Catalytic converter heating

Abstract

The rate at which a catalytic converter heats up to its normal operating temperature range, (e.g., during a start up phase) is increased by applying an external load to an internal combustion engine. Applying the external load causes the engine to generate more heat, which can be used to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

Description

BACKGROUND OF THE INVENTION

A significant proportion of the emissions from a modern automotive internal combustion engine occurs during the first few minutes of engine operation following a cold start. This is due to the catalytic converter not being able to function correctly until it achieves “light off”; that is, until it has reached its working temperature.

A catalytic converter can be very effective at reducing unwanted exhaust emissions when it is operating at its working temperature. However, until a catalytic converter reaches its working temperature, it is working inefficiently at best. As a result, untreated exhaust gas can exit the end of the exhaust or tail pipe. In the first two to three minutes of warm-up following a cold start, about 60% to 80% of exhaust or tail pipe emissions occur.

The regulatory authorities are imposing ever more strict emission regulations. In order to provide an effective reduction in exhaust emissions, it is therefore desirable to cause the catalytic converter to reach its working temperature as quickly as possible.

Various approaches have been employed to reduce the time that it takes a catalytic converter to reach its working temperature. One approach is to move the catalytic converter as close to the exhaust port as possible. Another approach is to provide electrical and/or flame heaters for catalytic converters. A further approach is to provide an exhaust gas combustion system. Yet a further approach is to provide a mechanism to retain the heat in a catalytic converter between engine operations. All of these approaches involve expensive modifications to an existing engine system and/or exhaust system and/or provide packaging challenges.

Other engine based approaches include providing precise fueling control, providing controlled ignition retarding, providing secondary air injection, using high starting engine speed and providing changes to the catalyst physics. These approaches include various disadvantages including a less enjoyable driving experience (e.g. due to increased noise), reductions in performance, complexity, combustion instability and cost.

Accordingly, there is still a need for an effective solution to reduce the time it takes for a catalytic converter to reach its working temperature.

BRIEF SUMMARY OF THE INVENTION

The invention may be embodied in a method of operating an engine system that includes an internal combustion engine operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass, and a control system. In an example embodiment, when the control system determines that the internal combustion engine is in a phase in which the catalytic converter is below its working temperature, it causes an external load to be applied to the internal combustion engine. By applying an external load, the engine generates more heat, which can be used to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

The invention may also be embodied in an engine system that includes an internal combustion engine operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass, and a control system. The control system, in response to a determination that the internal combustion engine is in a phase in which the catalytic converter is below its working temperature, can cause an external load to be applied to the internal combustion engine. A motor vehicle can be provided with such an engine system.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a chart illustrating an example of emissions during phases of operation of an engine system;

FIG. 2 is a chart illustrating accumulated emissions during operation of an engine system;

FIG. 3 is a schematic representation of a motor vehicle including an engine system;

FIG. 4 is a schematic representation of an engine system;

FIG. 5 is a schematic representation of the operation of an engine system in normal running;

FIG. 6 is a chart showing various parameters of the engine system during normal running;

FIG. 7 is a schematic representation of the operation of a prior art engine system in a start up phase;

FIG. 8 is a chart showing various parameters of the prior art engine system of FIG. 7 in a start up phase;

FIG. 9 is a schematic representation of the operation of an example engine system in accordance with the invention in a start up phase;

FIG. 10 is a chart showing various parameters of the example engine system of FIG. 9 in a start up phase;

FIG. 11 is an example of an engine system in accordance with the invention in which an external load is applied through a torque converter;

FIG. 12 is an example of an engine system in accordance with the invention in which an external load is applied through a crankshaft brake;

FIG. 13 is a chart comparing an example of catalytic converter temperatures over time;

FIG. 14 is a chart illustrating an example of an improvement in the increase of catalytic converter temperature over time; and

FIG. 15 is a chart showing various parameters of an engine system and consequent reduction in total fuel consumption in an example embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An example embodiment of the invention seeks to increase the rate at which a catalytic converter heats up to its normal operating temperature range by applying an external load to an internal combustion engine when the catalytic converter is below its working temperature, in order to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

Examples of phases of operation of an internal combustion engine in which a catalytic converter may be below a desired operating temperature range can include a start up phase, after a water splash or immersion in water, and in the case of a hybrid vehicle, during a phase in which power is taken from batteries rather than the internal combustion engine. The external load can be applied in different ways as will become apparent from the following description.

FIG. 1 is a chart illustrating an example of emissions during phases of operation of an engine system that includes an internal combustion engine. More specifically, FIG. 1 illustrates an example of the emissions of an internal combustion engine, for example a gasoline engine, over time from a cold start. As can be seen in FIG. 1, in the circled phase after start up, high emissions are seen.

FIG. 2 represents the accumulated emissions of gases such as hydrocarbons (HC), nitrogen oxides (NO_x) and carbon dioxide (CO₂). It can be seen from the charts in FIGS. 1 and 2 that a significant proportion of the undesired emissions occur during the early start up phase. This is the phase before the catalytic converter has heated up to its normal operating temperature range and in which the catalytic converter is ineffective or at least less effective that optimum. The time that the catalytic converter takes to get up to its normal operating temperature range is often called the “light off time”.

FIG. 3 is a schematic representation of a motor vehicle 10 including an engine system 12 according to an example embodiment of the invention. In FIG. 3 the motor vehicle is an automobile and the engine system includes an internal combustion engine 14 with a drive train 16 driving the driven wheels 18. In the present example, the vehicle 10 has rear wheel drive. However, it will be appreciated that in other examples front wheel drive or all wheel drive can be provided. In the present example the drive train 16 is understood to include the transmission 20. The transmission 20 in the present example is an automatic transmission with a torque converter, although in other examples a manual transmission or an electronically controlled manual transmission could be provided.

FIG. 4 is a schematic representation of an example of an engine system 12 in more detail. As shown in FIG. 4, the internal combustion engine 14 is provided with an air intake system 22 and an exhaust system 24 including an exhaust pipe or tail pipe 23. The exhaust system 24 includes a catalytic converter 25 for processing the exhaust gases. A control system 26 includes an engine management controller 28 that is responsive to various sensors, including one or more lambda probes 30, one or more catalytic converter temperature sensors 32, and one or more ambient temperature sensors 34, one or more crankshaft sensors 36, etc. In an example embodiment, the control system is also operable to control the automatic transmission 20, braking systems (not shown in FIG. 4) and other systems as well as controlling engine parameters such as ignition timing, fuel injection timings and so on.

FIG. 5 is a schematic representation of the operation of an engine system during normal running. FIG. 5 represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48.

FIG. 6 is a chart that represents, schematically, for the engine system of FIG. 5, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during normal running. It will be appreciated that FIG. 6 represents these conditions in a steady state situation. It will also be appreciated that in normal use, these parameters can be changed, for example during acceleration, deceleration, etc.

FIG. 7 is a schematic representation of the operation of a prior art engine system during a start up phase. FIG. 7 represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48.

FIG. 8 is a chart that represents, schematically, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during an example of operation of the prior art engine system of FIG. 7 during a start up phase. FIG. 8 illustrates that at an activation point, various parameters are changed. Specifically, it will be noted that after ignition (where the ignition trace drops) the throttle is increased, which also increases the engine speed and engine load caused by internal engine factors such as friction, etc. As a result, heat flux to the catalytic converter increases to start to heat the catalytic converter. Once again, it will be appreciated that FIG. 8 is schematic and is for illustrative purposes only.

FIG. 9 is a schematic representation of the operation of an example embodiment of an engine system in accordance with the invention during a start up phase. FIG. 9 represents, schematically, the internal combustion engine 14, the engine output shaft 42 (e.g. the crankshaft, an extension thereof, or a further shaft driven by the crankshaft), the transmission 20, including a torque converter 44 and a gearbox 46 (or in the case of a manual transmission, a clutch 44 and a gearbox 46), and a transmission drive shaft 48. FIG. 9 also illustrates, schematically, the application of an external load to the engine output shaft 42, symbolized by hand 50. It will be appreciated that the representation of a hand 50 in FIG. 9 is merely to illustrate the effect of applying an external load in accordance with example embodiments of the present invention. In practice the load is not provided by a hand, but rather by technical features of the engine system and/or the motor vehicle, as described in greater detail below.

FIG. 10 is a chart that represents, schematically, the conditions of various parameters including engine load, ignition retard, engine speed, throttle, external load and heat flux to the catalyst during an example of operation of the engine system of FIG. 9 during a start up phase. FIG. 10 illustrates that at an activation point, various parameters are changed. Specifically, it will be noted that after ignition (where the ignition trace drops) the throttle is increased by a greater amount than in the prior art example of FIG. 8, although the engine speed only increases by the same amount as in the prior art example of FIG. 8. This is because an external load is applied (see the lower circled portion in FIG. 10), which means than the overall engine load is increased more (see the upper circled portion in FIG. 10) than in the prior art example of FIG. 8. This is turn means that there is a greater heat flux to the catalytic converter (see the lower circled portion in FIG. 10) than in the prior art example of FIG. 8. Once again, it will be appreciated that FIG. 10 is schematic and is for illustrative purposes only. However, a comparison of FIGS. 8 and 10 can illustrate the effect of applying the external load to increase the heat flux to the catalytic converter and hence to reduce the light off time for the catalytic converter.

The external load can be applied until the catalytic converter has reached a predetermined temperature, for example a minimum efficient operating temperature, for a predetermined time, or a combination thereof (for example until it reaches the predetermined temperature or until a predetermined time has elapsed, which ever occurs first). As will be seen in FIG. 14 later, a significant benefit can be realized though the use of the applied external load within the first ten seconds of operation. Accordingly, the external load could be applied merely for a predetermined period, for example twenty seconds, or ten seconds, or five seconds. The choice of a particular duration of the load can also be dependent upon the amount of the loading that is applied. In general, the higher the loading, the shorter the time, although the loading should not be set such that it exerts excessive strain on the engine during the start up phase.

FIG. 11 is an example of an engine system in which an external load is applied through a torque converter. More specifically, FIG. 11 is a schematic representation of a front engined, rear wheel drive vehicle where drive from the engine 14 is supplied via an automatic transmission 20 that includes a torque converter 44 and gears 46 to a drive shaft 48. The drive shaft 48 is then connected via a differential 52 and secondary drive shafts 54 to the rear wheels 18. In the example shown in FIG. 8, an electrically operated parking brake 60 is provided that is used when the vehicle is stationary.

In operation of the engine system shown in FIG. 11, the control system 26 is operable to detect the activation point illustrated in FIG. 10 following ignition. This can be detected, for example, when ignition is achieved following a cold start of the engine or a start when the catalytic converter is below its normal operating range of temperatures. The control system 26 is then operable automatically to engage a driven gear (either forward or reverse) while at the same time engaging the parking brake. The brake 60 could be configured as a friction brake member that engages a secondary drive shaft 54. In the present example, an electrically operated friction brake is used, although in other examples other forms of operation could be used. Also, the brake could be in the form of a visco-mechanical coupling, an eddy current brake, a regenerative braking system, or indeed any other suitable form of brake that can apply a controllable braking force. This has the effect of the holding the torque converter still via the drive train. This in turn causes an external load to be applied to the engine over an above the normal loading caused by internal friction, etc., which means that the engine generates more heat for a given engine speed. The control system 26 can be operable to maintain the engine speed at a desired level to give smooth running under load by applying an appropriate amount of throttle. The result of applying the additional external load is that the light off time for the catalytic converter can be reduced compared to a prior art engine where an external load is not applied. Alternatively, the additional external load can enable the same amount of heating compared to a prior art engine where an external load is not applied, but at a reduced engine speed. A further advantage of proving the external load via the gearbox is that also reaches a normal operating temperature more quickly, reducing consumption due to reduced frictional losses.

FIG. 12 is an example of an engine system in which an external load is applied through an engine output shaft brake. More specifically, FIG. 12 is a schematic representation of a front engined, rear wheel drive vehicle where drive from the engine 14 is supplied via a manual transmission 20 that includes a clutch 45 and gears 46 to a drive shaft 48. Although a manual transmission is shown in FIG. 12, an automatic transmission could be provided instead. The drive shaft 48 is then connected via a differential 52 and secondary drive shafts 54 to the rear wheels 18. In the example shown in FIG. 12, the engine output shaft that connects the engine to the clutch 45 is provided with an electrically operated engine output shaft brake 62. The brake could be located outside of the engine casing, or it could be included within the engine casing and could act, for example, on a crankshaft of the engine.

In operation of the engine system shown in FIG. 12, the control system 26 is operable to detect the activation point illustrated in FIG. 10 following ignition. This can be detected, for example, when ignition is achieved following a cold start of the engine or a start when the catalytic converter is below its normal operating range of temperatures. The control system 26 is then operable automatically to apply a braking force to the engine output shaft using the engine output shaft brake 62. The brake force that is applied is set such that it is not sufficient to stop the engine from turning over, but is merely enough to apply an external loading to the output shaft. The brake 62 could be configured as a friction brake member that engages the output shaft. In the present example an electrically operated friction brake is used, although in other examples other forms of operation could be used. Also, the brake could be in the form of a visco-mechanical coupling, an eddy current brake, or indeed any other suitable form of brake that can apply a controllable braking force. This effect of the applied braking force is to cause an external load to be applied to the engine over an above the normal loading caused by internal friction, etc., which means that the engine generates more heat for a given engine speed. The control system 26 can be operable to maintain the engine speed at a desired level to give smooth running under load by applying an appropriate amount of throttle. The result of applying the additional external load is that the light off time for the catalytic converter can be reduced compared to a prior art engine where an external load is not applied. Alternatively, the additional external load can enable the same amount of heating compared to a prior art engine where an external load is not applied, but at a reduced engine speed.

FIG. 13 is a chart comparing an example of catalytic converter temperatures over time with and without the application of an external load. The upper curve 70 illustrates the heating of the catalytic converter with the externally applied load and the lower curve 72 illustrates the heating of the catalytic converter without the externally applied load.

FIG. 14 is a chart illustrating an example of an improvement in the increase of catalytic converter temperature over time. FIG. 14 illustrates the surprising result that within the first ten seconds of the order of a 50% to 100% improvement in the increase in temperature can be achieved with the use of the external load compared to not applying the external load.

FIG. 15 illustrates various parameters of an engine system and an example of a reduction in total fuel consumption, or at least re-gain of the extra fuel used during the initial catalytic heating phase during later phases of operation of the internal combustion engine. More specifically, as illustrated by the schematic accumulated fuel consumption chart of FIG. 15, initially fuel consumption could be slightly higher due to the application of an external load, although not necessarily since the prior art mode needs rich to run stable. However, as illustrated, the accumulated fuel consumption is possibly improved (reduced) or at least the initially higher consumption is re-gained due to rapid coolant and gear box heating, as schematically shown, which reduces the total friction loss, as also schematically shown. The initially higher consumption is depicted in the circled area in the left of the accumulated fuel consumption chart whereas the improved/reduced fuel consumption is illustrated in the circled section in the right of the accumulated fuel consumption chart.

Thus there has been described a method and apparatus that can increase the rate at which a catalytic converter heats up to its normal operating temperature range by applying an external load to an internal combustion engine during a phase in which a catalytic converter is below a desired operating temperature range. Applying the external load generates more heat that can be used to reduce the time that it takes to bring the catalytic converter up to its working temperature. As a result, a reduction in emissions can be achieved.

Example embodiments can be applied to vehicles having drive trains with manual and with automatic transmissions.

In one example with an automatic transmission having a torque converter, a drive mode is engaged with the torque converter immobilized. In one example the torque converter can be immobilized by applying a parking brake, for example an electrically operated parking brake. In other examples, the torque converter could be immobilized in other ways, for example by incorporating an additional brake in the gearbox, or by applying the vehicle's hydraulic braking system. As a further example, the braking could be applied using a regenerative braking system, for example in a hybrid vehicle. Through the use of a regenerative braking system, electrical energy could be generated and stored, for example in a battery or fuel cell, while still providing the advantage of the additional loading and more rapid catalytic converter heating.

Another example that can be used with manual and automatic transmissions uses an engine output shaft brake that is used to apply an external load to the engine output shaft, for example to the crankshaft of the engine. The external load in the form of a braking force can be applied in different ways; for example using an electrically controlled crankshaft or engine output shaft brake, a visco-mechanical coupling, etc.

In the above description, reference has been made to engine systems having manual transmissions and automatic transmissions with a torque converter. It will be appreciated that embodiments of the invention could be applied to other engine systems having other transmissions systems, for example a continuous variable transmission (CVT).

The external load can be applied using different approaches including, by way of example only, hydraulic braking systems, electrically operated braking systems, adaptive cruise control systems, regenerative braking systems, visco mechanical couplings, etc.

An embodiment of the invention can be operable to provide the external load during a phase of operation of the internal combustion engine when the catalytic converter is below its normal operating temperature range. Such phases of operation can include, by way of example only, a start up phase (e.g., following a cold start), a restart phase (e.g., following a temporary stop in traffic), a post-splash phase (e.g., following splashing or immersion of the catalytic converter in water), an electric drive phase (e.g., in operation of a hybrid vehicle when drive is powered by a battery rather than the internal combustion engine).

Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications as well as their equivalents. Thus, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method of operating an engine system, the engine system including an internal combustion engine that is operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass and a control system, the method comprising: determining whether the internal combustion engine is in a phase in which the catalytic converter is below its working temperature; and causing an external load to be applied to the internal combustion engine when the internal combustion engine is in a phase in which the catalytic converter is below its working temperature.

2. The method of claim 1, wherein the external load is applied to the drive train.

3. The method of claim 2, wherein the drive train includes an automatic transmission having a torque converter and wherein to apply said external load, the control system is operable to engage a drive mode with the torque converter immobilized.

4. The method of claim 3, wherein to immobilize the torque converter, the control system is operable to apply a parking brake.

5. The method of claim 4, wherein the parking brake is controlled electrically.

6. The method of claim 1, wherein the control system causes an external load to be applied to an engine output shaft.

7. The method of claim 6, wherein the engine output shaft is a crankshaft of the engine and wherein the control system causes a braking force to be applied to the crankshaft.

8. The method of claim 7, wherein the braking force is applied by an electrically controlled crankshaft brake.

9. The method of claim 7, wherein the braking force is applied by a visco-mechanical coupling.

10. The method of claim 1, wherein the external load is applied for a predetermined period.

11. The method of claim 1, wherein the external load is applied until the catalytic converter reaches a predetermined temperature.

12. An engine system comprising:

an internal combustion engine that is operable to apply drive to a drive train,

a catalytic converter through which exhaust gases from the internal combustion engine pass, and

a control system, wherein the control system is operable to determine when the internal combustion engine is in a phase in which the catalytic converter is below its working temperature; and to cause an external load to be applied to the internal combustion engine.

13. The engine system of claim 12, wherein the control system is operable to cause the external load to be applied to the drive train.

14. The engine system of claim 13, wherein the drive train includes an automatic transmission having a torque converter, and wherein the control system, in order to apply external load, is operable to engage a drive mode of the transmission and to immobilise the torque converter.

15. The engine system of claim 14, wherein the control system, in order to immobilise the torque converter, is operable to apply a parking brake.

16. The engine system of claim 15, wherein the parking brake is controlled electrically.

17. The engine system of claim 12, wherein the control system is operable to cause an external load to be applied to an engine output shaft.

18. The engine system of claim 17, wherein the engine output shaft is a crankshaft of the engine, and wherein the control system, is operable to cause a braking force to be applied to the crankshaft.

19. The engine system of claim 18, comprising an electrically controlled crankshaft brake for applying the braking force.

20. The engine system of claim 18, comprising a visco-mechanical coupling for applying the braking force.

21. A motor vehicle comprising an engine system, the engine system comprising an internal combustion engine that is operable to apply drive to a drive train, a catalytic converter through which exhaust gases from the internal combustion engine pass, and a control system, the control system being operable to determine when the internal combustion engine is in a phase in which the catalytic converter is below its working temperature; and to cause an external load to be applied to the internal combustion engine.