WO2018050858A1

WO2018050858A1 - An exhaust gas treatment system for an internal combustion engine and a method of treatment of exhaust gas

Info

Publication number: WO2018050858A1
Application number: PCT/EP2017/073349
Authority: WO
Inventors: Stephen Knight
Original assignee: Valeo Air Management Systems Uk Ltd
Priority date: 2016-09-16
Filing date: 2017-09-15
Publication date: 2018-03-22
Also published as: GB201615808D0; GB2553831A

Abstract

An exhaust gas treatment system for an internal combustion engine (2) having a catalytic convertor (4) for receiving exhaust gas from an internal combustion engine (2), a particulate filter (5) in fluid communication with an outlet (4b) of the catalytic convertor (4) to receive exhaust gas from the catalytic convertor (4) and to filter the gas, a pump (6) and a motor (7) arranged to drive the pump (6), wherein the particulate filter (5) is remote from the catalytic convertor (4) and the pump (6) is a positive displacement pump arranged to provide air to the gas passing from the catalytic convertor (4) to the particulate filter (5) to combust the gas such that the gas heats the particulate filter (5) to provide regeneration of the filter (5). A method of treatment of exhaust gas using an exhaust gas treatment system.

Description

An exhaust gas treatment system for an internal combustion engine and a method of treatment of exhaust gas

Technical Field

The present invention relates to an exhaust gas treatment system for an internal combustion engine. The present invention also relates to an engine system comprising an exhaust gas treatment system and to a vehicle comprising the engine system. The present invention also relates to method of treatment of exhaust gas of an internal combustion engine.

Background of the Invention

A known exhaust gas treatment system for an internal combustion engine comprises a catalytic convertor that receives exhaust gas from an internal combustion engine and converts toxic gases and pollutants in the exhaust gas to less toxic pollutants by catalysing a reaction (e.g. an oxidation and reduction reaction) of the exhaust gas. A particulate filter is located downstream of, and in fluid communication with, the catalytic convertor to filter the gas that has passed through the catalytic convertor so as to remove harmful and polluting particles from the gas.

A pump supplies air to the outlet manifold of the engine, so that the exhaust gases leaving the exhaust manifold are combusted with the air. These gases then heat the catalytic convertor as they pass through it, raising its temperature to its optimal operating temperature.

In this known arrangement, the particulate filter is close coupled to the catalytic convertor such that the combusted exhaust gases then heat the particulate filter as they then pass through it, to provide regeneration of the filter . However, the close coupling of the particulate filter and the catalytic convertor means that a relatively large volume within the engine bay must be allocated to the exhaust gas treatment system. This may undesirable due to space constraints, specifically within the engine bay.

The present invention seeks to address or mitigate at least some of the above mentioned problems. Alternatively, or additionally, the present invention seeks to provide an improved exhaust gas treatment system for an internal combustion engine. Alternatively, or additionally, the present invention seeks to provide an improved engine system comprising an exhaust gas treatment system. Alternatively, or additionally, the present invention seeks to provide an improved method of treatment of exhaust gas of an internal combustion engine.

Summary of the Invention

According to a first aspect of the invention there is provided an exhaust gas treatment system for an internal combustion engine comprising: a catalytic convertor for receiving exhaust gas from an internal combustion engine; a particulate filter in fluid communication with an outlet of the catalytic convertor to receive exhaust gas from the catalytic convertor and to filter the gas; a pump and a motor arranged to drive the pump, wherein the particulate filter is remote from the catalytic convertor, and the pump is a positive displacement pump arranged to provide air to the gas passing from the catalytic convertor to the particulate filter to combust the gas such that the gas heats the particulate filter to provide regeneration of the filter.

Locating the particulate filter remote from the catalytic convertor is advantageous in that it provides a more flexible configuration, than if the particulate filter was close- coupled to the catalytic convertor, such that it can be tailored to specific space requirements. For example, the particulate filter may be located external to the engine bay, thereby reducing the space taken up in the engine bay by the exhaust gas treatment system.

However, because the particulate filter is remote from the catalytic convertor, any combustion of the exhaust gas upstream of the catalytic convertor, to heat the catalytic convertor to its operating temperature, does not heat the particulate filter to regenerate the filter.

The use of a pump to provide air to the gas passing from the catalytic convertor to the particulate filter is advantageous in that it facilitates combustion of the gas passing to the particulate filter, which heats the particulate filter to provide regeneration of the filter.

The applicant has found that a positive displacement pump is particularly advantageous as it can be run at a relatively low speed, for example compared to a centrifugal pump, whilst still providing the required properties of flow of the air (including the required mass flow rate, pressure ratio and stall and surge points) that provide the necessary combustion of exhaust gas to regenerate the filter.

Accordingly it may be possible to drive the pump using a motor (e.g. an electric motor) that has a relatively low operating speed. This may allow the motor to be relatively small, thereby further reducing the space taken up by the exhaust gas treatment system.

Therefore there is a synergy between positioning the particulate filter remote from the catalytic convertor and the use of a positive displacement pump to supply air to the gas passing from the catalytic convertor to the particulate filter, to combust the gas to regenerate the filter, as together they allow for a reduction in the space taken up by the exhaust gas treatment system, whilst still providing regeneration of the particulate filter. The pump may be arranged to provide the air to the gas upstream of the particulate filter. Alternatively, or additionally, the pump may be arranged to provide the air to the gas at the particulate filter.

In embodiments of the invention the pump is arranged to provide air to the gas between the catalytic convertor and the particulate filter.

In embodiments of the invention the pump is arranged to provide air to the gas downstream of the catalytic convertor.

The pump may be a positive displacement compressor. Optionally the positive displacement pump is a rotary positive displacement pump.

Optionally the rotary positive displacement pump is a sliding vane pump.

A sliding vane pump is particularly advantageous in that it can be run at relatively slow speed (e.g. 1, 000 to 7,000 rpm) whilst still providing the required properties of flow of the air (in contrast a centrifugal pump would typically operate in the region of 60, 000 rpm), duty cycle and power consumption . In addition, a sliding vane pump has a relatively high efficiency. Also, it is relatively compact and produces relatively low noise and vibration. This is particularly advantageous where the exhaust gas treatment system is located in an engine bay since low noise, vibration and harshness are particularly desirable in an engine bay environment. In embodiments of the invention the sliding vane pump comprises a housing having an air inlet and an air outlet and a rotor arranged to rotate within the housing about a rotational axis that is offset from a central axis of the housing, such that the radial distance between a radially outer surface of the rotor and a radially inner surface of the housing varies in the circumferential direction, wherein at least one vane is slidably mounted on the rotor and is arranged to slide in the radial direction to maintain a seal against the inner surface of the housing as the rotor rotates such that the vane, the radially inner surface of the housing and the radially outer surface of the rotor, at least partially, define a chamber having a volume that varies as the rotor rotates such that during a first part of the rotation the volume of the chamber increases and air is received into the chamber through the air inlet, during a second part of the rotation the volume of the chamber decreases, thereby compressing the air in the chamber, and during a third part of the rotation the air is passed out of the air outlet. Optionally the at least one vane is biased in the radially outward direction, to maintain a seal with the inner surface of the housing. The at least one vane may be biased by a resiliently deformable biasing member, for example a spring.

Optionally the rotor comprises a plurality of said vanes distributed in the circumferential direction, which are each slidably mounted on the rotor and arranged to slide in the radial direction to maintain a seal against the inner surface of the housing, as the rotor rotates, such that the radially inner surface of the housing, the radially outer surface of the rotor, the vane and a circumferentially adjacent vane define a chamber having a volume that varies as the rotor rotates such that during a first part of the rotation the volume of the chamber increases and air is received into the chamber through the air inlet, during a second part of the rotation the volume of the chamber decreases, thereby compressing the air in the chamber, and during a third part of the rotation the air is passed out of the air outlet.

In embodiments of the invention, during the first part of the rotation the chamber is in fluid communication with the air inlet, during the second part of the rotation the chamber is not in fluid communication with either the air inlet or the air outlet and during the third part of the rotation the chamber is in fluid communication with the air outlet.

It will be appreciated that, unless otherwise stated, references to a radial or circumferential direction are in relation to the rotational axis of the rotor.

The radially inner surface of the housing may have a substantially circular cross-sectional shape. In this regard, the radially inner surface of the housing may have a substantially constant radius about the central axis of the housing .

The radially outer surface of the rotor may have a substantially circular cross-sectional shape. In this regard, the radially outer surface of the rotor may have a substantially constant radius about the rotational axis of the rotor .

Optionally the pump has an operating speed in the range 1,000 to 7,000 rpm. Optionally the pump has an operating speed in the range 3,000 to 4,000 rpm.

The particulate filter may have a regeneration temperature greater than 600°C. The particulate filter may have a regeneration temperature in the range 600°C to 700°C. The particulate filter may be any suitable type, including a diesel or petrol particulate filter, depending on whether the internal combustion engine is a diesel or petrol engine respectively. The diesel particulate filter may be arranged to remove diesel particulate matter or soot from the exhaust gas.

Optionally the motor is an electric motor.

Optionally the motor is a brushless electric motor. A brushless electric motor is advantageous in that it may generate a relatively low amount of interference with nearby electronics (compared to a brushed electric motor) .

Optionally the pump is a dry running pump. In this regard, optionally the pump does not require any lubricating fluid in order to operate.

According to a second aspect of the invention there is provided an engine system comprising an internal combustion engine and an exhaust gas treatment system according to the first aspect of the invention, wherein an inlet of the catalytic convertor is in fluid communication with an outlet of the internal combustion engine to receive exhaust gas from the internal combustion engine. Optionally the pump is also arranged to provide air to the exhaust gas passing from the internal combustion engine to the catalytic convertor to combust the gas such that the gas heats the catalytic convertor.

The pump may be arranged to provide the air to the outlet of the engine and/or downstream of the outlet of the engine.

The pump may be arranged to provide the air to the catalytic convertor and/or upstream of the catalytic convertor .

In embodiments of the invention the combustion is such that the gas heats the catalytic convertor to its operating temperature. The operating temperature may be 400°C or higher, for example.

Optionally the engine system is arranged such that air from the pump may be selectively provided to either the gas passing from the catalytic convertor to the particulate filter or to the exhaust gas passing from the internal combustion engine to the catalytic convertor.

Optionally the engine system comprises a valve assembly that is operable to direct the air to either the gas passing from the catalytic convertor to the particulate filter or to exhaust gas passing from the internal combustion engine to the catalytic convertor.

The valve assembly may comprise one or more valves.

Optionally a first air path fluidly connects an outlet of the pump to a fluid path that connects the catalytic convertor to the particulate filter and a second air path fluidly connects an outlet of the pump to the engine outlet or to a fluid path connecting the engine outlet to the catalytic convertor . Optionally a first valve is located in the first air path and a second valve is located in the second air path, wherein each valve is operable between an open and closed position to allow or prevent the flow of air through the valve.

An air path may be formed by a conduit or by a plurality of conduits that are in fluid connection.

Optionally the engine system comprises an engine control unit arranged to control the operation of the pump and internal combustion engine.

Optionally the engine control unit is arranged to control whether the air is supplied to the gas passing from the catalytic convertor to the particulate filter or to the exhaust gas passing from the internal combustion engine to the catalytic convertor. The engine control unit may be arranged to control the positions of the first and second valves.

In embodiments of the invention the particulate filter is not close-coupled to the catalytic convertor. In this regard, the combustion of the exhaust gas upstream of, or at, the catalytic convertor does not act to regenerate the particulate filter .

Optionally the engine system comprises a forced induction device arranged to supply compressed air to an inlet of the internal combustion engine.

Preferably the forced induction device is a turbocharger comprising a turbine arranged to be driven by exhaust gas from the internal combustion engine and a compressor that is driven by the turbine and arranged to compress air passing to the internal combustion engine.

According to a third aspect of the invention there is provided a vehicle comprising an engine system according to the second aspect of the invention.

According to a fourth aspect of the invention there is provided a method of treatment of exhaust gas of an internal combustion engine of an engine system, the engine system comprising an internal combustion engine and an exhaust gas treatment system, the exhaust gas treatment system comprising: a catalytic convertor having an inlet in fluid communication with an outlet of the internal combustion engine to receive exhaust gas from the internal combustion engine; a particulate filter in fluid communication with an outlet of the catalytic convertor to receive exhaust gas from the catalytic convertor and to filter the gas; a pump and a motor arranged to drive the pump, wherein the particulate filter is remote from the catalytic convertor and the pump is a positive displacement pump, and wherein the method comprises providing air from the pump to the gas passing from the catalytic convertor to the particulate filter to combust the gas such that the gas heats the particulate filter to provide regeneration of the filter.

Optionally the gas heats the particulate filter to a temperature greater than 600°C to provide the regeneration of the filter.

Optionally the method comprises selectively providing the air from the pump to either the gas passing from the catalytic convertor to the particulate filter to combust the gas such that the gas heats the particulate filter to provide regeneration of the filter or to the exhaust gas passing from the internal combustion engine to the catalytic convertor to combust the gas such that the gas heats the catalytic convertor.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of treatment of exhaust gas of an internal combustion engine may incorporate any of the features described with reference to the exhaust gas treatment system, or engine system, and vice versa.

Other preferred and advantageous features of the invention will be apparent from the following description.

Description of the Drawings

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a schematic view of a vehicle comprising an engine system according to an embodiment of the invention, and Figure 2 is a cross-sectional view of a sliding vane pump of the engine system shown in Figure 1.

Detailed Description

Referring to Figure 1 there is shown a vehicle 100 comprising an engine system 1 according to an embodiment of the invention. The engine system 1 is arranged to provide motive power to the vehicle 100.

In the currently described embodiment the vehicle 100 is a car, and the engine system 1 drives wheels of the car. However, it will be appreciated that the engine system 1 may be used with any type of vehicle.

The engine system 1 comprises an internal combustion engine 2 and an exhaust gas treatment system, according to an embodiment of the invention, arranged to treat exhaust gas from the engine 2.

The exhaust gas treatment system comprises a catalytic converter 4, a diesel particulate filter 5, a pump 6 and an electric motor 7 arranged to drive the pump 6. In the currently described embodiment the internal combustion engine 2 is a direct injection, four cylinder two- stroke diesel engine.

The engine 2 comprises four engine cylinders 9. A piston (not shown) is mounted in each cylinder 9 for reciprocal motion within the cylinder. An inlet of each cylinder is fluidly connected to an inlet manifold 8 and an outlet of each cylinder is fluidly connected to an outlet (exhaust) manifold 12.

The inlet manifold 8 is fluidly connected, by an engine inlet conduit 10, to a main air intake 11, which supplies air to each cylinder 9 of the engine 2. The outlet manifold 12 is fluidly connected, by an engine outlet conduit 13 to an inlet 4a of the catalytic convertor 4.

An outlet 4b of the catalytic convertor 4 is fluidly connected to an inlet 5a of the diesel particulate filter 5 by a conduit 17. An outlet 5b of the particulate filter 5 is connected to an exhaust 14 of the engine system 1 by an exhaust conduit 15.

The engine system 1 further comprises a turbocharger 25 comprising a compressor 26 and a turbine 27 which is coupled to the compressor 26 by a drive shaft 28 so as to drive the compressor 26.

In a conventional manner, the turbine 27 is located within the engine outlet conduit 13 and is arranged to be rotatably driven by exhaust gas from the engine 2. The compressor 26 is located in the engine inlet conduit

10 and is arranged to be driven by the turbine 27 to compress air passing to the engine inlet manifold 8.

An engine control unit 23 is operatively connected to and arranged to control the operation of the engine 2, the pump 6 and the turbocharger 25 (these connections are not shown for illustrative purposes) .

In use, each engine cylinder 9 receives air from the main air intake 11, via the engine inlet conduit 10 and the inlet manifold 8. Diesel fuel is supplied to each cylinder from a fuel supply (not shown) and the engine performs a two-stroke diesel cycle to drive a crankshaft (not shown) of the vehicle 100 which is drivably connected to wheels (not shown) of the vehicle . Exhaust gases from the engine 2 pass from the outlet of each cylinder 9 and out of the engine 2 through the outlet manifold 12.

The exhaust gases pass from the outlet manifold 12, along the engine outlet conduit 13 to the inlet 4a of the catalytic convertor 4.

The catalytic convertor 4 comprises a catalyst (e.g. of a mixture of precious metals such as platinum and palladium) arranged to convert toxic gases and pollutants in the exhaust gas to less toxic pollutants by catalysing a reaction (e.g. an oxidation and reduction reaction) of the exhaust.

The treated exhaust gas then passes from the outlet 4b of the catalytic convertor 4, along the conduit 17, to the particulate filter 5. The particulate filter 5 comprises a filter (e.g. made of ceramic fibre and/or metal fibre) arranged to filter the gas that has passed through the catalytic convertor 4 so as to remove harmful and polluting particles from the gas before it passes out of the engine system exhaust 14 to the external surroundings.

The turbine 27 of the turbocharger 25 is rotatably driven by exhaust gas from the engine 2 and rotatably drives the compressor 26, which compresses air passing to the engine inlet manifold 8, and thereby to the cylinders 9, so as to increase the power of the engine 2.

The pump 6 is a positive displacement pump (described in more detail below) and has an inlet 6a fluidly connected to the main air intake 11 by a pump inlet conduit 16 that is fluidly connected to the engine inlet conduit 10. An outlet 6b of the pump 6 is fluidly connected to a pump outlet conduit 18, which splits into a first air conduit 19 and a second air conduit 20. The first air conduit 19 fluidly connects the pump outlet 6b to the conduit 17 that connects the catalytic convertor 4 to the particulate filter 5. In this regard, the pump 6 is arranged to provide air to the exhaust gas at a location downstream of the catalytic convertor 4. The second air conduit 20 fluidly connects the pump outlet 6b to the engine outlet manifold 12.

A first valve 21 is located in the first air conduit 19 and a second valve 22 is located in the second air conduit 20. The first and second valves 21, 22 together form a valve assemb1y .

Each valve 21, 22 is operable between an open and closed position. When the valve 21, 22 is in its open position, air from the pump outlet 6b passes through the valve 21, 22 and downstream of the valve 21, 22 and when the valve 21, 22 is in its closed position, air is prevented from passing through the valve 21, 22 and therefore cannot pass downstream of the valve 21, 22. The operation of the valves 21, 22 will be described in more detail below.

The electric motor 7 driving the pump 6 is a brushless electric motor and is arranged to drive a drive shaft 24 which couples the motor 7 to the pump 6. The electric motor 7 is connected to an electric battery (not shown) of the vehicle 100, which powers the motor 7.

The pump 6 will now be described in more detail with reference to Figure 2, which shows a cross-sectional view of the pump 6.

The pump 6 is a rotary positive displacement pump in the form of a sliding vane pump 6.

The sliding vane pump 6 comprises a cylindrical housing 30 having an air inlet 6a and an air outlet 6b (the inlet 6a and outlet 6b of the pump 6) . A radially inner surface 35 of the housing 30 is cylindrical and has a substantially circular cross-sectional shape. In this regard the radially inner surface 35 has a substantially constant radius relative to a central longitudinal axis A of the housing 30.

A rotor, in the form of a circular wheel 33, is arranged to rotate within the housing 30 about a central rotational axis B, in the direction of arrow C (i.e. anti-clockwise when viewed as shown in Figure 2) . A radially outer surface 34 of the rotor 33 has a substantially circular cross-sectional shape. In this regard, the radially outer surface 34 has a substantially constant radius relative to the rotational axis B of the rotor 33.

The rotational axis B of the rotor 33 is offset from the central axis A of the housing 30, such that the radial distance between the radially outer surface 34 of the rotor 33 and the radially inner surface 35 of the housing 30 varies in the circumferential direction.

Six vanes 36 are slidably mounted on the rotor 33 and are distributed, equally spaced, in the circumferential direction. In Figure 2 three of the vanes 36 have been omitted for illustrative purposes. However, each vane 36 is identical and the below description also applies to the omitted vanes.

It will be appreciated that, unless otherwise stated, references to a radial or circumferential direction are in relation to the rotational axis B of the rotor 33.

Each vane 36 is slidably mounted in a respective channel 37 such that the vane 36 is slidable inwardly and outwardly in the radial direction, as the rotor 33 rotates.

In this regard, each vane 36 is biased in the radially outward direction by a resiliently deformable member in the form of a coiled spring 38, such that the vane 36 maintains a seal against the inner surface 35 of the housing 30, as the rotor 33 rotates.

As the rotor 33 rotates, the radially inner surface 35 of the housing 33, the radially outer surface 34 of the rotor 33 and circumferentially opposed surfaces 39, 40 of each vane 36 and a circumferentially adjacent vane 36 define a chamber 41 having a volume that varies as the rotor 33 rotates.

In this regard, during a first part of the rotation the chamber 41 is in fluid communication with the air inlet 6a and the volume of the chamber increases. As is does so, air is sucked into the chamber 41 through the air inlet 6a.

During a second part of the rotation (where the rotor 33 has rotated from the first position in the direction of arrow C) the chamber 41 is no longer in fluid communication with the air inlet 6a and the volume of the chamber 41 decreases, thereby compressing the air in the chamber 41. It will be appreciated that, during the second part of the rotation, the chamber 41 is also not in fluid communication with the air outlet 6b. During a third part of the rotation (where the rotor 33 has rotated from the second position in the direction of arrow C) , the chamber is brought into fluid communication with the air outlet 6b and the air is pumped out of the air outlet 6b.

Accordingly the pump 6 acts to receive air from the air intake 11 and to pump this air, by positive displacement, out of the pump outlet 6b. It will be appreciated that since the pump 6 pumps the air by compressing it, the pump 6 also acts as a compressor.

The pump 6 is a dry running pump. In this regard, the pump 6 does not require any lubricating fluid in order to operate . Referring back to Figure 1, the engine system 1 is arranged such that air from the pump 6 may be selectively provided to either the gas passing from the catalytic convertor 4 to the particulate filter 5 or to the exhaust gas passing from the internal combustion engine 2 to the catalytic convertor 4.

In this regard, the engine control unit 23 is also arranged to control the positions of the first and second valves 21, 22 between a first configuration and a second configuration.

In the first configuration (as shown in Figure 1), the first valve 21 is in its open position and the second valve 22 is in its closed position. In this configuration, the air from the pump 6 passes from the pump outlet 6b, along the first air conduit 19, to the conduit 17 that connects the catalytic convertor 4 to the particulate filter 5. Accordingly, the air is provided to the gas passing from the catalytic convertor 4 to the particulate filter 5.

This supply of air causes the exhaust gas in the conduit 17 to combust. This heats the exhaust gases such that, as they pass through the particulate filter 5, they heat the particulate filter 5 to a temperature that causes regeneration of the filter 5 by burning off particulates (e.g. soot) that have been deposited on the filter 5 (in the currently described embodiment this regeneration temperature would be in the range of 600°C to 700°C) .

In the first configuration the pump 6 is run at a speed in the range 3, 000 to 4, 000 rpm. It will be appreciated that, in other embodiments, the pump 6 may be run at a (low) speed that is outside this range, for example in the range 1, 000 to 7,000 rpm . In the second configuration, the first valve 21 is in its closed position and the second valve 22 is in its open position. In this configuration, the air from the pump 6 passes from the pump outlet 6b, along the second air conduit 20, to the engine outlet manifold 12.

This supply of air causes the exhaust gas passing from the internal combustion engine 2 to the catalytic convertor 4 to combust. This heats the exhaust gases such that, as they pass through the catalytic convertor 4, they heat the catalytic convertor 4 to its operating temperature of over 400 °C.

In use, the engine control unit 23 selectively controls the valves 21, 22 between the first configuration, when it is necessary to regenerate the particulate filter 5 and the second configuration when it is necessary to heat the catalytic convertor 4 to its operating temperature.

In a known arrangement a particulate filter is close coupled to a catalytic convertor (as stated above) . However in the described embodiment of the invention, the particulate filter 5 is remote from the catalytic convertor 4. In this regard, the particulate filter 5 is not close-coupled to the catalytic convertor 4 in that the combustion of the exhaust gas upstream of, or at, the catalytic convertor 4 does not act to regenerate the particulate filter 5. Locating the particulate filter 5 remote from the catalytic convertor 4 is advantageous in that it provides a more flexible configuration, than if the particulate filter 5 was close-coupled to the catalytic convertor 4, such that it can be tailored to specific space requirements. For example, the particulate filter 5 may be located external to an engine bay in which the engine 2 is mounted, thereby reducing the space taken up in the engine bay by the exhaust gas treatment system 1.

However, because the particulate filter 5 is remote from the catalytic convertor 4, any combustion of the exhaust gas upstream of the catalytic convertor 4, to heat the catalytic convertor 4 to its operating temperature (i.e. when the valves 21, 22 are in the second configuration), does not heat the particulate filter 5 to regenerate the filter 5.

The use of the pump 6 to provide air to the gas passing from the catalytic convertor 4 to the particulate filter 5, is advantageous in that it facilitates the combustion of the gas passing to the particulate filter 5, which heats the particulate filter 5 to provide regeneration of the filter 5 (as described above) .

A sliding vane pump 6 has been found to be particularly advantageous as it can be run at a relatively low speed (e.g. 1,000 to 7,000 rpm) , for example compared to a centrifugal pump, whilst still providing the required properties of flow of the air (including the required mass flow rate, pressure ratio and stall and surge points) that provide the necessary combustion of exhaust gas to regenerate the filter 5 (i.e. when the valves 21, 22 are in the first configuration) .

Accordingly it may be possible to drive the pump 6 using a motor (the electric motor 7) that has a relatively low operating speed. This allows the motor 7 to be relatively small, thereby further reducing the space taken up by the exhaust gas treatment system 1.

Therefore there is a synergy between positioning the particulate filter 5 remote from the catalytic convertor 4 and the use of the sliding vane pump 6 to supply air to the gas passing from the catalytic convertor 4 to the particulate filter 5, to combust the gas to regenerate the filter 5, as together they allow for a reduction in the space taken up by the exhaust gas treatment system 1, whilst still providing regeneration of the particulate filter 5.

It will be appreciated that features described in relation to one embodiment of the present invention may be incorporated into other embodiments of the present invention. For example, the method of treatment of exhaust gas described above may incorporate any of the features described with reference to the exhaust gas treatment system, or engine system, and vice-versa.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In the currently described embodiment, the positive displacement pump 6 is a sliding-vane pump. Other types of positive displacement pumps may be used. In this regard, rotary positive displacement pumps are particularly advantageous as they can be run at relatively slow speed whilst still providing the required properties of flow of the air .

Sliding vane pumps are particularly advantageous in that they can be run at relatively slow speed, whilst still providing the required properties of flow of the air, duty cycle and power consumption. In addition, a sliding vane pump has a relatively high efficiency. Also, it is relatively compact and produces relatively low noise and vibration, which is particularly desirable in an engine bay environment.

It will be appreciated that in the engine system 1, any suitable forced induction device (e.g. a supercharger) may be used in place of the turbocharger 25. Furthermore, the turbocharger 25 may be omitted where it is not necessary to provide forced induction.

The first and second valves 21, 22 may be replaced with a single valve arranged to direct the air from the pump outlet

6b to either the conduit 17 or to a fluid path from the engine outlet manifold 12 to the catalytic convertor 4.

The pump 6 may be arranged to only supply air to the conduit 17 between the catalytic convertor 4 and the particulate filter 5 and not to a fluid path from the engine outlet manifold 12 to the catalytic convertor 4, if it is not required to raise the temperature of the catalytic convertor 4. In this regard, the second air conduit 20 and the associated second valve 22 may be omitted. In the currently described embodiment the engine 2 is a diesel engine. However, any suitable type of internal combustion engine may be used, including a petrol engine. In this case, the catalytic convertor 4 and particulate filter 5 would be modified as appropriate (e.g. a petrol particulate filter would be used) so as to be suitable to treat the exhaust gas of the petrol engine. Furthermore, the engine 2 is not limited to a four cylinder, two-stroke engine and may have different numbers and arrangements of cylinders and different numbers of strokes per cycle (e.g. a four-stroke engine) . The internal combustion engine may be of any suitable injection type, including a multi-point injection engine or a direct injection engine.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

Claims

An exhaust gas treatment system for an internal combustion engine comprising: a catalytic convertor for receiving exhaust gas from an internal combustion engine; a particulate filter in fluid communication with an outlet of the catalytic convertor to receive exhaust gas from the catalytic convertor and to filter the gas; a pump and a motor arranged to drive the pump, wherein the particulate filter is remote from the catalytic convertor, and the pump is a positive displacement pump arranged to provide air to the gas passing from the catalytic convertor to the particulate filter to combust the gas such that the gas heats the particulate filter to provide regeneration of the filter.

An exhaust gas treatment system according to claim 1 wherein the positive displacement pump is a rotary positive displacement pump.

An exhaust gas treatment system according to claim 2 wherein the rotary positive displacement pump is a sliding vane pump .

An exhaust gas treatment system according to any preceding claim wherein the motor is an electric motor.

An exhaust gas treatment system according to claim 4 wherein the motor is a brushless electric motor.

6. An exhaust gas treatment system according to any preceding claim wherein the pump is a dry running pump.

7. An engine system comprising an internal combustion engine and an exhaust gas treatment system according to any preceding claim, wherein an inlet of the catalytic convertor is in fluid communication with an outlet of the internal combustion engine to receive exhaust gas from the internal combustion engine.

8. An engine system according to claim 7 wherein the pump is also arranged to provide air to the exhaust gas passing from the internal combustion engine to the catalytic convertor to combust the gas such that the gas heats the catalytic convertor .

9. An engine system according to claim 8 wherein the engine system is arranged such that air from the pump may be selectively provided to either the gas passing from the catalytic convertor to the particulate filter or to the exhaust gas passing from the internal combustion engine to the catalytic convertor.

10. A vehicle comprising an engine system according to any of claims 7 to 9.

11. A method of treatment of exhaust gas of an internal combustion engine of an engine system, the engine system comprising an internal combustion engine and an exhaust gas treatment system, the exhaust gas treatment system comprising : a catalytic convertor having an inlet in fluid communication with an outlet of the internal combustion engine to receive exhaust gas from the internal combustion engine; a particulate filter in fluid communication with an outlet of the catalytic convertor to receive exhaust gas from the catalytic convertor and to filter the gas; a pump and a motor arranged to drive the pump, wherein the particulate filter is remote from the catalytic convertor and the pump is a positive displacement pump, and wherein the method comprises providing air from the pump to the gas passing from the catalytic convertor to the particulate filter to combust the gas such that the gas heats the particulate filter to provide regeneration of the filter .

12. An exhaust gas treatment system substantially as described herein with reference to the Figures.

13. An engine system substantially as described herein with

reference to the Figures.

14. A vehicle substantially as described herein with reference to the Figures.

15. A method of treatment of exhaust gas of an internal

combustion engine substantially as described herein with reference to the Figures.