JP2012092796A - Control device for electrically-assisted turbocharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an electrically-assisted turbocharger that improves fuel consumption.SOLUTION: The control device for an electrically-assisted turbocharger includes: a rotation assist control part 3 for controlling an electric motor 807 according to the engine operating state; a vane opening-degree control part 4 for subjecting a vane to opening-degree control according to the engine operating state; and a vane cooperative control part 5 that subjects the vane to opening-degree control according to the engine operating state when there is no rotation assist by the electric motor 807 and controls the vane to be fully closed or to have an opening degree smaller than that of when there is no rotation assist during the rotation assist by the electric motor 807.

Description

  The present invention relates to an electrically assisted turbocharger control device that improves fuel consumption.

  When the engine is downsized, fuel efficiency is improved by reducing weight and reducing friction, and an engine with a small displacement is operated at high torque, thereby increasing efficiency and improving fuel efficiency. Improvement in fuel efficiency also leads to reduction of carbon dioxide emissions. However, when the engine is downsized, in order to ensure the same power performance as before, it is necessary to increase the supercharging performance by the turbocharger.

  The turbocharger has an impeller attached to each end of the turboshaft. One impeller is called a turbine wheel, and the other impeller is called a compressor wheel. In an exhaust turbine that contains a turbine wheel, the turbine wheel is rotated by applying an exhaust gas flow to the blades of the turbine wheel. To do. As described above, the turbocharger is a device that compresses intake air by work taken out from exhaust gas.

  As a kind of turbocharger, a turbocharger in which a vane for adjusting the strength of an exhaust gas flow hitting a blade of a turbine wheel is installed in an exhaust turbine is known (Patent Document 1). Although this type of turbocharger is called by various names such as a VG (Variable Geometry) turbocharger and a variable nozzle turbo (registered trademark), they are technically equivalent.

  While the turbocharger's supercharging performance varies greatly depending on the engine operating state, the turbocharger's supercharging performance can be improved by adjusting the strength of the exhaust gas flow by opening and closing the vanes according to the engine operating state. it can. Specifically, when the vane is opened, the rotation of the turbo shaft is difficult to increase, and the increase in the expansion ratio (inlet pressure / outlet pressure) with respect to the increase in the exhaust gas flow rate is small. On the other hand, when the vane is closed, the rotation of the turbo shaft is likely to increase, so that the expansion ratio increases with an increase in the exhaust gas flow rate.

  This allows a wide range of engine operating conditions where exhaust gas energy is high (exhaust gas temperature is high, exhaust gas flow is high) to engine operation state where exhaust gas energy is low (exhaust gas temperature is low, exhaust gas flow is low). Turbocharger can be used. FIG. 7 shows the supercharging pressure characteristics of a turbocharger without vanes and a turbocharger with vanes. The supercharged pressure drops in the low and high engine speed areas where the vane-free turbocharger characteristics indicated by the broken line fall, whereas the vane turbocharger characteristics indicated by the solid line indicate that the engine speed is low to high. It can be seen that a high supercharging pressure can be realized.

  On the other hand, an electrically assisted turbocharger that assists the rotation of the turbo shaft with an electric motor is known as means for increasing the supercharging pressure regardless of the engine operating state (Patent Document 2). FIG. 8 shows an electric assist turbocharger.

  As shown in FIG. 8, the electrically assisted turbocharger 801 includes an exhaust turbine 803 having a turbine wheel 802 that is rotated by exhaust gas, an intake compressor 805 having a compressor wheel 804 that compresses air by rotation, and a turbine wheel 802. A turbo shaft 806 that is integrated with the compressor wheel 804 and transmits rotation from the exhaust turbine side to the intake compressor side, and a rotor (not shown) of the electric motor 807 that is coaxial with the turbo shaft 806 and integrated with the turbo shaft 806. And a stator (not shown) of the electric motor 807 located on the outer periphery of the rotor.

  According to the electrically assisted turbocharger 801, even in an engine operating state where exhaust gas energy is insufficient, the turbo shaft 806 can be rotated at a high speed by the electric motor 807 to obtain a high supercharging pressure (Patent Document 3). .

Japanese Patent No. 3237565 JP 2006-320143 A JP 2010-209735 A

  By the way, in the electric assist turbocharger in which the vane and the electric assist turbocharger 801 are combined, there is a problem that the rotation of the turbo shaft 806 is difficult to increase if the vane is open at the time of rotation assist when the electric motor 807 assists the rotation. There is.

  Even in an engine operating state where exhaust gas energy is insufficient, exhaust gas is exhausted from the engine. If the vane is closed at the time of rotation assistance, the exhaust gas force acts on the turbine wheel 802 efficiently, and therefore the rotation of the turbo shaft 806 is likely to increase. On the other hand, if the vane is open at the time of rotation assistance, the exhaust gas force does not work efficiently on the turbine wheel 802, and therefore the rotation of the turbo shaft 806 is difficult to increase.

  Thus, if the vane is open at the time of rotation assistance, the rotation of the turbo shaft 806 is difficult to increase, and it takes time for the rotation of the turbo shaft 806 to reach the desired number of rotations. Is consumed, and fuel consumption deteriorates.

  Therefore, an object of the present invention is to provide an electric assist turbocharger control device that solves the above-described problems and improves fuel consumption.

  In order to achieve the above object, the present invention relates to an electric assist turbocharger comprising an electric motor for assisting rotation of a turboshaft and a vane for adjusting an exhaust gas flow to a turbine wheel. In the electric assist turbocharger control device that performs control, the opening degree of the vane is controlled according to the engine operating state when the electric motor does not assist the rotation, and when the electric motor assists the rotation, the vane is fully closed or when there is no rotation assist The vane cooperation control part which controls to a smaller opening degree is provided.

  The vane cooperative control unit may change the opening of the vane from the opening at the time of assisting rotation to the opening at the time of no rotation assistance at the end of the rotation assist.

  The present invention exhibits the following excellent effects.

  (1) The fuel consumption can be improved.

It is a block diagram of the electrically assisted turbocharger control apparatus which shows one Embodiment of this invention. It is a block diagram of the engine system carrying an electrically assisted turbocharger control apparatus. It is a flowchart which shows the control procedure in the electrically assisted turbocharger control apparatus of this invention. It is a graph which shows the intake flow volume versus pressure ratio characteristic (map) in an intake compressor. It is a graph which shows the exhaust gas flow volume versus expansion ratio characteristic (map) in an exhaust turbine. It is a graph which shows the transition locus of the cylinder internal volume and cylinder internal pressure in an engine. It is a graph which shows the supercharging pressure characteristic of a turbocharger without a vane and a turbocharger with a vane. It is a block diagram of an electrically assisted turbocharger.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, an electric assist turbocharger control device 1 according to the present invention includes an electric motor 807 that assists the rotation of a turboshaft 806 and a vane (not shown) that adjusts the exhaust gas flow to the turbine wheel 802. The electric assist turbocharger control device 1 controls the electric motor 807 and the vane for the electric assist turbocharger 2 including the above.

  The electric assist turbocharger control device 1 is intended to link the rotation assistance by the electric motor 807 with the vane opening degree control. The rotation assist control unit 3 controls the electric motor 807 according to the engine operation state, and the engine operation. A vane opening degree control unit 4 that controls the opening degree of the vane according to the state, and further controls the opening degree of the vane according to the engine operating state when the electric motor 807 does not assist the rotation, and the vane when the electric motor 807 assists the rotation. Is provided with a vane cooperative control section 5 for controlling the opening to a smaller opening than when fully closed or without rotation assistance.

  The electrically assisted turbocharger 2 has vanes (not shown) installed in the exhaust turbine 803 of the electrically assisted turbocharger 801 described with reference to FIG. The opening degree of the vane is adjusted by the actuator 6.

  The rotation assist control unit 3 controls the electric motor 807 according to the engine operating state to assist the rotation of the turbo shaft 806. Specifically, the rotation auxiliary control unit 3 is a rotation referred to by the engine rotation speed and the accelerator opening. Based on the auxiliary map 7, the electric motor 807 is driven or stopped, or the driving amount of the electric motor 807 is increased or decreased. For example, when the engine rotation speed is low and the accelerator opening is large, such as when the vehicle starts, the electric motor 807 is driven to assist rotation, and when the engine rotation speed is high or the accelerator opening is small, the electric motor 807 is driven. To stop rotation assistance.

  The vane opening degree control unit 4 controls the opening degree of the vanes according to the engine operating state and adjusts the strength of the exhaust gas flow hitting the blades of the turbine wheel 802. Specifically, the engine rotation speed and the accelerator are controlled. Based on the vane opening degree map 8 referred to as the opening degree, the vane is controlled to an optimum opening degree from fully closed to fully open.

  The vane cooperative control unit 5 executes the opening degree control by the vane opening degree control unit as it is when there is no rotation assistance, and unconditionally fully closes the vane during rotation assistance, or the opening degree given by the vane opening degree control unit 4 On the other hand, the opening correction map 9 is used to correct the vane in the closing direction.

  FIG. 2 shows an engine system 200 equipped with the electric assist turbocharger control device 1.

  The exhaust manifold 202 of the engine 201 is connected to an exhaust pipe 203 that guides and discharges exhaust gas from the engine 201 to the atmosphere. The exhaust gas is circulated from the exhaust manifold 202 to the intake manifold 204 in the uppermost stream of the exhaust pipe 203. EGR piping 205 is provided for this purpose. The EGR pipe 205 is provided with an EGR cooler 206 for cooling the exhaust gas and an EGR valve 207 for adjusting the EGR amount (or EGR rate).

  An exhaust turbine 209 of the high-pressure stage turbocharger 208 is provided downstream of the EGR pipe 205 of the exhaust pipe 203, and an exhaust turbine 211 of the low-pressure stage turbocharger 210 is provided downstream thereof. An exhaust gas purification device 212 is provided downstream of the exhaust turbine 211, and an exhaust throttle 213 that opens and closes the exhaust pipe 203 is provided further downstream. The exhaust gas purification device 212 is a known device that removes NOx and PM. The exhaust pipe 203 is opened to the atmosphere via a silencer 214 downstream of the exhaust throttle 213.

  An intake pipe 215 for taking air from the atmosphere into the engine 201 is connected to the intake manifold 204. The uppermost stream of the intake pipe 215 is open to the atmosphere, and an air cleaner 216 for removing foreign substances such as dust is provided downstream of the open end. An intake compressor 217 of the low-pressure stage turbocharger 210 is provided downstream of the air cleaner 216, and an intake air compressor 218 of the high-pressure stage turbocharger 208 is provided further downstream. An intercooler 219 for cooling the intake air compressed by the high-pressure turbocharger 208 is provided downstream of the intake compressor 218, and an intake throttle 220 for limiting the intake air amount is provided downstream thereof. The EGR pipe 205 is joined to the intake pipe 215 downstream of the intake throttle 220, and the intake pipe 215 is connected to the intake manifold 204 downstream thereof.

  As described above, the engine system 200 is a two-stage turbo engine system 200 in which the high-pressure stage turbocharger 208 and the low-pressure stage turbocharger 210 are arranged in series along the exhaust flow and the intake flow. It is preferable to provide bypass pipes that can be opened and closed with respect to the exhaust turbines 209 and 211 and the intake compressors 217 and 218 of the turbochargers of each stage, and switch the combination of stages to be used according to the engine state.

  In the present embodiment, the electric assist turbocharger 2 is used as the high-pressure stage turbocharger 208.

  The engine system 200 is provided with a known electronic control circuit (Engine Control Module; hereinafter referred to as ECM) 221 that controls the fuel injection amount by electronically controlling each part of the engine system 200 based on the engine operating state. It is done. The rotation auxiliary control unit 3, the vane opening degree control unit 4, the vane cooperative control unit 5, the rotation auxiliary map 7, the vane opening degree map 8, and the opening degree correction map 9 of the present invention may be added as programs and data in the ECM 221. .

  Next, the operation of the electric assist turbocharger control device 1 of the present invention will be described.

  During engine operation, the rotation assist controller 3 assists the rotation of the turbo shaft 806 by controlling the electric motor 807 based on the rotation assist map 7 referred to by the engine speed and the accelerator opening. For example, when the engine speed is low and the accelerator opening is large, such as when the vehicle starts, exhaust gas energy is insufficient, so that rotation assistance is provided to increase the intake air amount. On the other hand, the vane opening degree control unit 4 tries to control the vane opening degree based on the vane opening degree map 8 referred to by the engine speed and the accelerator opening degree.

  As shown in FIG. 3, during engine operation, in step S <b> 1, the vane cooperative control unit 5 determines whether or not the rotation assist control unit 3 is assisting rotation by the electric motor 807. If it is No, it will progress to step S2, and since it is a time of no rotation assistance, normal vane control, ie, the opening degree control by the vane opening degree control part 4, will be performed as it is.

  If the determination in step S1 is Yes, the process proceeds to step S3, and the rotation is assisted, so that the vane is fully closed or the opening is corrected smaller than the opening control by the vane opening controller 4 (for example, reduced by 50%). The opening degree control is executed.

  After step S <b> 3, it is determined whether or not the rotation assist control unit 3 is assisting rotation by the electric motor 807. If Yes, the control of vane fully closed or opening reduction is continued. If it is No, it will progress to step S5 and will return to normal vane control, ie, the opening degree control by the vane opening degree control part 4. FIG. However, in order to prevent hunting, it is preferable to gradually return the vane opening degree.

  Next, the effect of the present invention will be described.

  First, the effect of rotation assistance will be described with reference to FIG. As shown in FIG. 4, the flow rate of air sucked into the intake compressor 805 is taken on the horizontal axis, the pressure ratio (outlet pressure / inlet pressure) in the intake compressor 805 is taken on the vertical axis, and each turbo rotation (rotation speed of the turbo shaft 806). Plot the operating point of. The alternate long and short dash line represents turbo rotation. As shown in the figure, the pressure ratio is determined to be one at a certain air flow rate in a certain turbo rotation. The black circle is one such operating point when there is no rotation assistance. The vortex pattern by the broken lines shown inside the left and right limit lines B1 and B2 represents the region of the operating point where the efficiency is the same. The intake compressor 805 is designed so that the operating point comes closer to the center of the vortex pattern.

  Here, when the turbo rotation is increased by assisting rotation, the operating point increases in pressure ratio along the broken line, and the intake flow rate increases, and the operating point shifts to a black triangular operating point.

  Next, the effect of vane opening control will be described with reference to FIG. As shown in FIG. 5, the flow rate of the exhaust gas flowing out from the exhaust turbine 803 is taken on the horizontal axis, the expansion rate (inlet pressure / outlet pressure) in the exhaust turbine 803 is taken on the vertical axis, and the operating points are plotted for each vane opening. However, here, the plots are shifted in the horizontal axis direction according to the vane opening so that the plots do not overlap.

  When the vane is fully open, the turbo rotation is low when the exhaust gas flow rate is small, and the expansion rate is slightly increased even when the exhaust gas flow rate increases. As the exhaust gas flow rate increases and the turbo rotation becomes a medium low rotation, medium high rotation, and high rotation, the degree of increase in the expansion rate with respect to the increase in the exhaust gas flow rate gradually increases. In contrast, when the vane is fully closed, the turbo rotation is low when the exhaust gas flow rate is small, and when the exhaust gas flow rate is increased, the expansion rate is slightly higher than when the vane is fully opened. However, when the turbo rotation is medium / low rotation, medium / high rotation, or high rotation, the degree of increase in the expansion rate with respect to the increase in the exhaust gas flow rate is remarkably increased.

  As described above, when the vane is opened, the rotation of the turbo shaft 806 is difficult to increase. However, when the vane is closed, the rotation of the turbo shaft 806 is easily increased even when the exhaust gas flow rate is increased. If the vane opening is halfway between fully open and fully closed, the characteristic is also an intermediate characteristic. Therefore, the characteristics of the expansion coefficient with respect to the exhaust gas flow rate can be set to desired characteristics by controlling the opening degree of the vane.

  Next, the effect of combining vane opening control and rotation assistance will be described with reference to FIG.

  For example, it is assumed that the vane is fully closed when starting. At the time of start, the exhaust gas flow rate is extremely small, so that the rotation of the turbo shaft 806 is difficult to increase and the expansion rate does not increase. As a result, the amount of intake air to the engine 201 cannot be increased (black circle operating point). At this time, if rotation assistance is performed, the black circle operating point with low turbo rotation shifts to the black triangular operating point with medium to high turbo rotation, so the expansion rate increases dramatically. As a result, the amount of intake air to the engine 201 increases and the fuel injection amount can be increased, so that the start is smooth.

  When the vane is closed, the turbo rotation is efficiently increased. On the other hand, the exhaust gas flow is blocked by the vane, and the exhaust back pressure (pressure at the inlet of the exhaust turbine 803) increases. At this time, if rotation assistance is performed, the exhaust gas from the exhaust manifold 202 is forcibly drawn into the exhaust turbine 803, so that the exhaust back pressure decreases. In general, the engine 201 is preferable because the fuel efficiency improves when the exhaust back pressure decreases.

  Thereafter, the engine state changes to a high engine rotation speed and a high load, and the rotation assistance ends. Although the turbo rotation is reduced by the end of the rotation assistance, the exhaust gas flow rate does not change because it depends on the engine operating state. At this time, when the vane is opened at an appropriate opening degree, it is possible to shift to the black square operating point where the exhaust gas flow rate is the same and the expansion rate is low. Thus, if the expansion ratio is lowered without changing the exhaust gas flow rate, the exhaust back pressure of the engine 201 is lowered, and the fuel efficiency is improved.

  Here, the reason why the fuel consumption improves when the exhaust back pressure decreases will be described.

  As shown in FIG. 6, the in-cylinder volume and the in-cylinder pressure of the engine 201 transition along a locus along an arrow. In the intake stroke a, when the intake valve opens, the in-cylinder volume increases while maintaining the intake pressure at a low in-cylinder pressure. In the compression stroke b, the cylinder pressure increases as the cylinder volume decreases. In the expansion stroke c, the in-cylinder pressure decreases at a pressure higher than the compression stroke b as the in-cylinder volume increases. In the exhaust stroke d, while the exhaust valve is open, the in-cylinder volume decreases while the in-cylinder pressure maintains an exhaust pressure higher than the intake pressure in the intake stroke a.

  In FIG. 6, a positive work is done when the trajectory draws a clockwise loop. That is, work is taken out from the engine 201 to the outside. When the trajectory draws a counterclockwise loop, negative work is done. That is, the engine 201 is worked from the outside. In either case, the area of the loop represents the size of work. In the counterclockwise loop from the exhaust stroke d to the intake stroke a, a pumping loss is caused by supplying and discharging gas into the cylinder via the exhaust port and the intake port.

  Focusing on the locus (solid line) in FIG. 6 at the black triangle operating point in FIG. 5 from the end of the expansion stroke c to the exhaust stroke d, the exhaust back pressure is high, so that the cylinder pressure is high and the counterclockwise loop area Is big. That is, the pumping loss is large. On the other hand, when focusing on the locus (broken line) in FIG. 6 at the black square operation point in FIG. 5 from the end of the expansion stroke c to the exhaust stroke d, the in-cylinder pressure is lowered due to the lower exhaust back pressure. The area of the counterclockwise loop is reduced. That is, the pumping loss is reduced. Therefore, it can be seen that the fuel efficiency is improved if the vehicle is driven on the locus of the broken line.

  As described above, in the present invention, the normal vane opening degree control is performed when there is no rotation assistance, and the vane fully closed or reduced opening degree control is performed during rotation assistance. The rotation is easily increased, the time for which the rotation of the turbo shaft 806 is increased to a desired number of rotations is shortened, the power consumption of the electric motor 807 is reduced, and the fuel consumption is improved.

  Further, since the vane is controlled to open in the end of the rotation assistance, the pumping loss is reduced and the fuel efficiency is improved.

  In the present embodiment, the electric assist turbocharger control device 1 is mounted on the two-stage turbo engine system 200, but the present invention is also effective for a one-stage turbo engine system.

DESCRIPTION OF SYMBOLS 1 Electric assist turbocharger control apparatus 2 Electric assist turbocharger 3 Rotation assistance control part 4 Vane opening degree control part 5 Vane cooperation control part 6 Actuator 7 Rotation assistance map 8 Vane opening degree map 9 Opening degree correction map

Claims (2)

In the electric assist turbocharger control device for controlling the electric motor and the vane with respect to the electric assist turbocharger having an electric motor for assisting the rotation of the turbo shaft and a vane for adjusting the exhaust gas flow to the turbine wheel,
A vane cooperative control unit that controls the opening of the vane according to an engine operating state without rotation assistance by the electric motor, and controls the vane to be fully closed or smaller than that without rotation assistance when the rotation assistance by the electric motor is performed. An electrically assisted turbocharger control device comprising:   2. The electrically assisted turbocharger according to claim 1, wherein the vane cooperative control unit changes the opening degree of the vane from an opening degree at the time of assisting rotation to an opening degree when there is no rotation assistance at the end of the rotation assistance. Control device.