CN111255579A

CN111255579A - Control strategy for engine with low pressure EGR system and vehicle

Info

Publication number: CN111255579A
Application number: CN201811453727.XA
Authority: CN
Inventors: 崔亚彬; 张春辉; 吴飞; 齐洪飞
Original assignee: Great Wall Motor Co Ltd
Current assignee: Great Wall Motor Co Ltd
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2020-06-09

Abstract

The control strategy of the engine with the low-pressure EGR system according to the embodiment of the first aspect of the invention at least comprises the following steps: judging whether the vehicle enters a sliding mode or a braking mode according to the condition that a driver releases an accelerator and the condition that a brake pedal is stepped on; if the accelerator pedal is detected to be released and the brake pedal is stepped down, preliminarily judging that the vehicle enters a braking mode; if the situation that the accelerator pedal is loosened and the brake pedal is not stepped is detected, preliminarily judging that the vehicle enters a sliding mode; the EGR valve opening is adjusted according to the mode in which the vehicle is located. Like this, according to the driving mode of difference, the suitable EGR valve opening of corresponding selection makes EGR valve opening and different driving modes fit more.

Description

Control strategy for engine with low pressure EGR system and vehicle

Technical Field

The invention relates to the technical field of vehicles, in particular to a control strategy of an engine with a low-pressure EGR system and a vehicle.

Background

In the related art, an engine EGR system is external EGR, which introduces exhaust gas after a catalyst into an intake supercharger before the exhaust gas enters an engine cylinder through the supercharger, an intake intercooler and a throttle valve. Therefore, the pipeline through which the exhaust gas enters the engine combustion chamber again is long, when the automobile runs in a transient state, the EGR rate entering the engine combustion chamber is difficult to ensure to be the target EGR rate, and under the conditions of sliding and braking of the whole automobile, the position of the EGR valve can influence the combustion stability of the engine.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. To this end, one object of the present invention is to propose a control strategy for an engine with a low-pressure EGR system.

Another object of the present invention is to propose a vehicle employing the above engine and controlling the engine by the above control strategy.

The control strategy of the engine with the low-pressure EGR system according to the embodiment of the first aspect of the invention at least comprises the following steps: judging whether the vehicle enters a sliding mode or a braking mode according to the condition that a driver releases an accelerator and the condition that a brake pedal is stepped on; if the accelerator pedal is detected to be released and the brake pedal is stepped down, preliminarily judging that the vehicle enters a braking mode; if the situation that the accelerator pedal is loosened and the brake pedal is not stepped is detected, preliminarily judging that the vehicle enters a sliding mode; the EGR valve opening is adjusted according to the mode in which the vehicle is located.

According to the engine control strategy with the low-pressure EGR system, the proper EGR valve opening degree is correspondingly selected according to different driving modes, so that the EGR valve opening degree is more suitable for the different driving modes. According to some embodiments of the invention, after the vehicle is preliminarily judged to enter the coasting mode, when the vehicle speed is detected to be greater than or equal to the first vehicle speed and the engine speed is detected to be greater than or equal to the first engine speed, the vehicle is determined to be in the coasting mode.

In some embodiments, after the vehicle is preliminarily judged to enter the coasting mode, when it is detected that the vehicle speed is lower than the first vehicle speed and the engine speed is lower than the first engine speed, it is determined that the vehicle enters the braking mode.

Optionally, the first vehicle speed is 20km/h-40km/h, and the first engine speed is 1300r/min-1500 r/min.

Further, after determining that the vehicle is in the coast mode, the EGR valve opening is adjusted according to a coast mode control strategy.

Optionally, the coasting mode control strategy comprises: detecting an engine speed of the vehicle; determining the basic opening of the EGR valve according to the rotating speed of the engine; and multiplying the basic opening degree of the EGR valve and the slip coefficient of the EGR valve to obtain the actual opening degree of the EGR valve.

Further, the engine speed and the vehicle speed of the vehicle are detected, and the EGR valve sliding coefficient is determined according to the engine speed and the vehicle speed.

Further, if the vehicle is in the braking mode, the EGR valve is controlled to be fully closed.

A vehicle according to an embodiment of the second aspect of the invention comprises a control strategy for an engine with a low pressure EGR system as described in any of the above embodiments.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic diagram of a low pressure EGR system, according to an embodiment of the present invention;

FIG. 2 is a logic diagram of a control strategy according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a control process for EGR valve opening for a low pressure EGR system when the engine is in a coast down mode, according to an embodiment of the present disclosure;

FIG. 4 is a sliding coefficient map according to an embodiment of the present invention;

fig. 5 is a variation curve of the opening degree of the EGR valve according to the embodiment of the present invention.

Reference numerals:

100-a low-pressure EGR system, and,

1-air intake intercooler, 2-oil injector, 3-supercharger, 4-EGR cooler, 5-EGR valve and 6-throttle valve.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As shown in fig. 1, in the engine having the low-pressure EGR system 100 of the present embodiment, first, exhaust gas is taken in by a catalyst, passes through an EGR valve 5 and an EGR cooler 4, and then enters a cylinder through a supercharger 3 of the engine, an intake charge air cooler 1 and a throttle valve 6 before being introduced into the intake charge air cooler 1, and is mixed with oil gas sprayed from an injector 2 in the cylinder.

This results in that control of the EGR rate is prone to delay during transient vehicle operation, since the conduit through which exhaust gas needs to flow is too long.

Further, in the driving process, if the driver looses the accelerator pedal or reduces the opening degree of the accelerator pedal, the engine is under the working condition that the engine is dragged and rotated by the running whole vehicle, and the opening degree of the EGR valve 5 at the moment can influence the EGR rate actually entering the cylinder, so that certain influence is caused on combustion.

Therefore, it is necessary to determine whether to brake or coast after the driver releases the accelerator according to the driver's intention, and thus the operation mode of the EGR valve 5 is determined according to the driver's intention.

Further, when the vehicle enters the coast mode, the further action of the driver may be re-acceleration or braking, so the intended action of the vehicle in the coast mode may be to continue maintaining the coast state or to apply braking.

Thus, during driving, once the vehicle enters the coasting mode, the subsequent action of the driver needs to be determined, and further, when the driver expects re-acceleration, the opening degree of the EGR valve 5 cannot be left at the original position and cannot be directly closed, and the EGR rate impacts the gas path under the condition that sudden acceleration is caused by direct closing. At this time, the EGR valve 5 should be set to a proper opening degree, too large opening degree causes weak acceleration of the whole vehicle, too large EGR rate causes fire, and too small EGR rate causes insufficient EGR rate.

When the driver has a braking expectation, the EGR valve 5 can be completely closed, preventing fresh air from flowing directly into the exhaust system, preventing over-oxidation, causing the catalyst to sinter.

In summary, the control strategy of the present embodiment is proposed based on the above-mentioned problems of the low-pressure EGR system 100 and the adjustment method of the EGR valve 5 that needs to be performed during the running of the vehicle having the low-pressure EGR system 100, so as to effectively solve the above-mentioned problems.

The control strategy for an engine having a low pressure EGR system 100 according to an embodiment of the present invention is described below with reference to fig. 1-5.

As shown in fig. 2, the control strategy of the engine with the low-pressure EGR system 100 according to the embodiment of the first aspect of the invention includes at least the following steps: judging whether the vehicle enters a braking mode or a sliding mode according to the condition that a driver releases an accelerator and the condition that a brake pedal is stepped on; if the accelerator pedal is detected to be released and the brake pedal is stepped down, preliminarily judging that the vehicle enters a braking mode; and if the accelerator pedal is detected to be released and the brake pedal is not stepped, preliminarily judging that the vehicle enters a sliding mode, and adjusting the opening degree of the EGR valve 5 according to the mode of the vehicle.

Specifically, first, according to the operation action of the driver, it is determined whether the driver releases the accelerator (i.e., collects the opening signal of the throttle valve 6), and then it is determined whether the driver presses the brake pedal (i.e., the pedal stroke sensor) to determine whether the vehicle enters the coasting mode or the braking mode, and in the corresponding mode, an appropriate opening of the EGR valve 5 is selected (i.e., the opening of the EGR valve 5 is adjusted).

According to the engine control strategy with the low-pressure EGR system 100, the proper opening degree of the EGR valve 5 is correspondingly selected according to different driving modes, so that the opening degree of the EGR valve 5 is more suitable for different driving modes.

As shown in fig. 3, after the vehicle is preliminarily determined to enter the coasting mode, when it is detected that the vehicle speed is greater than or equal to the first vehicle speed and the engine speed is greater than or equal to the first engine speed, it is determined that the vehicle is in the coasting mode. That is, when the vehicle speed is equal to or greater than the first vehicle speed and the engine speed is equal to or greater than the first engine speed, the low-pressure EGR system 100 determines that the driver does not have a brake expectation and the vehicle is still in the coasting mode.

As shown in fig. 3, after the vehicle is initially determined to be in the coasting mode, when the vehicle speed is lower than the first vehicle speed and the engine speed is lower than the first engine speed, it is determined that the vehicle is about to enter the braking mode.

Wherein the first vehicle speed is 20km/h-40km/h, and the first engine rotating speed is 1300r/min-1500 r/min. And after the vehicle is determined to enter the coasting mode, the opening degree of the EGR valve 5 is adjusted according to the coasting mode control strategy, and when the vehicle is determined to be in the braking mode, the EGR valve 5 is controlled to be completely closed (namely, the low-pressure EGR system 100 gradually closes the EGR valve 5, so that fresh air is prevented from entering an exhaust system after the vehicle enters the braking mode).

In summary, when the vehicle is in the coasting mode, the subsequent driving mode of the vehicle is determined according to the vehicle speed condition and the engine speed condition of the vehicle, and when the vehicle speed is greater than or equal to the first vehicle speed and the engine speed is greater than or equal to the first engine speed, the low-pressure EGR system 100 determines that the driver has a strong expectation of reacceleration, confirms that the vehicle is maintained in the coasting mode, and controls the opening of the EGR valve 5 to be adjusted in real time; when the vehicle speed is lower than the first vehicle speed and the engine speed is lower than the first engine speed, the low-pressure EGR system 100 at this time determines that the driver's brake expectation is strong, confirms that the vehicle is about to enter the braking mode, and controls the EGR valve 5 to be gradually closed.

It should be noted that the first vehicle speed and the first engine speed are calibrated quantities (for example: 1500r/min and 30km/h), which are standard quantities selected and calibrated by the inventor according to vehicle tests and vehicle smoothness under multiple tests and years of working experience.

In the specific embodiment shown in fig. 2, if it is detected that the accelerator pedal is released and the brake pedal is not depressed, it is determined that the vehicle enters the coast mode.

It can be understood that when accelerator pedal loosens, fuel supply system supplies fuel gas mixture to the engine by a small amount, the vehicle slides under the inertia drive, the engine is under the operating mode of being driven with the rotation, the driver probably accelerates this moment, also can brake, therefore, need carry out real-time control to EGR valve 5's aperture when sliding the mode, thereby when avoiding the driver to accelerate, the EGR air input in unit interval is not enough, lead to the power of vehicle not enough, and can make the EGR rate of vehicle more reasonable, accurate, in order to reduce the gas circuit and assault, thereby improve air intake system's job stabilization nature.

As shown in FIG. 2, the coast mode control strategy includes: detecting an engine speed of the vehicle; determining the basic opening of the EGR valve according to the engine speed and the sliding opening curve of the EGR valve; and multiplying the basic opening degree of the EGR valve and the slip coefficient of the EGR valve to obtain the actual opening degree of the EGR valve.

That is, in the coasting mode, the actual opening degree of the EGR valve 5 may be obtained through the above control strategy, so that the opening degree of the EGR valve 5 in the coasting mode is more reasonable and meets the use requirement.

It should be noted that the EGR valve 5 sliding opening degree curve in the present invention is obtained by a large amount of test data after the inventor has performed a plurality of tests, and the basic opening degree of the EGR valve 5 may be determined from the engine speed and the EGR valve 5 sliding opening degree curve, or of course, the basic opening degree of the EGR valve 5 corresponding to the engine speed may be obtained by other methods, and the present invention does not limit the manner of obtaining the basic opening degree of the EGR valve 5.

Further, the engine speed and the vehicle speed of the vehicle are detected, and the slip coefficient of the EGR valve 5 is determined based on the engine speed, the vehicle speed, and the slip coefficient map.

Specifically, after the vehicle enters the coasting mode, the EGR valve 5 coasting opening curve can be consulted according to the engine speed to obtain the EGR valve 5 opening corresponding to the current engine speed, the EGR coasting coefficient map is consulted according to the engine speed and the vehicle speed to obtain the corresponding coasting coefficient, and the EGR valve 5 opening is multiplied by the coasting coefficient to obtain the EGR valve 5 coasting opening.

The EGR sliding coefficient map in the present invention is obtained through a large amount of test data after a plurality of tests by the inventors, and the sliding coefficient may be determined according to the engine speed, the vehicle speed, and the EGR sliding coefficient map, and of course, the sliding coefficient corresponding to the engine speed and the vehicle speed may be obtained by other methods, and the method for obtaining the sliding coefficient is not limited in the present invention.

During the vehicle coasting process, the driver may accelerate again at any time, and at this time, if the EGR valve 5 is closed, there may be a hysteresis phenomenon in the action of the EGR valve 5 when the driver accelerates, or the EGR valve 5 is suddenly opened, so that the EGR is suddenly introduced into the cylinder, which causes impact on the combustion in the cylinder and affects the emission.

Therefore, at this time, the EGR valve 5 needs to be set at a proper opening degree, so that on one hand, the air quantity is sufficient when the driver accelerates, and on the other hand, the EGR rate is accurate as much as possible when the driver accelerates, and impact is not caused on the cylinder and the exhaust system.

As shown in fig. 4 and 5, the abscissa of the coasting curve of the EGR valve 5 is the engine speed, and the ordinate is the coasting state basic opening degree, which are calculated according to a test and a formula and calibrated through the test. The abscissa of the EGR sliding coefficient map is the vehicle speed, the ordinate is the engine speed, and the content is a correction coefficient, wherein the correction coefficient is obtained by experimental collection and verification.

If the vehicle is in the braking mode, the EGR valve 5 is controlled to be completely closed, so that fresh air can be effectively prevented from entering the exhaust system in the braking mode, and the sintering of the catalyst is prevented.

It should be noted that the vehicle may enter the braking mode under two conditions, the first is in the normal driving mode, the driver releases the accelerator pedal and simultaneously depresses the braking pedal, at this time, the vehicle directly enters the braking mode, the second is in the normal driving mode, the accelerator pedal is firstly released, at this time, the vehicle is in the coasting mode, and then the braking pedal is depressed, and the vehicle is transited from the coasting mode to the braking mode.

That is, the control strategy of the engine of the low-pressure EGR system 100 has two corresponding determination processes as to whether the vehicle is in the braking mode: the first judging process corresponds to the condition that the vehicle directly enters a braking mode, and when the accelerator pedal is released and the brake pedal is stepped on, the vehicle directly enters the braking mode; the second determination procedure is that the vehicle first enters a coast mode in which the sensor continues to operate and quickly switches to a brake mode when the brake pedal is depressed.

It should be noted that the decision logic for entering the braking mode in the first case is shown by a solid line in fig. 2, and the decision logic for entering the braking mode in the second case is shown by a broken line in fig. 2.

Next, the control procedure in the coasting mode and the braking mode of the present embodiment will be described in detail with reference to fig. 2.

When the preliminary determination determines that the vehicle is in the coasting mode, during the time when the vehicle is in the coasting mode, it is determined whether the vehicle maintains the coasting mode or is about to switch the coasting mode to the braking mode (i.e., whether the driver has a braking expectation) based on the traveling speed of the vehicle and the engine speed, the opening degree of the EGR valve 5 is controlled in real time based on the time when the vehicle is in the coasting mode, and the EGR valve 5 is closed when the driver has a braking expectation and depresses the brake pedal. According to the engine control strategy with the low-pressure EGR system 100 of the embodiment of the invention, when a driver does not tread on an accelerator pedal, the running state of a vehicle is subdivided into a coasting mode and a braking mode, and the engine with the low-pressure EGR system 100 is enabled to have different working conditions of the EGR valve 5 in the two modes, particularly the opening degree of the EGR valve 5 in the coasting mode can be adjusted in real time. Like this, not only make low pressure EGR system 100's EGR rate control more accurate, EGR valve 5's operating mode and sliding mode are more appropriate, EGR valve 5 aperture is more reasonable, thereby can avoid that the vehicle accelerated response is slow, the too big engine of leading to of EGR rate catches fire, the waste of EGR rate undersize aggravation fuel, and can be when the vehicle enters into braking mode, control EGR valve 5 is closed, thereby can prevent that the higher fresh air of oxygen content from entering into exhaust system, in order to avoid peroxide oxidation to lead to the catalyst converter sintering, improve low pressure EGR system 100's life and job stabilization nature.

It is understood that when the vehicle enters the coasting mode, the corresponding low-pressure EGR system 100 enters the coasting state, and when the vehicle enters the braking mode, the corresponding low-pressure EGR system 100 enters the braking state.

It should be noted that the EGR rate is a ratio of EGR to the total amount of intake air taken into a cylinder (combustion chamber) of the engine, and is an important indicator of fuel economy, and too large or too small has a negative effect on the engine when the vehicle is in an idling state or an engine-off state.

Further, when the vehicle enters the braking mode, the EGR valve 5 is fully closed. In this way, fresh air may be prevented from entering the exhaust system, thereby preventing catalyst over-oxidation and extending the useful life of the low pressure EGR system 100.

The vehicle according to the embodiment of the second aspect of the invention includes the engine having the low-pressure EGR system 100 as in the above-described embodiment, and the engine is controlled by the control strategy of the engine having the low-pressure EGR system 100 as in the above-described embodiment.

According to the vehicle disclosed by the embodiment of the invention, the running of the vehicle is more stable and the power of the vehicle is more abundant, the fuel economy of the vehicle can be improved, and the service life of the low-pressure EGR system 100 of the vehicle is prolonged.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of the invention.

In the description of the present invention, "the first feature" and "the second feature" may include one or more of the features.

In the description of the present invention, "a plurality" means two or more.

In the description of the present invention, the first feature being "on" or "under" the second feature may include the first and second features being in direct contact, and may also include the first and second features being in contact with each other not directly but through another feature therebetween.

In the description of the invention, "above", "over" and "above" a first feature in a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples" or the like mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A control strategy for an engine having a low pressure EGR system, comprising at least the steps of:

judging whether the vehicle enters a sliding mode or a braking mode according to the condition that a driver releases an accelerator and the condition that a brake pedal is stepped on;

if the accelerator pedal is detected to be released and the brake pedal is stepped down, preliminarily judging that the vehicle enters a braking mode;

if the situation that the accelerator pedal is loosened and the brake pedal is not stepped is detected, preliminarily judging that the vehicle enters a sliding mode;

the EGR valve opening is adjusted according to the mode in which the vehicle is located.

2. The control strategy for an engine with a low-pressure EGR system according to claim 1, wherein after the vehicle is preliminarily judged to enter the coasting mode, when it is detected that the vehicle speed is equal to or higher than the first vehicle speed and the engine speed is equal to or higher than the first engine speed, it is determined that the vehicle is in the coasting mode.

3. The control strategy for an engine with a low-pressure EGR system according to claim 2, characterized in that after the vehicle is preliminarily judged to enter the coasting mode, when it is detected that the vehicle speed is lower than the first vehicle speed and the engine speed is lower than the first engine speed, it is determined that the vehicle enters the braking mode.

4. The control strategy of an engine with a low pressure EGR system according to claim 2 or 3, characterized in that the first vehicle speed is 20-40 km/h and the first engine speed is 1300-1500 r/min.

5. The control strategy for an engine with a low pressure EGR system of claim 2 wherein the EGR valve opening is adjusted according to a coasting mode control strategy after the vehicle is determined to be in coasting mode.

6. The control strategy for an engine having a low-pressure EGR system of claim 5, wherein the coast mode control strategy comprises:

detecting an engine speed of the vehicle;

determining the basic opening of the EGR valve according to the rotating speed of the engine;

and multiplying the basic opening degree of the EGR valve and the slip coefficient of the EGR valve to obtain the actual opening degree of the EGR valve.

7. The control strategy for an engine with a low pressure EGR system of claim 6 wherein engine speed and vehicle speed of the vehicle are sensed and the EGR valve slip factor is determined based on the engine speed and vehicle speed.

8. The control strategy for an engine with a low pressure EGR system according to claim 1 or 3, characterized by controlling the EGR valve to be fully closed if the vehicle is in braking mode.

9. A vehicle comprising a control strategy for an engine with a low pressure EGR system according to any of claims 1-8.