EP3423691A1

EP3423691A1 - Automotive powertrain

Info

Publication number: EP3423691A1
Application number: EP17709754.0A
Authority: EP
Inventors: Hao Xu; Bryn Geoffrey Roddick Richards
Original assignee: Aeristech Ltd
Current assignee: Aeristech Ltd
Priority date: 2016-03-01
Filing date: 2017-03-01
Publication date: 2019-01-09
Also published as: CN109072766A; GB201603549D0; WO2017149303A1

Abstract

An automotive powertrain (100) for driving an automobile is disclosed. In particular, an automotive powertrain (100) comprising: an engine (110) with a crankshaft (112); and an electric supercharger (120) for boosting the output torque of the engine (110). The supercharger (120) comprises: a compressor (122) for pressurizing air into an intake (114) of the engine (110); and an electric motor (124) for powering the compressor (122). In particular, the electric supercharger (120) is mechanically decoupled from the engine (110) and the electric supercharger (120) provides the sole system for boosting output of the engine (110).

Description

DESCRIPTION

AUTOMOTIVE POWERTRAIN

Field

The present invention relates to an automotive powertrain comprising an electric supercharger. In particular, an automotive powertrain for driving an automobile comprising an electric supercharger and an electric supercharger that provides the sole system for boosting output of the engine is described.

Background

New engine development programs in the passenger car industry are heavily directed by the need to reduce carbon dioxide (C02) emissions, with other engine industry sectors (vehicle and non-vehicle) either driven by similar legislation, driven by fuel economy which correlates to C02 emissions, or under threat of being subjected to similar legislation in the near future. So far, many technical approaches have been adopted to reduce C02 emissions and improve fuel economy. Engine downsizing is one of the most effective measures being employed. Engine power boosting technologies are essential for the development of downsizing engine platforms. This technology is a forced air charging system for boosting engine air intake into cylinders. The most widely used charging system is a turbocharger, which utilizing the waste gas to drive a turbine, and then through a co-axially fitted air compressor. A significant increase in the number of turbocharged vehicles in the market over the recent years is a demonstration of the popularity of the use of downsized engines in the passenger market.

One of the drawbacks of using a turbocharger is its lack of response at low engine speeds. This has limited the degree of engine downsizing that can be achieved. The selection of turbocharger has often been a compromise of low-speed response and high-speed performance. This compromise limits turbocharger efficiency (see, for example, WO2014140529). Different types of charging strategies have since then been developed and introduced, which range from bi/twin turbos, two staged charger system arrangements to, more recently, variable geometry turbochargers (VGT), variable nozzle turbochargers (VNT) and Two-scroll turbochargers. However, these arrangements are generally complex and costly, and only partially mitigate the problem. The fundamental problem of low-speed response trading off with highspeed performance derives from the turbocharger's "turbomachine" characteristic of gas flow being proportional to speed squared, while gas flow through a piston or Wankel engine is proportional to speed (no square). Thus, turbochargers can never be optimized to boost an engine across a wide range of gas flow rates, instead only, in theory, at one "match point". The selection of the match point and the easing of the inherent compromise away from the match point is collectively referred to as the problem of "turbo matching".

A study of recently developed new 'Green Cars' shows that the majority of them are still short from meeting the legislative requirements of a fleet average fuel consumption of 95 g/km by 2021 in EU countries. (There are different emission regulations in different regions cross the world). Since the non-compliance of original equipment manufacturers (OEMs) to the regulation attracts hefty financial penalties, it is clear that there is a significant pressure on all the OEMs to improve the overall fleet fuel consumption of their products. Results from the study also show that the trend in improvement in C02 of smaller engines is not keeping pace with the trend in the reduction of C02 for larger engines. This is believed to be associated with the more significant impact of turbo-lag upon the drivability of vehicles fitted with small engines.

Another forced induction system is the electric supercharger. Like conventional superchargers, the electric supercharger comprises a compressor for pressurizing air into an intake of an engine. However, electric superchargers can be mechanically decoupled from the engine and utilize an electric motor to drive the compressor. Such systems have been used, until now, in tandem and only with an associated turbocharger. This is because the supercharger provides a torque boost to the engine at low speed, whilst the turbocharger is spooling up to speed, with the supercharger then being bypassed at higher speeds. Whilst electric superchargers are known, such devices have not been used solely to boost the output of the engine due to an inability to operate at a high enough steady state rating.

Additionally, the torque response of an electric supercharger has been used to supplement and add to the torque response map of a turbocharger. Turbochargers provide a torque boost at high engine speeds due to the requirement for the engine to generate exhaust gas at a sufficient speed to spool the turbine. This dual boost device requirement adds complexity and cost.

There is a need for new technologies to address or ameliorate the above issues.

Summary

According to a first aspect of the present invention, there is provided an automotive powertrain for driving an automobile, said powertrain comprising: an engine with a crankshaft; and an electric supercharger for boosting the output torque of the engine, said supercharger comprising: a compressor for pressurizing air into an intake of the engine; and an electric motor for powering the compressor; wherein the electric supercharger is mechanically decoupled from the engine and wherein the electric supercharger provides the sole system for boosting output of the engine.

Unlike traditional, known, electric supercharger systems, the present invention sacrifices the benefits associated with a twin turbo system by only using an electric supercharger to solely boost the output of the engine. By mechanically decoupled, it is understood to mean that the traditional mechanical link between the engine and the supercharger is severed such that the rotational speed of the compressor of the supercharger is independent of the rotational speed of the crankshaft of the engine. So the supercharger is not mechanically driven by the crankshaft.

Advantages of using an electric supercharger to boost an engine as compared to no boost device being used include:

1. The opportunity to increase the specific power of the engine and thus downsize the engine to minimize friction losses and (in the case of gasoline fueled engines) reduce throttling losses leading to improved fuel economy; and

2. The above point 1 also leads to lower C02 emissions

3. The opportunity to enhance overall engine power more cheaply or more compactly than a larger engine or without investment in the development of a larger engine (allowing one engine to serve in multiple market segments with only minor changes to its boosting configuration)

Some advantages of using an electric supercharger as the sole charging device on an engine as compared to using a turbocharger are:

1. Achievement of higher peak torque at low engine speed, where a conventional turbocharger would typically not provide efficient recovery of exhaust gas energy and therefore be unsuited to provide high levels of boost (particularly useful in city driving where peak power is less important than engine responsiveness at low speeds)

2. Simpler packaging and especially packaging further back towards the passenger cab in front wheel drive vehicles where the exhaust gas is generally at the back of a transverse-mounted engine (a particularly common layout for smaller vehicles and smaller engines)

3. Enhanced altitude independence by the use of software adjustments to the compressor speed

4. A cooler engine bay, allowing a more compact layout and avoiding expensive materials

5. Simpler compliance with pedestrian impact legislation because of point 2 and because of avoiding the use of a "crossover pipe" to carry compressed air from the turbocharger mounted at the back of the engine to the inlet manifold mounted at the front

6. Enhanced product differentiation through software control of torque and torque response, especially at low engine speeds

7. Quicker warm-up of any catalytic converter by deletion of the turbine, resulting in lower emissions of nitrogen oxide (NOX), carbon monoxide (CO), and particulates, especially relevant to city-driven vehicles with start-stop duty cycles

8. The opportunity to avoid rotational speeds above 200000 RPM in the boost device, which arise particularly in small engine turbocharged applications in order that the turbine can be designed to function at very low gas flow rates

Similarly, some advantages of using an electric supercharger as the sole boosting device on an engine as compared to a mechanically driven supercharger are: 1. Power for the electric supercharger can be drawn at times when the engine is not subjected to peak load, and stored in a battery, capacitor, supercapacitor, or other storage device to be used in peak load events, as compared to a mechanical supercharger that generally cannot incorporate energy storage.

2. Power for the electric supercharger can be drawn at times when the engine is not working in efficient brake specific fuel consumption (BSFC) regions. The power top-up can be designed to take place at the high engine efficiency region, so that the overall fuel consumption can be reduced.

3. The packaging arrangement of an electric supercharger can be more flexible, not needing a separate connection to the engine's crankshaft and not requiring a mounting position in the same plane as the crankshaft pulley.

4. The electric supercharger can be designed to operate at a speed independent of engine speed, not being mechanically connected to the engine. This allows the use of turbomachine compressors, which require rotational speeds far in excess of engine speeds (eg above 50000 RPM). Turbomachine compressors are generally more compact, more efficient, and cheaper to manufacture than other types of compressors. Any of these advantages over conventional roots or screw -type mechanical compressors provides an advantage for electrically driven turbomachine compressors as superchargers, especially in small engine applications.

Additionally, some advantages of using an electric supercharger as the sole boosting device on an engine as compared to a multi-stage boosted engine (with multiple boost devices) will generally include a combination of the advantages described above that will be understood by experts, plus particularly:

1. A sole boosting device is generally less expensive than a multi-stage boosting system.

2. A multi-stage boosting device is generally difficult to package, especially in smaller vehicles with smaller engines.

The powertrain may further comprise an electric battery primarily associated with the automobile and wherein the electric motor is powered at least partially by the electric battery. By utilizing the existing electric battery of an automobile to power the electric motor a separate power source is not required.

The powertrain may further comprise an electrical generation system for supplying electrical energy to the or an electrical battery, said system comprising: a braking energy recovery system for converting thermal energy from a drive train of the automobile into electrical energy and/or an alternator for generating electrical energy from the crankshaft of the engine; wherein the electric motor is electrically powered directly or indirectly by the electrical generation system. The use of such electrical generation systems assist in removing alternative power sources for the electric motor, such as a turbocharger.

In embodiments, the electric motor may be solely powered by the electric battery. The electric supercharger may supplies an enthalpy to the air at the intake of the engine that is greater than the enthalpy lost at an outlet of the engine. The powertrain may further comprises a catalytic converter located in an exhaust outlet of the engine, upstream of any thermal drawoff devices, such as a turbine of a turbocharger or other exhaust energy recovery device.

For example, by timing intake and outtake valves an imbalance between the intake and the exhaust can be manifested. This results in the exhaust gas from the engine warming up any catalytic converter quicker, leading to the advantages described above.

The electric supercharger may provide continuous operation during a steady-state load requirement of the engine.

The electric motor may comprise a permanent magnet motor. The electric supercharger may further comprise a controller configured to supply a substantially square wave current signal to the electric motor.

In embodiments, the electric supercharger may be at least partially watercooled. According to a second aspect of the present invention, there is provided an electric supercharger for boosting the output torque of an automotive powertrain, said powertrain comprising an engine and a crankshaft for driving an automobile, wherein the electric supercharger comprises: a compressor for pressurizing air into an intake of the engine; and an electric motor for powering the compressor wherein the supercharger is mechanically decoupled from the engine and the crankshaft and provides the sole system for boosting output of the engine.

It can be appreciated that the associated advantages described in relation to the first aspect may be equally applicable to the second aspect.

In embodiments, the electric motor may comprise a permanent magnet motor. The supercharger may further comprise a controller configured to supply a substantially square wave current signal to the electric motor.

The electric supercharger may provide continuous operation during a steady-state load requirement of the engine. Such operation allows the supercharger to meet the power requirement of the engine. It can be appreciated that periods of over-rating, followed by periods of rest may be used, however such periods of rest are at a higher rating than for conventional steady state forced induction systems.

The electric motor may further comprise a rotor coupled to the compressor and a stator to drive the rotor, wherein the rotor acts as a centrifugal pump drawing cooling air into the supercharger. The rotor may comprise a central bore and a plurality of radial holes providing an air pathway such that rotation of the rotor draws the cooling air into the bore. The cooling air may also be drawn into the supercharger from an inlet, over electrical components of the or a controller and into the rotor by rotation of the rotor. This cooling pathway provides an efficient air cooling and may be particularly useful for passively cooled components, such as electrical filters.

A water cooling system may be used for reducing thermal energy heat loss from the supercharger. The water cooling system is configured to cool the electric motor and electrical components of the or a controller of the electric motor. The water cooling system may comprise a plurality of cavities surrounding components of the electric supercharger. The water cooling system may comprise one or more watercooling pipes configured to spray water into the cavities and/or onto the components. The water cooling system may allow the or any actively cooled electrical components of the or a controller to be operated outside of their rated conditions. The watercooling system may induce turbulent flow of coolant around the electrical components of the controller.

More general advantages of the present invention are described below.

A purpose of the present invention is to alleviate the problem of turbo matching by providing all of an engine's required inlet air through an electrically driven turbomachine compressor, whereby the electric motor driving the turbomachine compressor is controlled in such a way that target (ideal, as calculated by an onboard computer typically called an ECU - Electronic Control Unit) engine inlet air pressure is achieved by a motor speed setpoint and the aerodynamic properties of the compressor and engine inlet manifold and engine volumetric flow rate.

Electrified superchargers, known as electric superchargers or eSuperchargers, are currently being developed. They have the advantage of being able to be put in action whenever needed. Aeristech Ltd has also developed a high energy density high speed motor, and compact design of an electric supercharger which is so powerful that it is feasible to provide the air requirement of a small, nevertheless highly power rated, engine, at the same time is compact enough for fitting under the bonnet of a car. This makes it then feasible to use an eSupercharger as the sole charging device in support of a small displacement engine, with a torque higher than what can be achieved by the existing turbocharged and/or the torque being achieved at lower engine rotational speeds. In other words, the electric supercharger supports a better tradeoff between the engine's performance at high speed and responsiveness at low speed, whereby the relative advantage will be most keenly felt in small-engine applications as an improvement in low-speed responsiveness (where conventional turbochargers perform especially poorly on small engines). This will then facilitate a further increase in the engine efficiency and reduction in the engine size, which both can contribute to the reduction of C02 emissions and fuel consumption. This is particularly suited to smaller engine applications because (1) turbochargers are particularly poorly suited to smaller engines, having a characteristic that necessitates extremely high rotating speeds in the turbocharger when seeking to achieve adequate exhaust energy recovery at very low flow rates (at low engine speeds in small engine applications) and (2) electric superchargers, although constantly developing, tend to be limited by their size, cost, and efficiency in such a manner that smaller and less powerful electric superchargers are more technically and commercially feasible than larger electric superchargers, and this corresponds to applications with smaller engines and lower air flow requirements. As a corollary to point 2 above, the electric power available on a vehicle to support electric supercharging is driven by economics as well as the stage of technical development, and smaller engine vehicles tend to have smaller chassis and lower electrical loads than larger engine vehicles, indicating that vehicle electrical components (alternators and batteries) from larger vehicles can be sufficient to drive electric superchargers with minimal modifications after those large-vehicle components are transferred to a smaller engine applications with typically lower electrical demand (allowing headroom for the electric supercharger to draw its power). The primary target application of small cars is generally commuting trips in and around urban regions, with gearing usually selected for low-speed responsiveness. A turbo can hardly work efficiently in this circumstance. It is thus likely that, even without the use of a turbine for energy recovery, the electric supercharger will operate more efficiently than a turbocharged vehicle.

This invention particularly specifies electrically driven superchargers for small engine applications, often termed mechanically decoupled electric superchargers. By comparison to mechanically driven superchargers deriving their power from a physical connection to the engine's crankshaft, electrically driven superchargers can cost- effectively be designed to operate at higher rotational speeds than superchargers that are physically connected to the engine's crankshaft. This allows the use of low-cost, efficient turbomachine compressors in preference to positive displacement blowers and compressors such as roots blowers and screw compressors. The present invention therefore refers specifically to compressors which are more compact and lower in cost than mechanically driven compressors. The present invention, by referring specifically to electric superchargers, also incorporates the benefit of its power source being not instantaneously limited by available crankshaft power. In small engine applications with less inertia and lower idling torque, this feature of the present invention may be particularly significant because it means that the engine power is not reduced during critical transient events by the need to supply power instantaneously to the supercharger. Rather, the supercharger's power can be derived from the vehicle's battery and electrical architecture, having only a requirement for an average net draw of power from the engine crankshaft via the electrical alternator or generator to provide power for the electric supercharger over the period of driving. This can be structured in the operational conditions in that the engine is more efficient in power generation, and thus with an improved fuel efficiency. For example, charging can occur in conditions when adding torque load to the engine allows de-throttling and pushing the engine into a more thermally efficient operating condition.

Small engines are typically engines having displacement of 1.41 (1400cc) or less, such as 1.3, 1.2, 1.1 , 1 or less than 11.

It can be appreciated that, although certain examples and embodiments described above have been primarily described with respect to a single aspect, the features described are also applicable to the other aspects defined herein.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter. The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The Figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings.

Brief description of Drawings

Embodiments will be described, by way of example only, with reference to the drawings, in which

figure 1 illustrates a schematic diagram of a powertrain according to aspects of the present invention; figure 2 illustrates an electric supercharger forming part of the powertrain of figure 1 , with the rotor and compressor of the supercharger hidden for clarity;

figure 3 illustrates a longitudinal cross-sectional view of figure 2;

figure 4 illustrates a flat view of figure 3;

figure 5 illustrates a transverse cross-sectional view of figure 3, with the rotor shown;

figure 6a shows electrical components for controlling the electric supercharger shown in figures 2 to 5;

figure 6b shows further electrical components connected to the components of figure 6a; and

figure 7 shows a schematic representation of the torque-engine speed response of a naturally aspirated engine and an engine boosted by the present drivetrain shown in figure 1. It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments.

Detailed description of embodiments

Figure 1 shows a schematically overview of a powertrain 100 embodying the present invention. In particular, the powertrain 100 comprises an engine 1 10, shown in this instance as a 3 cylinder engine, although any suitable engine could be utilised. However, this invention is particularly suited to lower displacement engines of 1.41 and lower and is also tailored to automobile engines.

The powertrain 100 further comprises a crankshaft 1 12 coupled to the engine and configured to be driven by the engine 1 10 in a conventional manner. An engine air intake or input 114 to supply intake air to the engine 1 10 is provided and a corresponding engine exhaust 1 16 is used to expel exhaust gases and vapour.

The drivetrain 100 features an electric supercharger 120 coupled to the engine input 114. The electric supercharger is mechanically decoupled from the engine as thus is not mechanically directly driven by the crankshaft as per conventional superchargers. The electric supercharger 120 comprises a compressor 122 and a supercharger powertrain 124, which will be described in detail later. A supercharger bypass valve 130 allows the air intake to bypass the electric supercharger 120 if, for example, a standard aspiration torque response is required. The bypass valve 130 is coupled to the air intake line 114 via bypass line 132.

Also on the air intake line 114 is an intercooler 140, which acts to cool the air entering the engine after it is heated due to the action of the supercharger compressor 122.

Also defined as part of the powertrain for the purposes of this invention is a battery 150. The battery is typically an electric battery that forms part of the main automobile, meaning that it is primarily associated with the automobile.

The battery 150 has an electrical output 152 that provides power to the supercharger 120 via a supercharger power line 152. The battery may be replenished from an alternator or generator 160 or via a kinetic or braking energy recovery system (often referred to as a KERS) 156. Corresponding power lines 154, 158 electrically connect the electrical power recovery systems.

The final core component, considered part of the powerline in this disclosure, is a catalytic converter 170. The catalytic converter is an emission control device and is generally tailored to either a petrol or diesel fuelled engine. It can be appreciated that the described powertrain 100 works with either fuelled engine type.

In terms of performance, if the power output of the engine can be normalised to a value of 100 under un-boosted conditions, the alternator may be capable of recovering 5 units of this power and provide this electrical power to the battery 150. The KERS may recovery a further 5 units. The battery 150 may supply 3 of these units to the electrical supercharger 120. After losses, around 2 of these units may be used to pressurise the incident air into the engine 1 12, however this pressurisation results in an increase in the output of the engine by 20 units. This performance gain may then be factored in to the engine choice, allowing for a smaller, more fuel- efficient engine with lower emissions to be used to generate the same resultant power.

Figure 2 shows a perspective view of the electric supercharger 120 of figure 1 , which has been re-designated as 200 for ease. The compressor 122 and a rotor have been omitted for easier viewing of the casing. Broadly, the supercharger 200 comprises a housing having a faceplate 210 to which the compressor is mounted. Electrical components 220, 222, 224, namely capacitor banks 220, 222 and an inverter bank 224, which form part of a controller are also shown. Watercooling pipes 230, 232 are arranged on the side of the housing and will be discussed in greater detail below.

Figure 3 shows a partial longitudinal cross-section of figure 2. Figure 4 shows a complimentary side view. In these figures further electrical components, an inductor bank 226 and a DC converter formed of IGBT switches 228 are shown. Further watercooling pipes 234 are also shown.

Other components of the supercharger, namely the stator 260 of an electric motor used to rotate the compressor of the supercharger 200 is shown. The stator is arranged around a rotor as will be described in further detail below.

In order to aid cooling of the electrical components 222, 226, 228 and the stator 260, cavities 240, 242, 244, 246, 248 are provided within the housing of the supercharger 200 in which coolant fluid, such as a water/glycol 50:50 mix is provided. The coolant fluid is supplied by the watercooling system 230 - 234. The coolant fluid may be supplied by nozzles or holes within the watercooling pipes such that the fluid is sprayed onto the electrical components and/or the stator. The coolant fluid may be sprayed in a manner to induce turbulent flow.

Together the cavities 240-248 provide a watercooling jacket around the supercharger. Additionally, as well as watercooling the stator 260, by watercooling the electrical components, particularly the IGBT 228 and the inductors 226, these components may be overrated beyond their rated performance. This aids in increasing the output of the supercharger and assists it in providing sufficient torque to solely boost the output of the engine in a steady state, continuous operation without the need for an assisting turbocharger. Figure 5 shows a transverse cross-sectional view 300 through the supercharger 200. For ease, the housing and superfluous components have been omitted, whilst the rotor has been added.

The supercharger 200 comprises a rotor 310 having a rotor cavity 312. The rotor 310 is configured to have a series of radial holes. Accordingly, as the rotor 310 rotates, air is drawn into the cavity 312 via the holes, cooling the rotor. The air inlet path is over one or more of the electronic components, such that additional active cooling of these components occurs. In this manner the rotor 310 acts as a centrifugal pump drawing air into the rotor cavity 312 over the electrical components as the rotor rotates.

Arranged around the rotor are poles 314 that are permanent magnets such as NdFeB neodymium magnets (Nd₂Fe₁₄B) or SeCo magnet. The poles are separated by pole spacing 315. It can be appreciated that the pole configuration shown is higher than for a conventional rotor - the pole spacing is small such that the poles 314 form a semi- complete magnetic shell around the rotor. Typically greater than 75% of the rotor is covered by the poles. This rotor structure lends itself to be driven by a square wave current pulse applied to motor windings arranged and wound between the teeth 340 of the stator 260. A suitable controller capable of providing such a current pulse is described in GB2482762 and related family members. Additionally, a controller that can control the amplitude of current supplied to the windings independently of the commutation of the current may be used. Surrounding the poles is a rotor sleeve 320, typically carbon fibre, to hold the poles 314 in place. An air gap 330 then separates the rotor 310 from the stator teeth 340.

The cavity or jacket 240 is shown surrounding the stator 260. Inlets 350 are also shown where coolant can be sprayed onto the rotor to form the jacket 240. It can be appreciated that the configuration of the jacket 240 allows a greater number of components to be cooled. Even components not directly cooled, such as filters may be passively cooled by the jacket 240. Figures 6a and 6b show the electronic components of the supercharger in more detail. In particular, figure 6a shows a DC converter 400, whilst figure 6b shows a inverter 450. A DC input 410, 412 typically at 48V is fed through to outputs 420, 422. A capacitor bank 430 and inverter bank 440 is used to convert the DC input. The inverter bank is coupled to an inductor 232 and comprises a number of IGBT switches 441-444.

A hall effect current sensor 448 is coupled to the inverter bank 440 via an inductor 446 and is used to determine the relative position of the rotor/stator using the generated back-emf signal to determine commutation timings of the signal.

The output 420, 422 is fed into the inverter 450 at inputs 460, 462. A further capacitor bank 470 and IGBT inverter bank 480 is then used with a controller 482 to provide a 3-phase current supply 490, 492, 494.

Figure 7 shows a comparison of the torque to engine speed response between a naturally aspirated engine (dashed line) and the current configuration. The graph shows a steady state response. Such a response shown by the current configuration may be less than ideal for some engine uses, such as highway cruising, but may be ideally suited to urban driving where high torque response at medium engine speed is desirable.

As can be seen from the graph, there is shown a "Tip-in" event (there is an increase in the value of the target torque output of the engine). In particular, the current configuration provides a larger torque boost at lower engine speeds, but supplies maximum torque at a medium engine speed.

This configuration allows the controller of the electric motor to increase the target speed set-point of the electric supercharger. While maintaining limits on currents inline with maximum electric supercharger motor current and maximum permissible vehicle current draw, the controller can increase current delivered to the electric supercharger motor and thereby motor torque output. This higher motor torque brings about a change in the electric supercharger's speed over time. Accordingly, increased electric supercharger speed brings about, according to the electric supercharger's compressor map, an increase in the pressure at the supercharger's outlet and the engine's inlet manifold. This higher inlet manifold pressure in turn corresponds to higher density and allows the engine to consume a greater mass of air.

(Gasoline engines) The engine's controller then detects the increased consumption of air, limits it if required by the action of the throttle valve, and then responds by injecting a greater mass of fuel to increase the engine's torque output and thereby satisfy the "tip-in" event.

(Diesel engines) The enhanced air flow can then allow more complete combustion of the Diesel fuel and thus more engine torque output, in-line with the "tip-in" event. In most cases, fuel flow is limited by a controller that will detect the enhanced air flow before allowing the injection of additional fuel to achieve a consistent target quality of combustion, analogous to gasoline engine control.

Following the tip-in event, in most cases the engine's speed will increase in response to the increased torque output, causing an increase in the rate of air consumption. In response to the increased air flow to the engine, the electric supercharger's controller will adjust the supercharger's target speed as necessary to maintain target inlet manifold pressure according to the aerodynamic characteristics of the supercharger's compressor map.

In many cases, the engine's torque target will then be reduced by the driver to an un- boosted level (pressure ratio = 1) or a lower boosted level. In some cases, the same or nearly the same pressure ratio will be maintained from step 4 above.

Regardless of the expectation identified above, the electric supercharger is required to be capable of maintaining a high level of outlet pressure in steady-state to allow normal operation of the engine as typically expected. This requirement is fulfilled by using an electric motor capable of continuous torque delivery at high-speed. This is taken to involve using a high-speed motor controller with reduced switching frequency and switching losses (see, for example, GB2482762 and related family members). The ability to maintain continuous manifold pressure and engine torque output is a beneficial feature of the present design. This is in-line with mechanically powered superchargers but not in-line with other electric superchargers which overheat over time and are not capable of continuous operation at full load. Non-continuous electric superchargers are not capable of meeting the requirements of this application which include a legislative requirement (in Europe) to maintain rated engine torque output at any speed for at least 90 seconds and a broader requirement (worldwide) among typical engine users that all engine behavior is available in steady-state and repeatable across multiple successive events without any cool-down period.

The following clauses, which are not claims, broadly define the invention.

1. An electric supercharger as the sole engine boosting device

2. As above in small engine applications (e.g. less than 1.4L displacement capacity) where particular benefits such as torque at low engine speed are especially relevant

3. As above taking particular advantage of packaging flexibility

4. As above taking particular advantage of speed independence from the engine (no mechanical connection) allowing the use of a turbomachine compressor

5. As above taking particular advantage of the introduction of energy storage to avoid loading the engine's crankshaft at the time that levels of power output are required from the engine.

6. As above taking particular advantage of the de-throttling benefit in a gasoline engine application

7. As above taking particular advantage of rapid warm-up of the catalytic converter by deletion of the turbocharger turbine

From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of electric supercharger and forced induction systems in general, and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

For the sake of completeness it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims. Additionally, it can be appreciated that the structure of the claims, including the ordering of claim dependencies, is not necessarily intended to limit any dependent feature to all the features in a claim from which it depends if it is apparent that said features could be utilised independently of each other.

Claims

1. An automotive powertrain for driving an automobile, said powertrain comprising:

an engine with a crankshaft; and

an electric supercharger for boosting the output torque of the engine, said supercharger comprising:

a compressor for pressurizing air into an intake of the engine; and an electric motor for powering the compressor;

wherein the electric supercharger is mechanically decoupled from the engine and wherein the electric supercharger provides the sole system for boosting output of the engine.

2. The powertrain of claim 1 , wherein the powertrain further comprises an electric battery primarily associated with the automobile and wherein the electric motor is powered at least partially by the electric battery.

3. The powertrain of claim 1 or claim 2, wherein the powertrain further comprises an electrical generation system for supplying electrical energy to the or an electrical battery, said system comprising:

a braking energy recovery system for converting thermal energy from a drive train of the automobile into electrical energy and/or

an alternator for generating electrical energy from the crankshaft of the engine; wherein the electric motor is electrically powered directly or indirectly by the electrical generation system.

4. The powertrain of claim 2 or claim 3, wherein the electric motor is solely powered by the electric battery.

5. The powertrain of any preceding claim, wherein the electric supercharger supplies an enthalpy to the air at the intake of the engine that is greater than the enthalpy lost at an outlet of the engine.

6. The powertrain of any preceding claim 1 , wherein the powertrain further comprises a catalytic converter located in an exhaust outlet of the engine, upstream of any thermal drawoff devices.

7. The powertrain of any preceding claim, wherein the electric supercharger provides continuous operation during a steady-state load requirement of the engine.

8. The powertrain of any preceding claim, wherein the electric motor comprises a permanent magnet motor.

9. The powertrain of claim 8, wherein the electric supercharger further comprises a controller configured to supply a substantially square wave current signal to the electric motor.

10. The powertrain of any preceding claim, wherein the electric supercharger is at least partially watercooled.

11. An electric supercharger for boosting the output torque of an automotive powertrain, said powertrain comprising an engine and a crankshaft for driving an automobile, wherein the electric supercharger comprises:

a compressor for pressurizing air into an intake of the engine; and

an electric motor for powering the compressor

wherein the supercharger is mechanically decoupled from the engine and the crankshaft and provides the sole system for boosting output of the engine.

12. The supercharger of claim 1 1 , wherein the electric motor comprises a permanent magnet motor.

13. The supercharger of claim 11 or claim 12, wherein the supercharger further comprises a controller configured to supply a substantially square wave current signal to the electric motor.

14. The supercharger of any one of claims 11 to 13, wherein the electric supercharger provides continuous operation during a steady-state load requirement of the engine.

15. The supercharger of any one of claims 11 to 14, wherein the electric motor further comprises a rotor coupled to the compressor and a stator to drive the rotor, wherein the rotor acts as a centrifugal pump drawing cooling air into the supercharger.

16. The supercharger of claim 15 wherein the rotor comprises a central bore and a plurality of radial holes providing an air pathway such that rotation of the rotor draws the cooling air into the bore.

17. The supercharger of claim 15 or claim 16, wherein the cooling air is drawn into the supercharger from an inlet, over electrical components of the or a controller and into the rotor by rotation of the rotor.

18. The supercharger of any one of claims 11 to 17, further comprising a water cooling system for reducing thermal energy heat loss from the supercharger.

19. The supercharger of claim 18, wherein the water cooling system is configured to cool the electric motor and electrical components of the or a controller of the electric motor.

20. The supercharger of claim 18 or claim 19, wherein the water cooling system comprises a plurality of cavities surrounding components of the electric supercharger.

21. The supercharger of claim 20, wherein the water cooling system comprises one or more watercooling pipes configured to spray water into the cavities and/or onto the components.

22. The supercharger of any one of claims 18 to 21 , wherein the water cooling system allows the or any actively cooled electrical components of the or a controller to be operated outside of their rated conditions.

23. The supercharger of any claim directly or indirectly dependent on claim 19, wherein the watercooling system induces turbulent flow of coolant around the electrical components of the controller.