KR100534738B1 - Shift speed control method of continuous variable transmission - Google Patents

Abstract

According to the present invention, when a faster shift speed is required in a metal belt continuously variable transmission in which a line pressure is reduced to control a drive-side actuator, the shift speed of the continuously variable transmission can be improved by controlling the line pressure. A speed control method of a continuously variable transmission of a method of controlling a drive-side actuator by reducing a line pressure, wherein the target shift speed is determined by using a target speed ratio id and a current speed ratio i. di / dt target); If the target shift speed is calculated, comparing it with the maximum shift speed (di / dt max) obtainable at the current line pressure calculated from the maximum shift speed map; And performing a corresponding speed ratio control operation according to the difference between the compared target speed and the maximum speed.

Description

Shift speed control method of continuously variable transmission {SHIFT SPEED CONTROL METHOD OF CONTINUOUS VARIABLE TRANSMISSION}

The present invention relates to a shift speed control method of a continuously variable transmission.

Typically, the CVT continuous variable transmission (CVT) is supplied with a line pressure to a secondary pulley with a clamping force for transmitting a currently given torque as shown in FIG. Transmission ratio control pressure is supplied to the primary pulley.

At this time, the method of supplying the speed ratio control pressure is largely divided into a flow control method and a pressure control method. The former is a method of directly supplying the pressure required for the transmission ratio control through a pressure control valve, and the latter decompresses the line pressure when a shift ratio change is required. To supply the required flow rate.

Most of the continuously variable transmissions that have been developed up to now employ a flow rate control ratio control system that reduces the line pressure to supply the speed ratio control pressure. In this case, the maximum speed ratio control pressure cannot exceed the line pressure.

Therefore, the maximum shift speed is determined by the current given line pressure and to overcome this, the line pressure must be increased during shift.

In the case of the pressure control method, the line pressure and the gear ratio control pressure are controlled independently, so that the required shift speed can be obtained within each limited pressure range.

This shift speed is closely related to the performance of the vehicle such as kickdown and shift quality, and a relatively slow shift speed has been pointed out as one of the major disadvantages of the continuously variable transmission vehicle compared to the case of the short shift (manual transmission or automatic transmission). .

In order to improve the speed of the continuously variable transmission, a model-based control using a feedback linearization technique has been attempted. However, since the strong nonlinearity of the continuously variable transmission ratio control system has not been considered, it has not been practically applied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuously variable transmission that can improve shift speeds in up and down shifts by controlling the line pressure when a faster shift speed is required in a metal belt continuously variable transmission in which a line pressure is reduced to control a drive-side actuator. To provide a variable speed control method of

In order to achieve the above object, the present invention provides a continuously variable transmission speed control method of controlling a drive-side actuator by reducing a line pressure, using a target speed ratio (id) and a current speed ratio (i). Calculating (Desired Shift Speed, di / dt target); If the target shift speed is calculated, comparing it with the maximum shift speed (di / dt max) obtainable at the current line pressure calculated from the maximum shift speed map; And performing a corresponding speed ratio control operation according to the difference between the target speed change and the maximum speed change.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. While many specific details, such as the following description and the annexed drawings, are shown to provide a more general understanding of the invention, these specific details are illustrated for the purpose of explanation of the invention and are not meant to limit the invention thereto. And a detailed description of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

In metal belt continuously variable transmissions, hydraulic losses due to the use of high line pressures are a major factor in reducing power train efficiency.

In addition, as the torque capacity of the metal belt increases, the mounting of the metal belt continuously variable transmission is increasing in the medium-class vehicle.

In mid-sized vehicles, in combination with the torque converter, the transmission torque increases up to 400 Nm.

This trend requires greater line pressure.

However, excessive increases in line pressure are undesirable because they create unnecessary hydraulic losses, adversely affecting fuel economy and causing damage to the metal belt.

Conversely, if the line pressure is small, the metal belt will slip and lose torque transmission capacity as the clamping force decreases.

As a result, line pressure control accounts for the largest share in the design of metal belt continuously variable transmissions. Until now, most of the studies on line pressure control have been conducted due to the increase in line pressure within the range that the metal belt does not slip to transmit a given torque. There has been a focus on optimal line pressure control to minimize hydraulic losses.

According to an embodiment of the present invention, when a speed change type continuously variable transmission system requires a faster shift speed at a current line pressure, a metal belt continuously variable transmission speed improvement algorithm that can be implemented by simple logic using a line pressure control system is proposed. .

Since the metal belt continuously variable transmission continuously changes the speed ratio, there is a shift speed unlike the manual transmission and the automatic transmission, which can be defined as follows.

Where i is the speed ratio, t is the time, and subscripts 0 and 1 represent the previous and current states, respectively.

This shift speed is determined by the pressure of the driven pulley, that is, the difference between the line pressure and the shift ratio control pressure.

With proper modification of Ide's shift dynamics equation, the continuously variable transmission dynamics can be expressed as:

← Ide Shifting Dynamics

← Modified Shift Dynamics

Here, β (i) is an experimentally obtained value and ω _p is the rotational speed of the driving side pulley, P ^* _p is the driving side pressure for maintaining the current speed ratio at a given line pressure and transmission torque.

As can be seen from the shift dynamics equation, the rate of change of the speed ratio is determined as a function of drive side rotation speed, drive side pressure and line pressure.

As described above, most of the metal belt continuously variable transmissions control the actuator on the driving side by reducing the line pressure, so that the range of the speed ratio change rate is limited when the line pressure is constant.

Thus, if faster shift speeds are required, this can be achieved by controlling the line pressure.

In the embodiment of the present invention, the following method is proposed to improve the shift speed during the up and down shift.

Shift Speed Map

The modified shift dynamics equation may be used to derive a map of the shift speed (di / dt) relationship to the line pressure and the primary pressure as shown in FIG. 2.

Upshift

FIG. 2A illustrates shift speeds for the line pressure and the shift ratio control pressure when the upshift is performed at the lowest shift ratio (i = 2.48).

At this time, the rotational speed of the drive pulley is 2000 rpm.

Referring to Fig. 2A, when the line pressure is 25 bar in the steady state of the lowest speed ratio, i.e., di / dt = 0, the drive side pressure is set to 10 bar (point A).

At this time, when the driving pressure is increased to the maximum for the upshift, the driving pressure becomes the same as the line pressure, and the maximum possible speed ratio change rate is about -1.1 (point B).

Therefore, it can be seen that the line pressure should be increased when a faster speed ratio change rate is required.

For example, if the target speed ratio change rate should be about -1.6, it is possible to increase the line pressure to 35 bar from the speed map (point C).

Downshift

2 (b) shows the shift speeds for the line pressure and the shift ratio control pressure when downshifting at the highest speed ratio (i = 0.49).

At this time, the rotational speed of the drive pulley is 2000 rpm.

If the line pressure is 25 bar at the highest speed ratio, the drive pressure is 25 bar (point P).

At this time, if the pressure on the driving side is reduced, downshifting is achieved.

For example, when the pressure on the driving side is reduced to 15 bar (point Q), a speed ratio change rate of about 2.0 can be obtained.

However, if a faster speed ratio change rate is required, excessive decompression of the drive side pressure may cause the belt to slip.

For example, if the target speed ratio change rate is 6.0 at this time, the drive side pressure should be reduced to about 7 bar, but the steady state drive side pressure (when di / dt = 0) of the lowest speed ratio in the speed change map ((a) of FIG. 2). Since this is 10 bar, if the pressure is reduced below this during excessive shifting, the belt may slip.

Therefore, if the line pressure is increased to about 52 bar (point R) or the drive side pressure is first reduced and the line pressure is increased, the speed ratio change rate 6.0 can be obtained.

From the shift speed map derived as described above, the maximum up / down shift speed can be obtained from a given shift ratio and line pressure, and then shown in a 3D map.

For example, if the line pressure given at the minimum speed ratio is 35bar, the maximum speed at the upshift is calculated as 1.594 (1 / sec) from the map (Fig. 2 (a)).

In the same way, the maximum speed can be found at each line pressure and speed ratio.

The maximum shift speed map thus obtained is shown in FIG. 3.

Now you know the maximum speed attainable for a given speed ratio and line pressure.

If the target shift speed according to the change in the target shift ratio is smaller than the maximum shift speed that can be obtained at present, the desired shift speed can be obtained by controlling the shift ratio pressure alone without changing the line pressure.

However, if the target shift speed is greater than the current maximum shift speed, it is necessary to change the line pressure to obtain a larger shift speed. If so, the biggest problem is how to change the line pressure.

This is because an excessive rise in line pressure results in a large hydraulic loss, which adversely affects fuel economy.

From Fig. 3, once the target speed is determined at a given speed ratio, the line pressure to obtain this can be calculated in reverse.

For example, if the target shift speed given at speed ratio 2.0 is -1.5 (1 / sec), the minimum line pressure for implementing this is calculated from 4a to 42.1 bar.

In the same way, it is possible to calculate the line pressure at each speed ratio and the target speed (up / down shift), and construct a map to derive a line pressure map for improving the speed as shown in FIG. 4.

A shift speed improvement algorithm was developed as shown in FIG. 5 using the shift speed maps of FIGS. 3 and 4.

Referring to FIG. 5, a target shift speed (di / dt target) is calculated by using a target speed ratio id and a current speed ratio i (S510).

There are a number of methods for calculating the target speed change, but in the embodiment of the present invention is calculated as follows.

Here, Δt is a sampling time, and gain is a correction factor for preventing the target shift speed from being too fast or too slow.

When the target speed is determined, it is compared with the maximum speed (di / dt max) obtained from the current line pressure calculated from the maximum speed map (S520, S530).

At this time, if the target shift speed is smaller than the maximum shift speed, there is no need to correct the line pressure and thus the shift speed improvement algorithm is not applied (S540).

However, if the target shift speed is greater than the maximum shift speed, it is determined that the shift speed improvement is necessary and the line pressure should be corrected. Therefore, the line pressure calculated from the line pressure map for improving the shift speed of FIG. 3 is set as the target line pressure. Control is to be performed (S550, S560).

In order to verify the speed improvement algorithm, a test system using a continuously variable transmission was constructed and tested.

A schematic diagram of a performance test apparatus for a continuously variable transmission is shown in FIG. 6.

Test apparatus for a continuously variable transmission according to an embodiment of the present invention is a belt-pulley system (CVT Belt-Pulley System), a valve body (Valve Body) 610, an electric motor (620) and power of the continuously variable transmission. Unit (Hydraulic Power Unit) (630).

The experiment was performed for the upshift and downshift, respectively, and the results are shown in FIGS. 7 and 8.

Referring to FIG. 7, the upshift is compared with the case where the upshift is performed while maintaining the line pressure at 10 bar and the case where the line pressure is increased to 25 bar to follow the target shift speed simultaneously with the upshift.

As a result, when the line pressure was maintained at 10 bar, the upshift speed was observed to be about -0.44 (1 / sec).

However, when the line pressure was increased to 25 bar, about -0.75 (1 / sec) was observed.

Therefore, it can be seen that the shift speed can be improved by increasing the line pressure during the upshift.

Referring to FIG. 8, in the case of downshifting, the line pressure is generally increased and the speed ratio is changed. Therefore, the experiment shows that the line pressure is increased to 25bar simultaneously with downshifting from 10bar (typical case) and to follow the target shift speed. This was done for the case where the pressure was increased to 35 bar and compared.

As a result of the experiment, the shift speed was observed to be about 0.86 (1 / sec), and when the shift speed improvement algorithm is applied, the speed is improved to about 1.3 (1 / sec).

Therefore, when a faster shift speed is required, it is possible to improve the shift speed by an algorithm according to an embodiment of the present invention.

In a continuously variable transmission system in which the line pressure is reduced to supply the gear ratio control pressure, the required line speed can be obtained by increasing the line pressure.

As described above, the shift speed control method of the continuously variable transmission according to the present invention can be usefully used to improve shift quality by improving the shift speed of a relatively slow continuously variable transmission as compared to other transmissions, thereby improving vehicle movement performance and driving comfort. It can be effected.

In addition, if it causes an increase in the hydraulic loss, but can be applied to the actual vehicle if the optimum operation of the engine through the shift speed improvement can be further improved fuel economy.

1 is a view showing the configuration of a continuously variable transmission.

2 is a shift speed map.

3 is a maximum speed map.

4 is a three-dimensional line pressure map for shift speed improvement.

5 is a diagram illustrating a shift speed improvement algorithm.

6 is a schematic diagram of a performance test apparatus for a continuously variable transmission (Schematic Diagram).

7 and 8 show the results for the upshift and downshift.

Claims (5)

In the continuously variable transmission speed control method of the method of controlling the drive-side actuator by reducing the line pressure, Calculating a target shift speed (di / dt target) using the target shift ratio (id) and the current shift ratio (i); If the target shift speed is calculated, comparing it with the maximum shift speed (di / dt max) obtainable at the current line pressure calculated from the maximum shift speed map; A speed change control method of a continuously variable transmission comprising the step of performing a corresponding speed ratio control operation according to the difference between the target speed change and the maximum speed. The method of claim 1, wherein the target speed is calculated as follows. Here, Δt is a sampling time, and gain is a correction factor for preventing the target shift speed from being too fast or slower than the set speed. The method of claim 1, wherein the target shift speed is calculated using a modified shift dynamics equation. ← Ide Shifting Dynamics ← Modified Shift Dynamics Here, β (i) is an experimentally obtained value and ω _p is the rotational speed of the driving side pulley, P ^* _p is the driving side pressure for maintaining the current speed ratio at a given line pressure and transmission torque. The shift speed control method of a continuously variable transmission according to claim 1, wherein the line pressure is not corrected if the target shift speed is smaller than the maximum shift speed. The continuously variable transmission of claim 1, wherein if the target shift speed is greater than the maximum shift speed, the line pressure calculated from the line pressure map for improving the shift speed is set to the target line pressure to perform the line pressure control operation. Shift speed control method.