2011年7月24日 星期日

High Lift Camshaft 高角度凸輪軸

常聽人家講Hi-CAM或高角度凸輪軸, 什麼是高角度凸輪軸? 網路上查的到的資料大同小異, 汽車雜誌上也多有提到, 不外乎下列內容:
Hi-Cam, 改裝用的凸輪軸, 相較於原廠部品, 不僅揚程提升, 連作用角度也相對提高, 其目的在加大氣門開啟的深度, 進而拉長進排氣門的重疊角, 也就是加長進排氣門同時開啟的時間, 以求更多的混和氣進入燃燒室, 提升進排氣效率….etc…. bra… bra… bra…
    (揚程? 作用角度?? 重疊角??? )
簡單來說, Hi-CAM(高角度凸輪軸)比起原廠CAM, 它能有更長的進排汽閥門開啟時間, 增加進排氣量以得到增加馬力的效果.
常說的單凸引擎及雙凸引擎又是怎麼回事呢?
所謂單凸引擎(SOHC, Single OverHead Camshaft), 它的引擎進排氣閥門的動作由一支Camshaft控制; 相對的, 雙凸引擎(DOHC, Double OverHead Camshafts), 就有兩支Camshaft來控制進排氣閥門, 一支負責Intake(進氣), 一支負責Exhaust(排氣).
如果能了解引擎的構造及作動方式, 對於上述文字的理解就能更深入了.
先來看看引擎的構造及各部名稱, DOHC引擎為例說明:

I: Intake Camshaft(進氣端凸輪軸),
E: Exhaust Camshaft(排氣端凸輪軸),
S: Spark plug(火星塞),
V: Valves(氣門),
P: Piston(活塞),
R: Connecting rod(連桿),
C: Crankshaft(曲軸),
W: Coolant Flow(冷卻水路).
如果是SOHC引擎, 上面的IntakeExhaust就由同一支Camshaft控制.
引擎的作動流程:
1. 進氣(進氣閥門打開, 排氣閥門關閉)
2. 壓縮(進氣閥門關閉, 排氣閥門關閉)
3. 爆發(進氣閥門關閉, 排氣閥門關閉)
4. 排氣(進氣閥門關閉, 排氣閥門打開)
這四個行程循環, 就是源源不絕的引擎動力, 這裡有很清楚的動態圖解.
Camshaft(凸輪軸)就是控制進排氣閥門開啟的時間點及開啟時間長短的關鍵, 這裡有清楚的Camshaft動態圖解.
Camshaft的橫切面圖解.

Camshaft上面的突起(Nose), 它的形狀及Lift(揚程)就是把氣門打開(壓下)的關鍵, 如果以引擎運轉時它開始產生Valve(閥門)下壓動作(開啟)到下壓動作結束(關閉), 作用期間(Duration)所轉的角度, 就是一般在談的凸輪軸角度, Lift影響的是閥門開啟的大小, 稱Nose為Camshaft作動的關鍵也不為過.
Hi-CAM就是改變Camshaft上面的突起部(Nose)的形狀及Lift, 使得Valve開啟的時間(Duration)拉長及Valve開啟度變大, 一般談到高角度凸輪軸的264°272°280°等變化, 指的就是Duration相對Camshaft運行的角度.
下面這張圖, 左邊藍色的部份為Intake Valve的Duration區間, 右邊紅色的部份為Exhaust Valve的Duration區間, 進排氣CAM都以同樣的方向轉動; 下方放在一起看, 藍色與紅色重疊的地方即是上面提到的Overlap(重疊角); Camshaft的變化, 除了Duration的角度改變之外, Overlap亦會跟著改變, 配合前文第一段的說明, 就更容易理解了.

好了, 既然知道了Camshaft作動的原理, 再來討論一下High Lift Camshaft, Hi-CAM.
Hi-CAM對於引擎馬力及扭力的提升有很大的影響, 尤其原廠Turbo車在設定Cam的時候, 為了儘量減低Lag現象, 大多使用小Duration且低LiftCamshaft, 如果單純的把增壓值打高, 而沒有修正引擎汽缸的吞吐量, 灌入汽缸的壓縮空氣依然會受到限制; 同時排氣端若未能增加排氣效率、降低排氣壓力的話, 渦輪驅動端Turbine也得不到更強的驅動能力, 所以Turbo車若想要獲得爆炸性的馬力輸出, Hi-CAM是一個不錯的選擇.
TurboCAM角度的變化有一定之限制, 其重點是可以增加但不能有過大的氣門重疊時間(畢竟是強制增壓, 好不容易壓進去的氣體, 因為排氣閥門未關閉都流掉了), Camshaft的揚程改變, 增加Valve的開啟度, 才是增加進排氣效率的根本之道.
Turbo車改Cam能使馬力很輕鬆的提升, 連帶也使得再加速力有明顯的變化, 尤其是尾速的區域......


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貼一篇摘錄自DSMtuners的文章, 原文連結.

The old school cam list of "mods" is as follows from least to most aggressive:
Based on duration and lift:
Least aggressive:
1G turbo Auto cams
2G turbo cams
1G non-turbo cams (256i/248e), slightly higher lift and duration on the intake cam only.
1G turbo Manual cams (248i/248e), slightly higher lift on the exhaust cam only.
Evo 4-8 cams (reversed installation)
HKS 264/264 cams (or equivilant; FP1)
HKS 264/272 cams (or equivilant; FP2, DKS1)
HKS 272/272 cams (or equivilant; FP3, DKS2, BC2)
HKS 280 cams (or equivilant; FP3x or FP4, DKS3, BC3, and the infamous JUN 272's)
HKS 288 cams (or equivilant; BC4)
Most aggressive

The 1G turbo auto cams are extremely mild, but produced decent power levels in the 1000-3500rpm range, and were a good match for the stock torque convertor and a 13G turbo. Oh, and the old lady driving.
The 2G turbo cams just sucked, but it was more the T-25 (T-TOO-SMALL) turbo's fault than the cams. Made for good low end/midrange power/torque for sally little girls driving the cars when they were stock. These cams had nothing past 4200-4600rpms.
The 1G non-turbo cams actually had a more aggressive duration and lift on the intake cam than the turbo models, but the exhaust cam is slightly milder than the turbo version.
The 1G turbo manual cams are a nice upgrade for 2G owners that are using a T-25, a 14B or a 16G turbo without requiring an aftermarket cam. These cams die out in the 5200-5400rpm range.
The Evo 4-8 cams are slightly more aggressive than the 1G turbo manual cams, and would be considered as an upgrade over them. The intake cam and the exhaust cams have more aggressive lift, but the same duration as the 1G turbo manual cams. You would install the exhaust cam from the evo motor into the dsm as the intake cam; and the evo's intake cam would become the exhaust cam on the dsm. They have a better overall powerband than the 1G turbo manual cams, and likely die off around the 5400-5600rpm range.
The 264/264 cams have a higher lift and duration than ALL of the stock camshafts, but are still extremely streetable in the dsm, giving stock idle qualities, while increasing the power throughout the whole powerband up to the 6000-6200rpms range, while losing no low end power. Made for cars running a 14B, or a 16G.
The 264/272 cams have a higher lift/duration cam on the exhaust side than the 264/264 combo, and produce a solid increase in power throughout the powerband, emphasizing on the midrange/topend while retaining the stock-like idle, and very little low-end power loss over stock. Powerband now lasts into the 6800rpm range on a 2.0L. Made for cars running a 14B up to a 60-trim or 56-trim turbo (i.e. PTE SCM60 or SCM61). These are great with 50-trims and 20G's.
The 272/272 cams now have both high lift/high duration cams in action versus the 264/272 combo, and it shows. The car has a lopier idle (which can easily be retuned), and is smooth at 1000rpms. Power is strong from 4000+rpms, and has been proven to make solid power to 10K rpms. The low end from 1000-4000rpms is moderately depressing, but the light switch turns to fun at the 4000rpm mark and hold on for the fun to last until your prescribed redline. These cams are absolutely a riot with track-happy 50-trims, or street worthy 60-trims and up (stock block or race motor setups). An excellent combination for street power with all the popular Garrett turbos out there (GT35R, GT4088R, GT4094R, GT4294R) on a 2.0L or 2.3L race motor. Proven into the 8's.
The newer cams out there are the 280 and 288 cams. These cams ARE designed for race applications--these are top end only cams. If you want to run them on the street with your 16G, you are completely wasting your time. These cams have a wicked idle, and really like to run smooth from 1100-1200rpms and up. They don't make decent power until 5K rpms (280's) and up (288's) in a 2.0L motor, but will rev to the moon (10.5-12K rpms), creating a solid top end powerband for a high-revving, ball-bearing GT4094R or larger turbo'd car. In a 2.3L with a LARGE turbo (GT4088R and larger), the 280 cams will likely kick your ass from 4800rpms, while the 288's will be a few hundred rpms later (close to 5200-5500rpms) on a GT4088R or GT4094R, and closer to 6K rpms on the GT4294R/4202R setups. These new cams are proving themselves into the 8's and 7's; but then again, all those cars are RACE CARS. If you intend on running a full race motor with a LARGE turbo, then go for it. If you are running some stock block car with a 50-trim...you are completely wasting your time because the turbo will be way out of its flow map at the rpms that these cams make power to. I would also only run these 280 or 288 cams on cars using a T4-flanged turbo to handle the flow that they put out.
That said, I am still running 272/272's on my 2.3L, GT4088R-powered street car, and am going 9's; along with other members on here like Jake Hanhardt (topstreet) with his 2.3L, GT4294R'd 10,500rpm revving monster.
I hope that this in-depth answer will give you some insight. We don't go by numbered stages. If you are running a stage 2 cam, go buy a different car. I like to know the exact specifications. The 264/272 cams in your application are IDEAL for getting the most out of your 16G on a mildly built motor, while having room to upgrade to a larger turbo (like a 50-trim or a 60-trim). These will produce the best low end/midrange/top end compromise on your 16G. If you do any upgrading, purchase a HKS 272 Intake cam, and a pair of QUALITY adjustable cam gears (HKS, fidanza, AEM, VENOM, Greddy, Skunk2).
                                                                                        by twicks69

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