U.S. patent number 3,913,545 [Application Number 05/347,959] was granted by the patent office on 1975-10-21 for evaporative emission system.
This patent grant is currently assigned to Ford Motor Company. Invention is credited to Lawrence H. Haase, David R. Liimatta.
United States Patent |
3,913,545 |
Haase , et al. |
October 21, 1975 |
Evaporative emission system
Abstract
A fuel vapor recovery system for the adsorption, storage and
eventual recycling of vapors to an engine. The system has a
vapor-storage canister containing activated carbon for adsorbing
fuel vapors from various parts of the engine fuel system. The
system selectively purges the fuel vapors for introduction to the
engine intake manifold. The purging is controlled in response to
engine loading and engine speed for improved engine operation.
Inventors: |
Haase; Lawrence H. (Belleville,
MI), Liimatta; David R. (Livonia, MI) |
Assignee: |
Ford Motor Company (Dearborn,
MI)
|
Family
ID: |
23366037 |
Appl.
No.: |
05/347,959 |
Filed: |
April 4, 1973 |
Current U.S.
Class: |
123/520 |
Current CPC
Class: |
F02M
25/0836 (20130101) |
Current International
Class: |
F02M
25/08 (20060101); F02M 025/08 () |
Field of
Search: |
;123/136,121
;60/285,301 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Argenbright; Tony
Attorney, Agent or Firm: Malleck; Joseph W. Zerschling;
Keith L.
Claims
We claim:
1. In an internal combustion engine having a fuel system, an intake
manifold and a carburetor with a throttle to provide a gaseous
mixture engine flow, an apparatus for controlling the recovery of
fuel vapors in said system, comprising:
a. means for adsorbing and storing said fuel vapors,
b. a passage for purging said stored fuel vapors and for conveying
said vapors to said intake manifold,
c. a first control means responsive to vacuum upstream from said
throttle for maintaining said passage in either a fully opened or a
fully closed condition, said passage having internal walls defining
an aperture between said first control means and said means for
absorbing vapors and through which flow must pass in said passage,
and
d. a second control means responsive to vacuum in said intake
manifold for regulating the aperture of said passage whereby said
storing means is desorbed at a rate inversely proportional to
engine flow.
2. An apparatus as in claim 1, in which said second control means
comprises a valve biased to a minimum aperture condition and
progressively opened in opposition to said bias by an increase in
intake manifold vacuum.
3. An apparatus as in claim 2, in which said second means is
actuated in response to PCV port vacuum.
4. The apparatus as in claim 1, which further comprises, in
combination with said apparatus, an engine exhaust system having a
catalytic converter and means calibrated to vary in response to
predetermined air/fuel mixtures, said second control means being
effective to regulate desorption of fuel vapors from said storing
means in such amounts as to maintain said calibrated means in a
condition to provide an air/fuel mixture at least above 14/1
whereby the amount of carbon monoxide in said exhaust gas system is
maintained in a predetermined range compatible for operation of
said catalytic converter.
Description
BACKGROUND OF THE INVENTION
In an effort to reduce hydrocarbon emissions from the fuel system,
various evaporative loss control devices have been proposed, which
typically comprise a canister filled with suitable adsorbent
material, such as activated charcoal. The carbon adsorbs the
hydrocarbon vapors when the engine is not in operation; when the
engine is operative, means are provided to effect desorption or
purging of the vapors from the adsorbent material so that these
vapors can be fed to combustion chambers of the engine for
consumption therein. During engine operation, the running vapor
losses from both the fuel tank and carburetor bowl are being
consumed as they are generated. This approach has worked
successfully to reduce hydrocarbon emissions to the atmosphere, but
under certain engine operating conditions, the introduction of both
the stored and currently generated hydrocarbon vapors for
consumption in the engine affects engine operation or causes an
increase in the exhaust emission of unburned hydrocarbons. On other
occasions, only the stored vapors may cause an over rich air/fuel
mixture during the initial portion of the purged cycle. The latter
can result in such a rich mixture that engine performance becomes
irregular and poor (i.e., hesitation and stumble affecting
drivability) and most importantly the carbon monoxide content of
the exhaust is increased.
Although the prior vapor emission systems have been concerned with
the need for a controlled purge of hydrocarbon vapors to avoid some
of the above problems, the attempts have not been entirely
successful. For example, there has been proposed a system which
would have two adsorption beds connected in series to each other.
Upon purging, the series connected adsorbent beds are unloaded
sequentially thereby resulting in some degree of modulated
release.
Another approach is the use of a canister bypass for providing a
variable purge rate. The canister bypass attempts to smooth out the
air/fuel ratio since the amount of air going ultimately through the
throat of the carburetor will be constant, while the amount of air
going through the adsorbent material increases or decreases in the
response to the amount of air bypassing the adsorbent. In this
manner, a controlled amount of purged fuel vapors may be obtained
to some degree.
SUMMARY OF THE INVENTION
It is a primary object of this invention to provide an improved
apparatus and method for a fuel vapor recovery system; purging of
the system is controlled so that overrichness is avoided in the
mixture receiving the recovered vapors and thereby avoid momentary
sag or poor engine performance.
Still another object of this invention is to provide a means of
controlling the return of excess fuel vapors to the combustion
cycle of the engine in such a manner that the carburetor air-fuel
ratio is maintained at least above 14/1, thus avoiding a
significant change in the combustion products of the engine, such
as carbon monoxide. This becomes significant particularly with
respect to total auto emission controls which may employ a
catalytic converter to reduce unwanted gaseous constituents of the
exhaust; in many cases the catalytic converter requires a
controlled feed (within a limited range) of carbon monoxide as part
of the exhaust being introduced to the catalytic converter.
SUMMARY OF THE DRAWING
The FIGURE is a schematic illustration of various components
comprising an evaporative emission control system. There is shown
in cross-section a storage canister for fuel vapors as well as
first and second purge control means and a typical carburetor used
with a conventional internal combustion engine.
DETAILED DESCRIPTION
Referring now to the drawing, there is illustrated a fuel vapor
recovery system adapted for recovering fuel vapors which may
collect in the carburetor fuel bowl or the vehicle fuel tank. In
general, the recovery system comprises a canister A containing a
bed of adsorption material in the form of activated carbon, a
passage B communicating the interior of said canister with the
intake manifold C of an internal combustion engine D at a location
downstream of throttle 11. The recovery system further comprises a
first control means E employed to completely shut off or completely
open the passage B in response to a vacuum signal received from a
location 9 upstream from the throttle 11 of carburetor 12, but
downstream from the venturi restriction 13 of the carburetor; this
location is commonly referred to as the spark port. A second
control means F is employed to operate in series with said first
control means and is effective to modulate the flow of fuel vapors
through said passage in response to the magnitude of the vacuum
received from location 10, thereby controlling the aperture through
a portion of passage B.
The canister may typically comprise a container 14 having the bed
of adsorption material 15 substantially filling said container,
except for an air space 16 defined by a screen 20 at the bottom
thereof; a fresh air intake 17 is arranged to admit air to said
space 16 during a purging phase of the system. Fuel vapors are
conveyed to the canister at the top thereof by way of a conduit 18
leading from a vehicle fuel storage tank and a conduit 19 leading
from the carburetor fuel bowl. Thus, during inoperative conditions
of the engine or hot soak cycles, fuel vapors are released and
adsorbed by the adsorption bed 15, the passage B being closed
thereby maintaining atmospheric pressure therein suitable to
prevent an induced air flow through 17 but receptive to admit
vapors from conduits 18 and 19.
To purge the canister of collected vapors, passage B is placed in
communication with a vacuum obtained at location 10 in the intake
manifold immediately below the throttle of the carburetor (this
location is commonly referred to as the PCV port). The passage B is
maintained closed when purging is not desired by the first control
means E. Means E comprises a valve housing 26 having a boring or
channel 22, one end 22a of the channel serving as the inlet for
vacuum; a cross bore 21 intersects with boring 22. Passage B is
interrupted by means E so that one break in passage B becomes the
inlet at 22a and the other break in passage B becomes the outlet
for the vacuum through cross-bore 21. A valve 24 (urged by spring
29) is adapted to normally close off the connection between bore 21
and boring 22 by seating against surface 27. Valve 24 is attached
to a diaphragm 28 residing in chamber 23; the diaphragm is actuated
by a vacuum signal in conduit 25. The vacuum signal is taken at
location 9 (commonly referred to as the spark port) and the vacuum
here is relatively non-existent at idle or wide-open-throttle
conditions. Thus, passage B will be prepared to purge only during
intermediate engine loading conditions.
To further modulate the flow of vapors during purging, control
means F is employed to vary the aperture of passage B. Means F
comprises a valve housing 30 defining an interior valve seat 31
which is progressively closed, but never completely, by a spring
biased valve element 32 acting in response to intake manifold
vacuum in passage B thereby to vary the spacing between element 32
and the seat 31. Means F functions to allow more flow through, the
lower the vacuum pressure; the latter vacuum force purges the
vapors and acts proportionate to engine loading. There is a slight
bleed through means F even in its most restricted position when
vacuum pressure is the highest. Thus, the flow is not preprogrammed
independent of engine operation.
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