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Battery Management System for Small Electric Vehicles Developed "Intelligent battery" for greatly enhanced convenience

September 10, 1999

Yamaha Motor Co., Ltd. has recently succeeded in the development of a new environmental technology named "I.F.E.S."(Intelligent & Flexible Energy System) in which a CPU and IC memory are built into a battery box as an energy management system.

"I.F.E.S." represents a new-generation battery system for use on clean-energy small electric vehicles. From now on, this system will be adopted on Yamaha's main battery-powered products like the Yamaha PAS electro-hybrid bicycles to be released from now on.

The most notable feature of the I.F.E.S. system is the fact that a CPU-driven Battery Management Controller (BMC) consisting of a CPU and IC memory is to be built into a battery's case, making it in effect an "intelligent battery." With the I.F.E.S. system, we have made this intelligent battery work as a system with a CPU-fitted battery charger and the controller on the electric vehicle. 
This makes possible: 1) the ability to stabilize performance and extend the life of the battery, 2) detailed display of the state of the battery's charge, 3) shortening of the time required for recharging the battery (high-speed charging time is reduced by two-thirds compare to conventional units), 4) the world's first automatic refreshing function, and 5) this system makes it possible for the same charger to recharge batteries of different types, such as nickel-cadmium and nickel-metal hydride, 6) while also enabling an owner to change batteries to a different type and continue to use same vehicle and battery charger he or she is presently using.
Also, by applying this new I.F.E.S. technology to the next generation infrastructure planning it now becomes feasible to create public charging stations at places like train stations and other public facilities for the charging of a wide variety of products like electro-hybrid bicycles, electric scooters and electric wheelchairs.

Yamaha Motor plans to promote the use of this I.F.E.S. system widely among related industry manufacturers as an important system technology aimed at expanding the demand for a new generation of small electric vehicles.

I.F.E.S. System

Development aims and outlook

For an electro-hybrid bicycle or other small electric vehicles, the 1) battery, 2) charger and 3) the vehicle's controller are three important components that determine how practical and easy the vehicle is to use.
With research being conducted extensively in a number of directions, rapid progress has been made in recent years, especially with regard to batteries, concerning the needs for more higher performance, verification of charge level, versatility, compactness and lower cost.
However, in this research and development there has been a tendency for these three main components to be developed separately and exclusively for specific models, resulting in the need for a more practical and efficient system that reduces the cost burden on the users.

The new I.F.E.S. technology is the product of research and that began in the context of these market needs with the aim of "realizing a new way to bring out the full performance potential of a battery and put its energy into an easier to use form." In the development process it was realized that the condition of the battery, charger and vehicle controller all have a integral relationship to each others' functions. For this reason, a system was constructed that gave these three components functions that enabled relay of information and inter-communication.
Practically speaking, an "intelligent battery" has been newly developed by fitting a CPU-driven artificial intelligence unit into the main battery box. This gives the three components the interactive capability just cited and makes possible the desired electrical control functions in a way that brings out optimum performance from the battery. All of this makes the I.F.E.S. a system that offers a new standard for environment-friendly energy. 
Also, because the I.F.E.S. increases battery versatility with regard to recharging, a variety of electric vehicles that are compatible with this system could use the same public charging facilities. This presents the possibility for a next-generation community transportation system in which "charging stands" could be located at places like the vicinity of a train station, hospitals, shopping malls or the parking lots of housing communities to service a wide range of electric vehicles.

The Makeup of the I.F.E.S. (structural outline)

In the I.F.E.S. system a CPU-driven BMC (Battery Management Controller consisting of a CPU and IC memory) has been built into the battery box to create an "intelligent battery." This intelligent battery's BMC takes constant readings of the always-changing conditions of the battery (current flow, voltage, frequency of use, conditions of use, battery temperature, etc.). This information is computed by the CPU based on the data stored in the IC memory and calculates the optimum desired charging characteristics and discharging characteristics and communicates that information to the charger or the vehicle's controller.
For example, when the BMC sends information to the charger about the battery condition, the CPU in the charger performs calculations based on that information and, based on the results of those calculations, the charger sends electrical current with the optimum characteristics to charge the battery. Also, the BMC is constantly calculating the optimum amount of electrical outflow that should be allowed based on the state of charge in the battery at any given time, and the system is designed so that this information is communicated to the vehicle's controller unit.
In this way, the battery controls the amount of inflow and outflow (charging and discharging) of electricity so that they are optimum for the given conditions of the battery at any time based on the respective functions and parameters of the battery, charger and vehicle controller.
The result is a system with a number of advantages that include the ability to make the fullest possible use of the battery's power while avoiding excessive strain and promoting stable performance.

Main Features

1) Highly accurate display of battery information

The CPU in the system's BMC has been given the functions of sensing and measuring current flow, voltage and temperature among other things. This enables detailed recognition and calculation of the condition of the battery, which in turn makes it possible to display information about the state of charge in the battery, timing for refresher mode charging and degree of battery deterioration. This allows the user to get a more detailed understanding of the present state of the battery, such as Multi-level gauging of battery charge level, and plan its use with greater assurance.

2) More stable performance and longer life for the battery

The introduction of a BMC unit has made it possible to always maintain optimum charging and discharge characteristics amid the constantly changing conditions of the battery with regard to such factors as current flow, voltage, frequency of use, conditions of use and battery temperature. This means that over-charging and the occurrence of incorrect memory effects in the battery are prevented, thus keeping deterioration of the battery to a minimum. This lengthens the time between battery replacements, which means lower running cost over time.

3) Shortened charging time (about 1/3 the time for conventional units during rapid charging)

As a result of the optimized control functions of the BMC, not only has the strain on the battery during high-speed recharging been reduced, but the time required for recharging has also been greatly reduced (to about 1/3 the time of conventional systems).

4) World's first automatic refreshing function

Due to the fact that the BMC is able to measure the important factors contributing to memory effect in the battery, such as the number of times the battery has been charged, the temperature of the battery at the time of charging and the amount of electricity discharged, as well as calculating probable memory effect, it has been possible to give the battery with an "automatic refreshing function" that works when necessary simply by connecting the battery to the charger. This function is a world's first.

5) One charger can charge batteries of differing types (when the battery box and charger are compatible with the I.F.E.S. system)

Because the control characteristics involved when charging a nickel-cadmium battery and a nickel-metal hydride battery are different, until now two separate types of chargers have been made for these two types of batteries. Since with the I.F.E.S. system the battery BMC and the CPU in the charger have an information-exchange function, it is possible to achieve optimum control characteristics during charging. This has made it possible to charge different types of batteries from the same charger (when the battery box and charger are compatible with the I.F.E.S. system).

6) An existing vehicle and charger can still be used when the battery is changed to a different type (when the battery box, charger and vehicle controller are compatible with the I.F.E.S. system)

Because the battery BMC can simultaneously exchange information with the vehicle controller's CPU, a user can continue to use his current vehicle and charger when changing to a battery of different capacity or when changing the type of battery used from a nickel-cadmium type to a nickel-metal hydride.


This kind of system universality means that it is possible to use it with a variety of small electric vehicles such as electro-hybrid bicycles, electric scooters and electric wheelchairs. And this makes the concept of shared public charging stations at places like train stations feasible.


Conceptual image of public charging stations at places like parking lots
(train stations, hospitals and shopping districts, housing developments, etc.)

Conceptual image of public charging stations at places like parking lots(train stations, hospitals and shopping districts, housing developments, etc.)

Conceptual image of small electric vehicle rentals at a resort

Conceptual image of small electric vehicle rentals at a resort

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