JP7247900B2 - Control device for electric variable valve mechanism - Google Patents

Description

The present invention relates to a control device for an electric variable valve mechanism.

2. Description of the Related Art Conventionally, an electric variable valve mechanism is known that changes valve operating characteristics by being driven by a motor. For example, the following patent document discloses a hybrid vehicle equipped with an electric variable valve timing mechanism (hereinafter referred to as MD-VVT), which is one type of electric variable valve mechanism. For example, control data that defines the relationship between motor torque and rotational speed is used to control the electric variable valve mechanism.

JP 2016-205195 A

By the way, there is a type of internal combustion engine that can change the air-fuel ratio during operation. Since the fuel efficiency is affected by the combination of the air-fuel ratio and the valve operating characteristics, it is necessary to switch the valve operating characteristics when switching the air-fuel ratio. In this case, the electric variable valve mechanism is required to have high responsiveness in order to suppress deterioration of fuel consumption due to changes in the air amount. However, if high response performance is obtained, power consumption required to drive the electric variable valve mechanism increases. On the other hand, when the engine is operated with the air-fuel ratio fixed, high responsiveness is not required as when switching the air-fuel ratio. Rather, it is required to suppress power consumption even if response performance is suppressed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. The object is to provide a mechanism control device.

A control device according to the present invention has first control data and second control data as control data used for controlling an electric variable valve mechanism. The first control data is control data with a small upper limit of torque for driving the electric variable valve mechanism and a small energy per unit time. The second control data is control data with a larger upper limit of torque for driving the electric variable valve mechanism and larger energy per unit time than the first control data. The control device according to the present invention controls the electric variable valve mechanism using the first control data during operation in the stoichiometric mode or the lean mode, and changes combustion from the stoichiometric mode to the lean mode or from the lean mode to the stoichiometric mode. During mode switching, the second control data is used to control the electric variable valve mechanism.

According to the control device of the present invention, during operation in the stoichiometric mode or lean mode, in which high response performance is not required for switching the valve operating characteristics of the electric variable valve mechanism, the first control is used to control the electric variable valve mechanism. Since data is used, power consumption can be suppressed. On the other hand, when high response performance is required for switching the valve operating characteristics by the electric variable valve mechanism, that is, during switching of the combustion mode from the stoichiometric mode to the lean mode or from the lean mode to the stoichiometric mode, the electric variable valve Since the second control data is used for controlling the mechanism, deterioration of fuel consumption can be suppressed by shortening the switching time of the valve operating characteristics.

1 is a diagram showing the configuration of an MD-VVT drive system common to each embodiment of the present invention; FIG. 4 is a time chart of combustion mode switching control common to each embodiment of the present invention; It is a figure which shows the control data which concerns on the 1st Embodiment of this invention with a torque-rotational speed map. FIG. 4 is a diagram showing MD-VVT response characteristics based on each control data according to the first embodiment of the present invention; 4 is a flowchart of MD-VVT drive control based on control data according to the first embodiment of the present invention. It is a figure which shows the control data based on the 2nd Embodiment of this invention with a torque-rotational speed map. FIG. 10 is a diagram showing MD-VVT response characteristics based on each control data according to the second embodiment of the present invention;

An embodiment of the present invention will be described below with reference to the drawings. In the two embodiments described below, MD-VVT is used as the electric variable valve mechanism. The MD-VVT drive system is common to each embodiment. Combustion mode switching control for switching the combustion mode between stoichiometric operation and lean operation is represented by a common time chart.

1. MD-VVT Drive System First, the MD-VVT drive system will be described with reference to FIG. The MD-VVT drive system shown in FIG. 1 is a drive system for an MD-VVT mounted on a so-called mild hybrid vehicle having a 48V power supply. The drive system includes, as power supply systems, a 48V system connected to a 48V power supply and a 12V system connected to a 12V power supply. The 48V system and the 12V system are connected via a DC-DC converter. The MD-VVT belongs to the 48V system, and the ECU (control device) that controls the MD-VVT belongs to the 12V system. However, in the second embodiment, the MD-VVT is also connected to the 12V system so that the ECU can switch the power supply source.

2. Combustion Mode Switching Control FIG. 2 is a time chart of combustion mode switching control for switching the combustion mode from the stoichiometric mode to the lean mode. In the combustion mode switching control, throttle opening (TA) and valve timing (VT) are operated. When a combustion mode switching request is issued from the host ECU or another program in the ECU, valve timing switching is first started. In switching the valve timing, the target valve timing is switched from the stoichiometric mode to the lean mode at the same time as the combustion mode switching request. Then, the MD-VVT is controlled to achieve the target valve timing. The actual valve timing realized by the MD-VVT gradually changes following the target valve timing after switching.

When the target valve timing is achieved, A/F transient control is executed to change the air-fuel ratio from stoichiometric to lean. In the A/F transient control, the target air amount is switched from the stoichiometric mode to the lean mode, and the throttle opening is changed according to the target air amount. Since there is a delay in the change in the air amount with respect to the change in the throttle opening, the actual air amount realized after the throttle opening is manipulated gradually changes in accordance with the target air amount. Then, when the target air amount is achieved and the air-fuel ratio switches from stoichiometric to lean, the A/F transient control and combustion mode switching control are terminated, and operation in lean mode is started.

As described above, in switching the combustion mode from the stoichiometric mode to the lean mode, the valve timing is switched by the MD-VVT first, and after the switching is completed, the throttle opening is switched by the A/F transient control. . The same applies to the switching of the combustion mode from the lean mode to the stoichiometric mode, and the switching of the valve timing is performed prior to the switching of the throttle opening. This is to prevent torque fluctuations due to large changes in the amount of air. In the torque control, the in-cylinder fuel adhesion amount is estimated, and the in-cylinder fuel adhesion amount is also considered to determine the actual fuel injection amount. However, when the valve timing and the throttle opening are switched at the same time, the amount of air changes greatly, and the accuracy of estimating the in-cylinder fuel adhesion amount decreases. Therefore, in the combustion mode switching control, by switching the valve timing prior to the throttle opening, the torque fluctuation accompanying the change in the air amount is suppressed compared to the simultaneous switching.

However, during the preliminary control period in which the valve timing is switched prior to the A/F transient control, the valve timing suitable for stoichiometric operation is not obtained. Therefore, the fuel consumption during the pre-control period deteriorates. Therefore, in order to suppress deterioration of fuel consumption due to combustion mode switching, the MD-VVT is required to have high response performance in order to shorten the pre-control period as much as possible. On the other hand, if an attempt is made to provide the MD-VVT with high response performance, the power consumption required to drive the MD-VVT increases.

Therefore, in the two embodiments described below, the MD-VVT control data used during operation in the stoichiometric mode or lean mode is made different from the MD-VVT control data used during combustion mode switching control. This makes it possible to achieve both the proper response performance of the MD-VVT according to the operating state of the internal combustion engine and the reduction of power consumption. The former control data is called first control data, and the latter control data is called second control data. Although specifically described in each embodiment, the first control data is control data with a small upper limit of torque for driving the MD-VVT and with small energy per unit time. The second control data is control data with a larger upper limit of torque for driving the MD-VVT and larger energy per unit time than the first control data.

Power consumption can be suppressed by using the first control data for controlling the MD-VVT during operation in the stoichiometric mode or lean mode, in which high response performance is not required for valve timing switching. On the other hand, when high responsiveness is required for valve timing switching, that is, during combustion mode switching control, the second control data is used to control the MD-VVT, thereby shortening the valve timing switching time and improving fuel efficiency. deterioration can be suppressed.

3. Control Data According to First Embodiment FIG. 3 is a diagram showing the control data according to the first embodiment in the form of a rotation torque-rotation speed map. In the rotational torque-rotational speed map shown in FIG. 3, the first control data is represented as a control line for fixed A/F, and the second control data is represented as a control line for combustion mode switching control. A plurality of parallel straight lines having a negative slope are drawn on the rotational torque-rotational speed map. These straight lines are isovoltage lines, and straight lines farther from the zero point correspond to higher voltages. Since a 48V power supply is used to drive the MD-VVT, the highest voltage isovoltage line is the 48V line.

First, the control line for the combustion mode switching control, which is the second control data, will be described. At the start of combustion mode switching control, the MD-VVT is driven at the minimum rotational torque T1 and the minimum rotational speed b. The minimum rotation speed b is half the engine speed, and the minimum rotation torque T1 is the torque required for the MD-VVT to maintain the valve timing. When switching the valve timing, the rotational torque is increased to the maximum rotational torque T2 while maintaining the minimum rotational speed b. The maximum rotational torque T2 is the maximum rotational torque that can be output from a 48V power supply, and the control point determined by the maximum rotational torque T2 and the minimum rotational speed b is located on the 48V line. Next, the control point is moved along the 48V line, and the rotational speed is increased to the maximum rotational speed a. The maximum rotational speed a is the maximum rotational speed that can be achieved with a 48V power supply and is the rotational speed corresponding to the minimum rotational torque T1. The MD-VVT is driven at the maximum rotation speed a for a while, and when the valve timing approaches the target valve timing, the rotation speed is reduced to the minimum rotation speed b while maintaining the minimum rotation torque T1. This completes the switching of the valve timing.

Next, the control line when A/F is fixed, which is the first control data, will be described. When the air-fuel ratio is fixed, that is, when the engine is operated in the stoichiometric mode or lean mode, the MD-VVT is driven at the minimum rotational torque T1 and the minimum rotational speed b. When switching the valve timing, the rotational torque is increased to the intermediate rotational torque T2' while maintaining the minimum rotational speed b. A control point determined by the intermediate rotational torque T2' and the minimum rotational speed b is located on an isovoltage line (for example, the 12V line) lower than the 48V line. Next, while maintaining the intermediate rotational torque T2', the rotational speed is increased to move the control point to the 48V line. Next, the control point is moved along the 48V line, and the rotation speed is increased to the maximum rotation speed a. The MD-VVT is driven at the maximum rotation speed a for a while, and when the valve timing approaches the target valve timing, the rotation speed is reduced to the minimum rotation speed b while maintaining the minimum rotation torque T1. This completes the switching of the valve timing. The area of the region surrounded by each control line in FIG. 3 represents the magnitude of power consumption when the MD-VVT is controlled according to each control line. Power consumption can be suppressed by controlling the MD-VVT according to the control line for fixed A/F, which is the first control data.

FIG. 4 is a diagram showing MD-VVT response characteristics according to each control data. FIG. 4 shows the relationship between the required rotation speed and time when the combustion mode switching control is performed and when the A/F is fixed. During the combustion mode switching control using the second control data, the required rotation speed is quickly increased to the maximum rotation speed a. On the other hand, when the A/F is fixed using the first control data, the required rotation speed is gently increased to the maximum rotation speed a. The difference in the time required to reach the maximum rotational speed a is due to the difference in rotational torque driving the MD-VVT. During the combustion mode switching control, the rotational torque is increased to the maximum rotational torque T2, while when the A/F is fixed, it is suppressed to an intermediate rotational torque T2' lower than the maximum rotational torque T2. Due to this difference in rotational torque, valve timing can be switched more quickly during combustion mode switching control than when A/F is fixed.

FIG. 5 is a flowchart of MD-VVT drive control based on control data according to the first embodiment. In step S1, it is determined whether or not there is a request for A/F transient control that changes the air-fuel ratio. A request for A/F transient control means a request for switching the combustion mode described above. After the start of combustion mode switching control, A/F transient control is started after a pre-control period in which the MD-VVT is pre-driven.

If there is a request for A/F transient control, go to step S2. In step S2, the control for driving the MD-VVT at the fastest speed with the 48V power supply is turned on. That is, the MD-VVT drive control is executed using the above-described second control data.

In step S3, it is determined whether or not the target valve timing has been achieved by the MD-VVT. The period from the start of the control that drives the MD-VVT at the fastest speed with the 48V power source until the target valve timing is achieved is the pre-control period.

If the target valve timing has been achieved, the process proceeds to step S4. In step S4, A/F transient control is executed.

In step S5, it is determined whether or not the A/F transient control has ended, that is, whether or not the air-fuel ratio has changed.

If the A/F transient control has ended, the process proceeds to step S6. In step S6, the control for low-power driving the MD-VVT with the 48V power supply is turned on. That is, the MD-VVT drive control is executed using the above-described first control data.

4. Control Data According to Second Embodiment FIG. 6 is a diagram showing the control data according to the second embodiment in the form of a rotation torque-rotation speed map. In the rotational torque-rotational speed map shown in FIG. 6, the first control data is represented as a control line for fixed A/F, and the second control data is represented as a control line for combustion mode switching control. The control line for fixed A/F is a control line realized only by a 12V power supply, and the control line for combustion mode switching control is a control line realized only by a 48V power supply. In the second embodiment, the MD-VVT is driven by the 12V power supply when the first control data is used to control the MD-VVT, and the MD-VVT is driven by the second control data when the second control data is used to control the MD-VVT. -VVT is driven by a 48V power supply.

The control line for the combustion mode switching control, which is the second control data, is the same as that according to the first embodiment, so the description is omitted here.

A control line when A/F is fixed, which is the first control data, will be described. When the air-fuel ratio is fixed, that is, when the engine is operated in the stoichiometric mode or lean mode, the MD-VVT is driven at the minimum rotational torque T1 and the minimum rotational speed b. When switching the valve timing, the rotational torque is increased to the intermediate rotational torque T2' while maintaining the minimum rotational speed b. The intermediate rotational torque T2' is the maximum rotational torque that can be output from the 12V power source, and the control point determined by the intermediate rotational torque T2' and the minimum rotational speed b is located on the 12V line. Next, the control point is moved along the 12V line, and the rotational speed is increased to the intermediate rotational speed a'. The intermediate rotational speed a' is the maximum rotational speed that can be achieved with a 12V power supply and is a rotational speed corresponding to the minimum rotational torque T1. The MD-VVT is driven at the intermediate rotation speed a' for a while, and when the valve timing approaches the target valve timing, the rotation speed is reduced to the minimum rotation speed b while maintaining the minimum rotation torque T1. This completes the switching of the valve timing. The area of the region surrounded by each control line in FIG. 6 represents the magnitude of power consumption when the MD-VVT is controlled according to each control line. Power consumption can be suppressed by controlling the MD-VVT according to the control line for fixed A/F, which is the first control data.

FIG. 7 is a diagram showing MD-VVT response characteristics according to each control data. FIG. 7 shows the relationship between the required rotation speed and time when the combustion mode switching control is performed and when the A/F is fixed. During the combustion mode switching control using the second control data, the required rotation speed is quickly increased to the maximum rotation speed a. On the other hand, when the A/F is fixed using the first control data, the required rotation speed is gently increased to an intermediate rotation speed a' lower than the maximum rotation speed a. The difference between the time required to reach the maximum rotational speed a during combustion mode switching control and the time taken to reach the intermediate rotational speed a' during fixed A/F is due to the difference in rotational torque driving the MD-VVT. During the combustion mode switching control, the rotational torque is increased to the maximum rotational torque T2 that can be output with the 48V power supply, while when the A/F is fixed, the intermediate rotational torque T2', which is the maximum rotational torque that can be output with the 12V power supply. can be reduced to Due to this difference in rotational torque, the rotational speed can be increased more rapidly during combustion mode switching control than during fixed A/F. Since the maximum rotation speed a during combustion mode switching control is higher than the intermediate rotation speed a′, which is the maximum rotation speed when A/F is fixed, during combustion mode switching control, it is faster than when A/F is fixed. The valve timing can be switched quickly.

5. Others The present invention can also be applied to an electric variable valve mechanism other than the MD-VVT, such as an electric valve lift variable mechanism (MD-VVL).

Claims (1)

A control device for an electric variable valve mechanism mounted in an internal combustion engine capable of switching between a stoichiometric mode in which the air-fuel ratio is fixed at stoichiometric and a lean mode in which the air-fuel ratio is fixed at lean, comprising:
As control data used for controlling the electric variable valve mechanism,
first control data with a small upper limit of torque for driving the electric variable valve mechanism and with small energy per unit time;
second control data having a larger upper limit of torque for driving the electric variable valve mechanism and larger energy per unit time than the first control data;
controlling the electric variable valve mechanism using the first control data during operation in the stoichiometric mode or the lean mode;
wherein the second control data is used to control the electric variable valve mechanism during switching of the combustion mode from the stoichiometric mode to the lean mode or from the lean mode to the stoichiometric mode. Mechanism control device.

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