Claims:We claim:
1. A fluid injector (100) which functions as a positive displacement pump and comprises:
a housing (106) in which a piston chamber is formed;
a piston (108) which reciprocates in said piston chamber to define therewith a variable volume fluid pumping chamber (116);
a cover (102) to enclose said open end of said housing (106);
a one-way inlet valve (110) which allows flow of fluid into said pumping chamber (116) from a fluid inlet (112);
a one-way outlet valve (114) which allows flow of fluid out of said pumping chamber (116) to a fluid outlet (124); wherein in operation of said fluid injector (100) said piston (108) is cyclically moved to increase volume of said pumping chamber (116) and draw fluid into said pumping chamber (116) via said one-way inlet valve (110) and then said piston (108) is moved to decrease volume of said pumping chamber (116) and expel fluid from said pumping chamber (116) via said one-way outlet valve (114), characterized in that,
said fluid injector (100) is provided with at least one of a shim (120) and at least one indent (202) on a rim (206) of said piston (108).

2. The fluid injector (100) as claimed in claim 1, wherein said shim (120) is located between said housing (106) and said cover (102).

3. The fluid injector (100) as claimed in claim 1, wherein a thickness of said shim (120) defines a stroke length for said piston (108).

4. The fluid injector (100) as claimed in claim 1, wherein said shim (120) comprises a profile to conform with said piston (108).

5. The fluid injector (100) as claimed in claim 1, wherein said shim (120) comprises at least one protrusion (122) which faces towards said housing (106).

6. The fluid injector (100) as claimed in claim 5, wherein said at least one protrusion (122) of said shim (120) comprises four protrusions (122).

7. The fluid injector (100) as claimed in claim 1, wherein said at least one indent (202) of said rim (206) of said piston (108) comprises four indents (202).

8. The fluid injector (100) as claimed in claim 1, wherein said rim (206) of said piston (108) is coated with wear resistant material , Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed:

Field of the invention:
[0001] The present invention relates to a fluid injector which functions as a positive displacement pump.

Background of the invention:
[0002] Currently there exists assembly concerns of piston lift (stroke length) setting and the drift of stroke length over lifetime due to wear on moving parts which make the fuel quantity delivered to the engine inconsistent. There is a need to maintain component to component variation within specified limit and to achieve the same during component assembly with minimum takt time. The takt time is defined as product assembly time required to meet customer demand.

[0003] A desired stroke length can be adjusted during the assembly process. During the assembly, the inlet valve, housing, the piston, and solenoid (electric coil) forms a first assembly and are placed on outlet valve assembly. A cover (also known as back-iron component) is pushed on to the first assembly positioned over the outlet valve assembly, until it touches a head/rim of the piston. The cover is pulled back to desired stroke length and is welded/fixed to the housing at desired stroke length position. Now, maintaining the accuracy and repeatability of stroke length within the tolerance is challenging for series production. Additionally, a separate station in the assembly line is required for stroke length measurement, leading to increased takt time and manufacturing cost. Also, a drift in stroke length over lifetime is observed due to wear on contact surface between the piston and the cover. This leads to change in fuel injection quantity, which is difficult to correct/adjust beyond a limit. Further, the piston comes in contact with the cover forming circular surface contact. During the operation, hydraulic film between the piston and the cover creates stickiness and delays the piston travel in every cycle during Top Dead Center (TDC) to Bottom Dead Center (BDC) movement, leading to improper pressurization & injection duration.

[0004] A patent literature 7861/DELNP/2011 discloses a fluid injector having a novel inlet valve arrangement. The prior art provides a fluid injector which functions as a positive displacement pump and comprises: a housing in which a piston chamber is formed; a piston which reciprocates in the piston chamber to define therewith a variable volume fluid pumping chamber; a one-way inlet valve which allows flow of fluid into the pumping chamber from a fluid inlet; and a one-way outlet valve which allows flow of fluid out of the pumping chamber to a fluid outlet. In operation of the injector the piston cyclically moves to increase volume of the pumping chamber and draw fluid into the pumping chamber via the one-way inlet valve and then the piston moves to decrease volume of the pumping chamber and expel fluid from the pumping chamber via the one-way outlet valve.

Brief description of the accompanying drawings:
[0005] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0006] Fig. 1 illustrates a cut-section of a fluid injector, according to an embodiment of the present invention, and
[0007] Fig. 2 illustrates different views of a piston used in the fluid injector, according to an embodiment of the present invention.

Detailed description of the embodiments:
[0008] Fig. 1 illustrates a cut-section of a fluid injector, according to an embodiment of the present invention. The fluid injector 100 which functions as a positive displacement pump and comprises, a housing 106 in which a piston chamber is formed. The housing 106 comprises an annular bore/ hollow cylinder with a flange. A solenoid or electric coil 104 is assembled around the housing 106 and above the flange. A piston 108 which reciprocates in the piston chamber to define therewith a variable volume fluid pumping chamber 116. The piston 108 also comprises a cavity to hold a return spring 118. A cover 102 to enclose the open end of the housing 106 is provided. A one-way inlet valve 110 which allows flow of fluid into the pumping chamber 116 from a fluid inlet 112. A one-way outlet valve 114 which allows flow of fluid out of the pumping chamber 116 to the fluid outlet 124. In operation of the fluid injector 100, the piston 108 cyclically moves to increase volume of the pumping chamber 116 and draws fluid into the pumping chamber 116 via the one-way inlet valve 110 and then the piston 108 moves to decrease volume of the pumping chamber 116 and expels fluid from the pumping chamber 116 via the one-way outlet valve 114, characterized in that, the fluid injector 100 is provided with at least one of a shim 120 and at least one indent 202 on a rim 206 of the piston 108. The shim 120 is annular ring shaped which is shown in two views. The shim 120 is possible to be plural as well. A figure in left bottom corner of the fluid injector 100 shows a side view of the shim 120. A figure in right bottom corner of the fluid injector 100 shows a perspective view of the shim 120.

[0009] The operation of the piston 108 is controlled by a controller through the electric coil 104. The controller comprises memory element such as Random Access Memory (RAM) and/or Read Only Memory (ROM), Analog-to-Digital Converter (ADC) and vice-versa Digital-to-Analog Convertor (DAC), clocks, timers and at least one processor (capable of implementing machine learning) connected with the each other and to other components through communication bus channels. The memory element is pre-stored with logics or instructions or programs or applications and/or threshold values, which is/are accessed by the at least one processor as per the defined routines. The internal components of the controller are not explained for being state of the art, and the same must not be understood in a limiting manner. The controller may also comprise communication units to communicate with a server or cloud through wireless or wired means such as Global System for Mobile Communications (GSM), 3G, 4G, 5G, Wi-Fi, Bluetooth, Ethernet, serial networks and the like.

[0010] In accordance to an embodiment of the present invention, a thickness of the shim 120 defines a stroke length or piston lift for the piston 108. The shim 120 comprises a profile to conform with the piston 108. The shim 120 comprises at least one or plurality of protrusions 122 which faces towards the housing 106 or towards the piston 108. In an embodiment, the shim 120 comprises four protrusions 122. Further, the at least one indent 202 on the rim 206 or a peripheral end of the piston 108 which faces the cover 102 comprises plurality of indents 202 (shown in Fig. 2), such as four indents 202. The shim 120 enables selectively setting stroke length of the piston 108. The shim 120 is assembled between the housing 106 and the cover 102 to achieve specified stroke length for the piston 108. A height “A” of the piston 108 above the housing 106 is measured and desired stroke length “B” is added to select the suitable thickness of the shim 120. Accordingly, the cover 102 is assembled / welded with the housing 106 without any stroke length measurement in (or during) the assembly/ manufacturing.

[0011] In accordance to the present invention, the shim 120 with at least one protrusion 122 (or lugs or slots or other possible designs) is used between the housing 106 and the cover 102 for setting the stroke length of the piston 108. In the present invention, four protrusions 122 are shown on inner side/peripheral region of the shim 120 which interfaces with the shoulder 204 of the piston 108. However, two, three, five, and other number of protrusions 122 are equally possible to be used. Further, the protrusions 122 are designed in a manner to match the step/shoulder 204 (shown in Fig. 2) provided on the piston 108. The shim 120 provides ease of assembly process and eliminates measurement station considerably reducing the takt time and overall manufacturing costs.

[0012] In accordance to an embodiment of the present invention, the fluid injector 100 is implementable in vehicle comprising a two-wheeler such as a motorcycle, a scooter, a moped, etc. However, the controller is equally adaptable to be used for three-wheelers such as auto-rickshaws, four/multi wheelers such as cars bus, trucks and the other existing and new vehicles (even snow mobiles, water sports vehicles, etc.). In the context of vehicles, the fluid injector 100 is usable for injecting fuel or a fuel mixture, a diesel exhaust fluid, etc. Further, a fuel-based power tool can also use the fluid injector 100 for example lawn mowers, chain saw and other similar power tools. The applicability of the fluid injector 100 is not limited to vehicles/fuel engines but in other areas as well such as medical field where there is a need to dispense a liquid form medicament to a patient.

[0013] In accordance to another embodiment of the present invention, the fluid injector 100 is provided is with at least one of the shim 120 and the modified piston 108. In a first embodiment, the fluid injector 100 is provided with only the shim 120, in which case the piston 108 remains the same without indents 202. In a second embodiment, the fluid injector 100 is provided with only the modified piston 108, without the shim 120. In a third embodiment, the fluid injector 100 is provided with both of the shim 120 and the modified piston 108.

[0014] In accordance to the first embodiment, the fluid injector 100 which functions as a positive displacement pump and comprises, a housing 106 in which a piston chamber is formed. The housing 106 comprises an annular bore/ hollow cylinder with a flange. A solenoid or electric coil 104 is assembled around the housing 106 and above the flange. A piston 108 which reciprocates in the piston chamber to define therewith a variable volume fluid pumping chamber 116. The piston 108 also comprises a cavity to hold a return spring 118. A cover 102 to enclose the open end of the housing 106 is provided. A one-way inlet valve 110 which allows flow of fluid into the pumping chamber 116 from a fluid inlet 112. A one-way outlet valve 114 which allows flow of fluid out of the pumping chamber 116 to the fluid outlet 124. In operation of the fluid injector 100, the piston 108 cyclically moves to increase volume of the pumping chamber 116 and draws fluid into the pumping chamber 116 via the one-way inlet valve 110 and then the piston 108 moves to decrease volume of the pumping chamber 116 and expels fluid from the pumping chamber 116 via the one-way outlet valve 114, characterized in that, the fluid injector 100 is provided with at least one shim 120.

[0015] In accordance to the second embodiment of the present invention, the fluid injector 100 which functions as a positive displacement pump and comprises, a housing 106 in which a piston chamber is formed. The housing 106 comprises an annular bore/ hollow cylinder with a flange. A solenoid or electric coil 104 is assembled around the housing 106 and above the flange. A piston 108 which reciprocates in the piston chamber to define therewith a variable volume fluid pumping chamber 116. The piston 108 also comprises a cavity to hold a return spring 118. A cover 102 to enclose the open end of the housing 106 is provided. A one-way inlet valve 110 which allows flow of fluid into the pumping chamber 116 from a fluid inlet 112. A one-way outlet valve 114 which allows flow of fluid out of the pumping chamber 116 to the fluid outlet 124. In operation of the fluid injector 100, the piston 108 cyclically moves to increase volume of the pumping chamber 116 and draws fluid into the pumping chamber 116 via the one-way inlet valve 110 and then the piston 108 moves to decrease volume of the pumping chamber 116 and expels fluid from the pumping chamber 116 via the one-way outlet valve 114, characterized in that, the fluid injector 100 is provided with at least one indent 202 on the rim 206 of the piston 108.

[0016] In accordance to the third embodiment of the present invention, the fluid injector 100 which functions as a positive displacement pump and comprises, a housing 106 in which a piston chamber is formed. The housing 106 comprises an annular bore/ hollow cylinder with a flange. A solenoid or electric coil 104 is assembled around the housing 106 and above the flange. A piston 108 which reciprocates in the piston chamber to define therewith a variable volume fluid pumping chamber 116. The piston 108 also comprises a cavity to hold a return spring 118. A cover 102 to enclose the open end of the housing 106 is provided. A one-way inlet valve 110 which allows flow of fluid into the pumping chamber 116 from a fluid inlet 112. A one-way outlet valve 114 which allows flow of fluid out of the pumping chamber 116 to the fluid outlet 124. In operation of the fluid injector 100, the piston 108 cyclically moves to increase volume of the pumping chamber 116 and draws fluid into the pumping chamber 116 via the one-way inlet valve 110 and then the piston 108 moves to decrease volume of the pumping chamber 116 and expels fluid from the pumping chamber 116 via the one-way outlet valve 114, characterized in that, the fluid injector 100 is provided with at least one shim 120 and at least one indent 202 on the rim 206 of the piston 108.

[0017] In accordance to an embodiment of the present invention, the rim 206 of the piston 108, either with or without indents 202, is coated with wear resistant material.

[0018] Fig. 2 illustrates different views of a piston used in the fluid injector, according to an embodiment of the present invention. A side view 200, a cut-section 210, a perspective view 220 and the top view 230 of the piston 108 alone is shown.
The shim 120 is located between the housing 106 and the cover 102. The thickness of the shim 120 defines the stroke length for the piston 108. The shim 120 comprises the profile to conform with the piston 108. The shim 120 comprises at least one protrusion 122 or plurality of protrusions 122 which faces towards said housing 106 or the piston 108.

[0019] In accordance to an embodiment of the present invention, the indents 202 on the rim 206 of the piston 108 overcomes the hydraulic stickiness by breaking the complete contact surface between the top of piston 108 and the cover 102. Further, not only the hydraulic stickiness is eliminated, but formation of eddy current is also avoided or reduced. A magnetic network/circuit is formed between the piston 108 and the cover 102 which gives rise to eddy currents due to magnetization effect. In order to provide smooth backward / upward timely movement of the piston 108, the eddy current must also be prevented. The indents 202 (also known as slots or grooves) breaks the eddy current and enables the smooth travel of the piston 108 without any restrictions. Further, a suitable coating on the piston 108 is also possible to improve the lifetime.

[0020] According to the present invention, accurate setting of stroke length for the piston 108 and robustness measure in fluid injector 100 is provided. The fluid injector 100 is provided with the shim 120 with variable thickness between the housing 106 and the cover 102 to achieve the specified stroke length for the piston 108. By measuring the height of the piston 108 and the height of the housing 106, the shim 120 with suitable thickness is chosen for setting the stroke length. Thus, the measurement station specifically for the stroke length is completely eliminated. In addition to above function, the shim 120 also reduces the contact area of the piston 108 and the cover 102, both are of soft magnetic material type. The contact area between the shim 120 (harder material) and the piston 108 (softer material compared to the shim 120) is now comparatively lesser and reduces the wear. Further, robustness coating (C-Coating, HCC coating or suitable coating on the piston 108 and the cover 102 interface surface) is provided to address the drift of stroke length over lifetime concern. The design of the indents 202 on top surface of the piston 108 overcomes the hydraulic stickiness. The design of the indents 202 also breaks the eddy currents formed during magnetic field generation and thereby reduces its impact. Further, the introduction of the shim 120 improves the assembly and setting process of fluid injector 100.

[0021] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.