ETS Components
Technical description: ETS
ETS components
The main purpose of the electronic throttle system (ETS) is to control by electronic means the position of the throttle butterfly in the throttle housing. Apart from the electronic control unit itself, the system consists of comparatively few components.
The throttle housing is equipped with an actuator motor for the throttle butterfly, a vacuum unit, a throttle potentiometer and a safety switch.
Connected to the accelerator is a pedal sensor with a potentiometer and safety switch. Mounted on the bulkhead partition and right-hand wheel housing are solenoid valves and a non-return valve.
For additional safety, a parallel system incorporating a throttle cable is provided, which will take over for driving in the Limp-Home mode.
ETS control unit
The control unit is the brain of the ETS.
The control unit receives information about a variety of engine parameters which it processes before sending appropriate control signals to the throttle housing.
The control unit has an integral self-diagnosis function which is activated every time the ignition is switched off. In this "power-off"condition, automatic testing of all the functions takes place and the latest adaptive limits are programmed in the memory.
The control unit monitors system functions continuously and if any safety-related fault is detected it switches in the Limp-Home mode,
which means that throttle control will be by means of a conventional throttle cable.
The ETS control unit has a 38-pin interface and is mounted on the bracket under the driver's seat.
Throttle housing
In the throttle housing, the main purpose of which is to regulate the amount of air supplied to the engine, the position of the butterfly is controlled by means of a PWM d.c. motor (PWM stands for Pulse-Width Modulated). In the following, this will be referred to as the throttle actuator motor.
A conventional system incorporating a throttle cable is connected in parallel for use in the emergency Limp-Home mode.
Electronic control of the throttle by the control unit provides direct and very precise positioning of the throttle butterfly in proportion to
accelerator pedal travel.
Exhaustive testing of the control function has enabled the same pedal feel to be achieved as with a conventional accelerator.
Throttle housing, normal mode
When the engine is started, a vacuum is raised in the vacuum unit (1).
This causes the diaphragm rod and lever assembly (2) to move upwards, allowing the spring (3) to go slack.
This action also causes the throttle-cable attachment lever (4) to turn forwards, slackening the cable and allowing the butterfly (5) to be moved between the idling and full throttle positions by the motor (6). The motor actuates the throttle spindle (7) via a rod (8) attached at either end to levers on the motor and spindle.
Throttle housing, Limp-Home mode
If a fault should occur anywhere in the system, a safety valve (2) on the bulkhead partition immediately exhausts the vacuum in the vacuum unit (1).
The diaphragm rod and lever assembly (3) moves down, tensioning the spring (4) so that the full force of the spring is brought to bear on the throttle spindle (5)At the same time, the throttle butterfly and motor are returned to a position just before the idling position.
Since the motor is not powerful enough to overcome the force of the spring and operate the throttle butterfly, the throttle can only be operated by the throttle cable.
The car is now in the Limp-Home mode, which is clearly evident from the additional force required to depress the accelerator and the fact that the TCS CTRL lamp is alight.
Throttle housing, actuator motor
A PWM d.c. motor is used to control the throttle butterfly.
The action of the motor (1) is transferred to the butterfly (2) by a rod (3)connected at each end to levers (5) on the motor and throttle spindle (5).
Throttle housing, vacuum unit
The vacuum unit in the throttle housing is in communication with the inlet manifold via a safety valve on the bulkhead partition.
This communication is controlled by the valve, so that starting the engine causes a vacuum to be raised in the vacuum unit and the conventional manual throttle system becomes inoperative.
Safety switch
The actuator motor in the throttle housing incorporates a safety switch which closes when the butter-fly opens beyond a preset angle.
A similar safety switch is incorporated in the pedal sensor. If the status of the two switches - in the throttle housing and pedal sensor - is not the same, i.e. if the accelerator has been released and the butterfly is open too far or vice versa, the car will go into Limp-Home mode.
Position sensors (potentiometers)
The system incorporates two potentiometers, one in the throffle housing to sense the position of the buttertly and the other in the pedal sensor, which is the one that determines the position of the bullerfly.
The potentiometer in the throtte housing indicates the actual position of the butterfly and this signal is compared with the signal from the pedal sensor. The two signals should coincide with each other.
Safety valve
The safety valve is a solenoid valve mounted on the bulkhead partition.
When the engine is started, the valve opens cornmunication between the inlet manifold and the vacuum unit in the throttle housing and normally remains open while the engine is running.
Should a fault occur in the system, however, the valve opens the port to atmosphere, exhausting the vacuum in the vacuum unit. At the same time, the system switches to the Limp-Home mode and the conventional throttle-cable system takes over.
The conventional throttle system incorporates a spring which is too strong for the actuator motor to overcome. This eliminates any risk of the motor interfering with the conventional throttle-cable control.
Also connected to the safety valve is a non-return valve, the purpose of which is to prevent turbo pressure from entering the vacuum unit and so causing the conventional throttle-cable system to be activated.
Isolator valve for turbo bypass valve
Mounted on the left-hand wheel housing is a solenoid valve, the function of which is to isolate the turbo bypass valve under certain conditions.
The valve is activated when Cruise Control has been selected, and also when TCS braking occurs, to avoid the disruptive effect that the turbo bypass valve could otherwise have on drivability.
Operating principle of the turbo bypass valve
To understand the function of the isolator valve, it is necessary to be familiar with the way the turbo bypass valve works.
Accelerator depressed
When the turbocharger is in operation, the compressor pressurizes the air inside the turbo delivery pipe, throttle housing and inlet manifold, at the same time as a depression (negative pressure) forms in the intake pipe.
As long as the throttle is open, boost pressure acts on both sides of the diaphragm in the bypass valve, which is held closed by the combined efforts of the spring inside the valve and the boost pressure from the inlet manifold.
Accelerator released
When the throttle is closed, combustion inside the engine quickly creates negative pressure in the inlet manifold while the boost pressure upstream of the throttle remains unaffected.
To avoid a sudden rise in pressure inside the inlet manifold (and resultant jerky performance) when the throttle is opened again, the boost pressure upstream of the throttle must be "dumped".
Through the negative pressure in the inlet manifold, negative pressure also acts on the spring side of the bypass valve. Since the force of the spring alone is not sufficient to resist the pressure acting on the other side of the diaphragm, the valve opens and dumps the boost pressure from the turbo delivery pipe and throttle housing into the intake pipe.
Cruise Control selected or TCS braking active
When Cruise Control has been selected or TCS braking occurs, the isolator valve acts to shut off communication between the inlet manifold and the bypass valve.
Communication is opened instead to the throffle housing (upstream of the bufferfy), with the result that boost pressure acts on the spring side of the diaphragm in the bypass valve. The combined forces of the boost pressure and the spring are sufficient to hold the valve closed.
Boost pressure is still present upstream of the throttie butterfly.