Patent Application
20080041841
The present invention will be explained in detail with reference to the accompanying drawings below.
An exhaust pipe 14 is connected to an exhaust manifold 12 of an engine 10. The following members are disposed in the exhaust pipe 14 along a flowing direction of exhaust gas, i.e., an oxidation catalytic converter 16 for oxidizing nitric oxide (NO) into nitrogen dioxide (NO2), an injection nozzle 18 for injecting and supplying a necessary amount of urea aqueous solution suitable for an operation state of an engine, a NOx reduction catalytic converter 20 for reducing and purifying NOx by ammonia obtained by hydrolyzing the urea aqueous solution, and an ammonia oxidation catalytic converter 22 for oxidizing ammonia which has passed through the NOx reduction catalytic converter 20. The urea aqueous solution stored in a storage tank 24 is supplied to the injection nozzle 18 through a heater-attached piping 26 and a reducing agent supply device 28 in a mist state in which the urea aqueous solution is mixed with air. Excessive portion of the urea aqueous solution supplied to the reducing agent supply device 28 is returned into the storage tank 24 through a heater-attached piping 30. Here, the reason why the storage tank 24 and the reducing agent supply device 28 are connected to each other through the heater-attached pipings 26 and 30 is that the freezing point (ice point) of the urea aqueous solution is about −11° C. (about 262K), and when a vehicle runs on, for example, an area under cold climates or the cold latitudes, there might occur such an adverse possibility that urea aqueous solution supplied to the reducing agent supply device 28 from the storage tank 24 is frozen on its way to the reducing agent supply device 28 and as a result, NOx purifying ability might not be provided or be deteriorated due to lack of a reducing agent. It is preferable that the heater-attached piping 26 and 30 are controlled such that their heaters are appropriately operated in accordance with e.g., the outside temperature or the temperature in the storage tank 24.
A control unit 32 incorporating a computer is provided as a control system of the exhaust gas purification device. The control unit 32 controls an injection supply amount of the urea aqueous solution in accordance with the operation state of the engine. In the control unit 32, the reducing agent supply device 28 is controlled by a control program stored in a ROM (Read Only Memory) based on a signal from a rotating speed sensor 34 which detects engine rotating speed Ne and a load sensor 36 which detects engine load Q. As the engine load Q, it is possible to utilize a fuel injection amount, an inlet flow, an inlet negative pressure, an accelerator opening, a throttle valve opening and the like.
In such an exhaust gas purification device, the urea aqueous solution injected and supplied from the injection nozzle 18 is hydrolyzed by exhaust gas heat and water vapor in the exhaust gas, and ammonia is generated therefrom. It is known that the generated ammonia reacts with NOx in the exhaust gas, in the NOx reduction catalytic converter 20, and the ammonia is purified into water and harmless gas. To enhance the NOx purifying rate by the NOx reduction catalytic converter 20, NO is oxidized into NO2 by the oxidation catalytic converter 16, and the rate between NO and NO2 in the exhaust gas is improved to a rate suitable for the catalytic reduction reaction. The ammonia having passed through the NOx reduction catalytic converter 20 is oxidized by the ammonia oxidation catalytic converter 22 disposed downstream of exhaust gas, and thus, it is possible to prevent ammonia from being discharged into atmosphere.
As shown in
Terminal heat-retaining materials 54 are disposed around both ends of the nylon tube 38 as a heat-retaining layer made of substantially cylindrical silicon sponge or the like, instead of the heat-retaining layer 46, the vapor barrier 48 and the protecting cover 50 which are peeled off when a connector 52 as a mating device is connected. The terminal heat-retaining material 54 is coated with a heat-shrinkable tube 56 over substantially entire length thereof. A predetermined length portion of the cord-like heater 40, which is located between the nylon tube 38 and the terminal heat-retaining material 54, is arranged such that the heat-generative cord is disposed in a duplicated fashion to partially enable a duplicate amount of heat generation. More specifically, a predetermined length L of the end of the cord-like heater 40 is folded back as shown in
With this configuration, since the cord-like heater 40 is formed into the two-ply arrangement at the ends of the heater-attached pipings 26 and 30, heat generation is increased by about two times at that portion when the same amount of current is supplied, power consumption of the cord-like heater 40 is suppressed to a possible lowest limit, and the heat-retaining ability and defrosting ability at the end can be enhanced. If the predetermined length L to be formed into the two-ply arrangement is appropriately set in accordance with the heater capacity of the cord-like heater 40 and supplied current, it is possible to exhibit substantially equal heat-retaining ability and defrosting ability over substantially the entire length of the heater-attached piping, and it is possible to effectively retain heat and unfreeze the urea aqueous solution transferred through the piping comprised of the nylon tube 38.
Next, an explanation will be provided as to a procedure for connecting the connector 52 provided as an example of the mating device to the end of the heater-attached piping whose end is left cut, and the heat-equalizing layer 44, the heat-retaining layer 46, the vapor barrier 48 and the protecting cover 50 are sequentially disposed around the cord-like heater 40 and the lead wire 42 disposed along substantially the entire length of the nylon tube 38.
First, the protecting cover 50, the vapor barrier 48, the heat-retaining layer 46 and the heat-equalizing layer 44 are slit at appropriate positions from the end of the heater-attached piping, they are peeled off from the end as shown in
Accordingly, the protecting cover 50, the vapor barrier 48, the heat-retaining layer 46 and the heat-equalizing layer 44 which are located at the end are peeled off, the connector 52 is connected to the heater-attached piping, the cord-like heater 40 is formed into the duplex structure, the terminal heat-retaining material 54 is mounted, and its periphery is coated with the heat-shrinkable tube 56. These series of operations are sequentially carried out, and the heater-attached piping is connected to the mating device. Thus, it becomes easy to realize the heater-attached piping of the present invention using the general heater-attached piping, and producing cost can be reduced.
The heater-attached piping of the present invention is not limited to the exhaust gas purification device provided in a vehicle, and can be applied to water supply equipment and a gas analyzer in cold climate, of course.
