FIELD OF THE INVENTION
[001] The present invention relates generally to a starter which may be employed in starting an automotive engine, and more particularly to a solenoid plunger assembly, provided with "O" rings, to ensure relatively smooth engagement of the pinion and ring gear prior to the contact closing.
BACKGROUND OF THE INVENTION
[002] Starter motor assemblies that assist in starting engines, such as engines in vehicles, are well known. A conventional starter motor assembly is shown in FIG. 1
[003] More specifically, the conventional starter device 1, as shown in FIG. 1, comprises: a DC motor 2; an over-running clutch 4 mounted on the output rotary shaft 3 of the motor; an solenoid assembly 6 provided beside the DC motor 2; and a shift lever 10 having one end engaged with a hook 8 coupled to the plunger 7 of the solenoid assembly 6 and the other end engaged with the cylindrical rear end portion 9 of the over-running clutch 4 so as to slide the over-running clutch 4 with on the output rotary shaft 3.
[004] The solenoid assembly 6 for operating the shift lever 10 has a cylindrical outer frame 11 which has a wall 11a at one end. The aforementioned plunger 7 is inserted into the end wall 11a. A stationary iron core 1.2 is disposed at the other end of the outer frame 11 in such a manner

as to confront with the plunger 7. The iron core 12 has an end wall which is fixedly fitted in the rear end portion of the outer frame 11, thus forming a frame together with the outer frame 11. A coil bobbin 13 is accommodated in the frame thus formed. An exciting coil is wound on the coil bobbin 13. A return spring is interposed between the iron core 12 and the plunger 7. The iron core 12 has a central through-hole, into which a rod 16 is slidably inserted in such a manner that its one end portion (or front end portion) is extended from the iron core 12 towards the plunger 7. The other end portion (or rear end portion) of the rod 16 supports a movable contact 17.
[005] The solenoid assembly further comprises: a carrier rod 18 for returning the rod to a predetermined position; a cap 19 made of resin; and a terminal bolt 20 embedded in the cap 19 so that its inner end serves as a stationary contact with which the movable contact 17 is brought into contact.
[006] The plunger 7 is inserted into the central opening formed in the end wall 11a of the outer frame 11, and it is moved along the central axis of the coil bobbin 13 towards the iron core 12. The plunger 7 has a recess which is opened axially outward. The above-described connecting rod 8 is in the form of a piston and has a flange at the rear end. The connecting rod 8 is slidably inserted into the recess of the plunger 7 and is extended outside passing through the central hole that is formed in a holder 21, which closes the open end of the recess of the plunger 7. The outer end portion of the connecting rod 8 is engaged with the upper end of the shift lever 10. Inside the recess of

the plunger 7, a cylindrically coiled spring, namely, a mesh spring 22 is interposed between the holder 21 and the flange of connecting rod 8.
[007] The operation of the conventional starter thus constructed will be described in brief.
[008] When the key switch of the vehicle is turned on, the exciting coil of the electro-magnetic switch 6 is energized so that the plunger 7 is moved towards the iron core 12. As a result, the shift lever 10 is turned, whereby the over-running clutch 4 and the pinion 5 integral with the clutch inner portion are slid on the output rotary shaft 3. In this operation, when the pinion 5 abuts against the side of the engine ring gear, the turning of the shift lever 10 is stopped while the plunger 7 continues to move towards the iron core, the mesh spring 22 is compressed, so that the pinion is pushed against the engine ring gear through the shift lever 10.
[009] As the plunger 7 pushes the rod, the movable contact 17 is brought into contact with the stationary contact, so that the DC motor 2 is energized. As a result, as soon as the pinion 5 is rotated, it is engaged with the engine ring gear by the elastic force of the mesh spring 22.
[010] The purpose of solenoid assembly in the starter motor is to engage the pinion of the drive assembly of the starter motor to the ring gear of the engine and to provide electrical contact for the motor. But, the provision of Mesh ring in the solenoid plunger closes the contact, prior to the engagement of pinion

and ring gear, which results in the misalignment of the teeth's of the pinion and ring gear.
[011] Thus, there exists a need to identify a technique to engage the pinion and ring gear in a relatively smooth manner prior to the closing of the contacts, which increases the contact closing time.
[012] Accordingly, the present invention provides a solution, by which smooth meshing of the ring and pinion gear is ensured. This improvement enhances the performance and also attributes to the increased durability and lifetime of the starter.

OBJECTS OF THE INVENTION
[013] The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a starter solenoid assembly with "O" Rings, creates damping effect and thereby reduces the plunger travel speed to ensure smooth engagement of the pinion and ring gear prior to the contact closing.
[014] One object of the present invention prevents water or dust entry inside the plunger and contact assembly, which eliminates the need for an additional shroud in the plunger.
[015] Yet another object of the present invention, reduces the impact on the ring and pinion gear and prevent defective/poor performance of the starter. This eventually improves the durability and lifetime of the motor.
[016] Another object of the present invention is that, the "O" rings can be accommodated to the solenoid plunger with the existing design without any major modifications therein.

SUMMARY OF THE INVENTION
[017] In the view of the above-described problems, the primary object of the present invention is to provide a starter solenoid assembly with "O" rings, The said arrangement creates absolute damping effect and thereby reduces the plunger travel speed, which results in compressing the mesh ring only at the time of abutment. Hence, the motor is energized only after the smooth and full engagement of the pinion with the ring gear.
[018] The present invention also discloses the positioning of the "O" rings on the -plunger assembly to achieve the abovementioned benefits. It has to be noted that, one or more "O" rings can be mounted on the outer portion of the plunger i.e., on the tapered groove of the plunger assembly. The groove on either side has lubricant oil or grease to be maintained for smooth transition. Thus, it provides absolute damping effect between the plunger and the sleeve and decelerates the movement of the plunger, when the switch is energized.
[019] The methods and 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:
[020] The present invention will be better understood fully from the detailed description that is given herein below with reference to the accompanying drawings of 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:
[021] FIG. 1 is a sectional view of a conventional starter motor.
[022] FIG. 2 is an exploded view of a solenoid.
[023] FIG. 3 is the exploded view of solenoid assembly with the provision of O rings.
[024] FIG. 4 is a graphical representation showing the effect of the voltage against the time with the provision of O rings and also the showing the increase in the contact closing period.

DETAILED DESCRIPTION OF THE INVENTION
[025] 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. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of FIG 2-4.
[026] Referring to FIG. 2, the starter solenoid assembly comprises, a plunger assembly 7 which connects with frame 11 by means of return spring. The outer portion of the plunger 7 has a tapered groove on which the plurality of "O" rings 27 are positioned. The pull-in and hold-in coils with two leads are rounded on a bobbin 13, the plunger strip connects the bobbin and the contact plate 17 though the over travel spring and the other end of the contact plate is connected to the contact return spring. The whole solenoid 6 is closed through the cap assembly 19 with a gasket to avoid damages.
[027] The sequence is initiated by the solenoid when the terminal is energized from the ignition switch. It thereby energizes both the pull-in and hold-in coils, which creates a strong magnetic field pulling the plunger assembly toward the plunger stop. By means of one or more "O" ring structures on the plunger

assembly, the damping effect between the plunger and sleeve gradually decelerates the movement of the plunger. Thus, the mesh spring collapses only at the time of abutment and energizes the motor after the safe and smooth engagement of the pinion with ring gear. The said arrangement also creates additional air-friction between the plunger and the plunger stop, resulting in plunger displacement speed.
[028] Furthermore, The "O" rings used in the above mentioned invention can be conveniently replaced by oil seals or lip seals, which possess the same properties as that of "O" rings. The said "O" rings are composed of silicone rubber and mounted on the tapered groove of the plunger assembly. The grooves have lubricant oil or grease to maintain smooth transition. It has to be noted that, it need not to be the specific combination or construction and may be constructed in some other configuration or combination as per the needs.
[029] In yet another embodiment, the FIG. 2, illustrates the enlarged view of the "O" rings mounted on the plunger assembly. The Detail "A" given in the figure represents the "O" rings. The said ring structures are placed in the conical groove of the plunger to achieve the said advantages. Each groove has grease or lubricant oil to ensure smooth transition. During the forward movement, the rings are displaced to the larger portion of the groove; thereby it increases the damping effect between the plunger and sleeve. This arrangement, limits the plunger to move in only one direction. I.e., from the maximum air-gap to the zero air-gap. During the pinion reverse movement,

the "O" ring structures moves towards the smaller portion of the groove and relaxes the friction between the plunger and the sleeve. Hence, the reverse movement is faster than that of the forward movement.
[030] The FIG.3, shows the exploded view of the solenoid plunger assembly with "O" rings. The advantages are explained in the above said embodiments.
[031] In yet another embodiment of the present invention, refer FIG. 4, the contact closing time of the assembly is shown. The graph represents the voltage against the time behaviour for the said arrangement. As per the conventional solenoid assembly, the contact closing time is measured as 18 ms [represented in dotted line]; whereas it has considerably increased to 28 ms with the provision of "O" rings [represented as bold line]. The parameters and results may be selected according to the needs of a practitioner of the present invention, with each selected parameter falling within the scope of the present invention. The contact closing time mentioned here is for the given input, which can be varied as per the requirements. Hence, the preferred embodiment disclosed in the foregoing description should not construe as a limitation to the scope of the present invention.
[032] By the inclusion of "O" rings into the starter solenoid assembly, the plunger travel speed is greatly reduced, which results in smooth and safe engagement of pinion and ring gear. Thus, increases the contact closing time.

[033] The present invention also, increases the tear and wear of the ring and pinion gears and also suppresses foreign materials such as grit or dust or water inside of the housing. Thus, the lifetime and the durability of the motor are greatly improved.
[034] It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the preferred embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Each such implementation falls within the scope of the present invention as disclosed herein and in the appended claims.

CLAIMS
We claim:
1) A starter motor for an engine comprising;
a pinion; an electric motor for generating torque to move the said pinion; a solenoid assembly having a plunger assembly; and electrical contacts; plurality of "O" ring structures accommodated on the tapered groove of the plunger assembly, the said plunger is moved by the strong magnetic force, so as to slide the said drive assembly and pinion in an axial direction thereof; and the said arrangement act as a damper and reduces the plunger travel speed; the mesh spring compresses at the time of abutment;
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2) A starter motor according to claim 1:
Characterised in the plunger assembly are, Plurality "O" rings mounted on the tapered grooves of the assembly. Wherein, the said groove has grease or lubricant oil for smooth transition.
3) A starter motor according to claim 1,
The said "O" rings, significantly increases the contact closing time, for smooth engagement of pinion to the ring gear.

4) The starter motor according to claim 1;
The said arrangement further act as a shroud to prevent the grit or water or dust entry inside the plunger and contact assembly;
5) A starter motor according to claim 1:
Wherein the said "O" rings arrangement, create an additional air-friction between the plunger and the plunger stop, resulting in plunger displacement speed.