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Title:
APPARATUS AND METHOD FOR CONTROLLING CONTINUOUSLY VARIABLE TRANSMISSION AND PROGRAM FOR PERFORMING THE CONTROL METHOD
Document Type and Number:
WIPO Patent Application WO/2008/044143
Kind Code:
A2
Abstract:
The present invention relates an apparatus and method for controlling a CVT (500) (continuously variable transmission), and a program for executing the control method that reduces a transmission shock during a braking operation. When a foot brake switch (916) is turned on and a vehicle speed is less than or equal to a threshold speed V(O), the ECU (900) increases a clamping pressure applied to a transmission belt (510) to a pressure level P(ON) higher than a normal pressure P(OFF). When the vehicle speed falls to or below the threshold speed V(O) when the foot brake switch (916) is turned on, the ECU (900) prohibits an increase in the clamping pressure applied to the transmission belt (510).

Inventors:
INOUE DAISUKE (JP)
Application Number:
PCT/IB2007/003502
Publication Date:
April 17, 2008
Filing Date:
October 12, 2007
Export Citation:
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Assignee:
TOYOTA MOTOR CO LTD (JP)
INOUE DAISUKE (JP)
International Classes:
F16H61/662; F16H9/00; F16H61/02; F16H61/66; F16H59/44; F16H59/48; F16H59/54
Foreign References:
JPS6152457A1986-03-15
JPH02102960A1990-04-16
JP2002310276A2002-10-23
JPH08210453A1996-08-20
JPH08210450A1996-08-20
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Claims:

CLAMS:

1. A control apparatus for a belt-type continuously variable transmission comprising:

a brake operation determining unit that determines whether a brake of a vehicle is being

operated;

a vehicle speed determining unit that determines whether a speed of the vehicle is less than

or equal to a predetermined reference speed;

a clamping pressure control unit that controls a clamping pressure applied to the transmission

belt, wherein the clamping pressure control unit increases the clamping pressure if the brake

operation determining unit determines that the brakes are being operated and the vehicle speed is

less than or equal to the predetermined reference speed; and

a clamping-pressure increase prohibition unit that prohibits increasing the clamping pressure

applied to the transmission belt if a condition that the vehicle speed falls to or below the

predetermined reference speed when the brake operation determining unit determines that the

brake is being operated is met.

2. The control apparatus for the belt-type continuously variable transmission as set forth in

claim I 5 further comprising:

a vehicle deceleration determining unit that determines whether a deceleration of the vehicle

is less than or equal to a predetermined reference deceleration, wherein an additional condition for

prohibiting increase in the clamping pressure applied to the transmission belt is that the vehicle

deceleration determining unit determines that deceleration of the vehicle is less than or equal to

the predetermined reference deceleration.

3. The control apparatus for the belt-type continuously variable transmission as set forth in

claim 1 or 2, further comprising:

an elapsed time determining unit that determines whether time elapsed since the operation of

the brake began is greater than or equal to a predetermined reference time, wherein an additional

condition for prohibiting increase in the clamping pressure applied to the transmission belt is that

the elapsed time determining unit determines that the elapsed time since the operation of the brake

began is greater than or equal to the predetermined reference time.

4. A control apparatus.for a belt-type continuously variable transmission, comprising:

a brake operation determining unit that determines whether a brake of a vehicle is being

operated;

a vehicle speed determining unit that determines whether the vehicle speed is less than or

equal to a predetermined reference speed;

a clamping pressure control unit that controls the clamping pressure applied to the

transmission belt, wherein the clamping pressure control unit increases the clamping pressure if

the brake operation determining unit determines that the brake is being operated and the vehicle

speed is less than or equal to the predetermined reference speed; and

a clamping-pressure increase-rate reducing unit that reduces a rate of increase in the

clamping pressure applied to the transmission belt if the vehicle speed falls to or below the

predetermined reference speed when the brake operation determining unit determines that the

brake is being operated, wherein me clamping-pressure increase-rate is reduced to a lower

increase-rate than when the speed of the vehicle does not fall to or below the predetermined

reference speed.

5. A control apparatus for a belt-type continuously variable transmission, comprising:

a brake operation determining unit that determines whether a brake of a vehicle is being

operated;

a vehicle speed determining unit that determines whether a speed of a vehicle is less than or

equal to a predetermined reference speed;

a clamping pressure control unit that controls the clamping pressure applied to the

transmission belt, wherein the clamping pressure control unit increases the clamping pressure if

the brake is being operated and the vehicle speed is less than or equal to the predetermined

reference speed; and

a clamping-pressure increase-amount setting unit that sets an amount of increase in the

clamping pressure of the transmission belt to zero if the vehicle speed is higher than the

predetermined reference speed, and sets the amount of increase in the clamping pressure to a

higher value as the vehicle speed decreases when the speed of the vehicle is less than or equal to

the predetermined reference speed.

6. The control apparatus for the belt-type continuously variable transmission as set forth in any

one of claims 1 to 5, wherein the clamping pressure control unit increases the clamping pressure

to a clamping pressure greater than the clamping pressure set when the brake are not being

operated.

7. A control method for a belt-type continuously variable transmission, comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

prohibiting an increase in the clamping pressure of the transmission belt, if a condition that

the speed of the vehicle falls to or below the predetermined reference speed when it is determined

that the brake is being operated.

8. The control method for the belt-type continuously variable transmission as set forth in claim

7, further comprising:

determining whether deceleration of the vehicle is less than or equal to a predetermined

reference deceleration, wherein an additional condition for prohibiting increase in the clamping

pressure applied to the transmission belt is that the vehicle deceleration determining unit

determines that deceleration of the vehicle is less than or equal to the predetermined reference

deceleration.

9. The control method for the belt-type continuously variable transmission as set forth in claim 7

or 8, further comprising:

determining whether time elapsed since operation of the brake is greater than or equal to a

predetermined reference time, wherein an additional condition for prohibiting increase in the

clamping pressure applied to the transmission belt is that the elapsed time determining unit

determines that the elapsed time since the operation of the .brake began is greater than or equal to

the predetermined reference time.

10. A control method for a belt-type continuously variable transmission, comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

reducing the clamping-pressure increase-rate of the transmission belt when the speed of the

vehicle falls to or below the predetermined reference speed when it is determined that the brake is

being operated, wherein the clamping-pressure increase-rate is reduced to a lower increase-rate

than when the speed of the vehicle does not falls to or below the predetermined reference speed.

11. A control method for a belt-type continuously variable transmission, comprising:

determining whether a brake of a vehicle are being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

setting a clamping pressure increase-amount of the transmission belt to zero when the

vehicle speed is higher than the predetermined reference speed, and setting the clamping pressure

increase-amount of the transmission belt to a higher value as the vehicle speed decreases when the

speed of the vehicle is less than or equal to the predetermined reference speed.

12. The control method for the belt-type continuously variable transmission as set forth in any

one of claims 7 and 11, wherein the clamping pressure control unit increases the clamping

pressure to a clamping pressure greater than the clamping pressure set when the brakes are not

being operated.

13. A program for performing a control method for use in a belt-type continuously variable

transmission, comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

prohibiting an increase in the clamping pressure of the transmission belt, when the speed of

the vehicle falls to or below the predetermined reference speed when it is determined that the

brake is being operated,

14. A program for performing a control method for use in a belt-type continuously variable

transmission, comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

reducing the clamping-pressure increase-rate of the transmission belt when the speed of the

vehicle falls to or below the predetermined reference speed when it is determined that the brake is

being operated, wherein the clamping-pressure increase-rate is reduced to a lower increase-rate

than when the speed of the vehicle does not falls to or below the predetermined reference speed.

15. A program for performing a control method for use in a belt-type continuously variable

transmission, comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less man or equal to the predetermined reference speed; and

setting a clamping pressure increase-amount of the transmission belt to zero when the

vehicle speed is higher than the predetermined reference speed, and setting the clamping pressure

increase-amount of the transmission belt to a higher value as the vehicle speed decreases when the

speed of the vehicle is less than or equal to the predetermined reference speed.

16. A recordable medium for storing a program for performing the control method for use in a

belt-type continuously variable transmission by a computer, the control method comprising:

deteπnining whether a brake of a vehicle are being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

prohibiting an increase in the clamping pressure applied to the transmission belt, when the

speed of the vehicle falls to or below the predetermined reference speed when it is determined that

the brake is being operated.

17. A recordable medium for storing a program for performing the control method for use in a

belt-type continuously variable transmission by a computer, the control method comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

reducing the clamping-pressure increase-rate of the transmission belt when the speed of the

vehicle falls to or below the predetermined reference speed when it is determined that the brake is

being operated, wherein the clamping-pressure increase-rate is reduced to a lower increase-rate

than when the speed of the vehicle does not falls to or below the predetermined reference speed.

18. A recordable medium for storing a program for performing the control method for use in a

belt-type continuously variable transmission by a computer, the control method comprising:

determining whether a brake of a vehicle is being operated;

determining whether a speed of the vehicle is less than or equal to a predetermined reference

speed;

controlling clamping pressure applied to the transmission belt, wherein the clamping

pressure is increased when it is determined that the brake is being operated and the speed of the

vehicle is less than or equal to the predetermined reference speed; and

setting an amount of increase in the clamping pressure applied to the transmission belt to

zero when the vehicle speed is higher than the predetermined reference speed, and setting the

amount of increase in the clamping pressure to a higher value as the vehicle speed decreases when

the speed of the vehicle is less than or equal to the predetermined reference speed.

Description:

APPARATUS AND METHOD FOR CONTROLLING CONTINUOUSLY VARIABLE

TRANSMISSION AND PROGRAM FOR PERFORMING THE CONTROL METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates, in general, to an apparatus and method for

controlling a continuously variable transmission (CVT) and a program for performing the control

method. In particular, the invention relates to a technology for controlling the clamping pressure

of the transmission belt of the CVT.

2. Description of the Related Art

[0002] In the related art, a continuously variable transmission (CVT), in which a

transmission belt clamps a pair of pulleys having a variable groove width, is known. In the CVT,

clamping pressure of the transmission belt prevents slippage of the transmission belt on the

pulleys . However, during a quick braking operation of a vehicle, the output speed of the CVT is

quickly reduced, so that torque applied to the transmission belt is excessively increased, In the

above state, the transmission belt may slip on the pulleys due to the excessively increased torque.

To prevent the slippage of the transmission belt on the pulleys in the CVT during a quick braking

operation, a technique of increasing the clamping pressure of the transmission belt during the

quick braking operation has been proposed.

[0003] Japanese Patent Laid-Open Publication No. H8-210450 describes a line pressure

control apparatus for appropriately controlling the line pressure in a V-belt type CVT such that the

line pressure does not become higher or lower than reference levels during a braking operation of

a vehicle. In the V-belt type CVT using the line pressure control apparatus disclosed in Japanese

Patent Laid-Open Publication No. H8-210450, line pressure is applied to a movable flange of the

first pulley of a pair of pulleys clamped by a V-belt, while transmission control pressure, which is

obtained by reducing the line pressure using a transmission control valve, is applied to a movable

flange of the second pulley. Thus, the V-belt type CVT continuously controls the transmission

ratio using the difference between the transmission control pressure and the line pressure. The

line pressure control apparatus described in Japanese Patent Laid-Open Publication No.

H8-210450 comprises a braking operation detecting unit for detecting a braking operation of a

vehicle equipped with the V-belt type CVT, a transmission ratio calculating unit for calculating an

actual transmission ratio of the V-belt type CVT, and a line pressure increase unit for increasing

the line pressure to a level determined according to the actual transmission ratio during the

braking operation of the vehicle.

[0004] According to the line pressure control apparatus described in Japanese Patent

Laid-Open Publication No. H8-210450, the line pressure during a braking operation is increased

to the level determined according to the actual transmission ratio of the V-belt type CVT. Thus,

although the wheels of the vehicle during the braking operation are quickly braked and the speed

of the vehicle is quickly reduced by the braking operation, the line pressure in the V-belt type

CVT can be appropriately controlled such that the V-belt can be prevented from slippage on the

pulleys. Therefore, the line pressure control apparatus improves the durability of the V-belt. '

[0005] However, in the line pressure control apparatus described in Japanese Patent

Laid-Open Publication No. H8-210450, the line pressure during a braking operation of a vehicle

is increased. Thus, when a braking operation is executed while the vehicle is driven at a high

speed, the clamping pressure of the V-belt is increased. Meanwhile, when the speed of the

vehicle is high, excessive torque is not applied to the transmission belt. Thus, it is considered to

increase the clamping pressure of the transmission belt when the braking operation performs

while the vehicle is driven at a low speed. However, when the braking operation is started while

the vehicle is driven at a high speed, the clamping pressure of the transmission belt is increased

stepwisely at the time that the speed of the vehicle has been reduced to a predetermined low speed,

so that the clamping pressure of the transmission belt may deviate from the brake operation timing,

and may cause a transmission shock.

SUMMARY OF THE INVENTION

[0006] The present invention provides an apparatus and method for controlling a CVT

(continuously variable transmission) such that a transmission shock is reduced and a program for

performing (he control method.

[0007] In a first aspect, the present invention provides a control apparatus for a belt-type

CVT. The control apparatus includes: a brake operation determining unit that determines

whether a brake of a vehicle is being operated; a vehicle speed determining unit that determines

whether the vehicle speed is less than or equal to a predetermined reference speed; a clamping

pressure control unit that controls the clamping pressure applied to the transmission belt, wherein

the clamping pressure control unit increases the clamping pressure when the brake operation

determining unit determines that the brake is operated and the vehicle speed is less than or equal

to the predetermined reference speed; and a clamping-pressure increase prohibition unit that

prohibits increasing the clamping pressure applied to the transmission belt when the vehicle speed

falls to or below the predetermined reference speed when the brake operation determining unit

determines that the brake is being operated. A control method for a CVT in accordance with the

present invention includes the same conditions as the control apparatus for a CVT in accordance

with the second aspect of the present invention.

[0008] According to the first aspect, it is determined whether the brake of the vehicle is

being operated .and whether the speed of the vehicle is less than or equal to the predetermined

reference speed. When it is determined that the brake is being operated and the vehicle speed is

less than or equal to the predetermined reference speed, the clamping pressure applied to the

transmission belt is increased. Further, when the vehicle speed falls to or below the

predetermined reference speed when it is determined that the brake is being operated, an increase

in the clamping pressure applied to the transmission belt is prohibited. Also, the clamping

pressure control unit increases the clamping pressure above a normal clamping pressure, which is

set as the clamping pressure when the brake is not operated. Thus, when the vehicle speed falls

to or below the predetermined reference speed, the stepwise increase in the clamping pressure of

the transmission belt is prohibited. Thus, an apparatus and a method for controlling a CVT to

reduce a transmission shock are provided.

( [0009] A control apparatus of a CVT in accordance with a second aspect of the present

invention may further include a vehicle deceleration determining unit that determines whether

deceleration of the vehicle is less than or equal to a predetermined reference deceleration. The.

clamping pressure increase prohibition unit prohibits increases in the clamping pressure when the

deceleration of the vehicle is less than or equal to the predetermined reference deceleration if the

vehicle speed falls to or below the predetermined reference speed when the brake is being

operated. A control method for a CVT in accordance with the present invention includes the

same conditions as the control apparatus for a CVT in accordance with the second aspect of the '

present invention.

[0010] According to the second aspect, it is determined whether the deceleration of the

vehicle is less than or equal to a predetermined reference deceleration. When the deceleration of

the vehicle is less than or equal to the predetermined reference deceleration, the increase in the

clamping pressure applied to the transmission belt is prohibited. Thus, during a quick braking

operation, in which the deceleration of the vehicle is higher than the predetermined reference

deceleration, the clamping pressure applied to the transmission belt may be increased. However,

during a smooth and gradual braking operation, in which the deceleration of the vehicle is less

than or equal to the predetermined reference deceleration, increases in the clamping pressure

applied to the transmission belt are prohibited, Thus, when excessive torque is applied to the

transmission belt, the slippage of the transmission belt on the pulleys may be reduced by

increasing the clamping pressure applied to the transmission belt, However, when excessive

torque is not applied to the transmission belt, an increase in the clamping pressure applied to the

belt is avoided and a shock is reduced.

[0011] A control apparatus of a CVT in accordance with a third aspect of the present

invention may further includes an elapsed time determining unit that determines whether time

elapsed since operation of the brake is greater than or equal to a predetermined reference time.

The clamping pressure increase prohibition unit prohibits increases in the clamping pressure

applied to the transmission belt when the elapsed rime since operation of the brake is greater than

or equal to the predetermined reference time if the vehicle speed falls to or below the

predetermined reference speed when the brake is being operated. A control method for a CVT

in accordance with the present invention includes the same conditions as the control apparatus for

a CVT in accordance with the third aspect of the present invention.

[0012] According to the third aspect, it is determined whether the elapsed time since

operation of the brake is greater than or equal to the predetermined reference time. When it is

determined that the elapsed time since the operation of the brake is greater than or equal to the

predetermined reference time if the vehicle speed falls to or below the predetermined reference

speed when the brake is being operated, an increase in the clamping pressure of the transmission

belt is prohibited. Thus, when it is determined that the time elapsed since the operation of the

brake is less than the predetermined reference time and it is thus recognized that the vehicle is

undergoing a quick braking operation, the clamping pressure applied to the transmission belt may

be increased. Meanwhile, when it is determined that the time elapsed since the operation of the

brake is greater than or equal to the predetermined reference time and it is thus recognized mat the

vehicle is undergoing a smooth and gradual braking operation, an increase in the clamping

pressure applied to the transmission belt is prohibited. Thus, when excessive torque is applied to

the transmission belt, the slippage of the transmission belt on the pulleys can be reduced by

increasing the clamping pressure applied to the transmission belt. However, when excessive

torque is not applied to the transmission belt, an increase in the clamping pressure applied to the

transmission belt is avoided and a transmission shock is reduced.

[0013] In a forth aspect, the present invention provides a control apparatus for a belt-type

CVT. The control apparatus includes: a brake operation determining unit that determines

whether a brake of a vehicle is being operated; a vehicle speed determining unit that determines

whether the vehicle speed is less than or equal to a predetermined reference speed; a clamping

pressure control unit that controls the clamping pressure applied to the transmission belt, wherein

the clamping pressure control unit increases the clamping pressure if the brake operation

determining unit determines that the brake is being operated and the vehicle speed is less than or

equal to the predetermined reference speed; and a clamping-pressure increase-rate reducing unit

that reduces a rate of increase in the clamping pressure applied to the transmission belt if the

vehicle speed falls to or below the predetermined reference speed when the brake operation

determining unit determines that the brakes are being operated, wherein the clamping-pressure

increase-rate is reduced to a lower increase-rate than when the speed of the vehicle does not falls

to or below the predetermined reference speed. A control method for a CVT in accordance with

the present invention includes the same conditions as the control apparatus for a CVT in

accordance with the forth aspect of the present invention.

[0014] According to the fourth aspect, it is determined whether the brake of the vehicle is

being operated and whether the vehicle speed is less than or equal to the predetermined reference

speed. When it is determined that the brake is being operated and the vehicle speed is less than

or equal to the predetermined reference speed, the clamping pressure applied to the transmission

belt is increased. When the vehicle speed falls to or below the predetermined reference speed

when it is determined that the brake is being operated, the rate of increase in the clamping

pressure applied to the transmission belt is reduced to a lower increase-rate than when the speed

of the vehicle does not falls to or below. Thus, when the vehicle speed falls to or below the

predetermined reference value when the brake is being operated, the stepwise increase of the

clamping pressure of the transmission belt is prohibited. Thus, an apparatus or a method for

controlling a CVT such that a shock can be reduced is provided,

[0015] In a fifth aspect, the present invention provides a control apparatus for a belt-type

CVT. The control apparatus includes: a brake operation determining unit that determines

whether a brake of a vehicle is being operated; a vehicle speed determining unit that determines

whether the vehicle speed is less than or equal to a predetermined reference speed; a clamping

pressure control unit that controls the clamping pressure applied to the transmission belt, wherein

the clamping pressure control unit increases the clamping pressure if the brake is being operated

and the vehicle speed is less than or equal to the predetermined reference speed; and a

clamping-pressure increase-amount setting unit that sets an amount of increase in the clamping

pressure of the transmission belt to zero if the vehicle speed is higher than the predetermined

reference speed, and sets the amount of increase in the clamping pressure applied to the

transmission belt to a higher value as the vehicle speed decreases when the speed of the vehicle is

less than or equal to the predetermined reference speed. A control method for a CVT in

accordance with the present invention includes the same conditions as the control apparatus for a

CVT in accordance with the fifth aspect of the present invention.

[0016] According to the fifth aspect, it is determined whether the brake of the vehicle is

being operated and whether the vehicle speed is less than or equal to the predetermined reference

speed. When it is determined that the brake is being operated and the vehicle speed is less than

or equal to the predetermined reference speed, the clamping pressure applied to the transmission

belt is increased. When the vehicle speed is higher than the predetermined reference speed, the

amount of increase in the clamping pressure applied to the transmission belt is set to zero.

However, if the vehicle speed is less than or equal to the predetermined reference speed, the

amount of increase in the clamping pressure applied to the transmission belt is set to a higher

value as the vehicle speed decreases. Thus, when the clamping pressure of the belt is increased,

the amount of increase in the clamping pressure is reduced as the vehicle speed increases. Thus,

when the vehicle speed falls to or below the predetermined reference speed, the stepwise increase

of the clamping pressure applied to the transmission belt is prohibited. Thus, an apparatus or a

method for controlling a CVT such that a transmission shock can be reduced is provided.

[0017] The program according to a sixth aspect of the present invention is a program

executed on a computer to perform the control method for the CVT according to any one of the

above-mentioned aspects. The recording medium according to a seventh aspect of the present

invention is a computer-readable recording medium, which records therein the program that is

executed on a computer to perform the control method for the CVT according to any one of the

above-mentioned aspects.

[0018] According to the aspects, the control method for the CVT according to any one of

the above-mentioned aspects can be performed using a computer (general-purpose computer or

dedicated computer).

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other features and advantages of the present invention will become

apparent from the following description of example embodiments, given in conjunction with the

accompanying drawings, in which:

FIG. 1 is. a schematic diagram of a vehicle equipped with an ECU used as a control apparatus

according to a first embodiment of the present invention;

FIG. 2 is a block diagram illustrating the configuration of the ECU used as the control

apparatus according to the first embodiment of the present invention;

FIG. 3 is a circuit diagram illustrating a first example of a hydraulic pressure control circuit

according to the present invention (a first example);

FIG.4 is a circuit diagram illustrating a second example of the hydraulic pressure control

circuit according to the present invention (a second example);

FIG. 5 is a circuit diagram illustrating a third example of the hydraulic pressure control

circuit according to the present invention (a third example);

FIG. 6 is a view schematically illustrating a brake system according to the present invention;

HG.7 is a block diagram illustrating the function of the ECU used as the control apparatus

according to the first embodiment of the present invention;

FIG. 8 is a flowchart of a control structure of a program executed by the ECU used as the

control apparatus according to the first embodiment of the present invention;

FIG. 9 is a block diagram illustrating the function of an ECU used as a control apparatus

according to a second embodiment of the present invention;

FIG. 10 is a flowchart of a control structure of a program executed by the ECU used as the

control apparatus according to the second embodiment of the present invention;

FIG. 11 is a block diagram illustrating the function of an ECU used as a control apparatus

according to a third embodiment of the present invention; and

FIG. 12 is a flowchart of a control structure of a program executed by the ECU used as the

control apparatus according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Example embodiments of the present invention will now be described in detail

with reference to the accompanying drawings. In the following description, the same or like

elements throughout the various embodiments of the present invention carry the same or like

reference numerals. The same or like elements are given the same or like technical terms, and

they execute the same or like functions. Thus, detailed explanations of the same or like elements

are omitted for the sake of convenience.

[0021] A vehicle, equipped with a control apparatus according to the first embodiment of

the present invention, will be described below with reference to FIG. 1. The output power of an

engine 200, which is included in a drive unit 100 installed in the vehicle, is transmitted to a

belt-type CVT 500 both through a torque converter 300 and a forward/reverse drive switching

unit 400. The output power of the belt-type CVT 500 is transmitted both to a reduction gear 600

and to a differential gear unit 700, and is distributed to the left and right drive wheels 800. The

drive unit 100 is controlled by an Electronic Control Unit (ECU) 900, which will be described in

detail later herein, ϊn the embodiment, the control apparatus for the CVT is operated under the

control of the ECU 90O 5 which executes a program stored in a Read Only Memory (ROM) 930 of

the ECU 900.

[0022] The torque converter 300 comprises a pump blade 302, which is connected to the

crankshaft of the engine 200, and a turbine blade 306, which is connected to the forward/reverse

drive switching unit 400 through a turbine shaft 304. A lockup clutch 308 is provided between -

the pump blade 302 and the turbine blade 306. The lockup clutch 308 is engaged or disengaged

by changing the supply of hydraulic pressure to an engaging oil chamber or to a disengaging oil

chamber.

[0023] When the lockup clutch 308 is completely engaged, both the pump blade 302 and

the turbine blade 306 are rotated. The pump blade 302 is provided with a mechanical oil pump

310, which produces hydraulic pressure for controlling the transmission of the belt-type CVT 500,

generating the clamping pressure of the belt, and supplying lubricant to desired parts of the CVT.

[0024] The forward/backward drive switching unit 400 comprises a double pinion type

planetary gear mechanism. Ih the forward/backward drive switching unit 400, the turbine shaft

304 of the torque converter 300 is connected to a sun gear 402. The input shaft 502 of the

belt-type CVT 500 is connected to a gear carrier 404. The gear carrier 404 and the sun gear 402

are connected to each other through a forward clutch 406. The ring gear 408 is fixed to a

housing through a reverse brake 410. The forward clutch 406 and the reverse brake 410 are

fπctionally engaged with each other by the operation of a hydraulic cylinder. The input rpm of

the forward clutch 406 is equal to the rpm of the turbine shaft 304, which is called "the turbine

rpm NT".

[0025] When the forward clutch 406 is engaged and the reverse brake 410 is disengaged,

the forward/reverse drive switching unit 400 is brought into an engagement state for executing a

forward drive mode. In the above state, forward drive force is transmitted to the belt-type CVT

500. Meanwhile, when the reverse brake 410 is engaged and the forward clutch 406 is

disengaged, the forward/reverse drive switching unit 400 is brought into an engagement state for

executing a reverse drive mode. In the above state, the input shaft 502 is rotated in the opposite

direction relative to the turbine shaft 304. Thus, reverse drive force is transmitted to the

belt-type CVT 500. When both the forward clutch 406 and the reverse brake 410 are disengaged,

the forward/reverse drive switching unit 400 is brought into a neutral state, in which the CVT

does not transmit power.

[0026] The belt-type CVT 500 comprises a primary pulley 504 provided on the input

shaft 502, a secondary pulley 508 provided on the output shaft 506, and a transmission belt 510

clamping the primary and secondary pulleys 504 and 508. The belt-type CVT 500 can execute

power transmission due to ftictional contact between the transmission belt 510 and the two

pulleys 504 and 508.

[0027] The pulleys 504 and 508 comprise respective hydraulic cylinders for varying the

groove widths of the pulleys . The groove widths of the pulleys 504 and 508 can be changed by

controlling the hydraulic pressure applied to the hydraulic cylinder of the primary pulley 504.

Thus, the wrapping diameters of the transmission belt 510, which is wrapped around the primary

and secondary pulleys 504 and 508, change, so that the transmission ratio GR (= primary pulley

rpm Nm/secondary pulley rpm Nour) can be continuously changed.

[0028] As shown in HG. 2, the ECU 900 is connected to an engine speed sensor 902, a

turbine speed sensor 904, a vehicle speed sensor 906, a throttle opening degree sensor 908, a

coolant temperature sensor 910, an oil temperature sensor 912, an accelerator operation amount

sensor 914, a foot brake switch 916, a position sensor 918, a primary pulley speed sensor 922 and

a secondary pulley speed sensor 924.

[0029] The engine speed sensor 902 detects the rotational speed NE of the engine 200,

while the turbine speed sensor 904 detects the rotational speed NT of the turbine shaft 304. The

vehicle speed sensor 906 detects the speed V of the vehicle. The throttle opening degree sensor

908 detects the opening degree θ (TH) of an electronic throttle valve. The coolant temperature

sensor 910 detects the coolant temperature T(W) of the engine 200. The oil temperature sensor

912 detects the oil temperature T(C) of the belt-type CVT 500. The accelerator operation

amount sensor 914 detects the operation amount A(CC) of an accelerator pedal. The foot brake

switch 916 detects the operation of a foot brake. If the brake pedal is operated, the foot brake

switch 916 is turned on (ON). However, when the brake pedal is not operated, the foot brake

switch 916 is turned off (OFF).

[0030] The position sensor 918 determines whether a contact point, which is provided at a

location corresponding to a shifted position, is turned on or off, so that the position sensor 918

detects the position P (SH) of a shift lever 920. The primary pulley speed sensor 922 detects the

rotational speed N^ of the primary pulley 504. The secondary speed sensor 924 detects the

rotational speed NOUT of the secondary pulley 508. The signals indicating the detected results

are transmitted from the respective sensors to the ECU 900. In the above state, the turbine speed

NT is equal to the primary pulley speed NIN during the forward drive mode, wherein the forward

clutch 406 is engaged. Further, the vehicle speed V corresponds to the secondary speed N O UT-

Thus, when the vehicle is stopped and the forward clutch 406 is engaged, the turbine speed NT is

zero.

[0031] The ECU 900 comprises a CPU (Central Processing Unit), a memory and an

input/output interface. The CPU processes signals according to a program stored in the memory.

Thus, the CPU executes output power control for the engine 200, transmission control for the

belt-type CVT 500, clamping pressure control for the belt, engagement/disengagement control for

the forward clutch 406, and engagement/disengagement control for the reverse brake 410.

[0032] The output power control for the engine 200 is executed by an electronic throttle

valve 1000, a fuel injection unit 1100, and an ignition unit 1200. The transmission control for

the belt-type CVT 500, the clamping pressure control for the belt, the engagement/disengagement

control for the forward clutch 406 and the engagement/disengagement control for the reverse

brake 410 are executed by a hydraulic pressure control circuit 2000.

[0033] Below, part of the hydraulic pressure control circuit 2000 will be described with

reference to FIG. 3. The hydraulic pressure, which is generated by the oil pump 310, is applied

to a primary regulator -valve 2100, a first modulator valve 2310 and a third modulator valve 2330

through a line pressure hydraulic path 2002.

[0034] In the above state, control pressure is applied from one of an SLT linear solenoid

valve 2200 or an SLS linear solenoid valve 2210 to the primary regulator valve 2100. In the

embodiment, each of the SLT linear solenoid valve 2200 and SLS linear solenoid valve 2210 may

be selected from normal open type solenoid valves, which output the maximum hydraulic

pressure when no current is applied to the solenoid valves. Alternatively, each of the SLT linear

solenoid valve 2200 and the SLS linear solenoid valve 2210 may be selected from normal closed

type solenoid valves, which output the minimum hydraulic pressure (zero value) when no current

is applied to the solenoid valves.

[0035] The spool of the primary regulator valve 2100 slides upwards and downwards due

to the control pressure applied thereto. Thus, the hydraulic pressure generated by the oil pump

310 is regulated by the primary regulator valve 2100. The hydraulic pressure, regulated by the

primary regulator valve 2100, may be used as the line pressure PL. In the embodiment, (he line

pressure PL is increased as the control pressure applied to the primary regulator valve 2100

increases. However, it should be understood that the control apparatus may be configured such

that the line pressure PL is reduced as the control pressure applied to the primary regulator valve

2100 increases.

[0036] Hydraulic pressure, which is regulated from the line pressure PL as the source

pressure by the third modulator valve 2330, is applied both to the SLT linear solenoid valve 2200

and to the SLS linear solenoid valve 2210.

[0037] Both the SLT linear solenoid valve 2200 and the SLS linear solenoid valve 2210

generate control pressure according to an electric current value, which is determined by a duty

signal output from the ECU 900.

[0038] The control pressure to be applied to the primary regulator valve 2100 is selected

by a control valve 2400 from the control pressure (output hydraulic pressure) of the SLT linear

solenoid valve 2200 and fhe control pressure (output hydraulic pressure) of the SLS linear

solenoid valve 2210.

[0039] When the spool of the control valve 2400 is in the 'A' state in FIG, 3, control

pressure is applied from the SLT linear solenoid valve 2200 to the primary regulator valve 2100.

The line pressure PL is controlled by the control pressure of the SLT linear solenoid valve 2200.

[0040] However, when the spool of the control valve 2400 is in the 'B' state in FIG. 3, the

control pressure is applied from the SLS linear solenoid valve 2210 to the primary regulator valve

2100. In other words, the line pressure PL is controlled by the control pressure of the SLS linear

solenoid valve 2210.

[0041] Further, when the spool of the control valve 2400 is in the 'B' state in FIG. 3, the

control pressure of the SLT linear solenoid valve 2200 is applied to a manual valve 2600, which

will be described later herein.

[0042] The spool of the control valve 2400 is biased in one direction by a spring.

Hydraulic pressure is applied from both a first transmission control duty solenoid 2510 and a

second transmission control duty solenoid 2520 to the control valve 2400 in the direction opposite

the biasing direction of the spring.

[0043] When the hydraulic pressure is applied to the control valve 2400 from both the

first transmission control duty solenoid 2510 and the second transmission control duty solenoid

2520, the spool of the control valve 2400 enters the 1 B' state in FIG. 3.

[0044] If no hydraulic pressure is applied to the control valve 2400 from at least one of the

first transmission control duty solenoid 2510 or the second transmission control duty solenoid

2520, the spool of the control valve 2400 enters the 'A' state in FIG. 3 due to the biasing force of

the spring.

[0045] Hydraulic pressure, regulated by a fourth modulator valve 2340, is applied both to

the first transmission control duty solenoid 2510 and to the second transmission control duty

solenoid 2520. The fourth modulator valve 2340 regulates the hydraulic pressure applied from

the third modulator valve 2330, thus making the pressure constant.

[0046] The first modulator valve 2310 outputs hydraulic pressure, which is regulated from

the line pressure PL as the source pressure. The hydraulic pressure, output from the first

modulator valve 2310, is appli ed to the hydraulic cylinder of the secondary pulley 508. Because

the hydraulic pressure is applied to the hydraulic cylinder of the secondary pulley 508, the

transmission belt 510 can be prevented from slipping on the pulleys 504 and 508.

[0047] The first modulator valve 2310 comprises an axially movable spool and a spring,

which biases the spool in one direction. The first modulator valve 2310 regulates the line

pressure PL 5 introduced thereto, using pilot pressure, which is the output hydraulic pressure of the

SLS linear solenoid valve 2210. In the above state, the SLS linear solenoid valve 2210 is duty

controlled by the ECU 900. The hydraulic pressure, regulated by the first modulator valve 2310,

is applied to the hydraulic cylinder of the secondary pulley 508. The clamping pressure of the

belt is increased or decreased by the output hydraulic pressure of the first modulator valve 2310.

[0048] The SLS linear solenoid valve 2210 is controlled according to a map using both an

accelerator operating amount (ACC) and a transmission ratio GR as parameters, thus providing

appropriate clamping pressure capable of preventing slippage of the transmission belt on the

pulleys. Described in detail, the excitation current for the SLS linear solenoid valve 2210 is

controlled at a duty ratio in accordance with the clamping pressure of the belt, In the

embodiment, when the transmission torque suddenly varies during acceleration or deceleration of

a vehicle, the clamping pressure of the belt is increased to prevent slippage of the transmission

belt on the pulleys.

[0049] The hydraulic pressure, applied to the hydraulic cylinder of the secondary pulley

508, is detected by a pressure sensor 2312.

[0050] Below, the manual valve 2600 will be described with reference to FIG.4. The

manual valve 2600 is mechanically, controlled in response to operation of the shift lever 920.

The forward clutch 406 and (he reverse brake 410 may be engaged or disengaged in accordance

with the operation of the manual valve 2600.

[0051] The shift lever 920 is shifted between a P position for a parking mode, an R

position for a reverse driving mode, an N position for a neutral mode, in which power

transmission is cut, and a D position and a B position for forward driving modes.

[0052] At each of the P position and the N position, hydraulic pressure both in the forward

clutch 406 and in the reverse brake 410 is drained from the manual valve 2600. Thus, the

forward clutch 406 and the reverse brake 410 are in disengaged states.

[0053] At the R position, hydraulic pressure is applied from the manual valve 2600 to the

reverse brake 410. Thus, the reverse brake 410 is engaged. Further, in the above state,

hydraulic pressure in the forward clutch 406 is drained from the manual valve 2600. Thus, the

forward clutch 406 is released.

[0054] When the control valve 2400 is in the A state in FIG. 4 øeft-handed state),

modulator pressure PM, applied from a second modulator valve (not shown), is applied to the

manual valve 2600 through the control valve 2400. Due to the modulator pressure PM, the

reverse brake 410 is maintained in an engaged state.

[0055] When the control valve 2400 is in the B state in FIG. 4 (right-handed state), the

hydraulic pressure, regulated by the SLT linear solenoid valve 2200, is applied to the manual

valve 2600. Because the hydraulic pressure is regulated by the SLT linear solenoid valve 2200,

the reverse brake 410 is smoothly engaged, thus preventing the generation of shocks during

engagement.

[0056] At the D position or the B position, hydraulic pressure is applied from the manual

valve 2600 to the forward clutch 406. Thus, the forward clutch 406 is engaged. Further, in the

above state, the hydraulic pressure in the reverse brake 410 is drained from the manual valve 2600,

so that the reverse brake 410 is released.

[0057] When the control valve 2400 is in the A state in FIG.4 (left-handed state), the

modulator pressure PM from me second modulator valve (not shown) is applied to the manual

valve 2600 through the control valve 2400. The modulator pressure PM maintains the forward

clutch 406 in an engaged state.

[0058] When the control valve 2400 is in the B state in FIG. 4 (right-handed state), the

hydraulic pressure regulated by the SLT linear solenoid valve 2200 is applied to the manual valve

2600. Because the hydraulic pressure is regulated by the SLT linear solenoid valve 2200, the

forward clutch 406 is smoothly engaged and prevents the generation of shocks during

engagement.

[0059] The SLT linear solenoid valve 2200 controls the line pressure PL through the

control valve 2400. Further, the SLS linear solenoid valve 2210 controls the clamping pressure

of the belt through the first modulator valve 2310.

[0060] Meanwhile, when a neutral control execution condition for stopping the vehicle is

achieved and the speed of the vehicle becomes zero when the shift lever 920 is in the D position,

the SLT linear solenoid valve 2200 controls the engagement force of the forward clutch 406 to

reduce the engagement force of the forward clutch 406. The SLS linear solenoid valve 2210

controls the clamping pressure of the belt through the first modulator valve 2310 and controls the

line pressure PL on behalf of the SLT linear solenoid valve 2200.

[0061] When a garage shift, wherein the shift lever 920 is shifted from the N position to

the D position or to the R position, is executed, the SLT linear solenoid valve 2200 controls the

engagement force of the forward clutch 406 or the engagement force of the reverse brake 410

such that the forward clutch 406 or the reverse brake 410 is smoothly engaged. In the above

state, the SLS linear solenoid valve 2210 controls the clamping pressure of the belt through the

first modulator valve 2310 and controls the line pressure PL on behalf of the SLT linear solenoid

valve 2200.

[0062] Next, the construction for executing transmission control will be described in detail

with reference to FIG. 5. The transmission control is executed by controlling the application and

release of hydraulic pressure to and from the hydraulic cylinder of the primary pulley 504. The

supply and discharge of actuation oil relative to the hydraulic cylinder of the primary pulley 504 is

controlled both by a first ratio control valve 2710 and by a second ratio control valve 2720.

[0063] Both the first ratio control valve 2710 and the second ratio control valve 2720

communicate with the hydraulic cylinder of the primary pulley 504. The first ratio control valve

2710 supplies the line pressure PL to the hydraulic cylinder, while the second ratio control valve

2720 is connected to the drain unit.

[0064] The first ratio control valve 2710 is a valve for executing an upshift mode. The

first ratio control valve 2710 comprises a spool, which controls the hydraulic path between an

inlet port for introducing the line pressure PL into the valve 2710, and an outlet port, which is

connected to the hydraulic cylinder of the primary pulley 504.

[0065] A spring is placed in one end of the spool of the first ratio control valve 2710. A

control pressure inlet port is provided on the other end of the spool, opposite the spring, so that the

control pressure from the first transmission control duty solenoid 2510 is fed to the valve 2710.

Further, another control pressure inlet port is provided on the end of the spool having the spring so

that the control pressure from the second transmission control duty solenoid 2520 is fed to the

valve 2710.

[0066] When both the first and second transmission control duty solenoids 2510 and 2520

are controlled such that the first transmission control duty solenoid 2510 outputs high control

pressure and the second transmission control duty solenoid 2520 outputs zero control pressure, the

spool of the first ratio control valve 2710 achieves the D state in FIG. 5 (right-handed state).

[0067] In the above state, the hydraulic pressure applied to the hydraulic cylinder of the

primary pulley 504 is increased, thereby reducing the groove width of the primary pulley 504.

Therefore, the transmission ratio becomes reduced. This means that an upshift mode is executed.

Further, the shift speed in the above state can be increased by increasing the flow rate of the inlet

actuation oil.

[0068] The second ratio control valve 2720 is a valve for executing a downshift mode.

A spring is placed in one end of the spool of the second ratio control valve 2720, A control

pressure inlet port is provided on the other end of the spool opposite the spring, so that the control

pressure from the first transmission control duty solenoid 2510 is fed to the valve 2720. Further,

another control pressure inlet port is provided on the end of the spool having the spring, so that the

control pressure from the second transmission control duty solenoid 2520 is fed to the valve 2720.

[0069] When both the first and second transmission control duty solenoids 2510 and 2520

are controlled such that the second transmission control duty solenoid 2520 outputs high control

pressure and the first transmission control duty solenoid 2510 outputs zero control pressure, the

spools of the second control valve 2720 achieves the C state in HG. 5 (left-handed state). Then,

the spool of the first control valve 2710 also achieves (he C state in FIG. 5 (left-handed state).

[0070] In the above state, actuation oil is drained from the hydraulic cylinder of the

primary pulley 504 through both the first ratio control valve 2710 and the second ratio control

valve 2720. Thus, the groove width of the primary pulley 504 is increased, and thus the

transmission ratio is increased. This means that a downshift mode is executed. Further, the

shift speed in the above state may be increased by increasing the flow rate of the outlet actuation

oil.

[0071] Next, a brake system 1300, which brakes the vehicle, will be described in detail

with reference to FIG. 6. A brake pedal 1302 is connected to a master cylinder 1304. When

the brake pedal 1302 is being operated, hydraulic pressure in accordance with the brake operation

value is generated in the master cylinder 1304,

[0072] The hydraulic pressure, generated in the master cylinder 1304, is applied to

calipers 1311 * 1314. Due to the hydraulic pressure applied to the calipers 1311 1314, abraking

operation is executed. In the present invention, the calipers may be electrically operated calipers

instead of hydraulically operated calipers.

[0073] Next, the function of the ECU 900 used as the control apparatus according to the

embodiment will be described in detail -with reference to FIG.7. In the present invention, the

function, which will be described in the following description, may be executed using either

hardware or software.

[0074] The ECU 900 comprises a brake operation determining unit 940, a vehicle speed

determining unit 942, a vehicle deceleration determining unit 944, a measuring unit 946, an

elapsed time determining unit 948, a clarriping-φressure increasing unit 950, and a

clamping-pressure increase prohibition unit 952.

[0075] The brake operation determining unit 940 determines whether a foot brake switch

916 is turned on or off. Ih other words, the brake operation determining unit 940 determines

whether the brake is being operated. The vehicle speed determining unit 942 determines

whether the vehicle speed is less than or equal to a threshold speed V(O).

[0076] The deceleration determining unit 944 determines whether the deceleration,

obtained through the differentiation of the vehicle speed, is less than or equal to a threshold

deceleration DV(O). In the embodiment, the deceleration is calculated as a positive value.

[0077] The measuring unit 946 always counts the time and resets the counted time to zero

when the foot brake switch 916 is turned off, so that the measuring unit 946 can count the elapsed

time after the foot brake switch 916 is turned on (i.e., after the operation of the brake). The

elapsed time determining unit 948 determines whether time elapsed since the operation of the

brake is greater than or equal to a threshold time T(O).

[0078] When the brake operation determining unit 940 determines that the brake is being

operated and the vehicle speed determining unit 942 determines that the vehicle speed is less than

or equal to the threshold speed V(O), the clamping-pressure increasing unit 950 controls the SLS

linear solenoid valve 2210 to stepwisely increase the clamping pressure of the belt to a pressure

level P(ON) higher than a normal pressure P(OFF) when the brake is not being operated and the

foot brake switch 916 is turned off.

[0079] If the vehicle speed to or below the threshold speed V(O), the vehicle deceleration

is less than or equal to the threshold deceleration DV(O), and the time passed after the operation of

the brake is greater than or equal to the threshold time T(O) when the brake operation determining

unit 940 determines that the brake is being operated, the clamping-pressure increase prohibition

unit 952 prohibits an increase in the clamping pressure of the belt.

[0080] Next, the control structure of a program executed by the ECU 900 used as the

control apparatus according to the embodiment of the present invention will be described with

reference to HG. 8. In the embodiment, the program is periodically executed at predetermined

intervals.

[0081] At step 100 (hereinafter, the step is referred to simply as ' S'), ECU 900 determines

whether the foot brake switch 916 has been turned on or off (i.e., whether the brake has been

operated) in response to a signal ouiput from the foot brake switch 916. If it is determined that

the foot brake switch 916 has been turned on (i.e., YES at SlOO), the routine proceeds to S 102.

However, when it is determined that the foot brake switch 916 has been turned off (i.e., NO at

SlOO), the routine proceeds to S116.

[0082] At S 102, the ECU 900 detects the vehicle speed in response to a signal output from

the vehicle speed sensor 906. At S 104, the ECU 900 determines whether the vehicle speed is

less than or equal to the threshold speed V(O). When it is determined that the vehicle speed is

less than or equal to the threshold speed V(O) (i.e., YES at S104), the routine proceeds to S106.

However, when the opposite answer is obtained (i.e., NO at S 104), the routine proceeds to Sl 16.

[0083] At S 106, the ECU900 determines whether the vehicle speed falls to or below the

threshold speed V(O) (i.e. changes from a higher value than the threshold speed V(O) to a lower

value than the threshold speed V(O)) when it is determined that the foot brake switch 916 has been

turned on. If it is determined that the vehicle speed has fallen to or below the threshold speed

V(O) and it is determined that the foot brake switch 916 has been turned on (i.e., YES S106), the

routine proceeds to S 110. However, when the opposite answer is obtained (i.e., NO at S 106),

the routine proceeds to S 108.

[0084] At S 108, the ECU 900 increases the clamping pressure of the belt to a pressure

level P(ON) that is higher than the normal pressure P(OEF) when the foot brake switch 916 is

turned off.

[0085] At S 110, the ECU 900 determines whether the deceleration of the vehicle is less

than or equal to the threshold deceleration DV(O). When it is determined that the deceleration of

the vehicle is less than or equal to the threshold deceleration DV(O) (i.e., YES at Sl 10), the

routine proceeds to S112. However, when the opposite answer is obtained (i.e., NO at SIlO),

the routine proceeds to S 108.

[0086] At S 112, the ECU 900 determines whether the time passed after the operation of

the brake is greater than or equal to the threshold time T(O). When it is determined that the time

passed after the operation of the brake is greater than or equal to the threshold time T(O) (i.e., YES

at S 112), the routine proceeds to Sl 14. However, when the opposite answer is obtained (i.e.,

NO at Sl 12), the routine proceeds to S108.

[0087] At S 114, the ECU 900 prohibits an increase in the clamping pressure of the belt.

At Sl 16, the ECU 900 sets the clamping pressure of the belt to the normal pressure P(OFF) when

the foot brake switch 916 is turned off.

[0088] . Next, the operation of the ECU 900 used as the control apparatus according to the

embodiment of the present invention will be described based on the above-mentioned

configuration and flowchart.

[0089] While the vehicle is driven, the ECU 900 determines whether the foot brake switch

916 has been turned on or off, based on a signal output .from the foot brake switch 916 (SlOO).

If it is determined that the foot brake switch 916 has been turned off (i.e., NO at SlOO), in other

words, when a driver does not have the intention to stop the vehicle and does not operate the foot

brake, the clamping pressure of the belt is set to the normal pressure P(OFF) when the foot brake

switch 916 is turned off (Sl 16).

[0090] When the foot brake switch 916 is turned on (i.e., YES at S 100), the vehicle speed

is detected based on a signal output from the vehicle speed sensor 906 (S 102). If the vehicle

speed is higher than the threshold speed V(O) (i.e., NO at S 104), the torque acting on the

transmission belt 510 is not excessively high even though the vehicle is being braked. Thus, in

the above state, the clamping pressure of the belt is set to the normal pressure P(OFF) when the

foot brake switch 916 is turned off (Sl 16).

[0091] If the vehicle speed is less than or equal to the threshold speed V(O) (Le., YES at

S 104), the torque acting on the transmission belt 510 may be excessively increased if a quick

braking operation is executed. When the torque acting on the transmission belt 510 is

excessively increased in such a way, the transmission belt 510 may slip on the pulleys.

[0092] Thus, when the vehicle speed does not fall to or below the threshold speed V(O)

when the foot brake switch 916 has been turned on (i.e. 5 NO at S 106), the clamping pressure of

the belt is increased to the pressure level P(ON), which is higher than the normal pressure P(OFF),

which is set when the foot brake switch 916 is turned off (S108). In other words, when the brake

is being operated such that the foot brake switch 916 is changed from OFF to ON and the vehicle

speed is equal to or lower than the threshold speed V(O), the clamping pressure of the belt is

increased. Thus, the slippage of the transmission belt 510 on the pulleys is reduced.

[0093] If the vehicle speed falls to or below the threshold speed V(O) when the foot brake

switch 916 is turned on, in other words, when the brake is being operated (i.e., YES at S106), and

the clamping pressure of the belt is increased, it may cause a shock after the brake operation

timing. Such a shock may cause the driver some discomfort.

[0094] In the above state, when the deceleration of the vehicle is less than or equal to the

threshold deceleration DV(O) (i.e., YES at Sl 10), and the elapsed time since the operation of the

brake began is greater than or equal to the threshold time T(O) (i.e., YES at Sl 12), an increase in

the clamping pressure of the belt is prohibited (Sl 14). In other words, when the deceleration of

the vehicle is low and the brake is operated for a lengthy period of time and the brake is thus

recognized as being smoothly operated, increases in the clamping pressure of the belt is prohibited,

and thereby shocks are reduced.

[0095] Meanwhile, when the deceleration of the vehicle is higher than the threshold

deceleration DV(O) (i.e., NO at Sl 10), the brake is thus recognized as being a quick braking

operation. Further, if the elapsed time since the operation of the brake began is less than the

threshold time T(O) (i.e., NO at S 112), the vehicle may not be undergoing a smooth braking

operation, but may be undergoing a quick braking operation. In both cases, the torque acting on

the transmission belt 510 may be excessively increased,

[0096] Thus, when the deceleration of the vehicle is higher than the threshold deceleration

DV(O) (i.e., NO at S 110) or when the elapsed time after the operation of the brake is less than the

threshold time T(O) (i.e., NO at Sl 12), the clamping pressure of the belt is increased to the

pressure level P(ON), which is higher than the normal pressure P(OFF) (S 108). Thus, the

slippage of the transmission belt 510 on the pulleys can be reduced.

[0097] As described above, the ECU used as the control apparatus according to the

embodiment determines whether the brake is being operated. Thereafter, when it is determined

that the speed of the vehicle is less than or equal to the threshold speed V(O), the clamping

pressure applied to the transmission belt is increased. When the vehicle speed falls to or below

the threshold speed V(O) when it is determined that the brake is being operated, an increase in the

clamping pressure of the belt is prevented. Thus, the control apparatus reduces shock, which

may be induced by the braking operation.

[0098] Next, the second embodiment of the present invention will be described. Unlike

the first embodiment, in which an increase in the clamping pressure of the belt is prohibited, the

second embodiment reduces the rate of increase of the clamping pressure of the belt. Ih the

second embodiment, the general configuration and general function of the control apparatus

remain the same as in the first embodiment, and further explanation of the same elements is thus

not repeated.

[0099] The function of an ECU 900 used as the control apparatus according to the second

embodiment of the present invention will be described below with reference to FIG. 9. The

function, which will be described in the following description, may be executed using either

hardware or software. Furthermore, the same or like elements described in both the first and

second embodiments carry the same or like reference numerals. Thus, further explanation is

omitted herein.

[0100] The ECU 900 comprises a clamping-pressure increasing unit 954 and a

clamping-pressure stepwise increasing unit 956 in addition to the brake operation determining

unit 940 and the vehicle speed determining unit 942.

[0101] In the second embodiment when the brake operation determining unit 940

determines that the brake is being operated and the vehicle speed determining unit 942 determines

that the vehicle speed is less than or equal to a threshold speed V(O), the clamping-pressure

increasing unit 954 controls the SLS linear solenoid valve 2210 to increase the clamping pressure

of the belt stepwisely to a pressure P(ON) that is higher than a normal pressure P(OFF), which is

set when the brake is not being operated.

[0102] When the vehicle speed falls the threshold speed V(O) when the brake operation .

determining unit 940 determines that the brake is being operated, the clamping-pressure stepwise

increasing unit 956 controls the SLS linear solenoid valve 2210 to gradually increase the

clamping pressure of the belt at a predetermined gradient to the pressure level P(ON) that is

higher than the normal pressure P(OFF). In other words, in comparison with Hie

clamping-pressure increasing unit 954, the clamping-pressure stepwise increasing unit 956

reduces the rate of increase of the clamping pressure of the belt.

[0103] Next, the control structure of a program executed by the ECU 900 used as the

control apparatus according to the second embodiment of the present invention will be described

with reference to FIG. 10. In the embodiment, the program is executed periodically at

predetermined intervals. Further, the steps in the program common to both the first embodiment

and the second embodiment carry the same step numbers, and further explanation of the same

steps is thus deemed unnecessary.

[0104] At S200, the ECU 900 stepwisely increases the clamping pressure of the belt to the

pressure level P(ON) that is higher than the normal pressure P(OFF), which is set when the foot

brake switch 916 is turned off.

[0105] At S202, the ECU 900 gradually increases the clamping pressure of the belt at a

predetermined gradient to the pressure level P(ON) 5 which is higher than the normal pressure

P(OFF), which is set the foot brake switch 916 is turned off.

[0106] The advantage of the second embodiment is that, in addition to the operational

effects of the first embodiment, it prevents slippage of the transmission belt 510 on the pulleys

during a quick braking operation, in addition to the operational effects of the first embodiment.

[0107] Next, the third embodiment of the present invention will be described. Unlike the

first embodiment, in which an increase in the clamping pressure of the belt is prevented, the third

embodiment increases the clamping pressure of the belt by an increase-amount in accordance with

the vehicle speed. In the third embodiment, the general configuration and general function of the

control apparatus remain the same as in the first embodiment, and rurther explanation of the same

elements is thus not repeated.

[0108] The function of the EOJ 900 used as the control apparatus according to the third

embodiment of the present invention will be described below with reference to FIG. 11. The

function, which will be described in the following description, may be executed using either

hardware or software. Furthermore, the same or like elements described in both the first and

second embodiments carry the same or like reference numerals. Thus, further explanation is

omitted herein.

[0109] The ECU 900 comprises a clamping-pressure increase-amount setting unit 958 and

a clamping-pressure increasing unit 960 in addition to the brake operation determining unit 940

and the vehicle speed determining unit 942.

[0110] In the third embodiment, the clamping-pressure increase-amount setting unit 958

sets the amount of increase of the clamping pressure of the belt, which is increased by the

clamping-pressure increasing unit 960, according to the speed of the vehicle. When the vehicle

speed is higher than the threshold speed V(O), the increase-amount is set to zero (i.e. the clamping

pressure of the belt is not increased. However, when the vehicle speed is less than or equal to the

threshold speed V(O), the increase-amount is set to a higher value in inverse proportion to the

vehicle speed.

[0111] When the brake operating determining unit 940 determines that the brake is being

operated and the vehicle speed determining unit 942 determines that the vehicle speed is less than

or equal to the threshold speed V(O), the clamping-pressure increasing unit 960 according to the

third embodiment controls the SLS linear solenoid valve 2210 to increase the clamping pressure

of the belt by the increase-amount set by the clamping-pressure increase-amount setting unit 958.

[0112] Below, the control structure of the program executed by the ECU 900 will be

described with reference to FIG. 12. In the embodiment, the program is executed at periodic

intervals. Further, the steps in the program common to both the first embodiment and the third

embodiment carry the same step numbers, and further explanation of the same steps is thus

deemed unnecessary.

[0113] At S300, the ECU 900 detects the speed of the vehicle based on a signal output

from the vehicle speed sensor 906. At S301 , the ECU 900 sets the increase-amount of the

clamping pressure of the belt according to the detected vehicle speed. At S302, the ECU 900

increases the clamping pressure of the belt by the set increase amount.

[0114] In the third embodiment, when the clamping pressure of the belt is increased, the

increase-amount of the clamping pressure of the belt is reduced in inverse proportion to the

vehicle speed. Thus, as in the first embodiment, the third embodiment imposes a stepwise

increase in the clamping pressure of the transmission belt. Further, because the clamping

pressure of the belt is increased, the third embodiment prevents slippage of the transmission belt

510 on the pulleys during a quick braking operation.

[0115] While the invention has been shown and described with respect to the example

embodiments, it will be understood by those skilled in the art that various changes and

modification may be made without departing from the spirit and scope of the invention as defined

in the following claims.