JP2005016381A - Start controller for internal combustion engine with variable compression ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make starting property (shortening of start time) compatible with ensuring start in an internal combustion engine with a variable compression ratio mechanism. <P>SOLUTION: This start controller for the internal combustion engine with the variable compression ratio mechanism reads engine rotation speed, opening of an accelerator, engine water temperature, and battery voltage sequentially. When a start switch is turned ON for start (cranking), a target compression ratio set by reducing and compensating a high compression ratio for start when battery voltage is low and driving output for a starter is small is set to control the compression ratio to the target compression ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for controlling a compression ratio at the start (cranking) in an internal combustion engine that variably controls the compression ratio.
[0002]
[Prior art]
In an internal combustion engine in which the compression ratio can be made variable, the compression ratio is set low in a high load region in order to avoid knocking and ensure durability (Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 07-229431
[Problems to be solved by the invention]
According to the compression ratio control described above, since the start (cranking) starts from a state in which the filling efficiency in the cylinder is high (similar to almost the full load), the load compression region is similarly high, so the target compression ratio at the start is It will be set low.
[0005]
Some engines with a fixed compression ratio use a decompression mechanism or the like at the time of starting to release the compression pressure and reduce the friction to increase the cranking rotation speed to ensure startability. This is substantially the same effect as reducing the compression ratio at start-up.
[0006]
However, it is generally known that when the air-fuel mixture has the same λ, the higher the compression ratio, the better the ignitability. Since the load is high at the start, the target compression ratio is simply set low to lower the compression pressure. It has been found that the ignitability of the air-fuel mixture is reduced, the cranking time until the first explosion is increased, and the startability is deteriorated because a quick start cannot be performed.
[0007]
Furthermore, as a result, problems such as an increase in battery capacity consumption, an increase in load on the starter motor, and a decrease in drivability due to extension of the starting time also occur.
The present invention has been made paying attention to such a conventional problem, and an object thereof is to obtain a good startability by compression ratio control.
[0008]
[Means for Solving the Problems]
Therefore, the present invention is configured to set a target compression ratio for starting the engine, and to control the variable compression ratio mechanism so that the set target compression ratio for starting the engine is set when the engine is started.
[0009]
In addition to setting the target compression ratio according to the operation state after starting, setting and controlling the target compression ratio for starting the engine makes it possible to control the compression ratio optimal for starting. Specifically, at the time of start-up, the cranking time is basically shortened with a high compression ratio, and the engine is started quickly. Under conditions where the engine speed is difficult to increase, the compression ratio is reduced to the required cranking speed. It can be increased to ensure starting.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system configuration diagram of an internal combustion engine with a variable compression ratio mechanism according to an embodiment.
[0011]
An air flow meter 2 for detecting the intake air amount is disposed upstream of the compressor 53 in the intake passage 55 of the internal combustion engine 1, and a supercharging pressure is detected downstream of the intercooler 3 interposed downstream of the compressor 53. An intake pressure sensor 4 is arranged.
[0012]
Also, a crank angle sensor 5 for detecting the crank angle of the engine 1, an oxygen sensor 6 for detecting the oxygen concentration in the exhaust, a water temperature sensor 7 for detecting the cooling water temperature, a knocking sensor 8 for detecting knocking, and a throttle valve A throttle opening sensor 10 for detecting the opening of 9, an intake air temperature sensor 60 for detecting the intake air temperature at the outlet of the intercooler 3, a starter switch 61 for turning on and off a starter for starting (cranking) the engine 1, The detection signals of these sensors and the signal of the battery voltage VB are input to the engine control module (ECM) 11.
[0013]
The internal combustion engine 1 includes a turbocharger 51 as a supercharger.
The turbocharger 51 has a configuration in which a turbine 52 located in an exhaust passage 54 and a compressor 53 located in an intake passage 55 are coaxially arranged. In order to control the supercharging pressure in accordance with operating conditions, An exhaust bypass valve 56 for bypassing a part of the exhaust from the upstream side of the turbine 52 is provided.
[0014]
A fuel injection valve 16 is provided for each cylinder in the intake port portion of the engine 1, and an air-fuel mixture is formed in the combustion chamber by the fuel injected from the fuel injection valve 16.
The air-fuel mixture formed in the combustion chamber is ignited and burned by spark ignition by the spark plug 17, and the combustion exhaust gas is purified by the catalyst 19 after giving rotational energy to the turbine 52 and is exhausted through the muffler 20. To be released.
[0015]
Further, the internal combustion engine 1 of the present embodiment is provided with a variable compression ratio mechanism 100 having the configuration shown in FIG.
The crankshaft 31 of the engine 1 includes a plurality of journal portions 32, a crankpin portion 33, and a counterweight portion 31a, and the journal portion 32 is rotatably supported by a main bearing of a cylinder block (not shown). .
[0016]
The crankpin portion 33 is eccentric from the journal portion 32 by a predetermined amount, and a lower link 34 is rotatably connected thereto.
In the lower link 34, the crank pin portion 33 is fitted in a substantially central connecting hole.
[0017]
The upper link 35 has a lower end side rotatably connected to one end of the lower link 34 by a connecting pin 36, and an upper end side rotatably connected to a piston 38 by a piston pin 37.
[0018]
The piston 38 receives combustion pressure and reciprocates in the cylinder 39 of the cylinder block.
The upper end side of the control link 40 is rotatably connected to the other end of the lower link 34 by a connecting pin 41, and the lower end side is rotatably connected to an appropriate position of an engine body, for example, a cylinder block via a control shaft 42. .
[0019]
Specifically, the control shaft 42 is supported by the engine body so as to rotate about the small diameter portion 42b, and the lower end portion of the control link 40 is rotatable on the large diameter portion 42a that is eccentric to the small diameter portion 42b. Is fitted.
[0020]
In the variable compression ratio mechanism 100 as described above, when the control shaft 42 is rotated by the actuator 43, the axial center position of the large-diameter portion 42a that is eccentric with respect to the small-diameter portion 42b, particularly relative to the engine body. The position changes.
[0021]
Thereby, the rocking | fluctuation support position of the lower end of the control link 40 changes.
When the swing support position of the control link 40 changes, the stroke of the piston 38 changes, and the position of the piston 38 at the piston top dead center (TDC) increases or decreases.
[0022]
As a result, the engine compression ratio can be changed even during the intake stroke.
In the internal combustion engine having such a configuration, the engine control module (ECM) 11 performs control of the compression ratio by the variable compression ratio mechanism as well as various engine controls (fuel injection control, ignition control, etc.) as follows.
[0023]
FIG. 3 shows a flow of compression ratio control in the first embodiment which is a basic embodiment.
In FIG. 3, in step (denoted as S in the figure, the same applies hereinafter) 1, the engine rotational speed rNe1 detected by the rotational speed sensor 62 is read.
[0024]
In step 2, the accelerator opening degree rAPO1 detected by the accelerator opening degree sensor 61 is read.
In step 3, the engine water temperature rTw1 detected by the water temperature sensor 65 is read.
[0025]
In step 4, it is determined whether or not the starter switch 61 is ON.
When it is determined in step 4 that the starter switch 61 is ON (start), the process proceeds to step 5 where the target compression ratio # tεST for starting is read, and in step 6 the target compression ratio # tεST is set as the final target. Set as compression ratio tε. The target compression ratio # tεST for starting is set to a sufficiently high compression ratio with respect to a value set based on the normal (after starting) engine operating state (rotational speed and load). That is, FIG. 4 shows a map of the target compression ratio that is set based on the normal engine operating state (rotational speed and load). If the target compression ratio at the start is set on this map, the entire speed is reduced at the start. Since it is a high load state close to the load, a small target compression ratio is set, but the target compression ratio for starting # tεST set in this step is set in the normal map. It is set to a large compression ratio that is sufficiently larger than the target compression ratio and close to the maximum.
[0026]
As a result, the variable compression ratio mechanism is driven and, as shown in FIG. 5, the starter switch 61 is controlled to the high compression ratio # tεST during start-up (cranking), as shown in FIG. Thus, the compression pressure is increased and the ignitability is improved, so that the cranking time from the initial explosion to the start is shortened, and the startability is improved.
[0027]
Further, when it is determined in step 4 that the starter switch 61 is OFF, that is, after start-up, the process proceeds to step 6, and based on the engine rotational speed rNe and the accelerator opening rAPO representing the engine load, the map of FIG. The basic target compression ratio tε0 is searched.
[0028]
Next, the process proceeds to step 7 where a water temperature correction coefficient hos-Twε1 of the compression ratio is calculated from the table shown in FIG. 7 based on the engine water temperature rTw1, and in step 8, the water temperature correction coefficient hos-Twε1 is added to the basic target compression ratio tε0. To set a final target compression ratio tε. Here, the water temperature correction coefficient hos-Twε1 is set to a larger value (> 1.0) as the engine water temperature rTw1 is lower. That is, knocking is less likely to occur at a low water temperature, so that the engine output and thus the fuel consumption can be improved by setting the target compression ratio higher than usual.
[0029]
Next, an embodiment will be described in which a condition in which the engine speed is difficult to increase at the start is detected and the target compression ratio is corrected and set to be reduced when the condition is met.
FIG. 8 shows a flow of the second embodiment in which a decrease correction of the target compression ratio at the start is performed based on the battery voltage.
[0030]
As in the first embodiment, in steps 1 to 3, the engine rotational speed rNe1, the accelerator opening rAPO1, and the engine water temperature rTw1 are sequentially read. Then, the battery voltage VB is read in step 11, and the starter switch 61 is turned on in step 4. It is determined whether or not it is ON.
[0031]
If it is determined in step 4 that the starter switch 61 is ON, the process proceeds to step 5 ′, and the target compression ratio tεVB for starting is retrieved from the table of FIG. 9 based on the battery voltage VB. At 6 ′, this target compression ratio tεVB is set as the final target compression ratio tε. When the battery voltage VB is equal to or higher than the standard value, the target compression ratio tεVB for starting according to the battery voltage VB is the same as the value set in the first embodiment, and a large compression ratio close to the maximum (for example, 14), but as the battery voltage VB decreases, the value is corrected to decrease (lower limit value, for example, 8 or more).
[0032]
That is, as shown in FIG. 10, when the battery voltage is lowered, the drive output of the starter is lowered, so that the engine rotation speed is difficult to increase, and the engine cannot be started unless the allowable rotation speed is reached during the start. On the other hand, as shown in FIG. 11, the friction torque increases as the compression ratio of the engine is increased. Therefore, if the friction torque is decreased by decreasing the compression ratio, the engine rotation speed is likely to increase (FIG. 12). reference). Therefore, as the battery voltage decreases and the drive output of the starter decreases, the target compression ratio at the time of start can be greatly reduced and the friction torque can be greatly reduced to increase the allowable rotational speed during the start. , Starting can be ensured.
[0033]
After starting with the starter switch 61 turned OFF, the process proceeds to step 7 and the subsequent steps, and compression ratio control similar to that in the first embodiment is performed. The same applies to the following embodiments.
FIG. 13 shows a flow of the third embodiment in which the target compression ratio at the time of start-up is corrected based on the engine water temperature as the engine temperature.
[0034]
As in the first embodiment, in steps 1-3, the engine speed rNe1, the accelerator opening rAPO1, and the engine water temperature rTw1 are sequentially read. If it is determined in step 4 that the starter switch 61 is ON, Proceeding to step 5 ″, a target compression ratio tεTW for starting is retrieved from the table of FIG. 14 based on the engine water temperature rTw1, and this target compression ratio tεTW is set as the final target compression ratio tε in step 6 ″. To do. The target compression ratio tεTW for starting according to the engine water temperature rTw1 is set with a decrease correction when the engine water temperature rTw1 is low.
[0035]
That is, when the engine water temperature rTw1 is low, the oil viscosity is large and the engine friction is increased so that the engine rotation speed Ne is difficult to increase. Therefore, the target compression ratio at the time of starting is reduced and the friction torque is greatly reduced. It is possible to increase to the permissible rotational speed during startup, and to ensure startup.
[0036]
Moreover, it can also be set as embodiment which combined 2nd Embodiment and 3rd Embodiment. That is, with respect to the target compression ratio for starting # tεST set in step 4 of the first embodiment, the battery voltage correction coefficient that decreases as the battery voltage VB decreases (the same characteristic as in FIG. 9 is converted into a coefficient). The final target compression ratio tε is calculated and set by multiplying the engine water temperature correction coefficient (the same characteristic as in FIG. 14 converted into a coefficient) that decreases as the engine water temperature decreases. In this way, it is possible to ensure the start by increasing the rotational speed to an allowable rotational speed during the start in response to both the decrease in the drive output of the starter due to the battery voltage and the increase in the friction at a low temperature.
[0037]
FIG. 13 shows a flow of the fourth embodiment in which the target compression ratio at the time of start-up is corrected based on the engine speed during start-up.
Steps 1 to 5 are the same as those in the first embodiment, and after calculating the target compression ratio tw for starting at # tεST in Step 5, the process proceeds to Step 21 to check whether the correction flag is 1 or not. judge. This correction flag is set to 1 when a target compression ratio decrease correction described later is executed, and is reset to 0 otherwise.
[0038]
At the first time, the correction flag is reset to 0, and the routine proceeds to step 22 where the target compression ratio tε is set to the compression ratio # tεST calculated at step 5. Thereby, the compression ratio # tεST is controlled.
[0039]
After controlling to the compression ratio # tεST, the routine proceeds to step 23 (after a short set time has elapsed), and it is determined whether the engine rotational speed has reached an allowable rotational speed at which an initial explosion is possible.
If the allowable rotational speed has been reached, the correction flag is reset to 0 in step 24 while maintaining the target compression ratio # tεST as it is. If the allowable rotational speed is not reached, the process proceeds to step 25. Subtract and correct the target compression ratio. Specifically, the current value tεST2 is updated with a value obtained by subtracting the predetermined value # STEP−STtεDEC from the previous value tεST2 (initial value: # tεST), and the value tεST2 updated in step 25 is set as the target compression ratio tε in step 26. In step 27, the correction flag is set to 1.
[0040]
With such a configuration, as shown in FIG. 16, after the target compression ratio tε is controlled to the initial value # tεST for starting, if the permissible rotational speed is not reached, the target compression ratio tε is gradually decreased and corrected. The engine speed is increased by decreasing the torque. When the engine rotation speed increases and reaches an allowable rotation speed at which the first explosion is possible, the routine proceeds from step 23 to step 24 where the reduction correction of the target compression ratio tε is stopped and maintained at the currently set value.
[0041]
In this way, while detecting directly and accurately detecting all conditions under which the engine speed is difficult to increase due to a decrease in battery voltage, engine water temperature, and other causes, With the necessary minimum correction of the compression ratio, the engine can be reliably started up to an allowable rotational speed, and can be reliably started in as short a time as possible.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an internal combustion engine with a variable compression ratio mechanism according to the present invention.
FIG. 2 is a mechanism diagram of a variable compression ratio mechanism.
FIG. 3 is a flowchart showing compression ratio control in the first embodiment.
FIG. 4 is a diagram showing a characteristic of a target compression ratio set based on an engine operating state.
FIG. 5 is a time chart showing a state of compression ratio control according to the first embodiment.
FIG. 6 is a diagram showing the relationship between the compression ratio and the mixture ignitability.
FIG. 7 is a diagram showing a characteristic of a correction coefficient with respect to an engine water temperature of a compression ratio after starting.
FIG. 8 is a flowchart showing compression ratio control in the second embodiment.
FIG. 9 is a diagram showing characteristics of a target compression ratio for starting that is set based on a battery voltage.
FIG. 10 is a diagram illustrating a state of control according to the second embodiment.
FIG. 11 is a diagram showing the relationship between the compression ratio and the friction torque.
FIG. 12 is a diagram showing the relationship between the compression ratio and the cranking rotation speed.
FIG. 13 is a flowchart showing compression ratio control in the third embodiment.
FIG. 14 is a diagram showing characteristics of a target compression ratio for starting that is set based on engine water temperature.
FIG. 15 is a flowchart showing compression ratio control in the third embodiment.
FIG. 16 is a diagram showing a state of control according to the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Crank angle sensor 10 ... Throttle opening sensor 11 ... Engine control module 16 ... Fuel injection valve 34 ... Lower link 35 ... Upper link 40 ... Control link 42 ... Control shaft 43 ... Actuator 61 ... Starter switch 100 ... Variable compression ratio mechanism

Claims (8)

An internal combustion engine start control device including a variable compression ratio mechanism that makes a compression ratio variable,
An internal combustion engine with a variable compression ratio mechanism is characterized in that a target compression ratio for engine starting is set, and the variable compression ratio mechanism is controlled so that the set target compression ratio for starting is set when the engine is started. Start control device. 2. The internal combustion engine with a variable compression ratio mechanism according to claim 1, wherein the target compression ratio for starting the engine is set to a value higher than a target compression ratio set based on an engine operating state. Control device. 3. The variable compression ratio according to claim 1, wherein a condition in which the engine speed is difficult to increase at the time of starting the engine is detected, and the target compression ratio is reduced and set when the condition is satisfied. A start control device for an internal combustion engine with a mechanism. 4. The variable compression ratio mechanism according to claim 3, wherein a battery voltage is detected as a condition that makes it difficult for the engine rotation speed to increase when the engine is started, and a reduction correction amount of the target compression ratio is increased as the battery voltage is lower. A start control device for an internal combustion engine. 4. The variable compression ratio mechanism according to claim 3, wherein the engine temperature is detected as a condition that makes it difficult for the engine speed to increase when the engine is started, and the reduction correction amount of the target compression ratio is increased as the engine temperature is lower. A start control device for an internal combustion engine. 4. The start control device for an internal combustion engine with a variable compression ratio mechanism according to claim 3, wherein a condition in which the engine speed is difficult to increase at the time of starting the engine is detected based on the engine speed during startup. Immediately after start-up, control is made to the target compression ratio without correction, and when the engine speed does not increase to the permissible speed that allows the first explosion, the target compression ratio is gradually reduced and corrected until the engine speed can be confirmed. The start control device for an internal combustion engine with a variable compression ratio mechanism according to claim 6, wherein the reduction correction is stopped when the engine is stopped. The compression ratio variable mechanism is
An upper link having one end connected to the piston via a piston pin;
A lower link connected to the other end of the upper link via a first connecting pin and rotatably attached to the crankpin of the crankshaft;
A control link having one end connected to the lower link via a second connecting pin and the other end supported to be swingable with respect to the engine body;
A support position variable means for displacing the position of the other end of the control link with respect to the engine body when the compression ratio is changed;
The start control device for an internal combustion engine with a variable compression ratio mechanism according to any one of claims 1 to 7.

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