JP5300143B2 - Method for preventing over-rotation of high-pressure turbine in a two-stage turbocharging system - Google Patents

Description

  The present invention relates to a method for preventing over-rotation of a high-pressure turbine in a two-stage turbocharging system including a high-pressure turbocharger and a low-pressure turbocharger.

  FIG. 3 schematically shows a conventional two-stage turbocharging system, in which an intake 5 compressed by a high-pressure compressor 4 is operated by an exhaust 2 sent from a vehicle-mounted engine 1 and operated by a high-pressure turbine 3. The high pressure turbocharger 6 that is fed to 1 and the low pressure stage turbine 7 that is operated by the exhaust 2 that is delivered from the high pressure stage turbine 3 of the high pressure stage turbocharger 6 and compressed by the low pressure stage compressor 8 is used as the high pressure. A low-pressure stage turbocharger 9 for feeding to the stage compressor 4 is provided.

  Further, an EGR pipe 10 is provided from the upstream side of the high-pressure turbine 3 in the engine exhaust passage to the downstream side of the high-pressure compressor 4 in the engine intake passage. The EGR pipe 10 is connected to the engine intake passage. An EGR valve 11 for adjusting the flow rate of the exhaust 2 to be recirculated is provided (more specifically, an EGR cooler for water-cooling the recirculated exhaust 2 is also provided).

  Thus, in such a two-stage supercharging system, when the engine 1 is in an operating state, after the exhaust 2 delivered from the engine 1 flows into the high-pressure turbine 3 and drives the high-pressure compressor 4, The intake air 5 that flows into the low-pressure turbine 7 and drives the low-pressure compressor 8 and that is compressed by flowing into the low-pressure compressor 8 is supplied to the high-pressure compressor 4 and is compressed again by the high-pressure compressor 4. Therefore, if the amount of intake air 5 supplied to the cylinder is increased and the amount of fuel injection per cycle is increased, the output of the engine 1 can be increased.

  Further, a part of the exhaust gas 2 flows into the EGR pipe 10 and the exhaust gas 2 whose flow rate is adjusted by the EGR valve 11 is sent to the engine 1 together with the intake air 5. A reduction is achieved, and the generation of NOx is reduced.

  For example, Patent Documents 1 and 2 listed below already exist as the general technical level related to the two-stage supercharging system as described above.

JP 2005-147030 A JP-A-5-180089

  However, in this type of two-stage turbocharging system, it is considered to adopt a relatively small-diameter high-pressure turbocharger 6 in order to improve fuel efficiency in a low-speed and medium-load range, increase torque, and achieve a high EGR rate. However, such a relatively small-diameter high-pressure stage turbocharger 6 has a problem that the high-pressure stage turbine 3 is liable to over-rotate due to the turbine inertia during acceleration / deceleration of the vehicle. The stage turbine 3 may overshoot (the turbo boost pressure will be higher than the setting: the engine and turbine will be overloaded and cause a failure), or the high-pressure turbine 3 will rotate due to the turbine inertia during deceleration. Continued delay in lowering the supercharging pressure causes the exhaust turbine pressure to remain high even when steady, resulting in an excessive amount of exhaust gas recirculation. Jin smoke there is a possibility that generated in the exhaust gas 2 combustibility deteriorated in each cylinder 1.

  The present invention has been made in view of such a situation, and provides a method for preventing an overspeed of a high-pressure turbine in a two-stage turbocharging system capable of preventing the high-pressure turbine from over-rotating during acceleration / deceleration. It is aimed.

  The present invention relates to a high-pressure stage turbocharger that operates a high-pressure stage turbine by exhaust gas sent from an engine mounted on a vehicle and supplies intake air compressed by a high-pressure stage compressor to the engine, and a high-pressure stage turbine of the high-pressure stage turbocharger. Method for preventing over-rotation of high-pressure stage turbine in a two-stage turbocharging system comprising a low-pressure stage turbocharger that operates a low-pressure stage turbine by exhaust gas sent out and supplies intake air compressed by a low-pressure stage compressor to the high-pressure stage compressor A high-pressure turbine comprising: a bypass flow path that bypasses the exhaust from the engine to the low-pressure turbine by bypassing the high-pressure turbine; and a bypass valve that is provided in the middle of the bypass flow path and opens and closes the flow path The turbine rotation speed of the vehicle is constantly monitored by the rotation sensor. Estimate the turbine speed in the next engine cycle based on the current turbine speed of the stage turbine and the turbine speed in the previous engine cycle, and the estimated values are individually specified for acceleration and deceleration. When the value is not below the specified value, the bypass valve is opened to open the bypass flow path.

  Thus, even if the rotational speed of the high-pressure turbine rapidly increases during vehicle acceleration, the turbine rotational speed is constantly monitored by the rotation sensor to estimate the turbine rotational speed in the next engine cycle. Therefore, if the specified value at the time of acceleration is set appropriately within the range where the high-pressure turbine does not cause overshoot, the estimated value of the turbine speed in the next engine cycle will exceed the specified value. In this case, the bypass valve is opened and the bypass passage is opened, and the exhaust gas from the engine flows around the high-pressure turbine, so that the turbine rotation speed is lowered and the overshoot of the high-pressure turbine is prevented.

  On the other hand, even if the high-pressure turbine continues to rotate due to turbine inertia when the vehicle decelerates, the turbine speed is constantly monitored by the rotation sensor, so that the turbine speed in the next engine cycle is estimated. If the specified value at the time of acceleration is set appropriately within a range where the exhaust gas recirculation amount does not become excessive even during steady state after deceleration, the estimated value of the turbine speed in the next engine cycle will not fall below the specified value. The bypass valve is opened and the bypass flow path is opened, and the exhaust from the engine flows around the high-pressure turbine, so that the turbine speed decreases quickly without continuing inertial rotation. The generation of smoke caused by excessive recirculation and deterioration of engine flammability is prevented.

  Further, in the present invention, when estimating the turbine speed in the next engine cycle, the amount of time change in the turbine speed from the previous engine cycle to the present is calculated with respect to the current turbine speed. It is preferable to calculate the estimated value by adding together the amount of increase / decrease in the number and further adding the time variation of the turbine rotation speed corresponding to the response delay of the bypass valve.

  According to the method for preventing over-rotation of a high-pressure turbine in a two-stage turbocharging system of the present invention, the diameter of the high-pressure turbocharger is reduced in order to improve fuel efficiency, increase torque and achieve a high EGR rate in a low-speed and medium-load range. Even in this case, it is possible to reliably prevent the high-pressure turbine from over-rotating at the time of acceleration / deceleration, so the exhaust gas recirculation amount is excessive due to overshoot of the high-pressure turbine during acceleration and steady recovery after deceleration. It is possible to achieve an excellent effect that the generation of smoke accompanying the above can be surely prevented.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the control procedure in the control apparatus of FIG. It is the schematic which shows an example of the conventional two-stage supercharging system.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1 and 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 3 represent the same items.

  As shown in FIG. 1, the present embodiment is intended for a two-stage turbocharging system having the same basic configuration as that of the conventional two-stage turbocharging system described above with reference to FIG. In the example, a bypass passage 12 is provided to guide the exhaust 2 from the engine 1 to the low-pressure turbine 7 by bypassing the high-pressure turbine 3, and a bypass valve 13 for opening and closing the passage is provided in the middle of the bypass passage 12. It has been.

  Further, a rotation sensor 14 is attached to the high-pressure turbine 3 of the high-pressure turbocharger 6, and the rotation sensor 14 detects the turbine speed of the high-pressure turbine 3, and the detection signal 14a is an engine control computer (ECU: It is input to a control device 15 constituting an electronic control unit).

  Here, in the control device 15, the turbine speed of the high-pressure turbine 3 is constantly monitored by the rotation sensor 14 based on the detection signal 14 a from the rotation sensor 14, and when acceleration or deceleration of the vehicle is confirmed. The turbine rotation speed in the next engine cycle is estimated based on the current turbine rotation speed of the high-pressure turbine 3 and the turbine rotation speed in the previous engine cycle, and the estimated values are individually defined for acceleration and deceleration. A control signal 15a for opening the bypass valve 13 is output when the specified value is not below the specified value, and the bypass passage 12 is opened.

  That is, in the control device 15, the bypass valve 13 is controlled according to the control procedure shown in the flowchart of FIG. 2, and first, at step S1, the acceleration or deceleration of the vehicle is determined. ing.

  Here, since the control device 15 also serves as an engine control computer (ECU: Electronic Control Unit), it grasps information such as the accelerator opening and the fuel injection amount, and the unit of the accelerator opening and the fuel injection amount. It is possible to determine acceleration / deceleration of the vehicle from the rate of change per hour.

  If the determination of acceleration or deceleration is made in step S1, the process proceeds to the next step S2, where the turbine in the next engine cycle is based on the current turbine speed and the turbine speed in the previous engine cycle. The number of revolutions is estimated, and it is determined whether or not this estimated value is below a prescribed value that is individually prescribed for each of acceleration and deceleration.

  Here, when estimating the turbine speed in the next engine cycle, the amount of time change in the turbine speed from the previous engine cycle to the present is compared to the current turbine speed by the increase / decrease in the speed until the next engine cycle. For example, if the acceleration is determined in step S1, the time change amount of the turbine speed from the previous engine cycle to the present time is added as the speed increase until the next engine cycle. If the determination of deceleration is made in step S1, the time change amount of the turbine rotation speed from the previous engine cycle to the present time may be subtracted as the rotation speed decrease until the next engine cycle.

  In addition, it is preferable to calculate the estimated value by further adding the amount of time variation of the turbine speed corresponding to the response delay of the bypass valve 13, and in this way, it is possible to calculate a more accurate estimated value. It becomes. As for the time change amount, for example, the time change amount of the turbine speed corresponding to the response delay of the bypass valve 13 can be read from the two-dimensional control map of the engine speed and the load.

  At this time, the two-dimensional control map for reading out the time change amount of the turbine rotation speed corresponding to the response delay of the bypass valve 13 is provided in the control device 15 for acceleration and deceleration, and is positive during acceleration. The value may be read as a negative value during deceleration.

  Further, the specified value specified for acceleration is specified for the turbine speed in a range where the high-pressure turbine 3 does not cause overshoot, and the specified value specified for deceleration is the value after deceleration. This is defined as the turbine rotational speed in a range where the exhaust gas recirculation amount does not become excessive even during normal operation.

  If it is determined in step S2 that the estimated value does not fall below the specified value, the process proceeds to step S3 to output a control signal 15a for opening the bypass valve 13, and the estimated value falls below the specified value. If it is determined that the vehicle is down, the process proceeds to step S4 to determine whether or not the vehicle is already in an acceleration or deceleration state. If acceleration or deceleration of the vehicle continues, the process returns to step S2. If the same control is repeated and the vehicle has already been accelerated or decelerated, the control at the time of acceleration / deceleration is terminated.

  If the control of the bypass valve 13 is performed according to the control procedure of FIG. 2 as described above, even if the rotation speed of the high-pressure turbine 3 rapidly increases during vehicle acceleration, the rotation speed of the turbine is constantly monitored by the rotation sensor 14. When the estimated value of the turbine rotation speed in the engine cycle exceeds a specified value, the bypass valve 13 is opened and the bypass flow path 12 is opened, and the exhaust gas from the engine 1 flows around the high-pressure stage turbine 3 to flow through the turbine. The rotational speed is reduced, and overshoot of the high-pressure turbine 3 is prevented.

  On the other hand, even if the high-pressure turbine 3 continues to rotate due to the turbine inertia when the vehicle decelerates, the rotation speed of the turbine is constantly monitored by the rotation sensor 14, and the estimated value of the turbine speed in the next engine cycle falls below the specified value. The bypass valve 13 is opened when there is not, the bypass passage 12 is opened, and the exhaust from the engine 1 flows around the high-pressure turbine 3 so that the turbine speed decreases early without continuing inertial rotation, and after deceleration When the engine is in a steady state, the amount of exhaust gas recirculated becomes excessive, and the generation of smoke caused by the deterioration of the combustibility of the engine 1 is prevented.

  Therefore, according to the above-described embodiment, the high-pressure turbine 3 is accelerated or decelerated even if the high-pressure turbocharger 6 is reduced in diameter in order to improve fuel efficiency, increase torque, and achieve a high EGR rate in the low-speed and middle-load range. It is possible to reliably prevent excessive rotation at times, so that overshooting of the high-pressure turbine 3 during acceleration and generation of smoke due to excessive exhaust gas recirculation due to steady recovery after deceleration It can be surely prevented.

  Note that the method for preventing over-rotation of the high-pressure turbine in the two-stage turbocharging system of the present invention is not limited to the above-described embodiment, and for calculating the estimated value of the turbine rotation speed in the next engine cycle, Of course, it is possible to use methods other than those described in the embodiment, and various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust 3 High pressure stage turbine 4 High pressure stage compressor 5 Intake 6 High pressure stage turbocharger 7 Low pressure stage turbine 8 Low pressure stage compressor 9 Low pressure stage turbocharger 10 EGR piping 11 EGR valve 12 Bypass flow path 13 Bypass valve 14 Rotation sensor 14a Detection Signal 15 Control device 15a Control signal

Claims (2)

  A high-pressure turbocharger that operates a high-pressure turbine by exhaust gas delivered from a vehicle-mounted engine and supplies intake air compressed by a high-pressure compressor to the engine, and exhaust gas delivered from the high-pressure turbine of the high-pressure turbocharger A method of preventing over-rotation of the high-pressure turbine in a two-stage turbocharging system comprising a low-pressure turbocharger that operates the low-pressure turbine and supplies the intake air compressed by the low-pressure compressor to the high-pressure compressor. A bypass passage that bypasses the exhaust from the engine to the low-pressure turbine by bypassing the high-pressure turbine, and a bypass valve that is provided in the middle of the bypass passage and opens and closes the passage, and the turbine speed of the high-pressure turbine Is constantly monitored by a rotation sensor, and when acceleration or deceleration of the vehicle is confirmed, Estimates the turbine speed in the next engine cycle based on the current turbine speed and the turbine speed in the previous engine cycle, and the estimated value is specified separately for each of acceleration and deceleration A method for preventing over-rotation of a high-pressure turbine in a two-stage turbocharging system, wherein a bypass valve is opened to open a bypass passage when the pressure is not below the lower limit.   In estimating the turbine speed in the next engine cycle, the time variation of the turbine speed from the previous engine cycle to the present is added to the current turbine speed as an increase / decrease in the speed until the next engine cycle. 2. The overspeed prevention of the high-pressure turbine in the two-stage turbocharging system according to claim 1, wherein the estimated value is calculated by further adding the time variation of the turbine rotation speed corresponding to the response delay of the bypass valve. Method.

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