Operation of the Motronic System
Operation of the Motronic System
Start Control ( Fuel,Ignition Timing,Air)
Closed-Loop Operation
Part-Throttle Acceleration
Full-Load Acceleration
Knock Control
RPM Limitation
Coasting Cut-Off
掌握 MOTRONIC系统的控制原理
了解翻译技巧 — 句子成分转换
flood [fl?d] v.充满,淹没,溢出; n.洪水
compensate ['k?mpenseit] v.补偿,偿还
formation [f?:'mei∫?n] n.形成,形成量
turbocharge ['t?:bout∫ɑ:?] v.用涡轮增压
turbo ['t?bou] n.涡轮增压,涡轮增压器
intercooler [int?'ku:l?] n.中间冷却器,中冷器
sense [sens] v.理解,感到,感受,检测
override [ouv?'raid] v.超过(越),越过,压倒,占优势
overswing [ouv?'swi?] v.摆动过大
lambda ['l?md?] n,λ值,过量空气系数,氧传感器
endanger [in'dein] v.危及
trait [treit] n.特性,显著的特点
harmonics [hɑ:'m?niks] n.谐波 [音 ],谐波分量
recognition [rek?g'ni∫(?)n] n.承认,赏识,赞誉
modify ['m?difai] v.更改,修改
stratification [?str?tifi'kei∫?n] n.成层,分层
cutback ['k?tb?k] n.减少
scope [skoup] n.范围,领域,见识,示波器,指示器
simultaneous [sim?l'teinj?s] a.同时的,同时发生的,同步的
coast [koust] v.滑行,滑翔,沿海岸航行; n.海岸,沿岸
cut-off ['k?t?f] n.切断,关闭,停车
coastdown ['koustdaun] n.降低,下降,滑行
blank [blk] ad.空白的,空着的,没有表情的; n.空白
stall [st?:l] v.失速,熄火,(速度不够)停车 [停止转动 ]
refinement [ri'fainm?nt] n.精致,文雅,精巧
resume [ri'zju:m] v.恢复,重新开始
port injector 进气道喷油器
start injector 起动喷油器,冷起动喷油器
thermo-time switch 温控定时开关
turbocharged car 涡轮增压轿车
air-fuel ratio 空燃比
knock sensor 爆燃传感器
passenger compartment 乘客舱,乘员室
knock control regulator 爆燃控制调节器
be sorted from 与 … 分开,从 … 拣出
scope set 示波器
Operation of the Motronic System
In this section,let's look at operating conditions to see
how Motronic controls injection and ignition as well as idle-
speed bypass air for good engine management [1].
Start Control,Fuel
In most Motronics,start enrichment is provided by the port
injectors rather than the separate start injector/thermo-time
switch,For start control,the important inputs are rpm and
engine temperature,The control unit monitors cranking rpm,
and also the number of revolutions since the time cranking
began [2],The injection pulses may be longer than normal.
But at low engine temperatures,the control unit may
deliver instead several shorter injection pulses per revolution
to improve starting,Remember,these are 10 millisecond
pulses in a pulse period,or crankshaft revolution time of
To prevent flooding,fuel quantity will cut back after a measured
number of revolutions,or after the engine has reached a
cranking rpm that is temperature related,for example 200-300
Start Control,Ignition Timing
With a cold engine at low cranking speeds,timing will be
controlled near TDC,For normal cranking rpm,a large advance
in timing might fire too early,damaging the starter,Further,
starting would be difficult if not impossible,With a cold engine
at higher cranking rpm,however,timing will be advanced for
better starting,
For hot starts,or high intake air temperatures,timing will be
retarded because a hot cylinder can fire easier while the piston
is rising at cranking rpm,Retarded timing prevents knocking
that can occur in high-compression engines,and may be
masked by the starter sound,
Start Control,Air
As in L-Jetronic,the idle-speed stabilizer is normally driven
open more by increased dwell signals to provide extra bypass
air for cold starting.
Post-start-the 5-30 seconds when you want the engine to
keep running after you release the key from CRANK-is
affected by engine temperature as well as a timer in the
control unit,Colder engines get more fuel injected,Also,
colder engines get more timing advance,Based on the start-
up temperature,and the time since start,post-start
enrichment is gradually reduced,The idle-speed stabilizer
maintains rpm.
During warm up,the most important input,besides engine
load and rpm for basic pulse time,is engine temperature,The
control unit includes a ROM map of warm-up characteristics to
apply a correction factor based on load and engine speed,
greater at low loads and rpm than at high loads and rpms [3],
See Fig.4-4,Control unit outputs include injection pulses for
the proper mixture,ignition timing for driveability (advance
under part-load acceleration,retard on deceleration to reduce
HC emissions),and idle stabilization to help keep the engine
running at idle.
Remember,during warm-up,the temperature of the lambda
sensor is important,Unheated lambda sensors can be heated
faster by changing ignition timing,Motronic retards timing to
cause a hotter exhaust,That heats the oxygen sensor much
quicker and also heats the catalytic converter faster for more
Fig.4-4 Warm-up correction factors
Closed-Loop Operation
Based on the inputs of a warm engine,and oxygen-sensor
voltage when hot,the system normally operates closed-loop,
The oxygen sensor fine-tunes the fuel-injection delivery for
proper air-fuel ratios.
For every combination of inputs,the control unit looks in its
memory for the best timing,the best dwell angle,the best
lambda,or air-fuel ratio [4],On the basis of engine
temperature,Motronic controls ignition timing with independent
calibrations for starting,idling,deceleration,and acceleration,
both part-load and full-load or WOT (Wide Open Throttle),For
example,control of timing advance at idle reduces the need for
idle fuel enrichment.
Part-Throttle Acceleration
Just as in L-Jetronic,the overswing signal of the air-flow
sensor increases fuel delivery,compensated by temperature,
For air-mass sensors,the rate of increase of the voltage
signals acceleration,During part-throttle acceleration,the
normal pulse for steady cruise increases for just about one
second while you open the throttle,Then the pulse cuts back
even as the engine picks up speed; this saves fuel and
reduces emissions.
In addition,ignition timing can be retarded to avoid the
brief acceleration knock that could occur for the first few
cycles of engine acceleration,Ignition timing control also
reduces the formation of NOx,which is normal with
Rate of ignition timing change is also controlled;
· to avoid knocking,the control unit allows fast change
· to reduce jerk during transition,the control unit normally
changes ignition advance gradually
Full-Load Acceleration
Full-load enrichment is signaled by the throttle switch,As
long as the throttle is full-open,longer injection pulses will be
delivered for enrichment,Rich mixtures reduce the tendency
to knock,This enrichment is based solely on rpm,and
programmed from engine tests,The air-flow signal is ignored.
At the same time as rpm and throttle position control full-
load injection enrichment,air temperature and engine
temperature supply inputs to control the advance of ignition
timing for best acceleration without approaching knock [5],For
engines without knock sensors,timing advance is based on
engine test data stored in the timing map,The engine can
operate close to the ignition-advance limit,developing
maximum torque over the entire rpm range with least chance
of knocking based on three factors:
1,the timing curve can be programmed specifically for each
engine operating point
2,the system operates with narrow tolerances and freedom
from mechanical wear
3,timing is compensated according to engine temperature
and intake-air temperature
In some turbocharged cars,a second air-temperature sensor
is mounted in the manifold downstream of the turbo or the
intercooler to sense the temperature of the air entering the
engine,This is a special fast-response sensor overriding the
first air-temperature sensor to handle the quick changes in
temperature that can occur during full-throttle acceleration.
Knock Control
Programmed timing accuracy,even with compensations,can
be improved by a knock-sensor system that causes timing to
advance to just before the point where knock could damage the
engine,With a knock sensor controlling timing advance in a
separate closed-loop system,power output can be maximized
without endangering the engine.
Some engines,particularly turbocharged engines,include
knock sensors to pick up vibrations from the engine at the
first signs of knock,Some systems use two control traits,
mounted inside the passenger compartment,one for
Motronic,and a related knock control regulator,called KLR,
Knock-sensing inputs help both control units to work
together,The first and fastest output changes the timing,If
the engine is turbocharged,the second output controls the
boost,In the Motronic known as ML3,knock sensing and
engine management are combined in one control unit.
When the engine knocks,it vibrates with characteristic
frequencies of 5-10 kilohertz together with corresponding
harmonics,These vibrations must be sorted from other
engine vibrations in a recognition circuit in the control unit,
The Motronic control unit has accurate information on
crankshaft position and firing order so it is possible to
determine which cylinder is knocking (one cylinder usually
knocks before the others),Further,circuits operate with
such speed that ignition timing can be retarded only for the
knocking cylinder,and advanced for the firing of the next
cylinder,Each knock signal can modify timing in
milliseconds,When ignition retard eliminates the knock,
timing is advanced slowly in steps to the original value or
until knocking again occurs.
On turbocharged engines,if knock continues for seconds,
boost control reduces manifold pressure,Knock control
permits more boost,and higher compression ratios for
greater power,Automatically,it tends to adjust for the
octane-rating of the fuel being burned.
With precise control of ignition timing and turbo boost,
engines can be designed with higher compression ratios for
greater power output,On all engines,the knocking limits
depend on many factors:
· intake air temperature
· engine temperature
· engine deposits
· combustion-chamber form
· mixture composition,A/F ratio,and stratification
· fuel quality
· air density
For years,drivers have known that using higher-octane
fuel did not add to engine power unless ignition timing was
adjusted at the distributor to take advantage of the improved
anti-knock index,Now,with knock sensors and closed-loop
ignition-advance control,power output can depend on the
anti-knock index of the fuel being burned,It is not unusual to
see engine power specifications include the anti-knock index
of the fuel to be used [6].
RPM Limitation
If the rpm signal is greater than max-allowable rpm stored
in the computer memory,the control-unit signals a cutback of
the fuel-injection quantity,A scope set to read four pulses for
simultaneous injection for four cylinders shows the limitation
cutback of every other pulse,one pulse every other
crankshaft revolution,If you press the engine into the rpm-
limitation range,you will feel a surge as the limitation of fuel
injection cuts in and out.
Coasting Cut-Off
Signals of rpm,closed throttle,and engine temperature
control coasting cut-off of injection,On the scope during
coastdown,the single-injection pattern looks blank except
for the TDC pulse,No fuel is being injected,As rpm
approaches idle speed,the normal pulse will show again,If
the engine is colder,normal fuel injection returns at some
higher rpm,to prevent stalling,Motronic adds one
refinement,as fuel-delivery resumes,perhaps as the driver
resumes speed,ignition timing is gradually advanced to
smooth the transition from fuel cut-off to cruise or
Operation of the Motronic System
Start Control ( Fuel,Ignition Timing,Air)
Closed-Loop Operation
Part-Throttle Acceleration
Full-Load Acceleration
Knock Control
RPM Limitation
Coasting Cut-Off
Full-Load Acceleration
Knock Control