A love affair with knowledge will never end in heartbreak

作者: skyripper () 站內: EFI
標題: [研究]"speed-density" 噴射供油系統原理介紹
時間: Thu Mar 10 03:09:07 2005
 
 
只要你的車上裝有MAP(歧管壓力感知器), 就是這種形式的噴射供油
想要了解原理嗎? 看完本文我相信你會有相當程度的認知了 :)
 
 
 
原文刊載於 PGM-FI.org
 
Speed Density systems calculate the amount of air entering a motor using
sensors that monitor engine operating conditions. The Ideal Gas Law (PV =
nRT) is the basis for this type of engine management. Instead of directly
measuring the amount of air entering the motor ("n" in the above equation),
speed-density systems estimate it using n = PV / RT, and then applying
additional corrections. Fuel tables in a honda ECU (from a theoretical
standpoint) are Volumetric Efficiency (VE) tables.
 
Speed Density 系統, 是以監控引擎的各項感知器來計算出進入汽缸內的空氣量的。
這類引擎監理系統是以理想氣體方程式(PV=nRT)為理論來應用的。不直接偵測流進氣缸
內的空氣質量(指的便是上述方程式的"n"), 而以 n=PV/RT 來推測出空氣量, 並根據許
多額外的數據來補正這個值。本田ECU內的供油圖表(理論上來看)就是引擎容積率圖表。

Basic operation:
 
A Map Sensor is used to measure the pressure of air in the intake manifold
(DENSITY term in speed-density). This provides the P term in the Ideal Gas
Law calulation.
 
MAP(歧管絕對壓力感知器)是用來偵測進氣歧管的壓力(這裡指的即是speed-density中
DENSITY這個詞, 密度)。這便提供了在理想氣體方程式中計算所需的P(壓力)這項數據。
 
The engine's rotational speed (SPEED term in speed-density) is used to
estimate the volume of air entering the motor by multiplying how much air is
sucked into the cylinder each stroke (usually displacement divide by two) by
the number of engine revolutions. This provides the V term in the Ideal Gas
Law calculation.
 
而引擎的旋轉速度(指的即是speed-density中SPEED這個詞, 速度)是拿來推測進入引擎
中的空氣的體積, 以引擎轉速乘上每一行程有多少空氣被吸入汽缸(通常是排氣量除二)
來得到這個值。這便提供了在理想氣體方程式中計算所需的V(體積)這項數據。
 
The Intake Air Temperature Sensor measures the temperature of air entering
the engine, providing the T term in the Ideal Gas Law calculation.
R is a constant

而IAT(進氣溫度)感知器能偵測進入引擎的空氣溫度, 提供了在理想氣體方程式中計算
所需的T這項數據。R是常數。
 
Knowing P, V, R and T, the ECU can then calculate an estimate of n (moles of
air entering motor) from sensor data and n = PV / RT
Because speed-density calculates airflow instead of directly measuring it,
additional factors are often used to provide a better estimate. The Tps
Sensor is key in many of these - TPS tip-in enrichment is used to provide
more fuel that the Ideal Gas Law calculation suggests in order to provide
fueling for a rush of new air prior to the Map Sensor reaching a steady
state. Off-throttle leaning is used to prevent the motor running rich after
sudden decreases in throttle.
 
知道了P, V, R 和 T, ECU便能夠從 n=PV/RT 和這些數據計算推測出n這個值(有多少
mole的空氣進入引擎內)
因為 speed-density 系統計算流量而非直接的偵測該數據, 所以其他的重要因素也會
拿來做補正來得到較準確的推測值。TPS(油門開度感知器)是個重要關鍵 - TPS tip-in
補正增油便是用當來大量的新鮮空氣急遽進入汽缸時, 提供更多的油料, (這動作會比
MAP的改變來的快)隨後MAP才會提供穩定訊號。Off-throttle(收油)時的補正減油則是
能防止當突然鬆開油門時, 引擎的供油過度。(這是放炮主因喔!)
 
--
Here are some links to more information about speed-density systems:
 
http://www.asashop.org/autoinc/jan97/techtotech.htm - decent link, not TOO
techy.
http://www.wincom.net/trog/efi.html - quite technical but practically
oriented
http://www.simcar.com/literature/sae940759/sae940759.htm - highly technical
paper on practical use of speed density systems for air/fuel management. Has
excellent figures illustrating the role of secondary correction factors, like
TPS accel/decel.