June 22, 2012
Furukawa Electric Co., Ltd. and Furukawa Automotive Systems Inc. (Head Office: 1,000 Amago, Koura-cho, Inukami-gun, Shiga Prefecture; President: Michitoyo Kurokawa) have jointly developed the world’s first vehicle-mounted lead battery status detector sensor equipped with a pulse discharging circuit. The sensor enables high-accuracy monitoring of the lead battery status even when the engine is turned off or on vehicles not equipped with a starter motor. This function is useful for preventing depletion of the battery.
Background of development
The internal resistance(note 1) of batteries is an extremely important index for understanding discharging performance and the degree of depletion.
Internal resistance has conventionally been calculated based on the electric current and voltage response when the engine (starter motor) is started, but this method does not allow the internal resistance of lead batteries to be measured when the engine is turned off or on electric vehicles (EVs) and hybrid electric vehicles (HEVs) not equipped with a starter motor.
Our company has developed the technologies to install a discharging circuit in the sensor, make pulse-form discharges at the timing of the sensor control, and calculate the internal resistance based on the electric current and voltage response at that time. The sensor enables, for the first time in the world, monitoring of the lead battery status even when the engine is turned off or on EVs and HEVs not equipped with a starter motor. Electro-chemical expertise on battery phenomena possessed by our group company The Furukawa Battery Co., Ltd. has been utilized for increasing accuracy for battery status monitoring technologies.
Features of the developed product
- High-accuracy lead battery status monitoring is enabled.
- With a built-in pulse discharging circuit(note 2), high-accuracy monitoring of the engine restarting capacity (state of function [SOF])(note 4) and other aspects of the lead battery status are possible when the engine is turned off and on the accessory battery(note 3) of EVs and HEVs.
- Connection is established with the vehicle system(note 5) via multiplex communications.
- Numerous applications have been filed for related patents.Those already obtained include Japanese Patent No. 4015128 and No. 4532416.
The status detection sensor measures the battery voltage, charging and discharging current, temperature and other items along with the internal resistance caused by pulse discharging, then detects the battery status based on its unique algorithm and outputs the results to the vehicle system.
Quantities that indicate the battery status include state of charge (SOC)(note 8), state of health (SOH)(note 9) and SOF, which are necessary for suppressing power generation by the vehicle(note 6) and the function to stop idling(note 7).
Detection of the SOC and SOF of lead batteries is already possible(note 10), and work is underway for developing SOH detection technology.
Our company will conduct activities to win orders for vehicles equipped with the power generation suppressing and idling-stop functions, which enable improved vehicle mileage and reduced carbon dioxide emissions, with a target of attaining 10% or more of the global share by 2015.
(Note 1)Internal resistance
This refers to the electrical resistance inside batteries. The larger the internal resistance, the lower the voltage will be when discharging takes place. Internal resistance generally increases as the battery deteriorates.
(Note 2)Pulse discharging circuit
This is a circuit that lets through pulse-form discharging current between the battery terminals. The internal resistance can be measured only with the battery and the sensor, without relying on the load current.
(Note 3)Accessory batteries of EVs and HEVs
EVs and HEVs are currently equipped with a 12V lead battery as an accessory, which is used as the power source for the electronic control unit (ECU). When the accessory battery is exhausted, startup of the ECU is disabled and the vehicle cannot be started. Measurement of internal resistance based on the load current will also not be possible in principle because no engine starting current is generated. However, measurement is possible with the sensor since it is equipped with a pulse discharging circuit.
(Note 4)State of function (SOF)
State of function is an index indicating the discharging capacity for maintaining the prescribed voltage at times of specified large current discharging, such as when starting the engine.
(Note 5)Vehicle system
The system includes the electronic control unit (ECU) that controls the engine and alternator.
(Note 6)Power generation suppression
This is a technology for improving gas mileage by adjusting the alternator output to suppress unnecessary power generation. The effect can be enhanced if detection of the battery status becomes possible.
(Note 7)Idling-stop function
This is a technology to reduce carbon dioxide emissions by automatically turning off the engine when the vehicle comes to a halt at traffic lights and restarts the engine when the vehicle moves again. Troubles such as inability to restart the engine can be avoided if battery status detection becomes possible, which improves the effects of the function.
(Note 8)State of charge (SOC)
SOC is an index indicating the ratio of charging.
(Note 9)State of health (SOH)
SOH is an index indicating the degree of depletion.
(Note 10)Detection of the SOC and SOF is possible
There are restrictions depending on the battery manufacturer, size, etc.
Some of the patents already granted
Patent No. 4015128:
Method for estimating charging rate, device for estimating charging rate, battery system and battery system for vehicle.
Patent No. 4532416:
Method and apparatus for determining battery discharge capacity and power supply system.