JP2018119472A - engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine which can improve a brake force to a compression release brake while avoiding burdens imposed on a compression release mechanism and an engine cooling system.SOLUTION: When there is a requirement for operating a compression release brake device 27, a control device 24 controls only an opening of a movable vane 23 of a VGS turbocharger 4 when a measurement value R of a rotation number sensor 29 is within a low/middle speed range so that a measurement value K of a first pressure sensor 30 for measuring boost pressure reaches target boost pressure which is determined on the basis of an engine rotation number and preset first map data indicating a relationship between maximum boost pressure and maximum in-cylinder pressure, and on the other hand, when the measurement value R of the rotation number sensor 29 is within a middle/high speed range, controls the opening of the movable vane 23 and an opening of an exhaust throttle 28.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an engine, and more particularly to an engine that improves the braking force of a compression release brake while avoiding a burden on the compression release mechanism and the engine cooling system.

  In recent years, downsizing has been attracting attention to improve fuel efficiency by reducing the engine displacement while maintaining the same power performance as the base engine by adopting turbochargers such as turbochargers and superchargers. Yes. However, downsizing has the disadvantage that the engine braking capability is reduced because the engine displacement is reduced.

  It is conceivable to use a compression release brake, which is an auxiliary brake, as a supplementary means for reducing the engine brake capacity. The compression release brake generates absorption torque by opening the exhaust valve near the top dead center during the compression stroke to discharge high-pressure air in the cylinder and causing the expansion stroke to be performed in a state where the pressure in the cylinder is low. Thus, braking force is obtained. The braking force of the compression release brake can be improved by increasing the in-cylinder pressure during the compression stroke by increasing the supercharging pressure and increasing the amount of work absorbed during the expansion stroke.

  However, the increase in the supercharging pressure causes an increase in the maximum value of the in-cylinder pressure at the time of compression release (hereinafter referred to as “maximum in-cylinder pressure”). There is a limit. For this reason, when the compression release brake is operated, it is necessary to lower the supercharging pressure to a sufficient level so that the maximum in-cylinder pressure is less than the upper limit value. Note that the maximum in-cylinder pressure here corresponds to the in-cylinder pressure immediately before the exhaust valve is opened.

  On the other hand, in response to market demands for stricter exhaust gas regulations and fuel efficiency improvements, it is essential to use high-supercharging systems for engines. A general exhaust turbo type high supercharging system has a high expansion ratio characteristic, and therefore, when the compression release brake is operated, the supercharging pressure can be lowered to a sufficient level particularly in a high engine speed range. It becomes difficult and causes an increase in the maximum in-cylinder pressure.

  In order to solve such a problem, an exhaust gas is recirculated to the intake side to lower the supercharging pressure by opening the EGR valve when the compression release brake is operated (for example, see Patent Document 1). reference). However, when the EGR valve is opened, the exhaust pressure of the engine decreases, so that the pumping loss decreases and the work of absorption decreases. Moreover, since the high-temperature exhaust gas passes through the EGR cooler, the burden on the engine cooling system is increased.

JP-T-2004-527686

  The objective of this invention is providing the engine which can improve the braking force of a compression release brake, avoiding the burden to a compression release mechanism and an engine cooling system.

An engine of the present invention that achieves the above object is a compression release having a turbocharger having a movable vane upstream of a turbine interposed in an exhaust passage, and an exhaust valve that opens and closes an exhaust port communicating with the exhaust passage from a cylinder. In an engine including a brake device and a control device, an exhaust throttle is provided in the exhaust passage on the downstream side of the turbine, a rotational speed sensor that measures the rotational speed of the engine, and a supercharging pressure of the engine is measured. When the first pressure sensor is installed or the second pressure sensor that measures the pressure of the exhaust gas is installed, and the first pressure sensor is installed, the control device is requested to operate the compression release brake device. The measured value of the first pressure sensor is based on preset first map data indicating the relationship among the engine speed, the maximum boost pressure and the maximum in-cylinder pressure. When the second booster is installed so that the target boost pressure is determined or when the second pressure sensor is installed, the control device, when requested to operate the compression release brake device, The measured value of the rotational speed sensor is set to a low / medium speed range so that the measured value becomes a target exhaust pressure determined based on the second map data indicating the relationship between the engine speed, the maximum exhaust pressure, and the maximum in-cylinder pressure. In some cases, only the opening degree of the movable vane is controlled, while when the measured value of the rotational speed sensor is in the middle / high speed range, the opening degree of the movable vane and the opening degree of the exhaust throttle are controlled. It is comprised by these.

  According to the engine of the present invention, when the compression release brake is operated, when the engine speed is in the middle / high speed range, the exhaust pressure is used, and the boost pressure is maximized while suppressing the increase in the in-cylinder pressure below the upper limit value. Therefore, the braking force of the compression release brake can be improved while avoiding a burden on the compression release mechanism. Moreover, since it is not necessary to open the EGR valve, it is possible to avoid a burden on the engine cooling system.

It is a lineblock diagram of the engine which consists of a 1st embodiment of the present invention. It is a block diagram of the engine which consists of a 2nd Embodiment of this invention. It is the graph which compared the supercharging pressure in the engine of this invention, and the conventional engine. It is the graph which compared the maximum in-cylinder pressure in the engine of this invention, and the conventional engine. It is the graph which compared the cooling water absorption calorie | heat amount in the engine of this invention, and the conventional engine.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an engine according to a first embodiment of the present invention. In addition, the arrow in a figure has shown the direction through which the fluid flows.

  This engine 1A is a diesel engine mounted on a vehicle. In the engine 1A, the air A sucked into the intake passage 2 becomes intake air 3 and passes through an air cleaner (not shown), and then is compressed by a compressor 5 of a high-capacity variable capacity turbocharger 4 (VGS turbocharger). After being compressed and cooled by the intercooler 6, it is supplied to the engine body 8 through the intake manifold 7.

  The intake air 3 supplied to the engine body 8 is mixed and burned with injected fuel in a cylinder 12 composed of a piston 10 and a cylinder 11 connected to a crankshaft 9 to generate heat energy, and then the exhaust valve 13 Exhaust manifold 15 becomes exhaust gas 16 through exhaust port 14 installed, and is exhausted to exhaust passage 17. A part of the exhaust gas 16 is branched from the exhaust passage 17 and diverted to the EGR passage 18 connected to the intake passage 2 either upstream or downstream of the intercooler 6 as EGR gas 19. In the EGR passage 18, a water-cooled EGR cooler 20 that cools the EGR gas 19 and an EGR valve 21 that adjusts the flow rate of the EGR gas 19 are sequentially arranged from the exhaust passage 17 side.

On the other hand, the exhaust gas 16 that has not been diverted to the EGR passage 18 is removed from the VGS turbocharger 4.
After passing through a movable vane 23 installed in front of the turbine 22 and rotating the turbine 22, it is discharged into the atmosphere as exhaust gas G through an exhaust gas treatment device (not shown). The opening degree of the movable vane 23 of the VGS turbocharger 4 is controlled by a control device 24 such as an ECU according to the operating state of the engine 1A.

  The engine body 8 is cooled by an engine cooling circuit 26 through which the cooling water 25 circulates. A part of the cooling water 25 is used for cooling the EGR gas 19 in the water-cooled EGR cooler 20.

  Further, the engine 1A is equipped with a compression release brake device 27. When the operation request of the compression release brake device 27 is made by the driver, the control device 24 turns the exhaust valve 13 through the valve operating device (not shown) when the piston 10 reaches near the top dead center of the compression stroke. Control to release.

  In the exhaust passage 17 immediately after the turbine 22 of the VGS turbocharger 4, an exhaust throttle 28 capable of adjusting the flow rate of the exhaust gas 16 is provided. A rotation speed sensor 29 for measuring the engine rotation speed of the engine 1A is attached to the crankshaft 9. Further, the intake manifold 7 is provided with a first pressure sensor 30 for measuring the supercharging pressure of the engine 1A. The exhaust throttle 28, the rotation speed sensor 29, and the first pressure sensor 30 are connected to the control device 24 through a signal line (indicated by a one-dot chain line).

  The function of the control device 24 in the engine 1A will be described below.

  The control device 24 determines whether or not there is an operation request for the compression release brake device 27 by the driver, and when there is an operation request, inputs the measurement value R of the rotation speed sensor 29 and the measurement value K of the first pressure sensor 30. To do.

  Next, the control device 24 determines whether the measurement value R belongs to either the low / medium speed range or the medium / high speed range. Here, the low / medium speed region and the medium / high speed region indicate regions where the engine speed is 30 to 70% and 70 to 100%, respectively, with respect to the rated rotation speed.

  When the measured value R is in the low / medium speed range, the control device 24 sets in advance the measured value K of the first pressure sensor 30 indicates the relationship among the engine speed, the maximum boost pressure, and the maximum in-cylinder pressure. Only the opening degree of the movable vane 23 of the VGS turbocharger 4 is controlled so that the target supercharging pressure determined based on the first map data is obtained. At this time, the opening degree of the movable vane 23 and the measured value K have a negative correlation.

On the other hand, when the measured value R is in the middle / high speed range, the control device 24 determines the opening degree and the movable vane 23 so that the measured value K becomes the target boost pressure determined based on the first map data. The opening degree of the exhaust throttle 28 is controlled. The control content is not particularly limited, but the following two methods are exemplified.
(A) After setting the opening of the exhaust throttle 28 to a target opening determined in advance from the engine speed, the opening of the movable vane 23 is gradually increased.
(B) After the opening degree of the movable vane 23 is fully opened, the opening degree of the exhaust throttle 30 is gradually reduced.

  The target boost pressure is the maximum value of the boost pressure in a range where the maximum in-cylinder pressure is less than the upper limit value that may affect the compression release mechanism, and is determined from the measured value R and the first map data. Is done.

  FIG. 2 shows an engine according to a second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same location as FIG. 1, and the description is abbreviate | omitted.

  In this engine 1 </ b> B, a second pressure sensor 31 that measures the pressure of exhaust gas 16 (exhaust pressure) is installed in the exhaust manifold 15 instead of the first pressure sensor 30.

  The function of the control device 24 in the engine 1B will be described below.

  The control device 24 determines whether or not there is a request for operation of the compression release brake device 27 by the driver, and when there is an operation request, inputs the measured value R of the rotation speed sensor 29 and the measured value H of the second pressure sensor 31 respectively. To do.

  When the measured value R is in the low / medium speed range, the control device 24 sets the measured value H of the second pressure sensor 31 in advance indicating the relationship among the engine speed, the maximum exhaust pressure, and the maximum in-cylinder pressure. Only the opening degree of the movable vane 23 of the VGS turbocharger 4 is controlled so that the target exhaust pressure is determined based on the second map data. At this time, the opening degree of the movable vane 23 and the measured value H have a negative correlation.

  On the other hand, when the measured value R is in the middle / high speed range, the control device 24 determines the opening degree and the exhaust of the movable vane 23 so that the measured value H becomes the target exhaust pressure determined based on the second map data. The opening degree of the throttle 28 is controlled. As for this control content, two methods are exemplified as in the case of the engine 1A.

  By reducing the measured value H (exhaust pressure) in this way, the supercharging pressure of the engine 1B is reduced.

  The target exhaust pressure is the maximum value of the exhaust pressure in a range where the maximum in-cylinder pressure is less than the upper limit value that may affect the compression release mechanism, and is determined from the measured value R and the second map data. .

  As described above, when the compression release brake is operated, the outlet pressure of the turbine 22 is adjusted using the exhaust throttle 28 in the middle and high speed range of the engine speed, in which it is difficult to reduce the supercharging pressure to a sufficient level. As a result, the boost pressure is maximized while suppressing the increase in the in-cylinder pressure below the upper limit value, so that the braking force of the compression release brake can be improved while avoiding the burden on the compression release mechanism. It can be done. In addition, since it is not necessary to open the EGR valve 21, a burden on the engine cooling circuit 26 can be avoided.

  In the engine 1A of the present invention (example) and a conventional engine (conventional example) for controlling the opening degree of the EGR valve, the supercharging pressure when the compression release brake was operated at a specific engine speed was compared. The result is shown in FIG. 3, the result of comparing the maximum in-cylinder pressure is shown in FIG. 4, and the result of comparison of the amount of heat absorbed by the cooling water 25 is shown in FIG. 5.

  From these results, the engine 1A of the embodiment suppresses the increase in the maximum in-cylinder pressure by lowering the supercharging pressure to a sufficient level as compared with the engine of the conventional example, particularly when the engine speed is in the middle / high speed range. It can be seen that the amount of heat absorbed by the cooling water 25 decreases.

1A, 1B Engine 4 VGS turbocharger 8 Engine body 10 Piston 12 Cylinder 13 Exhaust valve 14 Exhaust port 16 Exhaust gas 17 Exhaust passage 21 EGR valve 22 Turbine 23 Movable vane 24 Controller 25 Cooling water 27 Compression release brake device 28 Exhaust throttle 29 Rotation Number sensor 30 First pressure sensor 31 Second pressure sensor

Claims (3)

In an engine comprising a turbocharger having a movable vane upstream of a turbine interposed in an exhaust passage, a compression release brake device having an exhaust valve for opening and closing an exhaust port communicating with the exhaust passage from a cylinder, and a control device ,
Providing an exhaust throttle in the exhaust passage downstream of the turbine;
A rotational speed sensor for measuring the rotational speed of the engine, and a first pressure sensor for measuring a supercharging pressure of the engine or a second pressure sensor for measuring the pressure of the exhaust gas,
In the case where the first pressure sensor is installed, when the control device is requested to operate the compression release brake device, the measured values of the first pressure sensor are the engine speed, the maximum boost pressure, and the maximum. In order to achieve a target supercharging pressure determined based on preset first map data indicating the relationship with the in-cylinder pressure,
Alternatively, in the case where the second pressure sensor is installed, and when the operation request for the compression release brake device is made, the control device determines that the measured value of the second pressure sensor is the engine speed and the maximum exhaust pressure. In order to achieve the target exhaust pressure determined based on the second map data indicating the relationship with the maximum in-cylinder pressure,
When the measured value of the rotational speed sensor is in the low / medium speed range, only the opening degree of the movable vane is controlled, whereas when the measured value of the rotational speed sensor is in the medium / high speed range, An engine configured to control an opening and an opening of the exhaust throttle. When the control device controls the opening degree of the movable vane and the opening degree of the exhaust throttle when the measured value of the rotation speed sensor is in a medium to high speed range,
2. The engine according to claim 1, wherein the control device is configured to control the opening degree of the movable vane after the opening degree of the exhaust throttle is set to a target opening degree determined in advance from an engine speed. When the control device controls the opening degree of the movable vane and the opening degree of the exhaust throttle when the measured value of the rotation speed sensor is in a medium to high speed range,
The engine according to claim 1, wherein the control device is configured to control the opening degree of the exhaust throttle after the opening degree of the movable vane is set to be fully open.

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