CN104029671B - Automobile engine stop position control method - Google Patents

Abstract

The invention discloses a method for controlling the stop position of an automobile engine, comprising the following steps: judging whether the current engine speed ω is lower than the minimum ignition speed ω _Max of the engine _; Continue to judge whether the engine speed is 0; if the engine speed is 0, then enter the engine stop position control process; compared with the prior art, the present invention has the advantage that: because the ISG motor is coaxial with the engine, and the ISG motor has a higher Position accuracy, when the engine is stopped, the ISG motor is driven to control the engine to stop at the position where the resistance torque is the smallest, and can ensure a high success rate of starting the engine by the ISG system.

Description

Automobile engine stop position control method

technical field

The invention relates to the field of engine shutdown position control of a hybrid electric vehicle, in particular to a method for controlling the engine shutdown position of an automobile.

Background technique

The grim situation of global energy and the environment, especially the huge impact of the international financial crisis on the automobile industry, has pushed countries around the world to accelerate the strategic transformation of transportation energy. New energy vehicles represented by hybrid vehicles, pure electric vehicles and fuel cell vehicles have become the future vehicles important direction of development.

Because electric vehicles are currently facing difficulties such as short driving range, expensive batteries, and imperfect infrastructure, it will take a considerable period of effort to gradually solve them; while hybrid vehicles have better industrialization conditions at this stage, Hybrid electric vehicles are of great significance to the development of my country's automobile industry. This means that for a long period of time, the powertrain of new energy vehicles will consist of lower power engines and motor drives.

Due to the limitations of cost, weight, size, and working conditions, the capacity of the power battery of the ISG system is limited, resulting in a soft output characteristic, which limits the low-speed torque of the ISG system and limits the success rate of the ISG system to start the engine; plus power At low and high temperatures, the output power of the battery is lower than that at normal temperature, resulting in a lower success rate of the ISG system for starting the engine at low temperatures.

In one working cycle of the engine, the resistance torque of the engine varies with the position of the engine crankshaft. In one working cycle of a certain four-cylinder, the engine resistance curve of the engine changing with the position of the crankshaft is shown in Figure 1 (0° corresponds to the position on the cylinder of the engine fulcrum). The engine usually stops near the position with the largest resistance torque, that is, near the upper fulcrum of the engine cylinder. At these points, the electric drive system needs to output a large torque to overcome the engine resistance torque and drag the engine to start. Due to the driving capacity of the electric drive system Certainly, the success rate of starting the engine near the upper fulcrum of the cylinder is limited, and at low temperature, the success rate of starting the engine is even lower.

The test proves that: at different positions of the engine crankshaft, due to the different resistance torque of the engine, under the same electric drive system, the starting success rate is different. The smaller the engine resistance torque is, the higher the engine starting success rate is, that is, the crankshaft When it is near the lower fulcrum of the engine cylinder (near the multiple of 90° in Figure 1, no more than 5 degrees), the starting success rate is the highest, and it is close to 100% at normal temperature.

Retrieve the existing patent, the method for controlling the stop position of the engine in a hybrid electric vehicle (CN101180897A), the method includes a) when the engine is about to stop, and the fuel supplied to the engine is cut off, using the motor according to the an engine speed reduction rate to reduce the engine speed; b) after the engine speed has been reduced to a first engine speed, using said electric machine according to a second engine speed reduction rate and by processing the signals from the crank sensor and the cam sensor to monitoring the current crank position to count the number of times said current crank position coincides with a given target engine stop position; and c) if said number is greater than a predetermined number, and if the actual engine speed is equal to or lower than a second reference speed, then at The engine is stopped using the electric machine when the current crank position coincides with the target engine shutdown position.

In this invention, the vehicle controller (HCU) collects the engine speed and crank position through CAN to calculate the braking torque of the ISG electric drive system, and sends the braking torque to the motor controller through CAN, and the motor controller brakes according to a given Torque to stop the engine to the designated position. Due to the limitation of CAN communication rate, the method in the literature has a large control delay, and the engine stop position belongs to angular position control, which requires high real-time control. The method in the literature is not effective in actual control.

Contents of the invention

The object of the present invention is to provide a method for controlling the stop position of an automobile engine.

In order to achieve the above object, the automobile engine shutdown position control method provided by the present invention comprises the following steps:

Step 1) judge whether the current engine speed ω is lower than the minimum ignition speed ω _Max of the engine by the motor controller;

Step 2) If the current engine speed is lower than the minimum ignition speed, that is, ω<ω _Max , continue to judge whether the engine speed is 0;

Step 3) If the engine speed is 0, then enter the engine shutdown position control process;

Compared with the prior art, the advantage of the present invention is: because the ISG motor is coaxial with the engine, and the ISG motor has higher position accuracy, when the engine stops, the ISG motor drives and controls the engine to stop to the position where the resistance torque is the smallest ( 90°odd multiple position in Figure 1), and can ensure a high success rate of starting the engine with the ISG system.

It is different from the invention patent "Method for Controlling Engine Shutdown Position in Hybrid Electric Vehicle" (hereinafter referred to as: Search Invention) as follows:

1. For different purposes:

(1) Retrieval invention: the stop position is controlled to reduce the torque fluctuation and vibration generated during the intake, compression and expansion strokes when the engine is started.

(2) In the present invention, the engine is stopped at the position where the engine resistance torque is the smallest through the ISG electric drive system, and when the engine is started next time, the engine is quickly dragged to the ignition speed with the minimum electric energy and the shortest start-up time; thereby Improve the starting success rate of the engine under various working conditions (including low temperature), and shorten the starting time.

2. The goals of control are different:

(1) Retrieval invention: every stop control will stop the engine to the same point.

(2) The present invention: for a multi-cylinder engine, within one circle of the engine, there are many points at the minimum position of the engine resistance torque, and each shutdown stops at the nearest point where the engine resistance torque is minimum;

3. Different control ideas:

(1) Retrieval invention: when the engine speed<the first speed, the engine speed decreases with a fixed slope, and the stop time is longer; the number of times the crank position matches the target stop position and the engine speed are used as the judgment conditions for stopping to the target position, because Engine inertia, there is a deviation between the stop position and the target position.

(2) The present invention: when the engine speed is less than the first speed, the difference between the target stop position and the current position of the engine is used in real time as the braking torque control input of the ISG electric system, and the closed-loop control engine speed reduction rate can be achieved in the shortest time. Stop the engine at the target position, theoretically the actual stop position and the target stop position can completely coincide, so that there is no static difference.

4. Different control methods

(1) Retrieval invention: the vehicle controller (HCU) collects the engine speed and crank position through CAN to calculate the braking torque of the ISG electric drive system, sends the braking torque to the motor controller through CAN, and the motor controller presses Stops the engine to a specified position with a given braking torque. Due to the limitation of CAN communication rate, the method in the literature has a large control delay, and the engine stop position belongs to angular position control, which requires high real-time control. The method in the literature is not effective in actual control.

(2) The present invention: according to the characteristics that the ISG motor is coaxial with the engine, and the ISG motor drive system has higher position accuracy and torque accuracy, the motor controller directly calculates the torque according to the current motor speed, angle and pre-stored engine torque table according to the angle Position closed-loop control algorithm to stop the engine to the target position. It has high real-time performance and control precision. The control algorithm is clear and clear, and has high feasibility.

Description of drawings

Figure 1 is the engine resistance curve.

Figure 2 is a block diagram of the engine stop position angle control based on the ISG system.

Figure 3 is a block diagram of the engine stop position angle control system based on the ISG system

Fig. 4 is a flow chart of determining engine stop position control based on the ISG system.

Fig. 5 is a flow chart of engine stop position control based on the ISG system.

Fig. 6 is a flow chart of the angle control of the engine stop position.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the present invention, in the main control CPU of the motor controller, the mapping table of the engine with angle and the resistance torque and the point (corresponding angle) of the minimum resistance torque of the engine in one mechanical cycle are prestored.

When the engine stops naturally (that is, the speed is zero), query the control point closest to the minimum engine resistance torque position according to the engine rotation direction, and set it as the target stop position, and then stop the engine at the designated position by controlling the ISG motor. The control principle block diagram and control system block diagram of the hybrid vehicle engine stop position control device based on the ISG system are shown in Figure 2 and Figure 3 respectively.

The method has a simple control method and is easy to realize in the ISG control system; the engine can be stopped to the target stop position within one engine cycle, and the angle control precision is high.

The present invention will be further described in detail below in conjunction with the control flow chart.

To realize the engine stop position control, it is first necessary to determine whether the engine is stopped. Only when the engine is stopped, the engine stop position control based on the ISG system can be executed. The specific engine stop position control determination process is shown in Figure 4.

Step 1) judge whether the current engine speed ω is lower than the minimum ignition speed ω _Max of the engine by the motor controller;

Step 2) If the current engine speed is lower than the minimum ignition speed, that is, ω<ω _Max , continue to judge whether the engine speed is 0;

Step 3) If the engine speed is 0, then enter the engine shutdown position control process;

The engine shutdown position control process is shown in Figure 5, and it includes the following steps:

Step 1) Determine the target stop position θ* of the engine according to the rotation direction of the current engine;

Step 2) Calculate the maximum speed ω _max in the process of controlling the stop position according to the determined target stop position, the specific calculation process is shown in formula (7);

Step 3) Set the engine acceleration flag, that is, F=1;

Step 4) The ISG system outputs the maximum assist torque Te _Max ;

Step 5) Determine whether the engine speed reaches the maximum speed controlled by the stop position, that is, ω≥ω _max ; if it does not reach the maximum speed controlled by the stop position, that is, ω<ω _max , then continue to step 4, and output the maximum assist torque Te _Max ; If ω≥ω _max , go to step 6;

Step 6) The engine acceleration flag is cleared, that is, F=0;

Step 7) enter the engine shutdown position angle control;

The engine stop position angle control process is shown in Figure 6, and it includes the following steps:

Step 1) judge whether the engine speed is not 0; if the engine speed is 0, the control process ends and returns; if the engine speed is not 0, enter step 2;

Step 2) Calculate the angle difference Δθ according to the current position θ of the motor and the target stop position θ ^* ;

Step 3) Judging whether the engine stops at the target stop position, that is, whether Δθ is 0; if Δθ=0, the control flow ends and returns; if Δθ≠0, then enter step 4;

Step 4) Calculate the braking torque Te according to the current engine speed ω and the angle difference Δθ, and output the braking torque.

The calculation method of the maximum rotational speed ω _max in the stop position control process mentioned in step 2 of the above-mentioned engine stop position control process is:

In the main control CPU of the motor controller, the mapping table of the engine with angle and the resistance torque and the point (corresponding angle) of the minimum resistance torque of the engine in one mechanical cycle are prestored.

When the ISG system outputs the maximum torque, the minimum angular acceleration of the power system is shown in formula (5).

${\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; Te</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}}{\mathrm{<span\; class="notranslate">\; J</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Where: β ₁ ——The minimum angular acceleration of the power system (rad/s ² )

Te _max —— ISG system output maximum torque (Nm)

M _max —— engine maximum resistance torque (Nm)

J——Composite moment of inertia of engine and ISG motor (kg m ² )

Under the minimum acceleration, the time required to stop the engine to the specified position is shown in formula (6). During the position adjustment control process, the corresponding maximum engine speed is ω _max .

$\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; J</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}}{{\mathrm{<span\; class="notranslate">\; Te</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Among them: t——the time required to stop the engine to the specified position (s)

Δθ——the angle difference between the current stop position and the target stop position (rad)

J——Composite moment of inertia of engine and ISG motor (kg m ² )

Te _max —— ISG system output maximum torque (Nm)

M _max —— engine maximum resistance torque (Nm)

${\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Te</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}}{\mathrm{<span\; class="notranslate">\; J</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them: ω _max ——the maximum motor speed during shutdown control (rad/s)

Δθ——the angle difference between the current stop position and the target stop position (rad)

J——Composite moment of inertia of engine and ISG motor (kg m ² )

Te _max —— ISG system output maximum torque (Nm)

M _max —— engine maximum resistance torque (Nm)

The calculation method of the required output braking torque Te mentioned in step 4 of the above-mentioned engine stop position angle control process is:

Since the upper limit speed is relatively low when the stop position is controlled, the movement resistance torque is ignored.

According to the relevant principles of kinematics:

Te(t)-M(θ)=J·β(1)

Among them: Te(t)——current electromagnetic torque of ISG motor (Nm)

M(θ)——Engine system resistance torque (Nm)

θ——ISG position angle/crankshaft position angle (rad)

J——Composite moment of inertia of engine and ISG motor (kg m ² )

β——angular acceleration (rad/s ² )

ω(t)＝ω ₀ +β·t(2)

Where: ω(t)——the angular velocity of the power system at the current moment (rad/s)

ω ₀ ——Initial angular velocity of the stop position control power system (rad/s)

β——angular acceleration (rad/s ² )

t——stop control elapsed time (s)

dθ=ω(t)dt(3)

Among them: dθ——angle variation (rad)

ω(t)——The angular velocity of the power system at the current moment (rad/s)

dt——the amount of time change

After the stop position control is over, the angular velocity of the power system ω=0, assuming that the angle change from the current position to the stop position is Δθ(t), combined with formulas (1), (2) and (3), the solution can be obtained as follows:

$\mathrm{<span\; class="notranslate">\; Te</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; J</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&Delta;\&theta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them: Te(t)——current electromagnetic torque of ISG motor (Nm)

M(θ)——Engine system resistance torque (Nm)

θ——ISG position angle/crankshaft position angle (rad)

J——Composite moment of inertia of engine and ISG motor (kg m ² )

ω ₀ ——Initial angular velocity of the stop position control power system (rad/s)

Δθ(t)——Angle change from the current position to the stop position (rad)

The above method adopts the angle closed-loop tracking control, and the angle control accuracy is high. After the engine stop position control is adopted, the success rate of the ISG system to start the engine can be improved and the time to start the engine can be shortened.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (1)

1. A method for controlling the stop position of an automobile engine, characterized in that it may further comprise the steps: Step 1) judge whether the current engine speed ω is lower than the minimum ignition speed ω _Max of the engine by the motor controller; Step 2) If the current engine speed is lower than the minimum ignition speed, that is, ω<ω _Max , continue to judge whether the engine speed is 0; Step 3) If the engine speed is 0, then enter the engine shutdown position control process; Said step 3) in the engine shutdown position control procedure, comprises the following steps: Step 31) Determine the target stop position θ* of the engine according to the rotation direction of the current engine; Step 32) Calculate the maximum motor speed ω _max during the shutdown control process according to the determined target shutdown position. The specific calculation process is shown in the following formula: ${\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Te</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; J</span>}}}<span\; class="notranslate">\; ,</span>$ Among them: ω _max ——the maximum motor speed during shutdown control (rad/s); Δθ—the angle difference between the current stop position and the target stop position (rad); J——combined moment of inertia of engine and ISG motor (kg m ² ); Te _max - the maximum torque output by the ISG system (Nm); M _max —— maximum engine resistance torque (Nm); Step 33) set the engine acceleration flag, that is, F=1; Step 34) The ISG system outputs the maximum torque Te _max ; Step 35) Judging whether the engine speed reaches the maximum motor speed in the shutdown control process, that is, ω≥ω _max ; if it does not reach the maximum motor speed in the shutdown control process, that is, ω<ω _max , then continue to step 34), and the ISG system outputs Maximum torque Te _max ; if ω≥ω _max , enter step 36); Step 36) The engine acceleration flag is cleared, that is, F=0; Step 37) Enter the engine stop position angle control; Said step 37) in the engine shutdown position angle control procedure, comprises the following steps: Step 371) judge whether the engine speed is not 0; if the engine speed is 0, then the control process ends; if the engine speed is not 0, enter step 372); Step 372) Calculate the angle difference Δθ according to the current position θ of the motor and the target stop position θ ^* ; Step 373) judging whether the engine stops at the target stop position, that is, whether Δθ is 0; if Δθ=0, the control flow ends; if Δθ≠0, then enter step 374); Step 374) Calculate the braking torque Te according to the current engine speed ω and the angle difference Δθ, and output the braking torque.