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PWM control signal for charging voltage generated by vehicle alternator

IP.com Disclosure Number: IPCOM000031121D
Publication Date: 2004-Sep-13
Document File: 3 page(s) / 22K

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The IP.com Prior Art Database

Related Documents

US6404163B1: PATENT [+4]

Abstract

The invention relates to a method and a system for adjusting the charging voltage generated by an alternator for a vehicle battery unit or supercapacitor. By measuring different parameters, such as State of Charge, it is possible to determine the optimal charging voltage for the battery unit. A control unit for the alternator then sends a controlling pulse width modulation (PWM) signal to the alternator. The PWM-signal both controls the on/off regulation and requests the determined optimal charging voltage.

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PWM control signal for charging voltage generated by vehicle alternator

Abstract

The invention relates to a method and a system for adjusting the charging voltage generated by an alternator for a vehicle battery unit or supercapacitor. By measuring different parameters, such as State of

Charge

, it is possible to determine the optimal charging voltage for the battery unit. A control unit for the alternator then sends a controlling pulse width modulation (PWM) signal to the alternator. The PWM-signal both controls the on/off regulation and requests the determined optimal charging voltage.

Background of the invention and Related art

A vehicle is normally equipped with an engine ECU (Electronic Control Unit) connected to an alternator for controlling the charging voltage output from the alternator. In a typical vehicle there are at least two lines between the engine ECU and the alternator. One line is used for sending an on/off-signal to the alternator. When the alternator is turned on it delivers a substantially fixed charging voltage, e.g. 28.3 V in trucks or busses.

Battery

wear is caused by repeated charging and discharging. A fixed charging voltage received from the alternator is not optimal in all charging situations, since an optimum charging voltage sometimes needs to be lower or higher than the fixed charging voltage in order to increase the battery life.

The patent documents US-6404163-B1, WO-03107020-A2, EP-1126575-A2 and US-5719485-A show battery recharging systems comprising means for PWM communication.

In US-6404163-B1 a duty cycle of the PWM signal represents a preferred output voltage of a generator. The charging (setpoint) voltage may be varied between 11.0 V and 15.5 V. When the duty cycle of the PWM-signal is 0-5% or 95-100% a default setpoint voltage of 13.75 V is set. The PWM-signal is however sent in a lamp circuit line. Such a combination is however not applicable for vehicles with more than one alternator. Furthermore, it is required for certain types of vehicles that the alternator is turned off when there is no signal or 0% duty cycle.

Also WO-03107020-A2 describes a battery recharging system with variable voltage output. A PWM signal is used for controlling the voltage level in a battery charger, not the output charging voltage from an alternator.

In EP-1126575-A2 the charging system charges two batteries of different voltages. The duty cycle of a PWM signal determines a variable output voltage of the alternator.

The charging system in US-5719485-A also comprises means for adjusting the output voltage of an alternator. A PWM signal is used for communicating a change of the voltage. According to a third embodiment, a PWM-signal controls the output voltage from the alternator between a lowest value and a highest value. The requested voltage is generated by letting a voltage regulator jump between an upper and lower value and that the requested voltage thereby, due to hysteresis, is between those values. In a fifth embodim...