JP2014206075A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, which avoids a problem that the re-startability of the internal combustion engine is deteriorated by the back flow of an exhaust gas to an intake passage while the engine is stopping.SOLUTION: A control device for an internal combustion engine is characterized in that, when an air/fuel ratio detected by an air/fuel ratio sensor disposed in a discharged passage changes toward a rich side after the internal combustion engine is stopped, it is determined that a backflow state, in which an exhaust gas on the downstream side of said air/fuel ratio sensor flows to an upstream side has occurred, thereby to start the internal combustion engine.

Description

  The present invention relates to a control device for an internal combustion engine mounted on a vehicle.

  2. Description of the Related Art An idling stop system that improves fuel efficiency by stopping idle rotation of an internal combustion engine when a vehicle is temporarily stopped, such as waiting for a signal, is well known.

  For example, when a vehicle with an idling stop is stopped, a strong wind blows from the rear of the vehicle, and the exhaust gas staying in the exhaust passage may flow backward to the upstream side.

  While the internal combustion engine is stopped, both the intake valve and the exhaust valve may be held open in any cylinder. In this case, the exhaust gas that flows backward reaches the intake passage.

  Then, when the internal combustion engine is started next time, intake air including exhaust gas that has flowed back flows into the combustion chamber of the cylinder. Therefore, combustion at the start of starting becomes unstable, and there is a problem that it takes time to start the internal combustion engine.

  In order to solve the above-mentioned problems, the intake valves and exhaust valves of each cylinder that can be opened and closed independently by electromagnetic force are adopted, and these electromagnetic intake valves and exhaust valves are installed after the internal combustion engine is stopped. It has been considered that the exhaust gas is controlled to be closed to prevent the exhaust gas from flowing back into the intake passage (see, for example, Patent Document 1 below).

  In addition, an electric compressor is provided in the intake passage, and after the internal combustion engine is stopped, air is introduced from the intake passage side to the exhaust passage side to prevent the exhaust gas from flowing back into the intake passage. The thing which made it do is also considered (for example, refer the following patent document 2).

  However, separately providing an electromagnetic valve or an electric compressor has a problem that the cost is relatively high.

JP 2002-188471 A JP 2010-48139 A

  The present invention pays attention to the above points, and an object of the present invention is to avoid the problem that the restartability of the internal combustion engine deteriorates due to the exhaust gas flowing back to the intake passage while the engine is stopped.

  In the present invention, after the internal combustion engine is stopped, when the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage changes toward the rich side, the exhaust gas downstream of the air-fuel ratio sensor moves upstream. It is determined that a flowing back flow state has occurred, and the internal combustion engine is started.

  According to the present invention, it is possible to avoid the problem that the restartability of the internal combustion engine deteriorates due to exhaust gas flowing back to the intake passage while the engine is stopped.

The figure which shows the whole structure of the internal combustion engine for vehicles in one Embodiment of this invention. The timing diagram which shows the stroke of each cylinder in the internal combustion engine of the embodiment. Diagram showing an output characteristic of the air-fuel ratio sensor according to the embodiment (O ₂ sensor). The flowchart which shows the example of the procedure of the process which the control apparatus of the embodiment implements.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine of the present embodiment is a port injection type four-stroke spark ignition engine, and includes three cylinders 1 (one of which is shown in FIG. 1). These cylinders 1 are arranged in series, and as shown in FIG. 2, the compression top dead center of each cylinder 1 appears at equal intervals, that is, every 240 ° CA (crank angle).

  In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream. An intake valve 35 is arranged in the intake port. The intake valve 35 is biased toward the valve closing side by a valve spring.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4. An exhaust valve 43 is arranged in the exhaust port. The exhaust valve 43 is urged toward the valve closing side by a valve spring.

An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas is provided upstream and downstream of the catalyst 41, respectively. The air-fuel ratio sensor may be a linear A / F sensor having a linear output characteristic proportional to the air-fuel ratio of the gas, and outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas. O ₂ sensors 44 and 45 having non-linear output characteristics may be used. In the present embodiment, O ₂ sensors 44 and 45 are assumed for the air-fuel ratio sensors upstream and downstream of the catalyst 41. As is well known, as shown in FIG. 3, the output characteristics of the O ₂ sensors 44 and 45 show a large and steep slope with a large output change rate with respect to the air-fuel ratio in a certain range near the theoretical air-fuel ratio called a window. However, a so-called Z characteristic curve is drawn, which gradually approaches the low saturation value in the lean region where the air-fuel ratio is large, and gradually approaches the high saturation value in the rich region where the air-fuel ratio is small.

  FIG. 2 shows the stroke of each cylinder 1 in a three-cylinder four-stroke engine. In the three-cylinder engine, when one of the cylinders becomes the compression top dead center, the intake valve 35 or the exhaust valve 43 in the remaining two cylinders is largely opened, and the intake cam or the exhaust cam is released from the valves 35 and 43. It is in a state of receiving a strong reaction force. Therefore, after the internal combustion engine is stopped, the intake valve 35 and the exhaust valve 43 rarely stop at the timing near the compression top dead center of each cylinder 1.

  On the contrary, the intake valve 35 and the exhaust valve 43 are stopped at the timing when the reaction force received by the intake cam or the exhaust cam from the valves 35 and 43 is the smallest. Specifically, at the time between the compression top dead center of a certain cylinder and the compression top dead center of the cylinder that reaches the next compression stroke, that is, when any cylinder becomes exhaust top dead center, the remaining two The intake valve 35 and the exhaust valve 43 in one cylinder are closed, and the reaction force received by the intake cam and the exhaust cam from the valves 35 and 43 is the smallest. In the cylinder at the exhaust top dead center, both the intake valve 35 and the exhaust valve 43 are open, that is, the valve overlaps.

  The ECU 0 serving as a control device for the internal combustion engine is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal (N signal) b output from an engine rotation sensor that detects the rotation angle of the crankshaft 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 an accelerator opening, and a battery that is output from a sensor that detects the voltage (or battery current) of a vehicle-mounted battery A voltage signal d, an intake air temperature / intake air pressure signal e output from a temperature / pressure sensor for detecting intake air temperature and intake air pressure in the intake passage 3 (particularly, the surge tank 33), an internal combustion engine coolant (or coolant) ) Of the coolant temperature signal f output from the fluid temperature sensor for detecting the temperature of the intake camshaft or the exhaust camshaft. Cam angle signal (G signal) g output from the cam angle sensor at the center angle, shift range signal h output from the sensor (or shift position switch) for knowing the range of the shift lever, upstream of the catalyst 41 The signal p output from the front O ₂ sensor 44 for detecting the air-fuel ratio of the exhaust gas on the side, the signal q output from the rear O ₂ sensor 45 for detecting the air-fuel ratio of the exhaust gas downstream of the catalyst 41, etc. are input. Is done. The accelerator opening is a so-called required load. The coolant temperature of the internal combustion engine indicates the temperature of the internal combustion engine.

  From the output interface, an ignition signal i is output to the igniter of the spark plug 12, a fuel injection signal j is output to the injector 11, an opening operation signal k is output to the throttle valve 32, and the like.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 obtains various information a, b, c, d, e, f, g, h, p, q necessary for operation control of the internal combustion engine through the input interface, and knows the engine speed, and the cylinder 1 Estimate the amount of intake air to be filled. Based on the engine speed, the intake air amount, and the like, various operating parameters such as required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, and ignition timing are determined. As the operation parameter determination method itself, a known method can be adopted. The ECU 0 applies various control signals i, j, k corresponding to the operation parameters via the output interface.

  In addition, the ECU 0 inputs a control signal s to the electric motor (starter motor or motor generator) when the internal combustion engine is started (a cold start or a return from an idling stop). Cranking is performed by rotating the crankshaft. Cranking ends when the internal combustion engine reaches from the first explosion to the continuous explosion and the engine speed, that is, the rotation speed of the crankshaft, exceeds a judgment value determined according to the coolant temperature, etc. (assuming that the explosion has been completed) To do.

Further, the ECU 0 compares the output voltage p of the front O ₂ sensor 44 that detects the air-fuel ratio of the gas upstream of the catalyst 41 with a predetermined voltage determination value. If the output voltage p is higher than the determination value, the ECU 0 is rich. If it is lower, it is determined as lean.

Further, the ECU 0 compares the output voltage q of the rear O ₂ sensor 45 that detects the air-fuel ratio of the gas downstream of the catalyst 41 with a predetermined voltage determination value. If the output voltage q is higher than the determination value, the ECU 0 is rich. If it is lower, it is determined as lean.

Thus, ECU0 of this embodiment, after stop of the internal combustion engine, when the air-fuel ratio which is the front O ₂ sensor 44 provided in the exhaust passage 4 to detect changes toward the rich side, the front O ₂ sensor 44 It is determined that a reverse flow state in which the exhaust gas on the downstream side flows upstream is started, and the internal combustion engine is started.

  FIG. 4 shows a procedure example of processing executed by the ECU 0 according to a program at the time of idling stop.

  When the idle stop condition is satisfied (step S1), the ECU 0 starts an idle stop for stopping the fuel injection from the injector 11 and the ignition by the spark plug 12 in the cylinder 1 (step S2). In step S1, the vehicle speed of the vehicle is a predetermined value (for example, 9 km / h) or less, the shift position is the traveling range (in the case of an AT vehicle), the brake pedal is depressed, and the master cylinder pressure is a predetermined value (for example, , 0.7 MPa), in addition, the condition of the idling stop condition is satisfied because all the conditions such as the voltage of the in-vehicle battery is higher than the predetermined value and the cooling water temperature of the internal combustion engine is higher than the predetermined value are satisfied. to decide.

Immediately after the idling stop, the intake air in the intake passage 3 is sent to the exhaust passage 4 side through the combustion chamber in a state where fuel is not supplied. Therefore, the exhaust passage 42 on the upstream side of the catalyst 41 in the exhaust passage 4 immediately after the internal combustion engine is automatically stopped is in a state where the amount of oxygen is larger than that on the downstream side of the catalyst 41. That is, with the increase in the amount of oxygen due to the inflow of intake air from the intake passage 3 side, the amount of oxygen detected by the front O ₂ sensor 44 provided in the exhaust passage 4 becomes relatively large, and the air-fuel ratio of the gas in the exhaust passage 4 increases. Head to Lean.

During the idling stop, the ECU 0 determines whether or not the exhaust gas is flowing backward (step S3). When the exhaust gas flows backward from the downstream side of the catalyst 41 to the upstream side, the amount of oxygen on the upstream side of the catalyst 41 becomes extremely small. That is, along with the reduction in the amount of oxygen due to the exhaust backflow from the exhaust passage 4 (downstream of the catalyst 41), the amount of oxygen detected by the front O ₂ sensor 44 provided in the exhaust passage 4 becomes extremely small, and the inside of the exhaust passage 4 The air-fuel ratio of the gas goes to rich.

Accordingly, in step S3, the ECU 0 determines whether or not the air-fuel ratio detected by the front O ₂ sensor 44 provided in the exhaust passage 4 has changed toward the rich side.

For example, the air-fuel ratio has changed toward the rich side.
・ The air-fuel ratio has changed from lean to rich.
The amount of change Δp in the positive direction of the output voltage p of the front O ₂ sensor 44 becomes a predetermined value or more when the air-fuel ratio is lean
The air-fuel ratio is rich and the amount of change Δp in the positive direction of the output voltage p of the front O ₂ sensor 44 has become a predetermined value or more.
When either of the above is satisfied. Note that it may be determined that the air-fuel ratio has changed toward the rich side when the output voltage of the air-fuel ratio sensor becomes equal to or higher than a predetermined value (for example, 0.8 V).

That is, in step S3, the ECU 0 compares the output voltage p of the front O ₂ sensor 44 with a predetermined determination value, and determines whether or not it has become higher than this determination value. If it is higher than the determination value, the air-fuel ratio is rich, and if it is lower than the determination value, the air-fuel ratio is lean. Further, the ECU 0 determines whether or not the amount of change Δp in the positive direction of the output voltage p of the front O ₂ sensor 44 is a predetermined value or more.

When it is determined in step S3 that the air-fuel ratio detected by the front O ₂ sensor 44 provided in the exhaust passage 4 has changed toward the rich side, the intake valve 35 and the exhaust valve 43 are simultaneously open. If it occurs in any cylinder 1 (step S4), it is determined that the exhaust gas that has flowed back can reach the intake passage 3 (step S5). In step S4, the ECU 0 refers to both the crank angle signal (N signal) b and the cam angle signal (G signal) g, and stops the intake valve 35 and the exhaust valve in any cylinder 1 while the internal combustion engine is stopped. It is known whether or not 43 is a valve overlap opened simultaneously.

  If it is determined in step S5 that the intake valve 35 and the exhaust valve 43 are simultaneously open in at least one cylinder 1, the idle stop is terminated (step S7). Specifically, the internal combustion engine is cranked by engaging the pinion gear of the starter motor with the ring gear on the outer periphery of the flywheel (in the case of MT vehicle) or drive plate (in the case of AT vehicle), and the fuel from the injector 11 The internal combustion engine is restarted by restarting injection (and ignition).

  When it is determined No in step S3 or step S4, the ECU 0 determines whether an idle stop end condition is satisfied (step S6). When the idle stop termination condition is satisfied, the idle stop is terminated (step S7). In step S6, specifically, the shift position is changed to the non-traveling range (in the case of an AT vehicle), the depression of the brake pedal is loosened, and the master cylinder pressure is a lower judgment value for restart (for example, 0. 0). 1 MPa) or less, or conversely, the amount of depression of the brake pedal has been increased and the master cylinder pressure has risen above the high judgment value for restart, or the accelerator pedal has been depressed for a predetermined time ( For example, it is determined that the idle stop termination condition has been satisfied, for example, after 3 minutes).

In the present embodiment, after the internal combustion engine is stopped, when the air-fuel ratio detected by the front O ₂ sensor 44 provided in the exhaust passage 4 changes toward the rich side, it is on the downstream side of the front O ₂ sensor 44. The internal combustion engine control device 0 is configured to determine that a reverse flow state in which the exhaust gas flows upstream is generated and start the internal combustion engine.

  According to the ECU 0 of the present embodiment, the internal combustion engine is automatically restarted before a situation occurs in which the exhaust gas that has flowed back remains in the intake passage 3 and it becomes difficult to start the internal combustion engine. Therefore, it is possible to avoid the problem that the restartability of the internal combustion engine deteriorates due to the exhaust gas flowing backward to the intake passage 3 while the engine is stopped. Therefore, it is possible to reduce a sense of discomfort to the driver.

Further, since the backflow of exhaust gas is determined using the output voltage p of the front O ₂ sensor 44 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41, a special sensor as a countermeasure against backflow of exhaust gas, There is no need to separately provide special parts such as a conventional electromagnetic valve or an electric compressor. That is, since the backflow of exhaust gas is detected using an existing sensor, the above-described problem can be solved at a low cost.

  In particular, in the case where an idle stop system such as this embodiment is installed, by restarting promptly, there is a risk that the restart is delayed and the rear vehicle is collided with a subsequent vehicle when starting from a signal waiting state. Can be prevented and safety can be improved.

In the present embodiment, the above state is detected by the air-fuel ratio sensor upstream of the catalyst 41. That is, since the front O ₂ sensor 44 that is an air-fuel ratio sensor closer to the combustion chamber is used, detection is performed compared to the case that the rear O ₂ sensor 45 that is an air-fuel ratio sensor further away from the combustion chamber is used. The system can be improved.

In particular, the ECU 0 according to the present embodiment includes means capable of detecting the state of the intake valve 35 after the internal combustion engine is stopped. The intake valve 35 and the exhaust valve 43 are open at the same time, and the front O ₂ sensor 44 is provided. The idling stop is ended only when the air-fuel ratio detected by the engine changes toward the rich side. That is, the ECU 0 is automatically restarted only when a condition for generating a backflow of exhaust gas to the intake passage 3 is satisfied. Therefore, it is possible to reduce a sense of discomfort to the driver.

  Further, in the three-cylinder engine as in the present embodiment, the intake valve 35 and the exhaust valve 43 are often stationary when any one of the cylinders 1 becomes exhaust top dead center, so during the stop period of the internal combustion engine, A situation in which the intake valve 35 and the exhaust valve 43 are simultaneously open tends to occur. Therefore, the control described above is particularly effective.

  The present invention is not limited to the embodiment described in detail above. The present invention can also be applied to an internal combustion engine having a number of cylinders other than three.

  Although the internal combustion engine in the above embodiment is of the port injection type, the present invention can also be applied to start control of a direct injection internal combustion engine that injects fuel directly into the combustion chamber of each cylinder.

The air-fuel ratio sensor of the present invention is a linear A / F sensor that outputs a signal proportional to the air-fuel ratio of exhaust gas, in addition to an O ₂ sensor that has nonlinear output characteristics with respect to the air-fuel ratio of exhaust gas. Also good. Further, the place where the air-fuel ratio sensor is provided can be variously changed. For example, when a so-called tandem catalyst in which a plurality of catalysts are connected in series to the exhaust passage is employed, an air-fuel ratio sensor may be provided downstream of the upstream catalyst and upstream of the downstream catalyst. It may be used. Further, an air-fuel ratio sensor on the downstream side of the catalyst may be used.

  Other specific configurations of each part can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
4 ... exhaust passage 44, 45 ... air-fuel ratio sensor _{(O 2} sensor)

Claims (1)

After the internal combustion engine is stopped, when the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage changes toward the rich side, there is a reverse flow state in which the exhaust gas downstream of the air-fuel ratio sensor flows upstream. A control device for an internal combustion engine, characterized in that it is determined that it has occurred and starts the internal combustion engine.

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