Abstrict The present invention relates to a positive displacement flow meter
having a pair of rotors to be rotatably engaged with each other
which are provided with tooth profile curves of a cycloid and of
a trochoid. Since the tooth profile of one rotor is equal to that
of the other rotor, transmission of energy between the two rotors
is uniform, and wear of teeth of the two rotors being reduced.
Claims What is claimed is:
1. A positive displacement flow meter having a pair of rotors of
helical tooth structure to be engageable with each other, wherein
the opposite flanks of each tooth have in a section normal to the
rotor axes at the addendum the form of a cycloid and at the dedendum
the form of a trochoid, and wherein each of said flanks has at the
addendum a convexly curved projection extending a small distance
radially inwardly of the addendum circle thereof and at the dedendum
convexly curved projection extending a short distance radially inwardly
of the pitch circle, said rotors engaging each other during their
rotation only at said projections.
2. A positive displacement flow meter having a pair of rotors having
helical teeth engaging each other in a plane normal to the axes
of said rotors, said rotors having the same outer diameters and
the same number of teeth respectively inclined to said axes at an
angle .beta., and in which L=i.times.(2R.pi./Z)/tan .beta., wherein
L=the axial length of each rotor, i is an integral number, R the
outer radius of each rotor and Z the number of teeth in each rotor.
3. A positive displacement flow meter as defined in claim 2 wherein
the number of teeth in each rotor is four.
4. A positive displacement flow meter as defined in claim 3 wherein
i is equal to two.
Description BACKGROUND OF THE INVENTION
Conventionally, a typical positive displacement flow meter has
a pair of rotors, there are known a non-circle tooth-type flow meter,
a Roots-type flow meter, a birotary-type flow meter and the like.
The non-circle tooth-type flow meter (which is called a flow meter
having the trademark "OVAL") has a relatively simple structure
and a high performance as to output the disadvantage thereof is
that the rotors are forced to be rotated with an unequal speed rotation
so that it is unavoidable to prevent vibrating noises due to pulsation.
Further, the disadvantage of the Roots-type flow meter is that because
the rotor itself does not rotate uniformly, it is indispensable
to employ a pilot gear, and subsequently a phase adjustment between
a pilot gear and a rotor and the assembling work become more complicated.
Consequently, the whole structure thereof also becomes complicated.
Still further, the disadvantage of the birotary-type flow meter
is that it is possible to prevent pulsation by selecting an appropriate
twist angle (which is normally provided with a twist angle of 1.5
pitch at the tooth width), but it is unavoidable to employ a pilot
gear just like in case of the above Roots-type flow meter. From
the theoretical point of view, the birotary-type flow meter can
transmit rotation without requiring a pilot gear, but the tooth
profile is provided with the so-called second tooth profile so that
its slippage is very big, and respective teeth are worn considerably
by their mutual engagement. Accordingly, it is substantially indispensable
to employ a pilot gear. Further, there exists the defect that the
casing diameter is inconsistent occasionally, and the cutting work
is troublesome and inefficient due to a different tooth profile
curve of a pair of rotors.
The following references corresponding to the foregoing known art
can be cited: U.S. Pat. Nos. 2410172 2243874 2287716 1821523
1965557 etc. Each cited reference has a pair of rotors to be
engaged with each other, wherein the tooth profile of a first rotor
is quite different from that of a second rotor. Consequently, transmission
of energy between the two rotors is not uniform, and a stronger
force of one rotor is applied to the other rotor. In view thereof,
the vibration due to mutual engagement of the two rotors is large
and it is impossible to avoid wear of teeth of the two rotors.
In order to remove the aforegoing defects of the conventional art,
the present invention has been made.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is the primary object of this invention to provide
a positive displacement flow meter which is provided with a pair
of rotors of helical tooth structure to be engaged with each other,
wherein an addendum of the tooth profile curve of a pair of rotors
is provided with cycloid, and a deddendum of the same is provided
with trochoid, and in which the pair of rotors have the same tooth
profile.
It is another object of this invention to provide a positive displacement
flow meter in which a pair of rotors are rotatable with an equal
speed of rotation, and which is adaptable for a large-scale flow
meter due to very small pulsation and vibrating noise.
It is another object of this invention to provide a positive displacement
flow meter which is capable of improving the manufacture of rotors
of helical tooth structure as well as reducing the manufacturing
cost since each of a pair of rotors has the same tooth profile.
It is another object of this invention to provide a positive displacement
flow meter in which the torque of a pair of rotors is always constant
during its one revolution, and transmission of energy between the
two rotors is mutually balanced.
It is another object of this invention to provide a positive displacement
flow meter of high accuracy in which the cross section of a pair
of rotors taken at a plane normal to the axes of the rotor is provided
with the same tooth profile and the same number of teeth.
It is another object of this invention to provide a positive displacement
flow meter in which a first tooth profile is formed by mounting
an arc tooth profile of the slippage zero to a portion of a second
tooth profile of a pair of rotors, and thereby a rotation of a pair
of rotors to be engaged with each other being obtainable without
using a pilot gear.
It is a further object of this invention to provide a positive
displacement flow meter in which a locking means to enable to lock
a pair of rotors with a tooth profile to be engageable adjacent
a pitch circle of a pair of rotors so as to perform the function
of a pilot gear, and thereby a very smooth rotation being obtainable
with less friction and less vibration.
It is still a further object of this invention to provide a pair
of rotors provided with a tooth profile curve of a cycloid and of
a trochoid, which are applicable not only to a positive displacement
flow meter, but also to a rotation pump, a motor and other various
devices.
It is still a further object of this invention to provide a positive
displacement flow meter, in which a convex tooth profile is provided
at one (or two) portion(s), while the other portion thereof is recessed,
thereby a pair of rotors being able to be rotated smoothly only
by the convex tooth profile.
Other features and advantages of this invention will be apparent
from the following description taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a section view of tooth profile curves of a pair of rotors
taken in a plane normal to the axes of the rotors which illustrates
an embodiment of a positive displacement flow meter according to
this invention.
FIG. 2a to FIG. 2j illustrate variations of rotation in mutual
engagement of a pair of rotors in FIG. 1.
FIG. 3 illustrates the path of engagement points of a pair of rotor
in FIG. 1.
FIG. 4a illustrates a tooth profile structure of engagement of
a pair of rotors showing another embodiment of a positive displacement
flow meter according to this invention.
FIG. 4b illustrates the path of engagement of a pair of rotors
in FIG. 4.
FIG. 5 illustrates a tooth profile structure showing another embodiment
of a pair of rotors.
FIG. 6 is a section view of the detailed structure of a positive
displacement flow meter according to this invention.
FIG. 7a shows the condition of instrumental correction of a positive
displacement flow meter according to this invention.
FIG. 7b is a graph showing the pressure loss in a positive displacement
flow meter according to this invention.
FIG. 8 is a section view of tooth profile curves of a pair of rotors
taken at an axially right angle which illustrates another embodiment
of a positive displacement flow meter according this invention.
FIG. 9a to FIG. 9h illustrate variations of rotation in mutual
engagement of a pair of rotors in FIG. 8.
FIG. 10 is a section view of tooth profile curves of a pair of
rotors having the same outer diameter and the same number of teeth
according to another embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a section view of a positive displacement flow
meter taken in a plane normal to the axes of the rotors wherein
a pair of helical teeth to be engaged with each other are provided
with a first rotor 1 having four teeth and a second rotor 2 having
three teeth. Under this structure a pair of rotors 1 2 are rotatable
freely in accordance with P=P.sub.1 -P.sub.2 i.e. the liquid pressure
difference toward a liquid flow outlet 4' from a flow inlet 4 installed
in a casing 3. Numerals 5 and 6 designate respectively the pitch
circle and the addendum circle of the rotor 1. Numerals 7 and 8
designate respectively the pitch circle and the addendum circle
of the rotor 2. Numerals 0.sub.1 and 0.sub.2 are centers of the
two rotors 1 2. A pitch point is denoted at M.
The curves A.sub.1 B.sub.1 and A.sub.2 B.sub.2 are tooth profile
curves which are formed at the addendum of the two rotors 1 2 respectively,
while the curves B.sub.1 C.sub.1 and B.sub.2 C.sub.2 are tooth profile
curves which are formed at the deddendum of the two rotors 1 2
respectively. In other words, by defining the pitch circles 5 7
of the two rotors 1 2 as a border, the tooth profile curves which
are formed toward the addendum from the pitch circles 5 7 correspond
to the curves A.sub.1 B.sub.1 and A.sub.2 B.sub.2 while the tooth
profile curves which are formed toward the deddendum from the pitch
circles 5 7 correspond to the curves B.sub.1 C.sub.1 and B.sub.2
C.sub.2.
The opposite section of these tooth profile curves is illustrated
symmetrically just like in case of the section in FIG. 1 so that
the description of the opposite section shall be omitted.
When a pair of rotors 1 2 are engaged with each other due to rolling
without slipping on the pitch circles 5 7 an intersecting point
A.sub.1 between the addendum circle 6 of the first rotor 1 and the
tooth profile curve thereof is engaged due to slipping along with
the tooth surface of the dedendum of the second rotor 2. In other
words, whereas the tooth profile curve of the dedendum of the second
rotor 2 is a track on the rotor 2 at the point A.sub.1 the tooth
profile curve of the addendum of the rotor 1 is a track on the rotor
1 at the point B.sub.2.
The points A.sub.1 and B.sub.2 become the intersecting points on
the tooth profile curves of either of the rotors 1 2 and further
are positioned on the circumference of the addendum circle 6 of
the first rotor 1 and on that of the pitch circle 7 of the second
rotor 2. If the intersecting points of the two circles 6 7 are
denoted at N and N', and an intersecting point between the line
connection axes of the both rotor 1 2 and the addendum circle 6
is denoted at K, the track in relation of the intersecting points
A.sub.1 B.sub.2 with the static co-ordinates becomes two arcs i.e.
NKN' and NMN', and subsequently the engagement of the two rotors
1 2 is completely sealed along the helical teeth surfaces while
maintaining contact on the teeth surfaces. In the same manner, concerning
the point B.sub.1 of the rotor 1 corresponding to the points A.sub.2
and B.sub.2 of the second rotor 2 corresponding to the point A.sub.1
if the intersecting points between the addendum circle 8 of the
second rotor 2 and the pitch circle 5 of the first rotor 1 are denoted
at S and S.sub.1 and if an intersecting point between the line
connecting the both rotors 1 2 axes, and the addendum circle 8
is denoted at U, as shown in the dotted line of FIG. 1 two arcs
i.e. SUS' and SMS' are obtainable as a track of the static co-ordinates
of the intersecting points A.sub.2 and B.sub.1.
When the two pitch circles 5 7 are rolled and contacted together
without slipping, the tooth profile curves A.sub.1 B.sub.1 and A.sub.2
B.sub.2 to be formed on the addendum of the two rotors 1 2 shows
the cycloid to be described by the points B.sub.2 and B.sub.1 on
the pitch circle, while the tooth profile curves B.sub.1 C.sub.1
and B.sub.2 C.sub.2 to be formed on the dedendum of the two rotors
1 2 show the trochoid to be described by the points A.sub.1 and
A.sub.2 on the addendum circle.
Accordingly, whereas the points B.sub.1 and B.sub.2 are the contacting
points contacting the cycloid A.sub.2 B.sub.2 and A.sub.1 B.sub.1
the points A.sub.1 and A.sub.2 are the contacting points contacting
the trochoid B.sub.2 C.sub.2 and B.sub.1 C.sub.1.
In other words, it is to be understood that the tooth profile curves
of a pair of rotors 1 2 to be engaged with each other are in the
form of a cycloid at the addendum and in the form of a trochoid
at the dedendum with the points B.sub.1 and B.sub.2 on the pitch
circle as the border.
The ends of the cycloid and of the trochoid to be positioned at
the addendum and the tooth bottom of the two rotors 1 2 are connected
by arcs.
Accordingly, a pair of rotors 1 2 can obtain the movement of engagement
without conflicting with each other. The variations of engagement
of a pair of rotors 1 2 are illustrated in FIG. 2a to FIG. 2j.
As will be understood from FIG. 2a to FIG. 2j, the track to be
described by the points A.sub.1 A.sub.2 and B.sub.1 B.sub.2 of the
two rotors 1 2 are provided with four arcs NKN', NMN', SUS' and
SMS'.
FIG. 10 illustrates an embodiment of the flow meter having two
rotors made with the same number of teeth and with the same diameters.
The entire description of the tooth profile curves depicted in FIG.
1 may be referred to FIG. 10.
The rotating torque of a flow meter A having a pair of rotors of
the aforegoing structure will be described hereinafter from the
theoretical point of view.
Now the torque T.sub.1 of the first rotor 1 will be denoted as
Ta.sub.1 at the addendum and as Td.sub.1 at the deddendum, and the
radii of the respective contacting points will be denoted as Ra.sub.1
and Rd.sub.1. And a X-axis will be taken to an axial direction.
Then, the following equations are obtained. ##EQU1## Wherein Ro.sub.1
: Radius of the addendum circle
R.sub.1 : Radius of the pitch circle
Rr.sub.1 : Radius of the tooth bottom circle.
In the same manner, the torque T.sub.2 of the second rotor 2 will
be denoted as Ta.sub.2 at the addendum and as Td.sub.2 at the dedendum,
and the radii of the respective contacting points will be denoted
as Ra.sub.2 and Rd.sub.2. Then, the following equations are obtained.
##EQU2## Wherein Ro.sub.2 : Radius of the addendum circle
R.sub.2 : Radius of the pitch circle
Rr.sub.2 : Radius of the tooth bottom circle
On the basis of the track view of the contacting points of the
rotors as shown in FIG. 3 the radii Ra.sub.1 Rd.sub.1 Ra.sub.2
and Rd.sub.2 of each contacting point are obtained by the following
equations. ##EQU3##
Since the respective tooth profile of a pair of rotors 1 2 has
a preferred twist angle .beta. to an axial direction of the rotors,
by inserting the related equation
the foregoing equations (1) and (2) can be rewritten as follows.
##EQU4##
When integrating the foregoing equations (4) and (5) by defining
the integral calculus of each rotation angle, the rotating torque
in each engagement position is obtained, but the torque is generally
variable.
The twist angle .beta. is to be twisted so as to be multiplied
by a certain integral number at the length L of each rotor. In other
words, the tooth surface of the front end of the rotors 1 2 respectively
and that of the rear end thereof are to be positioned so as to be
twisted by maintaining a certain integral number of the pitch, wherein
the number of teeth of the rotors 1 2 respectively will be Z.sub.1
Z.sub.2 and the positive integral number will be i. Then, the following
relation is obtained. ##EQU5##
Further, when the foregoing equation (6) will be integrated by
each rotation angle of the two rotors 1 2 the following equations
is obtained. ##EQU6##
At the same time, the following equation is obtained. ##EQU7##
All the numerical values of the foregoing equations (7) and (8)
show respectively a certain constant value, and no variable quantity
is included.
Accordingly, the followings are constant.
Further, when the sectional profiles of a pair of rotors 1 2 taken
at an axially right angle are identified with each other, the following
relations are obtained in accordance with the foregoing equations.
Accordingly, the following is obtained.
In order that a pair of rotors 1 2 are always rotatable with an
equal speed without pulsation, it is required to gain the condition
that the sum of the torques T.sub.1 and T.sub.2 of the two rotors
1 2 is fixed.
And, the difference between the two rotating torques T.sub.1 and
T.sub.2 expresses the transmission of energy during the rotation
of a pair of rotors 1 2. Then, the following cases will be explained.
(i) In case of T.sub.i`-T.sub.2 >0
This case shows that the first rotor 1 as the main drive rotates
the second rotor 2.
(ii) In case of T.sub.1 -T.sub.2 <0
This case shows that the second rotor 2 as the main drive rotates
the first rotor 1.
(iii) In case of T.sub.1 -T.sub.2 =0 i.e. T.sub.1 =T.sub.2
This case shows that the two rotors are rotated by themselves,
so that the superficial pressure of the contacting point is zero.
Accordingly, when the sum of the torques T.sub.1 and T.sub.2 of
a pair of rotors 1 2 is fixed, and T.sub.1 =T.sub.2 is obtainable,
an ideal positive displacement flow meter is established.
From the foregoing viewpoints, the equations (7), (8) and (9) will
be studied.
(I) In case of L.noteq.iR(2.pi./Z)/tg.beta.
Either T.sub.1 or T.sub.2 is not fixed, and the sum of them and
the difference between them are not fixed.
(II) In case of L=iR(2.pi./Z)/tg.beta.
Either T.sub.1 or T.sub.2 is fixed, and the sum of them and the
difference between them are fixed. However, when the number of teeth
of the first rotor 1 is not equal to that of the second rotor 2
the difference between T.sub.1 and T.sub.2 does not become zero.
But when the number of teeth of the former is equal to that of the
latter, as shown in FIG. 10 the difference between T.sub.1 and
T.sub.2 becomes zero whereby an ideal positive displacement flow
meter is established. When the twist angle .beta. is not multiplied
by a certain integral number of pitch and the phase of the front
and rear tooth surface of the rotor is slipped just by 1/2 pursuant
to
the torques T.sub.1 and T.sub.2 of the two rotors 1 2 are not
constant and the difference between them is not constant, and only
the sum of them is constant.
Under the foregoing circumstances the present invention can provide
a positive displacement flow meter having a pair of rotors of helical
tooth structure in which the addendum is provided with a cycloid
and the deddendum is provided with a trochoid. Further, when the
twist angle .beta. is of the pitch to be multiplied by a certain
integral number at the gear width, and the sectional profile of
the first rotor 1 taken at an axially right angle has the same shape
as that of the second rotor taken in the same manner, an ideal positive
displacement flow meter is established.
Although the tooth profile contacting point of such a positive
displacement flow meter has a zero pressure of the tooth surface,
since the engagement is secondary one the slippage is big and under
a slight load there is the danger of wear. Thus, it is required
to employ a pilot gear practically, consequently the whole structure
becoming complicated. In addition, there are many difficulties in
view of assembling and combination of the pilot gear and the rotors
as well.
One of the most advantageous features of this invention is to remove
a pilot gear which is required for the positive displacement flow
meter. Its detailed examples are shown in FIGS. 4a and 4b.
That is, a first tooth profile is formed at respective portions
of the cycloid tooth profile provided on the addendum of a pair
of rotors as well as of the trochoid tooth profile provided on the
dedendum. In addition, two convex respectively concave arc tooth
profiles 9 10 in the form of short circular segments of the slippage
zero are formed as shown in FIG. 4a.
At the section of a pair of rotors taken at right angle to the
axes of the rotors, the convex arc tooth profile 9 is formed at
the position of the addendum of the cycloid by defining the pitch
circle of a pair of rotors 1 2 as the border, while the other convex
arc tooth profile 10 is formed at the position of the pitch circle
of the trochoid by defining the pitch circle as the border. And
the cycloid and trochoid portion excluding the above convex arc
tooth profile 9 10 is formed concavely, i.e. maintained in a non-contact
position by providing a slight projection .DELTA..
Only at both side ends of the track view of the contacting points
in FIG. 4b i.e. at the position corresponding to the length of the
arc tooth profiles 9 10 the two rotors 1 2 are engageable with
each other and rotatable under the condition of the so-called zero
slippage. Accordingly, without using a pilot gear an ideal flow
measurement is obtainable by employing this positive displacement
flow meter.
Preferably, the projection .DELTA. of the convex arc tooth profiles
9 10 is very slight, so that there takes place a gap of only 2.DELTA..
However, it is possible to maintain a constantly fixed gap rather
than to adjust the gap between the convex teeth profiles 9 10 by
means of a pilot gear. Accordingly, the device according to the
present invention can maintain stability.
Since the positive displacement flow meter according to this invention
has a pair of rotors of helical tooth structure in which the tooth
profile curves of cycloid and trochoid are provided with the arc
tooth profiles 9 10 it is of simple structure as well as of a
very small pulsation and vibrating noise owing to equal speed rotation.
Further, it it an ideal product having no energy transmission between
the two rotors.
Referring to FIG. 5 a convex arc tooth profile 10a is formed with
a slight projection .DELTA. at the position of mutual engagement
(as shown in FIG. 4a) of a pair of arc tooth profiles 9 10. The
other portion excluding the convex arc tooth profile 10a is recessed
in a non-contact position.
The convex arc tooth profile 10a is applicable not only to the
tooth profile curve of the present embodiment as well as of the
other embodiment mentioned below, but also to all helical teeth
including an involute curve, a cycloid curve, a trochoid curve,
a circle envelope, an arc tooth profile and/or other artificial
curves. Needless to say, at the recessed portion arises a slight
gap which may cause leakage of liquid. This gap is however smaller
than the one that is necessary for a phase adjustment between a
rotor and a pilot gear in a Roots-type flow meter or the like. Accordingly,
such a slight gap constitutes actually no drawback at all. Conversely,
the gap dimension can always be stabilized.
FIG. 6 is a section view of the positive displacement flow meter
having a pair of rotors 1 2 each of which has the same number of
teeth, and has tooth profiles as shown in FIG. 4. Numeral 11 is
an output shaft and numerals 12 13 are rotation shafts. Numeral
14 is a magnet coupling.
FIG. 7a shows the condition of instrumental correction of the positive
displacement flow meter and FIG. 7b is a graph showing the pressure
loss therein.
As shown in FIG. 7a, change of instrumental correction is very
small. Additionally, a preferred curve is obtainable in relation
of the pressure loss with the flow.
Now I will compare the noise of the above positive displacement
flow meter with that of a non-circle tooth type flowmeter of the
same type. While that of the former has 75 decibles at the time
of the maximum flow, that of the latter has 90 to 92 decibles. Accordingly,
the former is superior to the latter in view of the noise prevention.
Another embodiment of the present invention will now be described
in reference to the accompanying drawings FIGS. 8 and 9.
Just like FIG. 1 FIG. 8 is a section view of tooth profile curves
taken at right angle to the axes of the rotors, which illustrates
another embodiment of a positive displacement flow meter according
to this invention. Whereas the first rotor 21 has four teeth, the
second rotors 22 has three teeth. In this structure, from the liquid
flow inlet 24 installed in a casing 23 toward the liquid flow outlet
24' a pair of rotors 21 22 are rotatable freely in accordance with
the pressure difference of liquid i.e. P=P.sub.1 -P.sub.2. Numerals
25 26 are a pitch circle and an addendum circle respectively of
the rotor 21 while numerals 27 28 are a pitch circle and an addendum
circle respectively of the rotor 22. The respective centers of the
pitch circles of the two rotors are denoted at 0.sub.1 and 0.sub.2.
The pitch point is denoted at M.
By defining the pitch circles 25 27 as the border, an addendum
is provided with the tooth profile curves A.sub.1 B.sub.1 and A.sub.2
B.sub.2 while a dedendum is provided with the tooth profile curves
B.sub.1 C.sub.1 and B.sub.2 C.sub.2. The detail view of the tooth
profile curves of the two rotors is illustrated in FIG. 1. The curves
29.sub.1 30.sub.1 and 29.sub.2 30.sub.2 are provided with an engaging
tooth profile curve like, e.g. an involute curve in which an addendum
and a dedendum from the points B.sub.1 B.sub.2 remote from the pitch
circles 25 27 of the two rotors 21 22. On the section taken to
the axes right angle a pair of rotors are contacted with each other
on the points, but maintain a linear contact along an axial direction.
Both rotors, 21 22 engage with each other along tracks QMR' and
RMQ' shown with a x-shaped dotted line having the center M at the
pitch point.
The track for the static co-ordinates on which the intersecting
points A.sub.1 A.sub.2 of the tooth profile curves of the two rotors
21 22 provided with the addendum adjacent the addendum circles
26 28 are contacting with each other, is SUS' and NKN' as shown
in the dotted line of FIG. 8. Further, the track of the remaining
static co-ordinates which the points B.sub.1 B.sub.2 contact is
shown with each arc of R'S', SR, Q'N', NQ. Due to these contacting
points of a pair of rotors the screwed tooth surface is completely
sealed.
Thus, just like the embodiment in FIG. 1 a pair of rotors 21
22 are firmly engaged with each other, thereby a positive displacement
flow meter having a high wear resistance being obtained.
In addition, the pair of rotors 21 22 are engaged together with
no interference with each other. The variations of mutual engagement
of the two rotors 21 22 are shown in FIG. 9a to FIG. 9h.
It is to be understood obviously that the tracks to be described
by the points A.sub.1 A.sub.2 and B.sub.1 B.sub.2 of the two rotors
consist of six arcs i.e. SUS', NKN', SR, R'S', NQ and Q'N' which
include the track of x-shape as described above, as well as of four
straight lines RM, MR'. QM, MQ'.
According to this invention, since the tooth form curves for engagement
to be provided with e.g. an involute curve are provided in the proximity
of the pitch circles of the two rotors, the danger of wear can be
eliminated although there is the disadvantage that an impure matter
in the liquid to be measured may be engaged in rotation. Further,
one of many remarkable advantages is that a pair of rotors are firmly
engaged with each other because of maintaining a x-shape contact
to an axial direction in spite of the point contact at the section
taken at an axially right angle. Accordingly, it is substantially
feasible to remove a so-called pilot gear. |