NF, 11 is a sensor that detects the rear wheel rotation speed NR, and 13 is a differential rotation speed between the front and rear wheels from the front wheel rotation speed NF and the rear wheel rotation speed N. The means for calculating ΔN, 14, calculates the target differential rotation speed ΔN.
15 is the deviation (ΔN-8No.) between the currently occurring differential rotation speed ΔN and the target differential rotation speed ΔN
), 16 is a means for calculating an addition/subtraction value ΔD of the current value to the actuator 8 by multiplying the deviation (ΔN-8No) by the feedback gain K, and 17 is a calculation means 16 for calculating the current value. This is an addition means that adds the addition/subtraction value ΔD obtained in , and calculates a new current value to be sent to the actuator 8. The actuator 8 generates a hydraulic pressure Pc according to the supplied current value, and uses this hydraulic pressure Pc to generate a differential iIIl.
Torque capacity of clutch 7 (front wheel 1L from automatic transmission 4 side
, the power transmitted to the 1R side). The configuration up to this point is not particularly different from the conventionally known configuration. Here, the 10 pieces 18 in FIG. 2 correspond to gain determining means for determining the feedback gain K in the calculating means 16. The gain determining means 18 receives information on the current value for controlling the actuator 8 from the adding means 17, and determines the current value according to the value of the current value, for example, as shown in FIG. The feedback gain K is determined by the characteristics shown in (B). As is clear from Figures 3 (A) and (B), the larger the current value, the greater the feedback gain K. It has been changed to increase the current value (to improve the response).This is because the differential 111611
This is because the torque capacity handled (transmitted) by the clutch 7 is increased, and it is presumed that the driving force of each of the front and rear wheels is large and the road is high. Note that the configuration of the four-wheel drive vehicle itself to which the present invention is applied is not particularly limited. That is, as in the above embodiment, the output from the automatic transmission is directly transmitted to the rear wheels 2L and 2R, and the output from the automatic transmission is directly transmitted to the rear wheels 2L and 2R.
A configuration may be used in which the power is transmitted to L11R via the differential control clutch 7, or a configuration as shown in FIG. 4, for example, may be used. The four-wheel drive vehicle shown in FIG. 4 uses the driving force of an engine 3 to rotate a carrier 42 of a planetary gear train 41 via an automatic transmission 4. The power taken out from the ring gear 44 drives the rear wheels, and the power taken out from the sun gear 45 drives the front wheels IL and IR. In this four-wheel drive vehicle, the differential control clutch 7 is disposed between the ring gear 44 and the sun gear 45, and the differential lI
When the I clutch 7 is fully engaged, the ring gear 44
and sun gear 45 are integrated to realize rigid four-wheel drive with no differential between the front and rear wheels. Furthermore, when the differential control latch 7 is completely released, the planetary gear train 41 functions as a so-called center differential, and a four-wheel drive state is realized in which differential movement between the front and rear wheels is allowed as appropriate depending on the reaction force from the road surface. . FIG. 5 shows a control flow executed in the embodiment apparatus of FIG. 2 (or FIG. 4). First, in step 101, the initial feedback gain and initial current value are read, and the flag is reset to zero. Next, in step 102, the front wheel rotation speed NF is determined. Rear wheel rotation speed NR is detected. In step 103, the differential rotation speed ΔN between the front and rear wheels is determined by calculating N*-NF. In step 104, it is determined whether the value of the flag is zero. Initially, it is determined that the flag is zero, so proceed to step 105 and calculate the difference 111 rotation speed Δ.
It is determined whether N is larger than a predetermined value ΔN1. When the differential rotational speed ΔN is smaller than the predetermined value ΔN1, the process ends here. That is, no particular feedback control is performed to set the differential rotation speed ΔN to the target rotation speed ΔN·. In step 105, the differential rotation speed ΔN is set to a predetermined value ΔN1.
Feedback when it is judged to be larger! i
In order to perform step 1111, the target differential rotation speed ΔNo is first determined by a well-known method. In step 107, the differential zero rotation number Δ
The deviation (ΔN-ΔNO) between N and the target differential rotation speed ΔNo is calculated, and in step 108, this is multiplied by the feedback gain K to calculate a current value ΔD corresponding to the deviation. The initial gain read in step 101 is used as the feedback gain here. In step 109, a current value Δ0 corresponding to the obtained deviation is added to the initial current value to obtain a new current value, and the futuator 8 is driven with this signal. Thereafter, the feedback gain K is determined based on the newly updated current value in step 109 according to the map shown in FIG. 3(A) or FIG. 3(B) (step 110).
. A flag is set to 1 in step 111. After the flag is set to 1, the process returns to step 102 and the above-described flow is repeated again. However, since the flag is set to 1, a negative determination is made in step 104, and the predetermined value (
II value) is changed to ΔN2, which is smaller than ΔN1. That is, when starting III114r, it is assumed that a somewhat large differential has occurred, but when stopping Ilm,
The process is stopped only when the differential converges to a smaller value ΔN2 or less, and an appropriate hysteresis is provided here. Incidentally, when the above-mentioned flow is expressed in a flock diagram, it becomes as shown in FIG. The specific explanation of FIG. 6 overlaps with the explanation of FIG. 2 or FIG. 6, so it will be omitted. [Effect of the invention 1] As explained above, according to the present invention, the state of the friction coefficient of the road surface is estimated based on the torque capacity of the differential clutch (or the oil pressure that determines the torque capacity or the value of tsmia*). Since the feedback gain K is increased or decreased by this, it is possible to achieve both improvement of responsiveness when driving on a high μ road and prevention of hunting when driving on a low μ road with an extremely simple configuration. It becomes like this.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the gist of the present invention, and FIG.
Four wheels 19 according to an embodiment of the present invention! Figures 3 (A) and 3 (B) are schematic block diagrams showing the configuration of the differential control device for vehicle operation.
FIG. 4 is a diagram showing the relationship between the control current value of the differential Ill'' clutch and the feedback gain, FIG. 4 is a skeleton diagram showing another configuration example of a four-wheel drive vehicle to which the present invention is applied, and FIG. , a flowchart showing the lllll flow executed in the above embodiment device, FIG. 6 is a block diagram showing the control system of the above embodiment device, and FIG. 7 is a miniature diagram showing the relationship between the slip ratio and the driving force coefficient. N p - front wheel rotation speed, N R - rear wheel rotation speed, ΔN
...Differential rotation speed, ΔN o -target differential rotation speed, K...Feedback gain, D...Ij current value for actuator 1 drive.

Claims (1)

[Claims] (1) Equipped with a differential control clutch for feedback controlling the differential state of the front and rear wheels so that the slip ratio or differential rotation speed between the front wheels and the rear wheels becomes the target slip ratio or target differential rotation speed. A differential control device for a four-wheel drive vehicle, comprising: means for detecting a torque capacity currently handled by the differential control clutch; and means for determining a gain of the feedback control according to a torque capacity currently handled by the differential control clutch. What is claimed is: 1. A differential control device for a four-wheel drive vehicle, characterized in that the differential control device comprises: a means for changing the differential;