This began when as a issue with a friend, he said that it is better 4 cylinders and I say that it is better 3 cylinders.
I based my studies in YZF-R1 2015, and both engines share the same bore.
- YZF-R1 Bore x stroke 79.0 mm x 50.9 mm
- YZF-R6 Bore x stroke 67.0 mm x 42.5 mm
- YZF-R675 Bore x stroke 79.0 mm x 45.9 mm
Mechanical
If you have 3 cylinders you have several advantages:
- Less parts, and therefore less probability of fault
- Engine smaller, 3 cyl thiner than 4 cylinder
- More displacement engine in competition rules, allow 3 cyl 675cc against 4 cyl 600cc
Mecanical Power |
Thermodynamic Power |
The Thermodynamic Power is the power that it is providing for the fuel. If we relation with the the power measure by dynamometer and we make the relation with Thermodynamic Power we have the engine efficiency
Other part to see it is the movement piston and rod, due to the piston have speed limit and it is near of 40m/s.
But if we make a simplitication to calculate we colud approx:
If we suppose two approximations to calculate the YZF-R675:
- The first line is with the same efficiency and the same rpm of maximum power.
- The last line is with the same piston speed for maximum power (admision and exhaust air speed) but the effiency of the YZF-R6.
The two calculates show more power tahn de current YZF-R6, but this is a exercise and this more complicated.
The next step I compared the engines with cranksahft the 3 to 120º and 4 cilinders with crossplane (90º).
The next chart shows the position, speed and acceleration of one piston, left current YZF-R6 and right the YZF-R675
YZF-R6 YZF-R675 |
If we see the two movent, the 675 has more stroke therefore have more speed, this is the reason that in the Supersport championship for 4 cylinder maximun 600cc and 3 cylinder until 675cc.
In this case to 10.000rpm
- YZF-R6 22.85m/s
- YZF-R675 24.72m/s
Also ins the speed is more, the acceleration is more
- YZF-R6 min -2.877e04 m/s2 max 1.783e04 m/s2
- YZF-R675 min -3.124e04 m/s2 max 1.908e04 m/s2
Flame speed and pressure
Into the each cylinder, the pressure is the same, the differences is the time to burn all mixture, beacause, the flame speed is the same, in this calculates, de flame speed is 100m/s, if we want all burn in the top dead centre (TDC), we need begin to burn several degrees before:
- YZF-R6 20.22º (10.000rpm)
- YZF-R675 23.81º (10.000rpm)
In this study the pressure is the same in both cases (16MPa peak 1.05MPa Mean)
YZF-R6 YZF-R675 |
- YZF-R6 259.67 Nm maximum and -74.87 Nm minimum peak, and 20.73 Nm mean
- YZF-R675 394.02 Nm maximum and -131.46 Nm minimum peak, and 30.54 Nm mean
- YZF-R6 20.73 Nm x 4 = 82.92 Nm
- YZF-R675 30.54 Nm x 3 = 91.63 Nm
Friction in cylinders.
Friction equations, I take simplified calculus of this with a little changes web
- Nring is 3
- e is ring thickness 0.8mm
- Pressure ring is 75.000N/m2
This equations is ideal case, for example is not contemplate the force per accelerations in the piston and this affect to lateral forces, if I have any time I update the calculus.
- YZF-R6 0 Nm maximum and -123.27 Nm minimum peak, and -17.32 Nm mean
- YZF-R675 0 Nm maximum and -160.41 Nm minimum peak, and -22.62 Nm mean
- YZF-R6 -17.32 Nm x 4 = -69.28 Nm
- YZF-R675 -22.62 Nm x 3 = -67.87 Nm
Therefore in this case, the advantage decrease and YZF-R675 take a 2% less friction than YZF-R6, this is due to the piston is bigger and the friction of lateral force increase this.
All cylinders.
Now I show the all cylinders compound, Friction and Torque, and together (calculate to 10.000rpm)
Torque
- YZF-R6 255.5 Nm maximum and -69.05 Nm minimum peak, and 82.93 Nm mean
- YZF-R675 396.61 Nm maximum and -133.77 Nm minimum peak, and 91.63 Nm mean
Friction
- YZF-R6 0 Nm maximum and -127.49 Nm minimum peak, and -69.29 Nm mean
- YZF-R675 -3.50 Nm maximum and -165.34 Nm minimum peak, and -67.87 Nm mean
Together
- YZF-R6 140.49 Nm maximum and -96.65 Nm minimum peak, and 13.63 Nm mean
- YZF-R675 248.58 Nm maximum and -175.38 Nm minimum peak, and 23.76 Nm mean
And other part important is standard deviation σ, this provide the smooth in the engine.
- YZF-R6 13.63 Nm mean and 66.42 Nm σ , and 20.83% mean/σ
- YZF-R675 23.76 Nm mean and 106.10 Nm σ , and 22.40% mean/σ
With TPS =0 and brake with engine.
- YZF-R6 -18.15 Nm mean and 29.62 Nm σ , and 61.28% mean/σ
- YZF-R675 -17.02 Nm mean and 42.19 Nm σ , and 40.35% mean/σ
The values have errors, but the important is not the values, the important is the relationship between values
The relation between Mean and σ provide the info that the 3 cylinder in acceleration is smoother than 4 cylinders (9% of difference), but the brake engine with 3 cylinder is rougher than 4 cylinders (52% of difference).
This problem is possible to solve with the slipper clutch. This clutch will be issue of other post.
Vibrations of the engine.
The axis used is show in the figure, and code for calculate is show in the end of post.
Inthe next figures show the forces in the supports A and B and the differents parts
Inthe next figures show the forces in the supports A and B and the differents parts
The parts calculates is:
- Cylinders, in the z axis
- Crankshaft, crankpins where connect with the rod
- Crankshaft, counterweights per rod
- Balancer, counter rotation axis
And finally togethers parts.
YZF-R6.
Cylinders (Each cylinder and all cylinders)
Balancer, counter rotation axis (Two mass in the extreme of axis)
All parts together
In the next number are the last figures the maximum and minimum values are showed
Cylinders (Each cylinder and all cylinders)
Crankshaft crankpins (Each crankpins and all cylinders)
Crankshaft, counterweights (Each counterweights and all cylinders)
All parts together
- Max Force Ax = 0 N
- Min Force Ax = 0 N
- Max Force Az = 1,178.9 N
- Min Force Az = -1,212.8 N
- Max Force Bx = 0 N
- Min Force Bx = 0 N
- Max Force Bz = 1,178.9 N
- Min Force Bz = -1,212.8 N
YZF-R675.
Cylinders (Each cylinder and all cylinders)
Crankshaft crankpins (Each crankpins and all cylinders)
Crankshaft, counterweights (Each counterweights and all cylinders)
Balancer, counter rotation axis (Two mass in the extreme of axis)
All parts together
- Max Force Ax = 351.5 N
- Min Force Ax = -351.5 N
- Max Force Az = 636.2 N
- Min Force Az = -635.9 N
- Max Force Bx = 351.5 N
- Min Force Bx = -351.5 N
- Max Force Bz = 635.3 N
- Min Force Bz = -634.6 N
If we compares the vibrations we could see, with balancer to double speed of crankshaft in the R6 the force in A and B would be over 600 N. Therefore the vibrarions is the same
Crankshaft inertia
- YZF-R6 = I' (1 cyl) = 0,0050 kg·m2 ; I' (4 cyl) = 0,0200 kg·m2 ;
- YZF-R675 = I' (1 cyl) = 0,0058 kg·m2 ; I' (3 cyl) = 0,0175 kg·m2 ;
The increase mass due to the mass calcualtes for vibrations:
- YZF-R6 = Crankshaft inertia 1.9457e-04 kg·m2
- YZF-R675 = Crankshaft inertia 7.6361e-04 kg·m2
Therefore
- YZF-R6 I' = 0,0203 kg·m2 ;
- YZF-R675 I' = 0,0183 kg·m2 ;
Therefore in this case, the advantage of YZF-R675 take a 10% by inertia forces than YZF-R6.
Conclusion
If YZF-R675 used the same piston than YZF-R1
- YZF-R6 7.5% more rpm than YZF-R675, but the YZF-R675 is 12.5% bigger than YZF-R6.
- YZF-R675 take a 10% more powerfull than YZF-R6, to same rpm.
- YZF-R675 take a 2% less friction than YZF-R6.
- YZF-R675 in acceleration is smoother than YZF-R6 (9% of difference)
- YZF-R6 in brake engine is smoother than YZF-R675 (52% of difference) this is possible to correct with Slipper Clutch.
- YZF-R675 vibrations is smoother than YZF-R6 (mean 22% of differences without balancer)
- YZF-R675 lenght os crankshaft is shorter than YZF-R6 (45% of difference)
- YZF-R675 cranckshaft inertia is smaller than YZF-R6 (10% more mass, more stroke, and more axis, but less cylinders)
And other advanteges are:
- Simplifications in parts because uses de same piston and valves than YZF-R1
- Less parts (one cylinder less)
- Slipper clutch and new materials mitigate the differences between 600cc and 675
My conclusion, is 675cc, it is true that I like this engine, and I would like see the YZF-R675 in the future, (I hope in the close future).
The code is in Matlab (it has several simplifications):
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