ETS, Principle of Operation
ETS, principle of operation
The main purpose of the ETS is to control the throttle butterfly electronically.
On the basis of the information supplied continuously to the ETS control unit, the throttle butterfly is moved to the correct position by the actuator motor according to the signals it receives from the control unit.
The only time the throttle cable operates the butterfly is when the system is in Limp-Home mode. At all other times, this cable is disconnected.
Apart from electronic control of the throttle, which is a condition for anti-spin control, the following functions are also integrated in the ETS:
^ automatic idling control (AIC)
^ increased engine rpm on starting
^ smoothing function on abrupt accelerator movement
^ Cruise Control
^ AC compensation when driving
Automatic Idling Control (AIC)
Although the AIC system used up to now has worked well and reliably, it has a number of weak points that have now been eliminated through the ETS.
Because the air mass that the AIC valve admitted through the throttle housing for idling speed compensation (when the AC system cut in, for example) varied according to pressure and temperature, the compensation it provided also tended to vary in some degree with ambient conditions.
However, since the AIC function in the ETS is adaptive, compensation for pressure and temperature takes place continuously so that the opening duration of the AIC valve and the angle of the throttle butterfly will always be exactly right in relation to the air mass required for correct idling speed compensation.
This means that the ETS compensates for power consumers not only at idling speed but also throughout the entire engine speed range, except at full throille.
The delay of 200 millisecond previously provided by the time relay has now been replaced in the ETS by an adaptive time function.
The result of these changes is that compensation for power-consuming equipment is now so smooth as to be scarcely perceptible - only the clicking of the AC relay can be heard.
The dashpot function in the ETS is incorporated as a control function in the AIC for reducing engine speed from about 1150 rpm to 850 rpm when the AC is switched on. The function switches off the AC at 1150 rpm and switches it on again once a stable speed of 850 rpm has been reached or after a maximum of five seconds (if the engine is cold, these rpm limits will be slightly higher).
Increased engine rpm on starting
Cold engine
Depending on the temperature of the coolant, engine rpm will be increased as appropriate immediately after starting
During the subsequent warm-up phase, engine speed is gradually reduced to nominal idling speed (850 rpm) in accordance with a preprogrammed map.
Warm engine
To improve starting when the engine is warm, a brief (about two seconds) increase in engine revs occurs on starting to help the engine cope with any additional load, vapour bubbles in the fuel supply, etc.
Smoothing function on abrupt accelerator movement
When there is a sudden change of load on the engine, through either acceleration or deceleration, the throille butterfly is moved to the new position in two stages.
In the first stage, it is moved to an intermediate position for about 80-200 milliseconds (the time varies according to how abruptly the accelerator is pressed or released) to give the engine mountings time to "stiffen up" before the bullerfly is moved to the required position in the second stage.
Through this two-stage operation, sudden changes in engine load are less noticeable.
The process itself is imperceptible to the driver, who will be unaware of any delay.
Cruise Control
The Cruise Control function is incorporated in the ETS. It is controlled by the relationship between torque and engine rpm at any given instant, in accordance with a preprogrammed map.
The throttle bullerfly angle is adjusted to maintain the selected speed at any given moment under all driving conditions (engine-load conditions). The system is automatically and immediately deactivated on depression of either the brake or clutch pedal, or if the switch is moved to the OFF position. The SET (tip-up) and RESUME (tip-down) bullons can be used to increase or decrease the speed of the car in steps of about 1.5 km/h (1 mph) at a time.
The Cruise Control system receives information on the following parameters:
^ speed signal from speedometer (1)
^ speed information from the TC/ABS (2)
^ engine rpm (3)
^ status of SET, RESUME and ON/OFF (4)
^ status of brake and clutch switches (5)
^ status of brake light switch (6)
The Cruise Control system transmits information on the following functions:
^ isolator valve for turbo bypass valve (7)
^ throttle butterfly angle (8)
ETS control unit input signals
The ETS control unit receives data on the following parameters:
^ Position of throffle butterfly (1)
^ Position of accelerator pedal (2)
^ Status of AC compressor (on or off) (3)
^ Road speed (from speedometer sensor) (4)
^ Engine rpm (from crankshaft sensor via Dl system) (5)
^ Engine load (Tq) from LH system (6)
^ Current status of various safety switches (7): throttle sensor, accelerator sensor, brake-pedal sensor, clutch-pedal sensor, brake light switch
^ Status of Cruise Control system (8)
^ Engine temperature (coolant temperature) (9)
^ TC/ABS information, e.g. wheel speed and torque reduction on occurrence of wheelspin (10)
All these input signals are continuously processed in the control unit, not only for continuous control of the throttle but also for monitoring and controlling other functions.
Throttle butterfly position
Since controlling and monitoring the position of the throttle butterfly are the main functions of the ETS, several circuits are connected between the control unit and the throttle housing.
The throttle housing accommodates the actuator motor, throttle potentiometer, safety switch and vacuum unit.
The position of the throttle (butterfly angle) is determined at any given moment by the control unit on the basis of the signal received on pin 16 (BU/WH) from pin 4 of the throttle potentiometer.
Safety switch (Throttle switch)
The safety switch, which is connected to the throttle butterfly, is open in the idling position~ In this position a certain decrease in voltage occurs across the fixed resistor connected in series with the supply to pin 28 of the control unit. When in response to accelerator depression the throttle butterfly moves past a certain opening angle, the safety switch closes and connects an additional resistor in parallel with the first resistor As a result, the voltage drop in the supply circuit changes and with it the voltage level on pin 28.
Accelerator position
A sensor (potentiometer) senses the current position of the accelerator pedal.
The control unit determines the pedal position from the signal received on pin 17 from pin 2 of the pedal potentiometer.
Variations in signal strength are translated by the control unit into information about the throttle openmg called for by the accelerator.
Safety switch (Pedal switch)
The safety switch, which is connected to the pedal potentiometer, is open in the idling position. In this position a certain decrease in voltage occurs across the fixed resistor connected in series with the sup ply to pin l4ofthe control unit. When in response to accelerator depression the pedal potentiometer moves past a certain position, the safety switch closes and connects an additional resistor in paral lel with the first resistor. As a result, the voltage drop in the supply circuit changes and with it the voltage level on pin 14.
Status of AC compressor
Since idling compensation when the AC is switched on is an intergrated function of the ETS, no separate A/C valve is fitted.
Since engine rpm compensation when the AC is switched on is governed by the ETS control unit, no change in engine rpm is perceptible.
Another improvement incorporated in the system is that engine rpm compensation when the AC is switched on occurs throughout the entire engine speed range.
Note that the AC cannot be switched on the system is in Limp-Home mode.
Road speed
The control unit receives information about the road speed from two different sources: from the speed sensor at the rear of the instrument, and from the TC/ABS control unit (the mean value of the two rear wheels).
By comparing these signals and indicating a fault when they do not coincide, it is possible to check that both systems are working properly and also achieve a high degree of safety.
The speed signal from the instrument is used for controlling the Cruise Control system, although the speed signal from pin 29 of the TC/ABS must also be correct for the Cruise Control to work properly.
Note:
On TCS automatic the ABS control unit sends in formation on wheel speed to the ASR control unit, which then forwards this information to pin 29 of the ETS control unit.
Engine rpm
The ETS control unit receives information about cur- rent engine rpm from the DI/APC control unit, which receives engine rpm signals from the crankshaft sensor behind the pulley on the crankshaft. This information is used by the system for temperature- related control of engine rpm immediately after starting.
Once the coolant temperature has reached 58°C (136°F), engine speed is gradually reduced to normal idling speed in accordance with a preprogrammed map.
Engine load
The engine-load signal (Tq). Which is recorded by the LH control unit, is an indication of the mass of the of the induction air and is used by the ETS when Cruise Control is selected and for detecting when fuel shut-off occurs.
The load signal (Tq) is also compared with the engine rpm signal (Td). If the relationship between Td and Tq is outside reasonable limits, the ETS control unit initiates a warning by setting fault code 2/44690.
Safety switches
Throttle switch ETS Components
Accelerator switch ETS Components
Brake-pedal and clutch-pedal switches
These switches are connected in series in the supply circuit to pin 36 of the control unit, which is supplied with battery voltage when neither pedal is depressed. Depressing either of the pedals immediately breaks the supply circuit and the level on pin 36 drops to 0 V, thus disconnecting the Cruise Control.
Brake light switch
The brake light switch is connected to pin 15 of the control unit. As long as the brake pedal is not depressed there will be no voltage on pin 15, but the pin will be supplied with battery voltage as soon as the pedal is depressed.
The control unit compares the status of pin 15 with the brake information received from the control unit.
Engine temperature
An NTC resistor is used to provide information about engine temperature (coolant temperature). This information is used for controlling the increase in engine rpm immediately after starting.
ETS control unit output signals
The ETS control unit emits the following output signals:
^ Signal to throttle butterfly actuator motor (PWM)(1)
^ Signal to turbo bypass valve (earth) (2)
^ Signal to ETS main relay (earth) (3)
^ Signal to ETS safety valve (earth) (4)
^ Diagnostics signal (pulse train) (5)
^ Signal to TCS-CTRL lamp (earth) (6)
^ Throttle information to other systems (PWM) (7)
^ Signal to AC relay (earth) (8)
Control signal for actuator motor
The signal from the pedal potentiometer is processed by the ETS control unit which sends a control signal to the throttle butterfly actuator motor, connected across pins 20 and 21 of the control unit.
The PWM signal to the actuator motor is pulse-width modulated, which means that the width of the pulse determines the butterfly angle set by the motor.
Output signal to isolator valve for turbo bypass valve
The purpose of the isolator valve is to isolate the turbo bypass valve when the car is driven with the Cruise Control system selected or when TCS braking occurs. This prevents the bypass valve from Oscillating between the open and closed positions, which would cause variations in boost pressure and speed.
When Cruise Control is selected or TCS braking occurs, the solenoid valve is earthed via pin 6 of the control unit, closing the circuit and causing the valve to close. When the valve is closed it no longer Oscillates between the open and closed positions and the force of the spring can hold it closed.
Signal to ETS main relay
When the operating current for the main relay is earthed via pin 13 of the control unit, the relay op- erates and connects the + 30 supply to the system.
When safety-related faults arise in the system, the earth connection at pin 13 is broken, the relay releases and the +30 supply is interrupted.
When this occurs, the power supply to the safety valve on the bulkhead partition will also be cut off. This causes the valve to close the vacuum hose between the inlet manifold and the vacuum unit of the throttle housing.
When the vacuum in the throttle housing is lost, the butterfly lever moves back to the idling position and the throttle cable is tensioned, i.e. the car goes into Limp-Home mode.
Output signal for diagnosis
The ETS interface with the ISAT is via pins 34 and 9. Communication is in the form of pulse trains which makes it possible for any fault codes to be transferred from the system to the ISAT, and for the ISAT to send command codes to the system for activating certain system functions, clearing fault codes from the memory, etc.
Output signal to TCS CTRL warning lamp
When a fault occurs in the ETS that can affect the performance of the system, the lamp circuit will be earthed at pin 23 of the control unit so that the warnmg lamp lights up.
To identify the fault that caused the warning lamp to light up, connect the ISAT to the diagnostics socket and carry out the relevant test procedures.