Battery charging method

Details Battery charging method Battery charging method

2000-11-13

2001-08-28

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell charging

With thermal condition detection

Reexamination Certificate

active

06281663

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery charging method and particularly to a technology for effectively shortening the charge time and suppressing deterioration in the life of the battery.
This application is based on patent application No. Hei 11-321803 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles that are provided with a motor in addition to an engine as a power source for running the vehicle, and electric vehicles that are provided solely with a motor as a power source for running the vehicle are known.
Because these vehicles drive a motor using electric power supplied from a battery, it is necessary to charge the battery when the remaining battery charge (state of charge) is reduced due to electric discharge.
When charging a discharged battery, in order to safeguard the battery, it is recommended that the charging be carried out for approximately 10 hours at one tenth of the rated capacity (0.1C). Because rapid charging of the battery leads to deterioration of the battery and a reduction in the lifetime thereof, it has not been very common.
In particular, it has been common with electric vehicles to charge the battery using nighttime power for use on the following day.
However, rapid charging of the battery is demanded in cases such as if the vehicle needs to be suddenly used during the night, or in order to recharge the battery after driving in order to continue to drive the vehicle (i.e. in order to extend the distance driven).
In cases such as these, if the charge current is increased excessively, because the allowable temperature during charging (i.e. the upper temperature limit without harming the battery) ends up being reached due to the heat given off by the battery, the charge current cannot be excessively increased. This is because if the allowable temperature is exceeded, the charging efficiency is reduced and it is not possible for the battery to be charged substantially. Alternatively, due to overcharge reaction, the battery temperature suddenly increases which has a deleterious effect on the battery life.
To counter this, battery cooling apparatuses (a cooling fan or the like) for cooling the battery during charging have been considered, however, because the cooling performance is insufficient, it has not been possible to sufficiently radiate the heat generated by the battery charging leading naturally to a limit on the charge current.
Moreover, as is shown in
FIG. 8
, if the allowable temperature limit during charging is reached, then a process of temporarily stopping the charging, waiting for the temperature to go down, and then starting the charging again has been repeated over and over and, in some cases, this has led to the charge time instead becoming lengthened.
If the charge time is lengthened, in this way, the problem arises that a waiting time is generated in the use of the apparatus and the usability thereof suffers.
SUMMARY OF THE INVENTION
The present invention was conceived in consideration of the above circumstances and it is an object thereof to achieve a reduction in charging time while suppressing any deterioration in the lifetime of the battery.
In order to achieve the above object, the battery charging method of the present invention comprises the steps of: detecting (S
2
) a battery temperature (Tinit) at the start of the charging; setting a value of an upper limit (Tmax) of the battery temperature during charging; determining (S
5
) a maximum value (Tmax) for a battery charge current such that the battery temperature (T) during charging does not exceed the value of the upper limit (Tmax) of the battery temperature, based on the battery temperature (Tinit) at the start of the charging and characteristics (in the embodiments, the characteristic view shown in
FIG. 2
) of battery temperature increase caused by charge current; and charging (S
10
-S
14
) the battery (
4
) based on the maximum value (Imax) for the battery charge current.
In this structure, because the temperature (T) of the battery during charging does not exceed the upper limit value (Tmax), there is no need for the charging to be temporarily halted in order for the battery to cool down, and any unnecessary temperature increase caused by an overcharging reaction can be prevented. As a result, a reduction in charging time is effectively achieved while any deterioration in the lifetime of the battery is suppressed.
In the above structure it is also possible to determine the maximum value (Imax) for the battery charge current using the battery temperature (Tinit) at the start of the charging, the battery state of charge at the start of the charging (initial state of charge SOCinit), the value of the upper limit (Tmax) of the battery temperature, and the battery state of charge at charge completion (target state of charge SOCend).
In this structure, not only when a full charge of the battery (SOC=100%) is desired, but even when it is only desired that the battery be charged enough to drive the vehicle (for example, SOC=50%), because it is possible to perform the charging based on the battery charge current maximum value (Imax) that has been determined using appropriate parameters, it becomes possible to effectively avoid having to temporarily stop the charging as well as overcharging reactions.
Specifically, the step of determining the maximum value for the battery charge current includes the steps of: determining an amount of current (the target charging capacity &Dgr;SOC=SOCend−SOCinit) for charging the battery (
4
) based on the battery state of charge (the initial state of charge SOCinit detected by the battery
4
) at the start of the charging and the battery state of charge at charge completion (the target state of charge SOCend set by the driver via the panel
1
); determining a battery temperature increase margin (&Dgr;T=Tmax−Tinit) from the battery temperature (Tinit) at the start of the charging and the value of the upper limit (Tmax) of the battery temperature; determining a value of an upper limit (&Dgr;T/&Dgr;SOC) of the battery temperature increase per unit of charge amount from the amount of current (&Dgr;SOC) for charging the battery and the battery temperature increase margin (&Dgr;T); and determining the maximum value for the battery charge current (by map referral using
FIG. 2
) based on the value of the upper limit (&Dgr;T/&Dgr;SOC) of the battery temperature increase per unit of charge amount and an amount of a decrease in the battery temperature caused by a battery cooling device (self-cooling plus the fan
5
).


REFERENCES:
patent: 5252906 (1993-10-01), Busson

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