GB2344087A - An engine and exhaust system combination - Google Patents

Abstract

An internal combustion engine having a turbocharger 219 in an exhaust system 212 which includes a catalytic converter 213 has an electrically heated gas jet 227 to inject gas into the exhaust system upstream of the turbocharger so the catalyst can be maintained at operational temperatures. Gas heated by the gas jet can be directed by a wastegate 226 through a bypass conduit 225 to help initial light-off of the converter. The engine can be used with a hybrid drive in which an electric traction motor can be utilised for regenerative braking, at least some of the electrical power used in the regenerative braking being utilised to power the heated gas jet. In an alternative arrangement a turbocharger 232 is provided downstream of the converter 213 in place of the turbocharger 219 and a second gas jet 231 is provided.

Description

AN ENGINE AND EXHAUST SYSTEM COMBINATION The present invention relates to an engine and exhaust system combination comprising an internal combustion engine having a turbocharger in an exhaust system which includes a catalytic converter, particularly, but not exclusively, for use in a motor vehicle in which the engine is associated with an electrical propulsion mechanism.

There is an on-going desire to reduce emissions of noxious gases of motor vehicles to improve environmental acceptability so that the catalytic converter is provided to convert any noxious gases or a sizeable proportion thereof to more acceptable or benign constituents. Unfortunately, such converters typically require elevated temperatures in order to be operational. Thus, when the engine is idling or only under partial load, the converter may not operate or not be efficiently operated. In such circumstances, vehicles with cold engines or which are operated over short term stop-start cycles may still emit significant proportions of noxious exhaust gases.

These problems are further exacerbated when a turbocharger is used to boost engine power. The turbocharger will inevitably absorb some energy, including heat energy, from the exhaust gas upstream of the converter with the result of delayed converter operation.

It is an objective of the present invention to provide an engine and exhaust system combination which substantially alleviates the above-mentioned problems.

In accordance with the present invention there is provided an engine and exhaust system combination comprising an internal combustion engine having a turbocharger in an exhaust system which includes a catalytic converter, the combination including gas compressing means to inject gas into the exhaust system upstream of the turbocharger and an electrical heater to heat the gas.

The combination may further comprise electrical propulsion means including an electrical traction motor which can be utilised for regenerative braking, at least some of the electrical power used in the regenerative braking being utilised to power the electrical heater.

Conveniently, the engine is coupled to an electrical generator and the electrical heater is arranged to disperse excess electrical energy produced by the engine to control the load on the engine.

The gas compressing means and the electric heater may be arranged to maintain the temperature of the catalytic converter for a time period after operation of the engine has been terminated.

In one arrangement of the combination the turbocharger is upstream of the catalytic converter. However, the turbocharger may be downstream of the catalytic converter, in which case the gas may be injected between the catalytic converter and the turbocharger. Also in such an arrangement, the or additional gas compressing means and the or an additional electrical heater may be provided to inject gas into the exhaust system upstream of the catalytic converter.

The invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of a known arrangement of an internal combustion engine coupled to an electrical propulsion mechanism in a series configuration; Fig. 2 is a schematic illustration of a known arrangement of an internal combustion engine coupled to an electrical propulsion mechanism in a parallel configuration; and Fig. 3 is a schematic illustration of an engine and exhaust system combination in accordance with the invention.

In Fig. l an engine 11, fitted with an exhaust system 12 including a catalytic converter 13, is arranged to drive an electrical generator 14 arranged in series with an electrical traction motor 15 coupled to a road wheel 16 in order to propel a vehicle. In this series hybrid arrangement, the generator 14 and the traction motor 15 are controlled by a control unit 17 such that a battery 18 can be recharged by operation of the engine 11 and so that, when required, the battery can supply some or all of the electrical power supplied to the motor. The exhaust system 12 includes a turbocharger 19 in order to provide enhanced power output for the engine 11.

In Fig. 2, an engine 111, fitted with an exhaust system 112 including a catalytic converter 113, is arranged to drive a vehicle road wheel 116 through a conventional mechanical change-speed transmission 121. An electric motor/generator 114 is driven by the transmission (or by the engine 111) and controlled by a control unit 117 to provide electrical power from a battery 118 to drive the road wheel 116, this drive being in parallel with the drive from the transmission, thereby supplementing or replacing the drive from the engine 111 in a parallel hybrid arrangement. Again, the engine 111 has a turbocharger 119 in order to provide enhanced power output.

Both the series (Fig. 1) and parallel (Fig. 2) hybrid configurations are known.

In addition to the engine recharging the battery 18,118 by the respective electrical generator 14 or motor/generator 114, additional recharging can be provided through regenerative braking whereby the motor 15 or motor/generator 114 acts as a generator to charge the respective battery rather than draw current for traction power.

In the design and operation of the exhaust system 12,112 there is a conflit between the requirements for turbocharger performance and catalytic converter performance. With regard to the turbocharger 19,119, in order to maximise supercharging performance and efficiency, it is necessary to extract as much energy as possible from the exhaust gas produced by the engine 11; 111.

Furthermore, as any engine 11,111 will have a wide operating range, typically the restrictions on turbine design are such that at low engine loads and speeds, the mass flow rate of exhaust gas will normally be below that for good turbine operation in the turbocharger 19,119 which in turn results in poor engine response. This poor response is known as the condition"turbo lag".

The noxious gas conversion rate of the catalytic converter 13,113 is to a large extent a function of the operating temperature of the catalyst. Normally, below a temperature of approximately 250 C there is minimum conversion of noxious gases and a normal operating temperature for a catalytic converter will be in the range 400-800 C for maximum efficiency and extended life. This problem of reaching and maintaining operational temperatures is exacerbated by the turbocharger 13, 113 which further diminishes the energy content of the exhaust gas and by the mass of the turbocharger acting as a heat sink in the initial period after a cold start or following engine idling.

Fig. 3 shows an engine and exhaust system combination which is particularly, but not exclusively, suitable for use with either of the hybrid arrangements shown in Figs. 1 and 2. A turbocharger 219 for an engine 211 is provided upstream of a catalytic converter 213 in an exhaust system 212. The turbocharger 219 may be bypassed by a bypass conduit 225 controlled by a wastegate 226. An electrically powered gas jet 227 is provided upstream of the turbocharger 219, the gas jet being electrically heated and propelled using an electric motor powered blower. and an electrical resistance heater element in the propelled flow of gas.

The converter 213 may be preheated by opening the wastegate 226 such that the hot gas is diverted through the conduit 225 to bypass the turbocharger 219 and so flow direct to heat the catalyst. However, once an appropriate operational temperature for the catalyst is detected by a temperature sensor 228, the wastegate 226 can be closed to divert flow to preheat the turbocharger turbine.

After the engine is started, the proportion of exhaust gas from the engine 211 and, more particularly, the powered gas jet 227 presented to the turbocharger 219 may be gradually increased as greater operational temperatures are reached in the catalytic converter 213.

To achieve maximum torque for the engine 211, the turbocharger 219 must be able to supply effective boost levels across the full range of engine operating conditions. By injecting a large quantity of gas through the propelled jet 227, rapid initial pressurisation of the turbocharger 219 can be achieved at low engine speeds. The volume and/or the temperature of the electrically powered gas jet 227 can be reduced as the available energy from the exhaust gas of the engine 211 builds up. Hence higher torques may be provided through a wider range of engine speeds than previously available, the electrically propelled gas jet 227 being used to supplement deficient mass flow rates of the exhaust gas at lower engine speeds.

By monitoring the turbocharger pressure and the engine load through engine management control, the temperature and, if required, the flow provided by the gas jet 227 can be adjusted to augment boost pressure to the turbocharger 47, particularly during engine load transients when the rotational inertia of the turbocharger 219 is also significant.

The electrically powered gas jet 227 may be used to equalise turbocharger boost over a wider range of engine speeds and also facilitate operational temperature maintenance of the catalytic converter 213 and for this the wastegate 226 can be under the control of a control system such that the proportions of electrically heated gas presented to the turbocharger 219 and through the bypass conduit 225 directly to the converter 213 can be varied in accordance with the required relative performance. In such circumstances, the temperature sensor 228 would act through the control system in order to control the wastegate 226 as necessary to achieve maintenance of an appropriate operational temperature within the catalyst.

Where a lambda sensor is used to determine proportioning of an air to fuel ratio for the engine 211, it will be appreciated that such sensors themselves require elevation to operational temperatures. Typically, the lambda sensor itself includes an internal heater to ensure that working temperature is rapidly achieved. The use of the heated gas jet 227 can obviate or reduce the need for such internal heaters.

In addition to depending solely upon the temperature sensor 228, the engine management system may be utilised to anticipate periods of low engine load or idle. The heated gas jet 227 can be highly responsive to engine load in order to ensure catalytic conversion efficiency is maintained by temperature regulation.

Furthermore, by such close monitoring of engine 31 load, the possibility of catalyst overheating within the exhaust arrangement 34 can be significantly diminished.

As an alternative to the arrangement described above with regard to Fig. 3, a variant could be to provide two electrically heated gas jets. Thus, in Fig. 3, the gas jet 227 could be immediately upstream of the converter 213 whilst a second gas jet 231 could be directed to a turbocharger 232 provided downstream of the converter in place of the turbocharger 219. In such an arrangement, the exhaust gas reaching the turbocharger 232 may be significantly cooler but loss of turbine performance may be compensated by the mass flow provided by the gas jets 227, 231. However, a lower turbine temperature can allow for simpler and cheaper materials to be used in construction of the turbocharger 232. The additional gas jet 231 is particularly appropriate if the catalyst temperature is to be maintained for a relatively long period of time. In any event, this arrangement can allow the turbocharger 232 to be designed to give a constant boost pressure from a substantially constant flow rate, i. e. principally provided by the second gas jet 231 which can be maintained independently of engine load and the requirements of the catalyst.

The arrangements described above with reference to Fig. 3 are particularly suited to the hybrid arrangements shown in Figs. l and 2 since these can readily provide the electrical energy required for the gas jets. Moreover, with regard to long downhill descents when the engine has a low load, there is the ability to generate electrical energy which can then be utilised to power the gas jets. Whilst this generated electrical energy will normally be absorbed and stored in the battery, it will be appreciated that once any battery is fully charged, any excess electrical energy must be dissipated to avoid use of the vehicle foundation brakes.

Thus, the electrically heated gas jets provides a further means for dissipation of this generated electrical energy whilst providing the benefits of better management of the catalyst operational temperature.

Although the electrically heated gas jets are mainly provided for use when the engine is operational, it will be appreciated that they may also be used to maintain catalyst temperature when the engine is idle or switched off for a time period. In order to limit the drain of electrical power, a time-out facility could be provided or the jets cut-off by a monitor of battery charge level.

Claims (10)

1. CLAIMS 1. An engine and exhaust system combination comprising an internal combustion engine having a turbocharger in an exhaust system which includes a catalytic converter, the combination including gas compressing means to inject gas into the exhaust system upstream of the turbocharger and an electrical heater to heat the gas.
2. 2. A combination as claimed in claim 1 and further comprising electrical propulsion means including an electrical traction motor which can be utilised for regenerative braking, at least some of the electrical power used in the regenerative braking being utilised to power the electrical heater.
3. 3. A combination as claimed in any preceding claim, wherein the engine is coupled to an electrical generator and the electrical heater is arranged to disperse excess electrical energy produced by the engine to control the load on the engine.
4. 4. A combination as claimed in any preceding claim wherein the gas compressing means and the electric heater are arranged to maintain the temperature of the catalytic converter for a time period after operation of the engine has been terminated.
5. 5. A combination as claimed in any preceding claim wherein the turbocharger is upstream of the catalytic converter.
6. 6. A combination as claimed in any of claims 1 to 4 wherein the turbocharger is downstream of the catalytic converter.
7. 7. A combination as claimed in claim 6 wherein the gas is injected between the catalytic converter and the turbocharger.
8. 8. A combination as claimed in claim 6 or claim 7 wherein the or additional gas compressing means and the or an additional electrical heater are provided to inject gas into the exhaust system upstream of the catalytic converter.
9. 9. An engine combination substantially as hereinbefore described with reference to the accompanying drawings.
10. 10. A motor vehicle including an engine combination as claimed in any preceding claim.