Battery discharge gas control system

A battery discharge gas control system, which releases a hydrogen gas generated from the battery assembly when the battery assembly is charged and discharged, is capable of keeping the battery structure highly resistant to water or humidity. The battery discharge gas control system has a battery having a gas release port, a passage connected to the gas release port, a control valve connected to the passage, a pressure sensor for detecting a pressure in the passage, and a control circuit for opening the control valve to release a gas generated by the battery from the passage, depending on the pressure in the passage as detected by the pressure sensor. During a period of time in which no hydrogen gas is generated or a generated hydrogen gas is not plenty enough to be released while the battery is being charged or discharged, the passage is closed for thereby keeping the battery structure highly resistant to water or humidity. The control valve has a solenoid-operated valve openable in response to a control signal outputted by the control circuit, and a relief valve mechanically openable depending on the pressure in the passage. Even in the event of a failure of the solenoid-operated valve, the relief valve is mechanically opened depending on the pressure in the passage, thereby protecting the passage from damage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a battery discharge gas control system, 
and more particularly to a battery discharge gas control system which is 
capable of safely and effectively releasing a hydrogen gas which is 
generated from a battery such as a storage gas mounted on an electric 
vehicle or the like when the battery is charged and discharged, while 
keeping a battery structure resistant to water or humidity. 
2. Description of the Related Art 
Recent years have seen much attention attracted to electric vehicles as 
pollution-free mobile units. Generally, electric vehicles have an electric 
motor as a propulsion source and a storage battery which energizes the 
electric motor. Since the electric motor consumes a large amount of 
electric energy and various other devices such as electric accessories 
mounted on the electric vehicle also consume a large amount of electric 
energy, they are supplied with required electric energy from a battery 
assembly which comprises a plurality of series-connected battery cells. 
One battery which has recently been proposed as such a battery assembly is 
an NiMH battery. The secondary cells of the NiMH battery discharge a 
hydrogen gas when they are charged and discharged. Therefore, many 
apparatus, including electric vehicles, which employ an NiMH battery 
incorporate a discharge gas control system for releasing a generated 
hydrogen gas. 
Japanese laid-open patent publication No. 60-246574, for example, discloses 
a discharge gas control system for releasing a hydrogen gas which is 
generated when a battery is charged and discharged. The disclosed 
discharge gas control system has a solenoid-operated valve disposed in a 
gas release port in the battery for selectively opening and closing the 
gas release port, and a valve controller for opening the solenoid-operated 
valve to release the hydrogen gas when the battery is charged. 
During a period of time in which no hydrogen gas is generated or a 
generated hydrogen gas is not plenty enough to be released while the 
battery is being charged or discharged, it is not necessary to open the 
solenoid-operated valve. Rather, it is preferable during such a period of 
time to close the solenoid-operated valve for thereby keeping the battery 
structure. 
In the conventional discharge gas control system, however, the 
solenoid-operated valve is opened to discharge a generated hydrogen gas 
when the battery is charged. The solenoid-operated valve remains open even 
if no hydrogen gas is generated when the battery is charged. While the 
solenoid-operated valve is being open, the battery structure is less 
resistant to water or humidity than while the solenoid-operated valve is 
being closed. Consequently, since the solenoid-operated valve is opened 
during a period of time in which no hydrogen gas needs to be released, the 
ability of the battery structure to be resistant to water or humidity is 
adversely affected during such a period of time. 
Another problem of the conventional discharge gas control system is that in 
the event of an undesired failure of the solenoid-operated valve, no 
hydrogen gas can be released, resulting in an abnormal gas pressure 
buildup in and hence a possibility of unwanted damage to a passage 
connected to the gas release port of the battery. 
SUMMARY OF THE INVENTION 
It is a general object of the present invention to provide a battery 
discharge gas control system for releasing a hydrogen gas generated from a 
battery when the battery is charged and discharged, the battery discharge 
gas control system being capable of keeping a battery structure highly 
resistant to water or humidity. 
A primary object of the present invention is to provide a battery discharge 
gas control system which, if the gas pressure in a passage connected to a 
gas release port of a battery is detected by a pressure sensor as being 
lower than a predetermined pressure level during a period of time in which 
no hydrogen gas is generated or a generated hydrogen gas is not plenty 
enough to be released while the battery is being charged or discharged, 
closes the passage for thereby keeping a battery structure highly 
resistant to water or humidity. 
Another object of the present invention is to provide a battery discharge 
gas control system which, during a period of time in which no hydrogen gas 
is generated or a generated hydrogen gas is not plenty enough to be 
released while a battery is being charged or discharged, intermittently 
opens a solenoid-operated valve thereby to keep a battery Structure highly 
resistant to water or humidity. 
Still another object of the present invention is to provide a battery 
discharge gas control system which, in the event of a failure of a 
solenoid-operated valve, operates valve means depending the gas pressure 
in a passage connected to a gas release port of a battery to mechanically 
open the solenoid-operated valve for thereby protecting the passage from 
damage. 
Yet still another object of the present invention is to provide a battery 
discharge gas control system which, during a period of time in which no 
hydrogen gas is generated or a generated hydrogen gas is not plenty enough 
to be released while a battery is being charged or discharged, 
intermittently opens a solenoid-operated valve thereby to keep a battery 
structure highly resistant to water or humidity, and which reduces the 
amount of a hydrogen gas generated per unit time for thereby lowering the 
concentration of the hydrogen gas in the vicinity of a gas release port 
(explosion-resistant filter) of the battery. 
A further object of the present invention is to provide a battery discharge 
gas control system which makes highly resistant to water or humidity a 
battery assembly that comprises a plurality of battery cells and a passage 
connected to gas release ports of the respective battery cells, and which, 
in the event of a failure of a solenoid-operated valve for opening and 
closing the passage, can mechanically close the passage to prevent an 
unwanted gas pressure buildup from being developed in the passage thereby 
to avoid damage to the passage. 
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 a battery discharge gas control system 10 according to the 
present invention, typically installed on an electric vehicle. The battery 
discharge gas control system 10 includes a battery assembly 14 comprising 
a plurality of electrically series-connected batter cells 12, typically 
NiMH battery cells. Each of the battery cells 12 has a gas release port 16 
for discharging a hydrogen gas which is generated when it is charged and 
discharged. The gas release ports 16 of the respective battery cells 12 
are interconnected by a passage 18 which is connected to a connecting pipe 
20 that is coupled to a pressure sensor 22 for detecting a pressure in the 
passage 18. The battery discharge gas control system 10 also includes a 
control circuit (management ECU (electronic control unit)) 24 which is 
supplied with a detected output signal from the pressure sensor 22 and a 
control valve 28 which has a solenoid-operated valve 27 magnetically 
actuatable by a solenoid 26 in response to a control signal outputted from 
the control circuit 24. 
The pressure in the passage 18 is detected by the pressure sensor 22, which 
applies its detected output signal to the control circuit 24. When the 
detected gas pressure exceeds a predetermined pressure level, the control 
circuit 24 outputs a control signal to energize the solenoid 26 for 
thereby opening the solenoid-operated valve 27. When the solenoid-operated 
valve 27 is opened, a hydrogen gas generated and discharged by the battery 
cells 12 passes through the control valve 28, and is discharged out of the 
battery discharge gas control system 10 through an explosion-resistant 
filter 30. 
The control valve 28 includes a relief valve 29 which is mechanically 
openable in response to a pressure in the passage 18. When the pressure in 
the passage 18 exceeds a certain pressure level, even if the 
solenoid-operated valve 27 fails to operate, the relief valve 29 is opened 
to discharge the hydrogen gas out of the battery discharge gas control 
system 10 through the explosion-resistant filter 30. The relief valve 29 
is normally closed by a helical spring 31 whose spring force is selected 
to be greater than a force that is applied by the solenoid 26 to open the 
solenoid-operated valve 27. 
A battery charger 32 for charging the battery assembly 14 is electrically 
connected to the control circuit 24. When the pressure in the passage 18 
is detected by the pressure sensor 22 as having reached the predetermined 
pressure level, the control circuit 24 turns off the battery charger 32 to 
cancel any charging process carried out thereby. A motor control ECU 34 
for controlling a motor 35 as a propulsion source on the electric vehicle 
is also electrically connected to the control circuit 24. When the 
pressure in the passage 18 has reached the predetermined pressure level as 
detected by the pressure sensor 22, the control circuit 24 controls the 
motor control ECU 34 to lower a threshold for the discharging voltage of 
the battery assembly 14. 
FIG. 2 shows in perspective a mechanical structure of the battery discharge 
gas control system 10, particularly battery assemblies 14 and a gas 
discharge system therefor. FIGS. 3 and 4 illustrate each of the battery 
assemblies 14 with the gas discharge system removed therefrom. In FIG. 2, 
a plurality of battery assemblies 14, each comprising a plurality of 
electrically series-connected batter cells 12, are housed in a battery box 
15 and electrically interconnected. 
As shown in FIG. 3, the battery cells 12 comprise respective single battery 
elements which are series-connected by electrodes 36. As described above, 
each of the battery cells 12 has the gas release port 16 for discharging a 
hydrogen gas which is generated when it is charged and discharged. As 
shown in FIG. 4 the gas release port 16 comprises a gas discharge hole 38 
for discharge a hydrogen gas through a check valve or the like when the 
gas pressure in the battery cell 12 exceeds a predetermined pressure 
level, and a cylindrical seal member 40 which defines the gas discharge 
hole 38 centrally therein. 
In FIG. 3, each of the electrodes 36 of the battery cells 12 is covered 
with an electrode cover 42 which extends between adjacent two of the 
battery cells 12 and encloses two of the electrodes 36 thereof. 
As shown in FIGS. 5 and 6, the gas release ports 16 of the battery cells 12 
are connected to each other by the passage 18 which is defined by a stay 
44 that extends across and over the battery cells 12 and is housed in the 
battery box 15. As shown in FIG. 2, the gas release ports 16 of the 
battery cells 12 of all the battery assemblies 14 which are housed in the 
battery box 15 are interconnected by the single passage 18. 
In FIG. 2, the pressure sensor 22 for detecting the pressure in the passage 
18 is connected to the connecting pipe 20 which is coupled to the passage 
18. The detected output signal from the pressure sensor 22 is converted by 
an A/D converter (not shown) into a digital signal which is then applied 
to the control circuit 24. The control valve 28 which includes the 
solenoid-operated valve 26 actuatable by a control signal from the control 
circuit 24 is connected to an end of the connecting pipe 20. The 
explosion-resistant filter 30 is connected to the control valve 28 and 
covered with a water-resistant cover 54. 
As shown in FIGS. 3, 5, and 6, the battery assembly 14 includes plate-like 
heat exchangers 60 mounted on sides of the battery cells 12 for radiating 
heat from the battery cells 12. 
Operation of the battery discharge gas control system 10 will be described 
below with reference to FIGS. 7, 8A, and 8B. 
For starting to charge or discharge the battery assembly 14, the control 
circuit 24 outputs a signal to open the control valve 28 for a 
predetermined period of time, equalizing the pressure in the passage 18 
substantially to the ambient atmospheric pressure. After the predetermined 
period of time has elapsed, the battery discharge gas control system 10 
starts operating upon a timer interrupt or the like. The pressure sensor 
22 detects the pressure in the passage 18 in a step ST1, and applies a 
detected output signal to the control circuit 24 in a step ST2. The 
control circuit 24, which may comprise a microprocessor or the like as a 
management ECU, receives the detected output signal from the pressure 
sensor 22, and determines the pressure in the passage 18 based on the 
detected output signal from the pressure sensor 22 in a step ST3. If the 
determined pressure in the passage 18 is lower than 1.2 kg/cm.sup.2, for 
example, then the control circuit 24 decides that it is not necessary to 
release a hydrogen gas from the passage 18, and brings its control process 
an end. If the determined pressure in the passage 18 is equal to or higher 
than 1.2 kg/cm.sup.2, then the control circuit 24 generates a control 
signal to actuate the control valve 28, e.g., a control signal to 
intermittently actuate the control valve 28. The solenoid-operated valve 
27 is now intermittently opened In a step ST4 for thereby discharging a 
hydrogen gas from the passage 18 through the explosion-resistant filter 
30. For example, the control signal generated to intermittently actuate 
the control valve 28 turns on the solenoid 26 for two seconds and then 
turns off the solenoid 26 for five seconds in each of successive cycles. 
Therefore, the operated valve 27 is opened for two seconds and then closed 
for five seconds in each of successive cycles. 
Thereafter, the control circuit 24 detects whether the battery charger 32 
is charging the battery assembly 14 or not in a step ST5. The control 
circuit 24 checks the battery charger 32 because if the battery charger 32 
is charging the battery assembly 14 with a hydrogen gas generated, the 
control circuit 24 can prevent a hydrogen gas from being newly generated 
by the battery assembly 14 by stopping the charging operation of the 
battery charger Therefore, if the battery charger 32 is charging the 
battery assembly 14, then the control circuit 24 stops the charging 
operation of the battery charger 32 in a step ST8, after which control 
goes to a step ST7. If the battery charger 32 is not charging the battery 
assembly 14, the control circuit 24 detects whether the battery assembly 
14 is being discharged or not in a step ST6. If the battery assembly is 
being discharged, then the control circuit 24 limits the amount of 
electric energy discharged from the battery assembly 14 in a step ST9, and 
thereafter control goes the step ST7. Specifically, the electric vehicle 
is usually running when the battery assembly 14 is discharged with a 
hydrogen gas generated. In order to reduce the amount of hydrogen gas 
which is generated, the control circuit limits the amount of electric 
energy discharged from the battery assembly 14 to achieve both running 
stability of the electric vehicle and hydrogen gas reduction. 
If the battery assembly 14 is not being discharged in the step ST6 or after 
the step ST8 or ST9, then the control circuit 24 issues a warning signal 
indicating that a hydrogen gas is being discharged from the battery 
assembly 14. Thereafter, control comes to an end, bringing the battery 
discharge gas control system 10 back to a state prior to the timer 
interrupt. 
The battery discharge gas control system 10 is capable of discharging a 
hydrogen gas from the battery assembly 14 for a preset period of time when 
the battery assembly 14 starts being charged, as shown in FIG. 8A, or when 
the battery assembly 14 starts being discharged, as shown in FIG. 8B. 
Specifically, as shown in FIG. 8A, when the battery assembly 14 starts 
being charged, the control circuit 24 is activated by an interrupt caused 
by a charge start signal from the battery charger 32 in a step ST11. Then, 
the control circuit 24 outputs a control signal to open the control valve 
28 in a step ST12. The control signal serves to energize the solenoid 26 
to control the control valve 28 to carry out in a predetermined operation, 
i.e., to open the solenoid-operated valve 27 for a preset period of time 
for thereby discharging a hydrogen gas from the passage 18. 
In a step ST13, the control circuit 24 determines whether the preset period 
of time has elapsed or not. If the preset period of time has elapsed, then 
the control circuit 24 outputs a control signal to close the 
solenoid-operated valve 27 in a step ST14. The solenoid 26 is now 
de-energized to close the solenoid-operated valve 27 for thereby stopping 
the discharge of the hydrogen gas from the passage 18. 
As shown in FIG. 8A, when the battery assembly 14 starts being discharged, 
the control circuit 24 is activated by an interrupt caused by a power 
supply ON signal, e.g., an ignition key signal from the electric vehicle, 
in a step ST15. 
In a step ST16, the control signal 24 detects whether the state of the 
shift lever of the electric vehicle is a first release from a parking 
range or not. If the state of the shift lever of the electric vehicle is 
not a first release from the parking range, then control comes to an end. 
If the state of the shift lever of the electric vehicle is a first release 
from the parking range, then the control circuit 24 outputs a control 
signal to actuate the control valve 28 to open the solenoid-operated valve 
27 in a step ST17. Specifically, when the state of the shift lever of the 
electric vehicle is a first release from the parking range, the battery 
assembly 14 begins to energize the motor 35. The battery assembly 14 has 
not been discharged before the state of the shift lever of the electric 
vehicle is a first release from the parking range. Since the battery 
assembly 14 starts being discharged possibly generating a hydrogen gas 
when the state of the shift lever of the electric vehicle is a first 
release from the parking range, the pressure in the passage 18 is brought 
back substantially to the ambient atmospheric pressure when the battery 
assembly 14 starts being discharged. When the battery assembly 14 starts 
being either charged or discharged, the control valve 28 is closed, and 
the fluid pressure in the passage 18 which is closed has increased or 
decreased due to a humidity change after the control valve 28 has finally 
been closed. Although the pressure in the passage 18 is detected in the 
step ST3 (see FIG. 7), the accuracy of the detected pressure increases by 
bringing the pressure in the passage 18 back to the ambient atmospheric 
pressure when the control process begins. The control signal in the step 
ST17 serves to energize the solenoid 26 to control the control valve 28 to 
carry out in a predetermined operation, i.e., to open the 
solenoid-operated valve 27 for a preset period of time for thereby 
discharging a hydrogen gas from the passage 18. 
In a step ST18, the control circuit 24 determines whether the preset period 
of time has elapsed or not. If the preset period of time has elapsed, then 
the control circuit 24 outputs a control signal to close the 
solenoid-operated valve 27 in a step ST19. The solenoid 26 is now 
de-energized to close the solenoid-operated valve 27 for thereby stopping 
the discharge of the hydrogen gas from the passage 18. 
As described above, the battery discharge gas control system according to 
the present invention, which releases a hydrogen gas generated from the 
battery assembly when the battery assembly is charged and discharged, is 
capable of keeping the battery structure highly resistant to water or 
humidity. Specifically, during a period of time in which no hydrogen gas 
is generated or a generated hydrogen gas is not plenty enough to be 
released while the battery assembly is being charged or discharged, the 
passage connected to the gas release ports of the battery cells is closed 
for thereby keeping the battery structure highly resistant to water or 
humidity. Since the amount of a hydrogen gas generated per unit time can 
be reduced, the concentration of a hydrogen gas in the vicinity of the gas 
release ports can be reduced to a low level. Even in the event of a 
failure of the solenoid-operated valve, the relief valve, or valve means, 
is mechanically opened depending on the pressure in the passage to protect 
the passage from damage. The battery assembly as a whole is thus highly 
durable. 
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.