Hej. Någon som vet om det ändrats något på T7 topparna genom åren?
Eller är det precis samma från 98-10?
Utskriftsvy
Hej. Någon som vet om det ändrats något på T7 topparna genom åren?
Eller är det precis samma från 98-10?
Biopower topparna har rostfria insugsventiler samt ventilsäten i annat material bl.a. Sen är det små skillnader på kamaxlarna, tex B235R är lite värre än B205E/L/R om jag inte missminner mig, men skillnaderna är så små att det är lika bra att gå på N/A kamaxlar från äldre motorer (B234i/B202)
Ventilerna skiljer i utformning på tidiga utföranden till 2000, sedan finns materialskillnader beroende på prestanda/motorvolym. Här finns info från EPC (notera dock att detta rör sig om reservdelar och inte vad som sattes dit från början): https://www.esaabparts.com/viewparts...tion=315066255
Ok, tack för svaren.
Vart påståendet om att BioPower modellerna skulle ha rostfria insugsventiler kommer ifrån vet jag inte, men det man ändrade var material i säten och ytbehandling av inloppsventilerna. Topplocket i sig ska dock vara samma och inte som hos Ecotec motorn där BioPower toppen gjöts i en annan aluminiumlegering då bensintoppen sprack då man körde på etanol.Citat:
Ursprungligen postat av wille61
Ett papper om Ecotec motorn från GM Powertrain Europe beskriver detta med ventilerna mer i detalj
Citat:
Regarding the valves, the positive experience from the Fam III, SAAB 95, BioPower engine
was utilized. A holistic approach is vital in that the valve and the valve seat cannot be
selected separately, valve parameters interact with valve seat insert material properties.
During model year 2006 the inlet valve supplied by TRW had previously been upgraded on
the 2.0 ECOTEC turbo gasoline engine, incorporating a stiffer valve head. For the
BioPower application, the valve was further modified in that the chrome plating of the valve
stem was replaced by a full nitriding of the entire valve. The removal of the chrome plating
of the valve stem to a large extent offset the extra cost of nitriding.
A concern with the nitriding was that the hardness of the induction hardened valve tip end
would be reduced during the nitriding process. This in turn could lead to extensive tip end
wear on the valve resulting from the high, localized, contact forces applied by the roller
finger follower. In engine testing it was found that the nitrided layer was robust enough to
protect for the lower hardness base material. The nitrided valve is currently being
considered for introduction into the pure gasoline variant of the engine.
The exhaust valve selected was again a carry-over item, this time from the 2.0L SIDI turbo
engine. The valve is sodium cooled with a Nimonic valve head without seat hard facing. It
features an upgraded valve tip material with increased hardenability to better withstand
valve tip end wear.
Given the existing valve seat insert material, it was known from previous engine programs
that substituting a Nimonic valve without a hardened seat face for a hard faced valve
would be beneficial in reducing wear. The Nimonic material has a high nickel content and
the wear reduction is achieved by increasing the dissimilarity between the valve material
and the valve seat material.
Valve Seat Inserts
The manufacturing strategy was to utilize existing machining equipment at the engine
plant, thus it was not possible to change valve seat geometry. If possible, it was requested
to carry over the current ECOTEC valve seat inserts as the machining line was not laid out
to handle valve seat variants. The baseline valve seat insert materials were Brico 3220 on
both inlet and exhaust side.
The majority of the valve recession was related to wear of the valve seat insert.
Parameters contributing to increased valve recession with E85 fuel are amongst others:
• Dry fuel
• Cleaner combustion giving less lubricating soot
• Higher contact forces due to increased combustion pressures
• Thermal effects, significant cooling of the inlet valve from the increased amount of
fuel and the increased cooling effect of evaporation of the fuel.
• Chemical effects, reduced build up of protecting oxide films on the valve and valve
seat wear surfaces.
The wear can be approximated by a material constant times surface load times sliding
distance, divided by surface hardness.
The wear is mainly abrasive in nature, the valve head flexes slightly when subjected to the
combustion pressure and a sliding motion of the valve relative to the valve seat insert is
developed. A stiffened valve head reduces the flexing, and hence the sliding distance,
reducing wear despite the resulting increase in surface pressure.
DOE Valve and Seat Parameters
A 24 parameter self learning Neural Network (24 parameters: VSI composition, pressure
load history, valve hardness, valve head stiffness, fuel, guide clearance etc.) was created,
using empirical recession data from Fam III BioPower as well as ECOTEC.
By using predictions from the neural network it was possible to quickly rank performance
of different combinations of valve designs and valve seat materials and narrow down the
list of candidates, minimizing the number of engine tests as well as reducing the necessary
number of prototypes.
On the inlet side it was found beneficial to minimize the amount of copper in the inlet valve
seat insert, and hence the thermal conductivity, offsetting part of the cooling effect of the
fuel. Increasing the surface hardness of the valve (via nitriding) and selecting a valve seat
insert material with higher amounts of tungsten, molybdenum and chrome was clearly
shown to be beneficial for increasing robustness.
Using the Neural Network model to feed an L18 orthogonal array Design Of Experiments
(DOE) gives the influence of exhaust valve parameters and some selected valve seat
insert material parameters on robustness and recession resistance. Increasing the signal
to noise (S/N) ratio increases the robustness of the system.
The three most effective parameters are nitriding of the valve and an increased amount of
the alloys tungsten and chromium in the valve seat insert. Actually, nitriding the exhaust
valve was found to be a more effective solution than using Nimonic, but this would have
meant introduction of yet another part number in the assembly line and was not a viable
option.
Hardness of the valve seat insert did not have a significant influence in the range surveyed
for the BioPower application. As on the inlet valve seat insert material, selection of a
material with increased amounts of tungsten and chromium was beneficial for both
robustness and wear reduction.
Effects of valve seating velocity and hence seating impact load on valve recession was
previously investigated on the Fam III BioPower engine, a threefold increase in seating
velocity was completely masked by the forces of the combustion pressure.