Toyota's Prius in many respects can be considered to have two engine controllers: one for the traditional, 1.5-liter gasoline engine and another for the electric motors used to power the car alternatively.
Starting with the petrol-powered side of the equation, the engine control module (ECM) must constantly monitor a number of input sensors to assess the state of the engine and its own primary inputs of fuel, air and fire. Airflow monitoring occurs by way of an optical chopper sensor whose output frequency is proportional to flow rate. An engineered vortex in the intake plenum creates a wake in which a mirrored vane flutters faster or slower depending on airflow, with the vane forming the mirrored reflector of the chopper. An oxygen sensor that monitors for proper air/fuel mixture is used as the input to detect either rich or lean conditions. Crankshaft and camshaft position, vehicle speed, throttle position, engine/intake-air temperature, knock detect and other engine conditions are among the additional inputs to the ECM.
Output functions of the ECM are primarily used to affect airflow, fuel injector delivery, intake valve closure angle and spark timing as a means to close the control loop in the engine, maintain optimal power delivery and minimize emissions. Injector solenoids are pulse-width-modulated to control fuel delivery volume and timing. Separately, the spark timing is driven to control detonation precisely. Ignition timing is retarded when the piezoelectric knock sensor input indicates pre-detonation. Further efficiency refinement is achieved by extending the intake valve opening (Atkinson Cycle operation) to reduce displacement effectively, since the intake valves remain open partway into the compression stroke.
The hybrid vehicle engine control unit (HVECU) manages control of the electrical drive plant. Heavy communication with the ECM coordinates the relative contributions of gas power, electric power or, in many cases, the combined efforts of the two systems to provide propulsion.
As with the ECM, the HVECU has its own set of inputs and outputs to implement a closed-loop control system. Much of the HVECU interaction occurs with the two motor generator units of the Prius (MG1 and MG2), which provide drive or recovered energy (the latter during regenerative braking). Here, a motor speed/position sensor in the MG1 and MG2 are used as inputs to the HVECU, along with shift-level position and even accelerator pedal position.
While the inverter/converter unit (ICU) handles all of the electrical conversion in the system, the HVECU is instrumental in the control of the ICU, whose operation is responsible for energy delivery and recovery to and from MG1 and MG2.
The ECM and HVECU share common attributes in their implementation. Although both are housed inside the car cabin, their physical construction reflects an emphasis on reliability, with sturdy housings and protective coatings on the entire circuit board assemblies. The quad flat packs and other peripheral-leaded IC device packaging used throughout both engine control boards boasts a long record of reliability. Without an emphasis on miniaturization, "what we know works" seems to drive technical choices.
The two engine control modules use a common Toyota-branded NEC µPD70F3155 32-bit microprocessor as the primary source of computing power. Neither the ECM nor the HVECU contain discrete memory components; the NEC processor die contains both the volatile working memory and the nonvolatile ROM used to store control code.
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The rest of the ECM components are custom to the module manufacturer, Denso, and most appear visually to implement mixed-signal interfaces at the inputs and outputs where sensors must be digitized and actuators driven.
A more complex set of ICs supports the NEC microprocessor on the HVECU. Two Mitsubishi 16-bit microprocessors are each paired with a Tamagawa AU6802N1 angle encoder and a custom Toshiba analog device, perhaps corresponding to the MG1 and MG2 input interfaces. Another pair of Mitsubishi 16-bit controllers in the HVECU probably manages communications with the ICU, ECM and skid-control module.
Custom Denso and Toyota chips found in the motor control and engine control modules speak to the design's unique requirements for mixed-signal interfaces.
It's also worth noting that the Mitsubishi controllers have die-level copyrights dating back as far as 1995--further evidence of the measured pace of change and conservative design practices found in the mission-critical elements of automotive electronics.
David Carey is President of Portelligent. The Austin, Texas company produces teardown reports and related industry research on Wireless, Mobile, and Personal Electronics. (www.teardown.com)
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