Transcript Electronic Throttle Control(ETC) System - ja505

ELECTRONIC THROTTLE
CONTROL(ETC) SYSTEM
LECTURER NAME: MR. KHAIRUL AKMAL BIN NUSI
HP. NO: 012-3458101
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HOW ELECTRONIC THROTTLE CONTROL WORKS
There are three basic components in electronic throttle control:
- A position sensor on the accelerator pedal (actually there are 2 or 3 position sensors
for redundancy).
- An electronically-controlled throttle body with a small electric motor to open/close
the throttle
- A control module (the PCM or a separate ETC module that talks to the PCM via the
CAN-bus or serial data link).
When the gas pedal is depressed, the electrical resistance of the potentiometers inside
the pedal sensors change. The control module notes the change in position and assumes
the driver wants to go faster. The module then looks at other sensor inputs (such as
engine RPM, engine load via the MAP sensor, possibly even vehicle speed and which
gear the transmission is in) and calculates how much throttle opening is needed. The
module then sends a command to the electric motor on the throttle body to open the
throttle a certain amount. A pair of throttle position sensors on the throttle shaft then
note the change in throttle position and provide feedback signals to the control module
so the module knows the exact position of the throttle and that everything is working
correctly.
ELECTRONIC THROTTLE CONTROL FAILSAFE OPERATION
 For redundancy backup and failsafe operation, the accelerator pedal
usually has two or even three position sensors. In a 2005 Mustang,
three sensors are used. Two decrease their resistance (increase voltage)
when the pedal is depressed, and the third increases its resistance
(decreases voltage). As long as the position sensor signals increase and
decrease by the same amount (mirror each other), the circuit is
assumed to be working correctly.
 On most vehicles, an electronic throttle fault will put the system into a
"limp-in" mode that will limit engine speed. On the Mustang, that
means idle speed only. On a Corvette, the limit is a maximum vehicle
speed of 30 mph. The throttle control system will remain in the limp-in
mode until the fault can be diagnosed and repaired.
Typical System Configuration
Driving DC-Throttle-motors with additional air by pass valve
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The main characteristic of a throttle valve, which is used tandem with a bypass
valve, is the neutral position. In the idle mode it is completely closed with a
strong spring and the air-bypass valve controls the idle speed. This means that
the motor has only to drive the throttle in one direction. Therefore the
electronic driving unit needs a half bridge or a single-switch together with a
freewheeling diode. One standard PWM capable output pin of a
microcontroller can be used for this task. Dead time generation is not required.
The rated position of the throttle is given by an ETC potentiometer. A
potentiometer is coupled with the gas pedal mechanics and gives a linear
voltage signal as input to the ECU.
 To generate a feedback signal, which is important for the control circuit, two
potentiometers are connected internally to the throttle valve. They supply the
ECU with two independent analog signals, in order to give information about
the actual position of the throttle. Normally one signal decreases while the
other signal increases. Both signals are proportional to the revolution angle of
the system. In principle only one of these two position signals is necessary for
the control circuit. But to improve the system accuracy, the second signal is
used as an additional control value
Driving DC-Throttle-motors with additional air by pass valve
 The throttle itself can also adjust the idle speed. Small air
masses must be controlled precisely. Therefore it is necessary
to drive the motor very exactly in both directions around the
neutral position. This system requires power-stages in an Hbridge configuration to realize the bi-directional mode of the
DC-motor. The capture compare unit of the microcontroller
should support the functionality of full bridge driving.
Control of the idle speed only
 Some throttles adjust only the idle speed with a motor,
but the acceleration and driving of the engine is still done
by a mechanical coupling to the acceleration pedal. As
already mentioned Infineon Technologies has two
products in the portfolio which support full bridge
driving combined with some additional functionality. The
devices can be controlled by PWM up to 2 kHz.
 The functional modes (turn clockwise, turn counter
clockwise and brake) are determined by the two input
pins. Depending on the allowed power dissipation and
the intended decay time the freewheeling can be done by
switching over to the second path of the bridge, with the
integrated diodes or with the brake-function, where both
low side switches are turned on.
Driving the full range of a throttle with standard H-bridge
 If the complete deflection of the throttle is done with the
motor, like in chapter 1 described, standard H-bridges like the
BTS780GP or the BTS7710GP can be used. They are suitable
for big throttles with high currents. These bridges consist of a
two channel smart power high side switch and two standard
power-MOSFETs, which are protected by the high side
switches against short of load and short circuit to ground.
 The power-MOSFETs can be pulsed with very high
frequencies, up to 100kHz. But the high side switches can not
be switched faster than 1kHz.
 Therefore they are not suitable to be switched on in the
freewheeling phase of the motor (active freewheeling) at high
frequencies. However, it is no problem to use the reverse
diode of the high side switch as freewheeling diode. The
special power package allows the bigger power losses caused
by this kind of driving.
Driving with dedicated bridges for throttle control
 Two new power-products on the roadmap, which are
specially designed for ETC-Systems (TLE5209 and
TLE6209). Similar to the TLE5205-2 family these
devices consist of an H-bridge and are controlled by two
input pins. However the new devices have a different
input logic. One of the two pins is a direction control,
and the other is an PWM-input. The first one, the
direction pin, adjusts the different modes “forward” and
“reverse”.
 The moving speed of the throttle control system is given
by the duty-cycle of the PWM signal on the second input
pin. That way only one fast PWM-channel of the
microcontroller is required. The TLE5209 is a low cost
solution. It is designed for continuous currents up to 5A
and peak currents of 7,5A at maximum which makes it
suitable for small throttles or for throttle idle speed
control.
 The maximum PWM-frequency is 1 kHz. Internal
monitoring functions protect the device against all
possible faults. Two status pins allow an error
diagnosis of the full-bridge. Figure 8 shows a
block diagram of this device. If both inputs are on
a high level, the bridge turns the current flow in
the reverse direction. During this phase the motor
is brake very strong. As a result, the decay time
decreases compared to the normal braking phase,
where only both high side switches are turned on.
 Electronic
throttle
control
(ETC)
is
an automobile technology which connects the
accelerator pedal to the throttle, replacing a
mechanical linkage. Most automobiles already use
a throttle position sensor (TPS) to provide input
to traction control, antilock brakes, fuel injection, and
other systems, but use abowden cable to directly
connect the pedal with the throttle.
 An ETC-equipped vehicle has no such cable. Instead,
the electronic control unit (ECU) determines the
required throttle position by calculations from data
measured by other sensors such as an accelerator
pedal position sensor, engine speed sensor, vehicle
speed sensor etc. The electric motor within the ETC is
then driven to the required position via a closedloop control algorithm within the ECU.
Control Module
 There are so many different PCMs, accurate identification of the
PCM and its correct replacement is absolutely essential to prevent
unnecessary returns. Accurately identifying the PCM requires not
only the vehicle year, make, model and engine size, but also the
OEM part number on the PCM itself. Most supplier catalogs list
replacement PCMs both ways. Many PCMs appear to be exactly
the same on the outside (same sized box and connectors) but may
be wired or calibrated differently inside.
 The wrong PCM is installed in a vehicle, it may run but probably
will not run well. Close enough is not good enough when it comes
to replacing PCMs. It must be the correct replacement to work
right. Always refer to the OEM number on the PCM and look it up
in the suppliers cross reference index to find the right part. On
some occasions, after the new PCM is installed, it requires a
"flash" operation, to "adapt it" specifically to the vehicle it is
installed in.
Throttle Actuator
 Throttle Actuator is designed to provide
remote control of an engine throttle in
conjunction with a Froude Hofmann
controller. The actuator comprises of a
brushless DC servomotor, driving a linear
precision ball screw. A flexible cable is
supplied for the connection between the
actuator and engine throttle. Alternatively a
customer supplied direct linkage may be used.
Throttle-By-Wire
 Throttle-By-Wire, which is the same as Electronic Throttle
Control (ETC), or "Throttle Actuator Control" (TAC), is
replacing the throttle linkage on more and more late model
vehicles. The mechanical linkage or cable between the
accelerator pedal and throttle body has been replaced with a gas
pedal position sensor and an electronically-operated throttle.
 Throttle-By-Wire eliminates the sticking and binding problems
that sometimes occur with mechanical linkages, and eturn
spring failures that may prevent the throttle from closing (a
runaway engine). Throtle-By-Wire also helps reduce emissions
and improves fuel economy. But the main advantage is that
Throttle-By-Wire allows the engine computer to integrate
torque management with cruise control, traction control and
stability control.
 With cruise control, integrating throttle control into the
engine management system eliminates the need for
external vacuum servos or motors to maintain a
constant vehicle speed. It also makes "adaptive" cruise
control possible (with some additional sensors) so a
vehicle can match the speed of the vehicle ahead of it
and maintain a safe following distance.
 Throttle-By-Wire also provides some warranty
advantages for the vehicle manufacturer, too, by
limiting "abusive driving" by lead-footed motorists. If
you put the pedal to the metal on a car with ThrottleBy-Wire, you won't impress anybody by smoking the
tires. It won't happen -- unless there is an over-ride
switch to deactivate traction control. Even then, the
computer may limit engine torque to certain limits to
protect the transmission and drivetrain from possible
damage.
THROTTLE-BY-WIRE FAILSAFE OPERATION
 For redundancy backup and failsafe operation, the
accelerator pedal usually has two or even three position
sensors. In a 2005 Mustang, three sensors are used. Two
decrease their resistance (increase voltage) when the
pedal is depressed, and the third increases its resistance
(decreases voltage). As long as the position sensor
signals increase and decrease by the same amount
(mirror each other), the circuit is assumed to be working
correctly. But if any of the position signals disagree, it
indicates a fault and the module sets a code and turns on
the Malfunction Indicator Lamp (MIL). On the
Mustang, an electronic throtttle conrol fault will also
illuminate a little yellow wrench warning light.
THROTTLE-BY-WIRE DIAGNOSTICS
 Most of the faults that occurr in a Throttle-By-Wire control
systems are things you would expect, like pedal or throttle
position sensors that wear out and skip or produce erratic
signals, motor failures in the throttle body, and electrical
problems like loose or corroded wiring connectors.
 A code reader or scan tool is required for diagnostics. Generic
OBD II trouble codes for possible pedal position sensor faults
include P0120 through P0124, P0220 through P0229, plus any
OEM enhanced P1 or P2 series codes for that specific vehicle.
 If a fault occurs in the motor on the throttle body, it will be
detected by the feedback signals from the throttle position
sensors. Generic OBD II codes for this kind of problem include
P0638 & P0639, plus any OEM enhanced P1 or P2 series codes
for that specific vehicle.
Throttle-By-Wire Service Precautions
 On some systems, a special relearn procedure is
required when parts have been replaced or the
throttle control wiring harness has been
disconnected. The relearn procedure is necessary
so the control module can learn the rest positions
of the gas pedal and throttle. On some vehicles
this occurs automatically every time the key is
turned on. But on others it requires a scan tool or
special manual procedure. Refer to the OEM
service literature for specific instructions.