JP2008138579A - Variable valve timing control device for internal combustion engine - Google Patents

Abstract

In a variable valve timing control system, fuel consumption and output at low temperatures are improved by increasing valve overlap at low temperatures within a range of combustion stability limits in accordance with variations in actual engine conditions.
When the engine is not warmed up, the target intake VVT advance value (target exhaust VVT retard value) is set to be a valve overlap from the conforming value within a range in which the combustion stability does not exceed a preset combustion stability limit. Correct in the direction to increase. In this way, even if the engine condition varies due to variations in engine manufacturing, changes over time, and oil viscosity, the engine condition is checked while checking the actual combustion stability so that the combustion stability limit is not exceeded at low temperatures. It is possible to control the actual intake / exhaust VVT in the direction of increasing the valve overlap within the range of the combustion stability limit according to the variation of the engine, and to improve the fuel efficiency and output improvement effect by variable valve timing control at low temperature it can.
[Selection] Figure 8

Description

  The present invention relates to a variable valve timing control device for an internal combustion engine with improved control characteristics of variable valve timing control at low temperatures.

  When the opening / closing timing (valve timing) of the intake valve or exhaust valve of the engine (internal combustion engine) changes, the valve overlap (period in which both valves are open) changes. This valve overlap changes the internal EGR (exhaust residual ratio) and has a large effect on fuel consumption and output. Therefore, in variable valve timing control, an appropriate valve overlap is ensured according to the engine operating state. A target valve timing is set.

Generally, when the temperature is low (when the engine is not warmed up), the combustion stability is lower and the friction loss is larger than when the engine is warmed up. Therefore, the valve overlap (advance amount of intake valve timing) should be reduced at low temperatures. The target valve timing is set to (see Patent Document 1). Moreover, in reality, the engine condition varies due to engine manufacturing variations, changes over time, and oil viscosity variations (friction loss variations). Therefore, during actual adaptation, as shown in FIG. The target valve timing at the time of low temperature is adapted to the safer side (= the direction in which the valve overlap is smaller) by looking at the margin for the state variation.
JP-A-5-156972

  As described above, the target valve timing at the low temperature is adapted to the safer side (= the direction in which the valve overlap is smaller) by looking at the margin for the variation in the engine state at the low temperature. Thus, the target valve timing (adapted value) is set excessively to the safe side with respect to the actual combustion stability limit at low temperatures, and as a result, the valve overlap (advance of the intake valve timing becomes the actual combustion stability limit). The valve overlap is controlled to be excessively small with respect to (angular value), and there is a problem that the effect of improving the fuel consumption and output by the variable valve timing control is reduced.

  The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to increase the valve overlap at low temperatures within the range of the combustion stability limit in accordance with the variation in the actual state of the internal combustion engine. Another object of the present invention is to provide a variable valve timing control device for an internal combustion engine that can enhance the effect of improving fuel consumption and output by variable valve timing control at low temperatures.

  In order to achieve the above object, an invention according to claim 1 is directed to an internal combustion engine that controls an opening / closing timing (hereinafter referred to as “valve timing”) of an intake valve and / or an exhaust valve of the internal combustion engine to a preset target valve timing. In this variable valve timing control apparatus, the combustion stability of the internal combustion engine is determined by the combustion stability determination means, and information related to the temperature of the internal combustion engine is detected by the engine temperature detection means, and the detected temperature of the internal combustion engine is equal to or lower than a predetermined temperature. Based on the determination result of the combustion stability determination means at a low temperature, the target valve timing is corrected so that the valve overlap is larger than the conforming value within the range where the combustion stability does not exceed the preset combustion stability limit. It is what you do. In this way, even if the internal combustion engine condition varies due to variations in internal combustion engine production, changes over time, and oil viscosity (friction loss), the actual combustion stability will not exceed the combustion stability limit at low temperatures. It is possible to control the actual valve timing in the direction of increasing the valve overlap within the range of the combustion stability limit according to the variation in the state of the internal combustion engine while checking the engine performance. The effect of improving the output can be enhanced.

  In general, as the combustion stability decreases, the operating state of the internal combustion engine becomes unstable, and the rotational fluctuation of the internal combustion engine tends to increase, or the air-fuel ratio fluctuation of the exhaust gas tends to increase. As described above, it is preferable to determine the combustion stability based on the fluctuation in the rotation speed of the internal combustion engine or the fluctuation in the air-fuel ratio of the exhaust gas. Thereby, combustion stability can be determined with sufficient accuracy.

  Further, as in claim 3, the target valve timing is corrected based on the determination result of the combustion stability determination means at a low temperature, and the corrected target valve timing is updated and stored in a rewritable nonvolatile memory as a learning value. At the subsequent start, the learning value of the target valve timing may be used. In this way, it is possible to learn an appropriate target valve timing according to the actual state of the internal combustion engine, so that an optimal valve overlap can be realized early for each internal combustion engine, and the variable at low temperatures can be realized. The effect of improving fuel economy and output by valve timing control can be further enhanced.

  Further, when the combustion stability determination value calculated by the combustion stability determination means at a low temperature does not exceed the determination threshold value for the combustion stability limit as in claim 4, the target valve timing is increased in the direction in which the valve overlap becomes larger. It is preferable to correct the target valve timing in a direction in which the valve overlap becomes smaller when the determination value of the combustion stability exceeds the determination threshold value of the combustion stability limit at the low temperature. In this way, the valve overlap can be maintained near the combustion stability limit at low temperatures, and the effect of improving fuel consumption and output by variable valve timing control at low temperatures can be maximized.

  Hereinafter, two Examples 1 and 2, which embody the best mode for carrying out the present invention, will be described.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. On the downstream side of the air flow meter 14, a throttle valve 15 whose opening is adjusted by a DC motor or the like and a throttle opening sensor 16 for detecting the throttle opening are provided.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 18 for detecting the intake pipe pressure is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 for introducing air into each cylinder of the engine 11, and a fuel injection valve 20 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 19 of each cylinder. Yes. A spark plug 21 is attached to each cylinder of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of each spark plug 21.

  The intake valve 32 of the engine 11 is provided with a variable intake valve timing device 33 that varies the valve timing of the intake valve 32 (hereinafter referred to as “intake VVT”), and the exhaust valve 34 includes the exhaust valve 32. A variable exhaust valve timing device 35 that varies the valve timing of 34 (hereinafter referred to as “exhaust VVT”) is provided.

  On the other hand, the exhaust pipe 22 of the engine 11 is provided with a catalyst 23 such as a three-way catalyst that purifies CO, HC, NOx, etc. in the exhaust gas, and detects the air-fuel ratio of the exhaust gas upstream of the catalyst 23. An air-fuel ratio sensor 24 is provided. In place of the air-fuel ratio sensor 24, an oxygen sensor for detecting rich / lean exhaust gas may be provided.

  Further, a pulse signal is output to the cylinder block of the engine 11 each time the coolant temperature sensor 25 (engine temperature detection means) that detects the coolant temperature as temperature information of the engine 11 or the crankshaft of the engine 11 rotates a predetermined crank angle. A crank angle sensor 26 is attached. Based on the output signal of the crank angle sensor 26, the crank angle and the engine speed are detected.

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 27. The ECU 27 is mainly composed of a microcomputer including a CPU 28, a ROM 29, a RAM 30, a backup RAM 31 (rewritable nonvolatile memory), and the like, and executes various engine control programs stored in the ROM 30 to operate the engine. The fuel injection amount of the fuel injection valve 20 and the ignition timing of the spark plug 21 are controlled according to the state.

  Further, the ECU 27 realizes the target intake / exhaust VVT value calculation function shown in FIG. 2 by the target intake / exhaust VVT value calculation program of FIG. The target intake / exhaust VVT value calculation function of the ECU 27 includes an engine warm-up state determination block 41, a combustion stability determination block 42, a target VVT value calculation block 43, a water temperature correction block 44, and a target VVT correction block 45. .

The engine warm-up state determination block 41 determines whether or not the engine 11 has been warmed up based on whether or not the coolant temperature detected by the coolant temperature sensor 25 exceeds the warm-up determination threshold value.
The combustion stability determination block 42 functions as a combustion stability determination means in the scope of the claims, and as shown in FIG. 4, as a determination value of the combustion stability, the fluctuation amount of the engine speed or the air-fuel ratio of the exhaust gas. The fluctuation amount (the air-fuel ratio fluctuation amount detected by the air-fuel ratio sensor 24) is detected, and the fluctuation amount is compared with a determination threshold value for the combustion stability limit. If the fluctuation amount is equal to or less than the determination threshold value, combustion stability is good. If the variation amount exceeds the determination threshold, it is determined that the combustion stability is poor.

The target VVT value calculation block 43 calculates a target intake VVT advance value and a target exhaust VVT retard value from a map or the like according to the engine operating state (for example, engine speed and load).
The water temperature correction block 44 calculates the intake VVT water temperature correction coefficient Kin and the exhaust VVT water temperature correction coefficient Kex according to the maps shown in FIGS. 5A and 5B in accordance with the cooling water temperature detected by the cooling water temperature sensor 25. The target intake VVT advance value calculated by the target VVT advance value calculation block 43 and the target exhaust VVT retard value are multiplied by the water temperature correction coefficients Kin and Kex, respectively, and the target intake VVT advance value and the target exhaust subjected to the water temperature correction processing are multiplied. A VVT retardation value is obtained. As shown in FIG. 6, the characteristics of the maps of the water temperature correction coefficients Kin and Kex are, for example, in the low temperature region of 10 ° C. or less, the water temperature correction coefficients Kin and Kex are minimum values “0”. In the warm-up region above 40 ° C., each water temperature correction coefficient Kin, Kex becomes the maximum value “1”, and in these intermediate temperature regions, each water temperature correction coefficient Kin, Kex increases as the cooling water temperature increases. Is set to

  The target VVT correction block 45 functions as control means in the claims, and when it is determined by the engine warm-up state determination block 41 that the engine is not warmed up (corresponding to “low temperature” in the claims). In addition, the target intake VVT advance value is corrected so that the valve overlap is larger than the appropriate value (value corrected by the water temperature correction coefficient Kin) within a range in which the combustion stability does not exceed the preset combustion stability limit. (Increase the target intake VVT advance value) and / or correct the target exhaust VVT retard value in a direction that makes the valve overlap larger than the appropriate value (value corrected by the water temperature correction coefficient Kex) (target) Increase the exhaust VVT retardation value).

  In this case, when the target VVT correction block 45 is not warmed up (at low temperature), the combustion stability determination value (the engine rotational speed fluctuation amount or the exhaust gas air-fuel ratio fluctuation amount) sets the combustion stability limit determination threshold value. If not, correct the target intake VVT advance value so that the valve overlap is larger than the appropriate value (value corrected by the water temperature correction coefficient Kin) (increase the target intake VVT advance value), and / or Alternatively, the target exhaust VVT retardation value is corrected so as to increase the valve overlap (the target exhaust VVT retardation value is increased) from the appropriate value (value corrected by the water temperature correction coefficient Kex). After that, when the combustion stability judgment value (the engine rotational speed fluctuation amount or the exhaust gas air-fuel ratio fluctuation amount) exceeds the combustion stability limit judgment threshold value, the target intake VVT advance value is reduced in the direction of decreasing the valve overlap. And / or the target exhaust VVT retardation value is corrected so as to reduce the valve overlap. Thus, the control is performed so that the valve overlap is maintained near the combustion stability limit when the engine is not warmed up (low temperature).

  The calculation processing of the target intake VVT advance value and the target exhaust VVT delay value of the first embodiment described above is executed by the ECU 27 according to the target intake / exhaust VVT value calculation program of FIG. The processing contents of the target intake / exhaust VVT value calculation program of FIG. 3 will be described below. In the following description, “target intake / exhaust VVT value” means “target intake VVT advance value” and “target exhaust VVT retard value”, and “actual intake / exhaust VVT value” means “actual intake VVT value”. It means “advance value” and “actual exhaust VVT retardation value”.

  The target intake / exhaust VVT value calculation program of FIG. 3 is executed at a predetermined cycle (control cycle of intake / exhaust VVT) during engine operation. When this program is started, first, at step 101, a target intake / exhaust VVT value is calculated by a map or the like according to the engine operating state (for example, engine speed and load). Thereafter, the process proceeds to step 102 where water temperature correction coefficients Kin, Kex are calculated according to the cooling water temperature detected by the cooling water temperature sensor 25 from the maps of FIGS. 5A and 5B, and the water temperature correction coefficients Kin, Kex are calculated. By multiplying the target intake / exhaust VVT value, the target intake / exhaust VVT value subjected to the water temperature correction processing is obtained.

  Thereafter, the process proceeds to step 103, where it is determined whether or not the engine 11 has been warmed up based on whether or not the coolant temperature detected by the coolant temperature sensor 25 has exceeded the warm-up determination threshold value. Then, the process proceeds to step 108, and the target intake / exhaust VVT value subjected to the water temperature correction process in step 102 is output as it is, and the actual intake / exhaust VVT value is controlled to coincide with the target intake / exhaust VVT value.

  On the other hand, if it is determined in step 103 that the coolant temperature is equal to or lower than the warm-up determination threshold value (when the engine is not warmed up), the process proceeds to step 104, where the combustion stability determination value (the engine rotational speed fluctuation amount or the exhaust amount is discharged). After detecting the gas air-fuel ratio fluctuation amount), the routine proceeds to step 105, where the combustion stability determination value is compared with the combustion stability limit determination threshold value, and if the combustion stability determination value is less than the determination threshold value, the combustion stability The process proceeds to step 106, where a predetermined value is added to the target intake / exhaust VVT value subjected to the water temperature correction process in step 102, and the target intake / exhaust VVT value is set larger than the conforming value. In the next step 108, the corrected target intake / exhaust VVT value is output, and the actual intake / exhaust VVT value is controlled to match the target intake / exhaust VVT value.

  If it is determined in step 105 that the combustion stability determination value is greater than or equal to the combustion stability limit determination threshold, it is determined that the combustion stability has exceeded the combustion stability limit and the combustion stability has deteriorated. Proceeding to step 107, a predetermined value is subtracted from the target intake / exhaust VVT value subjected to the water temperature correction process in step 102 to correct the target intake / exhaust VVT value in a direction to reduce the valve overlap. The subsequent target intake / exhaust VVT value is output, and the actual intake / exhaust VVT value is controlled to coincide with the target intake / exhaust VVT value. By the processing of these steps 105 to 108, control is performed so that the valve overlap is maintained near the combustion stability limit when not warmed up (at low temperature).

  According to the first embodiment described above, as shown in FIG. 8, when the engine is not warmed up (at low temperature), the target intake / exhaust VVT value is set within a range in which the combustion stability does not exceed a preset combustion stability limit. Since the valve overlap is corrected to be larger than the conforming value, even if the state of the engine 11 varies due to variations in manufacturing of the engine 11, changes with time, and variations in oil viscosity (friction loss variation), The actual intake / exhaust VVT value is controlled in the direction of increasing the valve overlap within the range of the combustion stability limit according to the variation in the state of the engine 11 while checking the actual combustion stability so as not to exceed the combustion stability limit at low temperatures. This makes it possible to improve the fuel efficiency and output by variable valve timing control at low temperatures.

In the second embodiment of the present invention shown in FIG. 9, the target intake / exhaust is performed in a range in which the combustion stability does not exceed a preset combustion stability limit when not warmed up (at a low temperature) by the same method as in the first embodiment. The VVT value is corrected so that the valve overlap is larger than the appropriate value, and the corrected target intake / exhaust VVT value is updated and stored in the backup RAM 31 (rewritable nonvolatile memory) of the ECU 27 as a learning value. At the next engine start, the learning value of the target intake / exhaust VVT value stored in the backup RAM 31 is read out, and this learned value is used as the initial value of the target intake / exhaust VVT value. The target intake / exhaust VVT value is corrected in a direction that makes the valve overlap larger than the learned value within a range not exceeding the stability limit.
In this case, the learning value of the target intake / exhaust VVT value may be learned for each cooling water temperature or each engine operating state in order to improve learning accuracy.

  According to the second embodiment described above, an appropriate target intake / exhaust VVT value corresponding to the actual state of the engine 11 can be learned, so that an optimal valve overlap can be realized early for each engine. Thus, the effect of improving fuel efficiency and output by variable valve timing control at low temperatures can be enhanced as compared with the first embodiment.

  In the first and second embodiments, the valve timing of both the intake valve 32 and the exhaust valve 34 is variably controlled. However, the valve timing of only one of the intake valve 32 and the exhaust valve 34 is variably controlled. The present invention can also be applied to a system.

It is a schematic block diagram of the whole engine control system in Example 1 of this invention. It is a block diagram which shows the target intake / exhaust VVT value calculation function of ECU. It is a flowchart which shows the flow of a process of the target intake / exhaust VVT value calculation program of Example 1. FIG. It is a figure explaining the determination method of combustion stability. (A) is a figure explaining an example of the map of the intake VVT water temperature correction coefficient Kin, and (b) is a figure explaining an example of the map of the exhaust VVT water temperature correction coefficient Kex. It is a figure which shows notionally an example of the map of the water temperature correction coefficients Kin and Kex for intake VVT / exhaust VVT. It is a time chart which shows an example of the control behavior of conventional control. 3 is a time chart illustrating an example of a control behavior according to the first embodiment. 10 is a time chart illustrating an example of control behavior according to the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 21 ... Spark plug, 22 ... Exhaust pipe, 25 ... Cooling water temperature sensor (engine temperature detection means), 27 ... ECU ( Combustion stability determination means, control means), 32 ... intake valve, 33 ... variable intake valve timing device, 34 ... exhaust valve, 35 ... variable exhaust valve timing device

Claims (4)

In a variable valve timing control device for an internal combustion engine that controls an opening / closing timing (hereinafter referred to as “valve timing”) of an intake valve and / or an exhaust valve of the internal combustion engine to a preset target valve timing,
Combustion stability determining means for determining combustion stability of the internal combustion engine;
Engine temperature detecting means for detecting information relating to the temperature of the internal combustion engine;
The target is within a range where the combustion stability does not exceed a preset combustion stability limit based on the determination result of the combustion stability determination means at a low temperature when the temperature of the internal combustion engine detected by the engine temperature detection means is lower than a predetermined temperature. A variable valve timing control device for an internal combustion engine, comprising: control means for correcting the valve timing in a direction in which the valve overlap is made larger than its conforming value.   2. The variable valve timing control device for an internal combustion engine according to claim 1, wherein the combustion stability determination means determines the combustion stability based on a rotational fluctuation of the internal combustion engine or an air-fuel ratio fluctuation of the exhaust gas.   The control means corrects the target valve timing based on the determination result of the combustion stability determination means at the low temperature, and updates and stores the corrected target valve timing in a rewritable nonvolatile memory as a learning value, and thereafter The variable valve timing control device for an internal combustion engine according to claim 1 or 2, wherein a learning value of the target valve timing is used at the time of starting the engine.   The control means corrects the target valve timing in a direction in which the valve overlap increases when the combustion stability judgment value calculated by the combustion stability judgment means does not exceed the combustion stability limit judgment threshold at the low temperature. 4. The target valve timing is corrected in a direction in which the valve overlap becomes smaller when the determination value of the combustion stability at the low temperature exceeds the determination threshold value of the combustion stability limit. The variable valve timing control device for an internal combustion engine according to any one of the above.

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