Group 18 - GM V-6 Engine Gate3
Gate 3: Coordination Review
- Engine Block: The engine block is made out of Cast iron. This is because the block must be able to withstand extreme heat, extremely well. It is also cast iron because iron is cheap but durable and casting it is the easiest and most efficient way to produce it. Iron is also a good vibration dampener. The forces acting on the block when mounted are those of weight and vibration; however the vibration forces are negligible and cancel each other out. The block itself is not very complex, because after all it is just a piece of metal, but when looking a complete engine, all the various and meticulous holes and slots drilled turn it into a relatively complex piece of machinery. Although the block itself is casted, various parts on the block were machined to allow for seals and threaded holes, as well as smooth bold holes that are crucial to operation. The block itself houses the pistons, connecting rods, crankshaft, the intake/exhaust valves, and is the chamber in which the Otto cycle takes places; there is only one block for the engine. The model number stamped on the block reads: G096.
- Piston:(Image #1) The Piston on our engine is made out of casted then Machined aluminum. This is because the piston must be completely smooth on all surfaces to reduce friction and the casting process does not allow for this to take place. Also aluminum is a lightweight metal that can also withstand great heat and is durable. There are six pistons in total on our V-6 engine, each with a force of 184 pounds acting on it. The piston converts the energy of the combustion to the crankshaft, which in turn creates rotational force. The piston is a simple device; it does not contain any other moving parts other than the pin and rings.
- Piston Rings: Piston rings are made of forged spring steel. Spring steel is made up of medium carbon steel, which has a high yield of strength and retains its shape after forces have been applied. The purpose of a piston ring is to seal the combustion chamber, and prevent the engine from burning unwanted oil. There are 2 piston rings per piston. (Totaling 12 rings per engine). Piston rings are extremely simple parts, and although aren’t complicated are important pieces of the piston.
- Connecting Rod:(Image # 1) The Connecting Rods are die-casted and are made out of high carbon steel. These are Die-casted because it is easy to make and the majority of the part itself does not need to be completely smooth. However they are machined where the rod must be connected the piston head, as well as where the bottom clamp is bolted to the upper rod. The function of a connecting rod is to connect the piston to the rotating crankshaft. There are 6 connecting rods (one for each piston). The force applied to the connecting rod is the equivalent force that is applied to the piston heads.
- Crank Shaft:(Image # 2) The crankshaft is made out of die-casted steel. This is because it is simple and cheap to make, but still withstands great force. It is also machined where it is mounted to the block for friction-reduced rotation and where the connecting rods attach to it. The force exerted on the shaft at each connection to a piston is equal to 184 pounds and the torque is equal to 230 foot pounds (which we researched online). The shape of the crank shaft is specifically designed to use offset pivot points to convert the forces form the pistons and connecting rods to a rotational force. The complexity of the crank shaft is minimal, although its simplicity is the reason it has been so successful over the years.
- Camshaft: The camshaft of our engine is made from machined steel. The shaft must be machined because of the ever changing shape it posses and the need for friction-free usage. The shape of the shaft itself works in a similar fashion as the crank shaft, except the process is reversed. This is because it converts rotational force into 12 different linear forces which control the intake and exhaust valves. The torque acting upon is two times greater than that of the crank shaft due to the gear ratio from the crankshaft itself.
- Flywheel: The flywheel is made from machined steel and is used to maintain the momentum of the engine in between each piston firing (very quick). The shape of the flywheel is a wheel of large diameter with slots on the outside similar gears. It also has holes cut out from the center of it in order to reduce unused material to conserve weight and potentially increase inertia. The torque on this piece is equivalent to the torque rating on the engine.
- Pushrods: (See solid model assembly) The pushrods are made from machined steel. They extend the linear force of the lifters to control the opening and closing of intake and exhaust valves. There is one pushrod for each valve (intake and exhaust) so there are 12 total.
- Timing chain: Made out of multiple links of machined steel, the chain transfers rotational energy from the crankshaft to the camshaft through a gear ratio. The steel chain is designed to be durable and easy to manufacture. The force on this chain is equal to the torque rating of the engine divided by the radius of the gear that is rides on. Assuming a radius of 2 inches the force is roughly 1100 lb.
- Oiler/Oiler Gear:(Image # 3) The oiler is made from die-cast steel. It is also machined at the ends where it rotates on the block. On one end there is a small gear which is connected to a gear running through the timing chain. The shape of the oiler is a rod with semi circles on opposite sides; this shape becomes a “paddle” which moves oil throughout the valve and camshaft assembly system to keep everything well lubricated including the pushrods and rockers.
- Lifters: (See solid model assembly) The lifters are made from machined stainless steel. This is so the reduce friction and stay rust free. They are shaped like a small tube with a free rotating wheel which rides on the camshaft, converting rotational force to linear force to control the valves on the head. The force on this piece is equivalent to the force the valve springs are capable of applying therefore are almost negligible in the broader scheme of the engine.
- Water Pump:(Image # 4) The water pump has a die-casted steel outer shell, which houses a machined steel gear pump. A gear pump forces water through rapidly spinning gears to increase the water pressure at the outlet. The water pumps purpose is to push coolant around the engine block, to keep the engine cooled down and running at a safe temperature which ensures efficiency. The pump is driven from a belt off of the crank pulley harmonic balancer.
- Intake Manifold:(Image # 5) The manifold is made out of die casted steel, and is machined where the manifold is sealed to the engine block. It is made from steel because, steel is cheap and the manifold is not load bearing this not required to have high impact resistiveness. The purpose of this piece is to evenly distribute a fuel/air mixture to each of the 6 cylinders. This part must be specifically designed to deliver the correct air/fuel mixture. |
- Exhaust Manifold:(Image # 6) The exhaust manifold is a piece of die-casted steel. This is a system of tubes which delivers the exhaust components to the tailpipe and out of the vehicle. The Exhaust converts the 6 streams of exhaust from each cylinder to one main stream out of the car. No forces besides gravity are acting on this part.
- Oil Pan:(Image # 7) The oil pan is made from a large piece of cast aluminum. This is aluminum because it is so large that aluminum is the only metal that would not become too heavy with heavy girth. Aluminum is also resistant to rust to ensure the pan to be long lasting since its under belly will be exposed to the road. The purpose of this piece is to house the majority of the oil to lubricate the engine. The oil pan experiences forces equivalent to the mass of oil in the reservoir multiplied by the rate of gravity. Assuming the car holds a total of 6 quarts of oil one quart at approximately 2 pounds the pan experiences 12 pounds of force maximum plus the weight of the pan.
- Harmonic Crankshaft Balancer: This is made out of two casted then machined- steel pieces (circular) separated by a rubber ring. When the crankshaft spins, the inner ring of the balancer spins with it, and the outer ring resists acceleration due to the rubber ring. This then in tern reduces vibration of the crankshaft. The object itself is not complex however its purpose is one that could be described with extremely complex physical laws. The torque on this piece is equivalent to the torque on the engine as a whole (230 lb-ft.).
- Distributer:(Image # 8) The distributor is a device that takes the high voltage electricity from the ignition coil, and routes it to the spark plug in the proper firing sequence. The cap of the distributor is made of molded plastic; and inside lies a steel rotating shaft. When the rotor spins, current jumps between small gaps in the shaft to the contacts that run from the distributor to the spark plugs. The rotational motion for the distributor is supplied by the camshaft so the piston location is synchronized with firing time. No forces are acting on the distributer besides centrifugal forces created by the rotating shaft.
• The GM V6 4300 Vortec engine is one that is typically used in SUVs or pickup trucks, so the target audience for this engine would be looking into power and performance of their vehicle. One way to get a boost in power out of this engine is to perform a procedure called “port and polish” to the air intake manifold component. This procedure involves using a dremel tool to sand down the side walls of the throttle body and using a polishing wheel with a chrome or metal finish to give the surface a smooth, glass-like finish. Making this surface smoother reduces air friction during the intake stroke of each piston. Reduced air friction means more efficient air intake is occurring and therefore a greater rate of combustion takes place in each piston. Increased combustion leads to an increased power output from the engine. The only potential problem with this procedure is that one must be very careful with the dremel because if too much material is removed, valves could become cracked and air may start to leak, so caution must be taken while executing this procedure.
• Another design change could be to change the material of the engine block. The engine block is currently made out of cast iron which is very heavy and adds most of the weight to the car. To make the car weigh less and perform better a different type of material would work better. Using aluminum for the engine would reduce the weight of the block significantly, so the horsepower would increase because the engine would have the same torque output while having less weight to move in the process. Also, by making the car lighter the fuel efficiency would be improved. Everyone is concerned about fuel efficiency is this economy. Finally, aluminum improves heat dispersion, so the engine is less likely to over-heat.
• One last design change could be to increase the compression ratio, which would increase the power and efficiency of the engine. A way to increase the compression ratio is to increase the cylinder swept volume, or in other words, increase the ratio of the volume of the cylinder at bottom dead center to the volume at top dead center. This would not change the combustion chamber volume only the cylinder volume. The compression ratio of the GM V6 engine is 9.1:1. By increasing the cylinder swept volume slightly it increases the compression ratio slightly. This will give an increased volume of the cylinder at the lowest point of each stroke, allowing more air/fuel mixture to enter the cylinder. More air and fuel leads to a larger combustion and therefore greater power output during each piston fire. However, the compression ratio should not exceed 10, or else engine knock could start to cause problems with the engine as a whole.
Solid Modeled Assembly
The following models are of the camshaft, a lifter, and a push rod. These components were chosen because they are key components of an engine but are not as familiar to most people as the crankshaft and pistons. By showing these parts, it can be seen how the intake and exhaust valves for each cylinder are opened and closed at the right time, in order for the cycle of compression and combustion to take place.
Solidworks was used to model these parts because it is an intuitive program and it was the most readily available.
This YouTube video shows these components being assembled in sequence. The video was made using Blender, a powerful open-source 3-D visualization program.
The following engineering analysis procedure could be used by an engineer to test the friction that occurs in the cylinders of the GM V6 engine due to a lack of lubrication and the power loss that would result from that friction. One should also note that this procedure is based on both the pistons and cylinders being completely dry. Results would vary with increased lubrication and therefore a different coefficient of kinetic friction.
Problem: Calculate the torque lost in the crankshaft after each piston fire of the engine due to dry friction between the pistons and cylinders.
• The oil runs completely dry instantly and now the steel pistons rub directly on the steel cylinders
• There are six pistons and six cylinders
• Distance between center of crankshaft and end of connecting rods = 2.5 inches = .2083 ft
• Torque applied to the crankshaft by lubricated cylinders = 230 ft•lb
• Length of the connecting rods = 7 inches
• Neglect the weight of the pistons and their connecting rods
• Coefficient of dry kinetic friction (steel on steel) = .6
• The angle θ represents the maximum angle between the connecting rod and the normal axis to the piston head
• Piston head radius = 2 inches = .167 ft
• Torque = (Force)(Distance)
• Kinetic Frictional Force = (Coefficient of Kinetic Friction)(Normal Force)
230 ft•lb = F*(.2083 ft)
F = 1104 lb
θ = sin^-1(radius/connecting rod length)
θ = sin^-1(2.5 in/7 in)
θ = 21°
FN = F*sin(θ)
FN = (1104 lb)*(2.5 in/7 in)
FN = 394.3 lb
Ff = μk*FN
Ff = (.6)*(394.3 lb)
Ff = 236.6 lb
τlost = Ff*(Piston radius)
τlost = (236.6 lb)*(.167 ft)
τlost = 39.4 ft•lb → Each time a piston is fired
All units check out and cancel properly in each step. All units are kept in the English system, as the engine is an American product. Units of length are converted to feet by multiplying the length in inches by 1/12 (ft/in). Forces are measured in pounds because on Earth, one pound mass is equal to one pound force, so there is no need to make a conversion from one to the other. The answer makes sense because the torque lost in one piston fire is approximately equal to one sixth of the fully lubricated torque, so the engine would within roughly six piston fires.
The calculations start with the given torque applied to the crankshaft converted into a linear force based on the distance from the center of the shaft to the start of each connecting rod. The reason that the assumption is made that the engine is operating with normal oil conditions initially is so that the crankshaft is receiving the most torque that it can. By assuming that the oil completely drops out instantly, it can be shown that 39.4 ft•lb of torque will be lost from the original 230 ft•lb each time that one of the six pistons is fired in its cylinder. The normal force on the piston was calculated by using the horizontal component of the force applied through the connecting rod. After frictional force is found, it is converted into torque as the τlost by multiplying by the distance to center of the piston, which is just the horizontal distance between the cylinder wall and the center of the crankshaft. The final result shows that by the time all six cylinders are fired, the engine should stop because the combined total of the torque lost at each piston (torque lost times six cylinders) will be greater than the original 230 ft•lb.
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