Microcomputer-built-in, on-vehicle electric unit

Details Microcomputer-built-in, on-vehicle electric unit Microcomputer-built-in, on-vehicle electric unit

1998-08-05

2001-01-02

Chin, Gary (Department: 3661)

Data processing: vehicles, navigation, and relative location

Vehicle control, guidance, operation, or indication

Vehicle subsystem or accessory control

C701S029000, C700S300000, C702S058000

Utility Patent

active

06169944

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to microcomputer-built-in, on-vehicle electric units, and more specifically, to a microcomputer-built-in, on-vehicle electric unit in which stored information in a memory section can be maintained by easy and inexpensive means when the microcomputer is reset because the voltage of an on-vehicle power supply which drives the on-vehicle unit is reduced for some reason.
2. Description of the Related Art
For an on-vehicle electric unit, for example, for an on-vehicle air conditioner, a product inspection test generally includes an item in which, even if the voltage of an on-vehicle power supply (battery) which drives the on-vehicle air conditioner is reduced for several milliseconds to several seconds, information indicating the operating condition which specifies an operating state immediately before the voltage reduction shall be maintained. An on-vehicle air conditioner which satisfies specifications, including such an item, is produced.
An on-vehicle electric unit, for example, an on-vehicle air conditioner usually includes a manual-operation section formed of a pushbutton operating member for selecting an air outlet, a pushbutton operating member for making a selection from in-vehicle air circulation and ventilation, and a sliding operating member for selecting an inside-vehicle temperature. A CPU is also mounted to efficiently control the on-vehicle air conditioner, and a random access memory (RAM) and a read only memory (ROM) are also provided together with the CPU to serve as a microcomputer as a whole. Operation setting information specified when the manual-operation section is operated, and information indicating the operating condition of the on-vehicle air conditioner at automatically-set setting information are stored in the RAM. An operation program for operating the microcomputer is stored in the ROM. The automatically-set setting information refers to automatically-specified setting information such as a setting in which a front-face outlet is automatically selected as an air outlet when the on-vehicle air conditioner serves as a cooling system (cooling), and a setting in which a lower outlet is automatically selected as an air outlet when the on-vehicle air conditioner serves as a heater (heating).
When the voltage of an on-vehicle power supply which drives the on-vehicle air conditioner is reduced for several milliseconds to several seconds, a voltage applied to a reset IC which resets the microcomputer is reduced, and thereby the microcomputer is reset. The RAM contents, namely, the information indicating the operating condition which must be maintained in the RAM even if the voltage of the power supply drops, is deleted.
In a known on-vehicle air conditioner, some countermeasures have been taken against such a voltage drop of an on-vehicle power supply, in order to prevent the information indicating the operating condition stored in the RAM from being deleted.
FIG. 5
is a block diagram of such a known on-vehicle air conditioner provided with a countermeasure against a voltage drop of an on-vehicle power supply.
As shown in
FIG. 5
, this on-vehicle air conditioner includes a one-chip microcomputer
50
formed of a central processing unit (CPU)
51
, a RAM
52
, and a ROM
53
, an input and output circuit
54
which includes a manual-operation section, an air-feeding compressor, and a temperature control mechanism, a regulator
55
connected to a power supply for adjusting a power-supply voltage, a reset circuit
56
for detecting a voltage drop of the output voltage of the regulator
55
and generating a reset signal to the CPU
51
, and a backup circuit
57
formed of a diode
58
connected in series and a large-capacitance capacitor
59
shunt-connected.
In this on-vehicle air conditioner, the large-capacitance capacitor
59
in the backup circuit
57
is always charged to have the voltage of an on-vehicle power supply (battery, not shown). If the voltage of the on-vehicle power supply is reduced for some reason, for example, due to an activation of a starter motor, a voltage drop is compensated for by discharging the charged voltage of the large-capacitance capacitor
59
to prevent the output voltage of the regulator
55
from being reduced.
FIG. 6
is a block diagram of another known on-vehicle air conditioner provided with a countermeasure against a voltage drop of a power supply.
As shown in
FIG. 6
, this on-vehicle air conditioner differs from the on-vehicle air conditioner shown in
FIG. 5
in that the backup circuit
57
is removed and an electrically erasable programmable read-only memory (EEPROM)
60
is provided instead.
In
FIG. 6
, the same symbols as those used in
FIG. 5
are assigned to the same elements as those shown in
FIG. 5
, and descriptions thereof will be omitted.
In this on-vehicle air conditioner, information indicating an operating condition is stored in the EEPROM
60
as well as in a RAM
52
at the same time. If the voltage of an on-vehicle power supply is reduced for some reason, a CPU
51
reset due to a voltage drop reads the information indicating the operating condition stored in the EEPROM
60
and stores it into a RAM
52
. Therefore, the information indicating the operating condition is always stored in the RAM
52
substantially.
In the known on-vehicle air conditioners each having a countermeasure against a voltage drop of the power supply, if the voltage of the on-vehicle power supply is reduced for several milliseconds to several seconds, by compensating the power-supply voltage by the use of the charged voltage of the large-capacitance capacitor
59
in the backup circuit
57
, or by always storing the information indicating the operating condition stored in the EEPROM
60
into the RAM
52
, the information indicating the operating condition stored in the RAM
52
is effectively maintained. Since special hardware, such as the backup circuit
57
and the EEPROM
60
, has been added, the number of components increases, the structure becomes complicated, and the number of assembling processes also increases. In addition to these causes, since the large-capacitance capacitor
59
in the backup circuit
57
and the EEPROM
60
are expensive circuit components, the manufacturing cost of the on-vehicle air conditioner is increased and the price of the on-vehicle air conditioner is also increased.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a microcomputer-built-in, on-vehicle electric unit which can maintain information indicating an operating condition stored in a RAM if a voltage of an on-vehicle power supply is reduced, without any special hardware with a least cost increase.
A RAM generally maintains its stored contents even if its power voltage drops for a short period of time. This short-time voltage drop in which the RAM maintains its stored contents is defined as a momentary interruption.
The foregoing object is achieved according to one aspect of the present invention through the provision of a microcomputer-built-in, on-vehicle electric unit including: a microcomputer formed of a RAM which stores information indicating an operating condition of the on-vehicle electric unit and momentary-power-supply-interruption check information, a ROM which stores an operation program of the microcomputer, an initial value for the information indicating the operating condition, and the momentary-power-supply-interruption check information, and a CPU which controls the on-vehicle electric unit according to the information indicating the operating condition and the operation program; and a reset circuit which resets the microcomputer if a voltage of an on-vehicle power supply which drives the on-vehicle electric unit is reduced, wherein the microcomputer checks whether the momentary-power-supply-interruption check information stored in the RAM remains when the microcomputer is reset by the reset circuit; when the momentary-power-supply-interruption check information is detected, the microcomputer dete

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