Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2000-08-31
2002-02-26
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S518000, C123S519000
Reexamination Certificate
active
06349707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for regenerating an activated carbon filter or carbon canister charged with hydrocarbons.
Because of the vapor pressure, gaseous fuel is constantly also present in the gas tank of a motor vehicle in addition to liquid fuel. Since the tank must have a vent opening for pressure balance, hydrocarbons would constantly escape into the atmosphere by vaporization of fuel. This effect increases with the temperature of the fuel. Such hydrocarbon emissions can be avoided by using activated carbon filters, i.e., carbon canisters, which are connected into the vent line and adsorb vaporized hydrocarbons from the tank. The system is required in order to fulfill the statutory conditions for vaporization losses.
The tank is therefore vented only via an activated carbon filter. Because of the restricted take-up volume of the activated carbon, the activated carbon filter or the activated carbon located therein must be regenerated. For this purpose, while the internal combustion engine is running, air is sucked in from the environment over the activated carbon filter, fed into the intake tract via a regeneration line and fed in this way to the internal combustion engine for combustion. In this process, the underpressure in the intake tract is utilized to aspirate in the air via the regeneration line. In order, in the process, to keep the exhaust emissions within desired limits, and not to have a negative influence on the running properties of the internal combustion engine, the air sucked in through the activated carbon filter and enriched with hydrocarbons must be introduced specifically into the intake tract of the internal combustion engine, and the normally fed fuel quantity must be adapted, for example by an injection correction.
It has become known from commonly assigned U.S. Pat. No. 5,988,151 (German patent DE 197 01 353 C1) to achieve this injection correction by means of the lambda control which is present in any case in an internal combustion engine which is equipped with a 3-way catalytic converter.
For this purpose, a control system drives a regeneration valve which is switched into the regeneration line. By suitably opening the regeneration valve it is possible to adjust the purging flow, which is sucked through the activated carbon filter and introduced into the intake tract. Here, the purging flow is a function of the opening cross section which the regeneration valve uncovers, the pressure difference between the intake tract and environment, and the temperature of the purging flow.
The purging flow is therefore adjusted by suitably driving the regeneration valve with the aid of values supported by a characteristic diagram.
There is a difficulty, in this case, however that this correction of the fuel quantity depends on the mass flow, introduced into the intake tract by the regeneration, of hydrocarbons, which is substantially influenced by the purging flow. It is therefore necessary to know the position of the regeneration valve. Because of this, there is a need for a regeneration valve which can be adjusted very exactly and preferably permits an indication of position.
However, such valves are relatively expensive. Moreover, particularly in the case of small opening cross sections the error between desired and actual values becomes relatively large. For that reason, no generation has yet been possible according to the prior art, for example during idling, in the case of which the regeneration valve would have to be virtually completely closed because of the high underpressure in the intake tract (see, Kraftfahrtechnisches Taschenbuch [Manual of Automotive Technology], 22nd ed., VDI-Verlag, 1995, page 477).
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for regenerating an activated carbon filter charged with hydrocarbons which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which satisfies the requirement for precision made of the regeneration valve, and with the aid of which regeneration can be carried out particularly during idling.
With the above and other objects in view there is provided, in accordance with the invention, a method for regenerating an activated carbon filter connected, on one hand, to ambient air and, on the other hand, via an adjustable regeneration valve, to an intake tract of an internal combustion engine, between the internal combustion engine and an adjustable throttle member in the intake tract. The method comprises the following steps, which are performed during an idling of the internal combustion engine:
adjusting the regeneration valve to a setting remote from a minimum opening;
concurrently opening the throttle member from a position assigned to idling, for reducing an underpressure in the intake tract; and
building a torque reserve by control intervention on the internal combustion engine, for maintaining an idling speed of the internal combustion engine constant despite the opening of the throttle member.
According to the invention, the regeneration is performed during idling of the internal combustion engine. In this case, the throttle member is opened from the closed position, in order to reduce the underpressure, i.e., the vacuum, in the intake tract. The internal combustion engine simultaneously thereby sucks in a higher air mass flow. Of course, a higher mass flow of hydrocarbons can also be introduced into this air mass flow, for which reason the regeneration valve can be opened further. Consequently, the regeneration valve is in a position remote from the minimum opening, in which even cost-effective regeneration valves are sufficiently accurate. In a preferred refinement of the invention, even a simple two-position valve suffices.
The idling controller builds up a torque reserve in order to prevent the idling speed of the internal combustion engine from rising owing to the opening of the throttle valve. In this case, a torque reserve is understood as a set of measures which act to reduce the torque output by the internal combustion engine, with the overall result that the speed remains constant. A known measure for building up such a torque reserve is, for example, varying the ignition angle.
The time required to regenerate the activated carbon filter is reduced by the increased purging flow through the regeneration valve. Moreover, the fuel quantity can be adapted more exactly through the higher accuracy of the regeneration valve in the larger opening region.
In accordance with an added feature of the invention, the torque reserve is built up with at least one of the following control interventions: adjusting the ignition angle, increasing the exhaust gas recirculation rate, varying the lambda value, and cylinder shutdown.
In accordance with an additional feature of the invention, a loading of the activated carbon filter with hydrocarbons is determined and the loading is expressed in a degree of loading, and the torque reserve is built up in dependence on the degree of loading.
In accordance with another feature of the invention, the regeneration valve is repeatedly opened and closed at a given clock rate.
In accordance with a further feature of the invention, the throttle member is opened ever wider during the regeneration of the activated carbon filter for increasing a purging flow.
In accordance with a concomitant feature of the invention, the regeneration valve is opened ever wider during the regeneration of the activated carbon filter for increasing the purging flow.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for regenerating an activated carbon filter loaded with hydrocarbons, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range
Neumann Klaus
Schneider Stefan
Greenberg Laurence A.
Lerner Herbert L.
Mohanty Bibhu
Siemens Aktiengesellschaft
Stemer Werner H.
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