Friday, July 31, 2015
Thursday, July 30, 2015
Sunday, July 26, 2015
Saturday, July 25, 2015
Tuesday, July 14, 2015
ENGINE BASICS
source: motorcycleuniversity Moto U Engine Types: In Depth
We should begin this discussion by saying that no single engine type is superior to any other, however, different engines do perform differently, and some engines are better choices for different riding styles. A person riding a bike in the dirt may favor sharp bursts of acceleration while a person riding interstates with a passenger and luggage may desire smoothness and passing power at speed.
We will explain engines from broad to more specific.
All engines use “The Otto Cycle” or “Four Stroke” which describes the process of burning fuel to create rotary power within an internal combustion engine (as opposed to an external combustion engine, i.e. a steam locomotive). The four parts of the Four Stroke / Otto Cycle are:
1 Intake
2 Compression
3 Ignition
4 Exhaust
1 Intake
2 Compression
3 Ignition
4 Exhaust
Also known in fun as: “Suck-Squeeze-Bang-Blow”
There are two major types of gasoline engines: Two-Stroke and Four-Stroke motors. The number of strokes defines how many times the piston changes direction in order to complete a power cycle.
Four Stroke Engines
On a Four-Stroke, the intake and exhaust cycles are controlled and kept mostly separate by valves. Four-stroke motors are more complex and heavier, but have better fuel economy and lower emissions. Four-stroke motors are almost universal in road-going motorcycles. For a given displacement, they are less powerful than Two-Stroke engines of equal displacement because they ignite the fuel-air mixture every other time the piston comes upward.
Two-Stroke Engines
Two-Stroke engines have been almost completely banned from public life. Most Two-Stroke motorcycles available today are either collectors items, or off-road racing bikes. They are still popular for racing because they are powerful, light-weight, mechanically simple, and cheap to maintain. They are more powerful for a given displacement because they ignite the fuel-air mixture (i.e. create power) each time the piston moves upward.On a Two-Stroke, the intake and exhaust cycles are not mechanically separate, which causes some unburned fuel to escape into the atmosphere, creating pollution (you can see a blue-gray tint in the exhaust of Two-Strokes). These engines are no longer allowed on most western roads, and are increasingly rare for dirt riding (but still in action). A Two- Stroke engine makes a distinctive “ring-ding-ding-ding” sound when it is revved up.
Two-Stroke engines also require lubricating oil in the fuel, creating additional pollution. Unfortunately, these chemicals create smog.
Displacement
Displacement is the volume of the cylinder measured when the piston is at the bottom of its stroke, and is usually expressed in Cubic Centimeters. Some American manufacturers describe the displacement of their engines in Cubic Inches. Displacement is a good predictor of performance. Large- displacement engines generally have more power than smaller-displacement engines. Therefore, most beginner bikes have smaller displacement engines.
Number of Cylinders
Generally, an engine with more pistons for a given displacement will have more power than an engine with fewer cylinders. Why? Surface area: the relationship between the volume of a cylinder and the diameter of the cylinder is such that if you divide one cylinder into two cylinders of equal volume and similar proportions, you actually increase the surface area of the pistons. This means that the burning fuel-air mixture has more surface area to push on during the ignition cycle, therefore, more power can be extracted. Why don't engines have eleven-teen cylinders? Because additional weight and mechanical friction eventually cancel out improvements in power output.
Most street motorcycles in the US market have engines of two or four cylinders. Production motorcycles have been made with one, two, three, four, and six cylinders. Worldwide, however, the most popular engine type is the small-displacement, single-cylinder because they are cheap to produce, easy to maintain, and thrifty on fuel.
In-Line, Vee, and Boxer.
In-Line arrangements have the cylinders parallel to each other, while Vee and Boxer engines have cylinders in two banks at an angle to each other.
An in-line engine has all of its cylinders mounted on a common plane. In-line engines can have any number of cylinders, with two, three and four being most common. There are six cylinder engines in large touring bikes.
A Vee engine has its cylinder banks mounted at an angle to one another yet acting on a common crankshaft. The V-Angle of the cylinder banks has a lot to do with the “character” of an engine, specifically regarding vibration.
Boxer engines are essentially a Vee engine, but the cylinder banks are 180 degrees opposite one another. A Vee or Boxer engine can have two, four, or six cylinders.
Engines can be designed for either transverse mounting or longitudinal mounting. Transverse mounted means that the crankshaft is perpendicular to the direction of travel. Longitudinal means the crankshaft is parallel to the direction of travel. Most motorcycles use the transverse-mounting arrangement for several reasons, but most importantly the rotational axis of the crankshaft, transmission, and rear wheel are all aligned in the same direction making it mechanically easier to move power through the drive train.
Final Drives
The final drive is the mechanical means by which the rotation of the engine is transmitted to the rear wheel where it drives the motorcycle forward, or how the engine is connected to the rear wheel.
Chains
The most common method is chain and sprockets. They are relatively inexpensive and quite reliable. By replacing components, they can also be used to alter the final drive ratio, i.e. how many RPM the engine spins for a given road speed. The downsides are that they require frequent maintenance, are consumable, and that the components are exposed to the world: rain, sand, road debris and road salt (if you live where it snows). These elements can cause a chain and sprockets to degrade and need replacement over time. Chain and sprockets are also sensitive to alignment, and can be noisy, but modern designs have reduced this problem, and chains are still the most common type.
Belts
Not as common, but mechanically similar to a chain and sprockets are belt drive. The belts are made of rubber and reinforced with space-age fiber such as kevlar. Belt drive has all the advantages of a chain, yet is completely maintenance free (i.e. no adjustment or lubrication ever) and nearly silent.
Shaft Drive
Drive shaft setups generally never need adjusting, they are very quiet, and are generally good for the life of the bike. The downsides are that if they do break, they are expensive to fix, and they are slightly less efficient than a chain.
Fuel Delivery: Carbs vs. EFI
In an engine, the fuel and air are combined to create a combustible mixture for the engine to burn. There are only two kinds of devices that do this: Carburetors, and Electronic Fuel Injection, commonly abbreviated as “EFI”.
Carburetors are mechanical devices which meter fuel and air and mix them together into a mist as the air is sucked into the engine. They utilize the Bernouli effect to draw fuel through a series of tubes and metering orifices called Jets. This is the same way a perfume mister or an airbrush works. Carburetors are “old school” and many people understand how to work on them. They do have drawbacks: because they use air flow to perform their task, they are sensitive to air density changes due to altitude, losing power at higher altitudes. They also are sensitive to dirt, long periods of storage, and orientation, i.e. if your bike tips over, fuel will spill out on the ground.
Electronic Fuel Injection is the modern solution to the task of mixing fuel and air. It utilizes a small computer and sensors to determine the instantaneous requirements of the engine, which enables better fuel economy and power. The fuel is pressurized by an electric fuel pump and fed to a fuel injector, which is a tiny little valve with a spray nozzle that injects a mist of fuel into the intake tract of the engine. Varying levels of power are achieved by how long the injector is held open. Because air and atmospheric pressure are not used to deliver fuel, and because their sensors can instruct the computer to adapt to differences in air density, EFI systems are not affected by altitude. The downsides of EFI are that they are complex electronic systems which are not easily diagnosed and repaired if they quit working correctly. They are also more expensive to repair, but are extremely reliable.
Cooling Systems
Air cooled engines use fins on the cylinder to increase the surface area so the excess heat can be carried away by the wind rushing over them while the bike is moving. Air cooling is simplicity itself. There are no moving parts and no maintenance. However, it cannot shed much heat when the bike is sitting still, leading to overheating. Air cooling limits the amount of heat which can be removed from the engine, which creates an upper limit of how much power the engine can create. Air cooling efficiency is also linked to ambient air temperature – it works best in cool air – not as well in hotter air. Burning fuel inside the engine creates power. This creates extreme heat inside the motor. Most of this energy is used to generate power, but some of it generates heat. The excess energy which cannot be turned into power becomes heat, and must be removed from the engine, or the internal parts will be melted or damaged. Removing excess heat is called Cooling.
Liquid cooling is the modern solution to this task. Most bikes sold today are liquid cooled. The system requires a pump, water passages around hot areas of the engine, a liquid coolant, a radiator, a thermostat, and a fan. Heat is carried by the liquid coolant to the radiator, where it is dispersed into the ambient air (just like on air-cooled bikes, only much better!).
If the bike is stationary and the coolant temperature rises, the thermostat senses this and turns on the fan, which forces air over the radiator, shedding excess heat. While the system is more complicated, it is completely proven, reliable technology. With the additional components and liquid, the system weighs more. Developments in manufacturing technology have produced significant weight savings in other areas, so liquid cooled engines are much lighter than they used to be, and this makes them the superior choice from a technological standpoint. The only maintenance requirement is to keep the coolant full, and flush the system every several years.
Transmission
Transmissions are usually incorporated into the engine cases (called a unit trans) but some bikes have separate transmissions, driven by a belt or chain. Transmissions are necessary because they multiply the RPM of the engine using different gear ratios to suit a wide range of road speeds. Gear ratio changes are done by moving the Shift Lever. Older bikes usually have fewer “speeds” i.e. gear ratio combinations. Newer bikes have more speeds to allow for better acceleration. Transmissions usually have 4, 5 or 6 speeds.
Some manufacturers have produced automatic transmissions which electronically select gear ratios, but these are unusual in general.
Most scooters use a “Continuously Variable Transmission”, or “CVT” which keeps the motor near its peak power output during acceleration, getting the most performance out of modest power. CVT trans have not been offered on full-size motorcycles despite offering potentially superior performance. Generally, transmissions do not require maintenance unless they are separate from the engine cases, in which case oil changes are required.
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Monday, July 13, 2015
basic parts a mechanical engineer must know..
Common Mechanical Engineering Terms
Ball and Detent (n) A simple mechanical arrangement used to hold a moving part in a temporarily fixed position relative to another part. The ball slides within a bored cylinder, against the pressure of a spring, which pushes the ball against the detent, a hole of smaller diameter than the ball. When the hole is in line with the cylinder, the ball falls partially into the hole under spring pressure, holding the parts at that position. Additional force will push the ball back into its cylinder, compressing the spring, and allowing the parts to move. (also shown: detent pins)
Bearing (ball, roller, and spherical shown ) (n) The part of a machine within which a rotating or sliding shaft is held. In some bearing types, balls or rollers are used between the bearing surfaces to reduce rolling friction.
Bell crank (n) A pivoting double lever used to change the direction of applied motion.
Boss (n) A cylindrical projection, as on a casting or a forging. Usually provides a contact surface around a hole.
Broach (v)To finish the inside of a hole to a shape other than round, as in a keyway (n) The tool for the process, which has serrated edges and is pushed or pulled through the hole to produce the required shape.
Burnish (v) To smooth or polish by a rolling or sliding tool under pressure.
Bushing (n) A smooth walled bearing (AKA a plain bearing). Also a tool guide in a jig or fixture.
Cam (n) A mechanical device consisting of an eccentric or multiply curved wheel mounted on a rotating shaft, used to produce variable or reciprocating motion in another engaged or contacted part (cam follower). Also Camshaft
Casting (n) Any object made by pouring molten metal into a mold.
Chamfer (n) A flat surface made by cutting off the edge or corner of a object (bevel) (v) the process of creating a chafer
Clevis (n) A U-shaped piece with holes into which a link is inserted and through which a pin or bolt is run. It is used as a fastening device which allows rotational motion.
Collar (n) A cylindrical feature on a part fitted on a shaft used to prevent sliding (axial) movement.
Collet (n) A cone-shaped sleeve used for holding circular or rodlike pieces in a lathe or other machine.
Core
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(v) To form the hollow part of a casting, using a solid form placed in the mold (n) The
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solid form used in the coring process, often made of wood, sand, or metal.
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Mold with CORE
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Final Cast Manifold
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Counterbore (n) A cylindrical flat-bottomed hole, which enlarges the diameter of an existing pilot hole. (v) The process used to create that feature. (the req’d tool is shown)
Countersink (n) A conical depression added to an existing hole to accommodate and the conic head of a fastener recessing it below the surface of a face. (v) The process used to create that feature. (the req’d tool is shown)
Coupling (n) A device used to connect two shafts together at their ends for the purpose of transmitting power. May be used to account for minor misalignment or for mitigating shock loads.
Die (n) One of a pair of hardened metal plates or impressing or forming desired shape. Also, a tool for cutting external threads.
Thread Rolling Dies
Face (v) To machine a flat surface perpendicular to the axis of rotation of a piece.
Fillet (n) A rounded surface filling the internal angle between two intersection surfaces. Also Rounds
Fit (n) The class of contact between two machined surfaces, based upon their respective specified size tolerances (clearance, transitional, interference)
Fixture (n) A device used to hold a workpiece while manufacturing operations are performed upon that workpiece.
Flange (see bushing example) (n) A projecting rim or edge for fastening, stiffening or positioning.
Gage (n) A device used for determining the accuracy of specified manufactured parts by direct comparison..
Gage blocks (n) Precision machined steel blocks having two flat, parallel surfaces whose separation distance is fabricated to a guaranteed accuracy of a few millionths of an inch;
Gear Hobbing
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(v) A special form of manufacturing that cuts gear tooth geometries. It is the
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major industrial process for cutting involute form spur gears of.
Geneva Cam (n) A device to turn constant rotational motion into intermittent rotational motion.
Gusset (plate) (n) A triangular metal piece used to strengthen a joint.
Hasp (n) A metal fastener with a slotted, hinged part that fits over a loop and is secured by a pin, bolt, or padlock
Idler
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(n) A mechanism used to regulate the tension in belt or chain. Or, a gear used between a
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driver and follower gear to maintain the direction of rotation.
Idler
Jig (n) A special device used to guide a cutting tool (drill jig) or to hold material in the correct position for cutting or fitting together (as in welding or brazing)
Journal
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(n) The part of a shaft that rotates within a bearing
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Kerf
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(n) A channel or groove cut by a saw or other tool.
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Key (Woodruff key shown)
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(n) A small block or wedge inserted between a shaft and hub to prevent
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circumferential movement.
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Keyseat
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(n) A slot or groove cut in a shaft to fit a key. A key rests in a keyseat.
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Keyway
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(n) A slot cut into a hub to fit a key. A key slides in a keyway. See Broach.
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Key/Keyway/Keyseat assembly
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(see above for individual definitions)
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Knurl
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(v) To roughen a turned surface, as in a handle or a knob.
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Lug (n) Projection on (typically) a cast or forged part to provide support or allow mounting or the attachment of another component.
Neck (v) To cut a groove around a shaft, usually toward the end or at a change in diameter.
(n) A portion of reduced diameter between the ends of a shaft.
Pad (n) A rectangular or irregular projection, as on a casting or a forging. Usually provides a contact surface around a set of holes.
Pawl (n) A device used to prevent a toothed wheel (ratchet) from rotating backwards, or a device that stops, locks, or releases a mechanism.
Pillow Block (n) A bearing housing which typically mounts to a single planar face. May be split or un- split to accommodate insertion /removal of the bearing.
Pinion (n) A plain gear, often the smallest gear in a gearset, often the driving gear. May be used in conjunction with a gear rack (rack and pinion, see below)
Planetary Gears (n) A gearset characterized by one or more planet gear(s) rotating around a sun gear. Epicyclic gearing systems include an outer ring gear (known as an annulas) with the planetary system.
Rack (w/pinion gear) (n) A toothed bar acting on (or acted upon), by a gear (pinion)
Ratchet
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(n) A mechanical device used to permit motion in one direction only.
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Relief
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(n) A groove or cut on a part used to facilitate machining.
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Retaining Ring (n) A tool steel ring used in conjunction with a shaft groove or internal groove to located or control position of a component.
Rocker Arm (n) A pivoted arm-like lever used to transfer the application direction of a linear force.
Round
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(n) A rounded external intersection between two surfaces. Compare to Fillet
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Scotch Yoke (n) Mechanism used to convert rotational motion to linear motion.
Sheave (n) A grooved wheel used to accommodate a belt for the transmission of power. Sometimes referred to as a pulley sheave.
Shim (n) A thin strip of metal inserted between two surfaces to adjust for fit. (v) The process of inserting shims.
Shoulder (n) A plane surface on a shaft, normal to the axis, produced by a change in diameter
Spline
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(n) A cylindrical pattern of keyways. May be external (L) or internal (R)
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Spotface (n) a round machine surface around a hole on a casting or forging, usually to provide a contact surface for a fastener or other mating component, (v) the process used to create that feature
Spotface
Standoffs (n) A mounting designed to position objects a predetermined distance above or away from the surface upon which they are mounted.
Tap
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(v) To cut internal machine threads in a hole, (n) the tool used to create that feature.
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Undercut (n) A cut having inward sloping sides, (v) to cut leaving an overhanging edge
Yoke
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(n) A clamp or vise that holds a machine part in place or controls its movement or that
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holds two such parts together. A crosshead of relatively thick cross section, that secures two or more components so that they move together.
Sunday, July 12, 2015
Monday, July 6, 2015
Thursday, July 2, 2015
basics of car engines
When you’re reading about cars, you’re going to run into engine specifications, i.e. a 2.0 liter 4-cylinder turbo producing 160 horsepower and 175 lb-ft of torque. What do all those numbers mean? That’s the subject of this Vroom Girls University lesson.
CYLINDERS
A cylinder is the power unit of an engine; it’s the chamber where the gasoline is burned and turned into power. (For more on what goes on inside the cylinders, see How Engines Work.) Most cars and SUV enginess have four, six, or eight cylinders. Generally, an engine with more cylinders produces more power, while an engine with fewer cylinders gets better fuel economy.
Cylinders will either be arranged in a straight line (an inline engine, i.e. “inline 4”, “I4” or “L4” ) or in two rows (a V engine, i.e. “V8”).
DISPLACEMENT (LITERS AND CUBIC INCHES)
Engines are measured by displacement, usually expressed in liters (L) or cubic centimeters (cc). Displacement is the total volume of all the cylinders in an engine. An engine with four cylinders of 569cc each totals 2276cc, and will be rounder off and referred to as a 2.3 liter engine. Larger engines tend to produce more power — specifically more torque (see below) — but use more fuel.
Up until the early 1980s, engines were measured in cubic inches. One liter equals about 61cc, so a 350 cubic inch engine is about 5.7 liters.
TURBOCHARGERS
A turbocharger is a device that is used to boost the power of an engine. A four-cylinder engine with a turbocharger can produce as much power as a six-cylinder engine, but uses less fuel when driven gently. (For more information, see How Turbochargers and Superchargers Work.) Engines with a turbo sometimes get a T after their displacement; “2.0T” denotes a 2-liter engine with a turbocharger.HORSEPOWER AND TORQUE
Horsepower and torque measure the amount of power an engine develops, with horsepower being the most commonly-used measurement. The difference between horsepower and torque is widely misunderstood (and difficult to explain).
Torque, which is measured in pound-feet (lb-ft or ft-lbs), measures pulling power; when you step on the gas pedal and the seat pushes into your back, you are feeling torque. Trucks need lots of torque to get their heavy loads moving. Horsepower is a function of torque and engine speed (RPM), and indicates how much sustained work the car can do. Racing cars need high horsepower to maintain high speeds. Generally, bigger-displacement engines develop more torque, but small engines can spin faster, which increases their horsepower output.
A car with high horsepower but low torque may feel sluggish from a stop, but will feel stronger as the engine spins faster and faster. A high-torque, low-hp engine will accelerate strongly from a stop, but will trail off as the engine speeds up (until the transmission shifts gears).
Horsepower and torque measurements are “peak” numbers; a 180 horsepower engine will only produce 180 horsepower at a certain engine speed — say, 6,000 RPM. At other speeds, the engine develops less horsepower. The same goes for torque, although some engines (especially those with turbochargers) have a sustained peak-torque range, developing their rated torque between, say, 1,800 and 4,000 RPM. An engine with strong mid-range torque (peaking between 2,000 and 4,000 RPM) will have good passing acceleration, while lot of low-end torque (below 1,500 RPM) is useful for towing trailers or driving off-road. However, cars with high-torque engines are more likely to slip and slide in rain and snow.
All that said, other factors, such as how much the car weighs, will affect acceleration. How the vehicle feels when you drive it is more important than the horsepower and torque ratings.
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