JP2005201092A - Supercharge system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercharge system for an internal combustion engine effectively avoiding surging of an electric compressor and performing supercharging assistance by sufficiently bringing out performance of the electric compressor. <P>SOLUTION: The supercharge system for the internal combustion engine comprises a turbocharger 2 having a compressor 2a and a turbine 2b, the electric compressor 3 provided on an intake pipe 4 upstream of the compressor 2a of the turbocharger 2, a bypass passage 6 bypassing the electric compressor 3, and a bypass valve 7 provided in the bypass passage 6 for adjusting an air inflow rate into the bypass passage 6. The supercharge system is equipped with a surging region judgment means 12 for judging entry in a surging region wherein the electric compressor 3 surges and a surging avoidance and control means 12 for controlling at least one of the electric compressor 3 and the bypass valve 7 to avoid surging when it enters the surging region or there is a fear of the entry. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a supercharging system for an internal combustion engine.

As a supercharging system for an internal combustion engine, there is known a system in which an electric compressor is connected in series or in parallel with a turbocharger and supercharging assist is performed by the electric compressor (see, for example, Patent Document 1). In addition, there is Patent Document 2 as a prior art document related to the present invention.
Special Table 2000-500544 Special table 2001-509561 gazette

  When the electric compressor is operated when the engine speed is low, a flow rate of air to be supplied to the electric compressor is insufficient, and a phenomenon such as vibration of a structure such as a casing of the electric compressor may occur. This phenomenon is called surging, and it is desirable to avoid the occurrence of surging in order to realize a stable supercharging system.

  However, Patent Document 1 only discloses a supercharging system that operates an electric compressor to compensate for a time lag of the turbocharger when sudden acceleration is predicted, and no consideration is given to the surging. . In general, in order to operate an electric compressor without causing surging, a safety factor of about 10% must be secured from the limit (surge limit) that causes surging. For this reason, especially when the maximum efficiency point of the electric compressor is in the vicinity of the surge limit, the ability of the electric compressor cannot be utilized to the maximum, and the supercharging assist by the electric compressor may be insufficient.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a supercharging system for an internal combustion engine that can efficiently avoid surging of an electric compressor and sufficiently perform the supercharging assist by fully extracting the capacity of the electric compressor.

  A supercharging system for an internal combustion engine according to the present invention includes a turbocharger having a compressor and a turbine, an electric compressor provided in an intake passage upstream of the compressor of the turbocharger, and a bypass bypassing the electric compressor In a supercharging system for an internal combustion engine that includes a passage and a first adjustment valve that is provided in the bypass passage and adjusts an inflow amount of air into the bypass passage, the electric compressor is connected to a surging region where surging occurs. A surging area determining means for determining whether or not there is an approach, and the electric compressor and the first so as to avoid the surging when it is determined by the surging area determining means that the surging area is entered or is likely to be entered. Surging avoidance control means for controlling at least one of the regulating valves To solve the problems described above by (claim 1).

  According to the present invention, the supercharging assist can be executed while avoiding the surging region, so that it is not necessary to operate with the output of the electric compressor kept low in order to prevent the occurrence of surging. Therefore, the supercharging assist can be performed by fully drawing out the capacity of the electric compressor.

  The supercharging system of the present invention further comprises temperature detecting means for detecting or estimating an intake air temperature downstream of the electric compressor, wherein the surging area determining means has a detection result of the temperature detecting means exceeding a predetermined limit temperature. If it is determined that there is a risk of entering or surging into the surging area, and the surging avoidance control means determines that the surging area determination means enters or is likely to enter the surging area. The electric compressor may be controlled so as to reduce the rotational speed of the electric compressor. When the electric compressor reaches surging, the downstream temperature rapidly increases. This characteristic is a property that appears in common regardless of individual differences of electric compressors. Therefore, according to this aspect, since the temperature downstream of the electric compressor is monitored, occurrence of surging can be efficiently avoided regardless of individual differences.

  The supercharging system of the present invention further comprises pressure detecting means for detecting or estimating a pressure downstream of the electric compressor, and the surging area determining means has a detection result obtained by the pressure detecting means having a predetermined limit pressure. When it is determined that there is a risk of entering or surging into the surging area on the condition that it has been exceeded, and the surging avoidance control means determines that there is a risk of entering or surging into the surging area by the surging area determination means Alternatively, the first regulating valve may be controlled to increase the flow rate of air flowing into the electric compressor. According to this aspect, the air that has flowed back through the bypass passage is again sucked up by the electric compressor, so that the air flow rate can be increased relative to the downstream intake pressure. This makes it possible to avoid entering the surging region while keeping the pressure ratio substantially constant. Accordingly, when there is a margin in the output of the electric compressor, the number of revolutions can be increased, so that the supercharging pressure can be increased while avoiding the surging region, and the capacity of the electric compressor 3 can be fully exploited. it can.

  The supercharging system of the present invention further includes a second regulating valve provided in the intake passage upstream of the electric compressor, wherein the surging avoidance control means is moved to the surging area by the surging area determining means. When the second regulating valve is closed to increase the intake air pressure upstream of the electric compressor and increase the air flow rate that reaches the surge limit of the electric compressor. (Claim 4). In this case, since the pressure on the upstream side of the electric compressor is increased and the air flowing backward through the bypass passage can be efficiently guided to the electric compressor, the air flow rate can be further increased.

  As described above, according to the present invention, it is possible to provide a supercharging system for an internal combustion engine that can effectively avoid surging of the electric compressor and sufficiently perform the supercharging assist by fully extracting the capacity of the electric compressor. it can.

(First embodiment)
A supercharging system for an internal combustion engine according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the overall configuration of the present embodiment. This supercharging system is applied to a diesel engine 1 (hereinafter sometimes referred to as an engine) as an internal combustion engine, and includes a turbocharger 2 and an electric compressor 3. As is well known, the turbocharger 2 has a compressor 2a for compressing the sucked air and a turbine 2b for driving the compressor 2a. The compressor 2a is provided in the intake pipe 4 as an intake passage. The turbine 2b is provided in the exhaust pipe 5. The turbocharger 2 rotates the turbine 2b with the exhaust gas flowing through the exhaust pipe 5 to drive the compressor 2a. Thereby, a desired supercharging pressure can be obtained.

  On the other hand, the electric compressor 3 is provided in the intake pipe 4 on the upstream side of the turbocharger 2. The electric compressor 3 includes an electric motor 3a as a driving device. The electric motor 3a is connected to a power source (not shown). By driving the electric motor 3a, the electric compressor 3 operates, and the air in the intake pipe 4 can be compressed.

  A desired supercharging pressure can be obtained by operating the turbocharger 2 and the electric compressor 3. Since the turbocharger 2 uses the energy of the exhaust gas as described above, a time lag occurs until a desired supercharging pressure is obtained (so-called turbo lag). This is particularly noticeable when rapid acceleration is required during low-speed traveling. Therefore, supercharging assistance is performed by the electric compressor 3 to compensate for the turbo lag and assist the turbocharger until a desired supercharging pressure is obtained.

  In the supercharging system, a bypass passage 6 that bypasses the electric compressor 3 is provided. In the middle of the bypass passage 6, a bypass valve 7 is provided as a first adjustment valve that adjusts the amount of air flowing into the bypass passage 6. The bypass valve 7 is basically fully closed when the electric compressor 3 is in operation, and the inflow of air into the bypass passage 6 is prohibited. Accordingly, substantially all the air upstream of the electric compressor 3 is guided to the electric compressor 3. On the other hand, when the electric compressor 3 is not in operation, it is basically fully opened, and air is guided to the bypass passage 6. The bypass valve 7 is linearly driven by a solenoid or the like from a fully closed state to a fully open state. Thereby, the flow volume of the air guide | induced to the bypass channel | path 6 can be adjusted. The intake pipe 4 on the upstream side of the electric compressor 3 is provided with a throttle valve 8 as a second adjustment valve for adjusting the air flow rate. Similar to the bypass valve 7, the throttle valve 8 is linearly driven from a fully closed state to a fully open state by a solenoid or the like, and can adjust the air flow rate flowing into the intake pipe 4.

  As shown in FIG. 1, an intercooler 9 is provided in the intake pipe 4 on the downstream side of the compressor 2a of the turbocharger 2 in order to cool the air compressed by the compressor 2a. Thereby, the supercharging efficiency can be increased. Further, for the same reason as described above, an intercooler 10 is provided in the intake pipe 4 between the electric compressor 3 and the compressor 2a of the turbocharger 2. By providing this intercooler 10, it is possible to further improve the supercharging efficiency, but it is not always necessary to provide it. In addition, an air cleaner 11 is provided in the intake pipe 4 on the upstream side of the electric compressor 3 to remove foreign substances in the intake air.

  The electric motor 3a generates heat and is preferably cooled. In this case, it is difficult to cool by air cooling, and the operation time of the electric compressor 3 may be limited. Therefore, for example, as shown in FIG. 2, a cooling system in which the cooling water W is circulated by the radiator 14 around the electric motor 3a may be employed. Although this radiator 14 may be used also as what is used for the engine 1, since the temperature of the cooling water of the engine 1 is high, it is more preferable to prepare for the electric compressor 3 separately. In this case, the temperature of the cooling water W is preferably about 30 ° C. Further, the radiator 14 can be used for cooling the compressor 2 a of the turbocharger 2. Such a configuration is very effective as a countermeasure against coking, which is a serious problem.

  With the above configuration, when the electric compressor 3 is in operation, the intake air that has passed through the air cleaner 11 is compressed by the electric compressor 3 and then guided to the compressor 2a of the turbocharger 2 for further compression. It is guided to the engine 1 by a desired supercharging pressure.

  As shown in FIG. 1, the supercharging system of the present embodiment is controlled mainly by an engine control unit (ECU) 12 that controls the fuel injection amount of the engine 1 and the like. ECU12 is comprised as a computer unit provided with peripheral devices, such as a microprocessor, ROM, and RAM. The ECU 12 controls the electric compressor 3, the bypass valve 7, and the throttle valve 8 based on input information from various sensors described later.

  As shown in FIG. 1, the supercharging system according to the present embodiment includes an accelerator opening sensor 20 that detects an accelerator opening and its change amount, an engine speed sensor 21 that detects an engine speed, and an electric compressor 3. A pressure sensor 23 as a pressure detection means for detecting the pressure of the downstream intake pipe, a temperature detection means for detecting the intake air temperature downstream of the electric compressor 3 provided in the intake pipe 4 between the electric compressor 3 and the intercooler 10. As a temperature sensor 24, an air flow meter 25 for detecting the mass flow rate of air flowing into the intake pipe 4, and a pressure sensor 25a for detecting the pressure of air flowing into the intake pipe, and the air flow meter 25. A built-in temperature sensor 25b for detecting the temperature of the air flowing into the intake pipe 4 is provided. These various sensors are appropriately used according to the control modes described below. These various sensors may be sensors that detect the physical quantity itself that is a detection target, or may estimate the physical quantity.

  FIG. 3 is a flowchart showing an outline of a control routine of the supercharging system according to the present embodiment. This control routine is repeatedly executed at predetermined intervals according to a program stored in the ROM or the like of the ECU 12. When the ECU 12 executes this control routine, it functions as a surging region determination unit and a surging avoidance control unit.

  As shown in FIG. 3, the ECU 12 first determines in step S1 whether or not the electric compressor 3 is in a non-operating (OFF) state. When an affirmative determination is made in step S1 that the electric compressor 3 is in a non-operating state, the ECU 12 proceeds to step S2 to determine whether or not an operation start condition for the electric compressor 3 is satisfied. The success or failure of this operation start condition is determined in consideration of the degree of acceleration request. For example, when the accelerator opening exceeds a predetermined threshold with reference to the output value of the accelerator opening sensor 20 (see FIG. 1), the activation start condition may be affirmed. The success or failure of the operation start condition may be determined based on the required fuel injection amount estimated in consideration of the accelerator opening and the engine speed. The engine speed can be acquired with reference to the output value of the speed sensor 21 (see FIG. 1).

  In step S2, when the operation start condition of the electric compressor 3 is not satisfied, the current routine is finished. On the other hand, when it is determined that this operation start condition is satisfied, the ECU 12 applies voltage to the electric motor 3a (see FIG. 1) in step S3 to operate the electric compressor 3 (electric compressor operation control). ). Then, the bypass valve 7 shown in FIG. 1 is closed to prohibit the inflow of air into the bypass passage 6 (switching valve closing control). Further, the throttle valve 16 described above is fully opened (throttle valve opening control), and the current routine is terminated. Thereby, the supercharging assistance of the electric compressor 3 is implement | achieved. Further, when the electric compressor 3 is operated in step S3, the bypass valve 7 is closed, so that intake air can be prevented from flowing back through the bypass passage 6.

  On the other hand, if a negative determination is made in step S1 that the electric compressor 3 is in the operating state, the ECU 12 advances the process to step S4. When the ECU 12 executes this step S4, the ECU 12 functions as a surging region determining means. That is, in step S4, the ECU 12 determines whether or not the electric compressor 3 enters or is likely to enter the surging area (details will be described later). If this condition is not satisfied, the current routine is terminated. On the other hand, if an affirmative determination is made in step S4 and there is a possibility of entering or surging into the surging area, the ECU 12 advances the process to step S5. In step S5, the ECU 12 performs surging avoidance control, which will be described later, and proceeds to the next step S6. The ECU 12 functions as surging avoidance control means by executing step S5.

  Next, in step S6, the ECU 12 determines whether or not a non-operation condition for the electric compressor 3 is satisfied. In step S6, a criterion for determining whether there is an excessive assist that causes the turbocharger 2 to over-rotate or the electric compressor 3 may choke is set, and whether or not this criterion is satisfied. The success or failure of the non-operating condition is determined by the above. If this non-operation condition is not satisfied, the current routine is terminated and the supercharging assist by the electric compressor 3 is continued. On the other hand, if this non-operation condition is satisfied, the ECU 12 advances the processing to step S7, stops supplying the electric power to the electric motor 3a, deactivates the electric compressor 3, and is shown in FIG. The bypass valve 7 is opened, control is performed so that air flows into the bypass passage 6 (electric compressor non-operation control), and the current routine is finished.

  Next, details of the surging region entry determination process in step S4 and the surging avoidance control in step S5 will be described with reference to FIGS. FIG. 4 shows the air flow performance of the electric compressor 3 with the horizontal axis representing the air flow rate and the vertical axis representing the pressure ratio before and after the electric compressor 3. A diagram 30 shows the supercharging characteristics when the electric compressor 3 is operated. Generally, surging occurs when the air flow rate to be supplied to the compressor is small relative to the pressure. A broken line SL indicates a surge limit, and a left region is a surging region. Lines 31, 32, and 33 are pressure ratio curves when the rotation speed of the electric compressor is constant. The rotational speed increases from the line diagrams 31 to 33. As shown in this figure, for example, when sudden acceleration is detected during low speed operation and the output of the electric compressor 3 is maximized, the air flow rate to be supplied to the electric compressor 3 is insufficient even if the pressure ratio suddenly rises. As a result, it enters the surging area as indicated by the oblique line 34. When the electric compressor 3 enters the surging region, vibration is generated, and in the worst case, the compressor impeller is destroyed.

  Therefore, in the supercharging system according to the present embodiment, it is determined whether or not there is a risk of entering or surging into the surging area as described above. FIG. 5 is a flowchart showing an example of the surging area entry determination process. As shown in this figure, the ECU 12 first obtains the intake air temperature downstream of the electric compressor 3 by referring to the output value of the temperature sensor 24 (see FIG. 1) in step S401. Next, in step S402, the ECU 12 determines whether or not this temperature exceeds a predetermined limit temperature. The predetermined limit temperature may be experimentally determined in advance and stored in the ROM of the ECU 12. The reason for determining whether or not to enter the surging region using the intake air temperature downstream of the electric compressor 3 is as follows.

  FIG. 6 shows the air flow rate and the temperature characteristics downstream of the electric compressor 3 when the rotation speed of the electric compressor 3 is increased on the horizontal axis. The right side of the broken line 35 is the surging area. A line 36 shows the air flow rate, and a line 37 shows the downstream temperature. As the rotational speed of the electric compressor 3 is increased, both the air flow rate and the downstream temperature increase. When the electric compressor 3 enters the surging region, the air flow rate becomes substantially constant, while the downstream temperature rapidly increases. This characteristic tends to be generally seen regardless of individual differences of electric compressors. Accordingly, a limit temperature is set as the upper limit value of the temperature in the vicinity 38 of the surging area, and the intake air temperature downstream of the electric compressor 3 is monitored to determine whether the electric compressor 3 has entered or is likely to enter the surging area. Regardless of whether it can be determined accurately.

  Therefore, as shown in FIG. 5, if the determination in step S402 is affirmative, it is determined that there is a risk of entering or surging into the surging area (step S403), and surging is avoided in step S5 shown in FIG. Control is implemented. Thereby, ECU12 functions as a surging avoidance control means. Specifically, the ECU 12 controls the electric motor 3a (see FIG. 1) so as to temporarily reduce the rotational speed of the electric compressor 3. On the other hand, when a negative determination is made in step S402, it is determined that there is no entry or a risk of entering the surging area (step S404).

  According to the first embodiment described above, the supercharging assist can be executed while avoiding the surging region. Therefore, it is necessary to operate with the output of the electric compressor 3 kept low in order to prevent the occurrence of surging. Absent. Therefore, the supercharging assist can be performed by fully drawing out the capacity of the electric compressor.

(Second Embodiment)
Next, a second embodiment according to the supercharging system of the present invention will be described. This embodiment is different from the first embodiment in the aspects of the surging region entry determination (step S4) and the surging avoidance control (step S5) shown in FIG. Other points are the same as those in the first embodiment, and thus redundant description is omitted. FIG. 7 is a flowchart showing surging approach determination processing according to the present embodiment, and FIG. 8 is a flowchart showing a control routine of surging avoidance control according to the present embodiment.

  As shown in FIG. 7, in step S405, the ECU 12 refers to the output value of the pressure sensor 23 (see FIG. 1) and acquires the pressure downstream of the electric compressor 3. Next, in step S406, the ECU 12 determines whether or not the pressure acquired in step S405 exceeds a predetermined limit pressure. The predetermined limit pressure may be experimentally determined in advance from the performance curve of the electric compressor 3 shown in FIG. 4 and stored in the ROM of the ECU 12. That is, the limit pressure that reaches the surge limit is obtained in advance according to the rotational speed of the electric compressor 3 and stored in the ROM of the ECU 12. Then, the pressure acquired in step S405 and the limit pressure corresponding to the rotational speed of the electric compressor 3 may be compared to determine whether or not the acquired pressure has reached this limit pressure. The rotation speed of the electric compressor 3 can be acquired from the electric motor 3a. Thereby, it can be determined whether or not the electric compressor 3 enters or is likely to enter the surge region.

  If a negative determination is made in step S406, it is determined that there is no risk of entering or surging into the surging area (step S407), and supercharging assistance by the electric compressor 3 is continued. On the other hand, when an affirmative determination is made, it is determined that there is a risk of entering or surging into the surging region (step S408), and the process proceeds to step S5 in FIG. 3 to perform surging avoidance control.

  Specifically, as shown in FIG. 8, the ECU 12 gradually opens the bypass valve 7 in step S501. Thereby, the air discharged from the electric compressor 3 flows backward in the bypass passage (in the direction opposite to the direction of the arrow in the figure). And since the backflowed air is sucked up by the electric compressor 3 again, the air flow rate can be increased relative to the downstream intake pressure. As a result, as shown in FIG. 4, it is possible to avoid entering the surging region while keeping the pressure ratio substantially constant (A → B in the figure). Preferably, in the next step S502, the ECU 12 may control the throttle valve 8 to the closed side. As a result, the pressure on the upstream side of the electric compressor 3 is increased, and the air that has flowed back through the bypass passage 6 can be efficiently guided to the electric compressor 3, so that the air flow rate can be further increased.

  In the subsequent step S503, if there is a margin in the output of the electric compressor 3, the rotational speed is increased. As a result, the supercharging pressure can be increased while avoiding the surging region as in 30 ′ shown in FIG. 4, so that the capacity of the electric compressor 3 can be sufficiently extracted.

  As mentioned above, although the supercharging system for internal combustion engines of this invention was demonstrated based on 1st and 2nd embodiment, this invention is not limited to these. For example, in the first and second embodiments, the diesel engine 1 is used as an application target of the supercharging system of the present invention, but the type of the internal combustion engine is not limited. Therefore, the present invention may be applied to a spark ignition type gasoline engine or may be applied to other gasoline engines.

  In the first and second embodiments, the electric compressor 3 is provided in the intake pipe 4 on the upstream side of the turbocharger 2. For example, the electric compressor 3 is provided on the downstream side of the turbocharger 2. The present invention can also be applied to the configuration provided in the intake pipe 4.

Schematic which shows the whole structure of the supercharging system which concerns on 1st Embodiment of this invention. The block diagram of the cooling system which circulates a cooling water by the radiator around an electric motor. The flowchart which showed the outline | summary of the control routine of the supercharging system which concerns on 1st Embodiment. The figure which showed the air flow rate performance of the electric compressor. The flowchart which showed an example of the surging area approach determination process. The figure which showed the air flow rate when raising the rotation speed of an electric compressor, and the temperature characteristic downstream of an electric compressor. The flowchart which showed the surging approach determination process which concerns on 2nd Embodiment. The flowchart which showed the control routine of the surging avoidance control which concerns on 2nd Embodiment.

Explanation of symbols

2 Turbocharger 2a Compressor 2b Turbine 3 Electric compressor 4 Intake pipe (intake passage)
6 Bypass passage 7 Bypass valve (first regulating valve)
8 Throttle valve (second adjusting valve)
12 ECU
23 Pressure sensor (pressure detection means)
24 Temperature sensor (temperature detection means)

Claims (4)

A turbocharger having a compressor and a turbine, an electric compressor provided in an intake passage upstream of the compressor of the turbocharger, a bypass passage bypassing the electric compressor, and provided in the bypass passage, A supercharging system for an internal combustion engine comprising: a first regulating valve that regulates an inflow amount of air into the bypass passage;
A surging area determining means for determining whether or not the electric compressor enters a surging area where surging occurs, and the surging area when the surging area determining means determines that the surging area enters or is likely to enter the surging area. A supercharging system for an internal combustion engine comprising surging avoidance control means for controlling at least one of the electric compressor and the first regulating valve so as to avoid it. Temperature detecting means for detecting or estimating the intake air temperature downstream of the electric compressor;
The surging area determination means determines that the detection result of the temperature detection means has entered or is likely to enter the surging area on the condition that a predetermined limit temperature has been exceeded,
The surging avoidance control means controls the electric compressor so as to reduce the rotation speed of the electric compressor when it is determined by the surging area determination means that the surging area has entered or is likely to enter the surging area. The supercharging system for an internal combustion engine according to claim 1, wherein Further comprising pressure detecting means for detecting or estimating the pressure downstream of the electric compressor;
The surging area determination means determines that there is a risk of entering or surging into the surging area on the condition that the detection result of the pressure detection means exceeds a predetermined limit pressure,
The surging avoidance control unit is configured to increase the flow rate of air flowing into the electric compressor when the surging region determination unit determines that the surging region enters or is likely to enter the surging region. The supercharging system for an internal combustion engine according to claim 1, wherein: A second regulating valve provided in the intake passage upstream of the electric compressor;
The surging avoidance control unit is configured to adjust the second adjustment so that the intake pressure upstream of the electric compressor increases when the surging region determination unit determines that the surging region has entered or is likely to enter the surging region. The supercharging system for an internal combustion engine according to claim 3, wherein the valve is controlled to be closed.

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