Control unit and control method for reductant supply device

Abstract

There are provided a reductant supply device and a control method for the reductant supply device, which can prevent heat damage of a reductant injection valve, and also prevent crystallization of urea solution due to excessive cooling of the solution reductant.The reductant supply device which is used in an exhaust gas purification device that injects and supplies, as a reductant, a urea solution to an exhaust gas upstream side of a reduction catalyst disposed in an exhaust gas passage of an internal combustion engine, and that reduces and purifies nitrogen oxides contained in exhaust gas using the reduction catalyst, the reductant supply device having a reductant injection valve that is fixed to an exhaust pipe on the exhaust gas upstream side of the reduction catalyst, includes: a cooling water circulation passage that circulates at least part of cooling water of the internal combustion engine to cool the reductant injection valve; flow rate control means for adjusting a flow rate of cooling water flowing through the cooling water circulation passage; temperature detection means for detecting a temperature of the reductant injection valve; and control means for controlling the flow rate control means based on the temperature of the reductant injection valve.

Description

TECHNICAL FIELD[0001]The present invention relates to a reductant supply device and a control method used in an exhaust gas purification device. Particularly, the present invention relates to a reductant supply device that uses a urea solution as a reductant and that cools a reductant injection valve by circulating cooling water for cooling an internal combustion engine, and a control method for the reductant supply device.BACKGROUND ART[0002]Generally, exhaust gas discharged from an internal combustion engine, such as a diesel engine, contains nitrogen oxides (hereinafter referred to as NOx) that may have an impact on the environment. As an exhaust gas purification device used to purify NOx, an exhaust gas purification device (an SCR system) is known which injects and supplies a liquid reductant, such as a urea solution, into exhaust gas on the upstream side of a reduction catalyst disposed in an exhaust gas passage, and which selectively reduces and purifies NOx using the reductio...

AI Technical Summary

Benefits of technology

[0017]According to the reductant supply device of the present invention, the reductant injection valve is cooled effectively by using the cooling water of the internal combustion engine. Further, while the temperature at the tip of the reductant injection valve is detected, the flow rate of the cooling water is adjusted in accordance with the detected temperature. As a result, it is possible to prevent excessive cooling of the reductant injection valve. Accordingly, heat damage of the reductant injection valve is prevented, and crystallization of urea in the vicinity of the reductant injection valve is prevented. Thus, stable atomization of the reductant is realized.

[0018]Further, in the reductant supply device of the present invention, the control means performs control such that the temperature of the reductant injection valve is maintained at a temperature lower than the heat resistance temperature. Thus, heat damage of the reductant injection valve is reliably prevented.

[0019]Further, in the reductant supply device of the present invention, the control means performs control such that the temperature of the reductant injection valve is maintained at a temperature equal to or higher than a boiling point of the urea solution. Thus, the urea solution that is exposed in the exhaust pipe is also rapidly vaporized due to exhaust heat, and crystallization of urea in the vicinity of the nozzle hole is reliably inhibited.

[0020]Further, in the reductant supply device of the present invention, the temperature detection means is means for calculating the temperature at the tip of the reductant injection valve. Therefore, it is possible to estimate the temperature at the tip of the reductant injection valve by using a known device structure, without using an additional temperature sensor.

[0021]Further, in the reductant supply device of the present invention, the cooling water of the internal combustion engine is used to adjust the temperature of the urea solution in the storage tank. Therefore, the urea solution having a temperature equal to or lower than the boiling point is inhibited from being injected without adjustment from the reductant injection valve. As a result, crystallization of urea in the vicinity of the nozzle hole is inhibited more reliably.

[0022]Moreover, according to the control method for the reductant supply device of the present invention, when the reductant injection valve is cooled by circulating the cooling water of the internal combustion engine, the circulation amount of the cooling water is adjusted based on the temperature of the reductant injection valve. Thus, heat damage of the reductant injection valve is prevented, and crystallization of urea due to excessive cooling of the reductant injection valve is prevented. Accordingly, stable atomization of the reductant is realized.

Problems solved by technology

In this type of exhaust gas purification device, if a urea solution is used as a liquid reductant and the temperature of the urea solution becomes excessively high, urea is hydrolyzed and crystallized before the urea solution is injected from the reductant injection valve.

As a result, there is a possibility that a supply system of the liquid reductant will be partially or completely clogged.

As a result, the electromagnetically controlled valve is likely to suffer from heat damage caused by heat being transferred from the exhaust pipe.

Images