U.S. patent application number 13/159046 was filed with the patent office on 2011-12-22 for ventilation system and method for supercharge engine.
This patent application is currently assigned to MAHLE FILTER SYSTEMS JAPAN CORPORATION. Invention is credited to Akihiro Kobayashi, Terumoto Mochizuki.
Application Number | 20110308504 13/159046 |
Document ID | / |
Family ID | 44584888 |
Filed Date | 2011-12-22 |
United States Patent
Application |
20110308504 |
Kind Code |
A1 |
Kobayashi; Akihiro ; et
al. |
December 22, 2011 |
VENTILATION SYSTEM AND METHOD FOR SUPERCHARGE ENGINE
Abstract
In ventilation system and method for a supercharge engine, in a
middle load driving region of the engine in which the boost
pressure of position of an intake air passage located at the
downstream side with respect to a throttle valve is positive and is
lower than a set pressure (P1), with importance placed on the
ventilation of a crank chamber, a relatively large quantity of
fresh air is introduced into the crank chamber and, on the other
hand, in a high load driving region in which the boost pressure is
equal to or higher than the set pressure (P1), with importance
placed on the engine output, the large quantity of fresh air is
supplied to the engine so that, while the deterioration of engine
oil within the crank chamber suppressed, the output reduction of
the engine in the high load driving region can be suppressed.
Inventors: |
Kobayashi; Akihiro;
(Niza-shi, JP) ; Mochizuki; Terumoto; (Iruma-gun,
JP) |
Assignee: |
MAHLE FILTER SYSTEMS JAPAN
CORPORATION
|
Family ID: |
44584888 |
Appl. No.: |
13/159046 |
Filed: |
June 13, 2011 |
Current U.S.
Class: |
123/574 |
Current CPC
Class: |
F01M 2013/0044 20130101;
F01M 2013/027 20130101; F01M 13/00 20130101 |
Class at
Publication: |
123/574 |
International
Class: |
F01M 13/04 20060101
F01M013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2010 |
JP |
2010-137849 |
Dec 22, 2010 |
JP |
2010-285450 |
Claims
1. A ventilation system for a supercharge engine, comprising: a
blowby gas reduction passage provided for communicating position of
an intake air passage of the engine which is located at a
downstream side with respect to a throttle valve with a crank
chamber of the engine; a fresh air introduction passage provided
for communicating position of the intake air passage which is
located at an upstream side with respect to the throttle valve and
the crank chamber; a PCV valve provided in the blowby gas reduction
passage for controlling a flow quantity of blowby gas directed
toward the intake air passage side in a case where a boost pressure
at position of intake air passage located at downstream side with
respect to the throttle valve indicates negative; and a fresh air
flow quantity control section configured to operatively introduce
fresh air into the crank chamber from position of intake air
passage which is located at the downstream side with respect to the
throttle valve in a case where the boost pressure at position of
the intake air passage which is located at the downstream side with
respect to the throttle valve is positive, wherein the fresh air
flow quantity control section is configured to introduce fresh air
into the crank chamber, in a middle load driving region in which
the boost pressure at position of the intake air passage which is
located at the downstream side with respect to the throttle valve
is positive and the boost pressure is lower than a set pressure,
and, in a high load driving region in which the boost pressure at
part of the intake air passage which is located at the downstream
side with respect to the throttle valve is equal to or higher than
the set pressure, is configured to stop an introduction of fresh
air from position of the intake air passage which is located at a
downstream side with respect to the throttle valve or is configured
to make a flow quantity of introduced fresh air at least smaller
than a maximum flow quantity in the middle load driving region.
2. The ventilation system for the supercharge engine as claimed in
claim 1, wherein a variable orifice functioning as the fresh air
flow quantity control section is installed in the blowby gas
reduction passage and, in the high load driving region, a flow
passage cross sectional area of the variable orifice which
functions as the fresh air flow quantity control section is at
least made smaller than the flow passage cross sectional area in
the middle load driving region.
3. The ventilation system for the supercharge engine as claimed in
claim 2, wherein the PCV valve includes a variable orifice
functioning as the fresh air flow quantity control section apart
from another variable orifice for a blowby gas flow quantity
control that the PCV valve naturally has.
4. The engine ventilation system as claimed in claim 1, wherein a
variable orifice functioning as the fresh air flow quantity control
section is juxtaposed to the PCV valve and, in the high load
driving region, a flow passage cross sectional area of the variable
orifice is made smaller than at least the flow passage cross
sectional area in the middle load driving region.
5. The engine ventilation system as claimed in claim 2, wherein the
variable orifice functioning as the fresh air flow quantity control
section is closed in the high load driving region.
6. The ventilation system for the supercharge engine as claimed in
claim 1, wherein a flow quantity of fresh air from position of the
intake air passage which is located at the downstream side with
respect to the throttle valve to the crank chamber, in the middle
load driving region (A2), is constant and, in the high load driving
region (A3), the flow quantity of fresh air from position of the
intake air passage which is located at the downstream side with
respect to the throttle valve is made equal to the flow quantity in
the middle load driving region.
7. A ventilation system for a supercharge engine, comprising:
blowby gas reduction passage means for communicating position of an
intake air passage of the engine which is located at a downstream
side with respect to a throttle valve with a crank chamber of the
engine; fresh air introduction passage means for communicating
position of the intake air passage which is located at an upstream
side with respect to the throttle valve and the crank chamber; PCV
valve means provided in the blowby gas reduction passage means for
controlling a flow quantity of blowby gas directed toward the
intake air passage side in a case where a boost pressure at
position of intake air passage located at downstream side with
respect to the throttle valve indicates negative; and fresh air
flow quantity control means for operatively introducing fresh air
into the crank chamber from position of intake air passage which is
located at the downstream side with respect to the throttle valve
in a case where the boost pressure at position of the intake air
passage which is located at the downstream side with respect to the
throttle valve is positive, wherein the fresh air flow quantity
control means introduces fresh air into the crank chamber, in a
middle load driving region in which the boost pressure at position
of the intake air passage which is located at the downstream side
with respect to the throttle valve is positive and the boost
pressure is lower than a set pressure, and, in a high load driving
region in which the boost pressure at part of the intake air
passage which is located at the downstream side with respect to the
throttle valve is equal to or higher than the set pressure, stops
an introduction of fresh air from position of the intake air
passage which is located at a downstream side with respect to the
throttle valve or makes a flow quantity of introduced fresh air at
least smaller than a maximum flow quantity in the middle load
driving region.
8. A ventilation method for a supercharge engine, comprising:
providing a blowby gas reduction passage for communicating position
of an intake air passage of the engine which is located at a
downstream side with respect to a throttle valve with a crank
chamber of the engine; providing a fresh air introduction passage
provided for communicating position of the intake air passage which
is located at an upstream side with respect to the throttle valve
and the crank chamber; providing a PCV valve in the blowby gas
reduction passage for controlling a flow quantity of blowby gas
directed toward the intake air passage side in a case where a boost
pressure at position of intake air passage located at downstream
side with respect to the throttle valve indicates negative; and
providing fresh air flow quantity control means for operatively
introducing fresh air into the crank chamber from position of
intake air passage which is located at the downstream side with
respect to the throttle valve in a case where the boost pressure at
position of the intake air passage which is located at the
downstream side with respect to the throttle valve is positive,
wherein fresh air is introduced into the crank chamber through
fresh air flow quantity control means, in a middle load driving
region in which the boost pressure at position of the intake air
passage which is located at the downstream side with respect to the
throttle valve is positive and the boost pressure is lower than a
set pressure, and, in a high load driving region in which the boost
pressure at part of the intake air passage which is located at the
downstream side with respect to the throttle valve is equal to or
higher than the set pressure, an introduction of fresh air from
position of the intake air passage which is located at a downstream
side with respect to the throttle valve is stopped or a flow
quantity of introduced fresh air is at least made smaller than a
maximum flow quantity in the middle load driving region.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] The present invention relates to ventilation system and
method for a supercharge engine having a turbocharger and
particularly relates to a PCV system (a positive crankcase
ventilation system) constituting a part of a blowby gas processing
system.
[0003] (2) Description of Related Art
[0004] A Japanese Patent Application First Publication (tokkai) No.
2007-016664 published on Jan. 25, 2007 exemplifies a first
previously proposed PCV system in a natural aspiration type engine
or non-supercharge type engine includes: a blowby gas reduction
passage which communicates between a downstream side position of an
intake air passage (intake manifold) with respect to a throttle
valve and a crank chamber (or a crankcase) of the engine; a fresh
air introduction passage which communicates between an upstream
side of the intake manifold with respect to the throttle valve and
the above-described crankcase (crank chamber); and a PCV valve
installed on the above-described blowby gas reduction passage.
[0005] In the first previously proposed engine ventilation system,
at a time of a high load of the engine, when a negative pressure
occurs within an inside of the engine due to an action of the PCV
valve, fresh air is introduced within the crank case (crank
chamber) via the fresh air introduction passage and, at the same
time, blowby gas is mixed with fresh air within the crank case.
Then, the mixed air is introduced at position of intake air passage
located at the downstream side with respect to the throttle valve
via the PCV valve. In this way, the crankcase is ventilated so that
a deterioration of engine oil within the crank case is
suppressed.
[0006] On the other hand, at a time of a high load of the engine,
the negative pressure within the intake manifold becomes reduced
(approaches to the positive pressure) and the quantity of blowby
gas exhausted via the PCV valve becomes less than the quantity of
blowby gas generated from the engine itself. Consequently, blowby
gas within the crankcase is also exhausted from the fresh air
introduction passage so that fresh air is not introduced into the
crankcase. Thus, engine oil within the crankcase is deteriorated
due to the blowby gas.
[0007] The above-described structure is basically the same as in a
case of a turbo charger equipped (supercharge) engine.
Specifically, in the turbo charged engine, as compared with the
natural inspiration type engine or non-supercharger engine, the
pressure in the intake manifold becomes high due to an influence of
the supercharge pressure. Hence, a driving region in which fresh
air is not introduced into the crankcase become increased. As a
consequence, engine oil within the crank case becomes easy to be
deteriorated due to the presence of blowby gas.
[0008] To avoid this inconvenience, the inventors have proposed a
second previously proposed engine ventilation system, as disclosed
in a Japanese Patent Application First Publication No. 2010-112178
published on May 20, 2010, in which an orifice for a fresh air
introduction is disposed on a PCV, in the supercharge (type)
engine, and fresh air is introduced within the crankcase via the
PCV valve in a case where the boost pressure which is the pressure
of the intake air passage indicates the positive pressure so that
deterioration of engine oil within the crankcase is suppressed.
SUMMARY OF THE INVENTION
[0009] However, although, in a technique disclosed in the second
previously proposed engine ventilation system, in a case where the
boost pressure indicates a positive pressure, a ventilation
efficiency of the crankcase is improved by introducing fresh air
within the crankcase via the PCV valve from a position of the
intake air passage which is located at the downstream side with
respect to the throttle valve, a flow quantity of fresh air
introduced into the crank chamber (crankcase) is not positively
controlled and there is still a room of improvement.
[0010] It is, hence, an object of the present invention to provide
ventilation system and method for the engine, especially, for the
supercharge engine in which quantity of fresh air is appropriate
for a present engine driving state in accordance with a driving
state of the engine when the boost pressure of the intake air
passage indicating the positive pressure is introduced within the
crankcase.
[0011] According to one aspect of the present invention, there is
provided with a ventilation system for a supercharge engine,
comprising: a blowby gas reduction passage provided for
communicating position of an intake air passage of the engine which
is located at a downstream side with respect to a throttle valve
with a crank chamber of the engine; a fresh air introduction
passage provided for communicating position of the intake air
passage which is located at an upstream side with respect to the
throttle valve and the crank chamber; a PCV valve provided in the
blowby gas reduction passage for controlling a flow quantity of
blowby gas directed toward the intake air passage side in a case
where a boost pressure at position of intake air passage located at
downstream side with respect to the throttle valve indicates
negative; and a fresh air flow quantity control section configured
to operatively introduce fresh air into the crank chamber from
position of intake air passage which is located at the downstream
side with respect to the throttle valve in a case where the boost
pressure at position of the intake air passage which is located at
the downstream side with respect to the throttle valve is positive,
wherein the fresh air flow quantity control section is configured
to introduce fresh air into the crank chamber, in a middle load
driving region in which the boost pressure at position of the
intake air passage which is located at the downstream side with
respect to the throttle valve is positive and the boost pressure is
lower than a set pressure, and, in a high load driving region in
which the boost pressure at part of the intake air passage which is
located at the downstream side with respect to the throttle valve
is equal to or higher than the set pressure, is configured to stop
an introduction of fresh air from position of the intake air
passage which is located at a downstream side with respect to the
throttle valve or is configured to make a flow quantity of
introduced fresh air at least smaller than a maximum flow quantity
in the middle load driving region.
[0012] According to another aspect of the present invention, there
is provided with ventilation method for a supercharge engine,
comprising: providing a blowby gas reduction passage for
communicating position of an intake air passage of the engine which
is located at a downstream side with respect to a throttle valve
with a crank chamber of the engine; providing a fresh air
introduction passage provided for communicating position of the
intake air passage which is located at an upstream side with
respect to the throttle valve and the crank chamber; providing a
PCV valve in the blowby gas reduction passage for controlling a
flow quantity of blowby gas directed toward the intake air passage
side in a case where a boost pressure at position of intake air
passage located at downstream side with respect to the throttle
valve indicates negative; and providing fresh air flow quantity
control means for operatively introducing fresh air into the crank
chamber from position of intake air passage which is located at the
downstream side with respect to the throttle valve in a case where
the boost pressure at position of the intake air passage which is
located at the downstream side with respect to the throttle valve
is positive, wherein fresh air is introduced into the crank chamber
through fresh air flow quantity control means, in a middle load
driving region in which the boost pressure at position of the
intake air passage which is located at the downstream side with
respect to the throttle valve is positive and the boost pressure is
lower than a set pressure, and, in a high load driving region in
which the boost pressure at part of the intake air passage which is
located at the downstream side with respect to the throttle valve
is equal to or higher than the set pressure, an introduction of
fresh air from position of the intake air passage which is located
at a downstream side with respect to the throttle valve is stopped
or a flow quantity of introduced fresh air is at least made smaller
than a maximum flow quantity in the middle load driving region.
[0013] The present invention described above is based on the
knowledge such that, if fresh air is introduced into the crank
chamber from position of the intake air passage which is located at
the downstream side with respect to the throttle valve, the
quantity of fresh air supplied to the engine is accordingly
decreased. That is to say, in the middle load driving region, fresh
air is introduced into the crank chamber from position of intake
air passage which is located at the downstream side with respect to
the throttle valve so that the crank chamber is positively
ventilated. On the other hand, in the high load driving region
requiring a high output of the engine, the introduction of fresh
air into the crank chamber from position of the intake air passage
which is located at the downstream side with respect to the
throttle valve is stopped or a flow quantity of fresh air is made
smaller than at least maximum flow quantity in the middle load
driving region, in order to suppress the decrease in the fresh air
quantity supplied to the engine.
[0014] According to the present invention described in the claims,
in the middle load driving region of the engine, with importance
placed on the ventilation of the crank chamber, relatively large
quantity of fresh air is introduced into the crank chamber and, on
the other hand, in the high load driving region, with importance
placed on the engine output, the large quantity of fresh air is
supplied to the engine so that, while the deterioration of engine
oil within the crank chamber is suppressed, the output reduction of
the engine in the high load driving region can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a systematic view of a ventilation system for a
supercharge engine in a first preferred embodiment according to the
present invention and representing streams of blowby gas and fresh
air in the ventilation system at a time of engine low load driving
state.
[0016] FIG. 2 is a systematic view of the engine ventilation system
in the first preferred embodiment according to the present
invention representing the streams of blowby gas and fresh air in
the ventilation system shown in FIG. 1 at a time of engine middle
load driving state.
[0017] FIG. 3 is a systematic view of the engine ventilation system
in the first preferred embodiment according to the present
invention representing the streams of blowby gas and fresh air in
the ventilation system shown in FIG. 1 at a time of engine high
load driving state.
[0018] FIG. 4 is a detailed cross sectional view of a PCV valve
used in the first embodiment shown in FIGS. 1 through 3.
[0019] FIG. 5 is a characteristic graph representing a relationship
between a boost pressure of an intake air system shown in FIGS. 1
through 3 and flow quantities of blowby gas and fresh air.
[0020] FIGS. 6A, 6B, and 6C are essential part expanded views
representing operation states of a fresh air flow quantity control
orifice shown in FIG. 4 and FIGS. 6A and 6B representing operation
states of the fresh air flow quantity control orifice in the middle
load driving region shown in FIG. 5 and FIG. 6C representing the
operation state of the fresh air flow quantity control orifice in
the high load driving region shown in FIG. 5.
[0021] FIG. 7 is a systematic view of the engine ventilation system
in a second preferred embodiment according to the present invention
representing streams of blowby gas and fresh air at the time of the
engine low load driving state.
[0022] FIG. 8 is a systematic view of the engine ventilation system
in the second preferred embodiment according to the present
invention representing the streams of blowby gas and fresh air in
the ventilation system shown in FIG. 7 at a time of engine middle
load state.
[0023] FIG. 9 is a systematic view of the engine ventilation system
in the second preferred embodiment according to the present
invention representing the streams of blowby gas and fresh air in
the ventilation system shown in FIG. 7 at a time of engine high
load driving state.
[0024] FIG. 10 is a detailed cross sectional view of the PCV valve
used in the second embodiment shown in FIGS. 7 through 9.
[0025] FIG. 11 is a detailed cross sectional view of a fresh air
flow quantity control valve used in the second embodiment shown in
FIGS. 7 through 9.
[0026] FIG. 12 is a systematic view of the engine ventilation
system in a third preferred embodiment according to the present
invention representing streams of blowby gas and fresh air at the
time of the engine low load driving state.
[0027] FIG. 13 is a detailed cross sectional view of a PCV valve
used in a fourth preferred embodiment according to the present
invention.
[0028] FIG. 14 is a perspective view of only a valve body of the
PCV valve shown in FIG. 13.
[0029] FIG. 15 is a characteristic graph representing a
relationship between a boost pressure of the intake air system in
the fourth embodiment and flow quantities of blowby gas and fresh
air.
[0030] FIGS. 16A, 16B, and 16C are essential part expanded views
representing operation states of a fresh air flow quantity control
orifice shown in FIG. 13 and FIGS. 16A and 16B representing
operation states of the fresh air flow quantity control orifice in
the middle load driving region shown in FIG. 15 and FIG. 16C
representing the operation state of the fresh air flow quantity
control orifice in the high load driving region shown in FIG.
5.
[0031] FIG. 17 is a perspective view of only a valve body of the
PCV valve in a case of a first alternative to the fourth embodiment
shown in FIG. 14.
[0032] FIG. 18 is a perspective view of only a valve body of the
PCV valve in a case of a second alternative to the fourth
embodiment shown in FIG. 14.
[0033] FIG. 19 is a characteristic graph representing the
relationship between the boost pressure of the intake air system of
the fourth embodiment and the flow quantities of the blowby gas and
the fresh air in a case where the PCV valve having the valve body
shown in FIG. 17 is applied.
[0034] FIG. 20 is a characteristic graph representing the
relationship between the boost pressure of the intake air system of
the fourth embodiment and the flow quantities of blowby gas and
fresh air in a case where the PCV valve having the valve body shown
in FIG. 18 is applied.
[0035] FIG. 21 is a detailed cross sectional view of the fresh air
flow quantity control valve in a fifth preferred embodiment of the
engine ventilation system according to the present invention.
[0036] FIG. 22 is a detailed cross sectional view of the fresh air
flow quantity control valve in a sixth preferred embodiment of the
engine ventilation system according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0037] Reference will, hereinafter, be made to the drawings in
order to facilitate a better understanding of the present
invention. FIGS. 1 through 6 show a first preferred embodiment of a
ventilation system for a supercharge engine according to the
present invention and, particularly, FIG. 1 represents streams of
blowby gas and fresh air at a time of an engine low load driving
state, FIG. 2 represents streams of blowby gas and fresh air at a
time of an engine middle load driving state, and FIG. 3 represents
streams of blowby gas and fresh air at a time of an engine high
load driving state.
[0038] In FIG. 1, a single cylinder of a supercharge inline
multi-cylinder engine is denoted by an engine 1 for a convenience
purpose. In an intake air system 2 as an intake air passage, in a
sequence from an upstream side of intake air system 2, an air
cleaner 3, an airflow meter 4, a compressor impeller 5b of a turbo
charger 5 which is a type of supercharger, an intercooler 6, and a
throttle valve 7 are respectively disposed. On the other hand, a
turbine impeller 5a of turbo charger 5 is intervened in an exhaust
system 8 of engine 1.
[0039] Then, as is well known, intake air is passed through air
cleaner 3 and airflow meter 4 and compressed (supercharged) by
means of compression impeller 5b of turbo charger 5 driven by
exhaust gas of engine 1. Thereafter, the compressed intake air is
cooled by means of a subsequent stage of intercooler 6 and a flow
quantity thereof is adjusted by means of throttle valve 7. Then,
the flow quantity adjusted intake air is introduced into a
combustion chamber of engine 1. It should be noted that part of
exhaust gas from engine 1 is circulated into intake air system 2
via an EGR cooler 9.
[0040] Then, a blowby gas reduction passage 10 which communicates
between position of intake air system 2 located at a downstream
side with respect to throttle valve 7 and crankcase (or crank
chamber) 1a of engine 1 is disposed and a fresh air introduction
passage 11 which communicates between position of intake air system
2 located at an upstream side with respect to throttle valve 7,
namely, the position of intake air system 2 which is located at the
upstream side with respect to compressor impeller 5b of turbo
charger 5 and crank chamber 1a of engine 1 is disposed.
[0041] PCV valve 12 and oilmist separator (OMS) 13 are serially
interposed for PCV valve 12 to be in a throttle valve side 7 in
blowby gas reduction passage 10. In addition, another oilmist
separator (OMS) 14 is intervened for fresh air introduction passage
11. Either of oilmist separators 13, 14 is disposed independently
of engine 1 and both of separators 13, 14 are installed so as to be
connected with engine via hoses and so forth and both of oilmist
separators 13, 14 are integrally installed together with a rocker
cover (a cylinder head cover) of engine 1.
[0042] Furthermore, PCV valve 12 is provided with: a blowby gas
flow quantity control orifice 15 which performs a flow quantity
control function that PCV valve 12 naturally has, namely, a
function to perform a control over a flow quantity of blowby gas
directed toward intake air system 2 side; and a fresh air flow
quantity control orifice 16 to control a flow quantity of fresh air
directed toward crank chamber is as will be described later as
fresh air flow quantity control means. In other words, while blowby
gas flow quantity control orifice 15 functions as a variable
orifice for a blowby gas flow quantity control, fresh air flow
quantity orifice 15 functions as the variable orifice for the fresh
air flow quantity control. In addition, fresh air flow quantity
control orifice 16 is serially disposed at oilmist separator 13
side of the blowby gas flow quantity control orifice 15.
[0043] FIG. 4 shows the details of PCV valve 12. A spool type valve
body 22 is slidably inserted within a hollow valve body 17 (casing
or housing) having a stepped cylindrical shape for inner and outer
peripheral surfaces thereof. Valve body 17 includes: a valve body
main frame 18 in a substantially bottomed cylindrical shape; and a
substantially cylindrical cover 19 connected with an opening
section of valve body main frame 18. These main frame 18 and cover
19 are divided into two in an axial center direction. A first port
20 which is an opening section of cover 19 which is located at an
opposing end against valve body main frame 18 which is connected
with the downstream side of intake air system 2 with respect to
throttle valve 7 in intake air system 2 and a second port 21 opened
and formed on a bottom wall of valve body main frame 18 is
connected with oilmist separator 13 side (crank chamber 1a side),
respectively.
[0044] A flange section 23 is formed on an intermediate section of
valve body 22 in the axial center direction of valve body 22. A
first compression coil spring 26 is intervened between flange
section 23 and cover 19. A second compression coil spring 27 is
intervened between flange section 23 and a bottom wall of valve
body main frame 18. Both tips of respective compressive coil
springs 26, 27 are largely separated from each other than a
thickness of flange section 23. When flange section 23 is seated on
one of both compressive coil springs 26, 27, a gap G is formed
between flange section 23 and the other of both coil springs 26,
27. In this way, a, so-called, play is provided on valve body 22
and an elastic force of only one of both compressive coil springs
26, 27 is acted upon valve body 22. Valve body 22 is so arranged as
to be in a stable operation.
[0045] In addition, a first throat section 19a having a step
section is formed on an opening section of cover 19 facing against
valve body main frame 18. Position of valve body 22 which is
located toward first port 22 against flange section 23 is formed as
a tipped blowby gas metering section 24 having the diameter which
becomes larger toward flange section 23. Then, when the boost
pressure of intake air system 2 indicates negative, valve body 16
expanded according to the negative pressure of the boost pressure
at intake air system 2 is slidably displaced against valve body 17.
Valve body 22 comes to a stand-still at a balanced position between
the boost pressure and first compressive coil spring 26. In other
words, first throat section 19a and blowby gas metering section 24
are relatively displaced in accordance with a magnitude of the
negative pressure so that an opening angle between first throat
section 19a and blowby gas metering section 24 are relatively moved
in accordance with a magnitude of the negative pressure so that the
opening angle formed therebetween, namely, the flow quantity of
blowby gas flowing into PCV valve 12 is variably controlled in a
continuous manner.
[0046] In other words, a gap formed between first throat section
19a and blowby gas metering section 24 functions as blowby gas flow
quantity control orifice 15.
[0047] On the other hand, a second port 21 formed on valve body
main frame 18 is formed in a taper shape whose diameter becomes
larger as it approaches to oilmist separator 13. Position of valve
body 22 which is nearer to second port 21 than flange section 23 is
formed as fresh air metering section 25 of a substantially stepped
column shape and whose diameter becomes larger as it becomes larger
in a stepwise manner.
[0048] Fresh air metering section 25 includes: a large diameter
section 25a formed on a base section of fresh air metering section
25 and having a larger diameter than a second throat section 18a
which is a minimum diameter section of second port 21; a middle
diameter section 25b having a smaller diameter than second throat
section 25b; and a taper section 25d formed between middle diameter
section 25b and smaller diameter section 25c and whose diameter
becomes gradually small toward small diameter section 25c.
[0049] Then, if the boost pressure at intake air system 2 indicates
positive pressure, valve body 16 pressed by means of the positive
pressure is slidably displaced and comes to the stand-still. Thus,
the valve body becomes stand-still at the balanced position
balanced between the boost pressure and the elastic force of second
compressive coil spring 27. That is to say, a relative movement of
second throat section 18a and fresh air metering section 25 occurs
so that the opening angle formed between both elements and the flow
quantity of fresh air flowing into PCV valve 12 is variably
controlled in a continuous manner. In other words, the gap formed
between second throat section 18a and fresh air metering section 25
functions as fresh air flow quantity control orifice 16.
[0050] FIG. 5 shows a graph representing the relationship between
the boost pressure of part of intake air passage (intake air
system) 2 located at the downstream side with respect to throttle
valve 7 and the flow quantity of blowby gas and so forth. A sign A
denotes a development quantity of blowby gas, a sign B denotes a
flow quantity characteristic of blowby gas in oilmist separator 13
at blowby gas reduction passage 10, and a sign C denotes a flow
quantity characteristic of blowby gas in oilmist separator 14 at
blowby gas reduction passage 11, respectively. It should be noted
that the boost pressure indicates negative pressure in FIG. 5 and
as the degree of negative boost pressure becomes larger, the load
becomes lower (toward rightward direction in FIG. 5). Conversely,
as the positive boost pressure becomes larger, the load becomes
higher (toward leftward direction in FIG. 5). In addition, for the
flow quantity characteristic of blowby gas denoted by signs B and
C, the stream of blowby gas from crank chamber is to intake air
system 2 indicates positive (+) and the stream of blowby gas from
crank chamber 2 toward intake air system 2 indicates negative
(-).
[0051] Then, in blowby gas reduction passage 10 shown in FIG. 1,
PCV valve 12 is serially disposed with oilmist separator 13. Hence,
the boost pressure-flow quantity characteristic of PCV valve 12 by
means of both flow quantity control orifices 15, 16 provides
substantially equal to the characteristic denoted by sign B in FIG.
5 and is previously adjusted.
[0052] When, in the ventilation system so constructed as described
above, the magnitude of the negative pressure with the boost
pressure negative is large as shown in FIGS. 1 and 5, namely, in a
rightmost region in FIG. 5 of engine low load driving region A1
shown in FIG. 5, valve body 22 of PCV valve 12 shown in FIG. 4 is
largely stretched toward a leftward direction so that a blowby gas
flow passage cross sectional area (opening angle) of blowby gas
flow quantity control orifice 15 becomes relatively small. Hence,
in the rightmost region of engine low load driving region A1 in
FIG. 5, the blowby gas flow quantity exhausted (reduced) toward
intake air system 2 through oilmist separator 13 and PCV valve 12
denoted by sign A in FIG. 5 becomes comparatively small and blowby
gas development quantity itself denoted by sign A in FIG. 5 becomes
small as compared with any other regions. At this time, the opening
angle of fresh air flow quantity control orifice 16 becomes
maximum.
[0053] Since, in this case, the blowby gas flow quantity denoted by
sign B exhausted toward intake air system 2 via blowby gas
reduction passage 10 is larger than the blowby gas development
quantity denoted by sign A in FIG. 5, fresh air whose quantity
corresponds to a difference in flow quantity of both flow
quantities signed by A and B is introduced into intake air system 2
from crank chamber 1a via fresh air introduction passage 11 as
denoted by sign C. While blowby gas is exhausted from crank chamber
1a to intake air system 2 via blowby gas reduction passage 10 and
fresh air is introduced to crank chamber 1a via fresh air
introduction passage 11. Thus, crank chamber 1a is ventilated.
[0054] In addition, the load of engine becomes large from the
above-described state and the boost pressure gradually approaches
to the positive pressure. At this time, valve body 22 of PCV valve
12 in FIG. 4 is slidably displaced toward the more rightward
direction than the above-described state so that a flow passage
cross sectional area (opening angle) in blowby gas flow quantity
control orifice 15 becomes larger than the above-described state.
Thus, blowby gas flow quantity of sign B exhausted toward intake
air system 2 side via blowby gas reduction passage 10 and the fresh
air quantity of sign C introduced toward intake air system 2 via
blowby gas introduction passage 11 are respectively increased.
[0055] Furthermore, in a positive pressure immediate prior state in
which the boost pressure approaches to the positive pressure
unlimitedly, the blowby gas flow quantity of sign B exhausted
toward intake air system 2 via oilmist separator 13 and PCV valve
12 of blowby gas reduction passage 10 becomes less than blowby gas
development quantity denoted by sign A. Then, the blowby gas is
soon exhausted even from fresh air introduction passage 11 as shown
in FIG. 2.
[0056] When the load of engine 1 becomes furthermore large, the
boost pressure in FIG. 5 is changed to the positive pressure due to
the influence of the supercharged pressure of turbo charger 5 shown
in FIG. 1, valve body 22 of PCV valve 12 shown in FIG. 4 is
slidably displaced toward the rightward direction in FIG. 4. As
shown in FIG. 2, fresh air streamed into blowby gas reduction
passage 10 due to the boost pressure from position of intake air
system 2 which is located at the downstream side with respect to
throttle valve 7 is reversely streamed toward crank chamber 1a via
oilmist separator 13 upon the metering by means of fresh air flow
quantity control orifice 16. At the same time, blowby gas developed
in engine 1 is mixed with fresh air within crank chamber 1a. The
mixed air is exhausted toward position of intake air system 2 which
is to located at the upstream side of throttle valve 7 via fresh
air introduction passage 11. Thus, crank chamber 1a is ventilated.
In other words, when the boost pressure is the positive pressure,
the opening angle of blowby gas flow quantity control orifice 15
becomes maximum. The flow is quantity of fresh air at oilmist
separator 13 of blowby gas reduction passage 10 side is controlled
by means of fresh air flow quantity control orifice 16 from among
PCV valve 12.
[0057] Thus, the gas flow quantity in blowby gas reduction passage
10 denoted by sign B is turned to minus (-) at a middle load
driving region A2 in which the boost pressure in FIG. 5 indicates
positive and is smaller than a predetermined set pressure P1. It
should be noted that, since the flow quantity of blowby gas
exhausted toward part of intake air system 2 located at the
upstream side with respect to throttle valve 7 through fresh air
introduction passage 11 is a quantity which is an addition of the
blowby gas development quantity denoted by sign A to the fresh air
flow quantity at blowby gas reduction passage 10, blowby gas flow
quantity at fresh air introduction passage 11 denoted by sign C is
in excess of the blowby gas development quantity denoted by sign
A.
[0058] FIGS. 6A through 6C are essential part expanded views
representing operation states of PCV valve 12 when the boost
pressure at part of intake air system 2 located at the downstream
side with respect to throttle valve 7 is positive. In a region in
which a magnitude of the positive pressure is relatively small in
the middle load driving region A2 in FIG. 5, valve body 22 is
slidably moved toward the rightward direction along with the
increase in the boost pressure so that the flow passage cross
sectional area of fresh air flow quantity control orifice 16 is
gradually decreased according to taper section 25d of fresh air
metering section 25. However, the flow quantity of fresh air at
blowby gas reduction passage 10 denoted by sign B in FIG. 5 becomes
gradually increased due to the influence of the increase in the
boost pressure and soon the flow quantity thereof becomes a maximum
flow quantity Q in is the middle load driving region A2.
[0059] Furthermore, when the flow quantity of fresh air at blowby
gas reduction passage 10 denoted by sign B in FIG. 5 is in excess
of a maximum flow quantity Q and approaches to a set pressure
immediate prior position at which the boost pressure approaches
unlimitedly to a predetermined set pressure P1, stepped section 25e
between large diameter section 25a and middle diameter section 25b
is approached to a bottom wall of valve body main frame 18 so that
the flow passage cross sectional area of fresh air flow control
orifice 16 becomes furthermore small. Thus, the flow quantity of
fresh air at blowby gas reduction passage 10 denoted by sign B in
FIG. 5 and the flow quantity of blowby gas at fresh air
introduction passage 11 denoted by sign C in FIG. 5 are gradually
decreased along with the increase in the boost pressure.
[0060] Then, when the boost pressure has reached to predetermined
set pressure P1, stepwise section 25e of fresh air metering section
25 is seated on the bottom wall of valve body 17, as shown in FIG.
6C, so that fresh air flow quantity control orifice 16 is in a
complete closure state. Thus, as shown in FIG. 3 in addition to
FIG. 5, in a high load driving region A3 in which the boost
pressure is equal to or higher than predetermined set pressure P1,
the flow quantity of fresh air at blowby gas reduction passage 10
denoted by sign B is substantially zeroed or extremely small and
fresh air which has been introduced into crank chamber 1a in middle
load driving region A2 is, in turn, supplied to engine 1. It should
be noted that the flow quantity of blowby gas at fresh air
introduction passage 11 side denoted by sign C in FIG. 5 becomes
equal to the development quantity of blowby gas denoted by sign
A.
[0061] Hence, in the first embodiment described above, is
importance is placed on the ventilation of crank chamber 1a in
middle load driving region A2 in FIG. 5 and fresh air is positively
introduced into crank chamber 1a through blowby gas reduction
passage 10. On the other hand, in high load driving region A3
requiring high output (power) by engine 1, an introduction of fresh
air into crank chamber 1a through blowby gas reduction passage 10
is stopped in order to supply a large quantity of fresh air into
engine 1. Thus, while the deterioration of engine oil due to blowby
gas is suppressed, the reduction in the output of engine 1 can be
prevented in high load driving region A3. It should be noted that
predetermined set pressure P1 may appropriately be set with the
balance between the engine output and a ventilation efficiency of
crank chamber 1a taken into consideration.
[0062] In addition, in the first embodiment, the introduction of
fresh air into crank chamber 1a through blowby gas reduction
passage 10 is stopped in high load driving region A3. However, the
flow quantity of fresh air introduced into crank chamber 1a at high
load driving region A3 is always not needed to be substantial zero
or to be extremely small. If the flow quantity of fresh air
introduced into crank chamber is in high load driving region A3 is
set to be smaller than maximum flow quantity Q in the case of
middle load driving region A2, at least the output reduction of
engine 1 can be suppressed. It should be noted that, in a case
where importance is placed on the engine output in high load
driving region A3, it goes without saying that it is desirable to
be set to the boost pressure-flow quantity characteristic shown in
FIG. 5.
Second Embodiment
[0063] FIGS. 7 through 11 show a second preferred embodiment of the
ventilation system for the supercharge engine according to the
present invention. FIG. 7 shows the streams of blowby gas and fresh
air at a time of the engine low load driving state, FIG. 9 shows
the streams of blowby gas and fresh air at a time of the engine
middle load driving state, and FIG. 10 shows the streams of blowby
gas and fresh air at a time of the engine high load driving state.
The same reference numerals as shown in FIGS. 7 through 9 designate
like elements shown in FIGS. 1 through 3.
[0064] In the second embodiment, in place of PCV valve 12 used in
the first embodiment, PCV valve 28 is adopted which controls only
the exhaust quantity of blowby gas from crank chamber is to intake
air system 2 side and fresh air flow quantity control valve 29 is
juxtaposed with PCV valve 28 which controls the introduction
quantity of fresh air from intake air system 2 to crank chamber 1a.
That is to say, blowby gas reduction passage 10 is branched or
joined from or into position of intake air system 2 which is
located at the downstream side with respect to throttle valve 7 in
the same way as the first embodiment. However, a bypass passage 30
is provided at the same position as described above (position of
intake air system 2 which is located at the upstream side with
respect to throttle valve 7). Fresh air flow quantity control valve
29 is provided in bypass passage 30. The other end of bypass
passage 30 is connected with oilmist separator 13. This is a
difference point in the second embodiment from the first
embodiment. The boost pressure-flow quantity characteristics of PCV
valve 28 and fresh air flow quantity control valve 29 are
previously adjusted to provide the same characteristics as those
denoted by sign B shown in FIG. 5.
[0065] FIG. 10 shows the detailed structure of PCV valve 28. This
PCV valve 28 includes: PCV valve 28 having the same structure as
PCV valve 12 in the first embodiment (so-called, two-piece
structured valve body 31); and spool type valve body 36 slidably
inserted within valve body 31. First port 34 located at cover 32 of
valve body 31 is connected with position of intake air system 2
which is located at a downstream side of throttle valve 7 and
second port 35 of valve body main frame 33 of valve body 31 is
connected with oilmist separator 13.
[0066] Valve body 36 includes a flange section 37 formed on a
terminal end of valve body 36 located at second port 35 side; and a
tipped blowby gas metering section 38 projected from flange section
37 toward first port 34 side. Compressive coil spring 39 interposed
between flange section 37 and cover 32 is formed to bias valve body
36 toward second port 35. A blowby gas flow quantity metering
section 38 of valve body 36 and throat section 32a on cover 32 are
formed in the same way as those described in the first embodiment.
A blowby gas flow quantity control orifice 40 which is equal to
that described in the first embodiment is formed between throat
section 32a and blowby gas metering section 38.
[0067] That is to say, in a case where the boost pressure within
intake air system 2 is negative, valve body 36 is slidably
displaced at the balanced position which is balanced between the
boost pressure and the biasing force of compressive coil spring 39.
The opening angle of blowby gas flow quantity control orifice 40
and the flow quantity of blowby gas streamed toward intake air
system 2 side is variably controlled. On the other hand, in a case
where the boost pressure of the intake air system 2 side is
positive, flange section 37 of valve body 36 is seated on the
bottom wall of valve body main frame 33 to close second port 35.
Thus, PCV valve 28 is closed.
[0068] FIG. 11 shows the details of fresh air flow quantity control
valve 29. This fresh air flow quantity control valve 29 includes,
so-called, two piece structured valve body 41 of the same structure
as PCV valve 28 and spool type valve body 46 slidably inserted into
valve body 41. First port 44 of valve body 41 at cover 42 side is
connected with position of intake air system 2 side located at the
downstream side with respect to throttle valve 7 and second port 45
of valve body main frame side of valve body 41 is connected with
oilmist separator 13 side.
[0069] Valve body 46 includes a flange section 47 formed on the end
of valve body 46 toward first port 44 and a substantially stepped
column shaped fresh air metering section 48 projected from flange
section 47 to first port 44. Valve body 46 is biased toward first
port 44 by means of compressive coil spring 49 intervened between
flange section 47 and the bottom wall of valve body main frame 43.
Then, fresh air metering section 48 of valve body 46 has large
diameter section 48a, middle diameter section 48b, small diameter
section 48c, and taper section 48d in the same way as the first
embodiment. Then, a fresh air flow quantity control orifice 50 is
formed between throat section 43c of a minimum diameter section of
second port 45 and small diameter section 48c. Throat section 43c
which is the minimum diameter section is formed as the same
structure in the first embodiment.
[0070] That is to say, in a case where the boost pressure at intake
air system 2 side is negative, flange section 47 of valve body 46
is seated on a bottom wall section 42a of cover 42 to close second
port 45 so that fresh air flow quantity control valve 29 is closed.
On the other hand, in a case where the boost pressure at intake air
system 2 side is positive, valve body 46 is slidably displaced at
the balanced position at which the boost pressure and the biasing
force of compressive coil spring 49 are balanced. Thus, the opening
angle of fresh air flow quantity control orifice 50, namely, the
flow quantity of fresh air flowing toward oilmist separator 13 is
variably controlled. It should be noted that, in a case where the
boost pressure in intake air system 2 side is positive, valve body
46 is slidably displaced at the balanced position at which the
boost pressure and the biasing force of compressive coil spring 49
are balanced so that the opening angle of fresh air flow quantity
control orifice 50, namely, the flow quantity of fresh air streamed
toward oilmist separator 13 is variably controlled. It should be
noted that a stepped section 48e between large diameter section 48a
and middle diameter section 48b of fresh air metering section 48 is
seated on the bottom wall of valve body main frame 43 to close
second port 45 in the same way as described in the first
embodiment.
[0071] As described in the second preferred embodiment, while
bypass passage 30 is interrupted by means of fresh air flow
quantity control valve 29 as shown in FIG. 7 in low load driving
region A1 in FIG. 5 in which the boost pressure at intake air
system 2 side is negative and the flow quantity of blowby gas
exhausted toward intake air system 2 side is controlled by means of
PCV valve 28 and blowby gas reduction passage 10 exhibits the
function that the passage naturally has.
[0072] In addition, in a case where the boost pressure of intake
air system 2 side is positive and the present engine driving region
is in middle load driving region A2 in FIG. 5 in which the boost
pressure is lower than set pressure P1, as shown in FIG. 8, blowby
gas reduction passage 10 is interrupted according to PCV valve 28
and fresh air metered by means of fresh air flow quantity control
valve 29 is introduced into crank chamber 1a via bypass passage 30.
Thus, crank chamber 1a is positively ventilated.
[0073] Furthermore, in a case of high load driving region A3 shown
in FIG. 5 in which the boost pressure at intake air system 2 side
is equal to or higher than set pressure P1, bypass passage 30 is
interrupted according to fresh air flow quantity control valve 29
as shown in FIG. 9 so that much fresh air is supplied to engine 1.
Thus, the output reduction of engine 1 is prevented.
[0074] Hence, according to the second preferred embodiment, the
same function as in the same way as the first embodiment has been
exhibited and fresh air flow quantity control valve 29 which
controls the flow quantity of fresh air introduced to crank chamber
1a when the boost pressure at intake air system 2 side is positive
is installed in addition to PCV valve 28. Hence, according to the
second embodiment, the flow quantity of fresh air introduced into
crank chamber 1a can highly accurately be controlled and can stably
be controlled.
Third Embodiment
[0075] FIG. 12 shows a variation of the above-described second
embodiment which corresponds to a third preferred embodiment
according to the present invention and represents the streams of
blowby gas and fresh air at a time of the engine low load driving
state in the same way as FIG. 7.
[0076] In the third embodiment, bypass passage 51 having fresh air
flow quantity control valve 29 is directly connected with crank
chamber is of engine 1 not via oilmist separator 13.
[0077] It goes without saying that, in this case, the same function
as the second embodiment is exhibited as described above.
Fourth Embodiment
[0078] FIGS. 13 through 16 show a fourth preferred embodiment
according to the present invention. The fourth embodiment is
applicable to the ventilation system shown in FIGS. 1 through 3
described in the first preferred embodiment according to the
present invention. Specifically, PCV valve 80 is interposed having
a different characteristic from that of PCV valve 12 in place of
above-described PCV valve 12.
[0079] FIG. 13 shows the detailed structure of PCV valve 80 in the
fourth preferred embodiment. It should be noted that the same
reference numerals as PCV valve 12 designate the same constituents
of PCV valve 12 and a duplicate explanation thereof will herein be
omitted.
[0080] This PCV valve 80 has substantially the same structure as
PCV valve 12. As shown in FIG. 14, fresh air metering section 81 of
valve body 22 is formed on a root position of fresh air metering
section 81. Fresh air metering section 81a includes: a large
diameter section 81a having a larger diameter than a second throat
section 18a which is a minimum diameter section of second port 21;
a taper section 81b formed to be adjacent to anti-flange section 23
of large diameter section 81a and having an outer diameter to
become gradually smaller as approaching toward second port 21 side;
small diameter section 81c formed on a tip of fresh air metering
section 81 and having the small diameter than taper section 81b; a
stepwise section 81d formed between large diameter section 81a and
taper section 81b; and a stepwise section 81e formed between taper
section 81b and small diameter section 81c.
[0081] In a case where the boost pressure in intake air system 2
side is positive, valve body 22 pressed by means of the positive
pressure is slidably displaced with respect to valve body 17 and
valve body 17 comes to stand-still at the position at which the
boost pressure and the spring force of second compressive coil
spring 27 are balanced.
[0082] In a case where fresh air metering section 81 is formed as
shown in FIG. 14, the boost pressure of part of intake air system 2
which is located at the downstream side with respect to throttle
valve 7 is changed to the positive pressure and valve body 22 is
slidably moved along with the increase in the boost pressure. At
this time, stepwise section 81d is seated on the bottom wall of
valve body main frame 18. Then, fresh air flow quantity control
orifice is completely closed. It should be noted that the gap
formed between second throat section 18a and fresh air metering
section 81 functions as fresh air flow quantity control orifice 16
described above.
[0083] FIG. 15 shows a graph representing a relationship between
the boost pressure at the downstream side of throttle valve 7 in
intake air system 2 and blowby gas in a case where PCV valve 80 is
applied to the ventilation system shown in FIGS. 1 through 3. Sign
A denotes a development quantity of blowby gas, sign B denotes a
flow quantity characteristic of blow by gas in oilmist separator 14
at fresh air introduction passage 11, and sign C denotes the flow
quantity characteristic of blowby gas in the oilmist separator 14
at fresh air introduction passage 11. It should be noted that, in
FIG. 15, in the same way as described above with reference to FIG.
5, the boost pressure becomes negative and the magnitude thereof
becomes large so to becomes approach to the rightward side, namely,
low load side and, on the contrary, the boost pressure becomes
positive and the magnitude thereof becomes large so as to become
approach to the leftward side, namely, high load side. In addition,
for the flow quantity characteristic such as blowby gas denoted by
signs B and C, the flow of blowby gas directed toward intake air
system 2 side is assumed to be "positive (+)" and the flow of
blowby gas directed toward crank chamber 1a from intake air system
2 side is assumed to be "negative (-)".
[0084] Then, in blowby gas reduction passage 10, PCV valve 80 is
serially disposed on oilmist separator 13. The boost pressure-flow
quantity characteristic of PCV valve 80 by means of flow quantity
control orifices 15, 16 is previously adjusted to provide
substantially equal characteristic as the characteristic denoted by
sign B in FIG. 15, in the fourth embodiment. In more details, from
among the engine load driving regions in which the boost pressure
of intake air system 2 side is positive, the middle load driving
region indicates that the flow quantity of fresh air streamed into
blowby gas reduction passage 10 from the downstream side of
throttle valve 7 indicates constant regardless of the boost
pressure. In the high load driving region, fresh air metering
section 101 is set so that the quantity of fresh air streamed from
the downstream side of throttle valve to blowby gas reduction
passage 10 becomes substantially zero or extremely small.
[0085] In such a fourth embodiment as described above, in low load
driving region A1 shown in FIG. 15, as the magnitude of negative
pressure of the boost pressure becomes larger, the flow passage
cross sectional area (opening angle) of blowby gas flow quantity
control orifice 15 becomes smaller. Hence, in the rightward region
in FIG. 15 in low load driving region A1, the blowby gas flow
quantity exhausted (circulated) toward intake air system 2 side
becomes relatively small. The blowby gas development quantity
itself denoted by a sign A in FIG. 15 becomes small as compared
with any other regions. It should be noted that, at this time, the
opening angle of fresh air flow quantity control orifice 16 becomes
maximum.
[0086] Then, even in this case, since blowby gas flow quantity
denoted by sign B exhausted toward intake air system 2 side through
blowby gas reduction passage 10 is larger than blowby gas
development quantity denoted by sign A in FIG. 15. As denoted by
sign C, fresh air whose flow quantity corresponds to the difference
in flow quantity of blowby gas development quantity denoted by sign
A and blowby gas flow quantity denoted by sign B is introduced into
crank chamber is through fresh air introduction passage 11. In this
way, while blowby gas is exhausted from crank chamber is to intake
air system 2 side via blowby gas reduction passage 10, fresh air is
introduced from crank chamber is to intake air system 2 side. Thus,
crank chamber is ventilated.
[0087] In such a state as described above, the load of engine
becomes large and the boost pressure gradually approaches to the
positive side, valve body 22 of PCV valve 80 in FIG. 13 is slidably
displaced toward the more rightward side and the flow passage cross
sectional area (opening angle) in blowby gas flow quantity control
orifice 15 becomes larger than the previous case (the
above-described state). Thereby, blowby gas flow quantity denoted
by sign B exhausted toward intake air system 2 side via blowby gas
reduction passage 10 and the fresh air flow quantity denoted by
sign C introduced into crank chamber is via fresh air introduction
passage 11 are, respectively, increased.
[0088] Furthermore, in a positive pressure immediate prior state in
which the boost pressure approaches to the positive pressure
unlimitedly, the blowby gas flow quantity of sign B exhausted from
intake air system 2 side through oilmist separator 13 of blowby gas
reduction passage 10 and PCV valve 80 becomes smaller than blowby
gas development quantity denoted by sign A and blowby gas is
exhausted soon from fresh air introduction passage 11.
[0089] As the load of engine 1 becomes furthermore increased and
the boost pressure in FIG. 15 turns to the positive pressure, valve
body 22 of PCV valve 80 in FIG. 13 is slidably displaced toward the
rightward direction upon receipt of the boost pressure so that
fresh air streamed into blowby gas reduction passage 10 from
position of intake air system 2 which is located at downstream side
with respect to throttle valve 7 is metered by means of fresh air
flow quantity control orifice 16 and is reversely caused to flow
toward crank chamber is via oilmist separator 13. At the same time,
blowby gas developed in engine 1 is mixed with fresh air within
crank chamber 1a and is exhausted toward part of intake air system
2 which is located at the upstream side with respect to throttle
valve 7 side via fresh air introduction passage 11. Thus, crank
chamber is becomes ventilated. In other words, when the boost
pressure of PCV valve 80 is positive, the opening angle of blowby
gas flow quantity control orifice 15 becomes maximum. Thus, the
flow quantity of fresh air at oilmist separator 13 in blowby gas
reduction passage 11 is controlled by means of fresh air flow
quantity control orifice 16 of PCV valve 80.
[0090] Thus, in the driving region in which boost pressure in FIG.
15 is positive, namely, in middle driving region A in which the
boost pressure is positive and is smaller than predetermined set
pressure P1 and in the high load driving region in which the boost
pressure is equal to or higher than predetermined set pressure P1,
the gas flow quantity in blowby gas reduction passage 10 side
denoted by sign B is turned to be minus (-). It should be noted
that, since the flow quantity of blowby gas exhausted toward the
position of intake air system 2 which is located at the upstream
side with respect to throttle valve 7 via fresh air introduction
passage 11 is an added value of the fresh air flow quantity at
blowby gas reduction passage 10 denoted by sign B to blowby gas
development quantity denoted by is sign A, the blowby gas flow
quantity at fresh air introduction passage 11 denoted by sign C is
in excess of blowby gas development quantity denoted by sign A.
[0091] FIGS. 16A through 16C are essential part expanded views
representing operation state of PCV valve 80 when the boost
pressure at position of intake air system 2 located at the
downstream side with respect to throttle valve 7 is positive. In
middle load driving region A2 in FIG. 15, valve body 22 is slidably
displaced toward the rightward direction as shown in FIGS. 16A and
16B along with the increase in the boost pressure and the flow
passage cross sectional area of fresh air flow quantity control
orifice 16 is gradually decreased. In the fourth embodiment, the
boost pressure-flow quantity characteristic of PCV valve 80 is set
so that the flow quantity of fresh air at blowby gas reduction
passage 10 denoted by sign B in FIG. 15 provides constant flow
quantity Q1 in middle load driving region A2 even when the boost
pressure of position of intake air system 2 located at downstream
side of throttle valve 7 becomes large when the boost pressure of
position of intake air system 2 which is located at downstream side
of throttle valve 7 is turned to the positive pressure.
[0092] Then, in the immediate prior position at which the boost
pressure approaches to predetermined set pressure P1 unlimitedly,
stepwise section 81d between large diameter section 81a and taper
section 81b approaches to the bottom wall of valve body main frame
18 so that the flow passage cross sectional area of fresh air flow
quantity control orifice 16 is furthermore made small.
[0093] Thus, the flow quantity of fresh air at blowby gas reduction
passage 10 denoted by sign C in FIG. 15 becomes gradually decreased
along with the increase in the boost pressure.
[0094] When the boost pressure has arrived at predetermined set
pressure P1, stepwise section 81d of fresh air metering section 81
as shown in FIG. 16C is seated on the bottom wall of valve body 17
so that fresh air flow quantity control orifice 16 is in a full
closure state. Thus, as shown in FIG. 15, in high load driving
region A3 in which the boost pressure is equal to or higher than
predetermined set pressure P1, the flow quantity of fresh air at
blowby gas reduction passage 10 denoted by sign B becomes
substantially zero or extremely small. Thus, fresh air introduced
into crank chamber 1a is supplied to engine 1 in middle load
driving region A2. It should be noted that, at this time, the flow
quantity of blowby gas at fresh air introduction passage 11 dented
by sign C in FIG. 15 becomes equal to blowby gas development
quantity denoted by sign A.
[0095] In the engine ventilation system in the fourth embodiment as
described above, importance is placed on the ventilation of crank
chamber 1a in the middle driving region and fresh air of constant
quantity Q1 is introduced to crank chamber 1a through blowby gas
reduction passage 10. In addition, in the high load driving region
of engine 1, fresh air is not substantially introduced into crank
chamber 1a through blowby gas reduction passage 10, thus importance
is placed on the engine output so that much of fresh air can be
supplied to the engine, in the region.
[0096] In a case where PCV valve 80 is applied, constant flow
quantity Q1 set in middle driving region A2 may appropriately be
set with the balance between the engine output and the ventilation
efficiency taken into consideration.
[0097] In addition, fresh air metering section 81 of valve body 22
in PCV valve 80 in the fourth embodiment may be structured as shown
in FIGS. 17 and 18.
[0098] In a first alternative shown in FIG. 17, the diameter of
fresh air metering section 91 of valve body 22 becomes large toward
flange section 23 and fresh air metering section 91 includes first
and second taper sections 91a, 91b having tips faced toward second
port 21 formed in a taper shape and stepwise section 91c formed
between first taper section 91a and second taper section 91b. First
taper section 91a has a larger diameter than second taper section
91b.
[0099] In a case where fresh air metering section 91 is formed as
shown in FIG. 17, the boost pressure of position of intake air
system 2 located at the downstream side of throttle valve 7 is
turned to the positive pressure. At this time, the flow quantity of
fresh air flowing through the PCV valve is controlled to be
switched into two stages in accordance with the load. In the case
of PCV valve in which valve body 22 having fresh air metering
section 91 is equipped, the gap formed between second throat
section 18a and fresh air metering section 91 functions as fresh
air flow quantity control orifice 16 described above.
[0100] FIG. 19 shows a graph representing the relationship between
the boost pressure at position of intake air system 2 side located
at the downstream side of throttle valve 7 and the flow quantity of
blowby gas in a case where the PCV valve in which valve body 22
having fresh air metering section 91 is applied to the engine
ventilation system in FIGS. 1 through 3.
[0101] In middle load driving region A2 in FIG. 19, the flow
passage cross sectional area of fresh air flow quantity cross
sectional area is gradually decreased according to second taper
section 91b of fresh air metering section 91 along with the
increase in the boost pressure. However, the boost pressure-flow
quantity characteristic of PCV valve is set so that fresh air at
blowby gas reduction passage 10 as denoted by sign B in FIG. 19
indicates constant flow quantity Q1. Then, in the immediate prior
position at which the boost pressure approaches to predetermined
set pressure P1 unlimitedly, stepwise section 91c approaches to the
bottom wall of valve body main frame 18 so that the flow passage
cross sectional area of fresh air flow quantity control orifice 16
is furthermore made small. Thus, the flow quantity of fresh air at
blowby gas reduction passage 10 denoted by sign C in FIG. 19
becomes gradually decreased along with the increase in the boost
pressure.
[0102] In addition, the flow passage cross sectional area of fresh
air flow quantity control orifice 16 is gradually decreased by
means of first taper section 91a along with the increase in the
boost pressure. However, the boost pressure-flow quantity
characteristic of the PCV valve is set so that fresh air at blowby
gas reduction passage 10 denoted by sign B in FIG. 19 provides
constant flow quantity Q2. It should be noted that constant flow
quantity Q2 at high load driving region A3 is set to be smaller
than constant quantity Q1 in middle load driving region A2.
[0103] Therefore, if PCV valve having valve body 22 having such a
fresh air metering section 91 as described above is applied, the
ventilation efficiency can be improved and the deterioration of
engine oil within crank chamber is can be suppressed without output
reduction of engine 1 at the time of high load of engine 1 although
the boost pressure at the position of intake air system 2 which is
located at the downstream side with respect to throttle valve 7 is
positive.
[0104] It should be noted that, in a case where the PCV valve
having valve body 22 having fresh air metering section 91 described
above is applied, constant flow quantity Q1 set at middle load
driving region A2 and constant flow quantity Q2 set at high load
driving region A3 may appropriately be set with the balance between
the engine output and high load driving region A3 taken into
consideration.
[0105] In a second alternative of FIG. 18, fresh air metering
section 101 includes: taper section 101a formed on position of
valve body 22 which is located toward second port than flange
section 23, having the diameter which becomes larger as taper
section 101a becomes nearer to second port 21, and of a truncated
cone shape; and a tip section 102b of a column shape and formed so
as to have the same diameter as the tip of taper section 101a.
[0106] In the PCV valve in which valve body 22 having this fresh
air metering section 101, second throat section 18a and fresh air
metering section 101 are relatively displaced in accordance with
the magnitude of positive pressure so that the opening angle formed
by both of sections 18a and 101 are variably controlled in the
continuous manner and are controlled for the flow quantity of fresh
air streamed into PCV valve to be constant irrespective of the
magnitude of the positive pressure. It should be noted that, in the
PCV valve in which valve body 22 having this fresh air metering
section 101, a gap formed between second throat section 18a and
fresh air metering section 101 functions as above-described fresh
air flow quantity control orifice 16.
[0107] FIG. 20 shows a graph representing the relationship between
the boost pressure of position of intake air system 2 located at
the downstream side with respect to throttle valve 7 and the flow
quantity of blowby gas and so forth, in a case where the PCV valve
in which valve body 22 having fresh air metering section 101 is
equipped is applied to the ventilation system shown in FIGS. 1
through 3.
[0108] In a region from high load driving region A3 to a region in
FIG. 20 in which the magnitude of positive pressure is
comparatively small, the flow passage cross sectional area of fresh
air flow quantity control orifice 16 is gradually decreased by
means of taper section 101a of fresh air flow quantity control
orifice 16. It should be noted that, in this embodiment, the boost
pressure-flow quantity characteristic of the PCV valve in which
valve body 22 having fresh air metering section 101 is equipped is
set so that the flow quantity of fresh air at blowby gas reduction
passage 10 denoted by sign B in FIG. 20 indicates constant flow
quantity Q1 even if the boost pressure of position of intake air
system 2 located at the downstream side with respect to throttle
valve 7 becomes large when the boost pressure of position of intake
air system located at the downstream side with respect to throttle
valve 7 becomes large when the boost pressure at the downstream
side is turned to be positive pressure.
[0109] In the PCV valve in which valve body 22 having fresh air
metering section 101 is equipped in the way constructed as
described above, the flow passage cross sectional area of fresh air
flow quantity control orifice 16 becomes smaller as the boost
pressure at position of intake air system which is located at the
downstream side with respect to throttle valve 7 becomes larger
positive pressure. Hence, it is possible to provide constant flow
quantity Q1 for fresh air quantity introduced into crank chamber 1a
via the PCV valve even if the boost pressure at the downstream side
of throttle valve 7 provides a large positive pressure.
[0110] In other words, even if the boost pressure of position of
intake air system 2 located at the downstream side with respect to
throttle valve 7 indicates the large positive pressure, the
quantity of fresh air introduced into crank chamber 1a through the
PCV valve in which valve body 22 having fresh air quantity metering
section 101 is equipped can provide constant. That is to say, even
if the boost pressure at position of intake air system 2 located at
the downstream side with respect to throttle valve 7 at the time of
high load driving state of engine 1 provides the large positive
pressure, fresh air quantity equal to or larger than the constant
quantity is not introduced into crank chamber 1a. Hence, at the
time of high load state of engine 1, the quantity of fresh air
flowing into engine 1 (intake air quantity) is not decreased.
[0111] Therefore, in a state in which the boost pressure of
position of intake air system 2 located at the downstream side with
respect to throttle valve 7 indicates the positive pressure, the
ventilation efficiency can be improved and the deterioration of
engine oil within crank chamber 1a can be suppressed.
[0112] It should be noted that, in a case of the application of the
PCV valve in which valve body 22 having fresh air metering section
101 is provided to the ventilation system, constant flow quantity
Q1 set at middle load driving region A2 and in high load driving
region A3 may appropriately be set with the balance between the
engine output and the engine ventilation efficiency of crank
chamber 1a taken into consideration.
Fifth Embodiment
[0113] FIG. 21 shows a fresh air flow quantity control valve 130
used in a fifth preferred embodiment of the engine ventilation
system according to the present invention.
[0114] In the fifth embodiment, in place of PCV quantity control
valve 29 described in the second embodiment, fresh air flow
quantity control valve 130 which controls the introduction quantity
of fresh air from intake air system 2 side to crank chamber 1a is
disposed in parallel to PCV valve 28.
[0115] The boost pressure-flow quantity characteristics of PCV
valve 28 and fresh air flow quantity control valve 130 are
previously adjusted to be equal to the characteristic of PCV valve
80 described in the fourth embodiment or to be substantially equal
to the characteristic denoted by sign B shown in FIG. 15.
[0116] FIG. 21 shows a detailed structure of fresh air flow
quantity control valve 130. This fresh air flow quantity control
valve 130 includes spool type valve body 146 slidably inserted into
valve body 141 having, so-called, two piece structure in the same
way as above-described fresh air flow quantity control valve 29.
First port 144 of valve body 141 faced toward cover 142 is
connected with position of intake air system 2 side located at the
downstream side with respect to throttle valve 7 and second port
145 of valve body 141 faced toward valve body main frame 143 side
is connected with oilmist separator 13 side.
[0117] Valve body 146 includes: a flange section 147 formed on an
end section of valve body 146 faced toward first port 144 side and
a fresh air metering section 148 in a substantially taper shape
projected from flange section 147 toward second port 145 side. A
compressive coil spring 149 interposed between flange section 147
and the bottom wall of valve body main frame 143 biases valve body
146 toward first port 144 side. Then, fresh air metering section
148 of valve body 146 includes: large diameter section 148a, taper
section 148b, small diameter section 148c, stepwise section 148d,
and a stepwise section 148e. Thus, in the same way as described
above, throat section 143a is formed in the same way as the fourth
embodiment which is the minimum diameter section of second port
145. Fresh air flow quantity control orifice 150 having the same
structure as the fourth embodiment is formed between throat section
143a and second port 145.
[0118] In a case where the boost pressure of intake air system 2
side described above is negative, flange section 147 of valve body
146 is seated on bottom wall section 142a of cover 142 so as to
close second port 145 and so that fresh air flow quantity control
valve 130 is closed. On the other hand, in a case where the boost
pressure at intake air system 2 side indicates positive pressure,
valve body 46 is slidably displaced at the balanced position at
which the boost pressure and the biasing force of compressive coil
spring 149 are balanced. Then, in the middle load driving region,
the quantity of fresh air streamed from position of intake air
system 2 located at the downstream side with respect to throttle
valve 7 to blowby gas reduction passage 10 provides the constant
quantity irrespective of the boost pressure. Thus, the boost
pressure-flow quantity characteristic of fresh air flow quantity
control valve 130 is set so that the quantity of fresh air streamed
from position of intake air system 2 located at the downstream side
of throttle valve 7 becomes substantially zero or extremely small
in the high load driving region.
[0119] In the fifth embodiment having the structure as described
above, in the low load driving region in which the boost pressure
at intake air system 2 side is negative, fresh air flow quantity
control valve 130 interrupts bypass passage 30 and, on the other
hand, the flow quantity of blowby gas exhausted toward intake air
system 2 side is controlled by means of PCV valve 28 so that blowby
gas reduction passage 10 exhibits the function that this passage
naturally has.
[0120] In the middle load driving region in which the boost
pressure at intake air system 2 side is positive pressure, blowby
gas reduction passage 10 is interrupted by means of PCV valve 28
and fresh air of constant flow quantity Q1 metered by means of
fresh air flow quantity control valve 130 is introduced into crank
chamber is through bypass passage 30. Thus, crank chamber 1a is
positively ventilated.
[0121] Then, in the high load driving region in which the boost
pressure at intake air system 2 side is positive, blowby gas
reduction passage 10 is interrupted by means of PCV valve 28 and
bypass passage 30 is also interrupted by means of fresh air flow
quantity control valve 130.
[0122] Hence, even in the fifth embodiment, the same function as
described in each of the embodiments can be exhibited. In addition,
fresh air flow quantity control valve 29 is additionally installed
as is different from PCV valve 28. Hence, the flow quantity of
fresh air introduced into crank chamber is can stably be controlled
with high accuracy. Especially, in the fifth preferred embodiment,
in the high load driving region in which the boost pressure at the
intake air system 2 side indicates positive, the quantity of fresh
air streamed from the downstream side of throttle valve 7 into
blowby gas reduction passage 10 is set to become substantially zero
or extremely small. Hence, importance is placed on the high load
driving region of the engine so that much of fresh air can be
supplied to the engine.
[0123] In the fifth embodiment described above, in place of fresh
air flow quantity control valve 130, it is possible to use fresh
air flow quantity control valve 160 shown in FIG. 22.
Sixth Embodiment
[0124] FIG. 22 shows fresh air flow quantity control valve 160 used
in a sixth preferred embodiment of the engine ventilation system
according to the present invention.
[0125] In the sixth embodiment, the boost pressure-flow quantity
characteristics of PCV valve 28 and fresh air flow quantity control
valve 160 are previously adjusted to provide the characteristics of
PCV valve of valve body 22 having fresh air metering section 101
and to provide the characteristic substantially equal to the
characteristic of sign B shown in FIG. 20.
[0126] FIG. 22 shows a detailed structure of fresh air flow
quantity control valve 160. This fresh air flow quantity control
valve 160 includes spool type valve body 166 slidably inserted into
valve body 161 having, so-called, two piece structure in the same
way as above-described fresh air flow quantity control valve 29.
First port 164 of valve body 161 faced toward cover 162 is
connected with position of intake air system 2 side located at the
downstream side of intake air system 2 with respect to throttle
valve 7 and second port 165 of valve body 161 faced toward valve
body main frame 163 side is connected with oilmist separator 13
side.
[0127] Valve body 166 includes a flange section 167 formed on an
end section of valve body 166 faced toward first port 164 side and
a fresh air metering section 168 in a substantially taper shape
projected from flange section 167 toward second port 165 side. A
compressive coil spring 169 interposed between flange section 167
and the bottom wall of valve body main frame 163 biases valve body
166 toward first port 164 side. Then, fresh air metering section
168 of valve body 166 includes: taper section 168a; and small
diameter section 168b of the column shape. Fresh air metering
section 168 is formed in the same way as fresh air metering section
101 in FIG. 18. A fresh air flow quantity control orifice 170 is
formed between throat section 163a which is the minimum diameter
section of second port 165 and fresh air metering section 168.
[0128] In a case where the boost pressure of intake air system 2
side is negative, flange section 167 of valve body 166 is seated on
bottom wall section 162a of cover 162 so as to close second port
165 and so that fresh air flow quantity control valve 160 is
closed. On the other hand, in a case where the boost pressure at
intake air system 2 side indicates positive pressure, valve body
166 is slidably displaced at the balanced position at which the
boost pressure and the biasing force of compressive coil spring 169
are balanced. Then, the flow passage cross sectional area of fresh
air flow quantity control orifice 150 becomes gradually small along
with the increase in the boost pressure. Thus, the boost
pressure-flow quantity characteristic of fresh air flow quantity
control valve 160 is set so that the flow quantity of fresh air
streamed to oilmist separator 13 side provides constant flow
quantity Q1.
[0129] In the sixth embodiment having the structure as described
above, in the low load driving region in which the boost pressure
at intake air system 2 side is negative, fresh air flow quantity
control valve 160 interrupts bypass passage 30 and, on the other
hand, the flow quantity of blowby gas exhausted toward intake air
system 2 side is controlled by means of PCV valve 28 so that blowby
gas reduction passage 10 exhibits the function that this passage
naturally has.
[0130] In addition, in the middle load driving region and in the
high load driving region in which the boost pressure at intake air
system 2 side indicates positive, blowby gas reduction passage 10
is interrupted by means of PCV valve 28. Then, fresh air of
constant flow quantity Q1 metered by means of fresh air flow
quantity control valve 160 is introduced into crank chamber 1a
through bypass passage 30. Thus, crank chamber 1a is positively
ventilated.
[0131] Hence, in the sixth embodiment, the action and advantage can
be obtained in the same way as in the case of the fifth embodiment.
In the sixth embodiment, fresh air of constant flow quantity Q1
even at high load driving region in which the boost pressure at
intake air system 2 side indicates positive is introduced from
position of intake air system 2 side located at downstream side
with respect to throttle valve 7 into crank chamber is via blowby
gas reduction passage 10. Hence, the ventilation efficiency at the
time of the high load driving state can be improved without
introduction of output reduction of engine 1 at the time of high
load and the deterioration of engine oil within crank chamber 1a
can be suppressed.
[0132] In addition, even in the fifth and sixth embodiments, fresh
air flow quantity control valve 110 may directly be communicated
with crank chamber 1a of engine 1 not with respect to oilmist
separator 13.
[0133] The effect of the present invention defined in each of
claims 1 and 7 has been described above in the summary of the
invention. According to the present invention described in the
claim 2 in which a variable orifice functioning as the fresh air
flow quantity control means is installed in the blowby gas
reduction passage and, in the high load driving region, a flow
passage cross sectional area of the variable orifice which
functions as the fresh air flow quantity control means is at least
made smaller than the flow passage cross sectional area in the
middle load driving region, since fresh air is introduced into the
crank chamber utilizing a known passage, it becomes advantageous in
terms of simplification of structure.
[0134] According to the present invention described in the claim 3
in which the PCV valve includes a variable orifice functioning as
the fresh air flow quantity control means apart from another
variable orifice for a blowby gas flow quantity control that the
PCV valve naturally has, since a slight improvement is added to
well known PCV valve to enable the achievement in the object of the
present invention, it becomes more advantageous in terms of
simplification of structure.
[0135] On the other hand, according to the present invention
described in the claim 4, the variable orifice which functions as
the fresh air flow quantity control means is installed in addition
to the PCV valve and the flow quantity introduced into the crank
chamber is controlled according to the variable orifice. Thus, the
flow quantity of fresh air introduced into the crank chamber can
stably be controlled with high accuracy.
[0136] According to the present invention described in the claim 5,
the introduction of fresh air to the crank chamber in the high load
driving region is stopped so that the output reduction of the
engine can effectively be suppressed.
[0137] Then, according to the present invention described in the
claim 6 in which a flow quantity of fresh air from position of the
intake air passage which is located at the downstream side with
respect to the throttle valve to the crank chamber, in the middle
load driving region (A2), is constant and, in the high load driving
region (A3), the flow quantity of fresh air from position of the
intake air passage which is located at the downstream side with
respect to the throttle valve is made equal to the flow quantity in
the middle load driving region, in a state in which the boost
pressure of position of the intake air passage located at the
downstream side with respect to the throttle valve indicates
positive, the quantity of fresh air introduced from position of
intake air passage located at the downstream side with respect to
the throttle valve does not provide the constant quantity or
larger. Hence, the ventilation efficiency can be improved without
introduction of engine output and the deterioration of engine oil
within the crank chamber can be suppressed.
[0138] This application is based on a prior Japanese Patent
Application No. 2010-285450 filed in Japan on Dec. 22, 2010 and No.
2010-137849 filed in Japan on Jun. 17, 2010. The entire contents of
these Japanese Patent Applications of No. 2010-285450 and No.
2010-137849 are hereby incorporated by reference. Although the
invention has been described above by reference to certain
embodiments of the invention, the invention is not limited to the
embodiments described above. Modifications and variations of the
embodiments described above will occur to those skilled in the art
in light of the above teachings. The scope of the invention is
defined with reference to the following claims.
* * * * *