Victa 2 stroke engine PDF

Preview

Summary

report on engine...

Description

Victa 2 stroke engine

By:

1 Introduction 1.1 Victa 160c.c Mk4 2-Stroke engine 1.1.1 Components 1.1.2 Operation 1.2 Advantages & disadvantages relative to a 4 stroke

3 3 3 4 5

2 Engine block 2.1 Components 2.2 Material selection

6 6 6

2.3 Engine Block material

7

3 Manufacturing processes 3.1 Sand casting 3.3 Flow chart

8 8 10

4 Quality check

11

5 Estimated costs

11

6 Photos

12

7 References

13

1

1 Introduction 1.1 Victa 160c.c Mk4

2-Stroke engine

Image from UTS online 1967 saw the beginning of a new era in lawnmowers, engine power lawnmowers were seeing an increase in popularity. Victa dominated the market with their 2 stroke engine powering the corvette and cortina lawnmowers. This lawnmower employed the use of a heavy 2 stroke engine in its budget conscious model, whilst the premium models employed a 4 stroke engine. A 2 stroke engine is the most common type of engine, found in products ranging from lawnmowers to boat engines.

1.1.1 Components The main components of a typical 2 stroke engine consist of the following:

Image from SavRee

-

Spark plug Piston & piston rings Exhaust port Inlet port Transfer port Connecting rod Crankshaft Crankcase Engine block Reed valve

2

1.1.2 Operation Images from SavRee 1. Suction When the piston begins its descent from the top of the chamber, the reed valve is opened to allow for fuel to mix with air whilst being sucked into the crankcase through the inlet valve. In this stage, the transfer port is left open and allows for the air fuel mixture to be pushed through the transfer port into the compression chamber.

2. Compresion As the piston rises, it covers the transfer port, exhaust port and temporarily covers the inlet port. As the exhaust port and transfer port is covered, the air fuel mixture is compressed at the top of the chamber, ultimately increasing temperature and pressure within the chamber. This occurs whilst leaving the inlet port open for suction to occur when the piston bottoms out.

3. Ignition As the piston is at the top of the camber, the spark plug ignites the fuel mixture, pushing the piston back down allowing for the process to restart.

4. Exhaust As the piston begins the descent, the exhaust port is revealed allowing for the combustion fumes to be exhausted through the exhaust port whilst simultaneously pulling air and fuel through the intake port.

3

1.2 Advantages & disadvantages relative to a 4 stroke Advantage ● More power as engine fires once a revolution, ultimately giving it a 1:1 rev to power stroke ratio ● Approximately 20-50% less components, reduces manufacturing costs, material usage and makes engine lighter (no push rods or camshafts) ● Can have same power as a 4 stroke engine in a smaller size ● Less maintenance required for engine parts ● Less power required to overcome friction from pistons ● Can operate in any orientation as there is no oil pump or filter

Disadvantage -

-

-

Poor thermal efficiency Overall efficiency and smoothness is considered to be worse than that of a 4 stroke More need for lubricating oils as engine operates at higher temperatures and doesn’t have a lubrication system, resulting in a high mixing ratio is ~50:1 Increased pollution due to inefficiency

4

2 Engine block 2.1 Components

From resources such as articles and ads from 1967, the two stroke variant of Victas lawnmower engines has the parts list and appropriate materials listed for the given various components. Many of the metals are produced using manufacturing methods to increase hardness and reduce thermal expansion. Manufacturing many of the engine components require high precision and accuracy to ensure uniformity within the production line. A 2 stroke engine is heavily impacted by impurities which can impact the efficiency of the engine further. The components within the 1967 variant of the Victa 2 stroke engine are listed below with the materials used for the original components. Image from UTS online

2.2 Material selection

Spark plugs Steel & porcelain

Steel is used for its hardness, low cost and easy workability. The outer jacket is made using porcelain Due to its strong insulation properties. The interior conductive component is made of a nickel alloy copper plated electrode to ignite the air fuel mix.

Cylinder head High-pressure casting aluminium alloy casting

High pressure aluminium alloy casts are used for the cylinder head due to its extremely good temperature resistance. The high pressure casting ensures that the cylinder head is dense and easy to machine.

Piston rings Cast iron

Piston rings are often made from cast iron as it is very ductile and durable in the sense that it maintains its shape under a variety of forces causing excessive heat, load and other forces. It's designed to both move oil and radiate heat away from the piston.

5

Piston Die-cast iron

Die-cast iron is used as iron is ductile, heat resistant and workable. This allows for several pistons to be machined to allow for intricate patterns or cut outs for components like piston rings.

Cylinder Grey cast iron

Grey cast iron can be made in complex geometries, it has very good machinability allowing for high precision cut outs for pistons and other ports. It is also dimensionally stable when exposed to a multitude of forces at various temperatures.

Connecting rod Drop Forged carbon steel

The connecting rod is a crucial component of the engine which is exposed to constant compression forces. Steel has a good balance between strength, cost and weight.

Crankshaft Drop forged carbon steel

The crankshaft is crucial in converting the up and down movement of the pistons into rotational forces for the output shaft of the engine.

Crankcase High-pressure casting aluminium alloy casting

The crankcase is made from the same high pressure aluminium casting alloy as the cylinder head as it is exposed to the same rigorous forces and extreme temperatures.

2.3 Engine Block material The engine block as such is part of the crankcase. The block is made entirely of a high-pressure aluminium casting alloy. This is done due to a multitude of reasons ranging from its high melting point, reasonable cost, strength and excellent machinability. The machinability enables the ability to cut fins into the cylinder chamber to allow for the heat to radiate and dissipate into the surrounding environment. Some properties that are sought after in an engine block for a lawnmower may be as follows 1. Dimensional stability under heat 2. High strength to withstand combustion 3. Weight to press mower down

Image from UTS online

Grey cast iron is best suited to engine blocks as it can be cast to virtually any shape. Grey cast iron is also very cheap when compared to other materials, this helps with reducing the cost of the lawnmower. The weight of cast iron is also very heavy compared to aluminium alloy, aiding with the stability of the lawnmower.

6

3 Manufacturing processes 3.1 Sand casting

Sand cavity mold

The sand cavity mold is the main mold which is used to form the majority of the engine block. The mold is made by placing sand around a replica made of wood or another material. The replica is typically larger than the final product to leave some tolerance for surface finishing and thermal constriction. As this engine is small, it is expected to be an expendable mold allowing for the engine block to be taken out easily after solidifying. This process slows down the production rate and production volume because of the constant need to create individual molds for each engine block.

Gating system

The gating system provides a funnel or channel for molten metal to flow into the sand cavity mold. This is usually done by adding and extrusion to the replica allowing for the sand to form around it.

Sand core

A sand core is a type of mold designed to occupy a volume within a model where metal should not be in, this is typically used in large holes like cut outs for pistons and crankshaft channels.

Liquid metal

The desired metal of choice is heated up till its melting point, making it a molten liquid. From there the metal is poured slowly into the cast through the gating system until the metal occupies the full volume of the engine, procedures are taken place to prevent air bubbles from occurring within the cast. After the metal has set within the mold, it is baked in a furnace to heat treat the metal to make it hard and temperature resistant.

Rough Machining

After the engine block has been casted and placed in the furnace, it is ready to be refined and cut precisely to accommodate the several components. Rough machining is used to cut off excess material around the piston cylinder and crankcase.

Decking Machining

Decking is a type of process which involves smoothing the interior surfaces near the top of the cylinder block to ensure a smooth flat finish.

Boring Machining

Boring is a process used to ensure that the cylinder is perpendicular to the top of the engine block and cylinder head, this ensures the correct movement of the piston through the cylinder. For an accurate cut, boring is often completed with a torque plate.

Honing Machining

Honing is a process used to improve the surface texture and form of the cylinder walls to ensure an even seal is formed between the piston rings and cylinder when the piston runs up and down through the cylinder.

Tapping

The final touch is tapping, a process in which holes are pre drilled for mounting holes so the block can be mounted to a chassis.

7

3.2 Cold chamber die casting

Steel mold

The mold is made using specific types of metal with high melting points, the budget friendly option being steel. The mold can be made using multiple blocks, typically 2 for a symmetrical component and more mold faces for a complex component. The mold is designed such that it can separate itself easily from the modeled component. The mold joins such that the centre of the 2 faces are hollow, at least one of the molds has a cavity running through it to allow for molten metal to be injected into the hollow cavity between where the 2 molds join.

Cold chamber

The cold chamber is a type of funnel which is used to force molten metals into the casting cavity, it houses the plunger and is crucial in defining how the final product turns out. It's crucial that the cold chamber prevents air bubbles from creating impurities within the product, this is done by either shaping the nozzle or by using a lath to slowly pour molten metal within the cold chamber.

Plunger

The plunger is another crucial component in determining the quality of the final product. The plunger must force the molten metal into the mold slowly and must apply adequate pressure to force the molten metal into various crevices within the mold for high detail and a high quality surface finish.

Image from the library of manufacturing

8

3.3 Flow chart Sand casting

Die casting

9

4 Quality check Quality checking is the process in which the final product is checked and scanned to ensure that defects on the engine block are minimised to ensure the engine runs smoothly without faults. Various processes are taken to ensure that the engine block is produced within standards. The first course of action to ensure that the engine is produced properly is by ensuring the equipment used is serviced well and functioning as per normal. The material is then double checked to ensure it is pure to minimise unexpected results or unwanted impurities. After the engine is cast, and put in the furnace, it undergoes visual inspection and later, other non-destructive tests for more precise checking. Forms of non-destructive testing ranges from using various types of caliper for small pre-drilled holes and forms of micrometers. An ultrasound test is required to ensure the block is not hollow or cast incorrectly as a simple visual inspection will not provide any insight onto the structure within the engine block. Certain areas of the engine block such as the piston cylinders and ports have their surface finish checked to ensure that there are no cracks or rough surfaces within the cut outs to minimise both friction and liquids from building up in unwanted areas.

5 Estimated costs As this product is a high volume, mass produced product, the manufacturing costs must be low. There must be a blend of high accuracy and cost saving measures to ensure for the product to be produced in large volumes. The 3 main factors which determine manufacturing costs are time required to produce the item. The equipment required to produce the item and if needed, the type of labour needed to finish the product.

Equipment

The equipment used for The cold die-cast system ranges from approximately $30,000 USD to $300,000 USD. As the complexity of the component is fairly low, the complexity and cost of the machine can be low. Routine machine servicing will not be as expensive or as a common occurrence. The cast cost may be expensive as the die should be durable enough to last multiple cycles with minimal changes in dimensional accuracy as the cast wears out over time. The most expensive component of the whole engine block manufacturing cost will most likely be the cast, simply due to the fact that it will need to be remade every so often to ensure the engine block stays within standards. Higher end cast systems allow for either slow, high accuracy yield for a refined product and some systems allow for fast, high yield production of the engine block.

Labour

Labour introduces a new dimension in costs, it typically increases the costs dependent on the type of labourer hired. Some engines require light manual labour to ensure a part is manufactured or to check if the component is within standards, however in some cases, typically for high end products, there may be a lot of labour required to finish assembling the engine.

10

6 Photos

Images from UTS online

11

7 References SavRee. (nd) 2 stroke engine [stock image]. https://savree.com/en/product/two-stroke-engine/ Marshall, B. (nd). How Two-stroke Engines Work. howstuffworks. https://science.howstuffworks.com/transport/engines-equipment/two-stroke1.htm ENGRRAIHAN. (2015, september 16 th). Advantage and disadvantage of two stroke over four stroke cycle engine. Wordpress https://mechaengineerings.wordpress.com/2015/09/16/two-stroke-engine-vs-four-stroke-engine/#:~:text=for%2 0Mechanical%20Engineers-,Advantage%20and%20disadvantage%20of%20two%20stroke%20over%20four% 20stroke%20cycle,and%20occupies%20less%20floor%20area. Piston and Piston Rings. (nd). University Of Windsor https://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20and%20Piston%20 Rings.htm#:~:text=Piston%20rings%20are%20commonly%20made,return%20oil%20to%20the%20crankcase. Carley, (2016, November 17 th). Head and Block Resurfacing Equipment. ENGINEBUILDER. https://www.enginebuildermag.com/2016/11/head-and-block-resurfacing-equipment/ Giampietro, C. (2020). Victa 2 Stroke Engine [Lecture Slideshow]. UTS. https://online.uts.edu.au/bbcswebdav/pid-4155858-dt-content-rid-66336813_1/xid-66336813_1 Cold Die Casting. (nd). The library of manufacturing. https://thelibraryofmanufacturing.com/cold_chamber_diecasting.html Al-Zubaydi, A. (2020). Manufacturing Engineering Lecture 4 [Lecture slideshow]. UTS. https://online.uts.edu.au/bbcswebdav/pid-4155903-dt-content-rid-66336790_1/courses/48621-2020-SPRING-CI TY/UTS%2048621%20Manufacturing%20Engineering-%20Lecture%20notes%204%20.pdf

12...