c*********r
发帖数: 19468 | 1 以前低估Valvetronic对减轻N55的turbo lag的作用了
虽然没有Valvetronic，Double VANOS一样可以通过增加气门重叠角来改善扫气
从而增加排气流量，减轻turbo lag，但是此时毕竟进气门的开放时程是固定的
提早开放也会提早关闭，影响填充效率
但是有了Valvetronic就不同了，它改变气门升程的同时其实也是改变时程
这样，低转高负荷（急加速）时，扫气和进气可以兼顾的很好 | w******x
发帖数: 4396 | 2 n55的turbo的back pressure是多少？加压是多少？
turbo上气门重叠能不能改善扫气是很大程度上是根据turbo的特征决定的。 | c*********r
发帖数: 19468 | 3
most newer direct-injection turbos are using this strategy (larger valve
overlap) to reduce turbo lag
as long as you give a direct-injection turbo a larger valve overlap under
low engine speed but high load condition, you can get the fresh air in and
out. this will increase the exhaust gas flow and therefore reduce the turbo
lag
【在 w******x 的大作中提到】
: n55的turbo的back pressure是多少？加压是多少？
: turbo上气门重叠能不能改善扫气是很大程度上是根据turbo的特征决定的。
| w******x
发帖数: 4396 | 4 how does it work? sure, n55 has a single big turbo so the back pressure at
low speed is low, but at low speed you don't have much of a boost to begin
with, how do you get the fresh air in?
turbo
【在 c*********r 的大作中提到】
:
: most newer direct-injection turbos are using this strategy (larger valve
: overlap) to reduce turbo lag
: as long as you give a direct-injection turbo a larger valve overlap under
: low engine speed but high load condition, you can get the fresh air in and
: out. this will increase the exhaust gas flow and therefore reduce the turbo
: lag
| c*********r
发帖数: 19468 | 5 it's a comparative advantage
compare A & B
A: a port-injection turbo
B: a direct-injection turbo
both are running at the same low engine speed
then you give them the same throttle opening angle
what will happen?
for A, because it sucks mixture, so you can't use a large overlap at all
here, we denote its exhaust gas flow as a(t) as a function of time
for B, you can give it a very large overlap, let's denote its exhaust gas flow as b(t)
here's two factors for the initial stage:
1) even without muc
【在 w******x 的大作中提到】
: how does it work? sure, n55 has a single big turbo so the back pressure at
: low speed is low, but at low speed you don't have much of a boost to begin
: with, how do you get the fresh air in?
:
: turbo
| w******x
发帖数: 4396 | 6 no no we are not talking about the same thing. i was talking about
backpressure forcing fresh air back out since every turbo has a backpressure
/boost ratio more than one. but that's measured at boost and VVT can take
care of it. but how does a turbo behave at low engine speed? i don't know. i
think it depends on the turbo.
flow as b(t)
【在 c*********r 的大作中提到】
: it's a comparative advantage
: compare A & B
: A: a port-injection turbo
: B: a direct-injection turbo
: both are running at the same low engine speed
: then you give them the same throttle opening angle
: what will happen?
: for A, because it sucks mixture, so you can't use a large overlap at all
: here, we denote its exhaust gas flow as a(t) as a function of time
: for B, you can give it a very large overlap, let's denote its exhaust gas flow as b(t)
| c*********r
发帖数: 19468 | 7
backpressure
i
I'm talking about how VVT helps reduce turbo lag on direct-injection turbo
engines
& why it could be even better with VVL
I'm not talking about how turbocharging helps improve scavenging
here scavenging is just used to reduce turbo lag
as for your question, even at low engine speed, even for an NA engine
without any boost at all, you still have the same logic for scavenging
as long as you give the engine wider throttle opening, it'll always suck
more air
burn more gas, so its exh
【在 w******x 的大作中提到】
: no no we are not talking about the same thing. i was talking about
: backpressure forcing fresh air back out since every turbo has a backpressure
: /boost ratio more than one. but that's measured at boost and VVT can take
: care of it. but how does a turbo behave at low engine speed? i don't know. i
: think it depends on the turbo.
:
: flow as b(t)
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