Method and apparatus for regulating boost pressure

TECHNICAL FIELD

The present invention relates to an internal combustion engine, more particularly it relates to a method and apparatus for regulating boost pressure and gas temperatures in an exhaust air turbocharged internal combustion engine.

BACKGROUND OF THE INVENTION

Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response for a vehicle. One way which may improve fuel economy is turbo charging in which wasted energy in engine exhaust gas is utilized to increase the performance of an ICE (Internal Combustion Engine). A turbocharger generally includes a turbine and a compressor. Exhaust gases from an ICE are directed to the turbine housing, causing the turbine to rotate. The turbine concomitantly rotates the compressor to force more air into the engine air intake, increasing the power output of the ICE. The additional pressure generated by the compressor is known as boost pressure, which is typically controlled by a wastegate. The wastegate regulates the flow of exhaust gas over the turbine, controlling the speed of the turbine and the compressor. When the high engine power is not needed, the wastegate can bypass the turbine dropping the boost pressure, allowing the engine to run closer to atmospheric intake manifold pressure for improving fuel economy. However, there is a need for further improving the fuel economy and the emissions in a turbocharged engine. By bypassing exhaust gases in a traditional wastegate, energy is wasted into the exhaust system. Another problem with a traditional wastegate is that when said waste gate is open a back pressure in the exhaust system will increase, which may influence the fuel economy of the vehicle.

SUMMARY OF THE INVENTION

As explained above, there is a problem associated with prior art engine where the fuel economy of the engine is undesirable high.

The object of the invention is to provide an engine of the kind referred to in the introduction, by means of which engine has improved fuel economy.

The object is achieved by an engine according to claim 1.

In a first example embodiment of an internal combustion engine according to the present invention comprises at least one exhaust gas manifold for taking exhaust gases from the engine's combustion chamber, at least one inlet manifold for supplying air to said combustion chamber. Said embodiment further comprising a first turbo charging system with a first turbine connected to said exhaust gas manifold and a first compressor, for recovery of energy from the engine's exhaust gas flow and pressurizing intake air to a combustion chamber. Said intake air from said first compressor is connected to a second compressor of a second turbo system. Said intake air is further connected to a said inlet manifold via a second turbine of said second turbo system. Said second turbine of said second turbo system has variable geometry.

In another example embodiment said internal combustion engine further comprising a charge air cooler provided between said second compressor and said second turbine of said second turbo system.

In still another example embodiment said internal combustion engine further comprising a charge air cooler provided between said first compressor of said first turbo charging system and the second compressor of the second turbo system.

In still another example embodiment of said internal combustion engine said first turbine has variable geometry.

In yet another example embodiment said internal combustion engine further comprising an exhaust gas recirculation (EGR) passage for recirculating exhaust gases from the at least one exhaust manifold to the inlet manifold of said internal combustion engine.

In yet another example embodiment said internal combustion engine further comprising an EGR cooler provided in said EGR passage

The invention also relates to a method for operating a turbocharged internal combustion engine, comprising the actions of providing at least one exhaust manifold, providing at least one inlet manifold, providing a first turbo system comprising a first turbine and a first compressor, providing a second turbo system comprising a second turbine and a second compressor, directing engine exhaust flow from said at least one exhaust manifold to said first turbine of said first turbo system, directing intake air from said first compressor of said first turbo system to said inlet manifold via firstly said second compressor of said second turbo system and secondly said turbine of said second turbo system, adjusting a boost pressure by regulating a geometry of said second turbine of said second turbo system.

In another example embodiment of the method of operating a turbocharged internal combustion engine said method further comprising the action of redirecting exhaust gases to said inlet manifold.

In still another example embodiment of the method of operating a turbocharged internal combustion engine, said method further comprising the action of providing a cooler between said second compressor of said second turbo system and said second turbine of said second turbo system.

In still another example embodiment of the method of operating a turbocharged internal combustion engine said method further comprising the action of providing a cooler between said first compressor of said first turbo system and said second compressor of said second turbo system.

In still another example embodiment of the method of operating a turbocharged internal engine said method further comprising the action of providing said first turbine of said first turbo system with a variable geometry.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 shows a schematic view illustrating of an example embodiment of an engine according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In Fig. 1 an example embodiment of an engine 10 according to the present invention is schematically illustrated. The engine 10 comprises a first turbo system 13, a second turbo system 21 , a first Charge Air Cooler 16, a second charge air cooler 18, an inlet manifold 24, a cylinder block 26, an exhaust manifold 28, an exhaust gas recirculation (EGR) pipe 48 and an EGR cooler 30.

The cylinder block 26 may comprise one or a plurality of cylinders. The cylinders may be arranged in a row, V form or boxer form. A displacement of one cylinder may vary in the range from 50cm ³ - 1000 000cm ³ . The fuel may

be diesel, gasoline, E85, methanol, ethanol, gas or any other combustible fuel. The engine may be compression ignited or spark plug ignited.

A cylinder head, attached to said cylinder block, may comprise at least one inlet valve and at least one exhaust valve. At least one camshaft for activating said valves may be arranged in the cylinder head, OHC (over head camshaft) for a single camshaft in the cylinder head and DOCH (Dual over head camshaft) for two camshafts in one cylinder head. In case of using two camshafts, one camshaft may activate at least one intake valve and another camshaft may active at least one outlet valve.

The exhaust manifold 28 is directing exhaust gases to an exhaust system from a combustion chamber via one or a plurality of exhaust valves and one or a plurality of exhaust channels provided in the cylinder head. The exhaust manifold 28 as depicted in figure 1 connects all exhaust channels from all four cylinders. In an alternative embodiment a first exhaust manifold may be used for one or a plurality of cylinders of the engine and a second manifold may be used for the rest of the cylinders in the engine. For instance, in an in line 6 cylinder engine, a first exhaust manifold may be used for connecting together exhaust channels from cylinders 1 , 2 and 3, and a second exhaust manifold may be used for connecting together exhaust channels from cylinders 4, 5 and 6. In a V-formed engine or a boxer engine, a left line of cylinders may use a first set of exhaust manifolds and a right line of cylinders may use a second set of exhaust manifolds. Said first and second set may comprise one or a plurality of separate exhaust manifolds.

Exhaust gases are directed from the exhaust manifold to a first turbine 14 of the first turbo system 13. Exhaust gases bring the first turbine 14 in said first turbo system 13 into rotation. Exhaust gases are thereafter directed from the turbine 14 into the exhaust system. Before said exhaust gases are introduced into the atmosphere they may pass one or several exhaust after treatment

system provided in the exhaust system, which serve as to clean the exhaust gases from one or several components therein.

Air is provided to the intake manifold 24 via a first compressor 12 in said first turbo system 13, the first charge air cooler 16, a second compressor 20 of the second turbo system 21 , the second charge air cooler 18, and a second turbine 22 of the second turbo system 21. This means that in the embodiment as depicted in figure 1, the first compressor 12, the first charge air cooler 16, the second compressor 20, the second charge air cooler 18 and the second turbine 22 are in fluid connection with each other and the inlet manifold 24.

The first compressor 12 of the first turbo system 13 is in mechanical connection with the first turbine 14 of said first turbo system 13, i.e., the exhaust gases bring the first turbine 14 in rotation, which in turn brings the first compressor 12 in rotation according to well known technique. The dimension of the turbine and the compressor are chosen with respect to many parameters. One rule of thumb is that the bigger the total displacement of the engine from which the exhaust gases are coming from, the bigger the turbine one may choose. For small engines the turbine is smaller in order to bring the turbine into rotation quicker, which in turn may lead to less turbo lag.

Compressed air from the first compressor 12 is then directed to a first charge air cooler 16. Compressed air out of the first compressor 12 will be hotter than the non compressed air provided into the compressor 12. In order to cool down said compressed air, a first charge air cooler 16 is provided after the first compressor 12 and in fluid connection with said first compressor 12.

The connection between said first compressor 12 and an intake side of said charge air cooler may for instance be a pipe of aluminium or steel.

An outlet side of said charge air cooler 16 is in fluid connection with the second compressor 20 of the second turbo system 21. Compressed air passing through said first charge air cooler 16 may loose 100-150 ⁰ C depending on the size of the first charge air cooler 16. Typically compressed air at the intake side of said first charge air cooler 16 has a temperature of 200 ⁰ C and compressed air at the outlet side of said first charge air cooler 16 has a temperature of 45 ⁰ C, at 3.0 bar boost pressure. The compressed air passing through said first charge air cooler 16 not only loosing some temperature but also some boost pressure, typically a normal size charge air cooler will affect the boost pressure of about 2-5 kPa.

The first charge air cooler 16 may be cooled by air or liquid or any other coolant means.

Compressed air passing through the second compressor 20 of said second turbo system 21 will increase pressure and gain some degrees in temperature. Compressed air is then directed from the second compressor 20 to the second charge air cooler 18. In said second charge air cooler 18 the compressed air will further drop in pressure and in temperature, the degree of drop in pressure and temperature is somewhat dependent on the size of the second charge air cooler 18 but also dependent on the coolant medium.

Compressed air is then directed from the second charge air cooler 18 to the second turbine 22 of the second turbo system 21. Compressed air, which have passed said second turbine 22, will drop in pressure and in temperature. The degree of temperature decrease and pressure drop is strongly affected by the geometry of said turbine. In the present invention said turbine 22 has variable geometry, which means that the degree of pressure drop and decrease in temperature can be varied.

In an example embodiment, intake air at atmospheric pressure and 20 degrees Celsius is provided to the intake side of the first compressor 12. At an outlet side of said first compressor 12, compressed air may have a pressure of 2 bar above atmospheric pressure and a temperature of 200 ⁰ C. Compressed air at an inlet side of said first charge air cooler 16 may have lost some degrees in temperature and some pressure depending on the material and length of a pipe 32 connecting the outlet of the first compressor 12 with the inlet side of the first charge air cooler 16.

Compressed air coming out from the first charge air cooler 16 may have a temperature of 45C and a pressure of 3.0 Bar. The degree of cooling is depending on the size of said first charge air cooler but also on the coolant medium. An outlet of said first charge air cooler 16 is connected to an inlet of said second compressor 20 via pipe 34. Compressed air coming out of the second compressor 20 may have a temperature of 200C and a pressure of 4.5 Bar. An outlet of said second compressor is connected to an inlet of said second charge air cooler 18 by a pipe 36.. Compressed air coming out of the second charge air cooler may have a temperature of 45 ⁰ C and a pressure of 4.5 Bar. An outlet of said second compressor 18 is connected to an inlet of the second turbine 22 by a pipe 38. Compressed air coming out of the second turbine may have a temperature of -25 ⁰ C and a pressure of 1.5-2.0 Bar. An outlet of said second turbine 22 is connected to the inlet manifold by pipe 40.

The variable geometry of the second turbine 22 may be used to regulate the boost pressure provided into the inlet manifold 24. If the boost pressure is too high, said variable turbine may be closed more or less in order to decrease the boost pressure more or less. At the same time as the boost pressure is decreased by restricting the passage through the second turbine 22 by changing its geometry, the temperature will also drop as a consequence of that. This means that the more one is decreasing the pressure the cooler the air directed from the second turbine 22 into the inlet manifold 24 will be.

When the boost pressure is too low, the passage through the second turbine may be opened and thereby the temperature may be increasing as well as the pressure of the compressed air fed to the inlet manifold 24. A control unit may be connected to a pressure sensor. Said pressure sensor may be provided on the pipe 42 connecting the exhaust manifold to the inlet of the first turbine 14. A signal from said pressure sensor may be directed to means for changing the variable geometry of the turbine 22 via said control unit. If for instance the derivative of the pressure signal is positive, then said control unit may control said means for restricting the passage through said turbine. If said derivate of the pressure signal is negative said control unit may control said means for opening the passage through said turbine 22. The means for changing the geometry of said turbine 22 may be an electrical motor, pneumatic pressure, air pressure which is mechanically connected to said turbine according to well known methods.

In yet another example embodiment, said first turbine may have variable geometry.

In the depicted example embodiment in figure 1 it is also illustrated an EGR cooler 30 and an EGR passage 48. Since the temperature of the compressed air in this embodiment according to the present invention is relatively low, said EGR cooler may be omitted. EGR may be cooled by means of the cold air provided from the second variable turbine 22 into the inlet manifold 24, i.e., ,the exhaust gases when mixed with the air in the inlet manifold 24 is not only mixed but also cooled because of the inventive arrangement as depicted in figure 1. VGT second turbine may also work as an EGR distributor.

The first turbo system 13 must be manufactured in a heat resistive material because of the extremely hot exhaust gases provided from the exhaust manifold 28 to the first turbine 14. However, the second turbo system 21 may be manufactured in a material less heat resistive than the first turbo system 13, The temperature at an intake side of the second compressor 20 maybe

around 10OC and the temperature of the compressed air at an outlet side of the second turbine is about -50C. This means a temperature difference of 150 C with a top value of +100 and a bottom value of -50C. With such a temperature range it may be possible to find other materials than commonly used in turbo systems nowadays, for instance polymeric materials, aluminium, etc. which may both be simpler in manufacturing than the commonly used materials for turbo system as well as lighter then the materials in commonly used turbo systems. Also much reduced clearances may be used inside the second turbine which will contribute significantly to stage efficiencies.

In addition to the inlet manifold, exhaust manifold and the depicted turbo systems, other components can be arranged inside and outside the engine. Such components can be arranged separately but usually they are attached to or suspended from the engine. Both engine components and non-engine components, which components can be driven by the engine, such as a power steering pump, have been omitted in figure 1 because of clarity reasons.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.