FIELD OF INVENTION:

This invention pertains to Inlet Valve for a CRAIL Diesel Engine.

BACKGROUND OF THE INVENTION:

Currently modern diesel engines coming with advanced fuel delivery and engine management systems allow engines to improve power, performance and emissions norms. The term“CRAIL” stands for“Common Rail Injection” system, which is one of the advanced fuel delivery system which economizes the amount of diesel entering the combustion chamber. It directly releases the fuel in chamber through a nozzle to reduce the chances of delay as well as for better efficiency. This CRAIL engine is designed for peak combustion pressure 180 bar and maximum predefined combustion temperature of 780°C as these are always in contact with exhaust gases for throwing them outside the engine. However, the Mono-metal design with Austenitic steel 21- 4N construction for inlet valve of this engine, which was in use for several decades for making inlet valve, had a defect that it was prone to wear and tear at tappet end, leading to breakdowns. Summary of Invention

This invention comprises a monometallic inlet valve for a CRAIL engine developed in a steel material that can be hardened. The steel material used may be amenable for induction hardening. In one embodiment, the steel material used is Martensitic EN-52 grade steel. However, another grade can also be used that may have properties similar to Martensitic EN-52 grade steel and can be induction hardened. if is an embodiment of this invention that the monometallic inlet valve for a CRAIL engine is induction hardened at tappet end. The the tappet end hardness may be 52 HRC min and through hardening depth is 12-16mm with Barrel hardness 490hv30 min. in a further embodiment, the monometallic inlet valve for a CRAIL engine according to this invention comprises inlet valve that is designed to perform under common CRAIL engine operating boundary conditions of peak combustion pressure 180 bar and maximum predefined combustion temperature 780°C. The monometallic inlet valve for a CRAIL engine according to this invention has the Design of Safety of 3.86.

DETAILED DESCRIPTION OF THE INVENTION

In addition to the defect that the Austenitic steel 21-4N, from which the monometallic inlet valve for crail engine were being made since several decades was prone to wear and tear at tappet end, leading to breakdowns, we also noted that it was expensive because it was a highly heat resistant material. However, its heat resistance for an inlet valve of this engine was not relevant because temperatures at inlet end are low due to continuous flow of air which keeps temperature of Inlet valve lesser than 500°C. For both the reasons, it was found necessary to explore alternative material for inlet valve of a CRAIL engine. This invention embodies an inlet valve for CRAIL engine which is made from a material which is not hard but can be hardened (harden-able). Martensitic steel EN 52 (X45CrSi93) was used to illustrate such a material and the invention.

The figures show mono-metal design feature of inlet valve of this invention which is made with Martensitic steel EN 52 (X45CrSi93) material which can be hardened (harden-able). Brief description of figures and legends:

Figure 1 : Indicates front view of solid inlet valve having following parts:

(1) Valve Face & Head Area

(2) Valve Seat Area (3) Valve Fillet & Neck Area

(4) Valve Stem Area

(5) Valve Groove Area

(6) Valve Induction hardened length up to valve tip

(7) Valve Tip/ Tappet end

Figure 2: Indicates vertical-sectional view of the inlet valve of Fig 1 Figure 3: Valve axial deformation in Y- direction. if signifies the change in original length (in micron) of inlet valve in axial direction under combustion pressure boundary condition. Figure 4: Von mises stress at valve tappet end

Von mises stress is tensile stress based yield criterion design, here indicating magnitude of stress at valve tip[Fig.1 : (7)]area

Figure 5: Von mises stress at valve groove [Fig.1 : (5)] portion

Von mises stress is tensile stress based yield criteria in design, here indicating magnitude of stress at valve groove area.

The Figure 1 illustrates Inlet valve features :(1) Valve Head and Face - Head diameter and face has a direct impact on airflow and engine power. Ideally the valve should be large enough so that it is not a restriction to airflow through the cylinder head. (2) Valve Seat Area -This is an angular surface joining valve head to valve fillet. Valve seat width accuracy has an influence on engine performance and volumetric efficiency of engine. (3) Valve Fillet and Neck Area-Valve fillet is radius of arc which connects valve seat to the valve stem portion designed to enhance both flow and valve strength. (4) Valve Stem Area: The valve stem is fitment portion which serves as a bearing area for the valve guide; valve stem diameter is determined by the desired strength and weight characteristics. (5) Valve Groove: Three-groove type locks have been used. These allow the valve to rotate independent of the valve spring and retainer, keeping the seating surfaces dean of debris and promoting valve longevity. (6) Valve Induction hardened length up to Valve Tip: The tip of the valve stem must be quite hard to withstand constant moving contact with the rocker arm load at tappet end of valve, so it is designed with induction hardening feature with 52 HRC (Rockwell hardness). (7) Valve Tip/ Tappet end: Fiat surface tip portion which is a precisely machined design to minimize the stresses due to impact and wear.

Figure 2 is vertical section of inlet valve shown in Figure 1. It shows solid structure of inlet valve.

Figure 3 indicates the finite element analysis result called axial deformation in microns. Here it signifies the measure of strain during virtual simulation. The highest deformation observed is 12.90 micron or 0.01290mm. The deformation value evaluation is important during valve lash adjustment in valve train assembly inside the engine.

Figure 4 indicates finite element analysis result called Von mises stresses; Von mises stresses is yield criteria in design process. The concept of Von mises stress arises from the distortion energy failure theory. Distortion energy failure theory is comparison between 2 kinds of energies, 1} Distortion energy in the actual case, 2) Distortion energy in a simple tension case at the time of failure. According to this theory, failure occurs when the distortion energy in actual case is more than the distortion energy in a simple tension case at the time of failure. In CRAIL's inlet valve design we evaluated the maximum working stress during loading condition, that is 87 N/mm ² (see fig.4 elements in dark grey colour) and it is less than yield strength of material (700 N/ ^' mm ² ) hence the design of safety criteria fairly satisfied in Finite element analysis.

Figure 5 indicates von mises stress distribution in groove portion which have shown highest value of 95.58 N/mm ² (biack colour)af groove or notch area, which is lower diameter portion than stem diameter (outer diameter), and it possesses stress concentration due to notch area (groove feature). Then if is evaluated for design of safety criteria by dividing Working stress (Fig.5) to Yield stress value of EN52 material and is seen to be within safe limit.

After studying operating boundary conditions for engine of the users," a static stress, strain finite element analysis” was performed The maximum magnitude of loading conditions were applied, consisting a Spring force of 438.2 Newton at tappet end (7) and Combustion pressure forces of 18 Newton/ millimetre square at valve face (1). Finally evaluation of stress, strain were done in virtual validation with CAE (Computer Aided Engineering) approach, which uses the Computer and Mathematical method (Finite Element Method) for engineering analysis, optimization and validation of product for reliability. in a practice that was established until this invention for use of inlet valve was to use 21-4N material that is Austenitic steel, for both intake and exhaust valves; say 21-2N or 21-4N, for example. However, we realized that it is possible to consider use of different alloys for the intake and exhaust valves because whereas an exhaust alloy needs to have good high temperature resistance and corrosion resistance, they were not needed for the valve on the intake side. During working cycle of internal combustion (1C) engine, intake valves get cooled by incoming air-fuel mixture; hence the temperature in which they run is typically around 500°C. Hence, the Inlet valve is not exposed to high temperatures of around 780°C that are encountered at exhaust side; and they are also not exposed to corrosion. The Inlet Valves are exposed to continuous constant moving contact with the rocker arm exposing it to high wear and tear at tappet end and needed hardness and wear resistance to prevent breakdown in use in course of time incidentally the Austenitic steel is not harden-able; hence it continued to be a drawback for a long time in the domain of GRAIL engines. Hence, for inlet Valves, wear resistance may be more important than high temperature strength or corrosion resistance.

We found that the solution was to use Martensitic steel grade EN~52(X45CrSi93) material for making an Inlet valve in the illustrated example. However, the invention is not limited to the material used in the illustration, and any other metal/alloy that is equivalent in properties to Martensitic steel grade EN-52 (X45CrSi93), i.e. a harden-abie metallic material can be used. Thus, for example, a harden-abie heat resistant silicon chromium steel that can withstand operating temperature upto 550°C can be used instead of Martensitic steel grade EN-52 (X45CrSi93) for practicing this invention. Thus, any metal/alloy that has wear resistance and has ability of sealing against specific combustion pressure can be used to repiace Martensitic steel grade EN-52 material to practice this invention. EN-52 material has tensile strength 900 N/mm ² and Yield strength 7Q0N/mm ² Also it has good oxidation resistance, toughness and hot corrosive resistance; and a mefa!/a!!oy having these properties can replace Martensitic steel grade EN-52 (X45CrSi93) for Inlet Valve for CRA!L diesel engine application. in the new design, induction hardening of the tip end was introduced since tip of the valve stem must be quite hard to withstand constant moving contact with the rocker arm. Thereafter, to validate new design,“Finite Element Analysis was performed with reference to engine boundary condition for proposed EN-52 inlet valve and found results in terms of stresses to be within safe limit of design. After evaluation of inlet valve in terms of stress and strain, EN 52 valve steel material is used with addition of induction hardening on tappet end. Tappet end induction hardening specification is designed to provide tappet end hardness 52 HRC min and hardening depth 12-16mm with barrel hardness 490hv3Q min from valve tip end (as shown in Fig.1 and Fig.2)

To predict performance of proposed EN52 material for inlet valves, we evaluated FEA (Finite Element Analysis) analysis results against engine boundary conditions using numerical method for engineering analysis by Computer Aided Engineering (CAE). Fig.3 indicates the axial deformation(U,U2)in Y-direction, Fig.4and Fig.5 indicate Von mises stresses (S) distribution across the valve. It is noted that maximum stress induced is 95.56MPa at valve groove portion (darker grey colour scale). The maximum von mises stress 95.56MPa is less than yield strength of this material, hence the design of safety is achieved in FEA validation.

Martensitic EN 52 grade steel material with a single piece construction was used since it allows valve to do induction hardened at tappet end. Due to induction hardening at tappet end, the valve exhibits better wear resistance as well as scratch resistance characteristics on tappet end during operational load. Risk of potential valve failure at inlet valve tip end due to tappet end loading and impact gets reduced as valve tip end is induction hardened having tappet end hardness 52 HRC min and hardening depth 12~16mm with barrel hardness 49Qbv3G min from valve tip end. Further, the cost also reduced because EN52 (Martensitic) steel grade which is cheaper than 21-4N (Austenitic) of past design.

Process of making the improved monometallic valve of this invention is given in the following. Long bars of EN-52 material were cut into required length by using abrasive cutting. Then by using induction upsetter and hot forging press, required valve profile was achieved. After forging, the valves were processed for required heat treatment process (hardening and tempering) followed by shot blasting. Computer Numerical Control (CNC) turning method was employed to do machining of valve face, head and neck profile feature which was required to achieve desired specification requirement. Groove grinding was done to achieve critical fitment with groove lock and groove profile. To improve fatigue properties and wear resistance, valve was case hardened with soft nitriding process to establish diffusive layer having depth of 10 microns on entire valve. After soft nitriding, valve tappet end was induction hardened up to depth of 12-16 m from valve tip end. Finally, precise grinding was done for valves seat and tappet end area to achieve required roughness, roundness and run-out specification. Table No.1 : EN 52 Material Mechanical and Thermal properties

Note: Megapascal unit (MPa) equivalent to Newton per square millimetre (N/mm ² )

In one embodiment, this invention comprises a CRA!L engine's monometallic inlet valve which is designed and developed in a steel material that can be hardened. Preferably the steel material should be any steel that is amenable for induction hardening. In illustrative example, monometallic Martensitic EN-52 grade steel material is used. In a further embodiment, this valve is induction hardened at tappet end. This inlet valve is designed to perform under common CRA!L engine operating boundary conditions of peak combustion pressure 180 bar and maximum predefined combustion temperature 780°C.

The tappet end hardness was 52 HRC min and through hardening depth was12-16mm with

Barrel hardness 490hv30 min. In working cycle of CRAIL diesel engine with inlet valve, the valve of this invention has been validated successfully for better performance using FEA analysis approach. The inventive inlet valve of this invention could be operated as well as it could withstand against higher loads at tappet end. Also induced stresses in working cycle observed in FEA were within the safe limit of stress as shown in fig 4.; the highest von-mises stress value is 95.56 N/rnrn ² . To check for design of safety criteria of minimum 1.3, following calculation carried out;

Design of Safety= Yield stress /Actual stress.

Where, Yield stress=350 MPa (Refer Table No.1 material specification)

Actual Maximum Stress = 95.56 MPa (Refer Fig. No.4 FEA Stress results), Hence, Design of Safety =3.66,

Therefore, it follows the design of safety criteria of minimum 1.3 value and here in CRAIL valve we are getting factor 3.66, which is acceptable.

Above satisfactory design of safety factor is due to harder tappet end [Fig.1-(7)] which helps to resist, bear the tappet surface against impact loading achieved. These valves have been validated with engine test bed. The valve has gone through physical testing and validation on Engine Test Bed Cell to check performance of whole engine, where valves performed as per design level in run of 200 hours of endurance cycle test. it is preferred to make through induction hardening process with specification of tappet end hardness as 52 HRC min and through hardening depth 12-16mm with Barrel hardness 490hv30 min indigenously. in this application validation methodology were used as per below sequence:

1. Design with CAE analysis, 2. Valve endurance in engine testing

3. Metallurgical testing of engine tested valves with scanning electron microscope (SEM)

1.SAE international Material standard SAE J7/5, Revision- November 2004, Issued 1981-06, Revised 2004-11 , SupersedingJ775 AUG1993 pp. 18-23 23

2. Kiyoshi FUNATANi, Heat Treatment of Automotive Components: Current status and Future Trends; !MST Institute, Nagoya, Aichi 467-0004, JAPAN, Revised form 30 May 2004 pp. 381- 398.

S.A.Kolchin and V. Demidov, Chapter no.15 Design of valve gear, Design of automotive engines, Mir Publishers, Moscow, First published 1984, Revised from second Russian edition pp 308-339.