Temperature detecting device

Details Temperature detecting device Temperature detecting device

2003-10-30

2004-11-30

Verbitsky, Gail (Department: 2859)

Thermal measuring and testing

Temperature measurement

By electrical or magnetic heat sensor

C374S001000, C702S099000

Reexamination Certificate

active

06824308

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to temperature detecting devices, and more particularly to a temperature detecting device for detecting a heat on a heater (power transistor or the like) of a power-operated auxiliary steering system mounted on a vehicle, say an automobile, by the use of a heat-sensitive resistance element (element having a resistance value changing sensitive to heat; thermistor, platinum ohmmeter or the like).
2. Description of the Related Art
In the power-operated auxiliary steering system, generally the manipulation amount of a steering wheel is converted into an electric signal and amplified by a power transistor. By an output of the transistor, the motor built in the steering unit is driven to generate an auxiliary steering force commensurate with the manipulation amount.
FIG. 13
is an essential-part device structural view of a power-operated auxiliary steering system. In this figure,
1
is a control unit for converting a manipulation amount of steering wheel into an electric signal,
2
is a power unit, and
3
is a motor. In many cases, the control unit
1
and the power unit
2
are accommodated within the separated cases. This is because of a countermeasure not to cause a malfunction in the constituent part (microcomputer and its peripheral circuits, etc.) of the control unit
1
under the influence of a heat of the power transistor
2
a
included in the power unit
2
.
The power transistor
2
a
included in the power unit
2
has a heat in an amount increasing with a drive current to the motor
3
. It also increases depending upon a temperature of service environment under the blazing sun in the daytime. For this reason, particularly, the power transistor
2
a
for vehicular application essentially necessitates a preventive measure against thermal degradation. It is a conventional practice to arrange heat-sensitive resistance elements
2
b
,
2
c
(reason for providing two elements will be referred later) such as thermistors in locations beside the power transistor
2
a
. The temperature-detection signal of the same is captured into the control unit
1
, to carry out a temperature compensation for reducing the driving current to the motor
3
when the temperature is high.
In the meanwhile, the “heat-sensitive resistance element” such as a thermistor suffers a failure of “disconnection” or “short circuit” to rarely occur. In the case of a disconnection failure of those, because device output is lost at once, the failure is easy to sense, e.g. measure can be readily taken including to issue an alarm to the driver. However, in the case of a short circuit failure, because symptom gradually proceeds from a partial short circuit into a whole short circuit, device output changes little by little thus making it difficult to sense a short circuit failure. For this reason, in the case of detecting a temperature lower than the actual temperature, the power transistor
2
a
is driven by an excessive driving current. This results in a disadvantage that the power transistor
2
a
is deteriorated acceleratedly.
Thus, there is known an art that a plurality of (usually, two) heat-sensitive resistance elements
2
b
,
2
c
are provided to compare between the detection signals thereof, making it possible to sense an occurrence of failure (disconnection or short circuit) in any one of the heat-sensitive resistance elements
2
b
,
2
c
. For example, Patent Document 1 has two thermistors having the same characteristics (e.g. negative characteristics that resistance value lowers with increasing temperature), so that the end-to-end voltage Va, Vb of the thermistors can be converted into detection temperatures Ta, Tb for extraction. Furthermore, the lower detection temperature of those is employed as a correct detection temperature.
Herein, the reason of “employing the lower detection temperature as a correct detection signal” is because of the following reason. Namely, as described in a passage [0061] of the document, “in the case that a short circuit failure occurs in any one of the two thermistors, errors are caused in the detection temperature Ta, Tb obtained from the thermistor end-to-end voltage Va, Vb. Because of the negative characteristic of thermistor, the error in the detection temperature Ta, Tb is toward the higher temperature. Accordingly, by employing the “lower” detection temperature, the thermistor on which a short circuit failure occurs can be ignored. Eventually, temperature detection is possible without encountering errors.”
[Patent Document 1]
JP-A-7-190576 (pages 2-7, FIG. 8)
However, the temperature detecting device in the prior art is nothing more than an arrangement with two heat-sensitive resistance elements in locations nearby the heater, or a power transistor, wherein detection signals thereof is captured into the control unit for the purpose of comparison and consideration, thus involving the following problem.
FIG. 14
is an essential-part connection diagram of a control unit
1
and a power unit
2
. The power unit
2
has a power transistor
2
a
as a heater and two heat-sensitive resistance elements
2
b
,
2
c
(hereinafter referred to as “a first heat-sensitive resistance element
2
b
, a second heat-sensitive resistance element
2
c
”) arranged in locations nearby the power transistor
2
a
. The control unit
1
has two pull-up resistances
1
a
,
1
b
(hereinafter referred to as “a first pull-up transistor
1
a
, a second pull-up transistor
1
b
”) and a microcomputer
1
e
incorporating (or satisfactorily attached externally with) two AD converters
1
c
,
1
d
(hereinafter referred to as “a first AD converter
1
c
, a second AD converter
1
d
”). Note that “AD converter” is an abbreviated form of analog-to-digital converter.
Four lines
3
a
-
3
d
are laid between the control unit
1
and the power unit
2
. The first heat-sensitive resistance element
2
b
has one end connected to an input terminal of the first AD converter
1
c
through the line
3
a
and to a power source VCC through the first pull-up resistance
1
a
. The other end of the first heat-sensitive resistance element
2
b
is connected to a ground
1
f
of the control unit
1
through the line
3
b
. Meanwhile, the second heat-sensitive resistance element
2
c
has one end connected to an input terminal of the second AD converter
1
d
through the line
3
c
and to the power source VCC through the second pull-up resistance
1
b
. The other end of the second heat-sensitive resistance element
2
c
is connected to the ground if of the control unit
1
through the line
3
d.
The disadvantages in this configuration lies in the four lines
3
a
-
3
d
needed between the control unit
1
and the power unit
2
, the two pull-up resistances
1
a
,
1
b
needed in the control unit
1
, and the two AD converters
1
c
,
1
d
needed in the control unit
1
. Eventually, the disadvantages are to pose a problem of increasing the number of parts and raising the cost of manufacturing.
Therefore, it is an object of the present invention to provide a temperature detecting device capable of reducing the number of lines between the control unit and the power unit, the number of pull-up resistances within the control unit or the number of AD converters within the control unit, thereby reducing the manufacturing cost.
SUMMARY OF THE INVENTION
A temperature detecting device according to this invention comprises: two heat-sensitive resistance elements arranged nearby an arbitrary heater and made even in characteristic; extraction-mode executing means for selectively executing a first voltage extraction mode for connecting the two heat-sensitive resistance elements in parallel between a power source and a ground through one of a pull-up resistance and a pull-down resistance and extracting a voltage of the two heat-sensitive resistance elements by a resistance divisional voltage, and a second voltage extraction mode for connecting any one of the two heat-sensitive resistance elements between the power source and the groun

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