Vehicle engine starting system and method

Details Vehicle engine starting system and method Vehicle engine starting system and method

2001-11-27

2003-11-18

Argenbright, Tony M. (Department: 3747)

Internal-combustion engines

Starting device

Condition responsive control of starting device

C320S135000

Reexamination Certificate

active

06647939

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of, and a system for starting an engine in a vehicle mounted with a secondary battery.
2. Description of the Related Art
A vehicle today may be mounted with a lithium secondary battery which is constituted as a battery pack achieved by, for instance, connecting in series a plurality of lithium ion cells. If a drive source of this vehicle is an internal combustion engine, the lithium secondary battery is utilized as the power source when driving the starter motor to start the engine.
The output performance (discharge characteristics) of a battery is greatly affected by the temperature under normal circumstances. It is difficult to achieve a sufficient output power level with a lithium secondary battery at a low temperature of, for instance, −30° C. In such a case, the torque and the rotation rate required at the starter motor cannot be assured and thus, the engine cannot be started.
Japanese Laid-Open Patent Publication No. H 10-285813 discloses a technology through which the required power level is obtained by heating the lithium secondary battery when the temperature is low.
FIG. 6
shows a schematic structure that may be assumed when this prior art technology is adopted in an engine starting system. A starter motor
30
is connected to a lithium secondary battery
1
via a starter relay
6
connected to a key switch
2
. This engine starting system includes the lithium secondary battery
1
, a heater
32
that heats the secondary battery
1
from the outside, a temperature sensor
34
that detects the temperature in the vicinity of the secondary battery
1
, a voltage sensor
9
that detects the terminal voltage at the secondary battery
1
and a battery controller
36
that controls the overall operation. The battery controller
36
is supplied with power from the secondary battery
1
via an ignition relay
3
. The heater
32
is controlled via a heater switch
33
.
If the terminal voltage at the lithium secondary battery
1
is equal to or lower than a specific voltage level and the temperature in the vicinity of the secondary battery
1
is low when the key switch is turned on and the starter motor drive starts, the battery controller
36
engages the heater
32
in operation to heat the vicinity of the secondary battery
1
. Once temperature of the secondary battery
1
reaches a level at which appropriate discharge characteristics are achieved and the terminal voltage at the secondary battery
1
exceeds the predetermined voltage level, the battery controller
36
implements control on the starter relay
6
so as to supply the power from the lithium secondary battery
1
to the starter motor
30
.
SUMMARY OF THE INVENTION
However, the engine starting system adopting the prior art technology described above requires the heater
32
for heating the lithium secondary battery
1
from the outside and the temperature sensor
34
for detecting the temperature in the vicinity of the secondary battery
1
in addition to the voltage sensor
9
, and thus, the number of required parts increases. In addition, since the battery controller
36
must engage in complex control processing during which the heater
32
is engaged in operation depending upon the terminal voltage at the secondary battery
1
and the temperature in the vicinity of the secondary battery
1
and then the starter relay
6
is controlled based upon the terminal voltage at the secondary battery
1
, the cost of the system is bound to be high. Furthermore, since numerous sensors must be utilized to start the engine, the reliability of engine start cannot be assured easily. For instance, if a failure occurs at the temperature sensor
34
, the engine start control is disabled.
It is possible to reduce the production costs by not providing the voltage sensor
9
. Namely, the lithium secondary battery
1
may be heated from the outside by the heater
32
and it may be judged as to whether or not power can be supplied based upon the temperature in the vicinity of the secondary battery
1
. However, since the secondary battery
1
is heated from the outside in this method, there is bound to be a difference between the surface temperature of the secondary battery
1
detected by the temperature sensor
34
and the temperature inside the battery
1
. Thus, a problem arises in that very different output characteristics may manifest even when the temperature in the vicinity of the secondary battery
1
detected by the temperature sensor
34
remains unchanged. The difference between the surface temperature and the internal temperature becomes more pronounced when the temperature of the secondary battery
1
is low.
This problem is now discussed in further detail in reference to FIG.
7
. Voltage characteristics D indicate the change in the terminal voltage that occurs over time after the heater
32
starts to heat the secondary battery
1
. Temperature characteristics H
1
indicate the change in the temperature near the secondary battery
1
and temperature characteristics H
2
indicate the change in the internal temperature of the secondary battery
1
. The discharge characteristics that allow the engine to be started by the starter motor
30
are achieved at the temperature &dgr;. Namely, the engine cannot be started at the temperature lower than the temperature &dgr;.
When the control described above is implemented, the heater
32
first heats the vicinity of the secondary battery
1
if the temperature of the secondary battery
1
is low. Subsequently, power is supplied to the starter motor
30
after the temperature (H
1
) detected in the vicinity of the secondary battery
1
reaches the temperature &dgr; (point P
1
). However, since the internal temperature (H
2
) of the secondary battery is lower than the temperature &dgr; in reality, the heater
32
must be further driven over a considerable length of time. Since the power from the secondary battery
1
is utilized to drive the heater
32
, the terminal voltage (D) continues to decrease. As a result, the terminal voltage is lowered to a lowest allowable voltage C (point P
2
) without achieving a sufficient output for starting the engine, and thus, the engine cannot be started. Under these circumstances, internal shorting may occur in the secondary battery itself to reduce the service life, as well.
It is also possible that a reference value indicating the temperature level at which it is judged that power can be supplied to the starter motor
30
may be set higher than the temperature &dgr; by taking into consideration the difference between the surface temperature and the internal temperature at the secondary battery
1
. However, this method poses a problem in that as the heater
32
is supplied with more power than it requires from the secondary battery
1
, the available power in the secondary battery
1
is wasted.
An object of the present invention is to provide a vehicle engine starting method and a vehicle engine starting system that make it possible to start an engine with a high degree of efficiency at a low temperature, prevent wasteful power consumption and achieve a high degree of reliability.
In a vehicle engine starting method for driving a starter motor by using a secondary battery as a power source, a voltage at the secondary battery is detected, the detected voltage at the secondary battery is compared with a predetermined value and a power discharge from the secondary battery to the starter motor is allowed if the detected voltage of the secondary battery is equal to or higher than the predetermined value and a discharge is disallowed from the secondary battery to the starter motor if the detected voltage is lower than the predetermined value.
A vehicle engine starting method for supplying power in a secondary battery to a starter motor provided to start an engine via a key switch and a starter relay comprises an engine start procedure during which a voltage at the secondary battery is detected, the detected voltage at the secondary battery is c

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