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Control device for diesel engineControl device for diesel engine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090107430, Control device for diesel engine. Brief Patent Description - Full Patent Description - Patent Application Claims
1. Field of the Invention This invention relates to a control device for a diesel engine, specifically, a control device for a diesel engine equipped with a valve timing switching mechanism capable of changing opening/closing timing for an exhaust valve of the engine, and an exhaust after-treatment device having a function of purifying exhaust gas of the engine. 2. Description of the Related Art A NOx catalyst for reducing NOx (nitrogen oxides) in exhaust gas of a diesel engine to purify the exhaust gas, a particulate filter for trapping particulate in exhaust gas to purify the exhaust gas, etc. have been conventionally used as exhaust after-treatment devices. In recent years, for example an ammonia selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) is used as a NOx catalyst. In an exhaust after-treatment device including an SCR catalyst, urea-water is supplied to upstream of the SCR catalyst, and ammonia produced as a result of the hydrolyzation of urea-water caused by heat from exhaust gas is supplied to the SCR catalyst. The SRC catalyst adsorbs the ammonia supplied to the SCR catalyst, and the SCR catalyst promotes denitrifying reaction between ammonia and NOx in the exhaust gas. The NOx is reduced in this manner. The SCR catalyst does not satisfactorily perform such exhaust purifying function until the temperature of exhaust gas flowing into the SCR catalyst rises to at least a level at which the SCR catalyst is activated. However, when the engine is cold, exhaust gas discharged from the engine is at low temperature, and an exhaust pipe, a pre-stage oxidizing catalyst, a particulate filter, etc. placed upstream of the SCR catalyst have not warmed enough. Thus, heat transfers from exhaust gas to these members, so that the exhaust flowing into the SCR catalyst has a greatly decreased temperature. Such decrease in exhaust temperature may prevent the SCR catalyst from performing the above-mentioned exhaust purifying function satisfactorily. Problems caused by decrease in exhaust temperature are observed not only in SCR catalyst. Similar problems are observed in a variety of catalysts and a particulate filter used as exhaust after-treatment devices. Specifically, in a catalyst used as exhaust after-treatment device, decreased exhaust temperature does not allow activation of the catalyst, therefore does not allow the catalyst to perform the catalytic function satisfactorily. In a particulate filter, decreased exhaust temperature makes continuous regeneration difficult and allows accumulation of particulate in the particulate filter, which results in decline of particulate trapping function. In order to solve the problems caused by decrease in exhaust temperature as mentioned above, Unexamined Japanese Patent Publication Hei 10-68332 (hereinafter referred to as Document 1) has proposed a valve timing control device designed to raise exhaust temperature by changing opening/closing timing for exhaust valves of the engine, when the engine is cold. The control device of Document 1 uses a mechanism which can vary the opening/closing timing for exhaust valves by changing the phase of an exhaust cam shaft relative to a crank shaft. When the engine is at low temperature, the opening/closing timing for the exhaust valves is advanced by a predetermined crank angle. This intends to encourage the discharge of combustion heat from cylinders to the exhaust device side, thereby causing a catalyst and the like to be activated early by the combustion heat. In the control device of Document 1, however, by changing the phase of the exhaust cam shaft relative to the crank shaft, the opening/closing timing for each exhaust valve is varied, while the period of time for which each exhaust valve is open remains unchanged. Thus, as a result of advancing the timing of start of opening of the exhaust valve, the timing of completion of closing of the exhaust valve is advanced before top dead center of exhaust stroke, so that the exhaust valve closes before the associated intake valve is opened. Consequently, when the exhaust valve closes, gases remaining in the cylinder is compressed again, and when the intake valve is opened after that, the remaining gases thus compressed are discharged through an intake port. This hinders fresh air from being sucked into the cylinder through the intake port, thereby causing a decrease in air excess ratio. This leads to problems such as production of a large amount of black smoke, and emission of HC (hydrocarbon) into the atmosphere. Further, the control device of Document 1 changes the phase of the exhaust cam shaft relative to the crank shaft by supplying oil pressure. When the engine is cold, a working oil supplied is also at low temperature and therefore high in viscosity. Thus, a phase change mechanism cannot be controlled stably until the working oil warms to some extent and decreases in viscosity. Thus, it is conceivable to configure the control device of Document 1 to maintain the exhaust valve opening/closing timing at the most advanced setting, while the working oil is at low temperature. In this case, however, if the engine comes to operate under a high load before the working oil temperature rises enough, the exhaust valve opening/closing timing is maintained at the most advanced setting for a while, since the working oil cannot be discharged smoothly. Consequently, the above-mentioned reduction in the fresh air sucked into the cylinder continues. Although the reduction in fresh air, to which combustion heat is transferred, results in a rise in exhaust temperature, great reduction in fresh air may lead to a large amount of black smoke produced by incomplete combustion and an excessive rise in exhaust temperature. An aspect of the present invention is directed to a control device for a diesel engine, comprising: a valve timing switching mechanism capable of selectively switching between first opening/closing timing and second opening/closing timing for an exhaust valve of the diesel engine; an exhaust after-treatment device for purifying exhaust gas discharged from the diesel engine; and a control means for controlling the valve timing switching mechanism so that the exhaust valve is opened and closed according to the first opening/closing timing, at least when the diesel engine is operating in a predetermined cold condition, wherein the first opening/closing timing is set such that the period for which the exhaust valve is open overlaps the period for which an intake valve associated with the same cylinder that the exhaust valve is associated with is open, and that opening start timing for the exhaust valve is after bottom dead center of expansion stroke of a piston in the cylinder, and the second opening/closing timing is set such that opening start timing for the exhaust valve is advanced compared with the opening start timing according to the first opening/closing timing. The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: Continue reading about Control device for diesel engine... Full patent description for Control device for diesel engine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Control device for diesel engine patent application. Patent Applications in related categories: 20090283062 - Actuator with self-locking helical gears for a continuously variable valve lift system - A CVVL system including a self-locking helical gear pair with, optionally, a transmission to increase output torque of the actuator. The self-locking helical gear pair provides high forward efficiency and a fully mechanically self-locking feature. 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