Battery charging system and electric vehicle with battery charging system

When a charging control computer energized by an auxiliary battery detects a failure of an external AC power supply based on a change in the level of a failure on/off signal while a battery, mounted as an energy source on an electric vehicle, is being charged by the external AC power supply, the charging control computer stores a charged time up to the failure of the external AC power supply. Then, the charging control computer immediately changes from a normal power consumption mode to a low power consumption mode. When the charging control computer subsequently detects when the external AC power supply recovers from the failure, the charging control computer calculates a new target charging time from an initial target charging time and the charged time. Wasteful power consumption by the auxiliary battery during the failure of the external AC power supply is minimized. After the external AC power supply recovers from the failure, the charging control computer can charge the battery accurately to its fully charged state.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a battery charging system for interrupting 
the charging of a battery when the power supply suffers a failure while 
the battery is being charged and continuing the charging of the battery 
when the power supply recovers from the failure, and an electric vehicle 
which has as an energy source the battery which is controlled by the 
battery charging system. 
2. Description of the Related Art 
Many electric vehicles which has as an energy source a vehicle-use battery 
having a high voltage of 288 V or the like carry a battery charger that 
allows the battery to be charged conveniently at home. 
When the vehicle-carried battery charger charges the battery, an input 
terminal of the vehicle-carried battery charger is electrically connected 
to an external power supply and an output terminal thereof is electrically 
connected to the battery. A charging control computer (charging 
controller) is connected to a control terminal of the vehicle-carried 
battery charger for controlling the charging of the battery. 
The charging control computer itself is energized by an auxiliary battery 
such as a vehicle-carried battery having a low voltage of 12 V or the like 
for energizing electronic parts including ICs. In order to distinguish 
from such an auxiliary battery, the battery as the energy source for the 
electric vehicle is referred to as a main battery. 
The auxiliary battery is charged by a current supplied from the main 
battery through a DC/DC converter. 
It has been found that when the external power supply suffers a failure 
while it is charging the main battery, if the power supply failure 
continues for a long time, then the auxiliary battery is discharged to the 
extent that its capacity becomes nil and hence the capacity of the main 
battery is also eliminated because the charging control computer is 
continuously operated. Once the capacity of the main battery is 
eliminated, even when the power supply recovers from the failure, the main 
battery will not start being charged until the auxiliary battery is 
recharged. 
One solution is to automatically shut down the charging control computer 
when the external power supply suffers a failure. Because the charging 
control computer is automatically shut down, the auxiliary battery is 
prevented from being fully discharged. However, even when the power supply 
recovers from the failure, the auxiliary battery does not resume its 
charging, and will not be fully charged. It is important to solve these 
problems because batteries on electric vehicles are usually charged at 
night and it normally takes several hours for the batteries to be fully 
charged. 
SUMMARY OF THE INVENTION 
It is a general object of the present invention to provide a battery 
charging system for preventing the electric energy stored in a 
vehicle-carried battery from being consumed wastefully and hence 
preventing the capacity of the vehicle-carried battery from being 
eliminated even when a power supply suffers a failure while the 
vehicle-carried battery is being charged and the failure continues for a 
long period of time, and an electric vehicle which incorporates the 
battery charging system. 
A major object of the present invention is to provide a battery charging 
system for resuming the charging of a vehicle-carried battery accurately 
to a fully charged state when a power supply, after it has suffered a 
failure while charging the vehicle-carried battery, recovers from the 
failure, and an electric vehicle which incorporates the battery charging 
system. 
The above and other objects, features, and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which a preferred 
embodiment of the present invention is shown by way of illustrative 
example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows in block form an electric vehicle 10 which incorporates a 
battery charging system according to the present invention. 
As shown in FIG. 1, the electric vehicle 10 carries a battery (hereinafter 
also referred to as a "main battery") 12 having a high rated voltage of 
+288 V. The battery 12 comprises, for example, 24 series-connected 
nickel-hydrogen secondary cells each having a rated voltage of +12 V. A 
voltage sensor (voltage detecting means) 14 is connected across the 
battery 12 for detecting a battery voltage Vb thereof. A temperature 
sensor (temperature detecting means) 16 is attached to the battery 12 for 
detecting the temperature thereof. A current sensor (current detecting 
means) 18 is connected in series to the battery 12 for detecting a 
charging current which flows into the battery 12 and a discharging current 
which flows from the battery 12. 
Positive and negative terminals of the battery 12 are connected to a 
vehicle-carried battery charger 20 through a contactor (not shown), and 
also connected to a DC/DC converter 22 and a propulsive electric motor 
(not shown), which serves as a load, through a motor drive unit (not 
shown). 
The DC/DC converter 22 lowers the voltage of the main battery 12 to a lower 
voltage of +12 V for charging an auxiliary battery (vehicle-carried 
battery) 24, and supplies a charging electric energy to the auxiliary 
battery 24. 
The auxiliary battery 24 serves as a +12V power supply and is connected to 
a charging control computer (charging controller) 30. 
A charging instruction switch 32 for selectively turning on and off a 
charging control process is connected to the charging control computer 30. 
The charging control computer 30 serves to perform various functions or 
operate as various means such as control, decision, processing, 
calculating, timing, clock, and storing means, for controlling the 
vehicle-carried battery charger 20 while communicating therewith. The 
vehicle-carried battery charger 20 supplies a failure on/off signal Si to 
the charging control computer 30. 
Each of the charging control computer 30 and the vehicle-carried battery 
charger 20 comprises a microcomputer including a ROM as a storing means 
(memory) for storing a system program and an application program for 
failure control, a RAM as a storing means (memory) operating as a work 
memory, a timer as a timing means for measuring time, and input/output 
interfaces including an A/D converter and a D/A converter. 
A RAM 38, indicated by the dotted line in the charging control computer 30, 
serves as a charging state storing means, and is backed up by the 
auxiliary battery 24 for holding its stored data. 
The vehicle-carried battery charger 20 has input terminals connected 
through a connector 34 to an external AC power supply 36 having an AC 
voltage of 200 V or the like. 
A first charging control process which is carried out when the external AC 
power supply 36 suffers a failure will be described below with reference 
to FIG. 2. 
The capacity of the battery 12 is expressed by the number of ampere-hours 
(AHD), and the charging control computer 30 serves as control in the 
charging control process and other processes described later on. 
According to the first charging control process, the battery 12 is judged 
as being fully charged (completed in charging) when the battery 12 has 
been charged with a constant current (charging current) for a 
predetermined time (target charging time). 
When the charging instruction switch 32 is turned on, a target charging 
time is calculated in a step S1 according to the following equation (1): 
EQU Target charging time={(fully charged capacity-remaining 
capacity).times.1.1}/charging current (1) 
where 1.1 is a constant determined by the charging efficiency. 
Since the fully charged capacity of the battery 12 is known, the remaining 
capacity thereof can be determined by calculating (charging and 
discharging current Ib.times.time). 
The battery 12 starts being charged with the constant charging current in 
the equation (1), and the charging time that is consumed by charging the 
battery 12 starts being measured by the timing means in a step S2. At this 
time, the electric energy supplied from the external AC power supply 36 is 
converted by the vehicle-carried battery charger 20 into a high-voltage DC 
electric energy that is supplied as the constant current to the battery 
12. 
Then, it is determined whether the external AC power supply 36 suffers a 
failure based on the level of the failure on/off signal Si (e.g., the 
level of the failure on/off signal Si is high when the external AC power 
supply 36 suffers a failure, and low when the external AC power supply 36 
does not suffer failure) in a step S3. 
If the external AC power supply 36 does not suffer a failure, i.e., if the 
level of the failure on/off signal Si is low (NO in the step S3), then 
control jumps to a step S4 which decides whether the charging of the 
battery 12 is completed, i.e., the battery 12 is fully charged, by 
checking if the charging time which is being measured has reached the 
target charging time according to the equation (1). 
If the external AC power supply 36 suffers a failure, i.e., if the level of 
the failure on/off signal Si goes high (YES in the step S3), then control 
proceeds from the step S3 to a step S5 for failure control. 
In the step S5, a period of time from the time when the battery 12 has 
started being charged to the time when the power supply failure is 
detected, i.e., a charged time, is stored in the RAM 38, and the time when 
the battery 12 has started suffering the failure is also stored in the RAM 
38. 
Then, the charging control computer 30 switches from a normal power 
consumption mode to a low power consumption mode, i.e., a sleep mode in a 
step S6. The current consumed by the charging control computer 30 now 
decreases from an ampere level in the normal power consumption mode to a 
milliampere level in the low power consumption mode, for example, and the 
charging control computer 30 starts temporarily interrupting the charging 
of the battery 12. Thereafter, the charging control computer 30 functions 
as a recovery-from-failure monitor. 
The charging control computer 30 monitors the level of the failure on/off 
signal Si in order to detect whether the external AC power supply 36 
recovers from the failure in a step S7. 
If the level of the failure on/off signal Si goes low, then the external AC 
power supply 36 is judged as recovering from the failure (YES in the step 
S7). 
The charging control computer 30 then switches from the low power 
consumption mode back to the normal power consumption mode in a step S8. 
The period of time in which the external AC power supply 36 has suffered 
from the failure, i.e., the failed time, is calculated from the time when 
the power supply failure started suffering the failure and the time 
(present time) when the external AC power supply 36 has recovered from the 
failure, and a capacity reduction (self-discharging current quantity) due 
to a self-discharging current that has flowed in the failed time is 
calculated in a step S9. 
Thereafter, in a step S10, a target charging time upon resuming the 
charging of the battery 12 is calculated according to the following 
equation (2): 
EQU Target charging time=initial target charging time-charged 
time+(self-discharging current quantity/charging current) (2) 
where the initial target charging time is the target charging time 
calculated in the step S1, the charged time is the charged time stored in 
the RAM 38 in the step S4, and the (self-discharging current 
quantity/charging current) is a charging time to make up for the capacity 
reduction due to the self-discharging current. 
Then, the charging of the battery 12 is resumed in a step S11. 
The step S4 decides whether the charging of the battery 12 is completed by 
checking if the charging time which is being measured has reached the 
target charging time upon resuming the charging of the battery 12 
according to the equation (2). If the charging of the battery 12 is not 
completed (NO in the step S4), then control goes back to the step S3 for 
monitoring the failure on/off signal Si. 
If the charging time which is being measured has reached the target 
charging time (YES in the step S4), regardless of whether the battery 12 
has continuously been charged without a power supply failure or the 
battery 12 has been charged after recovery from a power supply failure, 
then the charging of the battery 12 is stopped in a step S12. 
Thereafter, the charging control computer 30 switches from the normal power 
consumption mode to the low power consumption mode in a step S13. 
According to the first charging control process in which the charging of 
the battery 12 is controlled on the basis of the target charging time, the 
charging control computer 30 monitors the level of the failure on/off 
signal Si from the vehicle-carried battery charger 20 while the battery 12 
is being charged by the external AC power supply 36 through the 
vehicle-carried battery charger 20. When the charging control computer 30 
detects a failure of the external AC power supply 36 based on a transition 
from the low level to the high level of the failure on/off signal Si, the 
charging control computer 30 stores the charged time consumed until the 
time when the failure of the external AC power supply 36 has occurred, and 
immediately switches from the normal power consumption mode to the low 
power consumption mode. Thereafter, the charging control computer 30 
monitors the level of the failure on/off signal Si again. When the 
charging control computer 30 detects recovery of the external AC power 
supply 36 from the failure, the charging control computer 30 determines, 
as a new target charging time, a remaining charging time that is 
calculated by subtracting the charged time from the initial target 
charging time, taking into account the self-discharging current quantity, 
according to the equation (2), and resumes the charging of the battery 12 
using the new target charging time. 
During a failure of the external AC power supply 36, since the charging 
control computer 30 is in the low power consumption mode, the consumption 
of the electric energy stored in the auxiliary battery 24 is minimized, 
avoiding wasteful battery energy consumption. Furthermore, the battery 12 
can be charged accurately to a fully charged state because the charging of 
the battery 12 is resumed on the basis of the charged time of the battery 
12 at the time the failure of the external AC power supply 36 was 
detected. 
A second charging control process which is carried out when the external AC 
power supply 36 suffers a failure will be described below with reference 
to FIG. 3. 
According to the second charging control process, the battery 12 is judged 
as being fully charged (completed in charging) when the battery 12 has 
been charged with a constant current and a charged capacity (charging 
current quantity.times.charging time) thereof reaches a predetermined 
value. Steps of the second charging control process which are similar to 
those of the first charging control process are denoted by the step 
numbers of those of the first charging control process with "20" added 
thereto. 
When the charging instruction switch 32 is turned on, a target charged 
capacity (constant charging current.times.charging time) is calculated in 
a step S21 according to the following equation (3): 
EQU Target charged capacity=(fully charged capacity-remaining 
capacity).times.1.1 (3) 
where 1.1 is a constant determined by the charging efficiency. 
Since the fully charged capacity of the battery 12 is known, the remaining 
capacity thereof can be determined by calculating (charging and 
discharging current Ib.times.time). 
The battery 12 starts being charged with the constant charging current 
established when the target charged capacity is calculated, and the 
charging time that is consumed by charging the battery 12 starts being 
measured by the timing means in a step S22. At this time, the electric 
energy supplied from the external AC power supply 36 is converted by the 
vehicle-carried battery charger 20 into a high-voltage DC electric energy 
that is supplied as the constant current to the battery 12. 
Then, it is determined whether the external AC power supply 36 suffers a 
failure based on the level of the failure on/off signal Si in a step S23. 
If the external AC power supply 36 does not suffer a failure (NO in the 
step S23), then control jumps to a step S24 which decides whether the 
charging of the battery 12 is completed, i.e., the battery 12 is fully 
charged, by checking if the product of the charging time being measured 
and the established charging time, i.e., the charged capacity, has reached 
the target charging time according to the equation (3). Whether the 
battery 12 is fully charged or not may alternatively be decided by 
comparing a rate of change of the temperature of the battery 12 or a rate 
of change of the voltage across the battery 12 with a predetermined value, 
as disclosed in Japanese laid-open patent publication No. 8-331769, for 
example. 
If the external AC power supply 36 suffers a failure (YES in the step S23), 
then control proceeds from the step S23 to a step S25 for failure control. 
In the step S25, a charged capacity which is calculated by multiplying a 
period of time from the time when the battery 12 has started being charged 
to the time when the power supply failure is detected, by the established 
charging current is stored in the RAM 38, and the time when the battery 12 
has started suffering the failure is also stored in the RAM 38. 
Then, the charging control computer 30 switches from the normal power 
consumption mode to the low power consumption mode, i.e., the sleep mode 
in a step S26. 
The charging control computer 30 detects whether the external AC power 
supply 36 recovers from the failure in a step S27. 
If the external AC power supply 36 is judged as recovering from the failure 
(YES in the step S27), then the charging control computer 30 switches from 
the low power consumption mode back to the normal power consumption mode 
in a step S28. 
The period of time in which the external AC power supply 36 has suffered 
from the failure, i.e., the failed time, is calculated from the time when 
the external AC power supply 36 started to suffer the failure and the time 
(present time) when the external AC power supply 36 has recovered from the 
failure, and a capacity reduction (self-discharging current quantity) due 
to a self-discharging current that has flowed in the failed time is 
calculated in a step S29. 
Thereafter, in a step S30, a target charged capacity upon resuming the 
charging of the battery 12 is calculated according to the following 
equation (4): 
EQU Target charged capacity=initial target charged capacity-charged 
capacity+self-discharging current quantity (4) 
where the initial target charged capacity is the target charged capacity 
calculated in the step S21, and the charged capacity is the charged 
capacity stored in the RAM 38 in the step S24. 
Then, the charging of the battery 12 is resumed in a step S31. 
The step S24 decides whether the charging of the battery 12 is completed by 
checking if the target charged capacity upon resuming the charging of the 
battery 12 is reached according to the equation (4). If the charging of 
the battery 12 is not completed (NO in the step S24), then control goes 
back to the step S23 for monitoring the external AC power supply 36 for a 
failure. 
If the charging of the battery 12 up to the target charged capacity is 
completed (YES in the step S24), then the charging of the battery 12 is 
stopped in a step S32. 
Thereafter, the charging control computer 30 switches from the normal power 
consumption mode to the low power consumption mode in a step S33. 
According to the second charging control process in which the charging of 
the battery 12 is controlled on the basis of the target charged capacity, 
the consumption of the electric energy stored in the auxiliary battery 24 
is minimized during a failure of the external AC power supply 36, and when 
the external AC power supply 36 recovers from the failure, the charging of 
the battery 12 is controlled accurately in view of the charged state 
achieved thus far. In addition, the full charged capacity can be 
determined more accurately than in the first charging control process. 
A third charging control process which is carried out when the external AC 
power supply 36 suffers a failure will be described below with reference 
to FIG. 4. 
According to the third charging control process, the battery 12 is charged 
in various charging modes including constant-power charging modes and 
constant-current charging modes. Steps of the third charging control 
process which are similar to those of the first charging control process 
are denoted by the step numbers of those of the first charging control 
process with "40" added thereto. 
When the charging instruction switch 32 is turned on, a target charged 
capacity (constant charging current.times.charging time) is calculated in 
a step S41 according to the equation (3) referred to above. 
Based on the calculated target charged capacity, one of first through 
charging modes, given below, is determined in a step S41a. The greater the 
calculated target charged capacity, the smaller the ordinal number of a 
charging mode which is to be selected. 
First charging mode: a constant-power charging mode for charging the 
battery 12 at 5 kW; 
Second charging mode: a constant-power charging mode for charging the 
battery 12 at 2 kW; 
Third charging mode: a constant-current charging mode for charging the 
battery 12 at 5A; and 
Four charging mode: a constant-current charging mode for charging the 
battery 12 at 2A. 
In a step S42, the battery 12 starts being charged in the charging mode 
which is determined in the step S41a. 
Then, it is determined whether the external AC power supply 36 suffers a 
failure based on the level of the failure on/off signal Si in a step S43. 
If the external AC power supply 36 does not suffer a failure (NO in the 
step S43), then control jumps to a step S50 for determining the charging 
mode. After the step S50, the present charging mode is continued or 
changes to a next charging mode in a step S51. Then, a step S44 decides 
whether the charging of the battery 12 is completed, i.e., the battery 12 
is fully charged by comparing a rate of change of the temperature of the 
battery 12 or a rate of change of the voltage across the battery 12 with a 
predetermined value, as disclosed in Japanese laid-open patent publication 
No. 8-331769, for example. 
If the external AC power supply 36 suffers a failure (YES in the step S43), 
then control proceeds from the step S43 to a step S45 for failure control. 
In the step S45, the charging mode (one of the first through four charging 
modes) immediately prior to the failure of the external AC power supply 36 
is stored in the RAM 38. 
Then, the charging control computer 30 switches from the normal power 
consumption mode to the low power consumption mode, i.e., the sleep mode 
in a step S46. 
The charging control computer 30 detects whether the external AC power 
supply 36 recovers from the failure in a step S47. 
If the external AC power supply 36 is judged as recovering from the failure 
(YES in the step S47), then the charging control computer 30 switches from 
the low power consumption mode back to the normal power consumption mode 
in a step S48. 
Thereafter, the charging control computer 30 resumes the charging of the 
battery 12 in the charging mode which is stored in the RAM 38 in a step 
S49. 
Then, the charging control computer 30 decides whether the present charging 
mode is to change to a next charging mode in a step S50. The step S50 may 
be carried out by referring to a change in the voltage Vb (see FIG. 5) 
across the battery 12 which has been recognized and stored by the charging 
control computer 30. In FIG. 5, the battery voltage Vb is lower than a 
rated voltage and changes in a period T11 which represents the first 
charging mode. It can be seen from FIG. 5 that as the first charging mode 
draws to an end, the change of the battery voltage Vb, i.e., its 
differential, gradually becomes greater. The end at a time t11 of the 
first charging mode can be detected by continuously detecting the battery 
voltage Vb and the change of the battery voltage Vb, i.e., its 
differential. A period T12 from the time t11 to a time T12 represents the 
second charging mode, and a period T13 from the time t12 to a time t13 
represents the third charging mode. 
When the end of a charging mode is detected, the charging mode changes to a 
next charging mode in the step S51. If the end of the final charging mode 
or each of the charging modes is not detected (NO in the step S50), or 
after the present charging mode changes to a next charging mode in the 
step S51, the step S44 decides whether the charging of the battery 12 is 
completed. If the charging of the battery 12 is not completed (NO in the 
step S44), then control goes back to the step S43 for monitoring the 
external AC power supply 36 for a failure. 
If the charging of the battery 12 is completed (YES in the step S44), then 
the charging of the battery 12 is stopped in a step S52. 
Thereafter, the charging control computer 30 switches from the normal power 
consumption mode to the low power consumption mode in a step S53. 
According to the third charging control process in which the charging of 
the battery 12 is controlled on the basis of the charging modes, the 
consumption of the electric energy stored in the auxiliary battery 24 is 
minimized during a failure of the external AC power supply 36, and when 
the external AC power supply 36 recovers from the failure, the charging of 
the battery 12 is controlled accurately in view of the charged state 
achieved thus far. In addition, the full charged capacity can be 
determined more accurately than in the first charging control process. 
As described above, according to the present invention, when the external 
power supply suffers a failure while the battery is being charged, the 
charging controller switches from the normal power consumption mode to the 
low power consumption mode. Consequently, wasteful power consumption by 
the auxiliary battery and hence the main battery is held to a minimum 
during the failure of the external power supply. 
Since the charging controller switches from the low power consumption mode 
back to the normal power consumption mode when the external power supply 
recovers from the failure, the charging of the battery with the charging 
controller is automatically resumed. 
The charging of the battery is resumed on the basis of a state of the 
battery at the time the failure of the external power supply is detected, 
i.e., a history of the battery at the time the failure of the external 
power supply is detected. Therefore, the charging of the battery is 
resumed accurately by the charging controller. 
In the present invention, the case referred to as "the failure of the 
external power supply" involves all the situations in which electricity is 
not supplied to the vehicle-carried battery charger 20, such as a case of 
the failure of the external AC power supply 36 itself, a case of the 
unexpected disconnection of an unillustrated plug used to electrically 
connect between the unillustrated AC electric fixed outlet and the 
external AC power supply 36, a case of the interruption of power supply 
from an unillustrated transforming station etc. to the external AC power 
supply 36, and so on. 
Although a certain preferred embodiment of the present invention has been 
shown and described in detail, it should be understood that various 
changes and modifications may be made therein without departing from the 
scope of the appended claims.