Patent Description:
Internal combustion engines are often accompanied by a turbocharger within an engine system. The turbocharger increases the efficiency of an engine system by extracting work from hot exhaust gases emitted by the internal combustion engine and using this work to force air into the internal combustion engine; increasing the mass of air available for combustion. This increase in the pressure or mass of the air entering the internal combustion engine is commonly known as boost pressure or boost. The use of a turbocharger can improve the power output and/or improve fuel efficiency of the internal combustion engine and reduce emissions of certain species such as particulate matter and nitrous oxides NOx.

Nevertheless, turbocharged internal combustion engines suffer from several drawbacks. For example, present systems are often unable to increase engine load rapidly in response to transient load events, due to a lag between the event and the turbocharger's ability to increase the boost pressure. This lag is commonly known as turbo lag.

A number of technologies or solutions exist to reduce turbo lag. However, each of these technologies possesses significant drawbacks itself.

For example, superchargers - which are also known as electric superchargers, E-compressors, electric compressors - inject air mass into a turbocharged internal combustion engine prior to combustion. However, the ability of superchargers to reduce turbo lag is limited by the turbocharger compressor surge line and, therefore, the rate at which the boost pressure and engine load can be increased is limited and turbo lag is still observed.

E-turbochargers - also known as electrically assisted turbochargers or e-turbos - aim to solve turbo lag by electrically assisting the acceleration of the turbocharger and thereby improving responsiveness. However, electrically assisted turbochargers are often difficult to design, integrate and control such that their associated costs often significantly outweigh their benefits. Furthermore, it is typically not possible to convert an existing turbocharger into an e-turbocharger, limiting this the application of this technology.

Another potential solution is the use of variable geometry turbochargers. In this type of turbocharger, the aspect ratio of turbocharger can be changed to suit the engine load and thereby reduce turbo lag. However, variable geometry turbochargers are costly and complex to design and are often unreliable due to the inherent incompatibility of high temperatures and the intricate moving parts required to adjust the aspect ratio. For these reasons, variable geometry turbochargers are typically not designed or used with larger, more powerful internal combustion engines or efficient high-temperature internal combustion engines.

<CIT> relates to an internal combustion engine.

<CIT> relates to a method for on-board diagnostics of a turbocharger system for a vehicle.

<CIT> relates to turbo chargers for forced induction in internal combustion engines.

<CIT> relates to a watercraft and to a method for the operation of a watercraft power supply using an internal combustion engine.

<CIT> relates to the turbocharging of internal combustion engines.

<CIT> relates to a hydrogen powerplant and, more particularly, to a powerplant having a hydrogen combustion engine, a turbocharger and an afterburner.

Objects and aspects of the present invention aim to alleviate the problems associated with the turbocharged internal combustion engines and the present technologies used to reduce turbo lag.

According to a first aspect of the present invention, there is provided a turbocharged engine system comprising: an internal combustion engine, the internal combustion engine in fluid communication with an intake subsystem and an exhaust subsystem; a turbocharger arranged to supply a boost pressure to the internal combustion engine via a turbine coupled to a compressor wheel, the turbine being located in the exhaust subsystem and the compressor wheel being located in the intake subsystem; and an electric compressor arranged to inject a compressed fluid into the exhaust subsystem upstream of the turbine such that, in use, the compressed fluid injected by the electric compressor into the exhaust subsystem maintains the speed of or accelerates the turbine and thereby maintains or increases the boost pressure supplied to the internal combustion engine by the turbocharger, wherein the turbocharged engine system comprises one or more control valves arranged to control the injection timing, pressures and quantity of the compressed fluid into the exhaust by the electric compressor; characterised in that the one or more control valves comprises a bypass valve arranged to bypass the electric compressor, wherein the bypass valve is configured to lower the pressure of the compressed fluid injected by the electric compressor and increase the mass flow through the electric compressor to prevent compressor surge events on the electric compressor.

The injection of the compressed fluid, typically compressed air, into the exhaust subsystem by the electric compressor can be used to maintain the speed of or accelerate the turbine as the mass flow through and the expansion ratio across the turbine has been maintained or increased. This in turn maintains the speed of or accelerates the compressor wheel of the turbocharger which maintains or increases the boost pressure supplied to the engine due to the power imbalance between the compressor wheel and the turbine of the turbocharger. Since the electric compressor can be controlled independently to and can respond more quickly than the turbocharger, the electric compressor can effectively assist in controlling the boost pressure supplied and make the turbocharger more responsive. In this way, the turbo lag and transient load acceptance response times can be reduced.

The turbocharged engine system in accordance with the present invention is particularly beneficial for systems used in the high and medium power generation markets as it improves cold / pre-heated engine start times opening the potential for natural gas engines in the grid balancing, secondary frequency, emergency standby and datacentre markets. These markets are currently dominated by the less efficient and more polluting diesel engines. Another benefit of the turbocharged engine system is that the base design of the engine, efficiency or peak load of the engine do not need to be sacrificed in order to incorporate the electric compressor.

Furthermore, the provision of such an electric compressor is beneficial as once the desired boost pressure has been achieved the amount of compressed fluid supplied by the electric compressor can be reduced to avoid increasing the boost pressure over a desired or optimal value. In this way, the electric compressor can prevent the boost pressure from negatively affecting the internal combustion engine or its performance by, for example, overloading.

The provision of an electric compressor is also advantageous over other solutions to reducing turbo lag as it can be retrofitted to existing turbocharged engine systems relatively easily as only the exhaust subsystem needs to be altered to allow the injection of compressed fluid from the electric compressor.

The turbocharged engine system comprises one or more control valves arranged to control the injection of the compressed fluid into the exhaust by the electric compressor. Control over the injection of the compressed fluid by the one or more control valves may comprise controlling the timing, pressures and quantity of the injection. The provision of one or more control valves is advantageous as it affords an additional way to control the amount, or mass flow, or timing, of compressed fluid injected into the exhaust subsystem.

The one or more control valves comprises a bypass valve and may comprise one or more of an isolation valve, a blow-off valve, a check valve and a bypass valve alone or in any combination.

The one or more control valves may comprise an isolator valve arranged to prevent or inhibit the stream of compressed fluid into the exhaust subsystem. Usually, actuation of the isolator valve controls the flow of the compressed fluid into the exhaust subsystem by partially or fully occluding the conduit along which the stream of compressed fluid is flowing. Typically, the isolator valve is located between the electric compressor and exhaust subsystem. Additionally, the isolator valve can be actuated to prevent the back flow, which when exhaust fluid in the exhaust subsystem flows towards the electric compressor,.

The one or more control valves may comprise a blow-off valve arranged to control the venting of the compressed fluid produced by the electric compressor into the external environment. Compressed fluid can be vented to limit the pressure of the pressure-boosted stream and therefore the boost pressure supplied to the internal combustion engine. This is particularly advantageous when the operating point of the electric compressor approaches the surge line. Thus, the blow-off valve can prevent compressor surge events on the electric compressor. Additionally, compressed fluid can be vented to allow the electric compressor to accelerate to a desired speed at a lower pressure putting less load on the electric motor and speeding up the acceleration of the electric motor.

The one or more control valves may comprise a check valve arranged to prevent fluid in the exhaust subsystem flowing towards the electric compressor. The check valve - also known as a clack valve, non-return valve, reflux valve, retention valve or one-way valve - prevents the flow of exhaust fluid from exhaust subsystem towards the electric compressor. Additionally, the provision of a check valve controls the injection of compressed fluid as fluid will only be injected into the exhaust subsystem when the pressure of the compressed fluid is greater than the pressure of the fluid within the exhaust subsystem.

According to a second aspect of the present invention there is provided a method of controlling the boost pressure supplied to an internal combustion engine by a turbocharger, said method comprising the steps according to claim <NUM>.

The production of a stream of compressed fluid and the injection of the stream of compressed fluid afford control over the speed of the turbine. In this way, method provides control over the amount, or mass flow, or timing, of the stream of compressed fluid injected into the exhaust stream. Thus, turbo lag of the turbocharged internal combustion engine can be reduced as the turbocharger can be independently controlled by injection of the compressed fluid into the exhaust stream. This advantageously improves the response of the turbocharged engine to transient load events.

Preferably, the method controls the boost pressure supplied to the internal combustion engine by maintaining or increasing the boost pressure supplied to the internal combustion engine, such that the step of controlling the speed of the turbine comprises the step of maintaining the speed of or accelerating the turbine of the turbocharger using the pressure-boosted exhaust stream, thereby maintaining or increasing the boost pressure supplied to the internal combustion engine.

Increasing the boost pressure by accelerating the turbine using the injected stream of compressed fluid can be advantageously used to reduce turbo lag. Maintaining the boost pressure by maintaining the speed of the turbine using the injected stream of compressed fluid can be advantageously used to respond to fault conditions. For example, if the internal combustion engines experiences a fault condition such as coming off load, the boost pressure can be maintained such that the internal combustion engine can spin up more quickly, which saves time during its acceleration and reduces the impact of the fault condition.

Preferably, the method comprises the additional step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream when the load of the internal combustion engine, or engine load, or boost pressure achieves or exceeds a threshold or predetermined value.

Preferably, the step of reducing the amount of compressed fluid injected into the exhaust stream comprises a step of restricting the flow of compressed fluid into the exhaust stream.

Preferably, the method comprises an additional step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream when the load of the internal combustion engine or boost pressure is below or falls below a threshold or predetermined value.

Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of increasing the flow of compressed fluid into the exhaust stream.

Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of increasing the proportion of the compressed fluid stream that is injected into the exhaust stream.

Preferably, the step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream or the step of increasing the amount of the compressed fluid injected into the exhaust stream comprises a step of venting at least some of the compressed fluid into the external environment or bypassing the electric compressor.

Preferably, the stream of compressed fluid is compressed air. One advantage of using compressed air is the readily availability of air such that a dedicated fluid supply or tank is not required.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:.

When the turbocharged engine system <NUM> of <FIG> is operational, a mixture of air and fuel is supplied to an internal combustion engine <NUM> via an intake subsystem <NUM>. In this embodiment, and the subsequent embodiments, the internal combustion engine <NUM> is a spark-ignition engine. Other embodiments are envisaged for different types of internal combustion engine known in the art, such as compression-ignition engines.

The intake subsystem <NUM> comprises an air inlet conduit <NUM> with an aperture through which air is drawn into the intake subsystem <NUM>. This air is mixed with fuel from the gas supply <NUM> in the air inlet conduit <NUM>. The flow of fuel from the gas supply <NUM> to the air inlet conduit <NUM> is controlled by a fuel control valve <NUM>. The air and fuel mixture in the air inlet conduit <NUM> has a pressure P1 and a temperature T1 that can be measured by sensors (not shown) incorporated into the air inlet conduit <NUM>.

During operation, the air inlet conduit <NUM> supplies the air and fuel mixture to a compressor wheel <NUM> of a turbocharger <NUM>, where the mixture is compressed. The increased mass and pressure of the air and fuel mixture by the action of the compressor wheel <NUM> of the turbocharger <NUM> is known as the boost pressure or the boost. This compression of the air and fuel mixture by the compressor wheel <NUM> of the turbocharger <NUM> results in additional air being drawn into the air inlet conduit <NUM> as is well known in the art.

The intake subsystem <NUM> further comprises a radiator inlet conduit <NUM> that supplies the compressed air and fuel mixture exiting the compressor wheel <NUM> to a radiator <NUM>. The compressed air and fuel mixture in the radiator inlet conduit <NUM> has a pressure P2 and temperature T2 that can be measured by sensors (not shown) incorporated into the radiator inlet conduit <NUM>. The pressure P2 of the air and fuel mixture inside the radiator inlet conduit <NUM> is greater than the pressure P1 of the air and fuel mixture inside the air inlet conduit <NUM> due to the boost pressure imparted on the mixture by the compressor wheel <NUM> of the turbocharger <NUM>.

The radiator <NUM> cools the compressed air and fuel mixture to provide a cooled and compressed air and fuel mixture to an engine inlet conduit <NUM>. The cooled and compressed air and fuel mixture in the engine inlet conduit <NUM> has a pressure P2' and temperature T2' that can be measured by sensors (not shown) incorporated into the engine inlet conduit <NUM>. The radiator <NUM> and the engine inlet conduit <NUM> are part of the intake subsystem <NUM>.

The engine inlet conduit <NUM> channels the cooled compressed air and fuel mixture from the radiator <NUM> to the internal combustion engine <NUM>. During operation, the flow of the cooled compressed air and fuel mixture along the inlet engine conduit <NUM> into the internal combustion engine <NUM> is controlled by a throttle <NUM> in a manner as in known in the art.

During operation of the turbocharged engine system <NUM>, the internal combustion engine <NUM> combusts the cooled and compressed air fuel mixture producing mechanical power. The greater mass of air entering the engine <NUM> because of the action of the compressor wheel <NUM> of the turbocharger <NUM> can be used to increase the power output and/or fuel efficiency of the engine as well as reducing the emissions of certain species such as nitrous oxides NOx.

The combustion of the air and fuel mixture by the internal combustion engine <NUM> also produces waste or exhaust fluids that are expelled from the internal combustion engine <NUM> into the external environment via an exhaust subsystem <NUM>.

The exhaust subsystem <NUM> comprises an engine exhaust conduit <NUM> along which the exhaust fluids from the internal combustion engine <NUM> flow to a turbine <NUM> of the turbocharger <NUM>. The pressure P3 and temperature T3 of the exhaust fluid egressing the engine <NUM> can be measured by sensors (not shown) incorporated into the engine exhaust conduit <NUM>.

The turbine <NUM> is rotationally connected or coupled to the compressor wheel <NUM> by a turbocharger shaft <NUM>. Together the turbine <NUM>, the turbocharger shaft <NUM> and the compressor wheel <NUM> make up the turbocharger <NUM>.

The flow of the hot pressurised exhaust fluids from the engine exhaust conduit <NUM> rotates the turbine <NUM> that in turn drives the rotation of the turbocharger shaft <NUM> and the compressor wheel <NUM>. This power imbalance between the turbine <NUM> and the compressor wheel <NUM> causes it to compress the air and fluid mixture in intake subsystem <NUM>, increasing the air mass entering the engine <NUM>, as is known in the art for turbocharged engines.

After rotating the turbine <NUM>, the exhaust fluid is egressed through an exhaust conduit <NUM>. The exhaust conduit <NUM> forms part of the exhaust subsystem <NUM>. The pressure P4 and temperature T4 of the exhaust fluid within the exhaust conduit <NUM> can be measured by sensors (not shown) incorporated into the exhaust conduit <NUM>. The exhaust conduit <NUM> egress, or exhausts, the exhaust fluid into the environment via aftertreatment, heat recovery, noise attenuation or whatever equipment is installed downstream of the engine.

In accordance with the present invention, the exhaust subsystem <NUM> is fluidly connected with an electric compressor <NUM>. The electric compressor <NUM> comprises an electric motor <NUM> that rotationally drives a compressor shaft <NUM> that is coupled to a compressor <NUM>. The electric motor <NUM> is electrically connected to an external power source (not shown) such as the electrical grid or battery.

The rotation of the compressor <NUM> by the electric motor <NUM> draws in air through a compressor inlet conduit <NUM> and compresses it, boosting the pressure of the air. This pressure-boosted air is expelled from the compressor <NUM> into the compressor outlet conduit <NUM>. The pressure P5 and temperature T5 of the pressure-boosted air from the electric compressor <NUM> can be measured by sensors (not shown) incorporated into the compressor outlet conduit <NUM>.

The compressor outlet conduit <NUM> is fluidly connected to the engine exhaust conduit <NUM>. The pressure-boosted air from the electrical compressor <NUM> is injected into the exhaust conduit <NUM> and mixed with the exhaust fluid in the engine exhaust conduit <NUM> to form a mixture of exhaust fluid and air in the engine exhaust conduit <NUM>. The pressure P3' and temperature T3' of the exhaust fluid and air mixture can be measured by sensors (not shown) incorporated into the engine exhaust conduit <NUM> downstream of the fluid connection with the compressor outlet conduit <NUM>. When the electric compressor <NUM> is running, the air and exhaust fluid mix within the exhaust conduit can have a pressure P3' that is greater than would be measured if the electric compressor <NUM> were not installed or operational.

By increasing the pressure P3' of the fluid entering the turbine <NUM> of the turbocharger <NUM>, the boost pressure supplied to the engine <NUM> is increased as the compressor wheel <NUM> will rotate more quickly. In this way, the amount of boost pressure, i.e. the mass of air, supplied to engine <NUM> can be controlled by the speed of the electric motor <NUM> of the electric compressor <NUM>. Increasing the speed of the electric motor <NUM> increases the pressure of air mixed with the exhaust fluid, thereby increasing the rotation of the turbocharger <NUM> and increasing the boost pressure suppled to the engine <NUM>. This can be used to accelerate the turbocharger <NUM> and raise the boost pressure to a desired or optimal value when the internal combustion engine <NUM> is starting up or experiencing a transient load event.

<FIG> and <FIG> of the drawings depict schematic drawings of a second embodiment of a turbocharged engine system <NUM> and a third embodiment of a turbocharged engine system <NUM> in accordance with present invention.

The following features of the second embodiment and third embodiment are substantially identical in structure and function to the equivalent features of the first embodiment in <FIG> and the reference numerals for these features are maintained across the embodiments and their respective figures: the internal combustion engine <NUM>; the intake subsystem <NUM>; the air inlet conduit <NUM>; the gas supply <NUM>; the fuel control valve <NUM>; the compressor wheel <NUM>; the turbocharger <NUM>; the radiator inlet conduit <NUM>; the radiator <NUM>; the engine inlet conduit <NUM>; the throttle <NUM>; the exhaust subsystem <NUM>; the engine exhaust conduit <NUM>; the turbine <NUM>; the turbocharger shaft <NUM>; the exhaust conduit <NUM>; the electric compressor <NUM>; the electric motor <NUM>; the compressor shaft <NUM>; the compressor <NUM>; the compressor inlet conduit <NUM>; and compressor outlet conduit <NUM>.

The second embodiment of the turbocharged engine system <NUM> in <FIG> and the third embodiment of the turbocharged engine system <NUM> in <FIG> differ from the first embodiment in that they comprise valves in series or parallel with the electrical compressor <NUM> to assist in controlling the flow of pressure-boosted air from the electrical compressor <NUM> into the engine exhaust conduit <NUM>.

Referring to the second embodiment of the turbocharged engine system <NUM> in <FIG>, the compressor outlet conduit <NUM> comprises a blow off valve <NUM> downstream of the electric compressor <NUM> and a check valve <NUM> downstream of the blow off valve <NUM> prior to the connection with the engine exhaust conduit <NUM>.

The blow off valve <NUM> is configured to vent the pressure-boosted air produced by the electric compressor <NUM> into the environment prior to its entry into the exhaust subsystem <NUM>.

The check valve <NUM> is configured to prevent the pressurized exhaust fluid in the engine exhaust conduit <NUM> from flowing through the compressor outlet conduit <NUM> towards and into the electric compressor <NUM>. The check valve <NUM> can also be configured to open when the pressure P5 in the compressor outlet conduit <NUM>; the pressure P3 in the engine exhaust conduit <NUM>; or the pressure difference between the pressure P5 in the compressor outlet conduit <NUM> and the pressure P3' of the mixture of pressure-boosted air (P5-P3') exceeds or falls below a threshold or predetermined value.

In this way, the blow off valve <NUM> can be used to control or limit the pressure difference between the pressure P5 and pressure P3' (P5 - P3') supplied to the turbocharger <NUM> as the blow off valve <NUM> can be opened to vent any excess or shortfall in pressure P5 generated by the electric compressor <NUM>. Another example of when the blow off valve <NUM> may vent pressure-boosted air is when the pressure P3' of the air and exhaust fluid mixture prior to turbine <NUM> of the turbocharger <NUM> has reached an optimal or desired value the blow off valve <NUM> can open to prevent the pressure P3' exceeding the desired or optimal value. A further example is when the pressure P5 being produced by the electric compressor <NUM> has reached a desired or optimal value, the blow off valve <NUM> can open to prevent the pressure P5 exceeding the desired or optimal value.

Alternatively, the blow off valve <NUM> can be opened to allow the electric compressor <NUM> to ramp up to a desired speed. By opening the blow off valve <NUM> while accelerating the electric motor <NUM>, the load on the electric motor <NUM> is decreased as the pressure P5 within the compressor outlet conduit <NUM> is reduced due to the venting of the pressure-boosted air. This means that the electric motor <NUM> can accelerate to the desired or optimal speed more quickly and once the desired compressor <NUM> speed has been achieved, the blow off valve <NUM> can then be shut and the pressure-boosted air supplied to the turbocharger <NUM> via the engine exhaust conduit <NUM> when the check value <NUM> is open or opened. This will provide even more aggressive turbocharger speed increases at the early part of the transient and thus further improve the engine <NUM> load acceptance capability.

Referring to the third embodiment of the turbocharged engine system <NUM> in <FIG>, the compressor outlet conduit <NUM> comprises an isolator valve <NUM> downstream of the electric compressor <NUM> prior to the connection with the engine exhaust conduit <NUM>. The turbocharged engine system <NUM> further comprises a bypass conduit <NUM> that is connected between the compressor inlet conduit <NUM> and compressor outlet conduit <NUM> in parallel with the electric compressor <NUM>. The bypass conduit <NUM> comprises a compressor bypass valve <NUM>.

The isolator valve <NUM> is configured to control the flow of pressure-boosted air from the electric compressor <NUM> into the exhaust subsystem <NUM>. The isolator valve <NUM> can do this by occluding the compressor outlet conduit <NUM> partially or completely, thereby limiting the injection of pressure-boosted air form the compressor <NUM>. In this way, the pressure P3' of the air and fuel mixture prior to entry into the turbine <NUM> of turbocharger can be controlled. For example, this can be used to ramp up the electric motor <NUM> to a desired speed prior to opening. Further, the occlusion of the compressor outlet conduit <NUM> by the isolator valve <NUM> can prevent flow of the exhaust fluid from the exhaust subsystem <NUM> into or towards the electric compressor <NUM>.

The bypass valve <NUM> is configured to vent the pressure-boosted air produced by the electric compressor <NUM> back to the inlet of the electric compressor <NUM> prior to its entry into the exhaust subsystem <NUM>. For example, the bypass valve <NUM> can open to prevent pressure building up within the compressor outlet conduit <NUM> when the isolator valve <NUM> partially or completely occludes the compressor outlet conduit <NUM>, such as when the isolator valve <NUM> is shut and the electric motor <NUM> is ramping up to a desired speed. Alternatively, the bypass valve <NUM> can be actuated to relieve pressure or increase the flow through the electric compressor <NUM> as it approaches its surge line. The electric compressor <NUM> will approach its surge line when the isolator valve <NUM> (or the check valve 54in the second embodiment) is closed and the electric compressor <NUM> is still spinning, or when the pressure at P3' is equal to or close to being equal to P5 such that the flow of air through the electric compressor <NUM> will naturally decrease.

An immediate injection of pressure-boosted air can be supplied by closing the isolator valve <NUM> and opening the bypass valve <NUM> while the electric compressor <NUM> is running. During this time, the electric compressor <NUM> can be ramped or spun up to a desired, or maximum, speed raising the pressure P5 of the pressure-boosted air to a desired, or maximum, value. When a load increase occurs on or is requested by the internal combustion engine <NUM>, the isolator valve <NUM> can then be opened and the bypass valve <NUM> closed. This causes an instantaneous injection of pressure-boosted air from the electric compressor <NUM> into the exhaust subsystem <NUM>. The instantaneous injection rapidly accelerates the turbocharger <NUM> and rapidly increases the boost pressure, enabling rapid load acceptance by the internal combustion engine <NUM>.

Other embodiments are envisaged where a turbocharged engine system comprises alone or combination any of the blow-off valve of the second embodiment, the check valve of the second embodiment, the isolator valve of the third embodiment and the bypass valve of the third embodiment.

<FIG> of the drawings depicts a method of increasing the boost pressure supplied to the internal combustion engine <NUM> by a turbocharger <NUM> using the turbocharged engine systems <NUM>, <NUM>, <NUM> of <FIG>, <FIG> and <FIG>.

The method begins with the electric compressor <NUM> producing a stream of compressed fluid in step S1. The stream of compressed fluid, typically air, is produced by the action of the compressor <NUM> being rotated by the electric motor <NUM>. The pressure P5, mass and flow of the compressed fluid is therefore controlled by the speed of the electric motor <NUM>.

This stream of compressed fluid is then injected or added into the exhaust stream from the internal combustion engine in step S2. The stream of compressed fluid form the electric compressor <NUM> and exhaust stream mix within the engine exhaust conduit <NUM> to produce a pressure-boosted exhaust stream.

This pressure-boosted exhaust stream can then accelerate the turbine <NUM> of the turbocharger <NUM> in step S3, which causes the turbocharger <NUM> to supply a great boost pressure to the internal combustion engine <NUM>.

Claim 1:
A turbocharged engine system (<NUM>) comprising:
an internal combustion engine (<NUM>), the internal combustion engine (<NUM>) in fluid communication with an intake subsystem (<NUM>) and an exhaust subsystem (<NUM>);
a turbocharger (<NUM>) arranged to supply a boost pressure to the internal combustion engine (<NUM>) via a turbine (<NUM>) coupled to a compressor wheel (<NUM>), the turbine (<NUM>) being located in the exhaust subsystem (<NUM>) and the compressor wheel (<NUM>) being located in the intake subsystem (<NUM>); and
an electric compressor (<NUM>) arranged to inject a compressed fluid into the exhaust subsystem (<NUM>) upstream of the turbine (<NUM>) such that, in use, the compressed fluid injected by the electric compressor (<NUM>) into the exhaust subsystem (<NUM>) maintains the speed of or accelerates the turbine (<NUM>) and thereby maintains or increases the boost pressure supplied to the internal combustion engine (<NUM>) by the turbocharger (<NUM>),
wherein the turbocharged engine system comprises one or more control valves arranged to control the injection timing, pressures and quantity of the compressed fluid into the exhaust by the electric compressor (<NUM>);
characterised in that the one or more control valves comprises a bypass valve (<NUM>) arranged to bypass the electric compressor (<NUM>), wherein the bypass valve (<NUM>) is configured to lower the pressure of the compressed fluid injected by the electric compressor (<NUM>) and increase the mass flow through the electric compressor (<NUM>) to prevent compressor surge events on the electric compressor (<NUM>).