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EyeOnElectronics The adoption of Electronic Throttle Control may mean the command to ‘step on it’ will have a very different meaning for future generations of drivers. fter 22 years of making S-10s, by way of the cable itself. The assembly is a multi- General Motors announced this strand wire cable linked at each end to the gas fall the introduction of its new pedal and the throttle plate. This represents quite Chevy Colorado/GMC Canyon a few parts that must be assembled and installed Mike Dale trucks. Tucked in among all of into cramped spaces. A third issue is that what the the new and improved standard driver wants, and what the engine might need to features were the letters “ETC.” That stands for produce the best fuel economy and best emis- AElectronic Throttle Control, and it’s been sions performance, are often not the same. En- around in small volumes since BMW intro- gine tuners have known that software programs duced it in 1988. For the last three years, ETC that intervene between the driver and the engine has been finding its way into higher end domes- could result in more precise throttle control that tic vehicles. What’s new is that ETC is now a would lead to improved engine performance. standard feature on a mass-market, high-volume ETC, or drive-by-wire, is a great example of vehicle that sells for as little as 14 grand. how tactical can be turned to practical. Most GM is not the only carmaker that has added of the work to prove that these systems would ETC; Subaru has announced that all of its 2005 be safe in automobiles was first done to prove models will have it, and Ford’s flagship vehicle, the they were safe in military and civilian aircraft. F-150, has it as well. ETC as a technology has ma- Some of the newest planes cannot fly at all tured—the price is down, the value/performance without constant computer monitoring and ad- is up and as a result, ETC has gone mainstream. justment of the control surfaces. It was the Engine speed has always been controlled by need for ultra-reliable, remotely computer- controlling the amount of air flowing into the controlled actuation in airplanes that has driv- engine. This throttle plate positioning has tra- en drive-by-wire technology. ditionally been handled by a mechanical link- A driver’s intent is received by a Throttle Pedal age (a “Bowden” cable), in combination with Assembly (TPA), which may have as many as three springs, pulleys and other hardware. parallel, redundant position sensors. In addition, While the there are idle and WOT switches that monitor Bowden cable minimum and maximum input from the driver. assembly has The TPA also has the secondary purpose of creat- worked pretty ing the normal “feel” of the mechanical cable and well for a long springs it replaces. time, it has On the throttle body, throttle position is con- some disad- trolled by a motor that can rotate the throttle vantages. plate from 1° to 80°. In typical ETC systems, sig- From NVH nals from the computer can command the motor and assembly to rotate the throttle plate with an accuracy of standpoints, better than ±.5° over most of the range, with the throttle ca- even tighter .1° accuracy at idle. The motor itself ble represents is fitted with multiple position sensors to com- a hole through plete a feedback loop to the computer. Once the the firewall computer sends its instructions to the motor, it Photo: Mike Dale Mike Photo: This is the throttle position assembly that goes in and a passage- listens to the sensors to make sure the action has the 2004 Chevy Colorado. With only the wire harness way for engine taken place correctly. to attach to it, it’s easier for assembly line workers noise to get in- The motor itself works on the principle of to install, and there’s one less hole in the bulkhead. to the vehicle magnetic bucking. Here, there are two opposing continued on page 23 16 March 2004 Eye On Electronics magnetic fields, and pulse width mod- tion problems, with the result that the ulation techniques are used to deter- PCM reduces throttle angle despite mine the size of one field vs. the other. what the driver seems to want. By increasing the percentage of ON ETC makes the implementation of time, greater amounts of rotation are these vehicle features almost a matter achieved. As a fail-safe measure, the of a few switches and software. The throttle plate is spring-loaded so that if money taken out of cruise and traction power should fail, the plate returns to control more than offsets the cost of the idle position. the added ETC components. The automakers are after a handful of Another part of what made it feasi- the advantages ETC has to offer. One is ble to implement ETC is that the improved emissions performance. In the price came down. In the first-genera- deceleration mode, for example, the tion version of this technology (called driver takes his foot off the gas, closing Throttle Actuator Control), all the the throttle plate. The continued rotation processing of the sensor and actua- of the engine creates a high intake mani- tors was done by a separate TAC fold vacuum that can lead to fueling er- module that then fed its information rors. By putting software algorithms in to the PCM. The most recent PCMs between the TPA and the stepper motor, include the ability to take the sensor GM expects to realize as much as a 15% inputs directly, then respond with the reduction in HC and NOX. On one mod- appropriate information to the throt- el, GM was able to eliminate the AIR tle plate actuator. pump used to inject air into the exhaust One effect of this is improved vehicle system. From a corporate standpoint, reliability. By having a single throttle po- that allows more vehicles to fit into the sition controller, the overall number of Low Emission Vehicle (LEV) categories. parts is greatly reduced. Fewer parts In a paper published by SAE, Delphi means fewer electrical connections and points to other advantages to its version. mechanical interactions. Reliability re- Its system integrates unique driver per- search has shown this is the right thing to formance features such as driver-selec- do. From an electronics point of view, table pedal response (Power for perfor- any circuit is only as good as its connec- mance, Winter for control) altitude tions, and the fewer of them the better. compensation for more normal pedal This is more important than it may response in the mountains and vehicle sound. Microprocessor chips are inex- and engine speed governors to protect pensive (generally in the 80-cent range the vehicle and the engine from “un- for the simple ones). What’s expensive is wise” pedal positions. (You’d have to all the rest of the stuff needed to sup- think the rental car companies asked for port the microprocessor. Having a sepa- that feature.) There are a couple of rate TAC module means an extra pack- driveability-related features, as well— age, space for it, more cables and con- tip-in bump elimination on manual nectors, extra components such as a cir- transmissions and an engine timing re- cuit board, a clock oscillator, EMI/RFI tard feature to improve catalytic con- suppression, etc. By the time a micro- verter light-off on startup. processor that costs less than a buck is It may not seem obvious, but when packaged into the system, the cost you look at the vehicle as a whole, ETC could be more than ten times the cost is cheaper than the Bowden cable. of the silicon. Getting all of the process- What Delphi and other OEMs have ing inside the ECM was a major step. done is integrate the ETC feature into The current information is that about the cruise, idle and, if so equipped, trac- 25% of 2004 vehicles will have some tion/stability control strategies. Once variation of Electronic Throttle Control the actuator motor is in charge of throt- when production runs are completed. tle position, and under control of the Hella Corp., a manufacturer of throttle PCM, it can provide such functions as position assemblies, believes the entire idle control and speed control. This industry will have converted over within eliminates the IAC motor and the ten years. Given that ETC is a solution cruise control servo. ABS wheel speed that does more, and costs less, it may sensor data can be used to detect trac- happen a lot sooner than that. March 2004 23.

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