WO2003010023A1

WO2003010023A1 - Vehicle control device and control method therefor

Info

Publication number: WO2003010023A1
Application number: PCT/IB2002/002904
Authority: WO
Inventors: Kazuhisa Mogi; Yasushi Ito
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2001-07-26
Filing date: 2002-07-25
Publication date: 2003-02-06

Abstract

A control device of a vehicle having an engine (1) in which an expansion ratio during an expansion stroke of a piston is greater than a compression ratio during a compression stroke of the piston and a continuously variable transmission (2) connected to the output side of the engine (1) controls a gear ratio (γ) of the continuously variable transmission (2) so that an engine speed (Ne) is equal to or more than a predetermined value when a requirement output amount is determined to be equal to or more than a predetermined reference value (α) (S1: YES).

Description

VEHICLE CONTROL DEVICE AND CONTROL METHOD THEREFOR

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a control device and control method therefor for a vehicle installed with engine in which an expansion ratio is greater than a compression ratio, and more particularly to a control device and method therefor for controlling the output of the engine or the engine speed (revolution per minute) . 2. Description of the Related Art

It has been strongly desired to improve the vehicle fuel efficiency in global environmental viewpoint. For this purpose, there have been several related arts to improve the fuel efficiency of internal combustion engine used as a power source of a vehicle. Examples of such related arts include an engine (hereafter called a high expansion ratio engine) in which an expansion ratio is greater than a compression ratio, lean-burn engine and variable valve timing mechanism.

The high expansion ratio engine is an internal combustion engine operated with a heat cycle in which the expansion ratio is greater than the compression ratio. In the related art, the valve closing timing for the intake valve is delayed to increase the expansion ratio while avoiding knocking of the engine. However, retarding the valve closing timing may cause the decrease of the intake air due to the back flow of a portion of the intake air into the intake manifold side. This may lead to a reduction of output torque. This reduction of output torque may be pronounced in the area where the engine speed is not so high (so-called normal use zone: low or intermediate speed zone) . This is because the inertia effects of intake cannot be obtained.

As one of the related arts for compensating the insufficient output torque, hybrid vehicle has been developed. Such device disclosed in a Japanese Patent Laid Open publication 2000-170569 shows a control device for hybrid car having power sources of engine and motor which gradually increases assisting of motor during the vehicle running from engine partial load condition to full load condition. Another example is shown in the "Owner's Manual For Toyota Prius" (published by Toyota Motor Corporation on October 14, 1997). According to the publication, the control device for hybrid car installed with a high expansion ratio engine is disclosed which drives motor/generator in accordance with a required driving amount in addition to the engine to compensate the driving force of the engine.

In such hybrid car, the output torque from the motor to ensure the required driving torque compensates the insufficient output torque from the engine to obtain the sufficient driving torque. Accordingly, the internal combustion engine can be small in size with low output torque and also a high expansion ratio engine with high efficiency can be used which performs low output torque in low engine speed zone.

However, the hybrid car needs to have plurality of power sources and it is necessary to provide mechanism for connecting the plurality of power sources with drive mechanism such as transmission and mechanism for selectively using the power sources and further, plurality of control devices for respective power sources. As a whole, the device becomes too large in size to accommodate such additional mechanisms and control devices, which may reduce the installability and become complex and expensive due to increase of the number of members or components.

SUMMARY OF THE INVENTION

It is therefore, an object of the invention to provide a control device with good acceleration performance (response) by cooperatively controlling the internal combustion engine and continuously variable transmission.

In order to achieve the above object, according to a first aspect of the vehicle control device of the present invention the control device for vehicle includes an engine having an expansion ratio greater than an compression ratio and a continuously variable transmission connected to an output side of the high expansion ratio engine. The control device controls gear ratio of the transmission to maintain the engine speed to a predetermined value or more when an output value is required to be more than a predetermined reference value.

According to the first aspect of the control device of the invention the gear ratio of the transmission is controlled to maintain the engine speed to the predetermined value or more when the required output is equal to or more than the predetermined reference value. As the result, the engine is maintained to a higher engine speed when the required output is large and therefore, even when the engine is operated at a high expansion ratio cycle, sufficient intake air can be ensured by the inertia effects of the intake air to thereby prevent reduction of output torque. Thus, the vehicle dynamic performance can be improved by increasing the output torque while keeping the high efficiency of the engine. In addition, since only one power source is needed and only two control systems for engine control and transmission control in a normal vehicle are required to simplify the vehicle control system with a mechanical structured device. The device itself becomes compact in size and light in weight and inexpensive system can be achieved.

Further, according to the first aspect of the control device of the invention, it may include an expansion ratio control means for controlling the expansion ratio to be greater under the low load operation condition of the engine than under the high load operation condition.

This can reduce the pump loss under the low load operation condition by increasing the expansion ratio compared to the expansion ratio under the high load operation condition and increase the output torque by ensuring the sufficient amount of intake air under the high load operation condition.

Further, the gear ratio may be controlled to maintain the engine speed to the level where the high expansion ratio engine is operated at the maximum output point when the required output is determined to be the full load requirement.

The vehicle dynamic performance can be improved by controlling the gear ratio of the transmission to maintain the engine speed to the maximum output point. The control device according to the first aspect of the invention controls the intake valve operation condition to the higher side output torque when the required output is determined to be equal to or more than the predetermined value by an output requirement determining means and changes the gear ratio of the transmission in the direction where the engine speed increases and the control device of this aspect of the invention further controls the intake valve operation condition to a predetermined operation condition based on the fuel efficiency after the vehicle running condition becomes a predetermined condition by controlling the intake valve operation condition and the gear ratio of the transmission and controls the gear ratio of the transmission corresponding to a predetermined engine speed considering the fuel efficiency.

According to the above structure, when the required output becomes the predetermined value or more, the intake valve operation condition is changed to increase the output torque of the engine and the gear ratio of the transmission is changed to increase the engine speed. As the result, the drive torque rapidly increases in response to the increase of the engine output torque and the output increases in response to the increase of the engine speed. This can achieve a good acceleration performance in response to the required output. Thus, by increasing the engine output, both the intake valve operation condition and the gear ratio of the transmission are controlled to predetermined conditions considering the fuel efficiency after the vehicle reaches the predetermined condition. This can improve the fuel efficiency without reducing the acceleration response.

The intake valve opening and closing timings are advanced when the required output is determined to be equal to or more than the predetermined value by the output requirement determining means .

By advance control of the intake valve opening and closing timings, the internal combustion engine can be relatively operated with a high expansion ratio to improve the fuel efficiency under normal running condition and when the required output is large, the expansion ratio is relatively reduced and the output torque is increased to perform a good acceleration response of the vehicle.

According to a second aspect of the invention, the vehicle control method for a vehicle having an engine with a greater expansion ratio than a compression ratio, includes means for controlling the gear ratio of the transmission to maintain the engine speed to a predetermined value or more when the required output is equal to or more than the predetermined reference value.

According to the control method of the second aspect of the invention, the gear ratio is controlled to maintain the engine speed to the predetermined value or more when the required output is equal to or more than the predetermined reference value. As the result, the engine is maintained a engine speed to a higher level when the required output is high and therefore, even under the engine being operated with a high expansion ratio cycle, the inertia effects of the intake air to prevent the drop of output torque can ensure sufficient intake air. Thus the vehicle dynamic performance can be achieved by increasing the output torque while keeping the high efficiency characteristics of the high expansion ratio engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further aspects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings.

Fig. 1 is a schematic view of vehicle drive train including engine and continuously variable transmission;

Fig. 2 is a graph showing a relation between intake valve timing and engine;

Fig. 3 is a flowchart showing an example of control according to a first embodiment of the invention;

Fig. 4 is a graph showing a relation among the engine speed, drive force and gear ratio relative to the vehicle speed under the required output being large;

Fig. 5 is a graph similar to Fig. 4, but showing an automatic transmission with stepped gear shifting;

Fig. 6 is a flowchart showing an example of control according to a second embodiment of the invention;

Fig. 7 is a graph showing change of operation points controlled according to the flowchart of Fig. 6; and

Figs. 8A and 8B are graphs each showing a relation between the intake valve timing and engine load.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Next, the first embodiment of the present invention will be explained in detail with reference to the attached drawings. First, a vehicle used in this invention will be explained. In Fig.l, a continuously variable transmission (CVT) 2 is connected to an output side of the engine 1 and right and left drive wheels 4 are connected to the output side of the transmission 2 through differential gear 3.

The engine 1 is a reciprocation type engine having an intake valve and an exhaust valve opening and closing in accordance with a reciprocation of a piston 5 and more particularly, the engine 1 is of a gasoline engine type. Further, the engine 1 is a high expansion ratio cycle in which an expansion ratio is greater than a compression ratio. The high expansion ratio cycle is performed by delaying the closing timing of the intake valve 6.

Fig. 1 shows an example of such timing relation. The reference letter "A" indicates the period of opening of the intake valve 6 and similarly, the reference letter "B" indicates the period of opening of the exhaust valve 7. The closing timing of intake valve 6 is indicated at a point exceeding the bottom dead center BDC with a predetermined angle θa and the closing timing of exhaust valve 7 is indicated at a point before the bottom dead center BDC of the piston 5 with a predetermined angle θb (<θa) . In this embodiment, the angle θa for closing the intake valve timing is set to be equal to or more than 60° and preferably equal to or more than 65°. By setting the angle as above, the expansion ratio becomes greater than the compression ratio, which leads to the improvement of fuel efficiency. In this embodiment, the compression ratio is set to be equal to or more than 11.5 (or preferably, 12) to improve the fuel efficiency.

Further, the engine 1 is provided with a variable valve timing mechanism 8 (VVT) , which variably changes valve opening and closing timings for intake valve 6 and exhaust valve 7. Accordingly, changing the closing timing of intake valve 6 by this variable valve timing mechanism 8 can change the expansion ratio.

The engine 1 shown in Fig. 1 controls the valve closing timing of intake valve 6 based on the engine speed and as shown in Fig. 2, the closing timing can be advanced in the area where the engine load is large and the engine speed is high compared to the area where the engine speed is low. In other words, the closing timing is changed to the bottom dead center BDC side. The change amount increases according to the engine speed and higher the engine speed, earlier the closing timing. As the result, engine performance (output torque) is improved by the increase of intake air while refraining knocking. The expansion ratio controlling means corresponds to the means for changing the closing timing of intake valve 6 as shown in Fig. 2.

The continuously variable transmission 2 is a transmission, which can suitably set the input rotation (engine speed) and any type, such as belt type, traction type (troydal) can be used.

The gear ratio of the transmission 2 is controlled to maintain the engine speed to be optimal under a constant running condition. For example, a target driving force is obtained based on a required driving force represented by depression of an acceleration pedal (opening degree of throttle valve) and the vehicle speed. A target output for obtaining the target driving force is calculated by the target driving force and the vehicle speed. A target input rotation number (target engine speed) is obtained based on a map to obtain the target output under the best fuel efficiency condition. Thus the gear ratio of the continuously variable transmission 2 is controlled to achieve the target engine speed. On the other hand, the engine load is controlled to achieve a target torque calculated the target torque based on the target output and the engine speed.

An electronic control device 9 (E-ECU) is provided for controlling the throttle opening degree and valve timing. Further, an electronic control device 10 (T-ECU) is provided for controlling the gear ratio of the transmission 2 and a torque capacity (such as belt holding pressure) . These electronic control devices 9, 10 are formed by, for an example, a microcomputer and are mutually connected to each other to be able to transmit and receive data.

These electronic control devices 9, 10 receive data, such as vehicle speed, throttle opening degree, engine speed and engine cooling water temperature and calculate for executing above controls of engine 1 and transmission 2 based on the input data, map data memorized in advance and programs memorized in advance.

Accordingly, under a constant running condition, the vehicle is controlled along the optimum fuel consumption line where the engine speed is optimal for the fuel efficiency. This can be achieved by obtaining the target engine speed based on the target output and the map based on the required output and by controlling gear ratio of the transmission 2 to correspond to the target engine speed. However, in such engine control, the fuel efficiency is a high priority, there may be a case that the output torque is not sufficient for the required output. Accordingly, the control device of this invention can be performed different from normal control if the acceleration pedal is depressed for acceleration purpose, in which the required output is greater than a predetermined value.

The flowchart in Fig. 3 shows such control example, first in step SI corresponding to the output requirement amount determining means, the required driving force is determined whether to be equal to or more than a predetermined value α. This determines whether a degree of the requirement for increasing the engine output is greater or equal to a predetermined reference value or not. In more detail, this is determined based on the throttle valve opening degree, the change amount thereof or change rate thereof. In this step SI, the required driving force may be determined whether such required amount equals to full load condition (full throttle condition) or not.

In the step SI, if the determination is positive, proceed to step S2 corresponding to gear ratio controlling means and in the step S2, acceleration control is executed. In this acceleration control, the output is considered to be more important than fuel consumption and the engine output is increased in accordance with the required output. An example of such control is shown in Fig. 4. As shown in Fig. 4, the engine speed Ne is controlled as the target engine speed to be the engine speed at maximum output point when the acceleration pedal is depressed to increase the required output .

When the engine speed Ne reaches the maximum output point, the gear ratio γ and engine speed Ne are becoming high and accordingly, the driving force Fd becomes maximum. Thereafter, to keep the engine speed Ne to be the maximum level, the gear ratio γ is gradually decreased in accordance with the increase of the vehicle speed. Therefor, the driving force Fd is decreased in accordance with the decrease of the gear ratio γ.

When the required output is large, the gear ratio γ is continuously varied by the continuously variable transmission 2 to keep the engine speed to the maximum point in stable. Thus the engine output is kept high with stable condition, as the same as the engine speed, so as to improve an acceleration performance of the vehicle. It can obtain good acceleration performance even the engine 1 is a high expansion ratio type engine since the engine torque at acceleration operation can be raised to the maximum value and can be kept to the maximum level .

For the comparison purpose, instead of using the continuously variable transmission 2, when an automatic transmission with stepped gearshift is used, the transmission is up- shifted in accordance with the increase of the vehicle speed and the gear ratio is reduced in stepwise (step by step) . The engine speed Ne repeats the increase and stepping decrease as shown in Fig. 5. Thus in this case, the stable keeping of the engine speed to the maximum output point cannot be achieved. If a particular automatic transmission with stepped gearshift for this purpose is used, then the acceleration performance is not sufficient because of a repetition of temporal output drop.

On the other hand, when the determination at step SI is negative, normal control is executed (at step S3) . This is a control, which changes the engine speed Ne (i.e., gear ratio) to change an operation condition of the engine 1 (operation point) along the optimal fuel consumption line. Accordingly, in addition to obtaining a good fuel efficiency according to the operation condition of the engine, further improvement of the fuel efficiency can be obtained by the high expansion ratio cycle operation of the engine 1.

The present invention is not limited to the above embodiment. For example, the high expansion ratio engine can be provided with a mechanism, which performs either one of valve timing changes of intake valve and exhaust valve instead of providing such valve timing change mechanism for both intake and exhaust valves as shown in the embodiment .

Next, the second embodiment of the present invention will be explained hereinafter with reference to the attached drawings. Figs. 6 to 8. First, step Sll corresponding to a part of the output requirement determining means determines whether the acceleration requirement is given or not. This is determined by the acceleration throttle opening degree. When the acceleration requirement is not given and the step Sll determines as negative, the control ends and returns. On the contrary, when the acceleration requirement is given and step Sll determines as positive, then at step S12 corresponding to another part of the output requirement determining means, the amount of such output requirement is determined whether it is equal to or more than a predetermined value. In more detail, a sensor (not shown) detects the acceleration pedal depression angle and determines by calculating the angle change amount per time.

When step S12 determines as positive, at step S13 corresponding to a valve control means, valve advance control for intake valve 6 is executed by variable valve timing mechanism (VVT) . This is a control which changes valve timing from the condition shown in Fig. 8A to Fig. 8B. This enables to reduce the frequency of pushing back of the air suctioned in the cylinder and accordingly the amount of intake air is increased substantially to increase the engine output torque.

Next, at step S14 corresponding to a gear ratio control means, the gear ratio γ of the transmission 2 is increased i.e., downshifted. As the result, the engine speed is increased and engine output is increased accordingly.

At step S15, the engine output increased at step S14 is determined whether it has reached to the required output amount, when determined as negative at step S15, the control returns to step S14. In the step S14, the gear ratio γ is increased and the engine speed (engine output) is increased. When the engine output is increased to reach the required output amount, it is determined as positive at step S15. After the positive determination, the engine operation condition is controlled so that the required output can be achieved with the optimal fuel consumption. In more detail, the valve timing of intake valve 6 is delayed to the timing shown in Fig. 8A and the gear ratio γ of the transmission 2 is controlled to the level corresponding to the target engine speed based on the target output and the optimal fuel consumption map .

Accordingly, changing intake valve operation condition increases the engine output torque and thereafter, the engine is operated by the required output with optimal fuel consumption. Thus both fuel efficiency and acceleration performance can be improved.

When determined as negative at step S12, in other words, when acceleration is required but the throttle opening degree is small, proceed to step S14 to execute the gear ratio increasing control to downshift the transmission in accordance with such required output amount. If the required output is small, gear shifting can be executed keeping the optimal fuel consumption condition and no advance of valve timing is made under this condition.

Fig. 7 shows the change of operation point when the control in Fig. 6 is executed. Fig. 7 shows the relation between the engine speed Ne (x axis) and engine torque (y axis) . The engine torque (engine load) and the engine speed (gear ratio) are controlled so that the operation point under normal driving condition (no acceleration requirement) or small acceleration requirement is on the optimal fuel consumption line (bold line in Fig. 7) . The optimal fuel consumption line and torque line under valve timing delaying control (line indicating torque at VVT delaying control) are approximately the same.

The condition before the increase of required output (i.e. the initial condition before acceleration requirement) is indicated at point PI. If the output requirement reaches to be equal or more than the predetermined value in this condition, the valve timing of intake valve 6 is advanced to increase the engine torque before the engine speed Ne is not changed. The engine torque thus determined is the torque under full load torque condition shown in Fig. 7. In Fig. 7, the line indicating torque at valve advance timing control (torque at VVT advance timing) agrees to the full load line. The engine output torque reaches to its maximum value by increasing the engine torque to full load torque condition and good acceleration performance can be achieved.

The operation point obtain by increasing the engine torque to full load torque condition is indicated as P2 in Fig. 7. Since, as long as the rotation is unchanged, the engine torque will not increase further, the engine speed Ne and engine torque are increased in accordance with the increase of gear ratio γ of the transmission 2. The change of operation point approximately agrees to the full load line.

When the engine output is increased in accordance with the increase of throttle opening degree based on the increase of required output, change of valve timing and the increase of gear ratio γ, the engine output finally agrees to the required output amount. This is shown as point P3 in Fig. 7. Thereafter the engine operation condition is changed toward the target operation point on the optimal fuel consumption line (P4 in Fig. 7). This is the control, which changes the operation point along the equal output line indicating the output, which agrees to the required output amount. The valve timing is retarded to the condition shown in Fig. 8A and the gear ratio γ of the transmission 2 to be the engine speed Ne being the rotation number determined by the crossing point between the equal output line and the optimal fuel consumption line.

When the large acceleration requirement is given (increase of required output amount) , the valve timing is changed to high output torque side to increase the engine torque. Since the control response as above is faster than the gear ratio response, the driving force is increased rapidly so that acceleration feeling is obtained without delay. After the engine output reaches to the output corresponding to the required amount, the engine speed is controlled by the transmission 2 to be the operation condition which achieves a good fuel efficiency. It will improve the fuel efficiency and or avoiding or refraining the drop of the fuel consumption efficiency.

This invention is not limited to the embodiments above. In the above embodiments, at full load condition, the timing of intake valve is advanced to a possible timing in which the knocking of the engine is not generated. For example, the control of the valve timing can be controlled during the middle or light load condition instead of full load condition. In the above embodiment, the valve operation change control is achieved by advancing or delaying the opening or closing timing of intake valve. However, for example, such control can be achieved by controlling a substantial amount of the intake air. The amount of the intake air is controlled by an individual valve open/close control with using electromagnetic valve or by changing the valve- drifting amount.

Further, target operation point control can be achieved by moving the engine output from the point not completely agreed to the target output to the target operation point on the optimal fuel consumption line instead of moving to the target operation point on the optimal fuel consumption line after the engine output agrees to the target output. The engine in the embodiment of the invention is shown as the high expansion ratio engine, but such engine can be any internal combustion engine, which can change the valve operation condition and not limited to the high expansion ratio engine.

Claims

WHAT IS CLAIMED IS:

1. A control device for a vehicle having an engine (1) in which an expansion ratio is greater than a compression ratio, comprising : a continuously variable transmission (2) connected to an output side of the engine (1) ; output requirement amount determining means (SI) for detecting an output requirement amount of the engine and determining whether the output requirement amount is equal to or more than a predetermined reference value (α) : and gear ratio control means (S2) for controlling a gear ratio (γ) of the continuously variable transmission (2) so that an engine speed (Ne) is controlled to be equal to or more than a predetermined value when the output requirement amount determining means (SI) determines that the output requirement amount is equal to or more than the predetermined reference value.

2. The control device according to claim 1, characterized in that: the gear ratio control means (S2) controls the gear ratio (γ) so that the engine speed (Ne) is maintained to be equal to or more than the predetermined value when the output requirement amount determining means determines that the output requirement amount is equal to or more than the predetermined reference value.

3. The control device according to claim 1 or 2, further inc luding : an expansion ratio control means for controlling the expansion ratio to be greater when the engine (1) is under a low load operation condition than under a high load operation condition.

4. The control device according to claim 3, characterized in that the engine (1) further comprises a intake valve (6), the operation condition of which is variable, and the expansion ratio control means controls the expansion ratio to be greater by advancing a closing timing of the intake valve

(6) when the engine (1) is under the low load operation condition than when the engine (1) is under the high load operation condition .

5. The control device according to claims 1 to 4, characterized in that the gear ratio control means (S2) controls the gear ratio (γ) to maintain to the gear ratio (γ) that the engine (1) is operated with the engine speed (Ne) at the maximum output point when determining that the output requirement amount of the engine is a full load requirement amount.

6. The control device according to claims 1 to 5, characterized in that the engine (1) includes intake valve (6) and exhaust valve

(7) and is of reciprocating engine type with mechanical compression ratio to be equal to or more than 11:5.

7. The control device according to claim 6, characterized in that an opening timing of the intake valve (6) is at the timing equal to or more than 60 degree after bottom dead center of a piston of the engine.

8. The control device according to claim 1, characterized in that the engine (1) includes an intake valve (6) and the control device includes a valve control means (S13) for controlling an operation condition of the intake valve, wherein the valve control means (S13) controls the operation condition of the intake valve (6) to higher output torque side (PI to P2) and the gear ratio control means (S14) controls to change the gear ratio of the continuously variable transmission (2) toward a direction in which the engine speed increase (P2 to P3) when the output requirement amount determining means (Sll, S12) determines that the output requirement amount is equal to or more than the predetermined reference value, and the valve control means (S16) controls the operation condition of the intake valve (6) to a predetermined condition determined based on a fuel efficiency and the gear ratio control means (S16) controls the gear ratio (γ) of the continuously variable transmission (2) to a gear ratio corresponding to a predetermined engine speed (Ne) determined based on a consideration of the fuel efficiency after a running condition of the vehicle reaches to a predetermined condition (P3) by controlling the operation condition of the intake valve (6) by the valve control means (S13) and by controlling the gear ratio (γ) of the continuously variable transmission (2) by the gear ratio control means (S14) .

9. The control device according to claim 8, characterized in that when the running condition of the vehicle reaches to the predetermined running condition is the timing when the engine output reaches to the output requirement amount.

10. The control device according to claim 8 or 9, characterized in that the valve control means (S13) advances the open/close timing of the intake valve (6) when the output requirement amount is determined to be equal or more than the predetermined reference value by the output requirement determining means (Sll, S12) .

11. The control device according to claims 8 to 10, wherein the valve control means (S13) controls the operation condition of the intake valve to a condition that a torque of the engine (1) is increased to a full torque condition.

12. The control device according to claim 11, characterized in that the full torque condition is represented by a maximum torque line plotted by a maximum torque per every engine speed at the advance controlling of the open/close timing of the intake valve (6) under a relation between the engine speed (Ne) and the torque, and engine output is increased to the output requirement amount (P2 to P3) along the maximum torque line and by controlling the operation condition of the intake valve (6) and the gear ratio (γ) of the continuously variable transmission (2) .

13. The control device according to claims 8 to 12, wherein the operation condition of the intake valve (6) and the gear ratio (γ) of the continuously variable transmission (2) are controlled to be a condition that the output requirement amount is satisfied by an optimal fuel efficiency by the gear ratio control means (S16) and the valve control means (S16) after the engine output reaches an output value predetermined based on the output requirement amount.

14. A control method for a vehicle having an engine (1) with an expansion ratio higher than a compression ratio and a continuously variable transmission (2) connected to an output side of the engine (1), comprising the steps of: a first step (SI) detecting an output requirement amount and determining whether the detected output requirement amount is equal to or more than a predetermined reference value (α) , and a second step for controlling a gear ratio (γ) of the continuously variable transmission (2) so that an engine speed (Ne) is equal to or more than a predetermined value when the output requirement amount is determined to be equal to or more than the predetermined reference value (α) by the first step (SI) .

15 The control method according to claim 14, characterized in that gear ratio (γ) of the continuously variable transmission (2) is controlled at the second step (S2) so that the engine speed (Ne) is kept equal to or more than the predetermined value when the output requirement amount is determined to be equal to or more than the predetermined reference value (α) by the first step (SI) . 16 The control method according to claim 14, characterized in that the operation condition of the intake valve (6) is controlled to be changed to higher output torque side (PI to P2) and the gear ratio of the continuously variable transmission (2) is changed toward a direction in which the engine speed increase (P2 to P3) when the output requirement amount is determined to be equal to or more than the predetermined reference value by the first step (Sll, S12) , and the operation condition of the intake valve (6) is controlled to a predetermined condition determined based on a fuel efficiency and the gear ratio (γ) of the continuously variable transmission (2) is controlled to be a gear ratio corresponding to a predetermined engine speed (Ne) determined based on a consideration of the fuel efficiency after a running condition of the vehicle reaches to a predetermined condition (P3) by controlling the operation condition of the intake valve (6) and the gear ratio (γ) of the continuously variable transmission (2) .