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Power consumption in control microcomputers for HEVs reduced by up to 50%

Power consumption in control microcomputers for HEVs reduced by up to 50%

　Where previously motor control systems for hybrid electric vehicles (HEVs) and electronic power steering (EPS) were composed of multiple chips, Toshiba has managed to integrate the functionality of several chips into a single chip, simultaneously facilitating reduced power consumption, a more compact size and lower costs. Converting to a single chip is particularly beneficial for control in HEVs that use a two-motor system, comprising the motor and a generator. Power consumption is reduced by up to 50% in comparison to conventional systems composed of multiple chips. Toshiba plans to begin shipping samples of these chips before the end of the year. We asked Mr. Eiji Sato of Toshiba’s System LSI Business Division, In-Vehicle System Application Technology Department about the company’s technology for control microcomputers for automotive use.

　The greatest feature of Toshiba’s microcomputers for in-vehicle control is that the functionality of several chips has been integrated into just one single chip. In particular, although two microcomputers were previously required to control two-motor HEV systems comprising a motor and generator, implementation of Toshiba’s exclusive hardware engine will enable the same functionality to be achieved with a single CPU (Central Processing Unit).

CPU load reduced to 50 to 80% of conventional levels

　Systems for controlling two motor HEVs generally consist of 6 components: an microcomputer for controlling the motor, an microcomputer for controlling the generator, an RDC (Resolver to Digital Converter) for controlling the motor, an RDC for controlling the generator, a driver for motor control and an analog circuit. Toshiba has succeeded in integrating the first four of these components into a single chip, namely, the microcomputer for controlling the motor, microcomputer for controlling the generator, the RDC for controlling the motor and the RDC for controlling the generator.

　There are several possible approaches for integrating the functionality of several chips into a single chip. The first is to simply integrate these into a single chip, while another is to achieve a single CPU by giving it better, more advanced functionality. The former approach results in a larger chip size, thus negating any cost savings, and it is also difficult to prevent power consumption increases using this approach. The latter approach requires an increase in the CPU’s operating frequency, which creates both an increase in power consumption and EMI (electromagnetic interference) noise. Any increases in power consumption or EMI noise resulting from integration into a single chip must be suppressed to below permissible levels specified by automotive manufacturers. Otherwise, automotive manufacturers will be faced with the annoying problems of suppressing heat radiation and EMI noise.

　To resolve these issues relating to single chip integration, Toshiba decided to adopt a method of integrating a single CPU with a hardware engine used exclusively for performing the coordinate conversion required for motor control and executing the AD data processes. This has achieved a microcomputer for controlling 2-motor systems, which has better performance, lower power consumption, and a smaller chip size. Trial calculations by Toshiba indicate that this exclusive hardware engine can reduce the load on the CPU by 50 to 20% in comparison to conventional CPUs, and the synergistic effects with single-chip integration also enable a reduction in power consumption by up to 50%. In addition, if we assume power consumption of levels equivalent to those of conventional systems, the surplus CPU power produced by the hardware engine could be used to drive functions other than just the motor control, facilitating even better and more refined control.

　For one-motor systems, Toshiba has integrated the microcomputer and the RDC, which are both used for controlling the motor, into a single chip thus making the system more compact. Until now, ECUs (Electric Control Units) were approximately the size of a small brick. However, with the recent progress in modularization, some applications now incorporate the ECU into the motor assembly interior, or attach it to the shaft in the case of EPS. In light of this, there are increasingly more demands to make systems smaller and more compact. Furthermore, by integrating the microcomputer and the RDC into a single chip, the parts counts can be reduced, which in turn alleviates the task of certifying components for automotive manufacturers and Tier 1 suppliers.

Engineering samples are scheduled for shipment during 2010, with volume production to commence between 2013 and 2015.

　Toshiba is now focusing on developing systems for EPS, and as with HEVs, there is strong pressure to reduce the price of these systems. However, instead of embedding the RDV as a piece of exclusive hardware as is the case with HEV systems, Toshiba proposes to achieve this with software, thus taking an approach to improve cost-performance. As motor revolutions are comparatively slow in EPS systems, the software can sufficiently handle the conversion performed by RDC, and it would not be necessary to raise the CPU performance by much. Functional safety technology will be vital in the future, and this will be achieved using the 'Single Core coupling system’ rather than the dual lock step system, whilst also keeping low cost.

　As for time-to-market, Toshiba plans to begin offering engineering samples of control microcomputers for HEVs in 2010, with volume production scheduled to commence in 2014 or 2015. Conversely, engineering samples for EPS will be offered as soon as possible during 2011, with volume production targeted to commence in 2013.