Electronic Throttle Controle System
ABSTRACT The ETCS system allows the ECM to precisely control the opening and closing of the throttle valve based on drivers input and is also interrelated with chassis control ECUs such as Traction Control and Vehicle Stability Control (Skid Control ECU). Introduction The Accelerator Pedal Position Sensor (APPS) detects the accelerator pedal position (driver input) and sends a signal to the ECM. Based on the input from the APPS and other ECUs (ABS, TRAC and VSC), the engine ECM directs the Throttle Control Motor to change throttle valve position.
The Throttle Position Sensor (TPS) detects throttle valve angle and confirms to the ECM that the desired throttle valve position has been achieved. Both the APPS and the TPS have two sensing elements. ? Electronic Throttle Control System-intelligence provides several advantages over a mechanical linked throttle valve system as the ECM can position the throttle valve for optimum performance under a variety of conditions. ? The ETCS-i system gives the ECM precise control over the opening and closing of the throttle valve, based upon the driver’s input (accelerator pedal). And in conjunction with input from chassis control ECUs, such as those for Traction Control and Vehicle Stability Control (Skid Control ECU). ? This system not only enhances drive line control, but also assists in reducing tailpipe emissions and improving fuel economy. ETCS Control modes • The ECM drives the throttle valve to a specified angle as determined by operating conditions. • Different throttle valve angles in relation to the accelerator pedal position are used to achieve different engine output characteristics. • The following describes the different modes that affect throttle valve angles. Non-linear Control – Non-linear control means the ECM can control the throttle valve opening rate and position based on such factors as accelerator pedal effort and engine rpm to achieve better performance and comfort. In slippery conditions, the throttle valve can be controlled to aid in vehicle stability. ? Shift Shock Reduction Control – The throttle control is synchronized to the Electronically Controlled Transmission control during the shifting of the transmission to reduce the shift shock. ? Idle Speed Control – The ECM adjusts the throttle opening to maintain the target idle speed. TRAC Throttle Control – As part of the TRAC system, the throttle valve is closed by a demand signal from the ABS, TRAC, and VSC ECU if an excessive amount of slippage is occurring at the driven wheel. ? VSC Coordination Control – VSC performance is enhanced when the throttle valve opening angle is modified by the ABS, TRAC, and VSC ECUs. ? Cruise Control – ETCS-i eliminates the need for a separate cruise control system. Cruise control strategies and functions are incorporated into the ECM. [pic] Types of ETCS ? Link type system (1st Generation) ? Linkless type system (2nd Generation) pic] COMPONENTS OF ETCS ? Acceleration Pedal Position Sensor (APPS) ? Throttle Position Sensor ? Throttle Control Motor ? Magnetic Clutch ? Thermostat ? Fail-Safe ? Acceleration Pedal Position Sensor (APPS) – The APPS, which is mounted on the throttle body, is integrated with the throttle lever. The throttle lever is connected by cable to the accelerator pedal. As the driver moves the accelerator pedal the APPS signal voltage changes indicating pedal position. There are two voltage output signals from the APPS. The ECM uses these two signals to calculate the desired throttle valve angle.
Also, by using two signals the ECM is able to compare and detect if there is anything wrong with the APPS’s performance. Constructions The non-contact type accelerator pedal position sensor uses a Hall IC. The magnetic yoke that is mounted on the accelerator pedal arm rotates around the Hall IC in accordance with the amount of pressure that is applied to the accelerator pedal. The Hall IC converts the changes in the magnetic flux that occur at that time into electrical signals, and outputs them as accelerator pedal pressure to the engine ECU. The Hall IC contains circuits for the main and sub-signals.
It converts the angle of the depressed accelerator pedal into electric signals with two differing characteristics and outputs them to the engine ECU [pic] | | ? Throttle Position Sensor – The TPS is used to detect the actual angle of the throttle valve. This signal indicates to the ECM throttle valve position and that the throttle valve moved to the desired angle. Throttle valve position detection is necessary for the ECM to make adjustments to the throttle valve position and to detect if there is a failure in the system. Construction
The throttle valve position sensor is mounted on the throttle body to detect the opening angle of the throttle valve. Non-contact type throttle valve position sensors are used. The sensors use Hall ICs which are mounted on the throttle body. The Hall ICs are surrounded by magnetic yokes. The Hall ICs convert the changes that occur in the magnetic flux into electrical signals The Hall ICs contain circuits for the main and sub signals. They convert the throttle valve opening angles into electric signals with two different characteristics and output them to the engine ECU [pic] Throttle Control Motor – The throttle control motor is a DC motor controlled by the ECM. The ECM controls the direction and the amperage of the current through the motor. The circuit is pulsewidth modulated (duty ratio cycle regulated). If there is a malfunction in the system, the ECM shuts the circuit (and clutch circuit) off and the return springs close the throttle valve. The ECM will turn the motor off if there is excessive amperage or not enough amperage in the motor circuit. ? Magnetic Clutch – Under normal operation, the magnetic clutch connects the throttle control motor to the throttle valve.
The circuit is pulsewidth modulated reducing power consumption. If there is a malfunction in ETCS-i, the ECM turns off the clutch circuit (and motor) if there is too much or not enough amperage in the circuit. ? Thermostat – A thermostat is installed in the throttle body to shut off the flow of coolant when coolant temperature is high. This prevents the throttle body from heating up the intake air reducing performance. The thermostat uses a wax expansion valve to open and close the coolant passage. ? Fail-Safe – If an abnormal condition occurs with the ETCS-i, the MIL will illuminate to alert the driver.
At the same time, current to the throttle control motor and magnetic clutch are cut off. With no power to the motor or magnetic clutch, the return spring closes the throttle valve to the default position. In this situation, called limp mode, the accelerator pedal operates the limp mode lever. When in limp mode, the throttle can only be partially opened reducing engine power. Furthermore, ISC and cruise control systems will not operate. ETCS Throttle Motor Circuit Operation The ECM controls the direction and amount of current needed to activate the throttle control motor to adjust throttle valve position. | | | | | | | | | | | | | | | | | The throttle motor can be in any one of the following five modes: ? Default position ? Throttle closing ? Throttle opening ? Throttle hold ? Idle speed control. The motor circuit consists of four control transistors on the MO and MC circuits. One transistor supplies power and the other transistor completes the path to ground.
This configuration allows the ECM to control the direction of current through the motor. This circuit is also pulsewidth modulated to control the rate of throttle movement and to hold the throttle in a given position. For rapid throttle opening, the pulse width duty ratio will be high (current flow high) for rapid movement. To hold the throttle in the desired position, the ECM applies enough current to oppose spring pressure. If the traction control mode is engaged, the pulsewidth will be less, limiting the rate of opening from idle.
If the throttle valve is opened too far, the ECM will decrease the pulsewidth closing the throttle. ? Default Position When there is no current applied to the motor, the springs hold the throttle valve in the default position. This condition occurs when the engine ignition key is off or when the ECM has detected a failure in the ETCS-i system. When a failure is detected, current to the motor and clutch is turned off. These actions disengage the motor from the throttle shaft and prevent the motor moving the throttle valve.
In this state, the idle is higher than normal when the engine is at operating temperature. The throttle valve will move if the driver presses down further on the accelerator pedal. ? Throttle Hold To maintain the desired throttle valve angle, the applied duty ratio creates enough force in the motor to oppose spring pressure. ? Idle Speed Control The throttle valve is adjusted to maintain the desired idle speed. If the desired idle speed needs the throttle valve below the default position, the throttle close circuit is activated. Any decrease in duty ratio will open the throttle valve and raise engine RPM.
If the desired idle speed needs the throttle valve above the default position, the throttle open circuit is activated. How Electronic Throttle Control Systems Work Up until the late 1980s, most cars had a fairly straightforward throttle control. You stepped on the accelerator pedal, the throttle opened, and air flowed into the engine, where it mixed with gasoline and burned. This burning gas powered the car’s wheels, getting you down the road. If you wanted to go faster, all you had to do was step down harder — the throttle would open wider, giving the car more power.
But electronic throttle control, which is sometimes called drive-by-wire, uses electronic, instead of mechanical, signals to control the throttle. That means that when you step on your car’s gas pedal, instead of opening the throttle, you’re activating an accelerator pedal module, which converts the pressure you put on the pedal into an electric signal. That signal is then sent to an electronic control unit, which takes your inputs into account, as well as outside variables, to open the throttle for optimum efficiency and performance. Link type system operation The throttle motor operates the throttle valve. ? An electromagnetic clutch connects the throttle motor to the throttle valve. ? The throttle position sensor detects throttle valve angle. ? The Accelerator Pedal Position Sensor (APPS) detects accelerator pedal position. ? The throttle lever is connected by cable to the accelerator pedal. ? As the driver moves the accelerator pedal, the APPS signal voltage changes indicating a new pedal position. ? The ECM then adjusts the throttle angle based on the APPS signals, engine conditions and vehicle conditions. [pic]
Linkless type system operation ? The linkless ETCS-i uses a compact throttle body. ? No mechanical connection between the accelerator pedal and throttle body. ? The Accelerator Pedal Position Sensor is mounted at the accelerator pedal. ? As the driver moves the accelerator pedal, the APPS signal voltage changes indicating a new pedal position. ? The ECM then adjusts the throttle angle based on the APPS signals, engine conditions and vehicle conditions. ? The throttle position sensor detects throttle valve angle. ? This system does not use a magnetic clutch. Operation of this system is nearly identical to the link type [pic] Types of Accelerator and Throttle position sensors: 1. Non contact type sensor. 2. Contact type sensor • While the sensors generate their output signal in a different process, common similarities included: • The Sensor operate at 5. 0 volts which is supplied by the ECM’s VC power source • They utilize the same sensor ground terminals of the ECM, E2. • They both output a linear DC voltage • Fail Safe mode: • Accelerator position sensor: [pic]
The accelerator pedal position sensor is comprised of two sensor circuits. If a malfunction occurs in either one of the sensor circuits, the engine ECU detects the abnormal signal voltage difference between these two sensor circuits and switches to the ‘limp-home’ mode. The ‘limp-home’ mode operates by calculating the angle of the depressed accelerator pedal. If both circuits have a malfunction, the engine ECU detects the abnormal signal voltage from these two sensor circuits and stops the throttle control. At this time, the vehicle can be driven within idling range. Throttle position sensor: [pic] The throttle position sensor is comprised of two sensor circuits. If a malfunction occurs in either or both of the sensor circuits, the engine ECU detects the abnormal signal voltage difference between these two sensor circuits. It cuts off the current to the throttle control motor and switches to the ‘limp-home’ mode. The force of the return spring causes the throttle valve to return and stay at the prescribed opening angle. At this time, the engine output is regulated through the control of the fuel injection (intermittent fuel-cut) and ignition timing.
The same control as above is activated if the engine ECU detects a malfunction in the throttle control motor system [pic] Benefits of Electronic Throttle Control Electronic throttle control systems may seem a little silly. After all, if a mechanical throttle control system works, why make it more complicated? While it’s true that electronic throttle control adds complications, it also adds a number of benefits. The first is decreased maintenance. Mechanical throttle systems, because they are made up of a lot of moving parts, are subject to a lot of wear. Over the life of the car, the various components can wear out.
By comparison, an electronic throttle control system has comparatively few moving parts — it sends its signals by electric impulse, not moving parts. That reduces wear and the amount of maintenance needed on the system. Conclusion In a mechanical system, the throttle relies only on driver input to decide how far to open or close. With an electronic throttle control system, the main control unit not only reads input from the driver’s foot on the accelerator, but it also examines input from wheels that are slipping, wheels that have grip, the steering system and the brakes, helping correct driver error and keep the car under control.
In other words, a throttle control system can balance several factors that affect a car’s speed and direction — not just a foot on the pedal. Plus, electronic throttle control is a key component in most cruise control systems. Electronic throttle control may be a complex system, but it makes driving a car easier and safer, and it can reduce maintenance. References http://www. insideline. com/toyota/toyota-throttle-control-and-electromagnetic-interference-testing-presentation. html/ http://auto. howstuffworks. com/car-driving-safety/safety-regulatory-devices/electronic-throttle-control-systems1. html/ http://en. wikipedia. org