# Patent

## Title
Controller for continuously variable transmission

## Abstract

A controller for a continuously variable transmission (CVT) mounted in a vehicle. The controller includes a first setting unit for setting a basic speed ratio of the CVT; a second setting unit for setting an adjustment speed ratio of the CVT; and a control unit for controlling the CVT based on the basic speed ratio and adjustment speed ratio. The second setting unit includes an increasing unit for progressively increasing the adjustment speed ratio according to a increase in a target torque interrelated value in a first operating area, and a decreasing unit for progressively decreasing the adjustment speed ratio according to a decrease in the target torque interrelated value in a second operating area. Between the first operating area and the second operating area, the second setting unit maintains the adjustment speed ratio that is set finally.

## Background
CROSS-REFERENCE TO THE RELATED APPLICATION
This application incorporates by references the subject matter of Application No. 2005-117065 filed in Japan on Apr. 14, 2005 on which a priority claim is based under 35 U.S.C. § 119(a).
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a controller for a continuously variable transmission that is particularly suitable for use in vehicles.
(2) Description of the Related Art
Vehicles with a continuously variable transmission (CVT) have hitherto been put to practical use and are able to enhance fuel consumption while preventing a shock that is caused in changing vehicle speed.
The continuously variable transmission is designed so that stepless speed ratios are obtained. The speed ratios, as shown in FIG. 6, are produced based on a basic speed ratio RB100 previously set according to a vehicle speed Vs. If the accelerator pedal is depressed, the basic speed ratio RB100 is shifted (see dashed lines) Note that in the case of gasoline engines, throttle opening may be used instead of accelerator pedal position.
When the vehicle speed Vs is being held constant, there are cases where engine output control (e.g., control of throttle opening) interferes with speed ratio control relative to the CVT. The interference between them will be explained in detail in the following example. In this concrete example, it is assumed that engine output is controlled by a cruise control system. The continuously variable transmission is controlled by a CVT controller. The engine is a gasoline engine with an electronically controlled throttle valve.
For instance, the driver sets a target speed to a speed of 60 km/h. In this case, when the vehicle is traveling on a level road at a constant speed, the cruise control system controls the throttle valve so that it is opened according to the target speed.
Thereafter, if the vehicle begins to go up a slope, the vehicle speed will be reduced. Because of this, the cruise control system opens the throttle valve wider in order to maintain a speed of 60 km/h.
As a result, the vehicle speed reaches a speed of 60 km/h, but since the throttle valve is opened wider, the CVT controller controls the continuously variable transmission so that the speed ratio becomes higher (see a dashed arrow in FIG. 6). Because of this, the driving torque will increase and therefore the vehicle speed will exceed a speed of 60 km/h.
Therefore, the cruise control system reduces the throttle opening to maintain a speed of 60 km/h which is the target vehicle speed. The reduction in the throttle opening then causes the CVT controller to control the continuously variable transmission so that the speed ratio becomes lower. As a result, the driving torque will be reduced and the vehicle speed cannot maintain a speed of 60 km/h.
Japanese Laid-Open Patent Publication No. hei 11-314536 discloses a technique for preventing the engine output control from interfering with the speed ratio control relative to the CVT during travel at a constant speed.
The technique shown in the aforementioned Japanese Laid-Open Patent Publication, however, requires mathematical modeling of a vehicle and a control program therefor, which are fairly difficult and time-consuming. Moreover, fine adjustments to them involve considerable time, labor, and costs.
SUMMARY OF THE INVENTION
The present invention has been made in view of the circumstances described above. Accordingly, it is the primary object of the present invention to provide a structurally simpler controller for a continuously variable transmission which is capable of preventing the engine output control from interfering with the speed ratio control relative to the CVT during travel at a constant speed.
To achieve this end, there is provided a controller for a continuously variable transmission mounted in a vehicle which has an engine and a cruise control system for maintaining a target vehicle speed. The controller comprises three major components: (1) basic speed ratio setting means for setting a basic speed ratio of the continuously variable transmission based on the target vehicle speed; (2) adjustment speed ratio setting means for sequentially setting an adjustment speed ratio of the continuously variable transmission based on a target torque interrelated value which is a value interrelated with a target torque of the engine; and (3) speed ratio control means for controlling the continuously variable transmission so that an actual speed ratio of the continuously variable transmission becomes equal to a target speed ratio obtained by adding the adjustment speed ratio set by the adjustment speed ratio setting means to the basic speed ratio set by the basic speed ratio setting means. The aforementioned adjustment speed ratio setting means includes (1) adjustment speed ratio increasing means for progressively increasing the adjustment speed ratio according to an increase in the target torque interrelated value only when the target torque interrelated value is increased and when an operating point determined by the target torque interrelated value and adjustment speed ratio is present on a first operating area; and (2) adjustment speed ratio decreasing means for progressively decreasing the adjustment speed ratio according to a decrease in the target torque interrelated value only when the target torque interrelated value is decreased and when the operating point is present on a second operating area. When the operating point is present within a third operating area between the first operating area and the second operating area, the adjustment speed ratio setting means maintains the adjustment speed ratio that is set finally.
Thus, with a simpler construction, the engine output control can be prevented from interfering with the speed ratio control relative to the CVT during travel at a constant speed.



BRIEF DESCRIPTION OF THE DRAWINGS
The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference numerals and characters designate the same or similar parts throughout the figures and wherein:
FIG. 1 is a block diagram showing a controller for a continuously variable transmission constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram showing a basic speed ratio map employed in the controller;
FIG. 3 is a schematic diagram showing an addition speed ratio map employed in the controller;
FIG. 4 is a schematic diagram showing how target addition speed ratios are obtained according to the addition speed ratio map employed in the controller;
FIG. 5 is a block diagram showing how a target speed ratio is obtained by the controller; and
FIG. 6 is a schematic diagram showing how basic speed ratios are obtained by a conventional controller for a continuously variable transmission.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a controller for a continuously variable transmission constructed in accordance with a preferred embodiment of the present invention. As shown in the figure, a vehicle 10 includes a gasoline engine (hereinafter referred to simply as an engine (E/G)) 11 and a continuously variable transmission (CVT) 12 by which torque output from the engine 11 is transmitted to driving wheels 13. The engine 11 is equipped with an electronically controlled throttle valve (not shown), its throttle opening being controlled by an engine electronic control unit (E/G-ECU) 20 to be described later.
The vehicle 10 further includes a cruise control system 14 that can be switched on to maintain a target vehicle speed VS-T without the use of the accelerator pedal. The cruise control system 14 is connected with the engine 11 and CVT 12 and is mainly equipped with the E/G-ECU 20 and a CVT electronic control unit (CVT-ECU) 30.
The cruise control system 14 is further connected with a manipulation panel (target vehicle speed setting means) 40, through which the driver's demands are input to the system 14.
Among these components, the E/G-ECU 20 is an electronic control unit equipped with interfaces, memory devices, a central processing unit, etc., and includes a target torque setting unit (target torque setting means) 21. Based on a difference between the target vehicle speed VS-T and an actual vehicle speed VS-A, the target torque setting unit 21 calculates a target torque TQ-T so that the vehicle 10 can travel at the target vehicle speed VS-T. This target torque setting unit 21 is realized as software.
The target vehicle speed VS-T can be input by the driver via the manipulation panel 40 mounted in a steering wheel (not shown). An actual vehicle speed VS-A is detected by an actual vehicle speed detecting unit 31 that is to be described later.
The target torque setting unit 21 calculates a target throttle opening θTH-T (which is a value interrelated with a target torque) for obtaining the calculated target torque TQ-T, and controls the electronically controlled throttle valve (not shown) of the engine 11 so that the throttle opening of the throttle valve becomes the target throttle opening θTH-T.
The CVT-ECU 30, as with the E/G-ECU 20, is an electronic control unit equipped with interfaces, memory devices, a central processing unit, etc., and controls the continuously variable transmission 12 to obtain stepless speed ratios. The CVT-ECU 30 includes an actual vehicle speed detecting unit 31, a basic speed ratio setting unit 32, a target addition speed ratio setting unit 34, an actual addition speed ratio setting unit 36, and a speed ratio control unit 37, these units being realized as software.
Among these units, the actual vehicle speed detecting unit 31 calculates an actual vehicle speed VS-A of the vehicle 10 based on a detection signal from a vehicle speed sensor (not shown).
The basic speed ratio setting unit (basic speed ratio setting means) 32 sets the basic speed ratio RB of the continuously variable transmission 12 based on the target vehicle speed VS-T input via the manipulation panel 40 by the driver. This basic speed ratio RB is obtained according to a basic speed ratio map 33 (see FIG. 2) incorporated in the basic speed ratio setting unit 32.
The target addition speed ratio setting unit 34 sets a target addition speed ratio RA-T, based on an operating point that is determined by a target throttle opening θTH-T set by the target torque setting unit 21 of the E/G-ECU 20 and an actual addition speed ratio (actual adjustment speed ratio) RA-A detected by the actual addition speed ratio setting unit 36 (described later). More specifically, the target addition speed ratio RA-T is obtained according to a target addition speed ratio map 35 (adjustment speed ratio map (FIG. 3)) incorporated in the target addition speed ratio setting unit 34. The setting of the target addition speed ratio RA-T by the target addition speed ratio setting unit 34 is sequentially executed at extremely short intervals. The target addition speed ratio map 35 combines two functions; it acts both as adjustment speed ratio increasing means and as adjustment speed ratio decreasing means.
As shown in FIG. 5, the target addition speed ratio (adjustment speed ratio) RA-T is added to the basic speed ratio RB obtained by the basic speed ratio setting means 32. The addition of the target addition speed ratio RA-T to the basic speed ratio RB obtains a speed ratio (target speed ratio) RT of the continuously variable transmission 12.
That is, in the preferred embodiment, the basic speed ratio RB is constant, whereas the target addition speed ratio RA-T varies with the target throttle opening θTH-T. By adding the target addition speed ratio RA-T to the basic speed ratio RB, the target speed ratio RT is set. Note the setting of the target speed ratio RT is performed by the speed ratio control unit 37 to be described later.
As shown in FIG. 3, the target addition speed ratio map 35 has a minimum target addition speed ratio (minimum value) RA-min and a maximum target addition speed ratio (maximum value) RA-Max. The minimum speed ratio RA-min and maximum speed ratio RA-max satisfy the following Eq. (1):

RA-min<RA-max  (1)

The target addition speed ratio map 35 further has a first target throttle opening θTH-T1, a second target throttle opening θTH-T2, a third target throttle opening θTH-T3, and a fourth target throttle opening θTH-T4, which are the threshold values of the target throttle opening θTH-T. These are set so as to satisfy the following Eq. (2):

θTH-T1<θTH-T2<θTH-T3<θTH-T4  (2)

The target addition speed ratio map 35 further has a speed ratio decreasing line (adjustment speed ratio decreasing means) L4, a speed ratio increasing line (adjustment speed ratio increasing means) L2, a maximum clipping line L5, and a minimum clipping line L6.
Among these lines, the speed ratio decreasing line (adjustment speed ratio decreasing line) L4 is a line linking points C and D shown in FIG. 3, that is, a straight line linking the second target throttle opening θTH-T2 at the maximum speed ratio RA-max with the first target throttle opening θTH-T2 at the minimum speed ratio RA-min. The speed ratio decreasing line L4 is inclined at an angle θ1 to the horizontal axis (axis of the target throttle opening θTH-T).
Only in the case where the target throttle opening θTH-T is decreased under the speed ratio decreasing line L4, as shown by a narrow Y4 in FIG. 4, the target addition speed ratio RA-T is set along the speed ratio decreasing line L4. Therefore, if the target throttle opening θTH-T is increased over the speed ratio decreasing line L4, the line L4 has no influence on calculation of the target addition speed ratio RA-T. Note that the speed ratio decreasing line L4 has a second operating area thereon.
The speed ratio increasing line (adjustment speed ratio increasing line) L2 is a line linking points B and A shown in FIG. 3, that is, a straight line linking the fourth target throttle opening θTH-T4 at the maximum speed ratio RA-man with the third target throttle opening θTH-T3 at the minimum speed ratio RA-min. The speed ratio increasing line L2 is inclined at an angle θ2 to the horizontal axis (axis of the target throttle opening θTH-T).
In this embodiment, the angle θ1 of the speed ratio decreasing line L4 to the axis of the target throttle opening θTH-T is equal to the angle θ2 of the speed ratio increasing line L2. In other words, the speed ratio decreasing line L4 is set parallel to the speed ratio increasing line L2.
Only in the case where the target throttle opening θTH-T is increased over the speed ratio increasing line L4, as shown by a narrow Y2in FIG. 4, the target addition speed ratio RA-T is set along the speed ratio increasing line L2. Therefore, if the target throttle opening θTH-T is decreased under the speed ratio increasing line L2, the line L2 has no influence on calculation of the target addition speed ratio RA-T. Note that the speed ratio increasing line L2 has a first operating area thereon.
The maximum clipping line L5 is a straight line extending from the fourth target throttle opening θTH-T4 (point B) in the direction of increasing the target throttle opening θTH-T along the maximum speed ratio RA-max. If the target throttle opening θTH-T exceeds the fourth target throttle opening θTH-T4, the target addition speed ratio RA-T is clipped at the maximum speed ratio RA-max.
The minimum clipping line L6 is a straight line linking the origin with the first target throttle opening θTH-T1 (point D). If the target throttle opening θTH-T is decreased under the first target throttle opening θTH-T1, the target addition speed ratio RA-T is clipped at the minimum speed ratio RAA-min.
The target addition speed ratio map 35 further has a third operating area Z1, which is defined by (1) a minimum speed ratio line L1 linking the first throttle opening θTH-T (point D) at the minimum speed ratio RA-min with the third throttle opening θTH-T3 (point A) at the minimum speed ratio RA-min, (2) a maximum speed ratio line L3 linking the second throttle opening θTH-T2 (point C) at the maximum speed ratio RA-max with the fourth throttle opening θTH-T4 (point B) at the maximum speed ratio RA-max, (3) a speed ratio decreasing line L4 linking the first throttle opening θTH-T1 (point D) at the minimum speed ratio RA-min with the second throttle opening θTH-T2 (point C) at the maximum speed ratio RA-max, and (4) a speed ratio increasing line L2 linking the third throttle opening θTH-T3 (point A) at the minimum speed ratio RA-min with the fourth throttle opening θTH-T4 (point B) at the maximum speed ratio RA-max.
In the third operating area Z1, regardless of the magnitude of the target throttle opening θTH-T, an actual addition speed ratio (actual adjustment speed ratio) RA-A maintains the target addition speed ratio RA-T that was set last time.
The actual addition speed ratio detecting unit 36 is used to detect an actual addition speed ratio RA-A which is the current target addition speed ratio. More specifically, the detecting unit 36 regards as an actual addition speed ratio RA-A the target addition speed ratio RA-T set last time by the addition speed ratio setting unit 34 that sequentially calculates a target addition speed ratio RA-T at extremely short intervals.
The speed ratio control unit (speed ratio control means) 37, as shown in FIG. 5, adds a target addition speed ratio RA-T set by the target addition speed ratio setting unit 34 to a basic speed ratio RB set by the basic speed ratio setting unit 32, thereby obtaining a target speed ratio RT. The speed ratio control unit 37 controls the CVT 12 so that the speed ratio of the CVT 12 becomes equal to the target speed ratio RT obtained in the aforementioned manner.
Since the CVT controller of the preferred embodiment is constructed as described above, it possesses the following operation and advantages. A description will be given in the case where the target throttle opening θTH-T varies as shown by θTHE, θTHF, θTHG, θTHH, θTHJ, and θTHK in FIG. 4.
Initially, consider the case where since the target addition speed ratio setting unit 34 has not calculated a target addition speed ratio RA-T yet, the target addition speed ratio (i.e., actual addition speed ratio) RA-A obtained last time is zero, and where the target throttle opening θTH-T increases progressively from zero to θTHE. In this case, until the target throttle opening θTH-T increases from zero to the first target opening θTH-T1, the target addition speed ratio RA-T remains zero.
Thereafter, until the target throttle opening θTH-T increases from the first target opening θTH-T1 to the third target opening θTH-T3, the target addition speed ratio RA-T remains at the actual addition speed ratio RA-A. That is, it is maintained at the minimum speed ratio RA-min.
Thereafter, until the target throttle opening θTH-T increases to θTHE, the target addition speed ratio RA-T increases progressively along the speed ratio increasing line L2 from the minimum speed ratio RA-min to a value indicated at RA1 (see the speed ratio increasing line L2 between points A and E and arrow Y2).
Next, consider the case where the target throttle opening θTH-T is reduced to zero, from the state in which the actual addition speed ratio RA-A is RA1 and the target throttle opening θTH-T is θTHE (point E in FIG. 4). In this case, until the target throttle opening θTH-T reaches the speed ratio decreasing line L4, the target addition speed ratio RA-T is maintained at a predetermined actual addition speed ratio (RA1) (see an arrow Y5). After the target throttle opening θTH-T reaches the speed ratio decreasing line L4 (see point H), the target addition speed ratio RA-T is progressively decreased along the speed ratio decreasing line L4 (see the speed ratio decreasing line L4 between points H and D and arrow Y4). Thereafter, if the target throttle opening θTH-T reaches θTH-T1, the target addition speed ratio RA-T becomes the minimum speed ratio RA-min (see point D). If the target throttle opening θTH-T is further reduced, the target addition speed ratio RA-T is clipped at the minimum speed ratio RA-min (see the minimum clipping line L6).
Next, consider the case where the target throttle opening θTH-T is progressively increased to θTHF, from the state in which the actual addition speed ratio RA-A is RA1 and the target throttle opening θTH-T is θTHH (see point H in FIG. 4).
In this case, regardless of an increase in the target throttle opening θTH-T, the target addition speed ratio RA-T remains at RA1 without being increased from point H along the speed ratio decreasing line L4. This is because, only when the target throttle opening θTH-T is decreased under the speed ratio decreasing line L4, the target addition speed ratio RA-T is set along the speed ratio decreasing line L4 (see an arrow Y4). Therefore, when the target throttle opening θTH-T is increased over the speed ratio decreasing line L4, the line L4 has no influence on calculation of the target addition speed ratio RA-T.
Because of this, as indicated by an arrow Y5, the target addition speed ratio RA-T remains at RA1 until it reaches the speed ratio increasing line L2 (point E) that forms the right side of a parallelogram (third operating area Z1). Thereafter, if the target throttle opening θTH-T is increased over θTHE, the target addition speed ratio RA-T is progressively increased along the speed ratio increasing line L2 and reaches RA2 (point F).
Next, consider the case where the target throttle opening θTH-T is progressively increased to θTHJ, from the state in which the target throttle opening θTH-T is θTHG and the actual addition speed ratio RA-A is RA2 (see point G in FIG. 4).
In this case, as indicated by an arrow Y6, the target addition speed ratio RA-T remains at RA2 until it reaches the speed ratio increasing line L2 (point F). Thereafter, until the target throttle opening θTH-T reaches the fourth target opening θTH-T4, the target addition speed ratio RA-T is progressively increased along the speed ratio increasing line L2. Thereafter, until the target throttle opening θTH-T is increased from the fourth target opening θTH-T4 to θTHJ, the target addition speed ratio RA-T is clipped at the maximum speed ratio RA-max (see the maximum clipping line L5).
Next, consider the case where the target throttle opening θTH-T is progressively reduced to θTHF, from the state in which the target throttle opening θTH-T is θTHJ and the actual addition speed ratio RA-A is RA-max (see point J).
In this case, even when the target throttle opening θTH-T is decreased under the fourth target opening θTH-T4, the target addition speed ratio RA-T remains at RA-max, as indicated by an arrow Y3. This is because, only in the case where the target throttle opening θTH-T is increased over the speed ratio increasing line L2, the target addition speed ratio RA-T is set along the speed ratio increasing line L2 (see an arrow Y2). Therefore, when the target throttle opening θTH-T is decreased under the speed ratio increasing line L2 from θTH-T4, the line L2 has no influence on the setting of the target addition speed ratio RA-T.
Thus, according to the CVT controller of the preferred embodiment of the present invention, the target addition speed ratio map 35 is provided with the third operating area Z1, which is defined by the speed ratio decreasing line L4, speed ratio increasing line L2, maximum clipping line L5, and minimum clipping line L6. When an operating point, determined by the actual addition speed ratio RA-A and target throttle opening θTH-T, is present within the third operating area Z1, the target addition speed ratio RA-T is maintained at the actual addition speed ratio RA-A. Consequently, with a simpler construction, the interference between the output control relative to the engine 11 and the speed ratio control relative to the CVT 12 can be prevented and, at the same time, the occurrence of a shock that is caused in changing vehicle speed can be suppressed.
The target addition speed ratio map 35 is also provided with the speed ratio decreasing line L4. Therefore, if the target throttle opening θTH-T is decreased under the speed ratio decreasing line L4, the target addition speed ratio RA-T can be progressively decreased. This can prevent the driving force of the vehicle 10 from becoming too great and enhance fuel consumption.
The target addition speed ratio map 35 is further provided with the speed ratio increasing line L2. Therefore, if the target throttle opening θTH-T is increased over the speed ratio increasing line L2, the target addition speed ratio RA-T can be progressively increased. This can prevent the driving force of the vehicle 10 from becoming too small. For instance, even when the vehicle 10 travels on an upward slope, the required driving force can be attained.
As shown in FIG. 3, the speed ratio decreasing line L4 is set at an angle θ1 to the axis of the target throttle opening θTH-T. Similarly, the speed ratio increasing line L2 is set at an angle θ2 to the axis of the target throttle opening θTH-T.
Therefore, setting the target addition speed ratio RA-T along the speed ratio decreasing line L4 or speed ratio increasing line L2 makes it possible to set the target addition speed ratio RA-T gentle. Therefore, when the vehicle speed Vs is being held constant by the cruise control system 14, adjustments to the vehicle speed Vs by adjustments to the target throttle opening θTH-T can have priority over the speed ratio control of the CVT 12. As a result, since a rapid increase in the target addition speed ratio RA-T can be prevented, suitable driving torque can be obtained, while avoiding a shock that is caused in changing vehicle speed.
The target addition speed ratio map 35 is provided with the minimum clipping line L6 which, if the target throttle opening θTH-T is decreased under the first target opening θTH-T1, makes the target addition speed ratio RA-T constant at the minimum speed ratio RA-min. The target addition speed ratio map 35 is also provided with the maximum clipping line L5 which, if the target throttle opening θTH-T is increased over the fourth target opening θTH-T4, makes the target addition speed ratio RA-T constant at the maximum speed ratio RA-max.
This makes it possible to provide simpler control for obtaining the target addition speed ratio RA-T while avoiding the occurrence of a shock which is caused in changing vehicle speed.
In addition, the minimum speed ratio RA-min is set to zero. Therefore, when the target addition speed ratio RA-T is the minimum speed ratio RA-min, it is not necessary to add the target addition speed ratio RA-T to the basic speed ratio RB. The target speed ratio RT can be obtained by the basic speed ratio RB alone, so that control for obtaining the target speed ratio RT can be made simpler.
While the present invention has been described with reference to the preferred embodiment thereof, the invention is not to be limited to the details given herein, but may be modified within the scope of the invention hereinafter claimed.
For example, in the preferred embodiment, while the target torque setting unit 21 is provided in the E/G-ECU 20, the present invention is not limited to this construction. The target torque setting unit 21 may be provided in the CVT-ECU 30.
In the preferred embodiment, while the throttle valve of the engine 11 is electronically controlled, the present invention is not limited to this construction.
In the preferred embodiment, the target torque interrelated value employs the target throttle opening θTH-T. However, it may employ an accelerator pedal position. In the case of diesel engines, a fuel injection quantity may be employed.
The advantage of employing an accelerator pedal position as the target torque interrelated value is that the engine may be a gasoline engine or diesel engine. The advantage of employing a throttle opening as the target torque interrelated value is that a target torque for a gasoline engine can be accurately calculated. The advantage of employing a fuel injection quantity as the target torque interrelated value is that a target torque for a diesel engine can be accurately calculated.
In the preferred embodiment, while the target addition speed ratio setting unit 34 employs the target addition speed ratio map 35 to realize the aforementioned control, the present invention is not limited to this construction. For instance, a logic corresponding to the target addition speed ratio map 35 may be realized by a sequencer, etc.
In the preferred embodiment, although the angle θ1 of the speed ratio decreasing line L4 relative to the axis of the target throttle opening θTH-T is equal to the angle θ2 of the speed ratio increasing line L2 relative to the axis of the target throttle opening θTH-T, the present invention is not limited to this arrangement.
For example, if the angles θ1 and θ2 are made smaller, speed ratios can be gently increased or decreased. On the other hand, if the angles θ1 and θ2 are made greater, speed ratios can be steeply increased or decreased. Therefore, the setting of the angle θ1 or θ2 makes it possible to perform fine adjustments to the drive feel.
If the angles θ1 and θ2 are set so that they differ from each other, a response to the accelerator pedal can be varied between deceleration and acceleration and therefore even finer adjustments to the drive feel are possible.

## Claims

1. A controller for a continuously variable transmission mounted in a vehicle which has an engine and a cruise control system for maintaining a target vehicle speed, said controller comprising:
basic speed ratio setting means for setting a basic speed ratio of said continuously variable transmission based on said target vehicle speed;
adjustment speed ratio setting means for sequentially setting an adjustment speed ratio of said continuously variable transmission based on a target torque interrelated value which is a value interrelated with a target torque of said engine; and
speed ratio control means for controlling said continuously variable transmission so that an actual speed ratio of said continuously variable transmission becomes equal to a target speed ratio obtained by adding said adjustment speed ratio set by said adjustment speed ratio setting means to said basic speed ratio set by said basic speed ratio setting means;
wherein said adjustment speed ratio setting means comprises
adjustment speed ratio increasing means for progressively increasing said adjustment speed ratio according to an increase in said target torque interrelated value only when said target torque interrelated value is increased and when an operating point determined by said target torque interrelated value and adjustment speed ratio is present on a first operating area, and
adjustment speed ratio decreasing means for progressively decreasing said adjustment speed ratio according to a decrease in said target torque interrelated value only when said target torque interrelated value is decreased and when said operating point is present on a second operating area;

and wherein, when said operating point is present within a third operating area between said first operating area and said second operating area, said adjustment speed ratio setting means maintains said adjustment speed ratio that is set finally.

2. The controller according to claim 1, wherein said adjustment speed ratio setting means sets a maximum value and a minimum value of said adjustment speed ratio.

3. The controller according to claim 2, wherein
said adjustment speed ratio setting means includes an adjustment speed ratio map for setting said adjustment speed ratio based on said target torque interrelated value;
said first operating area is provided on an adjustment speed ratio increasing line which forms part of said adjustment speed ratio map;
said second operating area is provided on an adjustment speed ratio decreasing line which forms part of said adjustment speed ratio map;
if said target torque interrelated value is increased over said adjustment speed ratio increasing line, said adjustment speed ratio setting means sets said adjustment speed ratio along said adjustment speed ratio increasing line; and
if said target torque interrelated value is decreased under said adjustment speed ratio decreasing line, said adjustment speed ratio setting means sets said adjustment speed ratio along said adjustment speed ratio decreasing line.

4. The controller according to claim 3, wherein said target torque interrelated value is expressed in accelerator pedal position.

5. The controller according to claim 3, wherein said target torque interrelated value is expressed in throttle opening.

6. The controller according to claim 3, wherein said target torque interrelated value is expressed in fuel injection quantity.

7. The controller according to claim 2, wherein said target torque interrelated value is expressed in accelerator pedal position.

8. The controller according to claim 2, wherein said target torque interrelated value is expressed in throttle opening.

9. The controller according to claim 2, wherein said target torque interrelated value is expressed in fuel injection quantity.

10. The controller according to claim 1, wherein
said adjustment speed ratio setting means includes an adjustment speed ratio map for setting said adjustment speed ratio based on said target torque interrelated value;
said first operating area is provided on an adjustment speed ratio increasing line which forms part of said adjustment speed ratio map;
said second operating area is provided on an adjustment speed ratio decreasing line which forms part of said adjustment speed ratio map;
if said target torque interrelated value is increased over said adjustment speed ratio increasing line, said adjustment speed ratio setting means sets said adjustment speed ratio along said adjustment speed ratio increasing line; and
if said target torque interrelated value is decreased under said adjustment speed ratio decreasing line, said adjustment speed ratio setting means sets said adjustment speed ratio along said adjustment speed ratio decreasing line.

11. The controller according to claim 10, wherein said target torque interrelated value is expressed in accelerator pedal position.

12. The controller according to claim 10, wherein said target torque interrelated value is expressed in throttle opening.

13. The controller according to claim 10, wherein said target torque interrelated value is expressed in fuel injection quantity.

14. The controller according to claim 1, wherein said target torque interrelated value is expressed in accelerator pedal position.

15. The controller according to claim 1, wherein said target torque interrelated value is expressed in throttle opening.

16. The controller according to claim 1, wherein said target torque interrelated value is expressed in fuel injection quantity.