JPS6259125A - Transmission torque controller for four-wheel drive car - Google Patents

Abstract

PURPOSE:To improve the driving efficiency and traveling stability by detecting the slip states of the front and rear wheels and controlling the torque distribution ratio so that the torque distribution increases on the wheel having the less slip rate. CONSTITUTION:In a control unit 14, when a vehicle is in traveling, the front- wheel slip state DELTASF is obtained on the basis of the front-wheel revolution speed NF and the standard revolution speed No of the fifth wheel 28, and the rear-wheel slip state DELTASR is obtained on the basis of the rear-wheel revolution speed NR and the standard revolution speed No. When the front-wheel slip state is small where DELTASR-DELTASF>0, a power device 27 including a hydraulic variable clutch is controlled, and the torque distribution to the front wheels is increased. When the rear-wheel slip state is small where DELTASR-DELTASF<=0, the power device 27 is controlled similarly, and the torque distribution to the rear wheels is increased. Therefore, the generation of the nearly equal slip on all four wheels is permitted, and the slip limit of all four wheels is increased.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a transmission torque control means for a four-wheel drive vehicle.

(Prior art) As a four-wheel drive vehicle, for example,
As shown in the publication, a first drive shaft is directly connected to a power plant consisting of an engine, a transmission, etc., and a second drive shaft is connected to the power plant via a power transmission means such as a clutch mechanism. There is known a vehicle that can switch between two-wheel drive and four-wheel drive by controlling the engagement and release of the clutch mechanism.

To adjust the torque distribution ratio between front and rear wheels in a four-wheel drive vehicle,
For example, this can be done by adjusting the engagement force of a clutch mechanism that switches between two-wheel drive and four-wheel drive as described above, and controlling the amount of torque transmitted by this clutch mechanism.

(Problem to be solved by the invention) Originally, four-wheel drive vehicles attempted to achieve high drive efficiency by making full use of the frictional force generated in the tires. In cars, too, there is a problem in that when slip occurs in any of the tires, driving efficiency decreases and driving becomes unstable.

An object of the present invention is to provide a transmission torque control device for a four-wheel drive vehicle that can increase the slip limit, improve drive efficiency, and improve running stability.

(Means for Solving the Problems) The present invention provides a power transmission means with variable torque transmission amount provided in at least one of the torque transmission paths that transmits torque from a power plant to front and rear wheels, respectively. Controls the torque distribution to the front and rear wheels by variable control of the
A transmission torque control device for a wheel drive vehicle, comprising a control means for controlling a torque distribution ratio between front and rear wheels by changing the amount of torque transmitted by the power transmission means, and a slip detection means for detecting a slip state of the front and rear wheels. and the control means includes:
The vehicle is characterized by comprising means for controlling the torque distribution ratio so that the torque distribution becomes larger toward the side with a smaller slip ratio in response to a signal from the slip detection means.

(Function) In the present invention, since the torque distribution is increased for the side with a smaller slip ratio, the slip ratio is equalized, that is, almost the same slip occurs on the four wheel metal bodies, and the four wheel metal bodies slip limit increases.

(Effects of the Invention) In the present invention, the torque distribution ratio is controlled in accordance with the signal from the slip detection means so that the torque distribution is larger toward the side with a smaller slip ratio, so the slip limit is increased and the drive efficiency is improved. and driving stability.

(Embodiment) Hereinafter, a transmission torque control device for a four-wheel drive vehicle according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

3 and 4 show an embodiment of the present invention. In FIG. 3, reference numeral 1 indicates a power plant, and this power plant 1 consists of an engine, a transmission, and the like.

A front propeller shaft 4 is connected to the output shaft 2 of the power plant 1 via a gear train 3, and a rear propeller shaft 6 is connected via a hydraulic variable clutch 5, which is a power transmission means. ing. The front propeller shaft 4 is connected to a front wheel 8 via a final gear unit 7, and the rear propeller shaft 6 is connected to a rear wheel 10 via a final gear unit 9. In the above configuration, the pressure of the hydraulic oil applied to the clutch 5 is changed to change the amount of torque transmitted by the clutch 5, thereby adjusting the torque distribution ratio between the front and rear wheels.

In the transmission torque control device shown in FIG. 3.4, the torque distribution ratio is kept constant according to the rotational speed difference between the front and rear wheels, and the principle of this will be explained below.

(Principle for keeping the torque distribution ratio constant) First, the above-mentioned power transmission means is provided on the rear side, and the power plant output torque is set to Tp%, and the front and rear torques are respectively Tf%'rr%, and the distribution ratio is set to U. Then, the following formula holds true. □Tp
=Tr+T, ・・・・・・(1)T,
= u T, (2) Also, let the front and rear driving forces be F,, p,, respectively.
The front and rear tire slip ratios are S f , sr
%Front and rear tire angular velocity is ω2, 1, front and rear ground contact load is ω N t s Nr s Front and rear tire dynamic effective radius is Rf s Rr s Front and rear vehicle body speed averaged from left and right is V f , vr % drive coefficient μ
, let k be the constant determined by the tire slip characteristics,
The following formula holds. In addition, the driving coefficient μ and the constant mentioned above are values obtained from the slip characteristics specific to the tires used as shown in Fig. 9, μ=F/N (F: driving force, N: ground contact load) k=μ/
S (S; slip rate).

F, = μN r = k S r N r ...
...(4) F, = μN, = k S, N, ...
・(5) Furthermore, the front and rear gear ratios (pellet shaft/half shaft) are G r , cr %, and the respective speeds of the front and rear propeller shafts are nt S
nr respectively, the relationship between torque and angular rotational speed can be expressed by the following equation.

nr = Gy Q)t = -(10)n
r=GrtIJ, old... (11) From formulas (4), (6), (8), (10)...
(12) From equations (5), (7), (9), (11) to equation (12)...(14) From equation (13)...(15) Front and The rear vehicle speed ratio t can be expressed as follows. Equations (14), (15), (16
), (17) The relationship between rear torque and each rotational speed is expressed by equations (3) and (17
), it can be expressed as follows.

, ', Tr = (18) The relationship between the rear torque and the rotational speed difference between the front and rear wheels Δn can be expressed as follows.

Δn=nf-nr (19),'
, nr=nr -Δn (20) According to equations (18) and (20), vehicle driving conditions (e.g. vehicle speed and cornering)
In order to keep the target rear torque distribution ratio U set in advance constant according to The obtained value of Tr may be used. Note that the rear torque T obtained from the above equation (21) when the steering angle is constant and when the vehicle speed is constant.

The relationship between the rotational speed difference Δn and the rotational speed difference Δn is shown in FIGS. 1 and 2.

In addition, the distance between the front wheels is bl, the distance between the rear wheels is b2, and the distance between the front and rear wheels is! , α1 is the steering angle of the inside front wheel in the steered state, α2 is the steering angle of the outside front wheel, and R1 is the distance from the center of rotation to the inside and outside front wheels and the inside and outside rear wheels, respectively.
Assuming R2, R3, and R-, the vehicle speed ratio t can be expressed as follows.

tan α 凰 tan α2 Therefore, if the steering angle is known, the vehicle speed ratio t can be known.

As described above, the rear torque can be controlled according to the difference in rotational speed between the front and rear wheels, and the torque distribution ratio can be kept constant.

Next, a hydraulic control system for the clutch 5 will be explained with reference to FIG. As shown in the figure, the hydraulic oil in the oil tank 11 is sucked up by the pump 12,
It is discharged at a predetermined pressure and supplied to the hydraulic oil chamber 5a of the clutch 5 via the hydraulic control valve 13. The hydraulic control valve 13 is controlled by a control unit 14 to adjust its working hydraulic pressure. As a result, the pressure of the hydraulic oil in the hydraulic oil chamber 5a of the clutch 5 is adjusted, and the engagement force of the clutch 5 is controlled.

The control unit 14 detects the vehicle speed and receives a vehicle speed signal S.
A vehicle speed sensor 15 outputs a steering angle signal Sα, a steering angle sensor 16 detects a steering angle and outputs a steering angle signal Sα, and a rotational speed difference Δn between the front and rear propeller shafts 4.6 is detected and a speed difference signal SΔ A speed difference sensor 17 that outputs , is connected. In addition, as the vehicle speed sensor 15,
A rotational speed sensor that detects the rotational speed of the front propeller shaft 4 can be used. Furthermore, in order to obtain the rotational speed difference Δ7, a rotational speed sensor that detects the rotational speed of the rear propeller shaft 6 is connected to the control unit 14, and the calculation is performed by the control unit, without using the speed difference sensor. It's okay.

The control unit 14 inputs the three signals SV%Sα and SΔ, and outputs pre-stored first and second control maps M, as shown in FIGS. 6 and 7.
, M, and supplies the control current i to the hydraulic control valve 13 according to the control map M, , M2. These first and second control maps M1 and M2 are determined based on the characteristic diagrams shown in FIGS. 1 and 2, with the vertical axis representing the control current 1 and the horizontal axis representing the rotation speed. A difference Δ7 is shown. The first control map M1 is for straight-ahead driving, and has a plurality of control lines βI, 12, j! that move toward the side where the rotational speed difference is larger as the vehicle speed increases. It has 3. On the other hand, the second control map M2 is for steering, and includes a plurality of control lines 14, R3, and R16 that move toward the larger rotational speed difference side as the steering angle increases.

Next, the operation of the transmission torque control device will be explained.

The control unit 14 receives a vehicle speed signal SV% steering angle signal Sα and a rotational speed difference signal SΔ7 from each sensor 15, 16, 17.
is input, and it is determined from the steering angle signal Sα whether the vehicle is in a straight-ahead state or a steered state, and when the vehicle is in a straight-ahead state, the first control map M1 is read out, and when the vehicle is in a steered state, the second control map M2 is read out. First, to explain the control when the vehicle is traveling straight, appropriate control lines β1, !, are selected from the first control map M1 according to the vehicle speed signal Sv. 2 or l, and determine the control current 1 by comparing the rotational speed difference signal SΔゎ with this control line. This control current i is supplied to the hydraulic control valve 13,
The hydraulic control valve 13 supplies hydraulic oil at a pressure P proportional to the current l to the clutch 5 in accordance with the control current i. The clutch 5 is engaged at a pressure corresponding to the pressure P of the hydraulic oil, and transmits a torque T proportional to the engagement pressure to the rear propeller shaft 6.

On the other hand, in the steering state, an appropriate control line 1. is selected from the second control map according to the steering angle signal Sα. ．． 1° or 16 is selected and the control current i is determined by comparing the rotational speed difference signal SΔ with this control line, and the same control as above is performed thereafter.

As a result of the above, the rotational speed difference Δ. Knowing this, the torque distribution ratio U of the rear wheels can be maintained at a value determined according to the vehicle speed. In addition, although the above control has been explained in the form of determining the control current i using a control map, the form of determining the control current i by calculation is
Formula % Next, in the present invention, the slip state of the front and rear wheels is detected, and the torque distribution ratio is controlled so that the torque distribution becomes larger toward the side with a smaller slip ratio.

To explain based on FIG. 4, a slip detection sensor 25 is provided to detect the slip state of the front and rear wheels, and the control unit 14 distributes torque to the side with a smaller slip ratio in accordance with a signal from the slip detection sensor 25. The torque distribution ratio is controlled as follows. This increases the slip limit, which will be explained in detail below.

In FIG. 5, the vehicle 26 has the same configuration as in FIG. A front propeller shaft 4 and a rear propeller shaft 6 from a power unit 27 are connected to a front wheel 8 and a rear wheel 10, respectively. The signals of the front wheel rotation speed Np of the front wheels 8 and the rear wheel rotation speed NII of the rear wheels 10 are supplied to the control unit 14, and the signals of the reference rotation speed N0 of the fifth wheel 28 are supplied to the control unit 14. is supplied to the control unit 14.

The control unit 14 then controls the front wheel rotation speed Np and the reference rotation speed N. , the front wheel slip state and the rear wheel slip state are determined based on the rear wheel rotation speed N1 and the reference rotation speed N0, respectively, and the power unit 27 is controlled according to both slip conditions to select the one with the smaller slip ratio. The torque distribution ratio is controlled so that the torque distribution becomes large.

The operation of the control unit 14 described above will be explained based on the flowchart of FIG. 10.
In step 102, the front wheel rotation speed N and the reference rotation speed N0 are determined.
In step 104, the rear wheel slip state ΔS1 is determined based on the rear wheel rotational speed Nm and the reference rotational speed N0, and the process proceeds to step 106. In step 106, if ΔS, -ΔSp>0: (the front wheel slip condition is small), step 1°8'' front wheel'17)) increases 711aa by 1.'''
)'1110, and in step 106,
If 1ΔS, -ΔSp ≦0 (the rear wheel slip state □ is small), the torque distribution to the rear wheels is increased in step 112, and the process proceeds to end 110.

As described above, the torque distribution ratio is controlled so that the torque distribution is larger towards the side with a smaller slip ratio.
Increased slip limit.

Further, in the above embodiment, the front propeller shaft 4 is always connected to the output shaft 2 of the power plant 1,
A clutch 5 is installed between the rear propeller shaft 6 and the output shaft 2.
Although the explanation has been given on a case in which a second clutch 20 and a gear train 21 are provided between the output shaft 2 and the front propeller shaft 4, this may be reversed. It may also be possible to select the propeller shaft to be directly connected. Note that in this case, it is necessary to provide the second hydraulic control valve 22.

As shown in FIG. 8, two clutches 5.
20, the front and rear clutches 5.
The fastening force of 20 can be adjusted to increase the slip limit. In other words, by controlling the torque distribution ratio so that the torque distribution is larger towards the side with a smaller slip ratio,
achieved. In addition, the 11th rI! For J, the discriminant ΔS=
ToS.

The relationship between (rear wheel slip state) - ΔSp (front wheel slip state) and the torque distribution rate to the rear wheels is shown. In Fig. 11, when △S becomes large (when the front wheel slip condition is small), the torque distribution to the rear wheels is reduced to zero.
(at this time, the torque distribution to the front wheels increases),
Furthermore, it can be seen that when ΔS becomes smaller (when the rear wheel slip state is small), the torque distribution to the rear wheels increases and approaches 1 (at this time, the torque distribution to the front wheels decreases).

Note that the present invention is not only applicable to a power transmission means that detects vehicle speed, steering angle, and front and rear wheel rotation difference to control the power transmission means, but also to control the power transmission means using other methods. It can also be applied to things.

[Brief explanation of drawings]

Figure 1 is a graph showing the characteristics of the transmitted torque T and -rotational speed difference Δn when the torque distribution rate is constant and the steering angle is constant. Figure 2 is the graph showing the transmitted torque Tr when the torque distribution rate is constant and the vehicle speed is constant. Graph showing one rotational speed difference Δn characteristic; FIG. 3 is a schematic diagram showing a drive system of a four-wheel drive vehicle; FIG. 4 is a schematic diagram of a transmission torque control device according to an embodiment of the present invention; FIG. 6 and 7 are graphs showing the first and second control maps used for transmission torque control in the transmission torque control device, respectively, and FIG. 8 is a diagram showing the detection of a slip state, and FIG. A schematic diagram of a transmission torque control device according to another embodiment; FIG. 9 is a characteristic diagram showing the slip characteristics specific to tires; FIG. 10 is a flowchart showing the flow of controlling the torque distribution ratio according to the slip state of the front and rear wheels. Flowchart Figure 11 is a graph showing the relationship between the slip state and the torque distribution ratio to the rear wheels in the apparatus of Figure 8. 1... Power plant 2... Output shaft 4... Front propeller shaft 5...
...Clutch 6...Rear propeller shaft 13...
・Hydraulic control valve 14...Control unit 15・
... Vehicle speed sensor 16 ... Rudder angle sensor 17 ... Speed difference sensor 25 ... Slip detection sensor. Figure 5 Figure 6 U B Turnover Δ1 Figure 7 Figure 8 Figure 9 Discriminant formula S = ΔSRzF Procedural amendment 1 60.10.15 Showa year month day 1 Showa 60 Patent Application No. 198869
No. 2, Title of the invention Transmission torque control device for four-wheel drive vehicles 3, Person making the amendment Relationship to the case Applicant name (313) Mazda Motor Corporation 4, Agent 5, Date of amendment order Proprietor, Specification No. “Perobera” on page 7, lines 8 and 10
is corrected to "propeller". :, the formula % formula % on page 11 of the same book is revised as follows. "2°, Tr= ...... (18) j 3. The entire page 11 of the same book is revised as follows. 4. The first line of page 14 of the same book

Claims (1)

[Scope of Claims] At least one of the torque transmission paths that respectively transmits torque from the power plant to the front and rear wheels is provided with power transmission means that can vary the amount of torque transmission, and this power transmission means is variably controlled to transmit the torque to the front and rear wheels. A transmission torque control device for a four-wheel drive vehicle that controls torque distribution of a four-wheel drive vehicle, comprising: a control means that changes the torque transmission amount of the power transmission means to control a torque distribution ratio between the front and rear wheels; and a slip controller that detects a slip state of the front and rear wheels. detection means, and the control means includes means for controlling the torque distribution ratio so that the torque distribution becomes larger toward the side with a smaller slip ratio in response to a signal from the slip detection means. Transmission torque control device for 4-wheel drive vehicles.