JP7565761B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device that controls an internal combustion engine mounted on a vehicle, etc.

When an internal combustion engine that has been running is stopped, fuel injection and ignition combustion in the cylinders are stopped, but the crankshaft continues to rotate by inertia, and the pistons and crankshaft eventually come to a stop in a position where the rotational torque caused by the internal pressure of each cylinder is balanced.

In an in-line three-cylinder internal combustion engine, rotation often stops halfway between the compression top dead center of one cylinder and the compression top dead center of the next cylinder. At this time, the remaining cylinder is near the exhaust top dead center, and both the intake valve and exhaust valve of that cylinder are open, creating a valve overlap state.

When the internal combustion engine is stopped in a valve overlap state, the exhaust passage and the intake passage are connected via that cylinder, and exhaust gas remaining in the exhaust passage can flow back into the intake passage due to the temperature difference between the atmosphere in the exhaust passage and the atmosphere in the intake passage, natural wind blowing into the exhaust passage from the muffler, and other factors. This causes an oxygen deficiency in the atmosphere in the intake passage. If an attempt is made to start the internal combustion engine again under such circumstances, the amount of oxygen supplied to the cylinder during cranking is insufficient, the fuel does not ignite and burn properly, and sufficient engine torque is not generated to accelerate the rotation of the crankshaft, resulting in a start delay, i.e., a significantly longer cranking time.

One way to prevent this from happening, in other words to avoid the internal combustion engine stopping during a valve overlap state, is to generate electricity at the appropriate time using a generator (alternator) that is driven by the internal combustion engine to brake the crankshaft (see, for example, Patent Document 1 below). However, generators generate electromotive force through electromagnetic induction, and do not generate electricity, and therefore a load, unless the rotational speed is high enough. Therefore, in reality, it is difficult to obtain a large braking force just before the internal combustion engine stops.

It is possible to rotate the crankshaft using an electric motor (starter motor, cell motor) after the crankshaft stops rotating (see, for example, Patent Document 2 below). However, this method is premised on the ability to accurately sense the rotation angle of the crankshaft, in other words, the current position of the pistons in each cylinder, even just before the internal combustion engine stops. In order to grasp the final stopping position or posture of the crankshaft as it repeats forward and reverse rotations until it comes to a complete stop, it is essential to employ an advanced sensor that can detect both the forward and reverse rotation angles. Moreover, the increased frequency of starting the electric motor leads to disadvantages such as a decrease in the vehicle's NV (Noise and Vibration) performance and a shortened lifespan of the electric motor.

JP 2004-218449 A JP 2016-008552 A

The present invention aims to simply and reliably prevent the crankshaft of an internal combustion engine from stopping rotating when both the intake valve and exhaust valve of any cylinder are open, resulting in valve overlap.

In order to solve the above-mentioned problems, in the present invention, when stopping an in-line three-cylinder internal combustion engine, a throttle valve installed in an intake passage is fully closed or reduced to a nearly fully closed position to increase the intake negative pressure downstream of the throttle valve in the intake passage (or decrease the intake air pressure), and based on the current magnitude of kinetic energy or rotation speed of a crankshaft rotating by inertia, a prediction is made as to how many angles the crankshaft will rotate until its rotation stops, and based on the result of the prediction, a prediction is made as to whether the intake valve of any one of the cylinders will close. If it is determined that the rotation of the crankshaft will stop before the intake valve of another cylinder closes and the final timing for the intake valve to close is reached, the control device for an internal combustion engine is configured to increase the opening of the throttle valve at the timing when the intake valve of the one cylinder predicted to have the final opportunity to close the intake valve closes , and to make the intake negative pressure during the intake stroke of the other cylinder which will next enter the intake stroke and open its intake valve smaller than (or make the intake pressure larger than) the intake negative pressure during the intake stroke of the one cylinder which recently finished its intake stroke and whose intake valve was closed.

More specifically, each time the crankshaft rotates by a predetermined angle D while rotating by inertia, the current rotation speed N of the crankshaft is measured, and based on the currently measured rotation speed _Ni and the previously measured rotation speed Ni _-1 , the angle A through which the ^crankshaft will rotate until it stops is estimated as A = D x _Ni2 / (N _i-1 ² - _Ni2 ). When comparing ^this with the angle B through which the crankshaft rotates from the time the intake valve of one cylinder closes to the time the intake valve of the next cylinder closes, if A ≤ B is satisfied, it is determined that the crankshaft will stop rotating before the intake valve of one cylinder closes for the final time and before the intake valve of another cylinder closes .

In addition, in the present invention, when stopping an in-line three-cylinder internal combustion engine, an operation is performed to fully close a throttle valve installed in an intake passage or reduce the opening to a position close to fully closed to increase the intake negative pressure downstream of the throttle valve in the intake passage (or reduce the intake air pressure), and based on the current magnitude of kinetic energy or rotational speed of the crankshaft rotating by inertia, a prediction is made as to how many angles the crankshaft will rotate until its rotation stops. As a result of the prediction, it is determined that the final timing for the intake valve of any one cylinder to close has arrived and that the rotation of the crankshaft will stop before the intake valve of another cylinder closes, and if the intake negative pressure downstream of the throttle valve at that time is higher than a predetermined value (or the intake air pressure is lower than a predetermined value), the opening of the throttle valve is increased at the timing for the intake valve of the one cylinder predicted to have the final opportunity to close the intake valve. and then performs an operation to make the intake negative pressure during the intake stroke of the other cylinder which next enters the intake stroke and opens its intake valve smaller than the intake negative pressure during the intake stroke of the one cylinder which recently finished its intake stroke and closed its intake valve (or makes the intake pressure larger); however, if it is not determined that the crankshaft will stop rotating before the intake valve of the other cylinder is closed when the intake valve of any one cylinder is closed for the last time, or if it is determined that the crankshaft will stop rotating before the intake valve of the other cylinder is closed for the last time, the intake negative pressure downstream of the throttle valve is lower than the predetermined value (or the intake pressure is higher than the predetermined value) when the intake valve of any one cylinder is closed for the last time and it is determined that the crankshaft will stop rotating before the intake valve of the other cylinder is closed, the control device for an internal combustion engine is configured not to perform an operation to increase the opening of the throttle valve at the timing when the intake valve of the one cylinder which is predicted to have a last opportunity to close the intake valve is closed .

The present invention makes it possible to easily and reliably prevent the crankshaft of an internal combustion engine from stopping rotating when both the intake valve and exhaust valve of any cylinder are open, resulting in valve overlap.

1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; 2 is a diagram showing the stroke of each cylinder of the internal combustion engine according to the embodiment, and pulse trains of a crank angle signal and a cam angle signal. FIG. 4 is a flowchart showing an example of a processing procedure executed by the control device according to a program of the embodiment. 5 is a diagram for supplementary explanation of a calculation formula for an estimated remaining rotation angle A calculated by the control device of the embodiment. FIG. 5 is a diagram for explaining the control action by the control device of the embodiment; FIG. 5 is a diagram for explaining the control action by the control device of the embodiment; FIG.

One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overview of an internal combustion engine for a vehicle in this embodiment. The internal combustion engine in this embodiment is a spark-ignition four-stroke reciprocating engine, and has multiple cylinders 1 (e.g., three cylinders, one of which is shown in FIG. 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1. In addition, an ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 generates a spark discharge between a center electrode and a ground electrode when an induced voltage generated by an ignition coil is applied to the ignition plug 12.

The intake passage 3 for supplying intake air takes in air from the outside and directs it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream on the intake passage 3.

The exhaust passage 4 for discharging exhaust gases guides exhaust gases generated as a result of burning fuel in the cylinders 1 from the exhaust ports of each cylinder 1 to the outside. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gases are arranged on this exhaust passage 4.

The exhaust gas recirculation device 2 includes an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined location downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3 (in particular, the surge tank 33 or the intake manifold 34).

The ECU (Electronic Control Unit) 0, which is the control device for the internal combustion engine in this embodiment, is a microcomputer system having a processor, memory, an input interface, an output interface, etc. The ECU 0 may be configured by connecting multiple ECUs or controllers so that they can communicate with each other via an electric communication line such as a CAN (Controller Area Network).

The input interface of the ECU 0 receives a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft of the internal combustion engine and the engine speed, an accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as the accelerator opening (in other words, the engine torque or engine load factor required for the internal combustion engine), and a signal from the intake passage 3 (particularly the surge tank 33 or the intake manifold 34) connected to the cylinder 1. ), an intake air temperature/intake pressure signal d output from a temperature/pressure sensor that detects the intake air temperature and intake pressure in the engine, a cooling water temperature signal e output from a water temperature sensor that detects the cooling water temperature of the internal combustion engine, an air-fuel ratio signal f output from an air-fuel ratio sensor that detects the air-fuel ratio of the gas discharged from the cylinder 1 and flowing through the exhaust passage 4, a cam angle signal g output from a cam angle sensor at multiple cam angles of the intake camshaft or exhaust camshaft that drives the opening and closing of the intake and exhaust valves 13, 14 of each cylinder 1, and an atmospheric pressure signal h output from an atmospheric pressure sensor that detects the atmospheric pressure.

The crank angle sensor senses the rotation angle of a rotor that rotates together with the crankshaft. Teeth or protrusions are formed on the rotor at predetermined intervals along the direction of rotation of the crankshaft. Typically, a tooth or protrusion is placed every 10° of rotation of the crankshaft. The crank angle sensor faces the outer periphery of the rotor, detects when each tooth or protrusion passes near the sensor, and emits a pulse signal as a crank angle signal b each time.

However, 36 pulses are not output during one rotation of the crankshaft. Some teeth or protrusions on the crankshaft rotor are missing, and due to these missing teeth, some pulses are also missing from the pulse train of the crank angle signal b. For example, as shown in FIG. 2, the 17th, 18th, 20th, 21st, 35th, and 36th pulses are missing. Based on these missing pulses, ECU0 determines the absolute angle and position of the current crankshaft. If the timing of the first pulse following the missing 36th pulse is set to 0° CA (crank angle), then the timing of the 19th pulse following the missing 18th pulse will be 180° CA.

The cam angle sensor senses the rotation angle of a rotor that rotates together with the intake camshaft or exhaust camshaft. The rotor has teeth or protrusions formed at every angle calculated by dividing one rotation of the camshaft by the number of cylinders. In the case of a three-cylinder internal combustion engine, a tooth or protrusion is provided for every 120° rotation of the camshaft. The camshaft rotates by receiving torque transmitted from the crankshaft via a winding transmission mechanism or the like, and its rotation speed is half that of the crankshaft. Therefore, the above teeth or protrusions are provided every 240° CA when converted into crank angles. In addition, the rotor has one tooth or protrusion between the teeth or protrusions every 240° CA to generate an additional cam angle signal g.

The cam angle sensor faces the outer circumference of the rotor, detects each tooth or protrusion passing near the sensor, and transmits a pulse signal as a cam angle signal g each time. As shown in FIG. 2, the cam angle signal g indicates the timing near the compression top dead center of each cylinder 1, or a timing biased to the advance side by a certain crank angle from the compression top dead center. The ECU 0 refers to the crank angle signal b and the cam angle signal g to obtain the current stroke of each cylinder 1 and the position of the piston 15. Incidentally, in an internal combustion engine equipped with a so-called phase-changing variable valve timing mechanism, the cam angle signal g also indicates the opening and closing timing of the intake valve 13 or exhaust valve 14 adjusted by the VVT mechanism.

The output interface of ECU0 outputs an ignition signal i to the igniter 13 of the spark plug 12, a fuel injection signal j to the injector 11, an opening operation signal k to the throttle valve 32, an opening operation signal l to the EGR valve 23, etc.

The processor of ECU0 interprets and executes programs stored in memory in advance, and calculates operating parameters to control the operation of the internal combustion engine. ECU0 acquires various pieces of information a, b, c, d, e, f, g, and h required for controlling the operation of the internal combustion engine via the input interface, and estimates the amount of air (fresh air) drawn into cylinder 1 while learning the engine speed and accelerator opening. It then determines various operating parameters such as the required fuel injection amount appropriate to the amount of intake air, the fuel injection timing (including the number of fuel injections per combustion), the fuel injection pressure, the required EGR rate (or the amount of EGR gas), and the ignition timing (including the number of spark ignitions per combustion). ECU0 applies various control signals i, j, k, and l corresponding to the operating parameters via the output interface.

As shown in FIG. 3, when stopping an internal combustion engine that has been operating (step S1), the ECU 0 of this embodiment stops fuel injection from the injector 11 and spark ignition by the spark plug 12 (step S2). The trigger for stopping the operation of the internal combustion engine is typically when the driver of the vehicle turns the ignition switch (ignition key or power switch) from ON to OFF.

At the same time, the ECU 0 closes the throttle valve 32 in the intake passage 3 completely or closes it to a predetermined opening degree close to being completely closed (step S3). The purpose of reducing the opening degree of the throttle valve 32 is to increase the intake negative pressure downstream of the throttle valve 32 in the intake passage 3, in other words, to reduce the intake pressure in the intake passage 3 connected to the cylinder 1. This increases the pumping loss of the internal combustion engine, and the inertial rotation of the crankshaft is braked.

The load on the auxiliary equipment associated with the internal combustion engine is set to zero (step S4). The auxiliary equipment is, for example, an air conditioner refrigerant compressor or a generator that operates by receiving engine torque from the crankshaft of the internal combustion engine. In step S4, the clutch between the crankshaft and the compressor is disengaged, and the power (or output voltage or current) generated by the generator is set to zero. This step S4 keeps the mechanical load acting on the crankshaft constant while the crankshaft is rotating by inertia, thereby improving the accuracy of the prediction of the remaining rotation angle A in step S5 below.

Then, based on the current magnitude of kinetic energy or rotational speed of the crankshaft rotating by inertia, ECU0 predicts how many angles the crankshaft will rotate until it stops rotating (step S5).

Step S5 is performed each time the crankshaft rotates a predetermined angle D. The predetermined angle D is set to, for example, an angle obtained by dividing 720° CA, which corresponds to one cycle of cylinder 1 (a series of intake stroke-compression stroke-expansion stroke-exhaust stroke), by the number of cylinders 1. In a three-cylinder internal combustion engine, the predetermined angle D is 240° CA. By doing so, step S5 is performed at the same timing during the same stroke of each cylinder 1, and the prediction of the remaining rotation angle is stabilized, that is, the prediction accuracy is increased. However, step S5 can be performed at any time. It is also permissible to set the predetermined angle D to an angle smaller than 240° CA. It is preferable to perform step S5 at the timing when the intake valve 13 of each cylinder 1 closes or at a timing close to the timing. The closing timing of the intake valve 13 of each cylinder 1 can be obtained by referring to the crank angle signal b and the cam angle signal g.

In step S5, the ECU 0 measures the current rotation speed N of the crankshaft by referring to the crank angle signal b. Then, from the currently measured rotation speed N _i and the previously measured rotation speed N _i-1 (i.e., 240° CA ago), the ECU 0 calculates a predicted angle A of the crankshaft until it stops, as follows:
A=D×N _i ² /(N _i-1 ² −N _i ² )
It is estimated as follows.

A supplementary note on the above formula relating to the remaining rotation angle A. As shown in Figure 4, let us imagine a situation in which an object with mass M is on an uphill road with a gradient angle α and slides diagonally upward along the uphill road. A weight G acts vertically downward on the object, and a kinetic friction force F acts diagonally downward along the uphill road. When the object is at horizontal position _X1 , it has a speed _V'1 along the uphill road, and then it displaces to horizontal position _X2 , at which point its speed along the uphill road is _V'2 . In the process in which the object displaces from horizontal position _X1 to horizontal position _X2 along the uphill road, the increment U of the object's potential energy is U = MG( _X2 - _X1 ) tan α
and the friction loss L is L = F(X ₂ -X ₁ )/cos α
The difference between the kinetic energy that an object has when it is at horizontal position _X1 and the kinetic energy that the object has when it is at horizontal position _X2 means the kinetic energy that the object loses in moving from horizontal position _X1 to horizontal position _X2 along an uphill road. According to the law of conservation of energy, the difference is equal to the sum of the increment U of potential energy and the friction loss L. In other words,
(MV' ₁ ² /2) - (MV' ₂ ² /2) = (X ₂ - X ₁ ) (MGtanα-F/cosα)
The kinetic energy that the object possesses when it is at horizontal position _X2 is ( _MV'22 / ² ), and the kinetic energy that this object loses as it displaces the horizontal distance ( _X1 - _X2 ) along the uphill road is ( _X2 - _X1 )(MGtanα-F/cosα). Then, the remaining horizontal distance A that an object at horizontal position _X2 can travel before coming to a complete stop is:
A ⁼ (X ₂ - X ₁ ) (MV' ₂ ² /2) _/ {(X _{2 - X 1} ) (MGtanα-F ^{/ cos} α)} = ( _{X 2} -
If the velocities _V'1 and _V'2 directed obliquely upward along the uphill road are converted to horizontal velocities _V1 and _V2 , respectively, we get
V ₁ = V' ₁ cos α
_V2 = _V'2 cos α
Therefore,
A=(X ₂ -X ₁ )V ₂ ² /(V ₁ ² -V ₂ ² )
holds. If (X ₂ -X ₁ ) is replaced with D, V ₂ with N _i , and V ₁ with N _i-1 , the above equation relating to the remaining rotation angle A of the crankshaft is obtained. At least in the section of 240° CA just before the rotation of the crankshaft stops, it can be understood as being approximately equivalent to such a physical system. Of course, in reality, the sliding friction between the inner wall of the cylinder bore of the cylinder 1 and the piston ring, and the sliding friction between the crankshaft and camshaft and the bearings that support them, etc. change depending on the lubricating oil temperature, lubricating oil pressure, oil film thickness, etc.

Then, ECU0 compares the remaining rotation angle A of the crankshaft estimated in the most recent step S5 with a threshold value B (step S6). Threshold value B is the angle by which the crankshaft rotates from when the intake valve 13 of one cylinder 1 closes until the intake valve 13 of the next cylinder 1 closes, or an angle close to that angle. Typically, angle B is 720° CA divided by the number of cylinders 1, or 240° CA for a three-cylinder internal combustion engine. Step S6 is also performed each time the crankshaft rotates a predetermined angle D. Steps S5 and S6 may be performed simultaneously or approximately simultaneously.

The fact that the remaining rotation angle A of the crankshaft is greater than the threshold value B means that there will be at least one more intake valve 13 closing timing for any of the cylinders 1 before the crankshaft stops rotating, i.e., this is not the last opportunity for the intake valve 13 to close.

On the other hand, the remaining rotation angle A of the crankshaft being smaller than the threshold value B means that this is the last opportunity to close the intake valve 13. After that, the intake valve 13 of another cylinder 1 may open, but the rotation of the crankshaft stops before that intake valve 13 closes. When the ECU 0 of this embodiment determines that A≦B is established in step S6, it performs an operation to increase the opening of the throttle valve 32, which has been closed or reduced in opening, as soon as possible (step S7). The purpose of increasing the opening of the throttle valve 32 is to reduce the intake negative pressure downstream of the throttle valve 32 in the intake passage 3, in other words, to increase the intake pressure in the intake passage 3 connected to the cylinder 1. In step S7, it is not necessary to open the throttle valve 32 to its full opening.

On the other hand, if it is determined that A≦B does not hold, the opening of the throttle valve 32 is kept unchanged and steps S5 and S6 are repeated again.

Step S7 for opening the throttle valve 32 is preferably performed at or near the timing when the intake valve 13 of the cylinder 1 that will have the last opportunity to close the intake valve 13 closes. Step S6 for determining whether or not it is the last opportunity to close the intake valve 13 may be performed at any time between step S5 for predicting the remaining rotation angle and step S7 for opening the throttle valve 32, but is preferably performed at or near the timing when the intake valve 13 of each cylinder 1 closes. In general, it can be said that it is ideal to perform steps S5, S6, and S7 simultaneously or approximately simultaneously.

The significance of steps S3 to S7 will now be described. If steps S3 to S7 were not performed, i.e., if the inertial rotation of the crankshaft were simply stopped without changing the opening of the throttle valve 32 midway, the rotation would often stop at an intermediate position (e.g., crank angle 360° CA in FIG. 3) between the compression top dead center of a certain cylinder (e.g., the third cylinder) 1 and the compression top dead center of the following next cylinder (e.g., the first cylinder) 1, as shown diagrammatically in FIG. 5. The former cylinder (the third cylinder) 1 is in the latter part of the expansion stroke, and the latter cylinder (the first cylinder) 1 is in the early part of the compression stroke, and the intake valve 13 and exhaust valve 14 of both cylinders 1 are closed. The amount of intake air filling each cylinder 1 is roughly the same, and the pressure inside each cylinder 1 is balanced, so the crankshaft comes to rest at a position where the height (or cylinder volume) of the piston 15 in the former cylinder 1 is roughly equal to that of the latter cylinder 1.

At this time, the remaining cylinder (e.g., the second cylinder) 1 is near exhaust top dead center, i.e., between the exhaust stroke and the intake stroke, and the intake valve 13 and exhaust valve 14 of the cylinder 1 are both open in a valve overlap state. If this happens, the exhaust passage 4 and the intake passage 3 will communicate through the cylinder 1 while the internal combustion engine is stopped, and gas containing almost no oxygen will flow back from the exhaust passage 4 into the intake passage 3. If this happens, the atmosphere in the intake passage 3 will become oxygen-deficient, and the amount of oxygen supplied to the cylinder 1 when the internal combustion engine is later restarted will be insufficient, which could lead to a start delay, i.e., a significantly longer cranking time.

Therefore, in this embodiment, through steps S3 to S7, the throttle valve 32 on the intake passage 3 is closed or its opening is narrowed until the closing timing of the last intake valve 13 arrives, and the opening of the throttle valve 32 is expanded immediately after the closing timing of the last intake valve 13 arrives. If the opening of the throttle valve 32 is narrowed until the intake valve 13 of a certain cylinder (e.g., the third cylinder) 1 closes and the throttle valve 32 is expanded immediately thereafter, a larger amount of intake air can be filled into another cylinder (e.g., the first cylinder) 1 that will enter its next intake stroke and open its intake valve 13, compared to the cylinder (the third cylinder) 1 that recently finished its intake stroke and closed its intake valve 13. In other words, the intake negative pressure during the intake stroke of the former cylinder (third cylinder) 1 is larger (the intake air pressure is lower), and the intake negative pressure during the intake stroke of the latter cylinder (first cylinder) 1 is smaller (the intake air pressure is higher and closer to atmospheric pressure). Therefore, the crankshaft stops rotating before or after the intake valve 13 of the latter cylinder 1 closes.

As a result, as shown diagrammatically in FIG. 6, the crankshaft comes to rest at a position where the height (or in-cylinder volume) of the piston 15 of the former cylinder 1 is unequal to that of the latter cylinder 1. This makes it possible to avoid a valve overlap state in which both the intake valve 13 and exhaust valve 14 of the remaining cylinder 1 (e.g., the second cylinder) are open.

The above action is premised on the assumption that the intake negative pressure becomes sufficiently large (the intake air pressure decreases) when the throttle valve 32 is fully closed or reduced to a nearly fully closed position. However, depending on the operating range before the internal combustion engine is stopped, the intake negative pressure may not become sufficiently large even when the throttle valve 32 is fully closed. Therefore, even if the condition A≦B in step S6 is satisfied, if the intake negative pressure at that time is lower than a predetermined value (or the intake air pressure is higher than a predetermined value), step S7 of increasing the opening of the throttle valve 32 is not performed, and the throttle valve 32 is kept fully closed or nearly closed while waiting for the crankshaft to stop rotating. The intake air pressure downstream of the throttle valve 32 in the intake passage 3 can be obtained by referring to the intake air pressure signal d.

Even if the condition A≦B is satisfied, the closed throttle valve 32 is not opened if the intake negative pressure at that time is lower than a predetermined value for the following reasons. First, if the throttle valve 32 is left closed, even if the crankshaft rotates in the reverse direction just before it stops and the closed intake valve of cylinder 1 opens again, the difference in cylinder pressure between cylinders 1 is likely to remain, making it less likely that the internal combustion engine will stall near the exhaust top dead center of any of cylinders 1.

Secondly, it is possible to suppress the occurrence of vibration when the internal combustion engine comes to a stop. The mechanism by which vibration occurs when the internal combustion engine is stopped is as follows:
[i] Suppose that while the crankshaft is rotating by inertia, it stops briefly just before the top dead center of the compression stroke of the first cylinder 1, and then the crankshaft starts rotating in the reverse direction due to the reaction force that the piston receives from the compressed air in the first cylinder 1. At this time, the exhaust valve 14 of the second cylinder 1, which is in the exhaust stroke, opens, and the pressure inside the second cylinder 1 is no longer negative.
[ii] Depending on the position of the piston of each cylinder 1 when the inertial rotation of the crankshaft is temporarily stopped, the crankshaft may rotate in the reverse direction, causing the intake valve of the first cylinder 1, which was closed at the compression stroke, to reopen. If step S7 has already been performed to open the throttle valve 32 at the time the intake valve of the first cylinder 1 reopens, the internal pressure of the first cylinder 1 will no longer be negative.
[iii] Meanwhile, in the third cylinder 1 during the expansion stroke, the air is compressed by the reverse rotation of the crankshaft. The reaction force that the piston receives from the compressed air causes the crankshaft to change from reverse rotation to forward rotation.
[iv] When the crankshaft changes from reverse rotation to forward rotation, the air is compressed in the first cylinder 1, which is in the compression stroke. The reaction force that the piston receives from the compressed air causes the crankshaft to change from forward rotation to reverse rotation.
[v] Through the above process, the crankshaft rotates in the forward and reverse directions several times before coming to a complete stop. This repetition causes little attenuation of the energy per reciprocation, resulting in large vibrations in the internal combustion engine that cannot be ignored.
If the throttle valve 32 is not opened (closed) at the point [ii] above, the recompression of the air due to the compression stroke of the first cylinder 1 in [iv] above and the repeated forward and reverse rotation of the crankshaft are prevented, and large vibrations in the internal combustion engine are prevented.

According to this embodiment, when the operation of the internal combustion engine is stopped, it is possible to effectively avoid the crankshaft from stopping in a valve overlap state in which both the intake valve 13 and the exhaust valve 14 of any one of the cylinders 1 are open.

The control of this embodiment can be achieved at low cost without the need for adding new hardware, such as an advanced crank angle sensor capable of detecting both forward and reverse rotation angles.

The remaining rotation angle A is estimated taking into account the degree of decrease in the rotation speed of the crankshaft, which changes from moment to moment during inertial rotation, and the opening of the throttle valve 32 is controlled accordingly, allowing the crankshaft to stop in an appropriate position that does not result in valve overlap, while also dealing with individual differences in internal combustion engines, including aging, and differences in environmental conditions at any given time.

The present invention is not limited to the embodiment described above. For example, the threshold value B to be compared with the remaining rotation angle A in step S6 may be increased or decreased depending on the magnitude of the intake negative pressure at that time and other factors.

The number of cylinders in an internal combustion engine to which the present invention is applicable is not limited to three cylinders.

In addition, the specific configuration of each part and the processing procedures can be modified in various ways without departing from the spirit of the present invention.

The present invention can be used to control internal combustion engines installed in vehicles, etc.

0...Control unit (ECU)
1: cylinder; 13: intake valve; 14: exhaust valve; 3: intake passage; 32: throttle valve; 33: surge tank; 34: intake manifold; 4: exhaust passage; b: crank angle signal; d: intake pressure signal; g: cam angle signal; k: opening operation signal;

Claims (3)

When stopping an in-line three-cylinder internal combustion engine,
A throttle valve installed in an intake passage is fully closed or reduced in opening to a degree close to being fully closed to increase the intake negative pressure downstream of the throttle valve in the intake passage,
Based on the current magnitude of kinetic energy or rotation speed of the crankshaft rotating by inertia, a prediction is made of the angle by which the crankshaft will rotate until the rotation stops.
If the prediction determines that the crankshaft rotation will stop before the intake valve of one of the cylinders closes and the intake valve of another cylinder closes, the control device for an internal combustion engine increases the opening of the throttle valve at the timing when the intake valve of the one of the cylinders predicted to have the last opportunity to close will close , and makes the intake negative pressure during the intake stroke of the other cylinder which will next enter the intake stroke and open its intake valve smaller than the intake negative pressure during the intake stroke of the one of the cylinders which recently completed its intake stroke and whose intake valve was closed. Each time the crankshaft rotates by a predetermined angle D while rotating by inertia, the current rotation speed N of the crankshaft is measured;
Based on the rotation speed N _i measured this time and the rotation speed N _i-1 measured last time, the angle A of rotation until the crankshaft stops is calculated as A = D x N _i ² / (N _i-1 ² - N _i ² ).
The angle A is estimated as follows, and compared with the angle B of the crankshaft rotation from when the intake valve of one cylinder closes to when the intake valve of the next cylinder closes, A≦B.
2. The control device for an internal combustion engine according to claim 1, wherein, when the above expression is satisfied, it is determined that the rotation of the crankshaft will stop when the final timing for closing the intake valve of any one cylinder is reached and before the intake valve of another cylinder is closed. When stopping an in-line three-cylinder internal combustion engine,
A throttle valve installed in an intake passage is fully closed or reduced in opening to a degree close to being fully closed to increase the intake negative pressure downstream of the throttle valve in the intake passage,
Based on the current magnitude of kinetic energy or rotation speed of the crankshaft rotating by inertia, a prediction is made of the angle by which the crankshaft will rotate until the rotation stops.
If it is determined that the crankshaft rotation will stop before the intake valve of one of the cylinders closes and the intake valve of another cylinder closes as a result of the prediction, and the intake negative pressure downstream of the throttle valve at that time is higher than a predetermined value, the opening of the throttle valve is enlarged at the timing when the intake valve of the one cylinder predicted to have the last opportunity to close the intake valve closes , and the intake negative pressure during the intake stroke of the other cylinder which will next enter the intake stroke and open its intake valve is made smaller than the intake negative pressure during the intake stroke of the one cylinder which recently finished its intake stroke and whose intake valve closed,
A control device for an internal combustion engine that does not perform an operation to increase the opening of the throttle valve at the timing when the intake valve of one of the cylinders is predicted to have a final opportunity to close, if it has not determined that the crankshaft will stop rotating before the intake valve of the other cylinders closes, or if it has determined that the intake valve of one of the cylinders is final to close and that the crankshaft will stop rotating before the intake valve of the other cylinders closes , and

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