Clutch control system

A clutch control unit which includes a clutch (6); a first detector (9) for detecting a first rate of rotation of an input of the clutch; a second detector (5a) for detecting a second rate of rotation of an output of the clutch; a clutch learning unit (4b) for determining a clutch position at which both of the first and second rates of rotation meet predetermined conditions when said clutch is moved toward engagement from a preset learning starting point and storing a clutch characteristic; a signal generator (4c) for generating a learning underway signal indicating that the clutch learning unit is learning the clutch characteristic; and warning unit (16a) responsive to the learning underway signal to provide a warning display or sound.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to clutch control units for 
vehicles and, more particularly, to a clutch control unit for 
automatically engaging and disengaging the clutch by learning. 
2. Description of the Prior Art 
FIG. 3 shows an automatic transmission using a conventional clutch control 
unit of this type. A well-known parallel axis gear type transmission 1 is 
controlled by a transmission actuator 2 which consists of a select 
actuator 2a and a shift actuator 2b. Each of these actuators 2a and 2b is 
controlled under a hydraulic pressure of a hydraulic drive unit 3 which 
consists of a tank 3a, a pump 3b, an accumulator 3c, and a hydraulic 
pressure switching electromagnetic valve (not shown) to shift a driving 
gear of the transmission 1 via a piston rod 2c or 2d. This control is made 
by the central processing unit (CPU) of a transmission drive unit 2e, 
which in turn is controlled by a main control unit 4 which consists of a 
CPU, a random access memory (RAM) and a read only memory (ROM) through 
serial communications. 
A pair of potentiometers 2f and 2g are provided to detect the positions of 
the piston rods 2c and 2d, respectively, for controlling the gear 
position. More specifically, the actual position signals from the 
respective potentiometers 2f and 2g are fed back to the drive unit 2e so 
that they match the target position signals from the main control unit 4. 
An input shaft sensor 5a detects the rate of rotation v of an input shaft 
1a of the transmission 1, and a vehicle speed sensor 5b detects the 
vehicle speed or rate of rotation V' of an output shaft of the 
transmission 1. The output of each of these sensors 5a and 5b is inputted 
to the main control unit 4. 
A clutch 6 is linked to the piston rod 7a of a clutch actuator 7 for making 
connection or disconnection. The clutch actuator 7 is supplied with a 
hydraulic pressure from the hydraulic drive system 3 and subjected to a 
feedback control by the CPU of a clutch drive unit 7b so that the position 
signal of the piston rod 7a detected by the potentiometer 7c matches the 
target position signal from the main control unit 4. The clutch drive unit 
7b is also controlled by the main control unit 4 through serial 
communications. An engine 8 has a control unit 8a controlled by the main 
control unit 4. An engine speed sensor 9 detects the rate of rotation V of 
an output shaft 8b of the engine 8. The rotation of the engine 8 is 
transmitted to an axle 10 via the clutch 6 and the transmission 1. 
The output of the engine speed sensor 9 is inputted to the main control 
unit 4, to which more signals are inputted from an accelerator pedal 
sensor 11, a brake pedal sensor 12, a key switch 13, an exhaust brake 
switch 14, and a selector 15 to control the drive unit 2e, the clutch 
drive unit 7b, the engine control 8a, a display panel 16, and a control 
unit 17a which controls a gear position display panel 17. Thus, the main 
control unit 4 controls the clutch 6 and the transmission 1 according to 
the amount of pressdown of the accelerator pedal, the vehicle speed, and 
the shift position of the selector 15. The gear position is controlled by 
the select actuator 2a and the shift actuator 2b in response to the 
operation of the selector 15. If the set position is "1", "2", "3", or 
"R", it is controlled into the first, second, third, or reverse gear. If 
the set position is an automatic gear shift "4" or "5" , it is controlled 
based on the gear shift map according to the amount of pressdown of the 
accelerator pedal and the vehicle speed. The automatic gear shifts "4" and 
"5" provide gear shifts between the first and the fourth gear and the 
second and the fifth gear, respectively. 
The clutch 6 is disengaged and engaged by the main control unit 4 via the 
clutch drive unit 7b and the clutch actuator 7 before and after the gear 
shift operation. This control is made according to the clutch 
characteristic which is obtained by a learning activity under 
predetermined conditions. This learning activity will be described with 
reference to FIG. 4. A learning starting point S has been stored in the 
memory of the main control unit 4. When predetermined conditions, such as 
the gear is set in the neutral, are met, the activity starts from the 
learning starting point S toward engagement of the clutch 6 to determined 
a half clutch point F based on the rates of rotation V and v detected by 
the engine speed sensor 9 and the input shaft sensor 5a. Then, the clutch 
starting point Q and the clutch completion point P are determined by 
taking predetermined offset lengths (operational distances) 1.sub.1 and 
1.sub.2 toward the disengagement and engagement condition, respectively, 
from the half clutch point F. From the half clutch point F, the clutch 
starting point Q, and the clutch completion point P, a clutch 
characteristic M is constructed and stored in the memory. In the next 
learning cycle, the previous clutch starting point Q is taken as a new 
learning starting point S to perform a learning activity. The engagement 
and disengagement of the clutch 6 are controlled according to the clutch 
characteristic M to reduce the operational stroke of the clutch 6, thereby 
not only speeding up the gear shift but also providing the optimal clutch 
control taking the wear of the clutch 6 into consideration. 
In the above conventional clutch control unit, only a single half clutch 
point is determined by learning, but the Japanese Patent Application Kokai 
No. 60-34525 has proposed that two points--a clutch completion point and a 
engagement starting point--are determined by learning. 
As has been described above, in a vehicle equipped with the automatic 
transmission unit using a dry type clutch, a learning activity at the 
clutch meet point is necessary. However, it takes a few seconds for the 
whole learning activity including the determination of only a half clutch 
point so that if the driver moves the selector before the learning 
activity is completed, the learning activity is interrupted and failed. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a clutch 
control unit which is able to warns the driver to permit the learning 
activity to complete. 
According to the invention there is provided a clutch control unit which 
includes a clutch; a first detector for detecting a first rate of rotation 
of an input of the clutch; a second detector for detecting a second rate 
of rotation of an output of the clutch; a clutch learning unit for 
determining a clutch position at which both of the first and second rates 
of rotation meet predetermined conditions when said clutch is moved toward 
engagement from a preset learning starting point and storing a clutch 
characteristic; a signal generator for generating a learning underway 
signal indicating that the clutch learning means is learning the clutch 
characteristic; and a warning unit responsive to the learning underway 
signal to provide a warning display or sound. 
The clutch learning unit according to the invention generates a signal 
indicating that the clutch learning unit is under a learning activity or 
completes the learning activity so that the driver is able to learn that 
the clutch learning activity is under way or completed, thereby refraining 
himself from moving the selector or other operations which interrupt the 
learning activity until the learning activity is completed. 
The above and other objects, features, and advantages of the invention will 
become more apparent from the following description when taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, like reference characters denote like or corresponding parts or 
components of FIG. 3. A cylinder control unit 4a controls the hydraulic 
drive system via the drive unit 7b for controlling the cylinder within the 
clutch actuator 7. The cylinder control unit 4a, the drive unit 7b, and 
the clutch actuator 7 constitute a clutch control unit 20. A clutch 
learning unit 4b starts a learning activity when predetermined conditions 
are met and controls the cylinder control unit 4a according to the clutch 
characteristic which is obtained by learning in disengaging and engaging 
the clutch 6. This clutch learning unit 4b has a generator circuit 4c for 
generating a warning signal for informing that the learning activity is 
under way or completed. With this warning signal, the clutch learning 
light 16a of a display panel 16 is turned on and off. The clutch 
characteristic is stored in the memory 4d. The cylinder control unit 4a, 
the clutch learning unit 4b, and the memory 4d are implemented by the CPU, 
ROM, and RAM of the control unit 4. The engine speed sensor 9, the input 
shaft sensor 5a, the generator circuit 4c, and the clutch learning light 
16a correspond to the first detector, the second detector, the generator 
means, and the warning means, respectively, in the appended claims. 
The operation of the clutch control unit will be described with reference 
to FIG. 2. When the driver inserts the ignition key, the learning activity 
does not start so that the generator circuit 4c does not generate any 
warning signal, keeping the clutch learning light 16a off. This off 
condition warns the driver to start a clutch learning activity. Seeing 
that the light 16a is off, the driver learns that the learning activity is 
not completed and disengages the clutch to set the gear in the neutral. 
When the engine is run, with the gear in the neutral, the clutch learning 
unit 4b starts a learning activity. When the learning activity starts, the 
control moves from Step S1 to Step S4 in which the generator circuit 4c 
generates a warning signal for turning on and off the clutch learning 
light 16a. This flashing light 16a warns the driver that the clutch 
learning activity is under way and the driver waits for the completion of 
the learning activity while refraining himself from making a gear shift 
which interrupts the learning activity. When the learning activity for 
disengaging and engaging the clutch is completed a few seconds after the 
learning starting point, the control advances from Step S2 to Step S5 in 
which the generator circuit 4c generates a learning completion signal for 
turning on the clutch learning light 16a. Since the light 16a changes from 
the flashing to on condition, the driver learns that the learning activity 
is completed and advances to the next operation such as a gear shift 
operation. 
The clutch characteristic obtained from the above learning activity is 
stored in the memory 4d and used as data for automatic control of the 
clutch 6 by the cylinder control unit 4a or the next learning activity. 
Thereafter, whenever the learning conditions are met, the control advances 
from Step S1 to Step S4 in which the clutch learning light 16a flashes. 
When the learning activity is completed, the control advances from Step S1 
to Step S2 and S5 in which the light 16a is kept on. This is repeated 
until the ignition key is turned off. If the learning activity is 
interrupted by making a gear shift, for instance, while the learning light 
16a flashes in the period between turning on of the ignition key and 
completion of the first learning activity, the control advances from Step 
S1 to S2 and S3 in which the light 16a is turned off, which warns the 
driver to complete the learning activity. 
In the above embodiment, only a single half clutch point is determined by 
learning, but two points--a clutch complete point and a engagement 
starting point--may be determined as Japanese Patent Application Kokai No. 
60-34525 has taught. The flashing and on light indicate that the learning 
activity is under way and completed, respectively, but the use of only one 
of them may be sufficient. The display pattern consisting of "off", 
"flash," and "on" may be changed. For example, letters as such "START 
CLUTCH LEARNING", "CLUTCH LEARNING UNDER WAY", and "CLUTCH LEARNING 
COMPLETED" may be displayed or announced. In essence, it is only necessary 
to inform the driver that the learning activity is completed. The warning 
unit such as a light may be used for only warning or other purposes as 
well. 
As has been described above, with the clutch control unit according to the 
invention, the driver is able to learn whether the learning activity is 
under way or completed so that he is encouraged to complete the learning 
activity.