WO2000032917A1

WO2000032917A1 - Supercharged internal combustion engine with electrically driven compressor

Info

Publication number: WO2000032917A1
Application number: PCT/ZA1999/000127
Authority: WO
Inventors: Herman August Van Schalkwyk; Jacobus Abraham Fouche
Original assignee: Herman August Van Schalkwyk; Jacobus Abraham Fouche
Priority date: 1998-11-26
Filing date: 1999-11-26
Publication date: 2000-06-08
Also published as: AU1527300A

Abstract

A forced air induction system for an internal combustion engine (10) comprises a positive displacement rotary compressor (26) driven by an electric motor (28). The compressor (26) draws air via the inlet 20.2 and air-cleaner (22), compresses the air and supplies air under pressure via the ducting (21) to the air junction box (23) and ducting (24) to the internal combustion engine. Because of the increased pressure, the density of the air and thus also the mass of the air which can be inducted into the combustion chambers of the engine (10) are increased, thus increasing the power output of the engine (10).

Description

SUPERCHARGED INTERNAL COMBUSΗON ENGINE WITH ELECTRICALLY DRIVEN COMPRESSOR

TECHNICAL FIELD OF THE INVENTION

This invention relates to a method of operating an internal combustion engine, and to a forced induction system for an internal combustion engine.

BACKGROUND ART

Superchargers for internal combustion engines are designed to increase the capacity of internal combustion engines to induct air and they generally operate by providing pressurised air to the air intake system feeding the engine.

Prior art superchargers have the disadvantage that they are turned by power from the crankshaft. The power used therefore detracts from the power of the engine and although this loss may be insignificant when the engine is cruising, it may be as much as fifty horsepower or more when the engine is at full load. As a result the systems are designed to include a bypass to ensure that induction air is not fed through the supercharger at times when no boost is required, namely during idle and cruise modes.

Typical prior art turbocompressors are electrically driven such as those described in

US 5 577 385, US 5 638 796, US 5 406 797 and US 3 961 199. These electrically powered turbochargers have a number of disadvantages not the least of which is the fact that the high rotative speeds (30 000 to 100 000 rpm) required cannot be reached by electric motors with the power ratings required by turbo - or supercharges. As a consequence step-up drives may be included to attain these high rotative speeds, but these reduce the overall efficiency of the supercharger.

Furthermore, the typical power input requirements of turbocompressors at high rotative speeds are expected to be upwards of 5 kW which is beyond the range of power ready suppliable by current automotive systems for example. In addition, the pressure/flow volume characteristics of turbocompressors are prone to instabilities at reduced flows due to aerodynamic stalling of the turbine or centrifugal compressor vane elements.

It is therefore an object of this invention to provide a positive displacement compressor which is electrically driven, and has the highest pressure delivery at lowest engine speeds. The engine fuel supply (petrol or diesel) will be arranged in a way to accommodate the increased air mass flow resulting from the inlet air pressurisation.

It is a further object of the invention to provide a forced induction system which may be used in conjunction with a supercharger system. The systems may or may not be used in conjunction with an inter cooler system.

A still further object of the invention is to provide a forced induction system which can be controlled or even taken out of operation, independently of operation of the internal combustion engine. This allows the forced induction system to e controllable by and even to be capable of full integration into digital engine management systems.

THE INVENTION

In accordance with a first aspect of this invention, broadly, in applying forced induction to an internal combustion engine, there is provided the method of driving an air compressor, arranged to supply air under pressure to an inlet of the engine, by means of an electric motor. This compressor may be exclusively driven by the electric motor or it may be applied in conjunction with an engine driven mechanical drive system.

The method may include powering the electric motor from an alternator or generator drivingly connected to a crankshaft of the engine. Such driving connection may be indirect, e.g. via a camshaft of the engine, via a N-belt and pulley drive, or the like. In a prefeπed method, the alternator/generator, the electric motor, and the electric connection there between may be adapted to drive the compressor at a speed falling within a controllable speed range, i.e. not directly dependent from the engine speed. The electric motor may be a direct current type electric motor.

The internal combustion engine may be a reciprocating or rotary piston engine, e.g. a petrol or diesel engine. It may be a two stroke or a four stroke engine.

The compressor may be a positive displacement rotary compressor such as a Roots blower or twin screw type compressor. The applicant has a definite preference for a type of compressor having a high efficiency so as to minimise the power output requirements of the electric motor.

In accordance with a second aspect of the invention, there is provided for both a natural (atmospheric) and forced induction system for an internal combustion engine.

The natural induction system provides a direct path for air or fuel/air mixture to be inducted into said engine, bypassing the compressor. The natural induction channel contains a check valve or one way valve preventing reverse flow in this channel when forced induction occurs.

The forced induction system comprises a generator of electrical power such as an alternator having a driven member arranged to be driven from a source of rotary power of the internal combustion engine, and an electric motor electrically connected to the generator or alternator, which may or may not operate in conjunction with a direct mechanical drive system.

The direct mechanical drive system may operate through a free-wheeling coupling arrangement, allowing the electric motor to drive the compressor to supply air under pressure to an inlet of the internal combustion engine at low engine speed and the direct mechanical drive system to take over at higher engine speeds. The direct drive system may have a clutching arrangement (which can typically also be electrically operated), which is adapted to be turned on or off at will, as can the power supply to the electric motor of the electric drive system. Electrical control provides the option of turning off both electrically and mechanically driven boost and run the engine in the normal atmospherically aspirated mode. Alternatively, the electric power supply control (and mechanical clutching arrangement, if fitted) may be automated and/or integrated with the engine management system to optimise the power delivery profile by engaging the boost system(s) as a function of engine speed and load. The direct (engine driven) mechanical drive system is not part of this, invention, but is referred since it may co-operate in a synergistic way with the electric drive if these are used together.

The invention extends yet further to a vehicle driven by means of an internal combustion engine which is subjected to forced induction in accordance with the first aspect of the invention.

The applicant believes that the invention has a number of advantages over known forced induction systems, notably a supercharging system and a turbocharging system in specific situations. The applicant regards it as a particular advantage that the compressor is not driven at a speed which is directly dependent on the engine speed Thus, at low engine speeds, the compressor can still be driven at relatively high speeds, thus providing large boost even at low engine speeds. The applicant regards this as particularly significant as, in many applications, increased torque is required especially at low engine speeds. Thus, in contrast to superchargers, and especially turbochargers, high boost can be obtained at low engine speeds. The property of high boost at low engine speeds could make this invention an ideal complement to a supercharger or turbocharger system. The drawings appended do in fact illustrate the electrically driven induction system by way of example in combination with a direct mechanical drive system.

It is also an important advantage that the forced induction system can be controlled, even taken out of operation, independently of operation of the internal combustion engine.

This allows the forced induction system to be controllable by and even to be capable of full integration into digital engine management systems. The applicant believes that a system in accordance with this invention can be provided at competitive capital cost in relation to the gains secured since,

I . Installed on its own, its cost should be comparable to a turbo system, and

I I . if added to an existing supercharging system, it only requires the addition of an electric motor and free-wheeling coupling arrangement

In both of the cases above an initial investment would be required in adapting the digital engine management system or implementing a suitable dedicated control system.

The applicant believes that the feature of substantial boost at low engine speed will enhance the gains possible by variable cam timing at lower engine speeds by giving substantial boost at speeds from marginally above idling speed. It is also an advantage that the engine can be operated conventionally should the forced induction system fail or should it need to be taken out of operation for any reason.

The applicant is aware that the induction of air or mass liυw rate of air increases with increased engine speeds. Furthermore, it is a characteristic of a positive displacement rotary compressor driven at essentially constant speed, that the pressure at which air is delivered is generally inversely proportional to the mass flow rate. Thus at lower engine speeds and thus at lower mass flow rates, the forced induction systems can provide air at higher pressures which enhances the torque at lower engine speeds. Furthermore, the applicant regards it a useful self-regulatory feature of electrically-only driven boost system that, at high engine speeds and high air mass flow rates, the pressure at which the air is provided decreases thus preventing over stressing of the engine at high engine speeds. Furthermore, the consumption of electrical power will reduce at higher engine speeds since the positive displacement compressor will require less driving power at the lower pressure delivery. This feature is expected to result in increased boost and increased torque at low engine speeds thus simulating a larger capacity engine at low engine speeds, exactly where higher torque is required. This feature is expected to be particularly advantageous in respect of diesel engines, even more so in diesel engines for agricultural and construction equipment where high start-up torque and low speed torque properties are required for slow moving, heavily loaded equipment with frequent starts and stops. It is an important potential advantage that the advantageous or optimum range in respect of engine speed of a system in accordance with the invention lies generally below the optimum performance range in terms of engine 5 speed of conventional turbocharging or supercharging systems. Thus, apart from the co-driving arrangement on a supercharging system as referred before, it is envisaged that a forced induction system in accordance with the invention can also be used in conjunction with or superimposed on a turbocharging system.

By way of development, although not shown in the drawings, it is envisaged that 10 over pressure relief valves will be provided. Furthermore, as illustrated, a bypass conduit bypassing the compressor is provided if the compressor is taken out of operation.

Further by way of development, an engine management system may be provided adapted to manage engine operation in accordance with the output of the forced induction system. Instead, an existing engine management system can be adapted to make provision ι c for forced induction in accordance with the invention.

DESCRIPTION OF EMBODIMENT

The invention is now described by way of example with reference to the accompanying diagrammatic drawing showing, in three dimensional view, an internal combustion engine subjected to forced induction in accordance with the invention.

20 With reference to the drawings, an internal combustion engine is generally indicated by reference numeral 10. The internal combustion engine has an alternator generally indicated by reference numeral 12. As will later be explained, the alternator 12 may be a dedicated alternator for purposes of the invention, or it may be a heavy duty or upgraded alternator to enable it to fulfill its conventional requirements and be operated in accordance

2 with the invention The alternator 12 is driven from a main pulley 14 mounted at a fore-end of a crank shaft of the engine 10, via a V-belt 16. The alternator 12 generates electrical power conducted by means of conductors 18.1. Electrical power supplement and stabilisation is provided by the electrical storage battery 19 by means of interfacing conductors 18.2 This electrical storage battery may be the conventional vehicle battery or an additional battery dedicated to support any sporadic power requirements of this system. The battery can in either case be recharged by the normal regulated supply system of the vehicle.

The internal combustion engine has an air-cleaner 22, ..o which is fitted inlet ducts

20.1 and 20.2. Duct 20.1 is directly linked to the air junction box 23. An air tight check valve is fitted either in duct 20.1 or at its entry into the junction box 23 to allow only air flow in the direction of the engine and not back towards the air cleaner. Duct 20.1 inducts atmospheric air when the compressor is not running or when high speed engine demand exceeds compressor capacity. Duct 20.2 links the air cleaner 22 with the compressor 26 inlet. Specific design constraints may demand that separate air cleaners be placed on ducts 20.1 and 20.2. Duct 21 links the compressor pressure outlet with the air junction box 23. From the air junction box 23, duct 24 leads to an inlet system of the internal combustion engine 10.

In accordance with the invention, there is provided a compressor 26, conveniently immediately down-stream of the air-cleaner 22, arranged to induct air received via the inlet

20.2 and the air-cleaner 22 and to deliver air under pressure via the ducting 21.

The compressor 26 is driven by means of an electric motor 28 through a one-way coupling 17.1. For convenience it is illustrated to be integrated with the electric clutch 17.2 but may be physically separate. The electric clutch input drive member is directly or indirectly driven from the crank pulley by the flat (or "V") belt 15. The electric motor 28 is electrically connected to the alternator 12 and vehicle battery or special storage battery 19 by means of the conductors 18.1, 18.2 and 18.3.

The electric motor 28 is conveniently of short axial length and it is mounted suitably to drive the compressor 26. A rotor of the electric motor 28 and a rotor of trie compressor 26 may be mounted on a common axis. Instead, if desired, there may be an intermediate transmission system between the electric motor 28 and compressor 26. Such transmission system, if desired may have a speed change device such as to increase or decrease the rotative driving speed of the electric motor when transmitted to the compressor 26 if the gain in speed outweighs the disadvantage of some power loss in the drive.

The compressor 26, shown in the drawings, is a positive displacement rotary compressor. It may also be a vane compressor or the like. It may even be a reciprocating compressor, although a rotary compressor, especially a high efficiency type positive displacement type rotary compressor such as a Roots blower or twin screw compressor is preferred by the applicant.

In use, the alternator 12, driven from the crankshaft of the internal combustion engine 10, generates power, supplemented by the battery if required, which is electrically conducted to the electric motor 28 which, in turn, drives the compressor 26. The compressor 26 draws air via the inlet 20.2 and air-cleaner 22, compresses the air and supplies air under pressure via the ducting 21 to the air junction box 23 and ducting 24 to the internal combustion engine. Because of the increased pressure, the density of the air and thus also the mass of the air which can be inducted into the combustion chambers of the engine 10 are increased, thus increasing the power output of the engine 10.

Claims

1. A method of applying forced induction to an internal combustion engine characterised in that there is provided the method of driving an air compressor, arranged to supply air under pressure to an inlet of the engine, by means of an electric motor.

2. A method according to claim 1 characterised in that the compressor is driven by the electric motor in conjunction with an engine driven mechanical drive system.

3. A method according to claim 1 characterised in that the electric motor is powered from an alternator or generator drivingly connected to a crankshaft of the engine.

A method according to claim 3 characterised in that the driving connector is indirect.

5. A method according to claim 4 characterised in that the alternator or generator, the electric motor and the connection therebetween are adapted to drive the compressor at a speed falling within a controllable speed range.

6. A method according to any of the above claims characterised in that the electric motor is a direct current type electric motor.

7. A method according to claim 1 characterised in that the compressor is a positive displacement rotary compressor for example a Roots blower or twin screw type compressor.

8. A method according to claim 1 characterised in that it is adapted to provide both a natural (atmospheric) and a forced induction system operable separately or together.

9. A forced air induction system according to the method of claim 8 characterised in that the natural induction system provides a direct path for air or fuel/air mixture to be inducted into said engine, bypassing the compressor.

10. A method according to claim 9 characterised in that Ihe natural induction system includes a check valve or one way valve preventing reverse flow in this channel when forced induction occurs.

11. A method according to any of the above claims characterised in that it comprises a generator of electrical power, for example an alternator, the alternator having a driven member arranged to be driven from a source of rotary power of the internal combustion engine, and an electric motor electrically connected to the generator or alternator, which may or may not operate in conjunction with a direct mechanical drive system.

12. A method according to claim 11 characterised in that the mechanical drive system operates through a free-wheeling coupling arrangement, allowing the electric motor to drive the compressor to supply air under pressure to an inlet of the internal combustion engine at low engine speed and the direct mechanical drive system to take over at higher engine speeds, the free-wheeling coupling being adapted to disconnect the electric: motor rotatively under these conditions.

13. A method according to claim 12 characterised in that the direct drive system has a clutching arrangement (which can typically also be electrically operated), which is adapted to be turned on or off, the power supply to the electric motor of the electric drive system also being adapted to be switch on or off.

14. A method according to claim 13 characterised in that the clutching arrangement is electrically operated facilitating the turning off of both the electrically and mechanically driven boost, permitting the engine to run in the normal atmospherically aspirated mode.

15. A method according to claim 13 characterised in that the electrical power supply control and mechanical clutching arrangement, if fitted are automated and/or integrated with the engine management system to optimise the power delivery profile by engaging the boost system(s) as a function of engine speed and load.