Engine Control Unit

Abstract

To suppress early deterioration of a glow plug while ensuring a starting performance of an engine.SOLUTION: A control device is provided on an engine that is equipped with a plurality of glow plugs in which heating portions heated by energization are respectively disposed in combustion chambers, and can be automatically stopped and restarted. The control device decides a combustion starting cylinder that is a cylinder combusting mixture first when restarting the engine, and after automatic stop of the engine, energizes the glow plugs of the combustion starting cylinder when the temperature of the glow plug of the decided combustion starting cylinder is lower than a predetermined determination temperature, and suppresses the energization to the glow plug of the combustion starting cylinder when the temperature of the glow plug is the determination temperature or more.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a control device provided in an engine that has a plurality of cylinders, each having a combustion chamber, a fuel supply means for supplying fuel to each combustion chamber, and a plurality of glow plugs, each having a heating element that generates heat when electricity is applied, disposed in each combustion chamber, and that can be automatically stopped and restarted. [Background technology]

[0002] Conventionally, in vehicles equipped with engines, the engine is automatically stopped in order to improve fuel efficiency, and then the engine is automatically restarted when a predetermined condition is met. Also, in order to ensure combustion of the air-fuel mixture when starting the engine and improve startability, glow plugs are provided in the cylinders to raise the temperature inside the cylinders.

[0003] For example, Patent Document 1 discloses a four-cylinder diesel engine that automatically stops and restarts, with each cylinder provided with a glow plug. In this engine, the amount of electricity supplied to the glow plug of the cylinder that first generates combustion when the engine is restarted is made greater than the amount of electricity supplied to the glow plugs of the other cylinders, thereby ensuring the initial combustion and improving the startability of the engine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-46251 A Summary of the Invention [Problem to be solved by the invention]

[0005] In an engine that automatically stops and restarts, the frequency of stopping and restarting the engine increases, and the interval between restarts of the engine tends to become shorter. Therefore, in the above-mentioned configuration in which the amount of current supplied to the glow plug of a specific cylinder is simply increased when the engine is restarted, the glow plug that has received a large amount of current during the previous engine restart and become hot may again receive a large amount of current during the next engine restart before its temperature has sufficiently decreased, and there is a risk that the temperature of the glow plug will rise too high and deteriorate early.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide an engine control device that can suppress early deterioration of glow plugs while ensuring engine startability. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a control device for an engine which has a plurality of cylinders, a fuel supply means for supplying fuel to the combustion chambers of each cylinder, and a plurality of glow plugs, each of which has a heating portion that generates heat when energized and is disposed in each combustion chamber, and which can be automatically stopped and restarted, the control device comprising: a combustion start cylinder determination unit which determines a combustion start cylinder which is a cylinder that will first combust an air-fuel mixture when the engine is restarted after the engine is automatically stopped; a fuel control unit which controls the fuel supply means so that fuel is supplied first to the combustion chamber of the combustion start cylinder determined by the combustion start cylinder determination unit when the engine is restarted; and a glow control unit which controls the glow plug, and when the temperature of the glow plug of the combustion start cylinder determined by the combustion start cylinder determination unit is lower than a predetermined judgment temperature after the engine is automatically stopped, the glow plug of the combustion start cylinder is determined to be lower than the predetermined judgment temperature. a first energization control is performed to energize the glow plug of the cylinder in which combustion is started at a predetermined first voltage for a predetermined reference period, and after the first energization control is completed, a second energization control is performed to energize the glow plug of the cylinder in which combustion is started at a second voltage lower than the first voltage; When the temperature of the glow plug of the combustion start cylinder is equal to or higher than the judgment temperature, By prohibiting the execution of the first current supply control and executing only the second current supply control, The feature of this invention is that it suppresses the flow of electricity to the glow plug (Claim 1).

[0008] In the present invention, when the temperature of the glow plug of the starting cylinder in which combustion occurs first when the engine is restarted after the engine is automatically stopped is low, electricity is supplied to the glow plug of the starting cylinder. Therefore, the temperature of the glow plug of the starting cylinder can be reliably increased to reliably raise the temperature inside the starting cylinder when the engine is restarted. Therefore, the mixture can be reliably burned in the starting cylinder to increase the engine speed, thereby improving the startability of the engine. Moreover, in the present invention, when the temperature of the glow plug of the starting cylinder is high, electricity is suppressed from being supplied to the glow plug of the starting cylinder. Therefore, the starting ability can be ensured by keeping the inside of the starting cylinder warm with the high-temperature glow plug, while preventing the temperature of the glow plug from becoming excessively high and promoting deterioration.

[0010] specifically When the temperature of the glow plug of the cylinder where combustion starts is low, the glow plug of the cylinder where combustion starts is first energized with a high first voltage to reliably raise the temperature of the glow plug, and then the glow plug is energized with a low second voltage to maintain the temperature of the glow plug at a high temperature. Therefore, the high-temperature glow plug can reliably heat the cylinder where combustion starts, promoting combustion in the cylinder where combustion starts and improving the startability of the engine. When the temperature of the glow plug of the cylinder where combustion starts is high, the energization voltage of the glow plug of the cylinder where combustion starts is suppressed to the second voltage, so that the glow plug can be maintained at a high temperature to ensure the startability of the engine while preventing the glow plug from overheating and early deterioration.

[0011] In the above-mentioned configuration, preferably, the engine has six cylinders aligned in a row, and the combustion start cylinder determination unit determines, as the combustion start cylinder, a cylinder in which the position of the piston when stopped is near the bottom dead center of the intake stroke (see claim 2 ).

[0012] With this configuration, combustion occurs first in the cylinder where a relatively large amount of air is secured because the piston is near the bottom dead center of the intake stroke, which makes it possible to more reliably improve the combustibility of the mixture and, in turn, the startability of the engine. Effect of the Invention

[0013] As described above, according to the engine control device of the present invention, it is possible to suppress early deterioration of the glow plug while ensuring the startability of the engine. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of an engine to which a control device according to an embodiment of the present invention is applied; [Diagram 2] FIG. 2 is a schematic cross-sectional view of an engine body. [Diagram 3] FIG. 2 is a diagram showing the strokes performed in each cylinder of the engine. [Figure 4] FIG. 2 is a block diagram showing a control system of the engine. [Diagram 5] 4 is a flowchart showing a control procedure of a glow plug. [Figure 6] 4 is a time chart showing the change over time of each parameter when the temperature of the glow plug of the cylinder in which combustion starts is lower than a judgment temperature. [Figure 7] 4 is a time chart showing the change over time of each parameter when the temperature of the glow plug of the cylinder in which combustion starts is equal to or higher than a judgment temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of an engine E to which a control device according to an embodiment of the present invention is applied.

[0016] (1) Overall structure The engine E includes an engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an EGR device 60 that recirculates EGR gas, which is a part of the exhaust gas flowing through the exhaust passage 40, to the intake passage 30. The engine E also includes a turbocharger 50, which has a turbine 52 provided in the exhaust passage 40, and a compressor 51 provided in the intake passage 30 and rotated by the turbine 52. The engine E of this embodiment is a four-stroke diesel engine, and is driven by receiving a supply of fuel mainly composed of diesel. The engine E is mounted on a vehicle as its drive source.

[0017] The engine body 1 has a cylinder block 3 in which cylinders 2 are formed, and a cylinder head 4 that covers the cylinder block 3.

[0018] Fig. 3 is a schematic cross-sectional view of the engine body 1. As shown in Fig. 3, the engine E of this embodiment is an in-line six-cylinder engine, and the engine body 1 (more specifically, a cylinder block 3) is formed with six cylinders 2 arranged in a row (first cylinder 2A, second cylinder 2B, third cylinder 2C, fourth cylinder 2D, fifth cylinder 2E, and sixth cylinder 2F, in that order from one side along the arrangement direction of the cylinders 2).

[0019] A piston 5 is accommodated in each cylinder 2 so as to be capable of reciprocating and sliding. A combustion chamber 6 is formed above the piston 5 in each cylinder 2. Each piston 5 is connected to a crankshaft 7 via a connecting rod 8. The crankshaft 7 rotates around its central axis in response to the reciprocating motion of each piston 5. The crankshaft 7 is connected to the motor M via a clutch C that can connect and disconnect the crankshaft 7 and the motor M. When the engine E is started, the crankshaft 7 is forcibly rotated by the motor M. Specifically, when the engine E is started, the crankshaft 7 and the motor M are connected by the clutch C so that torque is transmitted between them, and the torque of the motor M is transmitted to the crankshaft 7. As a result, the crankshaft 7 is rotated, that is, the engine E is cranked.

[0020] An injector 15 that injects fuel into the combustion chamber 6 (cylinder 2) is attached to the cylinder head 4, one for each cylinder 2. The piston 5 reciprocates as the mixture of supplied fuel and air burns in the combustion chamber 6 and is pushed down by the expansion force caused by the combustion. The injector 15 corresponds to the "fuel supplying means" in the claims.

[0021] Glow plugs 16 for increasing the temperature inside the combustion chambers 6 (cylinders 2) are attached to the cylinder head 4, one for each cylinder 2. A heating portion provided at the tip of the glow plug 16 generates heat when electricity is applied. The glow plug 16 is attached to the cylinder head 4 so that the heating portion is disposed inside the combustion chamber 6.

[0022] The cylinder head 4 is provided with intake ports 9 for introducing intake air into each cylinder 2 (combustion chamber 6), intake valves 11 for opening and closing the intake ports 9, exhaust ports 10 for guiding exhaust gas generated in each cylinder 2 (combustion chamber 6), and exhaust valves 12 for opening and closing the exhaust ports 10, each for each cylinder 2. The engine body 1 is of a four-valve type, with two intake valves and two exhaust valves, and each cylinder 2 is provided with two intake ports 9 and two exhaust ports 10, as well as two intake valves 11 and two exhaust valves 12.

[0023] FIG. 4 is a diagram showing the strokes performed in each cylinder 2. As described above, the engine E is a four-stroke engine. Thus, in each cylinder 2, the intake stroke, compression stroke, expansion stroke, and exhaust stroke are performed in succession in this order. The engine E is an in-line six-cylinder engine. Thus, the pistons 5 provided in each cylinder 2A to 2F reciprocate with a phase difference of 120° CA (120 degrees in crank angle), and combustion occurs in the order of the first cylinder 2A → the fifth cylinder 2E → the third cylinder 2C → the sixth cylinder 2F → the second cylinder 2B → the fourth cylinder 2D every 120° CA. In FIG. 4, TDCe represents the exhaust top dead center, BDCi represents the intake bottom dead center, TDCc represents the compression top dead center, and BDCe represents the expansion bottom dead center.

[0024] The intake valves 11 of each cylinder 2 are driven by a valve train 13 including an intake camshaft arranged in the cylinder head 4. The valve train 13 for the intake valves 11 incorporates an intake S-VT 13a capable of changing the opening and closing timings of each intake valve 11 collectively. The intake S-VT 13a is a so-called phase-type variable mechanism, and changes the valve opening start timing and the valve closing timing of each intake valve 11 simultaneously and by the same amount. Similarly, the exhaust valves 12 of each cylinder 2 are driven by a valve train 14 including an exhaust camshaft arranged in the cylinder head 4, and the valve train 14 for the exhaust valves 12 also incorporates a phase-type exhaust S-VT capable of changing the opening and closing timings of each exhaust valve 12 collectively. The intake S-VT 13a is configured so that the closing timing of the intake valves 11 can be retarded from the intake bottom dead center.

[0025] The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. The intake passage 30 is provided with an air cleaner 31, a compressor 51, a throttle valve 32, an intercooler 33, and a surge tank 34 in this order from the upstream side. The compressor 51 is rotationally driven by the turbine 52 as described above, and compresses (supercharges) the air passing through the compressor 51. The air compressed by the compressor 51 and cooled by the intercooler 33 is introduced into the cylinder 2 (combustion chamber 6). The throttle valve 32 is a valve capable of opening and closing the intake passage 30. The amount of air flowing through the intake passage 30, and therefore the amount of intake air introduced into the cylinder 2 (combustion chamber 6), is changed according to the opening degree of the throttle valve 32.

[0026] The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. The exhaust passage 40 is provided with, in order from the upstream side, a turbine 52 and an exhaust purification device 41 for purifying the exhaust gas. The exhaust purification device 41 incorporates a three-way catalyst 42 and a DPF (diesel particulate filter) 43. The turbine 52 rotates by receiving energy from the exhaust gas flowing through the exhaust passage 40, and the compressor 51 rotates in conjunction with this.

[0027] The EGR device 60 includes an EGR passage 61 that connects the exhaust passage 40 and the intake passage 30, and an EGR valve 62 and an EGR cooler 63 that are provided in the EGR passage 61. The EGR passage 61 connects a portion of the exhaust passage 40 upstream of the turbine 52 to a portion of the intake passage 30 between the intercooler 33 and the surge tank 34. The EGR valve 62 is a valve that can open and close the EGR passage 61. The amount of EGR gas recirculated to the intake passage 30 is changed according to the opening degree of the EGR valve 62. The EGR cooler 63 cools the EGR gas by heat exchange.

[0028] (2) Control system Fig. 4 is a block diagram showing a control system of the engine E. The ECU 100 shown in Fig. 4 is a microprocessor for overall control of the engine E, and is composed of a known CPU, ROM, RAM, etc. The ECU 100 functionally includes a fuel control unit 101 for controlling the injector 15, a glow control unit 102 for controlling the glow plug 16, and a combustion start cylinder determination unit 103 for determining a combustion start cylinder, which will be described later.

[0029] The ECU 100 receives detection signals from various sensors.

[0030] Specifically, the cylinder block 3 is provided with a crank angle sensor SN1 for detecting the rotation angle of the crankshaft 7, i.e., the engine speed. The cylinder head 4 is provided with a cam angle sensor SN2 for detecting the angle of an intake cam included in the intake valve mechanism 13. The ECU 100 determines which cylinder is in which stroke based on the detection signal of the cam angle sensor SN2 and the detection signal of the crank angle sensor SN1. In addition, an air flow meter SN3 is provided in a portion between the air cleaner 31 and the compressor 51 of the intake passage 30 for detecting the intake amount, which is the flow rate of the intake air that passes through this portion and is introduced into the combustion chamber 6. The cylinder block 3 is provided with a water temperature sensor SN4 for detecting the temperature of the cooling water flowing inside the cylinder block 3 and the cylinder head 4, i.e., the engine water temperature. In addition, the vehicle on which the engine E is mounted is provided with an accelerator pedal position sensor SN5 for detecting the accelerator pedal position, which is the position of the accelerator pedal operated by the driver who drives the vehicle, a brake pedal sensor SN6 for detecting the amount of depression of the brake pedal operated by the driver, a vehicle speed sensor SN7 for detecting the vehicle speed, and the like. The ECU 100 sequentially receives information detected by these sensors SN1 to SN7.

[0031] The ECU 100 performs various determinations and calculations based on input information from each sensor, and controls each part of the engine E, such as the injector 15, the glow plug 16, the intake S-VT 13a, the throttle valve 32, and the EGR valve 62.

[0032] (Automatic engine stop / start control) The engine E of this embodiment is configured to be automatically stopped and restarted, that is, the ECU 100 has a function of automatically stopping and restarting the engine E under specific predetermined conditions.

[0033] The automatic stop condition, which is a condition for permitting automatic stopping of the engine E, and the restart condition, which is a condition for permitting restarting of the engine E after automatic stopping, may be set in various conditions depending on the type of vehicle, etc.

[0034] For example, in a vehicle in which the only power source for traveling is substantially an engine (so-called engine vehicle), the automatic stop condition may be satisfied when a number of conditions including (i) the vehicle is substantially stopped, (ii) the accelerator pedal is in an OFF state, and (iii) the brake pedal is in an ON state (depressed). In addition, in this vehicle, after the engine E is automatically stopped after the automatic stop condition is satisfied, the restart condition may be satisfied when a number of conditions including (i) the vehicle is substantially stopped, (ii) the accelerator pedal opening degree is greater than 0 (depressed), and (iii) the brake pedal is in an OFF state (not depressed). In this case, the ECU 100 determines whether the automatic stop condition is satisfied and whether the restart condition is satisfied based on information input from the vehicle speed sensor SN7, the accelerator pedal opening degree sensor SN5, and the brake pedal sensor SN6.

[0035] On the other hand, in a vehicle that also uses a motor M as a driving power source, that is, a so-called hybrid vehicle that can run in EV mode using only the motor M, the driving force of the engine E may become unnecessary even while the vehicle is running, and when such a situation occurs, the automatic stop condition may be established. In this case, the ECU 100 calculates the target torque of the driving source including the engine E and the motor M from the vehicle speed detected by the vehicle speed sensor SN7, the accelerator opening detected by the accelerator opening sensor SN5, etc., and determines whether or not engine output (positive output torque that contributes to running) is necessary based on various conditions including the calculated target torque. Then, if it is determined that engine output is unnecessary, it is determined that the automatic stop condition is established. In addition, in this vehicle, if it is determined that engine output is necessary in a state in which the engine E is automatically stopped after the automatic stop condition is established, it is determined that the restart condition is established.

[0036] When it is determined that the automatic stop condition is satisfied, the ECU 100 performs a fuel cut to stop fuel injection from the injector 15 of each cylinder 2. As a result, the engine speed gradually decreases and finally becomes 0, and the engine E stops completely.

[0037] Here, as described above, when starting the engine E, the engine E is rotated and cranked by being driven by the motor M. The output of the motor M required to crank the engine E differs depending on the stop position of each cylinder 2 of the engine E, and the output of the motor M is small when the position of the piston 5 of the compression stroke cylinder at the time of stop relative to the compression top dead center is approximately the same as the position of the piston 5 of the expansion stroke cylinder at the time of stop relative to the compression top dead center. The compression stroke cylinder at the time of stop is a cylinder whose stroke when the engine is stopped (when the engine E is completely stopped) is the compression stroke, and whose piston 5 is in the position between the compression top dead center (TDCc) and 120° CA before the compression top dead center (BTDCc). The above-mentioned stop-time expansion stroke cylinder is a cylinder that is one cylinder before the stop-time compression stroke cylinder in the combustion order, whose stroke when the engine is stopped (when the engine E is completely stopped) is the expansion stroke, and whose piston 5 position is in the range from compression top dead center (TDCc) to 120°CA after compression top dead center (ATDCc).

[0038] However, just before the engine E is stopped, the engine speed becomes very low, causing the pressure in the intake passage 30 to increase, so that the intake amount of the stop-time compression stroke cylinder, whose intake stroke follows the stop-time expansion stroke cylinder, tends to be greater than the intake amount of the stop-time expansion stroke cylinder. As a result, the stop position of the stop-time compression stroke cylinder tends to be closer to the compression top dead center than the stop position of the stop-time expansion stroke cylinder.

[0039] Therefore, in this embodiment, the amount of intake air blown back from the cylinder 2 of the stop-time compression stroke cylinder to the intake port 9 is increased immediately before the engine E is stopped, thereby reducing the intake amount of the cylinder 2. In this way, the intake amount of the stop-time compression stroke cylinder is prevented from becoming excessively larger than the intake amount of the stop-time expansion stroke cylinder whose intake stroke is earlier than that of the stop-time compression stroke cylinder, and the stop positions of these cylinders can be made approximately equal with respect to the compression top dead center. Specifically, the ECU 100 gradually retards the closing timing of the intake valve 11 toward the most retarded timing immediately before the engine E is stopped, and makes the retard amount of the intake valve closing timing from the intake bottom dead center immediately before the stop of the stop-time compression stroke cylinder larger than the retard amount of the intake valve closing timing from the intake bottom dead center immediately before the stop of the stop-time expansion stroke cylinder.

[0040] When the restart condition is satisfied after the engine E is automatically stopped as the automatic stop condition is satisfied as described above, the ECU 100 executes start control for starting (restarting) the engine E. Specifically, the ECU 100 engages the clutch C as described above to crank the engine E by the motor M, and resumes the fuel supply from the injector 15 to restart the engine.

[0041] In detail, the ECU 100 (combustion start cylinder determination unit 103) determines a cylinder whose piston 5 is located near the intake bottom dead center when the engine E is completely stopped and whose cylinder was in the intake stroke or compression stroke when the engine E was stopped as the combustion start cylinder, which is the cylinder that will first burn the mixture when the engine E is restarted. Then, the ECU 100 (fuel control unit 101) supplies fuel to the combustion chamber 6 of this combustion start cylinder first, and burns the mixture in this combustion chamber 6 first. In this embodiment, the cylinder whose piston 5 is located in the range from 60° CA before the intake bottom dead center (° CA: crank angle) to 60° CA after the intake bottom dead center when the engine E is completely stopped is determined as the combustion start cylinder. After supplying fuel from the injector 15 to the combustion start cylinder, the ECU 100 supplies fuel from the injector 15 to the combustion chamber 6 of each cylinder 2 in order according to the combustion order.

[0042] Furthermore, when the restart condition is satisfied, the ECU 100 drives the intake S-VT 13a so as to advance the closing timing of the intake valve 11. Specifically, as described above, in this embodiment, the closing timing of the intake valve 11 is retarded toward the most retarded timing immediately before the engine E is stopped, and the closing timing of the intake valve 11 when the engine E is stopped is the most retarded timing. Therefore, when the restart condition is satisfied, the ECU 100 drives the intake S-VT 13a to advance the closing timing of the intake valve 11 toward a predetermined timing on the advance side of the most retarded timing.

[0043] (Glow plug control) Next, an automatic stop glow plug control that is executed by the ECU 100 to control the glow plug 16 after the automatic stop condition is satisfied will be described.

[0044] The automatic stop glow control is a control for improving the startability of the engine E when it is restarted. In this embodiment, the automatic stop glow control is performed after the automatic stop condition is satisfied as described above, and is performed when the engine water temperature is within a predetermined range and the engine E is in a so-called semi-warmed state, which is neither a cold state nor a warmed state (warm-up completed state). In the automatic stop glow control, energization to the glow plugs 16 other than the cylinder that starts combustion is prohibited, and as described in detail below, only the glow plugs 16 of the cylinder that starts combustion are energized, and only the combustion chambers 6 of the cylinder that starts combustion are warmed by the glow plugs 16. Specifically, if the mixture is burned in the cylinder that starts combustion, the inertia force of the engine E increases and the rotation of the engine E is generally maintained. Therefore, the influence of energization to the glow plugs 16 of the cylinders other than the cylinder that starts combustion on the startability of the engine E is suppressed to a small value. In this embodiment, when the restart condition is satisfied as described above, the closing timing of the intake valve 11 is advanced from the most retarded timing. Therefore, in the cylinder where combustion occurs after the cylinder where combustion starts, the intake amount is increased by advancing the closing timing of the intake valve 11. Therefore, in the cylinder where combustion occurs after the cylinder where combustion starts, the combustibility of the mixture is good even without raising the temperature inside the combustion chamber 6 by the glow plug 16. For this reason, in this embodiment, in the glow control at the time of automatic stop, electricity is applied only to the glow plug 16 of the cylinder where combustion starts.

[0045] Fig. 5 is a flow chart showing a specific procedure of glow control during automatic stop. Step S1 in Fig. 5 is carried out when the engine water temperature is within a predetermined range and after the automatic stop condition is established.

[0046] First, in step S1, the ECU 100 determines whether the engine E has completely stopped, that is, whether the engine speed has become 0. The ECU 100 makes this determination based on the detection value of the crank angle sensor SN1.

[0047] If the determination in step S1 is NO, that is, the engine E has not yet completely stopped, the ECU 100 repeats step S1. On the other hand, if the determination in step S1 is YES, that is, the engine E has completely stopped after the automatic stop condition is satisfied, the ECU 100 proceeds to step S2.

[0048] In step S2, the ECU 100 determines the combustion start cylinder. As described above, in this embodiment, when the engine E comes to a complete stop, that is, when the engine E is stopped, the cylinder in which the position of the piston 5 is near the bottom dead center of the intake stroke is determined to be the combustion start cylinder. Thus, based on the detection results of the crank angle sensor SN1 and the cam angle sensor SN2, the ECU 100 determines, among the six cylinders 2, the cylinder in which the position of the piston 5 is in the above position as the combustion start cylinder.

[0049] After step S2, in step S3, the ECU 100 determines whether or not the temperature of the glow plug 16 in the combustion start cylinder is lower than a predetermined judgment temperature. The judgment temperature is set in advance and stored in the ECU 100. The judgment temperature is set to, for example, 800°C.

[0050] In this embodiment, the ECU 100 successively estimates the temperature of each glow plug 16 based on the history of energization of the glow plug 16, and makes the determination in step S3 based on this estimated value.

[0051] For example, when the glow plug 16 is energized at a first voltage and a second voltage, the ECU 100 estimates that the temperature of the glow plug 16 will rise to a predetermined maximum temperature (for example, 1300° C.) by energizing at the first voltage. When the energizing voltage is switched to the second voltage, the ECU 100 estimates that the temperature of the glow plug 16 will fall from the maximum temperature at a predetermined first fall rate. The first fall rate is set to a smaller value as the elapsed time from the switching of the energizing voltage from the first voltage to the second voltage increases. When the glow plug 16 is energized only at the second voltage without being energized at the first voltage, the ECU 100 estimates that the temperature of the glow plug 16 will rise from the temperature before energization at a predetermined second rise rate. The second rise rate is preset and stored in the ECU 100. The second increasing speed is a value slightly larger than 0, and the temperature increase amount of the glow plug 16 when the current supply is started at the second voltage is sufficiently smaller than the temperature increase amount when the current supply is started at the first voltage. When the glow plug 16 is not energized and the engine E is running, the ECU 100 estimates that the temperature of the glow plug 16 decreases at a predetermined second decreasing speed. The second decreasing speed is preset and stored in the ECU 100. When the glow plug 16 is not energized and the engine E is stopped, the ECU 100 estimates that the temperature of the glow plug 16 decreases at a predetermined third decreasing speed. The third decreasing speed is preset to a predetermined value smaller than the second decreasing speed and stored in the ECU 100.

[0052] When the determination in step S3 is YES and it is determined that the temperature of the glow plug 16 of the cylinder that starts combustion is lower than the determination temperature, the ECU 100 proceeds to step S4. In step S4, the ECU 100 energizes the glow plug 16 of the cylinder that starts combustion. The energizing voltage at this time is set to a predetermined first voltage, which is higher than a second voltage described later. The first voltage is set in advance and stored in the ECU 100. For example, the first voltage is about 11V, which is set to a value close to the maximum voltage that can be energized to the glow plug 16. Note that the control in step S4, that is, the control of energizing the glow plug 16 of the cylinder that starts combustion with the first voltage, corresponds to the "first energization control" in the claims.

[0053] After step S4, the process proceeds to step S5, where the ECU 100 judges whether a predetermined reference time has elapsed since the start of energization of the glow plug 16 of the combustion start cylinder with the first voltage. The reference time is set in advance and stored in the ECU 100. The reference time is set to the time required for the temperature of the glow plug 16 to rise from the judgment temperature to the above-mentioned maximum temperature when the glow plug 16 is energized with the first voltage. For example, the maximum temperature is set to 1300°C, and the reference time is set to about 1 second. This reference time corresponds to the "reference period" in the claims.

[0054] If the determination in step S5 is YES, that is, if the reference time has elapsed since the start of energization of the glow plug 16 of the combustion start cylinder with the first voltage, the ECU 100 proceeds to step S6.

[0055] On the other hand, if the determination in step S5 is NO and the reference time has not yet elapsed since the start of energization of the glow plug 16 of the combustion start cylinder at the first voltage, the ECU 100 returns to step S4. That is, the ECU 100 executes step S4 and continues energizing the glow plug 16 of the combustion start cylinder at the first voltage until the elapsed time reaches the reference time.

[0056] Returning to step S3, if the determination in step S3 is NO and it is determined that the temperature of the glow plug 16 in the combustion start cylinder is equal to or higher than the determination temperature, the ECU 100 proceeds to step S6.

[0057] In step S6, the ECU 100 energizes the glow plug 16 of the cylinder that starts combustion with a second voltage lower than the first voltage. After step S5, in step S7, the ECU 100 determines whether the restart condition is satisfied. As described above, the ECU 100 performs this determination based on the detection results of the accelerator opening sensor SN5, the brake pedal sensor SN6, and the like. The second voltage is preset and stored in the ECU 100. The second voltage is set to a voltage that can generally maintain the temperature of the glow plug 16 when the engine E is stopped and the temperature of the glow plug 16 is at a predetermined intermediate temperature that is higher than the judgment temperature and lower than the maximum temperature. The second voltage is set to, for example, 5V. Note that the control of step S6, that is, the control of energizing the glow plug 16 of the cylinder that starts combustion with the second voltage, corresponds to the "second energization control" in the claims.

[0058] If the determination in step S7 is YES, that is, if the restart condition is satisfied, the ECU 100 proceeds to step S8.

[0059] On the other hand, if the determination in step S7 is NO and the restart condition is not satisfied, the ECU 100 returns to step S6. That is, the ECU 100 continues to execute step S6 and energize the glow plug 16 of the combustion start cylinder with the second voltage until the restart condition is satisfied.

[0060] In step S8, the ECU 100 performs the above-mentioned start control. After step S8, the process proceeds to step S9, where the ECU 100 determines whether or not the start (restart) of the engine E has been completed. In this embodiment, when the engine speed reaches or exceeds a predetermined determination speed, it is determined that the start of the engine E has been completed, and the ECU 100 performs the determination in step S9 based on the detection result of the crank angle sensor SN1.

[0061] If the determination in step S9 is NO and the starting of the engine E is not completed, the process returns to step S8, and the ECU 100 continues the starting control. On the other hand, if the determination in step S9 is YES and the starting of the engine E is completed, the ECU 100 proceeds to step S10. In step S10, the ECU 100 stops the supply of electricity to the glow plugs 16. Here, the glow plugs 16 other than the one in which the combustion starts are not supplied with electricity. As a result, when the starting of the engine E is completed, the supply of electricity to the glow plugs 16 in the one in which the combustion starts is stopped, and the glow plugs 16 in the other cylinders are maintained in a non-energized state.

[0062] (Example of operation of each part with glow control during automatic stop) 6 and 7 are time charts showing the time changes of each parameter when the above-mentioned automatic stop glow control is performed. From the top, Fig. 6 and Fig. 7 show time charts of the engine speed, the energization voltage to the glow plug 16 of the cylinder where combustion starts, and the temperature of the glow plug 16 of the cylinder where combustion starts (the temperature of the tip of the glow plug 16).

[0063] FIG. 6 is a time chart in the case where the temperature of the glow plug 16 of the combustion start cylinder immediately after the automatic stop of the engine E is lower than the judgment temperature. As shown in FIG. 6, when fuel cut is performed, the engine speed gradually decreases. In the example of FIG. 6, fuel cut is performed at time t0 when the automatic stop condition is satisfied. As a result, the engine speed gradually decreases after time t0, and at time t1 the engine speed becomes 0, that is, the engine E completely stops. When the engine E completely stops at time t1, the energization of the glow plug 16 of the combustion start cylinder starts immediately thereafter at time t2.

[0064] 6, since the temperature of the glow plug 16 of the cylinder that starts combustion at time t2 is lower than the judgment temperature, the energization voltage (glow energization voltage) to the glow plug 16 of the cylinder that starts combustion at time t2 is set to the first voltage higher than the second voltage. As a result, the temperature of the glow plug 16 of the cylinder that starts combustion rises rapidly from time t2 and becomes sufficiently higher than the judgment temperature.

[0065] At time t3, which is a reference time after time t2, the voltage applied to the glow plug 16 of the cylinder that starts combustion is reduced to the second voltage. As a result, the temperature of the glow plug 16 of the cylinder that starts combustion stops increasing at time t3, and the temperature decreases after time t3. However, since the temperature has been increased to a sufficiently high temperature and the current is continued at the second voltage, the temperature of the glow plug 16 of the cylinder that starts combustion is maintained higher than the judgment temperature even after time t3.

[0066] In the example of Fig. 6, the restart condition is satisfied at time t4. Accordingly, cranking of the engine E is started by the motor M, fuel is first injected from the injector 15 into the combustion chamber 6 of the combustion start cylinder, and the engine E is restarted. Then, at time t5 after time t4, when the engine speed reaches or exceeds the determination speed, it is determined that the engine E has started, and the energization of the glow plug 16 of the combustion start cylinder is stopped.

[0067] Fig. 7 is a time chart in the case where the temperature of the glow plug 16 of the combustion start cylinder immediately after the automatic stop of the engine E is equal to or higher than the judgment temperature. As in Fig. 6, in the example of Fig. 7, the engine speed gradually decreases as a result of the fuel cut being performed at time t10. Then, the engine E completely stops at time t11, and immediately thereafter at time t12, the energization of the glow plug 16 of the combustion start cylinder is started.

[0068] In the example of FIG. 7, the temperature of the glow plug 16 of the combustion start cylinder at time t12 is lower than the judgment temperature. Thus, the energization voltage to the glow plug 16 of the combustion start cylinder at time t12 is set to a second voltage lower than the first voltage. Because the energization voltage is relatively low, the temperature rise of the glow plug 16 after the start of energization is suppressed to be smaller than in the example of FIG. 6. However, because the temperature of the glow plug 16 of the combustion start cylinder before the start of energization is higher than the judgment temperature, the temperature of the glow plug 16 is maintained higher than the judgment temperature even after time t12. In the example of FIG. 7, the restart condition is satisfied at time t13 thereafter, and the energization of the glow plug 16 of the combustion start cylinder is stopped as the engine speed becomes higher than the predetermined speed after time t14.

[0069] As described above, the second voltage is set to a voltage that can maintain the temperature of the glow plug 16 at the intermediate temperature. Thus, when the temperature of the glow plug 16 at time t12 is higher than the intermediate temperature, the temperature of the glow plug 16 drops toward the intermediate temperature after the second voltage is applied to the glow plug 16 at time t12, and when the temperature of the glow plug 16 before the second voltage is applied is lower than the intermediate temperature, the temperature of the glow plug 16 rises toward the intermediate temperature after the second voltage is applied. In the example of Fig. 7, since the temperature of the glow plug 16 at time t12 is lower than the intermediate temperature, the temperature of the glow plug 16 rises gradually after time t12.

[0070] (action, etc.) As described above, in the above embodiment, when the temperature of the glow plug 16 of the combustion start cylinder after the automatic stop of the engine E is lower than the judgment temperature, current is applied to the glow plug 16. Therefore, the temperature of the glow plug 16 of the combustion start cylinder can be increased to increase the temperature inside the combustion chamber 6 of the combustion start cylinder by the glow plug 16. Therefore, when the engine E is restarted, the air-fuel mixture can be reliably combusted in the combustion start cylinder to increase the engine speed, thereby improving the startability of the engine.

[0071] In particular, in the above embodiment, when the temperature of the glow plug 16 of the cylinder where the combustion starts is lower than the judgment temperature, the energizing voltage of the glow plug 16 is first set to a high voltage of the first voltage. Therefore, the temperature of the glow plug 16 of the cylinder where the combustion starts can be reliably increased. Moreover, after that, although the energizing voltage is reduced to a second voltage lower than the first voltage, the energizing voltage to the glow plug 16 of the cylinder where the combustion starts is continued. Therefore, the temperature of the glow plug 16 of the cylinder where the combustion starts when the engine E is restarted can be reliably increased to a high temperature, and the startability of the engine can be reliably improved. Furthermore, if the glow plug 16 is continuously energized at the high first voltage, there is a risk that the glow plug 16 will overheat. In response to this, the energizing voltage to the glow plug 16 of the cylinder where the combustion starts is reduced to the second voltage after a predetermined reference time has elapsed since the start of energizing the glow plug 16 of the cylinder where the combustion starts at the first voltage, so that the glow plug 16 of the cylinder where the combustion starts can be prevented from overheating and early deterioration of the glow plug 16 can be prevented.

[0072] Then, when the temperature of the glow plug 16 of the cylinder where the combustion starts after the automatic stop of the engine E is high, the glow plug 16 of the cylinder where the combustion starts is not energized at the first voltage, but is energized at the second voltage. In other words, when the temperature of the glow plug 16 of the cylinder where the combustion starts is high, energization of the glow plug 16 is suppressed. Therefore, it is possible to prevent the glow plug 16 from overheating due to energization at the high first voltage to the glow plug 16, which is already at a high temperature, and to prevent early deterioration of the glow plug 16. In addition, by energizing at the second voltage, it is possible to maintain the glow plug 16 of the cylinder where the combustion starts at a high temperature, and to improve the startability of the engine E.

[0073] (Modification) In the above embodiment, the case has been described where the glow plug 16 in the combustion start cylinder is energized with the second voltage even when the temperature of the glow plug 16 in the combustion start cylinder is equal to or higher than the determination temperature when the engine E is stopped, but the configuration may be such that when the temperature of the glow plug 16 in the combustion start cylinder is high, energization of the glow plug 16 is stopped. Even in this case, it is possible to prevent the high-temperature glow plug 16 from being overheated by further energizing it, and to prevent early deterioration of the glow plug 16.

[0074] In addition, in the above embodiment, when the temperature of the glow plug 16 in the cylinder where combustion starts when the engine E is stopped is lower than the judgment temperature, the voltage supplied to the glow plug 16 is changed to the first voltage and then to the second voltage. However, the voltage supplied to the glow plug 16 may be maintained constant.

[0075] In the above embodiment, the cylinder in which the piston 5 is located near the intake bottom dead center when the engine is stopped is set as the combustion start cylinder, but the combustion start cylinder may be another cylinder. However, in the above embodiment, the closing timing of the intake valve 11 is retarded to the most retarded timing when the engine E is stopped to reduce the intake amount of the compression stroke cylinder at the time of stopping. Therefore, if the combustion start cylinder is set as the compression stroke cylinder at the time of stopping, the combustion of the mixture and the startability of the engine E may be reduced due to the small intake amount in the cylinder. In addition, in the other cylinders, the time until the compression top dead center is passed is longer, so that the energy required for the motor M to rotate the crankshaft 7 at the time of starting the engine E is large. As a result, in a six-cylinder engine as in the above embodiment, if the cylinder in which the piston 5 is located near the intake bottom dead center when the engine is stopped is designated as the combustion start cylinder, the energy consumed by the motor M when starting the engine E can be reduced, and the amount of intake air into the combustion start cylinder can be increased, thereby improving the combustibility of the mixture in that cylinder and therefore the starting ability.

[0076] In the above embodiment, the engine E is a six-cylinder engine having six cylinders 2, but the number of cylinders of the engine E is not limited to this and may be four, etc. In a four-cylinder engine, it is highly likely that the closing timing of the intake valve 11 is not retarded to the most retarded timing when the engine E is stopped, and in a four-cylinder engine, the cylinder that is in the compression stroke when the engine is stopped may be the combustion start cylinder. [Explanation of symbols]

[0077] 1 Engine body 2-cylinder 5 Piston 7 Crankshaft 11 Intake valve 15 Injector (fuel supply means) 30 Intake passage 32 Throttle valve 100 ECU 101 Fuel control unit 102 Glow control section 103 Combustion start cylinder determination unit E-Engine M Motor (starting means)

Claims

1. A control device provided in an engine that includes a plurality of cylinders, a fuel supply means for supplying fuel to the combustion chambers of each cylinder, and a plurality of glow plugs each having a heat generating portion that generates heat when energized and disposed in each combustion chamber, the engine being capable of being automatically stopped and restarted, a combustion start cylinder determination unit that determines a combustion start cylinder that is a cylinder that will first combust an air-fuel mixture when the engine is restarted after the engine is automatically stopped; a fuel control unit that controls the fuel supply means so that fuel is supplied first to the combustion chamber of the combustion start cylinder determined by the combustion start cylinder determination unit when the engine is restarted; A glow plug control unit controls the glow plug. After the engine is automatically stopped, the glow control unit a first current supply control is implemented to supply current to the glow plug of the combustion start cylinder at a predetermined first voltage for a predetermined reference period when the temperature of the glow plug of the combustion start cylinder determined by the combustion start cylinder determination unit is lower than a predetermined judgment temperature, and after the first current supply control is completed, a second current supply control is implemented to supply current to the glow plug of the combustion start cylinder at a second voltage lower than the first voltage, a glow plug control unit that controls the supply of current to the glow plug when the temperature of the glow plug in the combustion start cylinder is equal to or higher than the threshold temperature, and the first current supply control unit controls only the second current supply control, thereby suppressing the supply of current to the glow plug.

2. 2. The engine control device according to claim 1, The engine has six cylinders arranged in a row. The engine control device according to claim 1, wherein the combustion start cylinder determination unit determines, as the combustion start cylinder, a cylinder in which a piston provided in each cylinder stops at a position near bottom dead center of intake air.

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