computer-aided design

650:388 CAD IN MECHANICAL ENGINEERING GROUP #5 MAY 1, 2023

1979 Honda CBX EngineVasyl IshchenkoJohn MusciSimon TangAlton BoharCharles Manolio

Introduction:In 1978, Honda's development team headed by the chief engineer Soichiro Honda, finished work on the 1047 cc, 24 valve, six cylinder "CBX." The choice was the winner of the three initial designs that were the four cylinder 1000cc and 1200cc engines, and this six cylinder 1047cc. The engine design had a number of complications: the main problem was the engine’s enormous 585 mm width that would conflict with the design of the bike’s frame. Narrowing the width of the crank case, widening the tank area and tilting the engine forward by 30 degrees were some of the design aspects that were used to make it work.

Objective and Motivation:Most of the people in our group are in Formula SAE racing car, so at first we wanted to do a Formula SAE race car, but this project was rejected, so being deeply interested in automobiles we decided to create an internal combustion engine. Mark Sproul, the Formula SAE advisor has a Honda CBX motorcycle that he uses for racing. We definitely wanted to do a 4 stroke internal combustion engine,

but since we could not get the automobile engine and take it apart to measure all the internal parts in time and none of the group members was willing to donate their car for the project: Nissan’s RB26TT, VQ35DE and QR25DE, we had to find some engine with the available measurements. We tried to find the dimensions of different automotive engines online, but none of the companies have the dimensions placed anywhere due to the copyright protection of their research, since it takes close to 5 year to fully develop an engine from scratch and than many more decades to completely improve it on the automobile itself. Mark Sproul has several 6 cylinder Honda CBX engines already apart, so it was the obvious choice for modeling. The engine itself is an interesting piece of work, since it’s the only motorcycle 6 cylinder engine with the timing chain and gearbox connection located in the center of the unit. At its time it was the most advanced motorcycle engine, which served as a guideline and inspiration, not only for the future Honda power units, but also for the whole industry. Engine head and block had many different extrusions in order to keep the engine cool, through the air flow over the engine (engine is air-cooled and has many metal fins to dissipate the heat. Mark’s motorcycle is used for drag racing, which only take 10 seconds, so the overheating is not such a big issue, so the block and head design could be simplified.

Engine Design:Double-overhead camshafts drive 24 valves which feed the motor through constant velocity carburetors. There are two individual gears located in the engine’s top center which govern the air intake/exhaust ports.Each cylinder has 2 intake valves, through which the air-fuel blend mixed by the carburetor enters the combustion chamber. Piston is moving down at this point in order to suck-in the mixture. Intake valves close and the piston moves up to compress the mixture

GROUP #5 HONDA CBX ENGINE RAY 1


at which point the spark plug ignites the fuel and the power stroke starts, burned gases under pressure push the piston, which through the connecting rod and the crankshaft translates the power from linear into rotational motion. Thanks to inertia the piston moves up and the exhaust gases are pushed out from the combustion chamber through the open exhaust valves. This is the working principle of the 4-stroke internal combustion engine. The firing sequence for the pistons is: 1,5,3,6,2,4 which leads to maximum power generation per stroke, which we emulated in our model. This engine is only two inches wider than the four cylinder Honda CB750 it replaced, boasting a 5-speed gearbox and svelte clutch produces 105 HP (76.6 kW) at 9,000 rpm. The bike itself weights only 500 pounds, so compared to today’s sports cars’ 10:1 weight-to-HP ratio, the Honda CBX’s 28 year old technology has an impressive 5:1 weight-to-HP ratio. The 6-cylinder engine configuration allows for a higher rev up speed, due to the fact that the connecting rod/piston assembly is much lighter which allows for a faster rev up compared to inline fours. Another advantage is the fact that 6-cylinder engine is smoother due to the fact that there is an overlap in power strokes of the two cylinders, unlike the four cylinders. Design Disadvantages include too many moving parts, extremely expensive to maintain and is rather heavy, very hard to maintain and regulate carburetors.

Performance Specifications:

Standing start ¼ mile: 12.66 seconds @ 111.11mph

Engine rpm at 60mph at top gear (5th):4272 revolutions per minute

Engine bore and stroke:64.4x53.4mm(2.54x2.10 in)

Engine displacement:1047cc (63.9 cu. in.)

Compression ratio:9.3:1

Engine Horsepower (original 78 design):71.59hp @ 9000rpm

Engine Torque:47.24lb/ft @ 6000rpm

Engine Parts:Crankshaft is the heart of an engine. It translates the linear motion of the pistons into the rotational motion, providing the inertia to keep spinning the engine when the pistons are at their top or bottom dead ends. It is especially important in this engine, because of the small flywheel which carries on inertia.



Crankshaft is the part of an engine that twists the bearings in the crankcase due to heavy loads. The CBX’s crank shaft is long (6 connecting rods) and has about a 120 degree phase shift between each piston. It would interesting to put the crankshaft in ANSYS and see how much load it could handle.

Connecting rods in the CBX connecting rods are short, having short stroke allow for a higher revolutions to produce more power. The CBX engine could redline at approximately 9500 RPM, but higher revolutions mean lower torques. Connecting rods join the piston through the wrist pin to the journal bearing of the crankshaft. Performance engines usually “throw” a connecting rod, when it gets out from the journal bearing and hits the hole through the engine block. Mechanics usually call it the “hand of friendship”. Vasyl’s group for DMC actually tested the CBX connecting rod on ANSYS to put the load on top which simulate the power stroke of the engine and the temperature gradient. Various improvements were made, by changing the geometry and material.

The Engine Block is the soul of the engine.



It houses the pistons, which are encased by the iron piston sleeves. The block is an all aluminum, to reduce the weight and has air cooled housing. Within the block the cast iron heat treated piston sleeves are press fitted into place to ensure compression and withstand cracking.

The pistons are connected to the connecting rods and transform the pressure of the expanding gasses created by the air-fuel explosion into linear motion. The pistons are then placed inside the head, where the 3 piston rings are placed about 90 degrees apart to ensure compression and to take off oil from the sleeve cylinders that ensures the low friction, low resistance motion. Compression ratio is 9.3:1

Engine Head was one of the hardest parts to create, because it had so many extrusions in order to air cool the valve train and spark plugs. It bolts on to the engine head in order to provide the compression and house all of the valve train (intake/exhaust cam shafts and valves). The engine valve train is the system that allows for the entering and exiting of fuel/air mixture and exhaust gasses. The cam shafts sit in the valve train and are connected to the timing chain. When the firing sequence begins, the cams spin slower than the crank shaft and open the exhaust and intake valve as needed according to the 4 stroke engine cycle: intake (intake valves are open to let the mixture in), compression (both valves are closed to provide closed combustion chamber to ensure mixture compression), power(both valves are closed to ensure that all of the expanding gasses push on the piston downwards), exhaust strokes(exhaust valves are open to let the gasses out). The longer the intake valves are open the more power engine gets, but the fuel economy suffers, so HONDA created variable valve timing system (VTEC) to change the time that the intake valves stay open depending on the revs, providing more power at higher rpm, but higher torque, lower fuel consumption and emissions at lower revs.



When the timing chain (belt, gears) breaks, the engine synchronization is destroyed and most likely the valves being open randomly meet the pistons (interference) and the engine is dead. In our simulation we used gear connections to connect the crankshaft to the intake and exhaust cam shafts, while using cam connection to connect all 24 valves with their retainers to two camshafts.

The engine crank case houses the crank shaft. The crank shaft sits in the crank case and is held in place by the bearings.

The camshafts open and close the intake and exhaust valves for the different stokes of the engine. The cam shafts are lobbed 120 degrees out of phase. Surprisingly, the cams are not held by bearings, they are held in place by replaceable shims. Camshafts are connected by cam connections to the valves, and by pin connection to the valve train and valve cover.



Difficulties and obstacles:Many dimensions were immeasurable because of their location, like valve guides and head internals, so what we did was to create the dimension that would fit the movement of the assembly. Imperfections in machining and the wear of the engine from hard usage (racing) meant that not all corresponding dimensions were equal like for example the engine head and cylinder wells were not symmetrical where they should be, so we mirrored the sketches accordingly. Slow computers took forever to create the 24 cam connections during which the program or our assembly file crashed several times due to difference in dimension of parts. The engine head contained many numerous extrusions with some of them difficult to measure.

Conclusions:This project had reflected all of our knowledge gained from the semester of ProEngineer and all the homework and workshops. With this knowledge from this project and the class in general we could design and model an internal combustion engine of our own design or any other

part. Some of the parts could have been measured more precisely with calipers in the lab, so this project also helped us with our measurements techniques (mechanical measurements class). During the summer we might take a step further and use ANSYS on each individual part in order to model the loads experienced by the engine and simulate its usage under regular (normal driving) and heavy load conditions (racing). Computer flow simulation program FLUENT could be generated in order to design better combustion chamber , valve surface, intake and exhaust manifolds in order to optimize the intake air-fuel mixture and exhaust gas flow in and out of the cylinders.



References:www. cbx world.com/ www. cbx club.com/ www. cbx 6.co.uk www. cbx man.com www.howstuffworks.comMark Sproul


http://www.howstuffworks.com/

http://www.cbxman.com/

http://www.cbx6.co.uk/

http://www.cbxclub.com/

http://www.cbxworld.com/

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