Automotive engine with controlled exhaust temperature and oxygen concentration

[0002] The field of the present invention is that of automotive engines, particularly low emission turbo-charged diesel engines and methods of operation thereof. The diesel engine arrangement of the present invention has particular application in small diesel engines used to power passenger cars, sport utility vehicles and pickup trucks.

[0003] Emission-after-treatment devices, such as particulate filters, oxidation catalysts and NOx catalysts, require certain conditions in the engine exhaust in order to perform optimally. In particular, NOx catalysts have a relatively narrow temperature window within which the conversion efficiency is sufficiently high. Diesel particulate filters require sufficient oxygen in order to maintain regeneration at high engine loads. Prior to the present invention, the required exhaust gas conditions could not always be achieved during normal operation of the engine. In particular, at high engine loads, it was difficult if not impossible to provide sufficiently high levels of oxygen required by the particulate filter. Also the exhaust gas temperature could only be influenced to a certain degree by the combustion system.

[0004] The present invention entails an engine arrangement with a bypass from a turbocharger compressor outlet directly into the exhaust system downstream of a turbocharger turbine. An electrically or pneumatically actuated control valve controls the flow of air through the bypass. The bypass is preferably used in conjunction with an actively controlled wastegate or a variable geometry turbocharger. The bypass allows for the introduction of the relatively cool air into the exhaust that leads to a reduction of the exhaust gas temperature and increased oxygen concentration. In combination with an actively controlled wastegate or a variable geometry turbocharger, the present invention allows for simultaneous control of oxygen content, exhaust temperature and boost pressure at relatively low cost. For engines equipped with a NOx catalyst, the invention enables control of the exhaust gas temperature so as to stay within the narrow temperature window with high catalyst conversion efficiency. For engines equipped with a particulate filter, the invention enables control of the exhaust gas oxygen content so as to supply sufficient oxygen to the filter during a regeneration event.

[0005] These and other features and advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.

[0006] FIG. 1 is a schematic view of a prior art turbo-charged diesel engine arrangement.

[0007] FIG. 2 is a schematic view of a preferred embodiment of a diesel engine arrangement according to the present invention.

[0008] FIG. 3 is an illustration of a simulation of high engine load operation of the diesel engine shown schematically in FIG. 1 demonstrating the relationships between wastegate valve position, exhaust oxygen concentration, fuel consumption and exhaust gas temperature.

[0009] FIG. 4 is an illustration of a simulation of high engine load operation of the diesel engine arrangement according to the present invention shown in FIG. 2 demonstrating relationships between bypass valve and wastegate valve position, exhaust oxygen concentration, fuel consumption, and exhaust gas temperature.

[0010] FIG. 5 is a partial schematic view similar to that of FIG. 2 illustrating an alternative preferred embodiment of the diesel engine arrangement of the present invention.

[0011] FIG. 1 schematically represents a prior internal combustion engine arrangement 6, having an engine block 10. The engine block 10 has a plurality of cylindrical work and combustion chambers 12. Reciprocally mounted to each chamber 12 is a piston (not shown). The chambers 12 by appropriate valving (not shown) are fluidly connected with a first compressed air inlet passage 14. The inlet passage 14 is fluidly connected with an outlet 16 of a turbocharger compressor 18.

[0012] To allow for the delivery of exhaust gas from the chambers 12 via appropriate valving (not shown), there is a second passage 26. The second passage 26 is also fluidly connected with an inlet 28 of a turbocharger turbine 24. An outlet 29 of the turbine 24 is fluidly connected with a third passage 30. The third passage 30 is fluidly connected with a particulate filter 34, an oxidation catalyst 40 and a NOx catalyst 44. Prior to passing through the oxidation catalyst 40 the exhaust will be exposed to an exhaust temperature sensor 48 and an exhaust oxygen concentration sensor 50. To allow for the recirculation of exhaust from the second passage 26 into the first passage 14 there is provided an EGR bypass passage 52. Controlling the flow of exhaust through the EGR bypass passage 52 is an EGR valve 54. The engine arrangement 6 additionally has a wastegate bypass passage 56. A wastegate valve 58 controls the exhaust flow between the second passage 26 and the third passage 30. The wastegate valve 58 accordingly controls the amount of exhaust gas that flows through the inlet 28 of the turbine 24.

[0013] Referring to FIG. 2, an automotive vehicle internal combustion diesel engine arrangement 7 is shown according to the present invention. Like items are given reference numbers similar to those shown in FIG. 1. The engine arrangement 7 additionally has a first bypass passage 70. The bypass passage 70 connects the first passage 14 with the third passage 30 bypassing both the engine block 10 and the turbine 24. The connection of the bypass passage 70 with the first passage 14 is located upstream of the connection of the EGR bypass passage 52 with the first passage 14. To control the flow of air through the bypass passage 70 there is a control value 72. Control valve 72 can be electrically or pneumatically actuated. Typically the connection of the bypass passage 70 with the third passage 30 will be upstream of the connection of the wastegate passage 56 with the third passage 30. The bypass passage 70 allows the introduction of fresh air into the third passage 30 to increase the levels of oxygen in the exhaust. Additionally, the introduction of relatively cold air into the exhaust leads to a lowering of the exhaust gas temperature. The control value 72 can be operated to provide a desired temperature in the third passage 30 in response to the difference between the measured temperature in the third passage 30 (downstream of any mixing point) and a desired exhaust gas temperature. Simultaneously or alternatively the control valve 72 can be operated in response to the measured oxygen concentration (downstream of any mixing point) in the third passage 30 to provide a desired oxygen concentration. An advantage of the diesel engine arrangement 7 is that the operation of the valve 72 provides for simultaneous control of the oxygen content exhaust temperature and boost pressure at relatively low cost. The bypass passage 70 also functions as a wastegate to prevent over-boosting at high engine loads. Since the pressure at the compressor outlet 16 is generally considerably higher than the turbine outlet 29 pressure, appropriate sizing of the bypass passage 70 can insure that there is always sufficient flow of fresh air into the exhaust stream within the third passage 30. The control valve 72 is placed in the clean fresh air environment instead of in an exhaust cooling loop as the EGR valve 54 and is not exposed to contamination and hot exhaust fumes.

[0014] Referring to FIG. 3, a simulation of high engine load (200 Nm) of engine arrangement 6 with wastegate control only, is presented. The wastegate valve 58 is used to keep the boost pressure below a specified level of 160 kPa. The first or top graph of FIG. 3 illustrates the wastegate valve 58 position between closed (0) and totally open (1) positions. The second graph of FIG. 3 illustrates the oxygen concentration in the exhaust as measured by the oxygen concentration sensor 50. The third graph of FIG. 3 shows fuel consumption in kilograms per hour. The fourth or lowest graph of FIG. 3 shows the exhaust temperature measured by the sensor 48.

[0015] Referring to the simulation shown in FIG. 4 (of the current invention shown in FIG. 2) and comparing it to the simulation of FIG. 3, it is evident that the exhaust gas temperature is significantly lowered. As shown in FIG. 4, the oxygen concentration is increased while there is virtually no fuel consumption penalty. Utilizing other control strategies, the temperature and exhaust oxygen concentration can be controlled to different levels than those illustrated.

[0016] In an alternative embodiment of the present invention (not shown), oxygen concentration is not measured at all. The control valve 72 is controlled in an open-loop fashion using predetermined maps that define oxygen concentration.

[0017] Referring to FIG. 5, an embodiment 107 of the present invention is provided with a variable geometry turbocharger 122. The use of the variable geometry turbocharger can optionally eliminate the wastegate bypass passage 56 and valve 58 to achieve results essentially similar to those explained for the embodiments of the present invention illustrated in FIGS. 2 and 4.

[0018] While the invention has been particularly shown and described with reference to preferred embodiments thereof, it is well understood by those skilled in the art that various changes and modifications can be made in the invention without departing from the spirit and the scope of the invention.