U.S. patent application number 14/879681 was filed with the patent office on 2016-04-28 for method for manufacturing cylinder block.
The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Yusei KUSAKA, Syoichi TSUCHIYA.
Application Number | 20160114386 14/879681 |
Document ID | / |
Family ID | 55083264 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160114386 |
Kind Code |
A1 |
KUSAKA; Yusei ; et
al. |
April 28, 2016 |
METHOD FOR MANUFACTURING CYLINDER BLOCK
Abstract
A method of manufacturing a cylinder block including a
semicircular bearing section that rotatably supports a crankshaft
is provided. The method of manufacturing a cylinder block includes
pressure-injecting molten metal into a cavity formed inside a metal
mold, and sliding a pressure pin disposed in the metal mold after
the pressure-injecting of the molten metal and thereby applying a
pressure to the molten metal injected in the cavity, in which in
the applying of the pressure to the molten metal, the pressure pin
is slid toward an area where the bearing section is formed, a tip
of the pressure pin protruding in an arc shape so as to conform to
a shape of the bearing section.
Inventors: |
KUSAKA; Yusei; (Toyota-shi,
JP) ; TSUCHIYA; Syoichi; (Toyota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Family ID: |
55083264 |
Appl. No.: |
14/879681 |
Filed: |
October 9, 2015 |
Current U.S.
Class: |
164/120 |
Current CPC
Class: |
B22D 17/2069 20130101;
B22D 17/20 20130101; F02F 7/0053 20130101 |
International
Class: |
B22D 17/20 20060101
B22D017/20; B22D 25/02 20060101 B22D025/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2014 |
JP |
2014-219541 |
Claims
1. A method for manufacturing a cylinder block comprising a
semicircular bearing section that rotatably supports a crankshaft,
the method comprising: pressure-injecting molten metal into a
cavity formed inside a metal mold; and sliding a pressure pin
disposed in the metal mold after the pressure-injecting of the
molten metal and thereby applying a pressure to the molten metal
injected in the cavity, wherein in the applying of the pressure to
the molten metal, the pressure pin is slid toward an area where the
bearing section is formed, a tip of the pressure pin protruding in
an arc shape so as to conform to a shape of the bearing
section.
2. The method for manufacturing a cylinder block according to claim
1, wherein the tip of the pressure pin is formed in a semicircular
shape.
3. The method for manufacturing a cylinder block according to claim
1, wherein the tip of the pressure pin is formed in an arc shape
shorter than a semicircle, and in the pressure-injecting of the
molten metal, no recess is formed in a boundary between the metal
mold and the pressure pin.
4. The method for manufacturing a cylinder block according to claim
3, wherein notches are formed on both edges of the tip of the
pressure pin, which are in contact with the metal mold, and in the
pressure-injecting of the molten metal, the boundary between the
metal mold and the pressure pin is flat without any difference in
level formed therein.
Description
INCORPORATION BY REFERENCE
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2014-219541, filed on
Oct. 28, 2014, the disclosure of which is incorporated herein in
its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention The present invention relates to a
method for manufacturing a cylinder block, and in particular to a
method for manufacturing a cylinder block of an engine for a
vehicle.
[0003] 2. Description of Related Art
[0004] Japanese Unexamined Patent Application Publication No.
2012-179629 discloses a technique used in a method for
manufacturing a die-cast article (i.e., a cylinder block) including
a semicircular support surface on which a crankshaft is rotatably
supported, in which a pressure is locally applied to molten metal
located at or near the summit of the semicircular support surface
by using a pressure pin. A pressure is applied to molten metal
located in an area directly ahead of the pressure pin in its
longitudinal direction by that pressure pin. As a result, the
formation of blowholes in that area can be reduced.
SUMMARY OF THE INVENTION
[0005] However, the technique disclosed in Japanese Unexamined
Patent Application Publication No. 2012-179629 cannot sufficiently
reduce the occurrences of blowholes in areas outside the area
directly ahead of the pressure pin in its longitudinal direction.
It should be noted that an oil flow channel extends from a main
gallery toward the semicircular support surface so that a lubricant
can be supplied to the crankshaft. For example, if this oil flow
channel is connected to a bolt hole for attaching a crank cap due
to the formation of a blowhole, an oil leak occurs, thus making the
die-cast article defective. That is, there has been a problem that
the yield of products deteriorates due to the formation of
blowholes.
[0006] The present invention has been made in view of the
above-described problem and an object thereof is to reduce the
formation of blowholes in a cylinder block better than the related
art does and thereby to improve the yield of products.
[0007] A first exemplary aspect of the present invention is a
method for manufacturing a cylinder block including a semicircular
bearing section that rotatably supports a crankshaft, the method
including:
[0008] pressure-injecting molten metal into a cavity formed inside
a metal mold; and
[0009] sliding a pressure pin disposed in the metal mold after the
pressure-injecting of the molten metal and thereby applying a
pressure to the molten metal injected in the cavity, in which
[0010] in the applying of the pressure to the molten metal, the
pressure pin is slid toward an area where the bearing section is
formed, a tip of the pressure pin protruding in an arc shape so as
to conform to a shape of the bearing section.
[0011] In the method for manufacturing a cylinder block according
to the above-described aspect of the present invention, the
pressure pin, whose tip protrudes in an arc shape so as to conform
to the shape of the bearing section, is slid toward the area where
the bearing section is formed in the step for applying a pressure
to the molten metal. Therefore, the pressure applied to the molten
metal is not only applied to the area located directly ahead of the
pressure pin in its longitudinal direction but also applied
radially from the center of the tip of the pressure pin. As a
result, the formation of blowholes can be reduced in the entire
area inside the cylinder block, thus leading to an improvement in
the yield of products.
[0012] The tip of the pressure pin is preferably formed in a
semicircular shape. This structure can reduce the machining margin
of the bearing section.
[0013] Further, the tip of the pressure pin is preferably formed in
an arc shape shorter than a semicircle, and hence, in the
pressure-injecting of the molten metal, no recess is formed in the
boundary between the metal mold and the pressure pin. This
structure can reduce deformations and cracking on the surface of
the bearing section caused by microscopic solidification
pieces.
[0014] Further, notches are formed on both edges of the tip of the
pressure pin, which are in contact with the metal mold, so that the
boundary between the metal mold and the pressure pin becomes flat
without any difference in level formed therein in the
pressure-injecting of the molten metal. This structure can reduce
deformations and cracking on the surface of the bearing section
caused by pulled-in solidification shells.
[0015] According to the present invention, it is possible to reduce
the formation of blowholes in a cylinder block better than the
related art does and thereby improve the yield of products.
[0016] The above and other objects, features and advantages of the
present invention will become more fully understood from the
detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic bottom view of a cylinder block
manufactured by a manufacturing method according to a first
exemplary embodiment;
[0018] FIG. 2 is a cross section taken along a line II-II in FIG.
1;
[0019] FIG. 3 is a cross section taken along a line III-III in FIG.
1;
[0020] FIG. 4 is a schematic cross section showing a method for
manufacturing a cylinder block according to the first exemplary
embodiment;
[0021] FIG. 5 is a schematic cross section showing a method for
manufacturing a cylinder block according to a second exemplary
embodiment;
[0022] FIG. 6 is an enlarged view of an area at or near the tip of
a pressure pin 33 shown in FIG. 4;
[0023] FIG. 7 is a schematic cross section showing a method for
manufacturing a cylinder block according to a third exemplary
embodiment;
[0024] FIG. 8 is a schematic cross section showing a method for
manufacturing a cylinder block according to a fourth exemplary
embodiment; and
[0025] FIG. 9 shows macro-photographs of ingots for explaining
effects of pressurization for molten metal.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0026] Specific exemplary embodiments to which the present
invention is applied are explained hereinafter in detail with
reference to the drawings. However, the present invention is not
limited to exemplary embodiments shown below. Further, the
following descriptions and the drawings are simplified as
appropriate for clarifying the explanation.
First Exemplary Embodiment
[0027] Firstly, a cylinder block manufactured by a manufacturing
method according to a first exemplary embodiment is explained with
reference to FIGS. 1 to 3. FIG. 1 is a schematic bottom view of the
cylinder block manufactured by the manufacturing method according
to the first exemplary embodiment. FIG. 2 is a cross section taken
along a line II-II in FIG. 1. FIG. 3 is a cross section taken along
a line III-III in FIG. 1. The cylinder block 1 shown in FIG. 1 is a
part of an inline four-cylinder engine in which four cylinder bores
11 each having an axis in parallel with the z-axis are arranged in
the x-axis direction. However, the number of cylinders can be
changed as desired. Further, the present invention can also be
applied to cylinder blocks of V-type engines and
horizontally-opposed cylinder engines as well as inline
engines.
[0028] Note that, needless to say, the right-handed xyz-coordinate
systems shown in FIGS. 1 to 3 are shown just for the sake of
convenience for explaining the positional relation among
components. The cylinder block 1 is typically mounted on a vehicle
in such a manner that the positive direction on the z-axis becomes
the vertically upward direction. Therefore, the following
explanation with reference to FIGS. 1 to 3 is given on the
assumption that the positive direction on the z-axis is the
vertically upward direction.
[0029] The cylinder block 1 is a die-cast article made of, for
example, an aluminum alloy. As shown in FIG. 2, the cylinder block
1 includes cylinder sections 10 with cylinder bores 11 formed
therein, and skirt sections 20. The skirt sections form a part of a
crank case that houses a crankshaft (not shown).
[0030] As shown in FIG. 1, a cylinder bore 11, which is a
cylindrical hole, is formed in each of the cylinder sections 10.
The part of the cylinder section 10 that surrounds the cylinder
bore 11 is a cylinder wall 12. A piston (not shown), which performs
a reciprocating motion inside the cylinder bore 11, is slid in the
cylinder bore 11 while remaining in contact with the inner
circumferential surface of the cylinder wall 12. Though it is not
shown in the figures, a cylinder liner made of for example, cast
iron having an excellent wear resistance or the like is usually
disposed on the inner circumferential surface of the cylinder wall
12 in order to reduce the abrasion caused by the sliding motion of
the piston.
[0031] A cylinder head (not shown) is mounted on the top end (end
on the positive side on the z-axis) of the cylinder wall 12, i.e.,
on the so-called "upper deck". Further, the cylinder bore 11, the
piston, and the cylinder head form a combustion chamber. A passage
(water jacket) 13 through which a coolant is circulated is formed
inside the cylinder wall 12, so that the cylinder section 10 can be
cooled to an appropriate temperature.
[0032] The skirt section 20 includes skirt walls 21 that form an
outer shell of the crank case, and bulkheads 22 that partition the
crank case into each cylinder bore 11. As shown in FIG. 2, a pair
of the skirt walls 21 are formed so that they seamlessly extend
from the cylinder wall 12 and spread in the y-axis direction while
being opposed to each other. Further, as shown in FIG. 1, a
plurality of pairs of the skirt walls 21 are arranged in the x-axis
direction. The bulkheads 22 are disposed in five places, i.e.,
between each pair of neighboring cylinder bores of the four
cylinder bores 11 (three places) and both sides of the four
cylinder bores 11 (two places). As shown in FIGS. 1 and 2, each of
the bulkheads 22 extends in the y-axis direction so as to straddle
a pair of the skirt walls 21.
[0033] A semicircular bearing section 23 for rotatably supporting a
journal (not shown) of the crankshaft is formed at the center of
the bottom end (end on the negative side on the z-axis) of each
bulkhead 22. Bolt holes 24 for attaching a crank cap (not shown)
are formed on both sides of the bearing section 23.
[0034] Further, to enable the journal to be supplied with a
lubricant, an oil flow channel 26 extends from a main gallery 25
toward the bearing section 23 inside each bulkhead 22. Note that as
shown in FIG. 2, the main gallery 25 is disposed in one of the two
connecting sections between the cylinder section 10 and the skirt
section 20. Further, as shown in FIG. 1, the main gallery 25
extends in the x-axis direction so as to intersect all of the
bulkheads 22. In this exemplary embodiment, the main gallery 25 is
formed by using a core pin when the die-cast article is cast. In
contrast to this, the oil flow channel 26 is formed by machining
after the casting process.
[0035] Further, a through hole 27 is formed near the center of each
bulkhead 22. The through hole 27 is formed to connect the spaces
partitioned by the bulkhead 22 with each other. In this exemplary
embodiment, the through hole 27 is formed by using a core pin when
the die-cast article is cast. However, needless to say, the through
hole 27 may be formed by machining after the casting process.
[0036] It should be noted that if the oil flow channel 26 is
connected to the bolt hole 24 or the through hole 27 in FIG. 3, for
example, an oil leak failure occurs, thus leading to a
deterioration in the yield of products. However, in the cylinder
block 1 manufactured by the manufacturing method according to this
exemplary embodiment, the formation of blowholes inside the
bulkhead 22 is reduced better than it is in the related art.
Therefore, the yield of products in the manufacturing method
according to this exemplary embodiment is superior to that in the
related art.
[0037] Next, a method for manufacturing a cylinder block according
to the first exemplary embodiment is explained with reference to
FIG. 4. FIG. 4 is a schematic cross section showing a method for
manufacturing a cylinder block according to the first exemplary
embodiment. The cylinder block 1 is manufactured by die casting.
Specifically, as shown in FIG. 4, a movable mold (or movable die)
30 is moved in the positive direction on the z-axis and brought
into contact with a fixed mold (or fixed die) 40. Then, molten
metal is pressure-injected into a cavity 2 formed in a gap between
these molds. As indicated by the xyz-coordinate system in FIG. 4,
the cylinder block 1 shown in FIG. 4 is rotated by 90.degree. with
respect to the cylinder block 1 shown in FIG. 3. In FIG. 4, the
positive direction on the y-axis corresponds to the vertically
upward direction. The main gallery 25 is formed by using a core pin
50 that can be moved forward and backward in the x-axis direction,
and the through hole 27 is formed by using another core pin 60 that
can also be moved forward and backward in the x-axis direction.
[0038] As shown in FIG. 4, the bottom surface (surface on the
negative side on the z-axis) of the bulkhead 22 of the cylinder
block 1 is formed by the front surface (surface on the positive
side on the z-axis) of the movable mold 30. Note that pins 34 for
forming rough holes (i.e., preparatory holes) for the bolt holes 24
are disposed on and protrude from the front surface of the movable
mold 30. The pins 34 are fixed to the movable mold 30.
[0039] Further, as shown in FIG. 4, a pressure pin 33 that can be
slid in the z-axis direction with respect to the movable mold 30 is
disposed in the movable mold 30. The pressure pin 33 forms the
bearing section 23 of the bulkhead 22 and can apply a pressure to
molten metal. It should be noted that in order to form the bearing
section 23, the tip of the pressure pin 33 is formed so as to
protrude in an arc shape to conform to the shape of the bearing
section 23.
[0040] When molten metal is injected, the pressure pin 33 is
positioned in a retreated position as indicated by a chain
double-dashed line in FIG. 4. When the molten metal starts to
solidify, the pressure pin 33 disposed in the movable mold 30 is
slid forward (in the positive direction on the z-axis), i.e., is
moved forward as indicated by a solid line in FIG. 4, and a
pressure is thereby applied to the molten metal. By doing so, the
formation of blowholes inside the bulkhead 22 can be reduced. The
sliding distance of the pressure pin 33 is, for example, in the
order of several millimeters.
[0041] It should be noted that in the related art, a pressure pin
whose tip is flat is slid toward an area where a bearing section is
formed. In contrast to this, in this exemplary embodiment, the
pressure pin 33, whose tip protrudes in an arc shape to conform to
the shape of the bearing section 23, is slid toward the area where
the bearing section 23 is formed. Therefore, the pressure applied
to the molten metal is not only applied to the area located
directly ahead of the pressure pin 33 in its longitudinal direction
(i.e., the area located on the positive side on the z-axis) but
also applied radially from the center of the tip of the pressure
pin 33. As a result, the formation of blowholes can be reduced in
the entire area inside the bulkhead 22, thus leading to an
improvement in the yield of products.
[0042] Further, since the tip of the pressure pin 33 protrudes in
an arc shape to conform to the shape of the bearing section 23, the
withdrawal resistance of the pressure pin 33. Further, the bearing
section 23 can be formed in a near net shape. That is, the maching
margin (excess metal) of the bearing section 23 can be reduced,
meaning that the productivity of this exemplary embodiment is
superior to the relate art.
[0043] In particular, in the first exemplary embodiment, the width
of the pressure pin 33 is roughly equal to the diameter of the
semicircular bearing section 23. That is, the tip of the pressure
pin 33 is formed in a semicircular shape to conform to the shape of
the bearing section 23. Therefore, the maching margin is
significantly reduced. In the related art, the pressure pin is
moved forward with a sufficient maching margin. Thus, compared to
this exemplary embodiment, the related art requires more time in a
subsequent machining process. Therefore, the productivity of the
related art is inferior to that of this exemplary embodiment.
[0044] Further, the width w of the pressure pin 33 according to
this exemplary embodiment is larger than that of a pressure pin in
the related art. Provided that the amount of the volume change in
the pressurization process in this exemplary embodiment is equal to
that in the related art, the traveling distance of the pressure pin
33 can be reduced compared to that in the related art. As a result,
the withdrawal resistance of the pressure pin 33 can be
reduced.
Second Exemplary Embodiment
[0045] Next, a method for manufacturing a cylinder block according
to a second exemplary embodiment is explained with reference to
FIG. 5. FIG. 5 is a schematic cross section showing a method for
manufacturing a cylinder block according to a second exemplary
embodiment. Firstly, a problem in the first exemplary embodiment is
explained with reference to FIG. 6. FIG. 6 is an enlarged view of
an area at or near the tip of the pressure pin 33 shown in FIG.
4.
[0046] As shown in FIG. 6, in the method for manufacturing a
cylinder block according to the first exemplary embodiment, a
wedge-shaped recess is formed between the movable mold 30 and the
pressure pin 33 before applying a pressure, i.e., in a state where
the pressure pin 33 is in a retreated position. Since molten metal
that has gotten into this recess solidifies quickly, microscopic
solidification pieces are formed as shown in FIG. 6. Then, when the
pressure pin 33 is moved forward in the pressurization process,
these microscopic solidification pieces could be pressed onto and
buried into the surface of the bearing section 23 of the cylinder
block 1, thus causing a possibility that deformations and cracking
occur in the surface of the bearing section 23.
[0047] To cope with this problem, in the method for manufacturing a
cylinder block according to the second exemplary embodiment, as
shown in FIG. 5, the width w of a pressure pin 33a is a size
smaller than that of the pressure pin 33 according to the first
exemplary embodiment. In other words, the width of the pressure pin
33a is smaller than the diameter of the semicircular bearing
section 23. That is, the tip of the pressure pin 33a is formed so
as to have an arc shape shorter than a semicircle.
[0048] This structure can reduce deformations and cracking on the
surface of the bearing section 23 caused by microscopic
solidification pieces because no recess is formed in the boundary
between the movable mold 30 and the pressure pin 33a before the
pressurization process. However, since the width w of the pressure
pin 33a is reduced, the maching margin could increase. Other
configurations are similar to those in the first exemplary
embodiment, and therefore their explanations are omitted. Similarly
to the first exemplary embodiment, the method for manufacturing a
cylinder block according to the second exemplary embodiment can
reduce the formation of blowholes in the entire area inside the
bulkhead 22, thus leading to an improvement in the yield of
products.
Third Exemplary Embodiment
[0049] Next, a method for manufacturing a cylinder block according
to a third exemplary embodiment is explained with reference to FIG.
7. FIG. 7 is a schematic cross section showing a method for
manufacturing a cylinder block according to a third exemplary
embodiment. As shown in FIG. 7, when compared to the pressure pin
33a according to the second exemplary embodiment, notches 35 are
formed on both edges of the tip of a pressure pin 33b according to
the third exemplary embodiment. In particular, these notches 35 are
formed in areas of the tip that are in contact with the movable
mold 30.
[0050] By this structure, the boundary between the movable mold 30
and the pressure pin 33b is flat without any difference in level
formed therein before the pressurization process. Therefore,
solidification shells that are continuously formed over the movable
mold 30 and the pressure pin 33b can be easily sheared (i.e., cut)
by moving the pressure pin 33b forward. As a result, deformations
and cracking on the surface of the bearing section 23 caused by
pulled-in solidification shells can be reduced even better than it
is in the second exemplary embodiment. However, since the notches
35 are formed, the maching margin could increase.
[0051] Other configurations are similar to those in the first and
second exemplary embodiments, and therefore their explanations are
omitted. Similarly to the first exemplary embodiment, the method
for manufacturing a cylinder block according to the third exemplary
embodiment can reduce the formation of blowholes in the entire area
inside the bulkhead 22, thus leading to an improvement in the yield
of products. Further, similarly to the second exemplary embodiment,
since no recess is formed between the movable mold 30 and the
pressure pin 33b before the pressurizing process, deformations and
cracking on the surface of the bearing section 23 caused by
microscopic solidification pieces can be reduced (or
prevented).
Fourth Exemplary Embodiment
[0052] Next, a method for manufacturing a cylinder block according
to a fourth exemplary embodiment is explained with reference to
FIG. 8. FIG. 8 is a schematic cross section showing a method for
manufacturing a cylinder block according to a fourth exemplary
embodiment. As shown in FIG. 8, a pressure pin 33c according to the
fourth exemplary embodiment applies a pressure to the whole area
where a crank cap is attached, instead of applying a pressure only
to the area where the bearing section 23 is formed. Even when this
configuration is employed, the formation of blowholes can be
reduced (or prevented) in the entire area inside the bulkhead 22 as
in the case of the first exemplary embodiment, thus leading to an
improvement in the yield of products.
Experiment Examples
[0053] Next, advantageous effects of the method for manufacturing a
cylinder block according to the first exemplary embodiment are
explained with reference to FIG. 9. FIG. 9 shows macro-photographs
of ingots for explaining effects of pressurization for molten
metal. We have conducted the below-shown Experiment examples 1 and
2 to examine the effects of pressurization for molten metal. The
experiment methods of Experiment examples 1 and 2 are explained
hereinafter. Experiment example 1 corresponds to an example
according to the present invention and Experiment example 2
corresponds to a comparative example.
[0054] In both experiment examples, a test piece was produced by
die casting as an imitation of a bulkhead 22 of a cylinder block as
shown in FIG. 9 by pressure-injecting molten metal of an aluminum
alloy (ADC12) under a pressure of 25 MPa. The distribution state of
blowholes in each of the test pieces was examined by observing its
macro-structure. Further, the volume rate of the blowholes was
obtained by measuring the specific gravity. Note that any of the
bolt hole 24, the main gallery 25, and the through hole 27 was not
formed in these test pieces. CL Experiment Example 1
[0055] Casting was performed in the following manner: two seconds
after molten metal was pressure-injected in a state where the
pressure pin 33 was in a retreated position, the pressure pin 33
was moved forward by 4 mm and a pressure of 160 MPa was thereby
applied to the molten metal.
Experiment Example 2
[0056] Casting was performed by pressure-injecting molten metal in
a state where the pressure pin 33 was in a retreated position
without moving the pressure pin 33.
[0057] As seen from the observations of the macro-structures shown
in FIG. 9, in the test piece in Experiment example 1, in which
molten metal was pressurized, the number of blowholes was fewer and
their sizes were smaller over the entire cross section than those
in the test piece in Experiment example 2, in which molten metal
was not pressurized. Further, the volume rate of the blowholes in
the test piece in Experiment example 1 was 1.0%, while that in the
test piece in Experiment example 2 was 3.5%. Based on these
experiment results, it has been proved that the method of
manufacturing a cylinder block according to the first exemplary
embodiment can reduce the formation of blowholes in the entire area
inside the bulkhead 22.
[0058] Note that the present invention is not limited to the
above-described exemplary embodiments, and various modifications
can be made without departing from the spirit and scope of the
present invention.
[0059] From the invention thus described, it will be obvious that
the embodiments of the invention may be varied in many ways. Such
variations are not to be regarded as a departure from the spirit
and scope of the invention, and all such modifications as would be
obvious to one skilled in the art are intended for inclusion within
the scope of the following claims.
* * * * *