JPH0372868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a control method for a continuously variable transmission used for power transmission in a vehicle, and in particular to a technique for cutting off fuel supply during periods when engine power is not required. It is related to.

Conventional Technology Continuously variable transmissions, such as belt-type continuously variable transmissions (CVT), can operate the engine at optimal fuel consumption efficiency because its speed ratio can be continuously controlled. , can be suitably used as a power transmission device for a vehicle. For this reason, in vehicles equipped with a continuously variable transmission, the target rotational speed is usually determined based on at least the required output value for the engine (e.g. throttle valve opening, accelerator operation amount, etc.), and the target rotational speed and the actual The rotational speed of the engine is controlled to match the rotational speed of the input shaft of the continuously variable transmission. and,
When the vehicle is running downhill or decelerating before stopping, the required engine output value is returned to the idling value (output value for maintaining idling rotation), so the target rotation speed is determined to be a small value. , the engine speed is controlled low.

Problems to be Solved by the Invention By the way, in the continuously variable transmission for vehicles as described above, in order to suppress fuel consumption while the vehicle is running, the engine rotation speed is set to the maximum fuel cut, which is the lower limit of the fuel cut implementation range. Some engines are equipped with fuel cut means that cuts off the fuel supplied to the engine when the engine speed exceeds the minimum rotational speed value and the required engine output value reaches the idling value. In such vehicles, the minimum fuel cut rotational speed value indicating the lower limit of the range in which fuel cut is performed is determined to be a value slightly larger than the idle rotational speed of the engine in order to prevent the engine from stopping.

Therefore, in the continuously variable transmission for vehicles as described above, since the actual engine rotation speed is controlled to match the target engine rotation speed,
If the accelerator pedal is released while the vehicle is running and the required engine output value is reduced, the actual engine speed will fall below the minimum fuel cut speed value, which indicates the lower limit of the fuel cut range. However, the fuel cut period while the vehicle is running is shortened, and the fuel cut means cannot sufficiently suppress fuel consumption.

On the other hand, as described in Japanese Patent Application Laid-Open No. 58-200843, when the vehicle speed is above a predetermined value and the engine required output value (throttle valve opening) is in the idle state, the engine rotation speed A control method has been proposed in which the fuel cut is executed by adjusting the speed ratio so that the cut rotation speed is equal to or higher than the minimum cut rotation speed value. In this way, the fuel cut area is expanded, so a fuel saving effect can be obtained, but since it does not take into account the vehicle's condition, there is a risk that the engine will stop when driving downhill, etc. Fuel cut could not be carried out.

The present invention has been made against the background of the above circumstances, and its purpose is to provide a control method for a continuously variable transmission for a vehicle that can appropriately cut fuel while the vehicle is running. There is a particular thing.

Means for Solving the Problems The gist of the method of the present invention for achieving the above object is to provide fuel for which the engine speed is at the lower limit of the fuel cut range in order to suppress fuel consumption while the vehicle is running. When the cut minimum rotational speed is higher than the minimum rotational speed value and the engine required output value reaches the idling value, the fuel supplied to the engine is cut off by the fuel cutter. A control method for a continuously variable transmission for controlling the speed ratio of a continuously variable transmission in a vehicle in which the speed ratio of the continuously variable transmission is controlled so that the rotational speed of the continuously variable transmission matches the rotational speed of the engine. If the required engine output value is at the idling value and the time differential value of the vehicle speed is greater than or equal to a predetermined value, the target engine rotation speed is set to the original target engine rotation speed when the engine required output value is at the idling value. Therefore, the purpose is to increase the fuel cut rotation speed to a value higher than the minimum rotation speed value.

Operation and Effects of the Invention In this way, when the vehicle is running with the accelerator pedal released, the time differential value of the vehicle speed is greater than a predetermined value, such as the period when the vehicle is accelerated when traveling downhill. Since the target rotational speed is increased to a value higher than the fuel cut minimum rotational speed value, the fuel cutter continues to cut fuel. In addition, when the time differential value of the vehicle speed falls below a predetermined value, for example when the acceleration of the vehicle becomes extremely small or when the vehicle is decelerated by braking, the increase in the target rotational speed is canceled and the actual engine speed is reduced. Since the rotational speed is lower than the fuel cut minimum rotational speed value,
The fuel cutoff is resolved by the fuel cut means,
Engine stall is reliably prevented. Therefore, according to the method of the present invention, fuel cutting can be appropriately performed to save fuel consumption while a vehicle equipped with a continuously variable transmission is running.

Note that the above control method is based on a vehicle in which the speed ratio of the continuously variable transmission is controlled so that the target rotation speed determined based on the engine required output value matches the actual engine rotation speed. Although,
The speed ratio is calculated by dividing the output shaft rotation speed of the continuously variable transmission, which corresponds to the vehicle speed, by the input shaft rotation speed of the continuously variable transmission, which corresponds to the engine rotation speed, so the required engine output A vehicle in which the speed ratio of a continuously variable transmission is controlled so that the target speed ratio determined based on the value matches the actual speed ratio is technically the same.

Example In Fig. 1, a belt type continuously variable transmission (hereinafter referred to as
(referred to as CVT) 10 is an input shaft 12 parallel to each other
and an output shaft 14. The input shaft 12 is
It is provided coaxially with the crankshaft 18 of the engine 16 and connects the crankshaft 18 through a clutch 20.
is connected to. A movable rotating body 22a is provided on the input shaft 12 so as to be movable in the axial direction but not rotatable around the axis, and a fixed rotating body 22b is fixedly provided. A movable rotating body 24 is attached to the output shaft 14.
A is provided so as to be movable in the axial direction but not rotatable around the axis, and a fixed rotating body 24b is fixedly provided. The movable rotating body 22a and the fixed rotating body 2
2b, and the movable rotating body 24a and the fixed rotating body 2
4b constitutes an input-side variable pulley and an output-side variable pulley, each of which has a variable effective diameter, and a transmission belt 26 is wound around the input-side variable pulley and the output-side variable pulley. The effective diameter of the input side variable pulley and the output side variable pulley is determined by the input side hydraulic cylinder 27 and output side hydraulic cylinder 29, and the V groove width between the movable rotary body 22a and the fixed rotary body 22b and the movable rotary body 24.
This can be changed by changing the width of the V-groove between a and the fixed rotating body 24b.

The power of the engine 16 transmitted to the input shaft 12 of the CVT 10 is transmitted from the output shaft 14 to a forward/reverse switching device (not shown), where it is switched to a desired rotation direction, and then transmitted to the driving wheels via a differential gear device. It is now being transmitted to

The oil pump 28 is driven by the engine 16 and pumps the hydraulic oil that has returned into the tank 30 toward the pressure regulating valve 32. Pressure regulating valve 32
is constituted by, for example, a pressure control servo valve, and controls the line oil pressure by adjusting the amount of oil released to the return oil path 34 in accordance with a signal from an electronic control device, which will be described later. This line oil pressure is supplied to the output side hydraulic cylinder 29 of the output side variable pulley via the line oil passage 36 in order to maintain the tension of the transmission belt 26, and is also supplied to the output side hydraulic cylinder 29 of the output side variable pulley.
It is supplied to a flow control valve 38 for changing the speed ratio of zero.

The flow rate control valve 38 is constituted by, for example, a flow rate control servo valve, and is configured to control the input side hydraulic cylinder 27 according to a signal from an electronic control device, which will be described later.
Supply hydraulic oil to the input side hydraulic cylinder 2
By draining the hydraulic oil in 7, CVT1
The speed ratio of 0 (=rotational speed _Nput of output shaft 14/rotational speed _Nio of input shaft 12) is changed. In this embodiment, since [pressure receiving area of input side hydraulic cylinder 27]>[pressure receiving area of output side hydraulic cylinder 29], [input side hydraulic cylinder 27 internal hydraulic pressure]≦[output side hydraulic cylinder 29 internal hydraulic pressure] ], it is possible to set [the thrust of the input side hydraulic cylinder 27]>[the thrust of the output side hydraulic cylinder 29].

In the vicinity of the input-side variable pulley and the output-side variable pulley, an input-side rotation sensor 42 for detecting the rotational speed N _io of the input shaft 12 and an output shaft 1 are provided.
Output-side rotation sensors 44 for detecting the rotational speeds _Nput of 4 are provided, respectively. Further, a water temperature sensor 46 for detecting the temperature of the cooling water of the engine 16 is provided. Further, an accelerator pedal 50 provided near the driver's seat 48 is operatively connected to a throttle valve provided in the intake pipe of the engine 16, and the opening degree θ of the throttle valve is determined by a throttle sensor 52. It is becoming more and more detected. And brake sensor 53
detects whether the brake pedal 55 is depressed, and the shift position sensor 54 detects the operating position of the shift lever.

Although not shown, in the vehicle of this embodiment, when the rotational speed N _e of the engine 16 is equal to or higher than the fuel cut minimum rotational speed value N _f and the throttle valve opening θ is the minimum idling value, ,
A fuel cut device is provided to reduce fuel consumption by cutting off fuel supplied to the intake pipe of the engine 16.

FIG. 2 is a block diagram showing the configuration of the electronic control device. In the figure, CPU58, RAM6
0, ROM62, I/F (interface) 6
4, A/D (analog/digital converter) 66,
and D/A (digital/analog converter) 68
are interconnected by a data bus line 56. I/F64 is input side rotation sensor 4
2. Output side rotation sensor 66, brake sensor 5
3. The A/D 66 receives the digital signal from the shift position sensor 54, receives the analog signal from the water temperature sensor and the throttle sensor 52, and converts the D/A
68 supplies a drive signal to the pressure regulating valve 32 and the flow rate control valve 38. The above CPU 58 has ROM 6 in advance.
The input signal is processed according to the program stored in the controller 2, and the pressure regulating valve 32 and the flow rate control valve 38 are driven. In the electronic control device configured as above,
The vehicle speed is equal to or higher than a predetermined value (for example, minimum fuel cut vehicle speed), but if the throttle valve opening θ is at the idling value and the time differential value of the vehicle speed is equal to or higher than the predetermined value, the fuel cut is performed. is configured to carry out.

FIG. 3 shows a relationship stored in advance in the ROM 62 for determining the target rotational speed N ₀ , that is, a function that varies the throttle valve opening θ (required engine output value) and the vehicle speed V. In the figure, vehicle speed V ₁ >vehicle speed V ₂ >vehicle speed V ₃ , and from the relationship regarding these three types of vehicle speeds, the target rotational speed N ₀ at various vehicle speeds is determined using an interpolation method. The relationship between the target rotational speed _N0 , the vehicle speed V, and the throttle valve opening θ may be stored as a functional expression, or may be stored as a data map. Here, in the above relationship, in the range where the throttle valve opening θ is smaller than the predetermined value θ ₁ , the target rotation speed N ₀ becomes a value smaller than the minimum fuel cut rotation speed value N _f indicating the lower limit of the fuel cut range. ing. The target rotational speed N _L for fuel cut is the third
As shown in the figure, above fuel cut minimum rotation speed value
N is set to a value slightly larger than _f .

FIG. 4 is a flowchart showing the operation of this embodiment.

In the figure, when the actual throttle valve opening θ and vehicle speed V are read in step 72, it is determined in step 74 whether the actual throttle valve opening θ is zero or not, in other words, the required engine output is in the idle state. It is determined whether or not. If it is determined that the actual throttle valve opening θ is not zero, the target rotational speed N ₀ is determined to the original value in step 80, and then steps 82 and subsequent steps are executed. The above-mentioned original value is the target rotation speed N ₀ determined based on the actual throttle valve opening θ and vehicle speed V from the relationship shown in FIG.

If it is determined in step 74 that the actual throttle valve opening θ is zero, then step 76 is performed.
, the time differential value of vehicle speed (vehicle acceleration) V
It is determined whether or not is larger than a predetermined judgment reference value X2. The criterion value X2 is appropriately selected from, for example, a relatively small value, zero, or a negative value.

If the judgment in step 76 is negative, the steps from step 80 onward are executed, but if the judgment in step 76 is affirmative, the vehicle is in a running state in which fuel cut should be performed, that is, a driving state in which the vehicle speed V is above a predetermined value. In addition, even if the throttle valve opening θ is zero, the time differential value V of the vehicle speed is larger than the predetermined judgment reference value X2. Therefore, in step 78, the target rotational speed N ₀ is set as N _L shown in FIG. 3 is adopted instead of the original value.
As a result, after the actual engine rotation speed N _e (=rotation speed N _io of the input shaft 12) is read in step 82, the deviation between the target rotation speed N ₀ and the actual engine rotation speed N _e is determined in step 84. The absolute value of |N ₀ −N _e | is compared with the judgment reference value C, and if |N ₀ −N _e |<C, in other words, the actual engine rotation speed N _e is equal to the target rotation speed N ₀ If they are close enough, the routine is terminated, but if |N ₀ −N _e |≧C, in other words, if the actual engine speed N _e is far from the target rotation speed N ₀ , then In step 86, the amount of change ΔV _i in the control voltage V _i to be supplied to the flow rate control valve 38 is determined by a pre-stored function f(N _{0 −N e ) such that the deviation |N 0 −N e |} After |N ₀ −N _e | is decreased by calculating and outputting it according to the following, steps 8 and subsequent steps are executed again. That is, the speed ratio of the CVT 10 is controlled so that the actual engine rotation speed N _e matches the target rotation speed N ₀ .

Therefore, in a state where the above control cycle is repeatedly executed, while the vehicle is running with the accelerator pedal released, the time differential value (acceleration) V of the vehicle speed is larger than the household value X2 due to a downhill slope, etc. In step 78, the content of the target rotational speed _N0 is increased to a value _NL higher than the minimum fuel cut rotational speed value _Nf , which is the lower limit value of the fuel cut execution range, so the fuel cut operation by the fuel cut device is performed. is carried out, and the fuel cut operation is performed in step 74 or 7.
This will continue until the judgment in step 6 is denied. That is, the fuel cut operation continues until the time differential value V of the vehicle speed becomes smaller than the predetermined value X2, so that the judgment at step 76 is denied and the content of the target rotational speed _N0 is set to the original value. . As a result, the fuel cut period is significantly expanded compared to the case where the target rotational speed N ₀ is controlled at its original value.

Then, when the differential value V of the vehicle speed becomes _smaller than the predetermined value
N _e is also below the fuel cut minimum rotational speed value N _f . For example, when the vehicle is running downhill and the acceleration decreases or a braking operation is performed, the content of the target rotational speed _N0 is set to _Ns , and the actual engine rotational speed is controlled to match _Ns .
N _e falls below the fuel cut minimum rotational speed value N _f .
As a result, the fuel cutoff by the fuel cut device is eliminated and the engine is allowed to rotate at idle, so that engine stall is suitably prevented.

In other words, in a vehicle equipped with a CVT using a conventional control method, fuel is simply cut when the throttle valve opening θ reaches the idling value while the vehicle speed V is above a predetermined value. However, in the vehicle equipped with the control device of this embodiment, there is an additional requirement to perform fuel cut that the time differential value V of the vehicle speed is equal to or greater than a predetermined value. For example, when the acceleration of the vehicle becomes extremely small or the vehicle is decelerated by braking, the increase in the target rotational speed N ₀ is canceled and the actual engine rotational speed N _e becomes the fuel cut minimum rotational speed value. Since it is less than N _f ,
The fuel cutoff caused by the fuel cut means is eliminated,
This reliably prevents the engine from stalling.

Note that the above embodiment is an example of application of the present invention, and the present invention is also applicable to other aspects.

[Brief explanation of drawings]

FIG. 1 is a diagram showing main parts of a power transmission device and a main part of a hydraulic circuit of a CVT-equipped vehicle to which the present invention is applied. FIG. 2 is a block diagram showing the configuration of an electronic control device provided in the apparatus of FIG. 1. FIG. 3 is a diagram showing the relationship between the throttle valve opening degree and vehicle speed and the target rotation speed, which are stored in advance in order to determine the target rotation speed in the control device of FIG. 2. FIG. 4 is a flowchart illustrating the control operation of FIG. 2. 10: Belt type continuously variable transmission.

Claims (1)

[Claims] 1. In order to suppress fuel consumption while the vehicle is running, the engine rotation speed is equal to or higher than the minimum fuel cut rotation speed value which is the lower limit of the fuel cut implementation range, and the engine required output value is equal to the idling value. While the fuel supplied to the engine is cut off by the fuel cut means, the speed of the continuously variable transmission is adjusted so that the target rotation speed determined based on the engine required output value matches the actual engine rotation speed. A control method for a continuously variable transmission for a vehicle for controlling the speed ratio of the continuously variable transmission in a vehicle of the type in which the ratio is controlled, the method comprising: a required engine output value being at an idling value, and a time derivative of the vehicle speed. If the value is greater than or equal to the specified value,
A continuously variable transmission for a vehicle, characterized in that the target engine rotation speed is increased from the original target engine rotation speed when the required engine output value is at an idling value to a value higher than the fuel cut minimum rotation speed value. Control method.