JP2002285854A - Engine with turbocharger - Google Patents

Abstract

(57) [Problem] To provide a supercharged engine capable of efficiently reducing NOx emissions. SOLUTION: A compressor 2b of an exhaust turbocharger 2 is provided.
An air supply throttle valve 7 is provided in an air supply passage 6 that does not have an intercooler that connects the intake manifold 5 and the intake manifold 5. An EGR cooler 9 is provided in an EGR passage 8 that branches off from the exhaust manifold 4 and reaches the intake manifold 5.
By providing a control unit for controlling the exhaust turbocharger 2 so that the pressure ratio and the turbine speed lower than the equal turbine speed curve including the highest efficiency point on the compressor map are in the normal range, the low to medium The fuel consumption is improved by the effect of suppressing the supply of excess air in the load region and the effect of reducing the exhaust pressure by the EGR, and the flow rate of the EGR gas is sufficiently ensured even in the high load region to appropriately reduce the NOx emission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supercharged engine, and more particularly, to a supercharged engine capable of greatly reducing NOx emissions from the engine.

[0002]

2. Description of the Related Art One of the techniques for reducing the amount of NOx emitted from an engine is EGR in which part of exhaust gas is recirculated to an air supply system.
Providing the device is said to be effective. When such an EGR device is applied to a supercharged engine, the EG
Since the supply amount of fresh air is reduced by an amount corresponding to the amount of the R gas, there is a concern that output may be insufficient in a high load region.

On the other hand, in an engine equipped with an exhaust turbocharger, an intercooler is provided in a supply passage from a compressor of the exhaust turbocharger to an intake manifold, thereby suppressing an increase in supply air temperature and reducing NOx. It helped to reduce.

However, when an EGR device is provided in such an engine with a turbo cooler, the supply pressure increases as the load increases, so that it becomes difficult to secure the EGR amount in a high load region and NOx There was a concern that it would be difficult to sufficiently reduce emissions.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a supercharged engine capable of efficiently reducing NOx emissions.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to connect an intake manifold with a compressor of an exhaust turbocharger through an air supply passage without an intercooler, and to connect the air supply passage to the compressor. An air supply throttle valve is provided. In addition, an EGR cooler is provided in an EGR passage branching from the exhaust manifold to the intake manifold, and a pressure ratio and a turbine speed lower than a turbine rotation curve including the highest efficiency point on the compressor map are set to a normal range. And a control unit for controlling the exhaust turbocharger.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment in which a supercharged engine according to the present invention is applied to a diesel engine.

In FIG. 1, a diesel engine 1 is provided with an exhaust turbocharger 2 and an EGR device 3.
An exhaust manifold 4 is connected to the inlet of the turbine 2a of the exhaust turbocharger 2 via an air supply passage 6 without an intercooler.
Outlet of compressor 2b and intake manifold 5
Are connected.

An air supply throttle valve 7 is provided near the end of the air supply passage 6, while an EGR passage 8 branched from the exhaust manifold 4 and reaching the intake manifold 5 is provided in the EGR passage 8.
A GR cooler 9 is provided. An EGR valve 10 is provided in an EGR passage 8 downstream of the EGR cooler 9, and the air supply throttle valve 7 and the EGR valve 10 are controlled in opening by a control unit (not shown), so that the flow rates of the supply air and the EGR gas are respectively controlled. Optimum control is performed.

In the supercharged engine having the above-described structure, when the diesel engine 1 is operated, the exhaust turbocharger 2 is driven to perform a supercharging operation. At the same time, the EG removed from the exhaust manifold 4
After heat exchange in the EGR cooler 9, the R gas is subjected to flow control by the EGR valve 10, is supplied to the intake manifold 5 together with supply air whose flow is controlled by the air supply throttle valve 7, and is supplied to the combustion chamber.

The exhaust turbo supercharger 2 performing the supercharging operation receives a control signal from a control unit (not shown), and obtains a turbocharger based on an iso-turbine rotation curve including a maximum efficiency point on a compressor map of the supercharger. It is also operated with a low pressure ratio and turbine speed in the normal range.

That is, in addition to the air supply throttle valve 7 and the EGR valve 10, the control unit is a turbine output control means typified by fuel injection means (not shown), a waste gate valve or a vane opening of a variable blade turbine. By controlling at least one of the turbochargers, the turbocharger is operated so that the pressure ratio and the turbine speed lower than the iso-turbine rotation curve including the highest efficiency point on the compressor map of the turbocharger are set to the normal range. The feeder 2 is controlled.

Accordingly, the volumetric efficiency ηv of the engine containing the EGR gas according to the embodiment is, as shown by a thick solid line in FIG. Is higher than the volumetric efficiency ηv. However, as shown by a thin solid line in the figure, fresh air not containing EGR gas alone has a lower volumetric efficiency ηv than that of a non-supercharged engine as a whole, but has a higher In this case, the volume efficiency ηv is higher than in the case of (1), and the output is secured.

For this reason, in addition to the effect of suppressing the supply of excess air, which is concerned in the low to medium load range, the effect of reducing the exhaust pressure by EGR is seen, so that pumping loss is reduced and fuel efficiency is improved. At the same time, a shortage of output is avoided because a sufficient amount of fresh air is supplied in a high load region. In addition,
The exhaust turbocharger 2 is controlled such that the pressure ratio and the turbine speed lower than the equal turbine rotation curve including the highest efficiency point on the compressor map of the turbocharger are set in the normal range. Therefore, since the temperature rise of the supply air due to the pressurizing action of the compressor is suppressed to a low level, the supply air temperature does not become excessively high even if the intercooler is not provided.

That is, in a conventional engine with a turbo intercooler in which an intercooler is provided in an air supply passage so as to perform air supply cooling, a higher pressure ratio and a higher turbine speed unless the supercharger falls into overspeed. The output control means is controlled so as to commonly use the above. For this reason, as shown by the chain line in FIG. 2, the volume efficiency ηv becomes higher than the volume efficiency ηv of the supercharged engine in all the operating ranges. Therefore, in the case of a conventional engine with a turbo intercooler, there is a concern that fuel consumption will deteriorate due to excessive pumping loss and excess pumping in a low to medium load range, and a high load range in which the supply pressure increases. As a result, the flow rate of the EGR gas is insufficient, and accordingly, there is a possibility that the NOx emission amount in the exhaust gas cannot be sufficiently reduced.

However, as in the present embodiment, while controlling the exhaust turbocharger such that the pressure ratio and the turbine speed lower than the equal turbine rotation curve including the highest efficiency point on the compressor map are in the normal range, In the case where the air supply amount is optimally controlled by the air supply throttle valve 7, the pumping loss is reduced because the exhaust pressure reduction effect by the EGR is obtained while the supply of the excess air in the low to medium load region is suppressed. The fuel economy is improved.

Further, even in a high load range, as long as a pressure ratio lower than the turbine rotation curve including the highest efficiency point on the compressor map is used, the exhaust pressure is always higher than the supercharging pressure. Since the flow rate of the EGR gas can be sufficiently secured and the flow rate of the EGR gas can be optimally controlled in all the operation regions, the engine N
Ox emissions can be accurately reduced.

[0018]

As is apparent from the above description, according to the present invention, the compressor and the intake manifold of the exhaust turbocharger are connected via an air supply passage without an intercooler, and the air supply passage is supplied to the air supply passage. While only a throttle valve is provided, an EGR cooler is provided in an EGR passage branching from an exhaust manifold to an intake manifold, and a pressure ratio lower than an equal turbine rotation curve including a highest efficiency point on a compressor map of a supercharger and It is provided with a control unit that operates with the turbine speed in a normal range.

Therefore, according to the supercharged engine according to the present invention, the effect of suppressing the supply of excess air in the low to medium load range and the E
Although the fuel efficiency can be improved by the exhaust pressure reduction effect of the GR, the supercharging pressure can be kept lower than the exhaust pressure even in a high load range, so that the flow rate of the EGR gas can be sufficiently secured. The amount of NOx emission from the engine can be accurately reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which a supercharged engine according to the present invention is applied to a diesel engine.

FIG. 2 is a characteristic diagram of volume efficiency with respect to load in the conventional example and the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust turbocharger 2a Turbine 2b Compressor 3 EGR device 4 Exhaust manifold 5 Intake manifold 6 Air supply passage 7 Air supply throttle valve 8 EGR passage 9 EGR cooler 10 EGR valve

Claims (1)

[Claims] An exhaust turbocharger and an EGR device are provided, and a compressor and an intake manifold of the exhaust turbocharger are connected through an air supply passage without an intercooler, and an air supply throttle is provided in the air supply passage. While providing a valve, an EGR cooler is provided in the EGR passage branching from the exhaust manifold to the intake manifold, and a pressure ratio and a turbine rotation speed lower than an equal turbine rotation curve including the highest efficiency point on a compressor map are set in a normal range. An engine with a turbocharger, comprising a control unit for controlling the exhaust turbocharger.