FORM-2
THEPATENT ACT, 1970
(39 of 1970)
COMPLETESPECIFICATION
Title:
A HERRINGBONE GEAR AND PROCESS OF MANUFACTURING THE
HERRINGBONE GEAR USING TWO HELICAL GEARS

(a) Applicant Name: Elecon Engineering Company Ltd.
(b) Nationality:Indian
(C) Address- Elecon Engineering Co. Ltd.
Anand Sojitra Road
Vallabh Vidyanagar - 388120
Gujarat, India.
The following specification particularly describes and ascertains the nature of this
invention and the manner in which it is to be performed.
COMPLETE

DESCRIPTION Technical Field
[0001] The present patent application relates to a herringbone gear and Process of manufacturing the Herringbone Gear using two helical gears. More particularly present invention provides method for precisely combining two opposite hand side toothed helical gear to receive herringbone gear by using simple steps.
Background
[0002] Mechanical drives are used to transmit motion, torque and power from driver shaft (usually a prime mover like electric motor) to driven shaft (such as machine unit). There are four mechanical drives, namely gear drive, belt drive, chain drive and rope drive. Each of them has specific features and is suitable for certain type of applications. A gear drive is preferred for power transmission over small distance. It is one positive drive and can be designed to transmit power at any angle and any plane. There are four basic types of gears—spur gear, helical gear, bevel gear and worm gear. A spur gear has straight teeth parallel to the gear axis and can transmit power between parallel shafts only. However, due to sudden contact between teeth of two mating spur gears, tooth experiences shock or impact loading.
[0003] Problems associated with impact loading can be eliminated by utilizing helical gear. Like spur gear, helical gear is also used for parallel shafts; however, teeth are cut in the form of helix on the cylindrical gear blank. The helical teeth of two mating gears gradually come in contact, resulting a gradual loading on the teeth (instead of impact loading as in case of spur gear). This also increases power

transmission capability and at the same time reduces vibration. However, helical profile of the tooth induces axial thrust load on the bearing, which is sometimes detrimental and limits the maximum allowable speed of application. In order to eliminate the thrust force maintaining the helical form of teeth intact, either herringbone gear or double helical gear can be employed.
[0004] In both the cases, teeth are cut in two halves of the gear blank maintaining same module, number of teeth and helix angle but opposite hand of helix. Thus thrust force produces by each half of the gear is equal and opposite and thus eliminates each other. Although herringbone gear or double helical gear is free from axial load, there are few differences between them in terms of constructional feature and their manufacturing. In double helical gear, small relief gap is provided between two halves. So teeth of left hand helix do not physically touch the teeth of right hand helix. However, in case of herringbone gear, no such gap is provided and thus teeth having left hand helix touch the teeth having right hand helix. A relief gap between the left hand helix teeth and right hand helix teeth is the main differentiating factor. In herringbone gear, no gap is provided and thus left hand helix teeth remain in physical contact with right hand helix teeth. In double helical gear, a small gap (2 -10cm based on size) is maintained between left hand helix teeth and right hand helix teeth.
[0005] While cutting the gear teeth for herringbone gear, the cutter is not allowed to move beyond the teeth face in one side (where junction exists). Any overstepping will create undesired groove on other half as intermediate groove or space does not exist. This makes the manufacturing complicated and a dedicated machine is

required to cut such gear teeth. In case of double helical gear, the small relief gap allows the cutter to move freely beyond the teeth face. Due to difficulty in manufacturing, cost of herringbone gear is marginally higher than the cost of similar double helical gear.
[0006] Width or thickness of the gear actually determines tooth strength and power transmission capability. Due to presence of small relief gap in double helical gear [Fig. 1], tooth face width is not equivalent to the gear width. For same gear width and other features, teeth face width of herringbone gear [Fig. 2] will be larger and consequently its transmission capability will be higher. Inversely, for specified power transmission, a thinner herringbone gear can be employed. This is particularly suitable for designing a compact machine unit having limited available space.
[0007] Helical gears are the gears whose tooth is inclined with their axis, respective to angle called as helix angle. Due to the inclined cylindrical faces of the tooth, they offer lesser noise and wear together with uniform loading, leading to smooth and reliable operations making them ideal for power transmission. One of the disadvantages of helical gear is to produce axial thrust during operations. During larger torque transmission, this axial thrust becomes severe and affects the working life of gears and bearings used for supporting the shaft over which gears are mounted.
[0008] Helical gears, which have teeth cut at an acute angle to the axis, are designed to have numerous teeth meshing at all points of rotation and to distribute pressure evenly along the entire length of each tooth. Thus, they provide smooth operation and reliability, and they are ideal for power transmission applications.

Because of the angle of the teeth on a single helix gear (also referred to as a twisted spur gear), an axial thrust is created, but by using two opposing helices at complementary angles, induced axial thrust is eliminated.
[0009] In the cases where higher torque transmission is to be done and to overcome the effect of axial thrust due to single helical gear, Herringbone gears are preferred. Herringbone gears are the double helical gears, however they are differs to the double helical gear in terms of two helical gears of opposite hands joined face to face without any gap between them. In terms of gear contact face width, the double helical gear could produce similar effect with the herringbone gear, but the space between two helical gears increases the material cost as well machining cost.
[00010] Herringbone gears are difficult to manufacture, since the opposite handing gear termination at the joining point lefts some material otherwise blank space to be left in between which requires added material cost similar to double helical gear.
[00011] Herringbone gears have been limited to manufacture by Sykes gear generators or shapers, in which the two opposing helices are machined simultaneously by reciprocating cutters which alternately cut the left and then the right helix with each machine strike. The cutters cut the tooth profile as they stroke to the center of the gear face. A limitation to this process is the scarcity of large-pitch high-accuracy Sykes cutters. Further, because these cutters cannot cut metals of hardness greater than Rockwell C, the finishing process is limited to through-hardened gearing. The tooth finishing process is equally inaccurate and statistically unpredictable.

[00012] Herringbone gears are used as pump rotors and as power transmission gears in applications which require high torque with lower speed, particularly where the face width of the gearing is limited. Although continuous beam double helical gearing has been in use for over fifty years, the hardness of the parts and the tooth dimension accuracy has been limited due to manufacturing difficulties inherent in machining the teeth at the apex.
[00013] In state of the art Hobbing is not preferred process for cutting herringbone gears as the hob (cutter) can run over the other half in the same way because of no gap. It is usually cut by gear shaper, which is a slow and inaccurate process.
[00014] In state of the art, CA2495574C,discloses the method for manufacturing of herringbone gear. Their ideology is based generation of herringbone gear teeth. But their ideology of manufacturing leaves some gap between the two oppositely handed helical gears, which increases material cost.
[00015] US005865239A have presented the injection molding process for herringbone gear manufacturing related to gear pump application, which involves low torque transmission only.
[00016] US 1,480,910 discloses a process for manufacturing herringbone gears comprising the steps of forming cylindrical features on a stock and roughing a plurality of double helical gear teeth along a helix angle on said stock with each of said plurality of double helical gear teeth having an apex located at said circumference

[00017] WO 2008/101291 have patented a rack and pinion steering gear where herringbone gear like tooth they generated.
[00018] Indeed, the current state of the art does not provide any easy to adapt and economical process for manufacturing herringbone gears.
OBJECT OF INVENTION
[00019] The prime object of the present invention is to herringbone gear and a process of manufacturing Herringbone Gear using two helical gears.
[00020] An object of the present invention is to provide simple method to combine two adjacent helical gears through dowel.
[00021] A further object of the invention is to provide herringbone gear prepared by precisely combining two helical gear using laser marking technologies.
[00022] Another object of the present invention is to provide method for combining two opposite hand faced helical gear by use of dowels.
[00023] Yet another object of the present invention is to provide herringbone gear with central shaft having combined two helical gears.
[00024] Further object of the present invention is to provide method of manufacturing herringbone gear by combining two opposite hand side helical gear through dowel.
SUMMARY
[00025] The present invention provides a herringbone gear and a method of manufacturing the same by combining two helical gears. The helical gear with opposite hand sides is drilled at precise point to receive dowel pin. The shaft is

inserted in center part of one of the helical gear and opposite handed helical gear is fix matching same dimension at junction. Then dowel pin were inserted through dowel holes made in both of the helical gears. The dowel pins are fixed with special adhesive to receive combined helical gears i.e. herringbone gear. The said process is economical and fast compared to available state of the methods i.e. hardening tool and induction mold method. The present invention provides easy to adapt or assemble compared to helical gear and conventional herringbone gears.
BRIEF DESCRIPTION OF THE DRAWINGS
[00026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate disclosed embodiments and, together with the description, serve to explain the disclosed embodiments. In the drawings:
[00027] FIG. 1 illustrates perspective side view of double helical gear available in state of the art
[00028] Fig. 2 illustrates perspective side view of two opposite side hand helical gears
[00029] Fig. 3 illustrates side view of helical gear with dowel hole preparation
[00030] Fig. 4 illustrates perspective view of central shaft to be embedded with helical gears
[00031] Fig. 5 illustrates perspective view of central shaft embedded with one helical gear in the present invention

[00032] Fig. 6 illustrates perspective side view of herring bone gear according to present invention
[00033] Fig. 7 shows a loading and boundary condition and mesh model of the Herringbonegear assembly.
[00034] Fig. 8 shows the Von-misses stresses acting on the herringbone gear assembly.
[00035] Fig. 9 illustrates total deformation on the herringbone gear assembly.
DETAILED DESCRIPTION
[00036] Reference will now be made in detail to the disclosed embodiments, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
[00037] Fig. 1 illustrates double helical gear (4) where gear contact face width, the double helical gear could produce similar effect with the herringbone gear, but the space [5] between two helical gears increases the material cost as well machining cost. Due to intermediate gap in between two helical gears, it requires more axial space. Hobbing, a high productive gear cutting process, can be advantageously used for cutting double helical gears. As can be seen from drawing a small gap is maintained by cutting a groove between two identical helical gears with opposite hands of helix. While joining two helical gears, a small gap is sometimes maintained in between them. Primarily based on the presence or

absence of this intermediate gap, two varieties of the helical gear have evolved double helical gear and herringbone gear.
[00038] FIG. 2 illustrates perspective side view of helical gears having opposite, one has left hand helix and other one has right hand helix. As shown in figure 2 helical gear (7) is left hand helix arrangement and helical gear (8) is right hand helix arrangement. Generally, in helical gears, teeth are cut at an angle (called helix angle) with the gear axis in the form of helix on the cylindrical gear blank. It replaces sudden engagement and disengagement of teeth (as in spur gear) by gradual mating and thereby reduces wear, vibration and noise. However, a pair of mating helical gears induces axial thrust force that is ultimately transferred to the bearings, which necessitates bulky and costly bearings. In order to eliminate this thrust force on bearings, two identical helical gears having same module and number of teeth and are joined on same axis but having teeth in opposite directions (one has left hand helix and other one has right hand helix) can be employed. As shown in Figure 2, helical gears (7, 8) have dowel bore and central bore (14) to accommodate dowel pin (17) and central shaftbore (14) respectively
[00039] The process of manufacturing of two helical gears [7 & 8] of opposite gear handing (one left and other right handing) is known in state of the art. It includes usual gear manufacturing process i.e. preparing forging ring, first turning, lifting holes drilling-tapping, hobbing with grinding allowance, heat treatment (carburizing & hardening), shot blasting, final turning with grinding allowance, bore & face grinding and final gear profile grinding.

[00040] Fig. 3 discloses perspective side view of one of helical gear (9) with dowel hole.The dowel holes or bores preparation step is crucial in this process asthe same will be done with at most care using finite or precise drilling bore preparation (10) at two specific spot in the each helical gear (7,8).
[00041] Fig. 3 shows the detail for dowelling holes. A face of a tooth on the gear 7 is fine machined using milling operation [hatched area represented as 12 in Fig. 3]. The drilling tool is reference using a point on pitch circle diameter 13 on this fine finished area, then moved radially towards 11 on both side to obtain dowel holes 10. 14 being the bore previously machined during manufacturing of gear 7. The accuracy of the final herringbone gear will depends on the accuracy with which this dowel holes will be positioned and carried out. It is submitted that milling and drilling is crucial in each helical gears (7,8) as their final conjugation side by side defines the accurate herringbone in the present method. Any defect or misalignment leads to create flaws in the final product.
[00042] Fig. 4 discloses perspective side sectional view of central shaft (15) as per the present invention. The shaft (15) contain key hole for engagement with driven or driver part. The shaft (15) also contains ring arrangement for hold one of the helical gear at finite position as described in Fig. 5. The dimension of the shaft depends on the ultimate herringbone dimension and its end application.
[00043] Fig.5 describes the shaft with embedded helical gear. Once the one helical gear (7) having dowel hole (10) is fixed on shaft (15) by heating and subsequent cooling. The same procedure will be repeated for other helical gear (8) to fix two helical gear side by side on the shaft. Then dowel (17) is inserted/passed

over matching hole bore (10) to lock the system over the shaft (15) to receive final herringbone gear (18). The shaft has provisions to firmly hold combined helical gears (7,8) at central part and key hole provisions to attach with drive modes in the system.
[00044] Fig. 6 describes combined herringbone gear (18). The second helical gear will be mounted on shaft (15). The present process mentioned that once the one helical gear (7) having dowel hole (10) is fixed on shaft (15) by heating and subsequent cooling. The same procedure will be repeated for other helical gear (8) to fix two helical gears side by side on the shaft (15). Then dowel (17) is inserted/passed over matching hole bore (10) to lock the system over the shaft (15) to receive final herringbone gear (18).Similarly bore of gear 8 is to be heated upto specified temperature for shrinking over the shaft 15 just after the gear 7. The dowel holes 10 and dowel 17 will play a significant role during accurate positioning of gear 8.
[00045] The herringbone (18) will be finally prepared giving herringbone gear (19). The present invention process obtains herringbone gear with maximum load sharing between tooth.
[00046] It observed that economical significance of this procedure lead to provide benefit in terms of raw material cost ad resource cost that provides 25-30% cost saving compared to state of the art helical gears.
[00047] It is submitted that in preferred embodiment the Grade of material for gear wheels is alloy i.e. 18CrNiMo7-6, and Dowel is made of through hardened material is EN-31 (BS 970).

[00048] The present study objective is to analyze and simulate the herringbone gear made out of two opposite handed helical gears, for their safety after the assembly through the process invention presented in GPD-05. The structural analysis of the herringbone gear for the possible load due to operation is considered and simulated. The operation is simplified for the ease of simulation. The shaft 15 and the herringbone gear 19 assembly were considered during simulation.
[00049] An advanced FEA static structural analysis tool Ansys 14.5 was used.
[00050] The present analysis is based on standard procedure of Finite Element Analysis of static structural analysis. The margin of the graph has not considered the influence at actual field response.
[00051] Fig. 7 shows a loading and boundary condition and mesh model of the Herringbone gear assembly.
[00052] Fig. 8 shows the Von-misses stresses acting on the herringbone gear assembly. Maximum stresses observed to be 284.57 MPa at area on the gear wheel. The recorded values are quite lesser than the limiting stress of the material (1000 to 1200 MPa), which reveals that the present design of the herringbone gear assembly is safe statically.
[00053] Fig. 9 reveals total deformation on the herringbone gear assembly. The tooth tips are subjected to maximum deformation of 0.1 mm, which is under limiting deformation of the material.

[00054] Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations or alterations based on the present disclosure. The elements in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the steps of the disclosed methods can be modified in any manner, including by reordering steps or inserting or deleting steps. It is intended, therefore, that the specification and examples be considered as example only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents.

We claim, 1. A process for manufacturing herringbone gears comprising the steps of,
a. Preparing two helical gears (7, 8)with opposite gear handing by essential
process features including preparing forging ring, first turning, lifting holes
drilling-tapping, hobbing with grinding allowance, heat treatment
(carburizing & hardening), shot blasting, final turning with grinding
allowance, bore and face grinding and final gear profile grinding
b. Making bore (14) at central part of the both helical gears obtained in step
(a),
c. Making corresponding dowel holes (10)from one face of the gear wheel of
both of the helical gear (7, 8) received in step, a through precision
matching of said parallel positioned holes using drilling tool that is
reference using a point on pitch circle diameter (13) on fine finished area,
then moved radially towards (11) on both side to obtain dowel holes (10),
d. Heating bore (14) of the helical gear (7) to shrink fit said gear over the
shaft in close proximity with side ring,
e. Cooling the said assembly received in step (d) to create foundation
between shaft (15) and helical gear (7),
f. Inserting dowels (17) into the dowel holes (10) of gear (7),
g. Heating helical gear (8) after setting aligned with bore and dowel hole of
established corresponding helical gear (7) and shaft (15).

2. The process for manufacturing herringbone gears as claimed in claim 1 wherein for gear wheels is alloy18CrNiMo7-6 used in preferred embodiment.
3. The process for manufacturing herringbone gears as claimed in claim 1 wherein Dowel is made of through hardened material is EN-31 (BS 970) used in preferred embodiment.
4. A hearing bone gear made by using process of any of the preceding claims.