GB2489415A

GB2489415A - An internal combustion engine with exhuast gas recirculation

Info

Publication number: GB2489415A
Application number: GB1105018.4A
Authority: GB
Inventors: David William Henry Tennant; Stephen Garrett
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2011-03-25
Filing date: 2011-03-25
Publication date: 2012-10-03
Also published as: GB201105018D0

Abstract

An internal combustion engine 1 with a turbocharger, having a turbine 6 and a first compressor 7, and an exhaust gas recirculation (EGR) path 5a in fluid communication with the exhaust path 5. An EGR pump 12 directs a recirculation flow of exhaust gas to the air intake path 4. A second compressor 10 upstream or downstream of the turbocharger compressor in the air intake path provides additional boost pressure. The EGR pump 12 and the second compressor 10 are driven by a common electrical machine 11 such as a double-ended motor. Clutches 13 may also be fitted on the output shaft 15 between the electrical machine 11 and the EGR pump 12 and the second compressor 10.

Description

I

AN INTERNAL COMBUSTION ENGINE WITH EXHUAST GAS RECIRCULATION

The present invention relates to an internal combustion engine and in particular to such an engine having a turbocharger and exhaust gas recirculation (EGR).

Turbochargers are well-known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing.

The compressor wheel delivers compressed air to the intake manifold of the engine, thereby increasing engine power. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housing.

Exhaust gas emissions are the subject of increasingly stringent legislation and a consequence of this is an increased demand for higher boost pressures for a given engine size so that performance is not materially compromised.

Oxides of nitrogen (NOr), which are recognised to be harmful to the environment, are produced during the combustion process in an engine. In order to meet legislation intended to limit emissions exhaust gas recirculation (EGR) systems are used, in which a portion of the engine exhaust gas is recirculated through the combustion chambers.

This is typically achieved by directing an amount of the exhaust gas from the exhaust manifold to the inlet manifold of the engine. The recirculated exhaust gas partially quenches the combustion process of the engine and hence lowers the peak temperature produced during combustion. As NO production increases with increased peak temperature, recirculation of exhaust gas reduces the amount of undesirable NO formed. Turbochargers may form part of the EGR system.

In order to introduce exhaust gas into the intake manifold, the recirculated exhaust gas must be at a higher pressure than that of the intake gas. However, in a turbocharged engine, the intake gas is typically at a pressure higher than that of the exhaust gas as the turbocharger compressor increases the pressure of the intake gas. The pressure differential between the exhaust gas and intake gas thus prevents flow from the exhaust system to the intake system and in order to overcome this it is known to provide a pump or compressor to create a pressure differential sufficient to force the diverted exhaust gas into the intake manifold.

There is still a requirement for a simple, efficient and inexpensive approach to ensuring that sufficient differential pressure is created to force the diverted exhaust gas into the intake manifold for all the appropriate operating conditions of the engine.

It is one object of the present invention to obviate or mitigate the aforesaid disadvantages. It is also an object of the present invention to provide for an improved or alternative internal combustion engine with exhaust gas recirculation or a turbocharger with an improved or alternative exhaust gas recirculation system.

According to a first aspect of the present invention there is provided an internal combustion engine having an air intake path, an exhaust path and a turbocharger having a turbine in the exhaust path and a first compressor in the air intake path for supplying compressed air, an exhaust gas recirculation (EGR) path in fluid communication with the exhaust path and having an EGR pump for directing a recirculation flow of exhaust gas to the air intake path, a second compressor upstream or downstream of the first compressor in the air intake path, the EGR pump and the second compressor being driveable by a common electrical machine.

The common electrical machine may have an output shaft with a first end and a second end. The first end may be connected to second compressor and the second end may be connected to the EGR pump.

The electrical machine may be a motor.

The EGR pump may be a compressor.

A first clutch may be disposed between the electrical machine and the EGR pump for selective operation such that drive is transmitted from the electrical machine to the EGR pump when the clutch is engaged. The selective operation of the clutch may be dictated by a control unit.

A valve may be disposed in the exhaust gas recirculation path. The valve may be disposed upstream of the inlet of the EGR pump. A portion of exhaust gas may be selectively diverted by the valve, in one valve position the gas is diverted from the exhaust gas path upstream of the turbocharger to the EGR pump. The diverted exhaust gas may be pumped by the EGR pump into the air intake path. It may be pumped to a location downstream of the turbocharger compressor such that it is forced into an air intake manifold of the engine. In an alternative valve position the valve prevents exhaust gas recirculation.

The valve may be operable such that gas bypasses the EGR pump but is nevertheless directed along an exhaust gas recirculation path. In such a circumstance the recirculation would be unassisted. This would be used during certain engine operating conditions when the pressure of the exhaust gas is greater than the air inlet pressure.

In addition, or as an alternative, a second clutch may be provided between the electrical machine and the second compressor. The second clutch is selectively operable to transmit drive from the electrical machine to the second compressor.

A bypass valve may be provided to permit fluid to bypass the second compressor.

In the instance where the second compressor is upstream of the first compressor the bypass valve may be located between an outlet path of the second compressor and an inlet to the first compressor. The valve may have a first inlet port into which air may be delivered and a second inlet port in fluid communication with an outlet of the second compressor and at least one outlet port that is in fluid communication with the inlet of the first compressor.

Alternatively, when the second compressor is downstream of the first compressor the bypass valve is located in the outlet path of the first compressor, between the first compressor and the air intake of the engine. The bypass valve may be disposed downstream of an inlet to the second compressor. The bypass valve may preferably be a non-return valve.

When the second compressor is disengaged from the electric machine, the bypass valve may be open to allow air to bypass the second compressor. The bypass valve is operable to a closed position when the second compressor is driven by the electric machine so that air is forced to pass through the second compressor before or after entering the first compressor.

According to a second aspect of the present invention there is provided a method for controlling intake to an internal combustion engine with a turbocharger, the turbocharger comprising an exhaust gas turbine that drives a first compressor, the method comprising selectively recirculating exhaust gas from the turbine of the turbocharger to an air intake of the internal combustion engine using an EGR pump in response to a first control signal, and selectively driving a second compressor upstream or downstream of the first compressor in the air intake path in response to a second control signal in order to provide an additional air intake boost pressure, the EGR pump and the second compressor being selectively driveable by a common electrical machine.

The first and second control signal may be generated by an engine control or management unit in response to operating parameters of the engine and/or turbocharger.

The EGR pump and the second compressor may be selectively driven by a clutch which is selectively engaged or disengaged with the common electrical machine.

The method may further comprise selectively operating a first valve to open or close an exhaust gas recirculation path. In the open position the valve may serve to divert at least a portion of exhaust gas to the EGR pump.

The method may further comprise selectively operating a second valve to allow fluid by bypass the second compressor. In the instance where the second compressor is upstream of the first compressor the second valve may be located between an outlet path of the second compressor and an inlet path of the first compressor. In the instance where the second compressor is downstream of the first compressor the second valve may be located in the outlet path of the first compressor, between the first compressor an the air intake of the engine Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a first embodiment of an internal combustion engine fitted with a turbocharger and including exhaust gas recirculation in accordance with the invention; Figure 2 is a diagrammatic representation of a second embodiment of an internal combustion engine fitted with a turbocharger and including exhaust gas recirculation path in accordance with the invention; and Figure 3 is a diagrammatic representation of a third embodiment of an internal combustion engine fitted with a turbocharger and including exhaust gas recirculation in accordance with the invention.

Referring now to the drawings, figure 1 schematically represents an internal combustion engine 1, such as a diesel engine for a vehicle, with exhaust gas recirculation. The engine has an intake manifold 2 and an exhaust gas outlet manifold 3 which are connected respectively to an air intake path 4 and an exhaust gas path 5.

A turbocharger mounted on the engine comprises a turbine 6 disposed in the exhaust gas path 5 and a compressor 7 disposed in the air intake path 4. The turbine 6 and compressor 7 are mounted on a common rotary shaft 8 for rotation together. Exhaust gas from the outlet manifold 3 of the engine 1 drives the turbine 6 in rotation which in turn drives the compressor 7 in rotation via the shaft. Air entering the compressor is compressed and delivered to the air intake manifold 2 of the engine via the air intake path 4 so as to boost the air pressure and increase the engine power.

A pre-compressor 10 upstream of the turbocharger compressor 7 in the air intake path 4 provides an initial compression of the air before it enters the turbocharger compressor 7 and is driven by one end of a double-ended motor 11. The provision of a pre-compressor 10 provides for a two-stage compression of the air so providing high boost levels.

An exhaust gas recirculation (EGR) pump 12 is disposed in an exhaust gas recirculation path 5a between the exhaust gas path 5 and the air intake path 4. A portion of exhaust gas is selectively diverted from the exhaust gas path 5 upstream of the turbocharger to the pump 12 from where it is pumped into the air intake path 4 downstream of the turbocharger compressor 7 such that it is forced into the air intake manifold 2 of the engine 1. The selective diversion is achieved by means of a valve 14 which, when open, diverts exhaust gas to the EGR pump 12 and when closed prevents exhaust gas recirculation. The operation of the valve 14 may be controlled, for example, by the engine management unit (not shown). In the event that the EGR pump 12 is disengaged from the motor lithe valve is closed so as to ensure unrestricted flow of the exhaust gas to the turbocharger turbine 6. The valve may have an optional mode of operation in which it directs exhaust gas into the exhaust gas recirculation path but bypasses the EGR pump. This mode of operation may be adopted in certain engine conditions where there is a sufficient pressure differential between the exhaust iS gas pressure and the air pressure at the manifold intake 2 to ensure the gas can recirculate unassisted.

The EGR pump 12 is driven by a second end of the double-ended motor ii via a clutch 13. If necessary a gear transmission may be interposed between the motor Ii and the pump 12. The clutch allows for selective disengagement of the drive torque from the motor 11 to the EGR pump 12.

The motor 11 may have a single output shaft 15 that defines the two ends to which the pre-compressor 10 and the EGR pump 12 are respectively connected.

The EGR pump 12 may be of any suitable type including, for example, a compressor. It operates to pressurise the recirculated exhaust gas to a level where it can be forced into the intake manifold 2.

A control regime may operate to provide exhaust gas recirculation flow as required by operation of the clutch 13 and the valve 14. This ensures that the flow is not limited by engine speed or exhaust gas flow pressure or the like. Moreover, it allows the exhaust gas recirculation flow to be blocked in the event that the engine operating conditions are not favourable. The control regime may operate to modulate the opening of the valve 14 and so control the volume of exhaust gas that is recirculated depending on other monitored parameters.

In the embodiment shown in figure 1 the pie-compressor 10 is continuously operational and serves to increase the pressure of air admitted into the turbocharger compressor 7.

The controller is operable to control the rotational speed of the motor such that when the EGR pump is driven the impact on the operation of the pre-compressor is not compromised.

In an alternative embodiment shown in figure 2, there is a second clutch 16 between the pre-compressor 10 and the motor 11. The second clutch is operable selectively to transmit or disengage torque from the motor 11 to the pre-compressor 10. This allows for selective or intermittent operation of the pre-compressor 10. A bypass valve 17 is associated with the pre-compressor 10 between its outlet and the inlet to the turbocharger compressor 7. It has a first inlet port connected to atmospheric air, a second inlet port in fluid communication with the outlet of the pre-compressor 10 and an outlet port in fluid communication with an inlet of the turbocharger compressor 7.

When the pre-compressor 10 is disengaged from the motor 11, the bypass valve 17 may be open so that the pre-compressor does not represent a restriction to the flow of air into the system and air is able to pass directly to the turbocharger compressor 7.

The valve 17 remains closed when the pre-compressor 10 is driven so that air is forced to pass through the pre-compressor before entering the turbocharger compressor 7.

In the event that the speed of the motor required to operate the pre-coinpressor effectively is too high to be compatible with the exhaust gas recirculation flow requirement the valve 14 associated with the EGR pump 12 may be modulated to restrict the recirculation flow rate through the pump 12.

In a further alternative embodiment (not shown) there is a clutch between the pre-compressor and the motor but not between the motor and the pump. In such an arrangement the pump is a continuous load but the pre-compressor is operated intermittently as required.

Figure 3 shows an alternative embodiment in which the pre-compressor 10 is replaced with a "post-compressor" ba. Instead of a second compressor being provided upstream of the turbocharger compressor 7 it is located downstream. In some instances this may be a more preferable arrangement as the impeller of the compressor lOa would be of a smaller size and more similar to the size and speed of the impeller of the EGR pump 12 and therefore better suited to being driven by the same motor 11.

In this embodiment a bypass valve 17 is again provided so that compressed air that exits from the turbocharger compressor 7 may bypass the second compressor lOa by virtue of the valve being open. When the valve is closed air passes to the second compressor lOa before entering the engine intake 2. The bypass valve is disposed downstream of an inlet of the second compressor ba but may be positioned at the junction of the outlet path from the turbocharger compressor 7 and the inlet path to the second compressor lOa.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, other suitable electrical machines may be used instead of a motor.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

CLAIMS1. An internal combustion engine having an air intake path, an exhaust path and a turbocharger having a turbine in the exhaust path and a first compressor in the air intake path for supplying compressed air, an exhaust gas recirculation (EGR) path in fluid communication with the exhaust path and having an EGR pump for directing a recirculation flow of exhaust gas to the air intake path, a second compressor upstream or downstream of the first compressor in the air intake path, the EGR pump and the second compressor being driveable by a common electrical machine.
2. An internal combustion engine according to claim 1, wherein the common electrical machine has an output shaft with a first end and a second end, the first end being connected to the second compressor and the second end being connected to the EGR pump.
3. An internal combustion engine according to claim 1 or 2, wherein the electrical machine is a motor.
4. An internal combustion engine according to claim 1, 2 or 3, wherein the EGR pump is a compressor.
5. An internal combustion engine according to any preceding claim, wherein a first clutch is disposed between the electrical machine and the EGR pump for selective operation such that drive is transmitted from the electrical machine to the EGR pump when the clutch is engaged.
6. An internal combustion engine according to claim 5, wherein a valve is disposed in the exhaust gas recirculation path for selective diversion of exhaust gas from the exhaust gas path to the EGR pump.
7. An internal combustion engine according to claim 6, wherein the valve is operable to allow exhaust gas to bypass the EGR pump and recirculate to the air intake path.
8. An internal combustion engine according to any preceding claim, wherein a second clutch is provided between the electrical machine and the second compressor for selective operation such that drive is transmitted from the electrical machine to the second compressor when the clutch is engaged.
9. An internal combustion engine according to claim 8, wherein the second compressor is upstream of the first compressor, and a bypass valve is disposed between an outlet path of the second compressor and an inlet to the first compressor for selectively allowing and preventing fluid to bypass the second compressor.
10. An internal combustion engine according to claim 8, wherein the second compressor is downstream of the first compressor, and a bypass valve is disposed in an outlet path of the first compressor for selectively allowing fluid to bypass the second compressor.
11. A method for controlling intake to an internal combustion engine with a turbocharger, the turbocharger comprising an exhaust gas turbine that drives a first compressor, the method comprising selectively recirculating exhaust gas from the turbine of the turbocharger to an air intake of the internal combustion engine using an EGR pump in response to a first control signal, and selectively driving a second compressor upstream or downstream of the first compressor in the air intake path in response to a second control signal in order to provide an additional air intake boost pressure, the EGR pump and the second compressor being driveable by a common electrical machine.
12. A method according to claim 11, wherein the EGR pump and the second compressor are selectively driveable by the common electrical machine.
13. A method according to claim 11 or 12, wherein the first and second control signals are generated by an engine control or management unit in response to operating parameters of the engine and/or turbocharger.
14. A method according to claim 11, 12 or 13, wherein the EGR pump is selectively driven via a first clutch.
15. A method according to any one of claims 11 to 14, wherein the second compressor is selectively driven via a second clutch.
16. A method according to any one of claims I to 15, further comprising selectively operating a first valve to open or close an exhaust gas recirculation path.
17. A method according to claim 16, further comprising selectively operating the first valve to allow exhaust gas to bypass the EGR pump and proceed along the exhaust gas recirculation path.
18. A method according to any one of claims 11 to 17, further comprising selectively operating a second valve to prevent or allow fluid to bypass the second compressor.