GB2390642A

GB2390642A - Turbocharged i.c engine

Info

Publication number: GB2390642A
Application number: GB0215843A
Authority: GB
Inventors: Brian Horner
Original assignee: Honeywell UK Ltd
Current assignee: Honeywell UK Ltd
Priority date: 2002-07-09
Filing date: 2002-07-09
Publication date: 2004-01-14
Also published as: GB0215843D0

Abstract

A turbocharged internal combustion engine comprises an air inlet; an exhaust gas outlet; a turbocharger having a turbine gas inlet, a variable turbine, a compressor and a gas outlet from the compressor; and further comprising a bypass valve interposed between the engine exhaust gas outlet and the turbine inlet. This engine is preferably operated by reducing the effective area of the variable turbine while the bypass valve is kept closed, monitoring the outlet air pressure from the compressor or the turbocharger speed, detecting when one of these parameters reaches a predetermined value and then opening the bypass valve while keeping the variable turbine in the closed position until the predetermined values are re-achieved. This arrangement is particularly useful to improve engine braking and improve exhaust gas recirculation.

Description

1 2390642

TURBOCHARGER

DESCRIETION

5 The present invention relates to a turbocharger for an internal combustion engine, and particularly to the manner of handling the exhaust gases for recirculation or engine braking. 10 In an internal combustion engine, one possible way of meeting statutory requirements is to return a portion of the exhaust gases to the engine inlet to reduce the emissions of noxious gases such as oxides of nitrogen. This is known as exhaust gas recirculation or EGR. Typically up to 50% of the 15 exhaust gases are recirculated.

Normally the exhaust gas is recirculated directly from the engine exhaust to the engine inlet manifold. However, in certain applications, for example in heavy-duty diesel 20 engines, the legislated emission regulations are such as to require the exhaust gas to be recirculated under conditions when the pressure in the engine inlet is greater than that in the engine exhaust. This positive engine pressure differential prevents the return flow of exhaust gas thus 25 precluding the use of the simple normal EGR route. Other routes have been tried but all have serious disadvantages.

The use of a variable geometry turbine (VGT) to improve internal combustion engine performance is well known. In 30 addition, reducing the effective area of the variable turbine increases the flow restriction consequently increasing the pressure in the engine exhaust manifold. Thus reducing the flow area of the VGT can help to produce a negative engine differential pressure thereby providing 35 conditions where the normal EGR system is viable.

-2 However a problem occurs with high efficiency turbochargers where reducing the effective area of the turbine can cause the turbocharger to overspend. Hence the negative level of engine differential pressure is limited therefore the amount of possible EGR is also limited.

In addition, engine braking, which is the energy internally absorbed by the engine to retard the vehicle, is 10 increased as the level of negative engine differential pressure is increased. The amount of engine braking that can be achieved is also limited by the turbocharger speed.

According to a first aspect of the present invention 15 there is provided a turbocharged internal combustion engine comprising: an engine with an air inlet manifold; and an exhaust gas outlet manifold; and a turbocharger having a variable geometry turbine with a gas inlet, and a compressor with a gas outlet; wherein a bypass valve is interposed 20 between the engine exhaust gas outlet manifold and the variable geometry turbine, and an exhaust gas recirculation path connects the engine exhaust gas outlet manifold to the engine inlet manifold.

25 According to a preferred embodiment there is further included an exhaust gas recirculation path connecting the engine exhaust gas outlet manifold to the engine inlet manifold to improve exhaust gas recirculation. A gas path may also bypass the turbocharger and an exhaust gas 30 recirculation valve may be interposed in the recirculation path, receiving gas on the bypass path and from the compressor outlet.

Alternatively the engine of the first aspect may be 35 used to improve engine braking.

According to a second aspect of the present invention there is provided a method of operating an internal combustion engine with a turbocharger having a variable 5 geometry turbine and a turbine bypass path operated by a bypass valve, the method comprising the steps of: closing the turbine bypass valve, reducing the effective area of the variable geometry turbine, monitoring at least one turbocharger operating condition and opening the bypass 10 valve to contain at least one monitored turbocharger operating condition within a predetermined envelope.

The method of the second aspect may be applied to the engine of the first aspect.

According to one preferred embodiment the method is used to improve engine braking. This may be achieved by closing the bypass valve and substantially reducing or closing the available area of the variable nozzle of the 20 turbine until the required compressor pressure (P2c) is achieved, then opening the bypass valve but keeping the nozzle closed until the compressor pressure (P2c) is attained again. This causes a rise in the turbine inlet pressure Pit and provides optimum conditions for engine 25 braking.

According to a second preferred embodiment the method is used to improve exhaust gas recirculation in an engine with an exhaust gas recirculation path bypassing the 30 turbocharger, optionally controlled by a valve.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in 35 which:

-4 Figure 1 is a schematic flow diagram of a turbocharged internal combustion engine according to the present invention, 5 Figure 2 is a schematic flow diagram of a turbocharged internal combustion engine according to the present invention, in engine braking mode.

Figure 3 is a schematic flow diagram of a turbocharged 10 internal combustion engine according to the present invention, in exhaust gas recirculation (EGR) mode.

The invention can be used in the modes shown in figures 15 2 and 3 either simultaneously or separately.

In all figures 1, 2 and 3 an internal combustion engine 1 is shown with an inlet manifold 2 and an exhaust gas outlet manifold 3. A variable geometry turbine turbocharger 20 4 comprises a compressor 5 and a variable nozzle turbine 6.

The turbocharger 4 is connected to supply air, compressed by compressor 5, at pressure P2c (typically up to 4 bar abs), to the engine inlet manifold 2. An ambient air intake to the compressor 5 is shown at 13 and an exhaust outlet 14 from 25 the turbine is shown.

The exhaust gas, emerging from engine outlet manifold 3, passes through a bypass valve 7 which can be set to divide the exhaust gas flow such that a first portion flows 30 into the turbine 6 at a pressure Pit (normally 1- 3 bar abs), and a second portion flows through a recirculation arm 8, to bypass the variable nozzle turbine 6.

The compressed air at the engine inlet manifold 2 is 35 typically at a pressure P2c of up to 4 bar abs and the gas

-5 flow into turbine 6 is normally at a pressure Plt of around 1-3 bar abs. However pressure Plt can rise to a maximum of around 5 bar abs transiently and when Plt is higher than P2c then EGR takes place naturally but only momentarily.

s Figure 1 shows a first cooler 11 in the recirculation arm 8 and a second cooler 12 in the path between the compressor 5 and the engine inlet manifold 2.

10 In figure 2 the system is configured to improve engine braking. Optimum engine braking is achieved through a combination of high compressor pressure to increase the airflow through the engine, in combination with a high exhaust backpressure to increase the pumping mean effective IS pressure. In accordance with the invention the nozzle of the variable turbine 6 is kept closed until the desired compressor outlet pressure P2c is achieved. Then the bypass valve 7 is opened but the nozzle of the variable turbine 6 is kept closed until the required compressor outlet pressure 20 P2c is regained. At this stage the turbine 6 is operating off its design point and the stage efficiency is consequently very low. A low efficiency requires a significantly increased turbine inlet pressure Plt (typically up to 10 bar abs during the braking cycle) to 25 retain the charge pressure P2c and thus provides the conditions required for increased braking.

In figure 3 the system is configured to improve exhaust gas recirculation (EGR). An exhaust gas recirculation path 30 10 is shown with an EGR valve 9. (The EGR valve is optional) At high engine loads, especially at lower speeds with an efficient turbocharger, the compressor outlet pressure P2c is greater than the turbine inlet pressure Plt (P2c > Plt) and this positive differential pressure normally prevents 35 the natural flow of EGR across the turbocharger 1.

-6 However, a negative differential pressure sufficient to satisfactorily drive the exhaust gas recirculation without the need for additional pumps can be achieved by a method according to the invention, ie. by keeping the nozzle of the 5 variable turbine 6 closed until the desired compressor outlet pressure P2c is achieved, then opening the bypass valve 7 but keeping the nozzle of the variable turbine 6 closed until the required compressor outlet pressure P2c is regained, and thus effectively reducing the turbine 10 efficiency.

In each case the bypass valve 7, the variable nozzle turbine 6 and the EGR valve 9 (if fitted) could be controlled in a known, conventional manner, with pneumatic 15 actuators modulated by an engine electronic control unit (ECU) through a pulse width modulating valve (PWM).

Alternatively electric actuators could be used. These would be controlled directly from the ECU.

The detailed control strategy and timing of the valve release would be determined by the specific application depending upon whether EGR, or engine braking, or both, were required, and of course on the specific parameters of the 25 engine and turbocharger involved. Such details are within the capability of the skilled man in the art without inventive input.

Effectively the turbine bypass valve 7 (also known as 30 a wastegate) results in a lower efficiency and allows the turbine 6 to operate at a lower flow than normal. At the lower flow the efficiency falls even further achieving the double effect of ensuring that not all the exhaust is used to drive the turbine and driving the turbine at a reduced 35 efficiency. The bypass is designed not to operate during

-7 normal operation of the turbocharger so that under normal conditions the maximum engine efficiency is retained. The bypass could be operated temporarily or permanently.

Claims

-8 CLAIMS

l. A turbocharged internal combustion engine comprising: an engine with an air inlet manifold; 5 and an exhaust gas outlet manifold; a turbocharger having a variable geometry turbine with a gas inlet, and a compressor with a gas outlet; and a bypass valve interposed between the engine exhaust gas outlet manifold and the variable geometry 10 turbine.
2. An internal combustion engine according to claim l, further comprising an exhaust gas recirculation path from the engine exhaust gas outlet manifold to the engine inlet 15 manifold to improve exhaust gas recirculation.
3. An internal combustion engine according to claims l or claims 2 further comprising a gas path arranged to bypass the turbocharger.
4. An internal combustion engine according to claim 3 further comprising a recirculation valve receiving gas on the bypass gas path and gas from the compressor outlet.

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5. An internal combustion engine according to claim l when used to improve engine braking.
6. An internal combustion engine substantially as hereinbefore described with reference to figure l optionally 30 in combination with figure 2 and/or figure 3.
7. A method of operating an internal combustion engine with a turbocharger having a variable geometry turbine and a turbine bypass path operated by a bypass valve the method 35 comprising the steps of:

closing the turbine bypass valve, reducing the effective area of the variable geometry turbine, monitoring at least one turbocharger operating 5 conditions and, opening the bypass valve to contain at least one monitored turbocharger operating condition within a predetermined envelope.
8. A method according to claim 7 wherein the monitored 10 turbocharger operating condition comprises the outlet air pressure from the compressor.
9. A method according to claim 7 wherein the monitored turbocharger operating condition comprises the turbocharger IS speed.
10. A method according to any one of claims 7 to 9 when used to improve engine braking.

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11. A method according to claim 10 comprising: closing the bypass valve; reducing the available area of the nozzle of the turbine until a predetermined compressor pressure is achieved; 25 opening the bypass valve but keeping the nozzle closed until the predetermined compressor pressure is achieved again.
12. A method according to any one of claims 7 to 9 when 30 used to improve exhaust gas recirculation in an engine with an exhaust gas recirculation path bypassing the turbocharger.
13. A method of operating an internal combustion engine, 35 substantially as hereinbefore described with reference to

- lo -

figure 1 optionally in combination with figure 2 and/or figure 3.