FIELD OF THE INVENTION:
[002] The present invention generally relates to a starter for a motor vehicle, and particularly relates to the shroud of the starter solenoid.
BACKGROUND OF THE INVENTION:
[003] The starter motor is an electro-mechanical product which is used to ignite and start the automotive engine. The conventional starter motor comprises a motor, solenoid assembly, armature assembly, brush holder assembly, frame assembly, output drive assembly, over running clutch and End plate.
[004] The solenoid is mounted on the housing by means of screws and connected to the drive assembly through the shift lever. It provides the necessary force to pull the drive assembly into the engagement with the ring gear of the engine and further provides a high current switch to energize the starter motor.
[005] The solenoid linear movement has to be activated in few milliseconds for starter and engine ring gear engagement, which is crucial aspect of it. The frame assembly provides the main support structure for many of the starter subassemblies and also serves to complete the flux path required for the magnetic circuit. Size control is critical in order to maintain tight air gap tolerances and maximize starter output and efficiency.

[006] The parts, which are involved in solenoid's linear movement are receptive to severe environmental conditions i.e., Temperature, Mud, Water, Dust etc., which impacts durability, warranty and reliability. Inspite of these condition, the starter motor has to work on the multiple operative and environmental conditions without fail.
[007] The solenoid are prone to water entry and freezing, which may lead to failure. To help prevent the water entry, the solenoid is sealed with a bead of silicone around the metal frame, where it is crimped over the top. This crimp area is the most likely source of the water entry from the outside. This issue will prevent the plunger movement and result in solenoid malfunction.
[008] Several concepts were used in prior arts to arrest the problem. Such as., sealing cap, O-rings, Gasket etc. sealing cap are used for dust prevention in the solenoid but it does not meet the requirement as they allow small amount of fluid to pass across and doesn't withstand high temperatures.
[009] O-rings is a mechanical gasket, which is made of an elastomer with a round cross section, which are compressed during assembly between two or more parts creating a seal at the interface. In Stater applications, it is used to seal the oil or air leakage but it is not suitable for solenoid application. The O-ring may be used in static or in dynamic applications.
[010] Gasket is a mechanical seal, which fills the space between two or more parts to prevent leakage from or into the joined parts while under compression. It is widely used as a static seal, which will not deform under dynamic conditions.
[011] EP1985842A1 describes about a starter having an inner peripheral hollow part of an
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ventilation hole is formed in the sealing cap. The inside of the electromagnetic relay

communicates with outside atmosphere through the ventilation rom and the open passage formed in the housing and the ventilation hole. The sealing cap is positioned toward the circumferential direction by the positioning means formed in the housing and the sealing cap so that the ventilation hole is placed at the upper part of the ventilation room when the starter is mounted to a vehicle. This structure protects the inside of the electromagnetic relay from the water invasion through the ventilation hole even if water enters the ventilation room.
[012] The EP0398627A1 patent explains about a solenoid apparatus having a solenoid case with an open end and a substantially closed end, a plunger, electromagnetically movably mounted in the solenoid case, and a substantially cup-shaped flexible water-tight boot. The cup-shaped boot surrounds an end portion of the plunger projecting from the solenoid case and connected to the open end of the solenoid case, the flexible boot having a bottom wall central portion intimately secured to the end portion of the plunger. The flexible boot comprises a vent hole defined by a hollow tube extending through the boot wall in parallel to the plunger and a flexible valve plate formed integral with and inside of the boot wall and biased by the elasticity of the material of the boot into an open position. The water cover arrangement is suitable for a solenoid switch having a water-proof flexible boot which prevent the generation of an undesirable pressure difference between the inside and the outside of the boot.
[013] Compared to the existing prior arts, our novel idea aims to provide uniform compression/displacement / axisymmetric during the solenoid axial movement as well as higher temperatures. Provide better sealing property for water /dust entry (foreign particles) additionally acts as a breather.
[014] The above mentioned prior arts discusses about having a cap or boot or seal to prevent the water and dust invasion into the solenoid. But none the art discusses about redesigning
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reliability and performance.

[015] Additionally, a suitable silicone polymer material is identified for the shroud to withstand temperature and sustain the non-linear characteristic feature of the solenoid for Start-Stop application.
OBJECTS OF THE INVENTION:
[016] The object of the present invention is to redesign the shroud of the solenoid, to provide a uniform displacement during solenoid activation.
[017] Yet another aspect of the present invention is to modify the material of the shroud, to withstand the temperature and non-linear characteristic of the solenoid.
[018] Yet another aspect of the invention is to improve the durability, reliability and to minimize the warranty cost incurred.
[019] Other objects and advantages of the present invention will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the invention.
SUMMARY OF THE INVENTION
[020] The starter motor is an electro-mechanical product which is used to start the automotive engine for vehicle activation. The starter motor consists of solenoid, motor, planetary gears, drive and Pinion system.
|^i[Q21 ]?Asza=gen,eraj:ru l,erfthe-?o ler^oid-s hould-al^way.s ^be; directjy-rri ou nted-pnjthe-sta rter-motor by means of screws and connected to the drive assembly through the shift lever. The two main

functions are to close the circuit between the battery and the motor and performs the meshing of the starter motor pinion into the ring gear of the flywheel by the movement of the solenoid plunger and the shift lever on the motor.
[022] The starter motor mounted on the engine housing block and it is outside exposed to the severe environmental conditions like heat, cold, mud, rain, dust and etc., The starter has to work in multiple operating conditions and environmental factors without failure. The solenoid is the electromechanical subsystem in the starter motor which is assisting to engage and disengage the pinion gear to the ring gear. The solenoid is electrified by the battery power and the plunger moves towards the terminals then the contact get connected and motor gets power to rotate the pinion gear through the armature and planetary gear systems.
[023] The shroud one end of the outer circumference is fitted on the Solenoid frame and housing and another end of the shroud inner circumference is fitted on the plunger. When the Plunger moves towards the electrical terminals, it pulls the shroud inside the solenoid frame which may give severe stress to the shroud, which may affect the durability.
[024] In mild hybrid applications, the durability is increased to 500 thousands cycles which is very high compared to the conventional starter application, which is 150 thousands cycles only. Various aspects are experimented to increase the durability factor. One such

improvement is incorporating the shroud, inside the housing, that comes along with the solenoid assembly. The shroud displacement is linear along the axis of the solenoid assembly. The required total displacement is fixed based on the pinion engagement distance and shift lever ration. The design loads of the shroud, depends on the many factor as shown in the below table.
[025] While designing the shroud, the most important aspect to consider is the environmental factor, such as hot temperature, cold temperature, mud, dust and water ingress. These factors does impact the durability and reliability of the motor. Durability cycle is based on the vehicle requirements and type of engine application. If the engine is used for mild hybrid applications, the durability of the starter is more, hence the shroud duty cycle requirement is more. The shroud has to be properly seated in the housing, to perform its function without any wear and tear.
[026] Another feature is the material for the shroud, which again depends on the application. The material should be more flexible for large displacement under tension as well as compression, to function properly. Prior arts used rubber as the base material for the conventional starter motor applications.
[027] Incase of mild hybrid applications, the silicone material is opted. The neoprene and silicone are the rubber medium and exhibit hyper-elastic material behavior which is highly non¬linear contact and non-linear material. They are chosen for their thermal stability and are resilient to environmental factors.

[028] The existing shroud is 13mm the larger size of the shroud used before which is optimized to 10.7mm as per the present invention and additionally offers smooth transition. It also offers package advantages.
[029] The shroud is made up of Neoprene material and its displacement has been calculated as 13mm based on the solenoid plunger axial displacement. In the simulation analysis, the same displacement 13mm is applied at shroud end face to predict the shroud behavior. The displacement results have been extracted at every instance of 3.1mm, 6.1mm, 9.25mm and 13mm. In the first two instances the shroud movements are smooth and no abnormality identified in the compression of the neoprene shroud material. But, in the consecutive instances of displacement, the shroud is compressed and squeezed which abnormally affected the performance and durability. The shear elastic strain level of the existing shroud is 13mm displacement condition is 31.7%.
Analysis of New Shroud Design:
[030] The New shroud is designed to address the increased durability (Cf), increased
temperature (Tf) environmental and shroud compression issues. The shroud material, is

chosen as Silicone rubber material and its displacement (Df) has been calculated is 10.50mm based on the solenoid plunger axial movement. The same displacement 10.5mm is applied at the shroud end face in the simulation setup and predicted the shroud behavior. The displacement results have been extracted at every instance of 3.1mm, 5.27mm, 7.5mm and 10.5mm as shroud displacement characteristics. In all the displacement instances, the shroud movement is smooth and no abnormality in the compression of the new geometry shroud with silicone material. This affects positively to increase the performance and durability life of the solenoid and starter motor. The Shear elastic strain level of the new geometry (Gf) shroud at 10.5mm displacement condition is 21.7% as shown in the figure.
[031] The new geometry shroud has been checked for the plunger ring and solenoid mounting sealing (Sf), capability. This will ensure that the shroud will not come out from plunger mounting and solenoid-housing mounting. The new shroud design also ensures that enough space is available inside the housing (Hf) for the compression and expansion. This has been checked by finite element analysis by more iterations with modified shroud geometries. The surface finishing of the housing also maintained for the better wear rate and compression set property while the shroud is fitted with solenoid and housing. The new geometry Shroud is studied for the mouldability (Uf) for quick and better manufacturing quality.
[032] The arrangement of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following brief description, which together serve to explain certain principles of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS:
[033] The present invention will be better understood fully from the detailed description that is
given herein below with reference to the accompanying" drawings- wor the-preferred

embodiments of the present invention, which, however should not be deemed to be a limitation to the invention to the specific embodiments, but are for the purpose of explanation and understanding only.
In the drawings:
FIG.1. is the perspective view showing a conventional starter motor and Solenoid assembly
FIG.2. is the sectional view showing new arrangement of solenoid assembly with the shroud according to the present invention
FIG. 3. Is the sectional and full view of the shroud design as per the present invention
FIG.4. is a graph to depict the shear strain convergence characteristics of the shroud according to the present invention
DETAILED DESCRIPTION OF THE INVENTION:
[034] While this invention is susceptible of embodiments in many different forms, the detailed description of the preferred embodiments with reference to the corresponding drawings shown herein below are to be understood that the present disclosure shall be deemed as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described.
[035] In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of FIG 1 - 5.

[036] Referring to FIG. 1a, discloses the conventional starter, comprises: a motor 1 and solenoid assembly 2. The solenoid assembly as in FIG. 1 b further comprises a shroud 3, Ring 4 and Rod 5. The solenoid frame holds the primary and secondary coil along with the plunger rod (5). Also it helps the shroud mounting and connecting with the plunger rod (5) through ring (4) fitted to the plunger rod (5). This total assemlby is mounted on the starter housing. The primary function of the solenoid assembly is to provide the necessary force to pull the drive assembly into engagement with the ring gear. Additonally, it also provide high curent switch to energize the starter motor.
[037] Referring FIG. 2, discloses a sectional view of the solenoid assembly, where it depicts the arrangement of the shroud inside the solenoid. The seating ring is provided for the additional fit for one end of the shroud during the assembly of solenoid with the starter housing. The other end is fitted with the ring onto the solenoid to prevent the entry/invasion of dust/water/oil. As the shroud design is novel and unique for axisymmetric uniform displacement, the said end fittings assist to perform the shroud better interims of higher durability, relaibility and to limit the water ingression. Additionally it also withstands temperature fluctuations and offers smooth transistion of the plunger to avoid high pulling force requirment.
[038] Referring FIG. 3, discloses a sectional and full view of the shroud design as per the
present invention, which is designed with multiple parameter, which affects the performance
of the solenoid and the starter motor durability. The shroud housing is designed in such a way
to mount on the solenoid frame with an adequate contact pressure with the help of frame lips
- ie, 2 nos. The ring land (10), which is perfectly desgined to make a proper seating on the
ring to have a good contact pressure. It also prevents water ingressrond during the solenoid
plunger displacement. The frame slope specfically design to give a bending support for the
shroud duringL theJotaL.cqnipj:ession..supported-by„the_shrnijd-sJopel-inner (A 2)-and-shroud
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slope outer (13) such a way to give a uniform displacement start from the initial displacement

to final displacement of the solenoid plunger movement. So, the variation of the thickness is considered. The bend radius is to support the shroud at maximum compression and maximum displacement to provide stiffness to the shroud.
[039] The ring stiffener inner (15) is specially designed to address the premature shroud collapse in the beginning of the shroud displacement. The ring flat (16) and the ring radius
(17) are given to accommodate the ring land (10) and inside the ring radius (17) for smooth mounting respectively. Specifically, the breather hole (18) is provided at the shroud bend radius (14) to limit the stress during shroud compression and displacement. The breather hole
(18) acts as a wall inside the shroud to perform during the compression and the axisymmetric shroud is mounted on the solenoid assembly of the starter motor.
[040] The graph depicts the shear elastic strain convergence of the novel shroud design, where the displacement of the shroud is directly proportional to the elastic strain, which is shown in the graph.The novel design addresses the improved durability (Cf), increased temperature (Tf), environment and shroud compression issues. The selected shroud metarial is Silicone and the displacement is calculated as 10.50mm based on the solenoid plunger axial movement.
[041] The existing shroud geometry is inadequate for smooth compression and expansion function to meet the solenoid and starter durability life. The new geometry is designed and optimized for better shorud design and it has been analyzed with finite analysis method for indentifying its functional characteristitucs.
Shroud design factors (Dsf) = f(Df, Mf, Gf, Sf, Hf, Xf, Tf, Cf, Uf) (1)
Where,
Mf - Shroud Material

Gf - Shroud geometry
Sf - Sealing compatibility
Hf - Space available inside the housing
Xf - Housing surface finish
Tf - Starter motor working temperature
Cf- Durability cycle
Uf - Shroud material mould compatibility
[042] Thus, the effect of geometry of the shroud for smooth solenoid operation has been explained, which impacts the application of shroud in the electrical solenoid of the starter motor.

I/We hereby claim that,
A starter motor comprising: a pinion; an electric motor for generating torque to rotate the said pinion; an electromagnetic switch having a plunger assembly; the said plunger assembly and frame assembly connected through a return spring; which holds the primary and secondary coil with the plunger rod; a shroud, which is positioned on the solenoid, where one end of the outer circumference is fitted on the solenoid frame and housing and; the inner circumferncee is fixed on the plunger ring of the solenoid; the said shroud is axisymmetric and tappered in circumferential shape with the both ends having the thickness to fit onto the solenoid and plunger ring in a leak proof feature.
The starter motor according to claim 1:
Wherein the said shroud is positioned inside the solenoid assemlby
The starter motor according to claim 1:
Wherein the shroud is made of silicone material, and it is not limited to silicone, any materials with high thermal properties may be used.
The solenoid for the starter motor accoridng to claim 1:
Wherein the said shroud effectively prevents water/dust/oil entry and offers smooth transistion of the plunger to avoid severe stress and prolongs the shroud life.