Field of the Invention
The present invention relates to an interlocking device for rigidly holding together the
body and flange of a hydraulic machine using oval-shaped dowels. The interlocking
mechanism according to the present invention can also be employed for hydraulic pumps,
motors, valves, etc. where containment of pressurized fluid is required with due
consideration for minimal deflection of the load bearing elements.
Background of the Invention
For the effective functioning of a hydraulic machine, it is essential that the relative
positional displacement amongst the various component parts, viz., body, flange and cover
are controlled within reasonable limits. This factor helps to maintain reduced clearance
between the gear tip circle diameter and the bore of the body, so that the hydraulic
machine's volumetric efficiency can be kept optimum at various levels of oil pressure.
The desired performance is met by the hydraulic machine construction by employing
positive close fit dowel arrangement between the flange and the body. Such a construction
ensures that the relative movement amongst these two components is minimal.
Presently, the design of hydraulic machines is such that they are provided with dowels
disposed on the body at the inlet side in case of two hollow dowels and at both inlet and
outlet sides in case of four hollow dowels. These hollow dowels accommodate the mounting
bolts of the hydraulic machine to pass through.
Figure 1 of the drawings accompanying the specification depicts the profile of a pump
body used in a conventional gear pump. Gear pumps using such profile and having two
hollow dowels are, and can be, employed satisfactorily for applications requiring upto 3000
lbs./in> (207 bar) oil pressure. The hollow dowels used in the body of a conventional gear
pump is shown in Figure 2 of the drawings accompanying the specification.
-1-

Figure 3 of the drawings accompanying the specification shows the profile of a gear
pump body used in a conventional gear pump where the application pressure required is
high. Gear pumps using such profile and having four hollow dowels are, and can be,
employed satisfactorily for applications requiring upto 4000 lbs./in:(275 bar) oil pressure.
It is known from GB-A-2247923 to provide one or both ends of the housing with a
non-circular inner rim which is received within a recess of matching non-circular shape
defined by a flange projecting from a peripheral region of a respective end cover in a
direction parallel to the axis of rotation of the meshing rotors. One or both open ends of the
housing is thus supported by its end cover against outward deflection under the effect of
fluid pressure in the chambers in a plane transverse to the axes of rotation of the meshing
rotors.
GB-A-2247923 further discloses that the non-circular inner rim and matching non-
circular recess are difficult to machine accurately and require complex CNC programming.
Also, although this arrangement provides good alignment and support in a direction normal
to the aforesaid plane (i.e. in the direction of the minor axis), no support is given in the
direction of the major axis. Under the influence of internal pressure, the major sides of the
housing deflect outwards to a small extent whilst the minor sides of the housing contract
away from the mating edges of the peripheral flange on the end cover. The flange thus only
limits body deflection in an outwards direction. Furthermore, there has to be an axial
clearance between the peripheral flange and the end face of the housing in order to ensure
that the end face of the inner rim seats against the base of the recess. The end cover is
secured to the housing by bolts and this axial clearance results in a bolt load overhang which
imposes a considerable bending load on the flange profile.
It is also known from GB 2408070A to provide a rotary positive displacement hydraulic
machine in the form of a gear pump or motor comprising defining two mutually intersecting
parallel working chambers having a low pressure inlet side and a high pressure outlet side,
-2-

two meshing rotors mounted for rotation in the two chambers respectively, and two bearing
supports at opposite ends of the chambers and each supporting bearings in which the two
rotors are journalled for rotation, wherein at least one end of the housing is closed by a
separate end cover and wherein the separate end cover and an adjacent end of the housing
each has at least one elongate recess on each of the two major sides of the working
chambers, the recesses in the end cover being alignable with respective recesses in the
adjacent end of the housing and there being at least one keying element in each pair of
aligned recesses so that the open end of the housing is supported against outward deflection
by differential fluid pressure in the chambers in a direction transverse to a plane containing
the axes of rotation of the meshing rotors.
There was a long-felt need in the art for an interlocking device for hydraulic machines,
in particular, gear pumps operating at pressure in excess of 275 bar that prevents the undue
relative displacement and the undesirable orientation of the gear pump body with respect to
its flange and cover. A higher relative displacement between the structural component parts
of the gear pump will correspondingly lower the performance of the pump, particularly its
volumetric efficiency, as discussed above. A crucial factor, and hence a matter of concern for
gear pump designers, is the effectiveness of the doweling arrangement to prevent relative
displacement of the pump body and the flange at the operating pressure.
Therefore, the strategy for improving the effectiveness of the interlocking
arrangement is considered as a major step towards achieving high pump performance levels
with increased volumetric efficiency.
With the above objective, the present invention is oriented towards optimizing the
configuration of the dowel, i.e., its shape and size and also its disposition on the body of the
hydraulic machine. This critical shape and size of the locating dowel and its optimal
positioning have been arrived in the present invention through in-depth estimation of the
hydraulic forces occurring inside the pump body, which significantly behaves like a close knit
pressure vessel, while being in high pressure operation.
-3-

In order to identify the optimum interlocking concept, pump interlocking arrangement
using four oval-shaped dowels (as depicted in Figure 4 of the accompanying drawings) has
been evaluated for gear pumps operating at higher application pressure in the range of 330
bar, and compared for the relative strength and optimality with respect to the conventional
hollow dowel arrangement.
Summary of the Invention
Accordingly, the present invention provides an interlocking device for rigidly holding
together the body and flange of a hydraulic machine comprising a body, flange, gears,
sealing means acting as body seal and lobe seal adapted to effectively seal pressurized oil
pockets within the hydraulic machine with a back-up ring that prevents squeezing of said
lobe seal and to retain it in its original position, appropriately dimensioned bush bearings
adapted to act as load bearing journals, wherein said interlocking device comprises a plurality
of oval-shaped dowels located at both inlet and outlet sides that hold the body and flange
together with minimum relative displacement to ensure high volumetric efficiency of said
hydraulic machine even at high operating pressures in excess of 275 bar.
Preferably, the number of oval-shaped dowels used is four. The major axis of each of
the oval-shaped dowels is aligned at right angle with the resultant force direction and their
minor axis is aligned with the resultant force direction. The width of said body is proportional
to the fluid flow capacity. Said body is made from high grade specially alloyed cast iron or
aluminium materials depending upon the application and pressure ratings. Said gears are
made from special steels. Said flange is made from cast iron castings. The profiles of said
body and the flange are such that adequate reinforcing is maintained at appropriate zones to
enhance its load bearing capacity and its rigidity.
Both said body and said flange are equipped with a provision for accommodating said
oval-shaped interlocking dowels. The profile of the lobe seal material matches with that of
-4-

the corresponding pressure plate. Said bush bearings, which are used as a load bearing
journal, are PTFE lined.
It would appear clear to persons skilled in the art that numerous developments and
modifications are possible without departing from the scope and spirit of the invention, which
has been described for illustrative purposes only, by way of example of an interlocking device
for rigidly holding together the body and flange of a hydraulic machine, wherein said
hydraulic machine is a gear pump.
Brief Description of the Accompanying Drawings
Embodiments of the invention for use with a hydraulic gear pump, will now be
described by way of example only, with reference to the accompanying drawings wherein :
Figure 1 shows the profile of a pump body used in a conventional gear pump.
Figure 2 shows the hollow dowels used in the body of a conventional gear pump.
Figure 3 shows the profile of a gear pump body used in a conventional gear pump
where the application pressure required is high.
Figure 4 shows pump interlocking arrangement using four oval-shaped dowels
according to the present invention.
Figure 5 depicts the optimized profile of a body of a pump body using oval-shaped
dowel.
Figure 6 shows a oval-shaped dowel for a pump body.
Figure 7 is a free body diagram for a conventional pump body with oil pressure
loading.
Figure 8 is a linear representation of force diagram within a conventional pump body.
Figure 9 is a free body diagram for a pump body according to the present invention
with oil pressure loading.
Figure 10 is a linear representation of force diagram within a pump body according to
the present invention.
Figure 11 shows an overall pump assembly.
-5-

Figure 12 is an exploded view of the pump assembly having an interlocking
mechanism using oval-shaped dowels according to the present invention.
Description of the Preferred Embodiments
Finite element analysis (FEA) was carried out for the conventional interlocking
mechanism and for the interlocking mechanism according to the present invention for a
pressure range of 207 bar which the conventional interlocking devices are able to withstand,
while applying to similar pump body profile. The FEA results are given in Table-1.
Table-1
Summary of Deflection and Stress Analysis

SI. Type of Interlocking
Between Pump
Body and Flange Maximum Deflection Maximum Stress

Value in
Micron Location Value in
N/mm2 Location
1 2 Hollow Dowels
(Conventional) 45 Inlet Porting 355 Inlet Side Dowel
Holes
2 4 Hollow Dowels
(Conventional) 30 Outlet Porting 516 Outlet Side Dowel
Holes
3 4 Oval-Shaped Dowels
(according to the
invention) 25 Inlet and Outlet
Porting 246 At Outlet Dowels
The FEA results indicate that hydraulic machines with oval-shaped dowels with built-in
bolt hole guarantees a better performance level with respect to the conventional design of 2
and 4 hollow dowels since both the maximum principal stress magnitude and the maximum
deflection values are less. The above table thus provides an indication of the resilience of
oval-shaped dowels to withstand a higher pressure range, in view of low values of both
deflection and stress for the configuration.
-6-

Having identified that an oval-shaped doweling arrangement is the optimum solution
for a gear pump-flange interlocking arrangement, effort was channelized to arrive at an ideal
pump body profile.
The preferred embodiments of the invention is described below with reference to the
drawings.
Figure 5 represents the optimized profile of the pump body according to the present
invention using oval-shaped dowel.
Figure 6 shows an oval-shaped dowel for a pump body according to the present
invention.
In order to account for the benefits accruing out of an interlocking mechanism using
oval-shaped dowel over conventional hollow dowel, both conventional and a pump body
profile according to the present invention having body width proportional to similar flow
capacity are taken into consideration. The profile of the pump body according to the present
invention must necessarily be different from that of the conventional body profile in order to
attain optimality from the strength point of view.
The force and maximum stress for a conventional pump body using hollow dowel
construction was estimated and Figure 7 represents the free body diagram for a conventional
pump body profile with indication of oil pressure from the suction side at "A" to maximum
outlet pressure at position Bl (or B2). The maximum pressure is assumed to be as 250 bar.
As can be seen from Figure 7, the resultant force "F" can be resolved into coplanar force "F"
acting at the hollow dowel at the location PI (or P2) along with a turning couple of
magnitude F x L. The couple tends to cause bending of the body halves about the hollow
dowel axis PI (or P2). This phenomenon is detrimental since it tends to increase the tip circle
clearance at the gear outer diameter cum body bore interface at the high pressure outlet
side.
-7-

Also, the 3466 kgf force acts on a slender hollow dowel projected area of [{(3.142 x
13)/2> x 11] sq. mm. = 224.6 sq. mm (Refer Figure 2 with D and L as 13 mm and 11 mm
respectively) and the net compressive stress on each of the hollow dowel amounts to
3466/224.6 = 15.4 kgf/sq. mm. The maximum bearing pressure for the dowel made of EN 8
material specification is allowed between 10 to 12 kgf/sq. mm. Hence, this clearly indicates
that the maximum compressive stress is on the higher side.
Figure 8 details the linear representation of force diagram as occurring within a
conventional pump body. The total resultant force amounts to 3466 kgf and occurring at the
position Cl (or C2) oriented at an angle of 38 degrees with respect to the vertical axis (as
shown in Figure 7). The values of resultant force and its angular location are specific to the
profile of the body bore geometry.
The force and maximum stress for the pump body with oval-shaped dowel
construction according to the invention was estimated. While making a comparative analysis
for the pump body using the oval-shaped dowel according to the invention, the body profile
was correspondingly modified to accommodate the oval-shaped dowel.
The stress induced in the dowels is computed using the following mathematical
relationship :
For hollow dowel :
D = Dowel outer diameter
T = Dowel thickness
F = Resultant force acting on the dowel
Projected dowel area, A = (n*D)/2*T
Net Compressive Stress on Dowel, S = F/A
-8-

For Oval-Shaped Dowel :
L = projected length of the dowel
T = Dowel thickness
F = Resultant force acting on the dowel
Projected dowel area, A = L * T
Net Compressive Stress on Dowel, S = F/A
Figure 9 represents the free body diagram for the pump body profile according to the
present invention with indication of oil pressure variation from the suction side at Al (or A2)
to the maximum outlet pressure at position Bl (or B2). The maximum pressure was assumed
to be 250 bar.
Figure 10 details the linear representation of force diagram as occurring within a pump
body according to the present invention. The total resultant force amounts to 4953 kgf and
occurring at the position Cl (or C2) oriented at an angle of 38 degrees with respect to the
vertical axis (as shown in Figure 9).
As can be seen from Figure 9, the major axis of the oval-shaped dowel is located
directly perpendicular to the line of resultant force "F", while the minor axis aligns with the
line of force. The effect of positioning the oval dowel in this manner eventually eliminates
any possible chance of occurrence of turning moment, and thus reduces the possibilities of
increased gear tip circle clearance.
The resultant force of 4953 kgf acts on the oval-shaped dowel cross-section of 36.2 x
15 = 543 sq. mm. (see Figure 6 with Dy and T as 36.2 mm and 15 mm respectively) and the
net compressive stress on each of the oval-shaped dowel amounts to 4953/543 = 9.1 kgf/sq.
mm. The maximum bearing pressure for the dowel made of EN 8 material specification is
allowed between 10 to 12 kgf/sq. mm. Hence, this clearly indicates that the maximum
compressive stress is within the permissible limit and the design of the oval-shaped dowel is
-9-

satisfactory from the strength point of view. It is also noted that the compressive stress
acting on the oval-shaped dowel is 1.70 times less compared to the hollow dowel for gear
pumps having similar flow and pressure ratings.
The overall pump assembly and the exploded view of the gear pump assembly having
an interlocking mechanism using oval-shaped dowels according to the invention is depicted in
Figures 11 and 12 respectively. The structural components parts of the pump are illustrated
with the help of reference numerals.
The pump body (1) is made from high grade specially alloyed cast iron or aluminium
materials depending upon the application and pressure ratings, whereas the flanges (2) are
made from cast iron castings. The pump body and flange profiles are such that adequate
reinforcing is maintained at appropriate zones to enhance its load bearing capacity and its
rigidity, which in turn directly increases the pump pressure holding capacity. Both the pump
body and flange are suitably adapted to accommodate oval-shaped interlocking dowels.
The pump gears (12, 13) are made from special steels with strict adherence to the
heat treatment requirements arising from its operational requirements. While designing the
gears, special attention has been paid to the load bearing property, particularly while catering
to high pressure and high flow requirements. The optimum sizing of the journal diameter is
one of the important parameters in this regard.
The specially designed oil seals (7, 10) known as body seal and lobe seal have been
developed with a view to successfully cater to efficient sealing of pressurized oil pockets
inside the pump. Along with lobe seal material, its profile which has to match with the
corresponding pressure plate profile, is of crucial importance for the successful operation of
the pump. Back-up rings (9) are used to prevent squeezing of lobe seal and to retain the lobe
seal in its original position.
-10-

Pressure plates (11) are a very important component of a hydraulic gear pump having
an interlocking mechanism according to the invention. It can be regarded as a sole
functionary responsible for the efficient functioning of the pump. The intricately machined
profile of the plate and its material composition are of immense importance, since it has to
optimally match with various other mating elements and operating conditions.
Optimally designed and appropriately dimensioned PTFE lined bush bearings (8) are
used as a load bearing journal.
The oval-shaped dowels (3) {4 nos.} enables clamping both pump body and flange
together resulting in a definitive near single unit for the pump assembly. This singular item is
responsible for imparting the various advantages.
The present invention offers the following distinct advantages :
(a) Higher volumetric efficiency of the gear pump
(b) Reduced heat loss due to lower internal oil leakage
(c) Longer life of the pump since low internal heat, generation results in higher
performance and longevity of all the sealing materials
(d) Suitable for design of hydraulic machine applicable for high pressure and
unfavorable operating conditions.
With reference to the pump assembly shown in Figure 11, during operation of the gear
pump, a high pressure profile within the pump body (1) is generated with pressure varying
from the suction to the outlet as shown in Figure 9. The resultant of the hydraulic load "F"
acts on the gear pump body. This force which has a magnitude proportional to the outlet oil
pressure tends to cause spatial displacement for the pump body (1) with respect to the pump
flange (2), thereby increasing the gear tip circle cutting into the pump body bore,
-11-

and increasing the gear tip-body bore clearance. This phenomenon has a negative bearing on
the volumetric efficiency of the pump as already discussed and hence, needs to be
minimized.
The interlocking device acts in opposition with this disturbing hydraulic force "F", and
assists in maintaining the dimensional rigidity between the pump body and the flange, and
thus ensures reduced gear tip circle cutting into the pump body, resulting in maximization of
volumetric efficiency.
Various alternatives of the possible modes of combining the pump body and flange
using the conventional 2 hollow dowels and the proposed 4 oval-shaped dowels have been
considered. Finite element analysis was carried out for both maximum deflection and
principle stress values while employing gear pumps with the alternative interlocking
arrangements mentioned above with a maximum pressure of 250 bar. The detailed analysis
reveals the optimum suitability and superiority of the oval-shaped dowel mechanism over
conventional techniques.
The salient features of the interlocking mechanism for gear pump using oval-shaped
dowels according to the present invention can be appreciated by comparing the finite
element method (FEM) analysis outputs for both conventional and the interlocking
mechanism as per the invention.
Finite element analysis (FEA) was carried out in detail for both the conventional
interlocking mechanism and for the interlocking mechanism according to the present
invention. The summary of the deflection and stress analysis is given in Table-2. This FEA is
based on an optimized body profile that can withstand pressure upto 275 bar and also
intermittent pressure upto 330 bar.
-12-

Table-2
Summary of Deflection and Stress Analysis

SI. Type of Interlocking
Between Pump
Body and Flange Maximum Deflection Maximum Stress

Value in
Micron Location Value in
N/mnv Location
1 2 Hollow Dowels
(Conventional) 72 Outlet Porting 831 Inlet Side Bolt
Holes
2 4 Oval-Shaped Dowels 45 Rear Portion of
Pump Body 522 Inlet Side Bolt
Holes
The comparison as detailed above clearly indicates the superiority of the oval-shaped
dowel over the conventional hollow dowel concept. The use of oval-shaped dowel as pump
body-flange interlocking mechanism according to the present invention helps to achieve
higher volumetric efficiency of the gear pump during operation at high pressure due to the
fact that the relative deflection at the pump body-flange interface is minimized owing to
higher rigidity in dowel mounting, as evidenced in the computation of bearing stress at the
dowel.
Further, the use of four oval-shaped dowels (instead of two hollow dowels in the
conventional technique) establishes an all around rigidity factor at the separating joint face.
The optimum location of the oval-shaped dowel having the major axis aligned at right
angle with the resultant force direction and the minor axis aligning with the resultant force
direction ensures total avoidance of the turning couple while using the oval-shaped dowel.
This mechanism assists in maintaining the oil tight chamber at the gear tip-body bore, thus
ensuring higher pump volumetric efficiency.
The substantial variation in the volumetric efficiency during the operation of the gear
pump at a wide range of varying pressure compared to the initial running-in pressure is
-13-

considerably reduced since the pump gear deflection is minimized owing to the more rigid
interface joint through four oval-shaped dowels.
With the advent of CNC machining technology, the machining of the oval-shaped
dowels and the corresponding dowel slots on the gear pump body and flange becomes highly
reproducible and complimentary to their respective slots and dowels because of identical
program being deployed for the machining.
The foregoing is to be considered as illustrative only of the principles of the present
invention. Further, since numerous modifications and changes will readily occur to those
skilled in the art, it is not desired to limit the invention to the exact construction and.
applications shown and described, and accordingly, all suitable modifications, developments
and equivalents may be resorted to, falling within the scope of the invention in the appended
claims and their equivalents. Although the invention has been described above with reference
to a hydraulic gear pump, the scope of the invention is not limited to hydraulic gear pump
alone and it can be employed by all hydraulic machines or devices including hydraulic pumps,
motors, valves, etc. where containment of pressurized fluid is required with due
consideration for minimal deflection of the load bearing elements.
-14-

WE CLAIM :
1. An interlocking device for rigidly holding together the body (1) and flange (2) of a
hydraulic machine comprising a body (1), flange (2), gears (12, 13), sealing means (7, 10)
acting as a body seal and lobe seal adapted to effectively seal pressurized oil pockets
within said hydraulic machine with a back-up ring (9) that prevents squeezing of said lobe
seal and to retain it in its original position, appropriately dimensioned bush bearings (8)
adapted to act as load bearing journals, wherein said interlocking device comprises a
plurality of oval-shaped dowels located at both inlet and outlet sides that hold the body
and flange together with minimum relative displacement to ensure high volumetric
efficiency of said hydraulic machine even at high operating pressures of 275 bar or higher.
2. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed
in claim 1, wherein the number of oval-shaped dowels used is four, which enables
clamping of the body and the flange together resulting in a definitive near single unit for
the hydraulic machine assembly.
3. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed
in claim 1, wherein the major axis of each of the oval-shaped dowels is aligned at right
angle with the resultant force direction and their minor axis is aligned with the resultant
force direction.
4. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed
in claim 1, wherein the width of said body is proportional to the fluid flow capacity.
5. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed
in claim 1, wherein said body (1) is made from high grade specially alloyed cast iron or
aluminium materials depending upon the application and pressure ratings.
-15-

6. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein said gears (12, 13) are made from special steels.
7. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein said flange is made from cast iron castings.
8. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein the profiles of said body and the flange are such that adequate reinforcing
is maintained at appropriate zones to enhance its load bearing capacity and its rigidity.
9. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein both said body and said flange are provided with corresponding recesses for
accommodating said oval-shaped interlocking dowels.
10. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein the profile of the lobe seal material matches with that of the corresponding
pressure plate.
11. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein said bush bearings (8), which are used as a load bearing journal, are PTFE
lined.
12. An interlocking device for a hydraulic machine using oval-shaped dowels as claimed in
claim 1, wherein said oil seals (7, 10) are body seal and lobe seal, and a back-up ring (9)
prevents squeezing of said lobe seal and retain it in its original position.
13. An interlocking device for rigidly holding together the body (1) and flange (2) of a
hydraulic machine, wherein said hydraulic machine is a gear pump.
-16-

14. An interlocking device as claimed in any preceding claim, wherein the machine or
pump body is designed to withstand a pressure upto 330 bar.
15. A hydraulic machine incorporating an interlocking device as claimed in any one or
more of the preceding claims.
16. An interlocking device for rigidly holding together the body and flange of a
hydraulic machine using oval-shaped dowel, substantially as herein described,
particularly with reference to and as illustrated in the Figures 4-6 and 9-12 of the
accompanying drawings.
Dated this 28th day of September, 2005.

An interlocking device for rigidly holding together the body (1) and flange (2) of a
hydraulic machine comprises a today (1), flange (2), gears (12, 13), sealing means (7, 10)
acting as a body seal and lobe seal adapted to effectively seal pressurized oil pockets
within the hydraulic machine with a back-up ring (9) that prevents squeezing of said lobe
seal and to retain it in its original position, appropriately dimensioned bush bearings (8)
adapted to act as load bearing journals, wherein said interlocking device comprises a
Plurality of oval-shaped dowels located at both inlet and outlet sides that hold the body
and flange together with minimum relative displacement to ensure high volumetric
efficiency of said hydraulic machine even at high operating pressures of 275 bar or higher.