JP6809253B2 - engine - Google Patents

Description

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

In recent years, downsizing, which aims to improve fuel efficiency by reducing the exhaust amount of the engine while ensuring the same power performance as the base engine by adopting a supercharger such as a turbocharger or supercharger, has attracted attention. There is. However, downsizing has the disadvantage that the engine braking capacity is reduced because the displacement is reduced.

As a means for compensating for the decrease in engine braking capacity, it is conceivable to use a compression release brake which is an auxiliary brake. 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 performing the expansion stroke while the pressure in the cylinder is low. To obtain braking force. The braking force of this compression release brake can be improved by increasing the in-cylinder pressure in the compression stroke by increasing the boost pressure and increasing the absorption work during the expansion stroke.

However, an increase in the boost 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. Therefore, when the compression release brake is operated, it is necessary to reduce the boost pressure to a sufficient level so that the maximum in-cylinder pressure is less than the upper limit value. The maximum in-cylinder pressure referred to here corresponds to the in-cylinder pressure immediately before the exhaust valve is opened.

On the other hand, in response to the market demands for tightening exhaust gas regulations and improving fuel efficiency, it is essential to adopt a high supercharging system for engines. Since a general exhaust turbo type high supercharging system has a high expansion ratio characteristic, it is possible to reduce the supercharging pressure to a sufficient level when the compression release brake is activated, especially in the high engine speed range. It becomes difficult and causes an increase in the maximum in-cylinder pressure.

In order to solve such a problem, by opening the EGR valve when the compression release brake is operated, the exhaust gas is returned to the intake side to reduce the boost pressure (for example, Patent Document 1). reference). However, when the EGR valve is opened, the exhaust pressure of the engine is lowered, so that the pumping loss is reduced and the absorption work amount is lowered. In addition, since the high-temperature exhaust gas passes through the EGR cooler, the load on the cooling system of the engine increases.

Special Table 2004-527686

An object of the present invention is to provide an engine capable of improving the braking force of a compression release brake while avoiding a burden on a compression release mechanism and an engine cooling system.

The engine of the present invention that achieves the above object is compressed and released having a turbocharger having a movable vane upstream of a turbine provided in an exhaust passage and an exhaust valve for opening and closing an exhaust port communicating from a cylinder to the exhaust passage. In an engine equipped with a braking device and a control device, an exhaust throttle is provided in the exhaust passage on the downstream side of the turbine, a rotation speed sensor for measuring the rotation speed of the engine, and a boost pressure of the engine are measured. When a first pressure sensor or a second pressure sensor for measuring the pressure of the exhaust gas is installed and the first pressure sensor is installed, the control device receives a request for operation of the compression / release braking device. Is such that the measured value of the first pressure sensor becomes the target boost pressure determined based on the preset first map data showing the relationship between the engine speed, the maximum boost pressure and the maximum in-cylinder pressure. Or, when the second pressure sensor is installed, when the control device receives a request for operation of the compression / release brake device, the measured values of the second pressure sensor are the engine speed and the maximum exhaust pressure. When the measured value of the rotation speed sensor is in the low to medium speed range, only the opening degree of the movable vane is obtained so that the target exhaust pressure is determined based on the second map data showing the relationship between the pressure and the maximum cylinder pressure. On the other hand, when the measured value of the rotation speed sensor is in the middle and high speed range, it is characterized in that it is configured to control the opening degree of the movable vane and the opening degree of the exhaust throttle. Is.

According to the engine of the present invention, when the compression release brake is activated and the engine speed is in the medium to high speed range, the exhaust throttle is used to maximize the boost pressure while suppressing the increase in the in-cylinder pressure to less than the upper limit. Therefore, it is possible to improve the braking force of the compression release brake while avoiding the burden on the compression release mechanism. Further, 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 block diagram of the engine which comprises the 1st Embodiment of this invention. It is a block diagram of the engine which comprises the 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 a graph which compared the maximum in-cylinder pressure in the engine of this invention and the conventional engine. It is a graph comparing the amount of heat absorption of cooling water in the engine of this invention and the conventional engine.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an engine according to the first embodiment of the present invention. The arrows in the figure indicate the direction in 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 the intake air 3, passes through an air cleaner (not shown), and then is driven by the compressor 5 of the highly supercharged variable capacity turbocharger 4 (VGS turbocharger). After being compressed and cooled by the intercooler 6, it is supplied to the engine body 8 via the intake manifold 7.

The intake air 3 supplied to the engine body 8 is mixed and burned with the injected fuel in the cylinder 12 including the piston 10 and the cylinder 11 connected to the crankshaft 9, and then the exhaust valve 13 generates heat energy. Exhaust gas 16 is exhausted from the exhaust manifold 15 to the exhaust passage 17 through the installed exhaust port 14. A part of the exhaust gas 16 branches from the exhaust passage 17 and divides into the EGR passage 18 connected to the intake passage 2 on either the upstream side or the downstream side of the intercooler 6 as the EGR gas 19. In the EGR passage 18, a water-cooled EGR cooler 20 for cooling the EGR gas 19 and an EGR valve 21 for adjusting the flow rate of the EGR gas 19 are arranged in order from the exhaust passage 17 side.

On the other hand, the exhaust gas 16 that did not flow into the EGR passage 18 is the VGS turbocharger 4.
After passing through a movable vane 23 installed in front of the turbine 22 and rotationally driving the turbine 22, the turbine 22 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 the engine cooling circuit 26 in 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 driver requests the operation of the compression / release brake device 27, the control device 24 sets the exhaust valve 13 through the valve gear (not shown) when the piston 10 reaches near the top dead center of the compression stroke. Control to open.

An exhaust throttle 28 capable of adjusting the flow rate of the exhaust gas 16 is provided in the exhaust passage 17 immediately after the turbine 22 of the VGS turbocharger 4. Further, a rotation speed sensor 29 for measuring the engine rotation speed of the engine 1A is attached to the crankshaft 9. Further, a first pressure sensor 30 for measuring the boost pressure of the engine 1A is installed in the intake manifold 7. 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 dashed line).

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

The control device 24 determines whether or not the driver has requested the operation of the compression / release braking device 27, and when the operation request is made, inputs the measured value R of the rotation speed sensor 29 and the measured value K of the first pressure sensor 30, respectively. To do.

Next, the control device 24 determines whether the measured value R belongs to either the low / medium speed range or the medium / high speed range. Here, the low / medium speed range and the medium / high speed range refer to regions in which 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 to medium speed range, the control device 24 presets the measured value K of the first pressure sensor 30 to indicate the relationship between 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 boost 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 medium to high speed range, the control device 24 adjusts the opening degree of the movable vane 23 and 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 degree of the exhaust throttle 28 to a target opening degree predetermined from the engine speed, the opening degree 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 the 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. Will be done.

FIG. 2 shows an engine according to a second embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the engine 1B, instead of the first pressure sensor 30, a second pressure sensor 31 for measuring the pressure (exhaust pressure) of the exhaust gas 16 is installed in the exhaust manifold 15.

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

The control device 24 determines whether or not the driver has requested the operation of the compression / release braking device 27, and when the operation request is made, 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 to medium speed range, the control device 24 is preset in which the measured value H of the second pressure sensor 31 indicates the relationship between 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 medium to high speed range, the control device 24 increases the opening degree and 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 the control content, two methods are exemplified as in the case of the engine 1A.

By lowering the measured value H (exhaust pressure) in this way, the boost pressure of the engine 1B is lowered.

The target exhaust pressure is the maximum value of the exhaust pressure in the 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, the exhaust throttle 28 is used to adjust the outlet pressure of the turbine 22 when the compression release brake is activated, especially in the medium and high speed range of the engine speed where it is difficult to reduce the boost pressure to a sufficient level. By doing so, the boost pressure is maximized while suppressing the increase in the in-cylinder pressure below the upper limit, so it is possible to improve the braking force of the compression release brake while avoiding the burden on the compression release mechanism. You can. Further, since it is not necessary to open the EGR valve 21, the burden on the engine cooling circuit 26 can be avoided.

The boost pressures of the engine 1A (Example) of the present invention and the conventional engine (conventional example) that controls the opening degree of the EGR valve when the compression release brake is operated at a specific engine speed are compared. The results are shown in FIG. 3, the result of comparing the maximum in-cylinder pressure is shown in FIG. 4, and the result of comparing the amount of heat absorbed by the cooling water 25 is shown in FIG.

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

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 Control device 25 Cooling water 27 Compression release brake device 28 Exhaust throttle 29 rotation Number sensor 30 1st pressure sensor 31 2nd pressure sensor

Claims (3)

In an engine equipped with a turbocharger having a movable vane upstream of a turbine provided in an exhaust passage, a compression / release brake device having an exhaust valve for opening and closing an exhaust port communicating from a cylinder to the exhaust passage, and a control device. ,
An exhaust throttle is provided in the exhaust passage on the downstream side of the turbine, and an exhaust throttle is provided.
A rotation speed sensor for measuring the rotation speed of the engine and a first pressure sensor for measuring the boost pressure of the engine or a second pressure sensor for measuring the pressure of the exhaust gas are installed.
When the first pressure sensor is installed, when the control device receives a request to operate the compression / release braking device, the measured values of the first pressure sensor are the engine speed, the maximum boost pressure, and the maximum. The target boost pressure is determined based on the preset first map data showing the relationship with the in-cylinder pressure.
Alternatively, when the second pressure sensor is installed, the control device sets the measured value of the second pressure sensor as the engine speed and the maximum exhaust pressure when the operation request of the compression / release brake device is made. To reach the target exhaust pressure determined based on the second map data showing the relationship with the maximum in-cylinder pressure.
When the measured value of the rotation speed sensor is in the low to medium speed range, only the opening degree of the movable vane is controlled, while when the measured value of the rotation speed sensor is in the medium to high speed range, the movable vane is controlled. An engine characterized in that it is configured to control the opening degree and the opening degree 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 the middle and high speed range,
The engine according to claim 1, wherein the control device is configured to control the opening degree of the movable vane after setting the opening degree of the exhaust throttle to a target opening degree predetermined from the 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 the middle and 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 setting the opening degree of the movable vane to fully open.

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