7500rpm+
12-30-2003, 12:11 AM
#1
Senior Member
Thread Starter
Join Date: Dec 2003
Location: Minneapolis,MN
Posts: 500
Considering a clearenced engine with gobs of oil pressure/vol what are the main reasons a rotary would fail above 7500 rpms. Its kind of a weakest link in relation to rpm's
e-shaft distortion?
Stationary gear distortion?
weight of apex seal?
GregW
e-shaft distortion?
Stationary gear distortion?
weight of apex seal?
GregW
12-30-2003, 12:23 AM
#2
Junior Member
Join Date: Dec 2003
Posts: 13
Well Ive been researching this as well. I have a technical background but little rotary experience. Seems people claim to know dont really know, or hang onto their "secrets" as if it were gold.
Point to consider is that inertial loads rise to the square of RPM.
1. Stationary gears. The gear profile isnt a good choice and worse it has resonant frequencies under operation at 8000rpm+ that causes the parts to have fatigue failures. Replace it with the GURU gears. S6 engines had revisions to improve it but it isnt as good as the GURU solution.
2. Eccentric shaft. The shaft will deform elastically under load causing all sorts of clearance and fatigue problems. GURU 2 piece eccentric shaft is an easy fix. Im thinking about machining the shaft and putting a bearing into the center plate as a possible cost saver. The modolus of elasticity for steels is about the same so really you need to support the shaft like the GURU setup.
3. As the power loads increase one third goes into the cooling system and this stresses the components further which is compounded by the additonal problems of materials where the specific properties of the materials gets worse the hotter they get. Its wise to improve the oil cooling system to run more pressure. Also there is things like multi window bearings that feed more cooling oil into the engine. A rotary does alot of oil cooling in comparison to a piston engine.
4. Sealing is tricky, also related to chattering / floating of the seals. Ideally you want to reduce the inertia of the seals as much as possible. Ceramic seals have a low mass. There is also the other problem of wearing the housing out quickly at high RPM.
One thing the wankel has in its favour is atleast the rotor isnt coming to a complete stop and doing a reverse stress cycle like a piston engine.
Point to consider is that inertial loads rise to the square of RPM.
1. Stationary gears. The gear profile isnt a good choice and worse it has resonant frequencies under operation at 8000rpm+ that causes the parts to have fatigue failures. Replace it with the GURU gears. S6 engines had revisions to improve it but it isnt as good as the GURU solution.
2. Eccentric shaft. The shaft will deform elastically under load causing all sorts of clearance and fatigue problems. GURU 2 piece eccentric shaft is an easy fix. Im thinking about machining the shaft and putting a bearing into the center plate as a possible cost saver. The modolus of elasticity for steels is about the same so really you need to support the shaft like the GURU setup.
3. As the power loads increase one third goes into the cooling system and this stresses the components further which is compounded by the additonal problems of materials where the specific properties of the materials gets worse the hotter they get. Its wise to improve the oil cooling system to run more pressure. Also there is things like multi window bearings that feed more cooling oil into the engine. A rotary does alot of oil cooling in comparison to a piston engine.
4. Sealing is tricky, also related to chattering / floating of the seals. Ideally you want to reduce the inertia of the seals as much as possible. Ceramic seals have a low mass. There is also the other problem of wearing the housing out quickly at high RPM.
One thing the wankel has in its favour is atleast the rotor isnt coming to a complete stop and doing a reverse stress cycle like a piston engine.
12-30-2003, 02:44 AM
#4
Senior Member
Join Date: Jul 2002
Posts: 2,315
i'm thinking e-shaft even with high oil pressure. i think the guys from japan use stock fd bearings that cope with crazy hp levels at high rpms pretty decently. and since you explained the whole chatter mark phenomina i really can't think of a time that i've heard many problems from it.
12-30-2003, 04:17 AM
#5
Junior Member
Join Date: Dec 2003
Posts: 13
