Part 3 ― Advanced Solutions for Vehicle Control Applications

The Renesas Approach to Vehicle Control: Powertrain Control Solutions

The role of a vehicle’s powertrain is to burn fuel efficiently in the engine and then smoothly transfer the resulting power to the tires via the transmission and other drivetrain components. This interconnected mission requires the most sophisticated and complex control electronics of any of the systems in the vehicle. The microcomputers that Renesas supplies for this application have always been the fastest available models with internal flash memory. The devices currently used are members of the SuperH family that feature a large flash memory capacity and an on-chip floating point unit (FPU).

It is well known that vehicle emissions are one of the causes of air pollution and global warming. Accordingly, companies in the automotive industry continue to work diligently to reduce emissions and make them cleaner, while striving to achieve better mileage by improving the efficiency with which fuel is converted into power and transferred to the tires to move the vehicle. Precise electronic control of the powertrain is essential for reducing emissions and boosting fuel economy.

The main components of the powertrain of a car or truck include the engine, automatic transmission (or clutch and manual transmission), differential gear, and drive-shafts. Multiple electronic control units (ECUs) run software that implements precise control of the engine and transmission to achieve the smooth, efficient powertrain operation that drivers want. Large control algorithms that perform complex control functions are needed to do this, and the software has to be executed at high speed. Therefore, each ECU requires a microcomputer that operates at the highest possible speed and has a large internal flash memory capacity for storing the software.

The ECUs used for engine and transmission control in many of the vehicles now being manufactured in large volumes use popular high-end Renesas SuperH flash memory microcomputers (see Figure 1). Recently, we have been supplying SuperH family models that have the SH-2 core and incorporate a floating point arithmetic unit (FPU). These devices have the top market share for powertrain microcomputers in Japan (based on Renesas data).

The large amounts of flash memory built into the SuperH family microcomputers used for engine control applications store the many different control modes needed to respond to driver inputs and variations in engine load. During vehicle operation, for example, the engine control ECU determines the best control mode for the current driving conditions, then performs detailed optimizations of factors such as fuel and air volumes and ignition timing. It selects the appropriate control mode by comparing data stored in memory to information from multiple sensors about environmental conditions and whether the vehicle is accelerating, decelerating, climbing or descending, among other things.

When very precise engine control is required, it common design practice to have the engine ECU perform parallel calculations on not only the control mode currently being used, but also on alternative modes. Then if the driving conditions change suddenly ― as when the vehicle encounters a hill, for instance ― the ECU can switch the engine instantly to another mode better suited for the new conditions. Obviously, the fast processing performance that SuperH devices deliver is essential for implementing this capability because calculations for multiple control modes must be performed simultaneously.

The microcomputers used for powertrain control applications have to deliver the necessary features and performance, of course. Beyond that, though, they must be able to tolerate high temperatures. That’s because in recent vehicles the engine control ECU is often located in the engine bay, while the transmission control ECU might be immersed in transmission oil. Obviously, both of these environments are hot. For this reason, Renesas offers versions of the SH7055, SH7058, and SH7059 microcomputers that guarantee stable operation at temperatures as high as 125°C.

The SH7055 has 512Kbytes of internal flash memory and 32Kbytes of internal RAM. At its maximum operating frequency of 40MHz, its maximum processing performance is 52MIPS. The higher-rated SH7058 model has twice the SH7055's flash memory capacity and operating frequency. It provides 1Mbyte of internal flash memory and 48Kbytes of internal RAM. Operating at 80MHz, the SH7058 achieves a maximum processing performance of 104 MIPS. The SH7059 also operates at 80MHz, but has more internal flash memory: 1.5Mbyte.

All three microcomputers include an on-chip, 2-channel CAN interface for networked applications and have an SH-2 CPU core with a built-in floating point unit (FPU). The hardware FPU is important because floating point mathematical operations are one of the processor functions required for powertrain control. Although floating point operations can be implemented in software, microcomputers with on-chip FPUs can deliver faster processing speeds.

The most advanced SuperH microcomputers for powertrain control are the devices in the SH725x series, which is currently under development. They have the SH2A-FPU core, a superscalar design that also has an internal FPU and achieves processing performance 1.5 times that of the SH-2 core. To help engineers begin creating powertrain control software for ECUs that will use SH725x-series microcomputers, Renesas has announced the SH72546RFCC (see Figure 2), a special device that is the industry’s first microcomputer with on-chip flash memory built with a 90nm (nanometer) semiconductor manufacturing process.

At its 200MHz maximum operating frequency, the SH72546RFCC microcomputer delivers 400MIPS maximum processing performance, sufficient for rapidly executing control programs that are much more complex. Moreover, the device's on-chip flash memory capacity is among the largest currently offered ― 3.75 Mbytes ― enough to the store cutting-edge high-precision real-time control algorithms necessary for meeting stricter emission regulations and environmental-protection measures. Techniques such as internal cache memory make it possible for the CPU core to complete most accesses to the internal flash memory in a single clock cycle.

The comprehensive on-chip peripheral functions provided by this special microcomputer include a multifunction timer unit (ATU-III: Advanced Timer Unit III) with up to 106 outputs, a high-speed 37-channel 12-bit A/D converter, a 3-channel CAN interface, and a serial peripheral interface (SPI). To improve program development efficiency, the special device has a large-capacity on-chip emulation RAM that is separate from the user RAM and overlaps the flash memory area. The emulation RAM lets engineers make real-time adjustments of application program control parameters while data is rewritten during microcomputer operation.

By using the SH72546RFCC for control program development, designers of powertrain control units can start work now, then transfer (port) their finished designs directly to the mass-production versions of the SH725x series microcomputers that we plan to release beginning in 2008. Development work is eased by built-in debugging functions and powerful system development tools. The microcomputer is supported by the USB bus-powered E10A-USB on-chip debugging emulator that requires no external power supply, and by the E200F full-spec emulator. We also provide the High-performance Embedded Workshop (HEW) integrated development environment with compiler, assembler, and linker, project management tools, and more.

Looking further into the future (as the automotive industry always does!), Renesas is following a solid, regularly updated technology roadmap for our various product lines. A portion of the roadmap aims to ensure that the semiconductors we produce will continue to contribute to the design and implementation of ever more complex powertrain control systems. One of the semiconductor development strategies being pursued for devices in the SuperH family is the adoption of multi-core technology. This approach will allow the achievement of higher levels of performance, while maintaining the relatively low power consumption that characterizes SuperH microcomputers.

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