Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1999-03-08
2001-07-10
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S049700, C073S049200, C073S118040, C123S520000
Reexamination Certificate
active
06257050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for diagnosing leakage of evaporative fuel contained in a fuel tank and fed to an intake or induction system of an internal combustion engine.
2. Description of Related Art
For having better understanding of the concept underlying the present invention, technical background thereof will first be reviewed in some detail.
FIG. 19
is a schematic diagram showing a structure of a conventional evaporative fuel leak diagnosing apparatus for an internal combustion engine which is disclosed in Japanese Unexamined Patent Application Publication No. 159158/1994 (JP-A-6-159158). Referring to the figure, a fuel tank
1
contains an evaporative fuel
1
a
. A fuel pipe system
2
is disposed between the fuel tank
1
and an intake or induction manifold (not shown) of the internal combustion engine (not shown either). The fuel pipe system
2
is constituted by fuel pipes
2
a
,
2
b
and
2
c
disposed sequentially in this order as viewed from the side of the fuel tank. A check valve
7
is installed between the fuel pipes
2
a
and
2
b
, while installed between the fuel pipes
2
b
and
2
c
is a canister
3
for adsorbing fuel vapor. Further, a purge cut valve
4
is provided at the intake manifold side of the engine.
The canister
3
is provided with a drain cut valve
5
for allowing the canister
3
to be selectively communicated to the atmosphere. Additionally, a pressure sensor
6
is mounted on a blanch pipe
2
d
at a free end thereof. The purge cut valve
4
, the drain cut valve
5
and the pressure sensor
6
are electrically connected to a computer unit
50
installed for controlling operations of the internal combustion engine.
Next, description will turn to operations of the evaporative fuel leak diagnosing apparatus.
When the fuel vapor pressure exceeds a preset level at which the check valve
7
is forced to open, the fuel vapor generated within the fuel tank
1
is introduced into the canister
3
by way of the fuel pipe
2
a
, the check valve
7
and the fuel pipe
2
b
. The fuel vapor fed to the canister
3
is adsorbed by an adsorbent therein. When the engine is put into operation, the purge cut valve
4
is opened, whereby the fuel adsorbed is purged into the intake manifold of the engine by way of the fuel pipe
2
c
and the purge cut valve
4
. In this manner, fuel vapor generated within the fuel tank
1
ultimately undergoes combustion within the engine cylinders. With the evaporative fuel emission preventing arrangement described above, emission of the evaporative fuel to the atmosphere and hence environmental pollution due to the fuel vapor emission can be prevented.
The pressure sensor
6
is employed for detecting the pressure within the fuel tank
1
in the system-closed-state in which both the drain cut valve
5
and the purge cut valve
4
are closed. The detection signal outputted from the pressure sensor
6
is supplied to the computer unit
50
for detecting the leakage of the fuel vapor by checking whether the rate of pressure increase or rise within the fuel tank
1
exceeds or does not exceed a predetermined value
The pressure sensor
6
used to this end exhibits ordinarily such a linear characteristic as illustrated in FIG.
6
.
Needless to say, a fault or defect may occur in the pipes which are usually formed of rubber or the like or at juncture(s) between the pipes and/or parts constituting the evaporative fuel emission preventing apparatus. In that case, the fuel vapor will leak through the faulty or defective portion into the atmosphere. The pressure sensor
6
is provided for the purpose of detecting such leakage and emission of the fuel vapor.
Incidentally, according to the recommendation issued recently by the Environmental Protection Agency of the U.S.A., installation of such fuel vapor detection facility is required for checking whether or not the evaporative fuel emission preventing apparatus is operating normally.
As can readily be understood, the pressure sensor employed in the evaporative fuel leak diagnosing apparatus for the internal combustion engine is required to exhibit a high sensitivity. That is, the pressure sensor should be so designed as to be able to respond to a feeble or minute pressure change with a large output. To this end, a diaphragm constituting a sensing element of the pressure sensor is implemented in a reduced thickness with a large pressure receiving surface (or large diameter) to thereby ensure high sensitivity.
In this conjunction, it is however noted that the reduced thickness of the diaphragm serving as the sensor element involves deterioration in the linearity of the output characteristic of the pressure sensor. For this reason, in the conventional evaporative fuel leak diagnosing apparatus for the internal combustion engine known heretofore, hardwarewise measures are adopted to compensate for deterioration in the linearity of the output characteristic while taking into consideration the S/N ratio of the sensor output signal. Consequently, the conventional evaporative fuel leak diagnosing apparatus is very expensive. Besides, limitation is naturally encountered in the effort for increasing the sensitivity of the pressure sensor.
SUMMARY OF THE INVENTION
In the light of the state of the art described above, it is an object of the present invention to provide an evaporative fuel leak diagnosing apparatus for an internal combustion engine which can detect a pressure of concern with high accuracy and reliability in a structure implemented inexpensively, to thereby ensure high accuracy for the detection of leakage of the fuel vapor.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to an aspect of the present invention an evaporative fuel leak diagnosing apparatus for an internal combustion engine, which apparatus includes a pressure sensor means for detecting a pressure within a fuel tank containing an evaporative fuel to be supplied to the internal combustion engine through an intake manifold, a fuel tank seal-off means for isolating hermetically the fuel tank from the intake manifold and the atmosphere, and a computer means for fetching directly nonlinear output of the pressure sensor in a state where the fuel tank is hermetically isolated by the seal-off means, determining a pressure detection value indicative of a pressure level prevailing within the fuel tank on the basis of the non-linear output value obtained from the pressure sensor and data registered previously on the basis of the non-linear output values of the pressure sensor, and making decision as to leakage of the evaporative fuel on the basis of a rate at which the pressure detection value increases.
By virtue of the arrangement of the evaporative fuel leak diagnosing apparatus described above, the non-linear output of the pressure sensor can be made use of without need for correcting non-linearity thereof, whereby the external circuit(s). Required heretofore for the linearization processing can be spared. Besides, in designing the sensor element, no consideration needs to be paid for designing the sensor element so that it exhibits minimum possible linearity. Thus, the pressure sensor of high sensitivity can be used, whereby the evaporative fuel leak diagnosing apparatus for the internal combustion engine can be realized inexpensively while ensuring enhanced leakage detection accuracy.
In a preferred mode for carrying out the invention, a plurality of output values generated by the pressure sensor in response to a plurality of pressure values applied to the pressure sensor, respectively, may be registered in advance in the computer means for use the data to be referenced against. In that case, when a pressure value corresponding to any one of the plural registered computer means for use in evaluating the internal pressure corresponding to a noted output values is fetched from the output of the pressure sensor, the registered pressure value corresponding to the output value may
Nagano Susumu
Oakes Martin
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wiggins David J.
Williams Hezron
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