1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
ELECTRIC POWER STEERING DEVICE
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
TECHNICAL FIELD
[0001] The present disclosure relates to an electric power
steering device.
5
BACKGROUND ART
[0002] In a system that performs automatic parking of a
vehicle, it has been known that, when a vehicle stops at a
turnabout position and performs turnabout, static steering is
10 performed to turn a steering wheel while the vehicle is
stopped. Applying an excessive load on an Electric Power
Steering (EPS), the static steering is likely to cause the
EPS to be overheated. To prevent overheat damage of the EPS,
currents need to be limited and overheat protection needs to
15 be performed.
[0003] To solve these problems, there is a method of
estimating the necessary number of static steering and, so as
not to cause overheat protection to start unexpectedly during
parking assistance, notifying a driver of the estimated
20 number before the start of overheat protection (see Patent
Document 1). Alternatively, after static steering has been
performed and then the vehicle has been advanced, the
steering direction is changed at a stage slightly earlier
than when next static steering is performed. In this way, a
25 static steering amount is reduced (see Patent Document 2).
3
In addition, there is still another method of determining one
route including static steering and another route not
including static steering, and the static steering amount,
depending on the temperature of the EPS (see Patent Document
5 3).
CITATION LIST
PATENT DOCUMENT
[0004] Patent Document 1: Japanese Laid-Open Patent
10 Publication No. 2009-190531
Patent Document 2: Japanese Laid-Open Patent
Publication No. 2015-3565
Patent Document 3: Japanese Patent No. 6079596
15 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] In a method disclosed in Patent Document 1,
limitation or cancellation of parking assistance by overheat
protection cannot be prevented.
20 [0006] In a method disclosed in Patent Document 2, after
static steering has been performed and then the vehicle has
been advanced, the direction is changed into the next
steering direction at the stage earlier than usual, thereby
reducing the steering angle for performing static steering.
25 However, since a load state of a steering device is not
4
detected, even if parking involving static steering by the
steering device is sufficiently possible, a vehicle is parked
through the route for reducing the static steering amount.
Thus, the number of turnabouts until the completion of
5 parking may be increased.
[0007] In a method disclosed in Patent Document 3,
presence/absence of static steering is determined at the
place for turnabout, on the basis of the temperature of the
EPS. Accordingly, another route needs to be regenerated
10 during parking control. The route different from the route
initially set is to be used, thereby increasing the amount of
steering until the completion of parking. Furthermore, a
motor may be overheated due to the increased steering amount,
and thus automatic parking may be interrupted.
15 [0008] The present disclosure has been made to solve the
above problems, and an object of the present disclosure is to
provide an electric power steering device that can avoid a
steering disabled state and cancellation of parking
assistance caused by an overheated motor during parking
20 control and that allows parking control even in an overheat
condition of the motor.
SOLUTION TO THE PROBLEMS
[0009] An electric power steering device according to the
25 present disclosure includes: route generation means for
5
generating a route for driving from an own vehicle position
to a target parking position; calculation command means for
calculating a target steering angle command for causing a
vehicle to drive along the route generated by the route
5 generation means; an automatic steering control unit for
calculating motor current for causing a steering angle to be
formed according to the target steering angle command; an
overheat protection current limit unit for calculating an
overheat protection current limit value from the motor
10 current; and a statically-steerable number determination unit
for calculating a statically-steerable upper limit number on
the basis of the overheat protection current limit value.
EFFECT OF THE INVENTION
15 [0010] Such an electric power steering device disclosed in
the present disclosure can avoid a steering disabled state
and cancellation of parking assistance caused by an
overheated motor during parking control, and allows parking
control even in an overheat condition of the motor.
20
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] [FIG. 1] FIG. 1 is a schematic configuration
diagram of an electric power steering device according to
embodiment 1.
25 [FIG. 2] FIG. 2 is a flowchart illustrating
6
operation of a statically-steerable number determination unit
according to embodiment 1.
[FIG. 3] FIG. 3 is a schematic configuration
diagram of an electric power steering device according to
5 embodiment 2.
[FIG. 4] FIG. 4 is a flowchart illustrating
behavior of a statically-steerable number determination unit
according to embodiment 2.
[FIG. 5] FIG. 5 is a schematic configuration
10 diagram of an electric power steering device according to
embodiment 3.
[FIG. 6] FIG. 6 is another schematic configuration
diagram of the electric power steering device according to
embodiment 3.
15 [FIG. 7] FIG. 7 is an example of a hardware
configuration diagram of the electric power steering device
according to each of embodiments 1 to 3.
DESCRIPTION OF EMBODIMENTS
20 [0012] Hereinafter, an electric power steering device
according to preferred embodiments for carrying out the
present disclosure will be described in detail with reference
to the drawings. In the drawings, the same reference
characters denote the same or corresponding parts, and
25 detailed description thereof will be omitted. Also in the
7
subsequent embodiments, repeated description of components
denoted by the same reference characters will be omitted in
the same manner.
[0013] Embodiment 1.
5 FIG. 1 is a schematic configuration diagram of an
electric power steering device according to embodiment 1.
The electric power steering device includes, as main
components, a surrounding environment sensor group 1, a
parking assistance device 2, an electric power steering (EPS)
10 3, and a steering angle sensor 4.
[0014] As the surrounding environment sensor group 1, a
camera and sonar for monitoring the front, rear, or sides of
a vehicle, a marker sensor for detecting markers in a parking
lot, a GPS device for obtaining GPS information, a reception
15 device for receiving map data in a parking lot, and the like
are mounted in a vehicle. These sensors or devices detect
condition information of the vehicle itself and surrounding
information thereof. The information is transmitted to the
parking assistance device 2 through a communication line of
20 the vehicle such as a communication line of a Controller Area
Network (CAN).
[0015] The parking assistance device 2 is a device for
performing so-called automatic parking, and for outputting a
command for changing vehicle behavior by using various
25 information from the surrounding environment sensor group 1.
8
[0016] The parking assistance device 2 includes: route
generation means 23 for receiving information from the
surrounding environment sensor group 1, calculating own
vehicle position information 21 and target parking position
5 information 22, and generating a route to a target parking
position; and calculation command means 24 for calculating a
signal for a control command on the basis of output from the
route generation means 23. Output from the calculation
command means 24 is outputted to control the electric power
10 steering (EPS) 3, a braking device 5, and a driving device 6.
[0017] In detail, the route generation means 23 detects,
for example, a distance to a vehicle located to the front,
rear, or side, lanes, a parking frame line, an obstacle, and
the like, on the basis of information from the camera of the
15 surrounding environment sensor group 1. From among the
information, map information in a parking lot, GPS
information, and the like, the route generation means 23
selects information necessary for performing parking control.
On the basis of the selected information, the route
20 generation means 23 calculates the own vehicle position
information 21 and the target parking position information 22,
and generates a route from an own vehicle position to a
target parking position.
[0018] The calculation command means 24 calculates the
25 target steering angle command 25 needed from the own vehicle
9
position to the target parking position, according to route
information generated by the route generation means 23, and
outputs the target steering angle command 25 to the electric
power steering (EPS) 3. In addition, the calculation command
5 means 24 calculates and outputs an acceleration and
deceleration command to the driving device 6 and a braking
command to the braking device 5. For example, the
calculation command means 24 issues commands, such as
accelerating so as to travel along a route, steering to cause
10 the vehicle to park between parking vehicles, braking wheels
to cause the vehicle to stop at a vehicle stop position
according to a route, and the like. That is, commands for
performing vehicle speed control needed until the completion
of parking are outputted to the electric power steering (EPS)
15 3, the braking device 5, and the driving device 6.
[0019] Furthermore, the calculation command means 24
calculates a target steering angle 26a and a target vehicle
speed 26b needed from an own vehicle position to a target
parking position. The difference between the target steering
20 angle command 25 and the target steering angle 26a described
above is as follows.
The target steering angle command 25 is a target
steering angle needed for the calculation command means 24 to
operate the vehicle according to the route generated by the
25 route generation means 23, and is a command to be performed
10
in real time. Meanwhile, the target steering angle 26a
refers to all steering to be performed by the calculation
command means 24 until the completion of parking along the
route generated by the route generation means. The target
5 steering angle 26a refers to all the steering, but also
refers to reduced data thereof with contents limited to only
specific points, such as the place where turnabout is
performed, because the data amount for all the time-series
data is enormous.
10 [0020] The electric power steering (EPS) 3 includes an
automatic steering control unit 31, an overheat protection
current limit unit 32, a statically-steerable number
determination unit 33, and a motor control unit 34 that
outputs motor current according to a target current.
15 [0021] The automatic steering control unit 31 receives the
target steering angle command 25 from the parking assistance
device 2 and steering angle information 41 from the steering
angle sensor 4, and calculates a motor target current needed
for steering according to the target steering angle.
20 [0022] The overheat protection current limit unit 32
limits the target current by using an overheat protection
current limit value Y calculated from a motor current amount
of the electric power steering (EPS) 3, to prevent damage due
to overheat of the electric power steering (EPS) 3. That is,
25 the overheat protection current limit value Y is a maximum
11
current value of current that can flow through the motor at
present, to prevent the motor from damaging itself.
[0023] With reference to a flowchart in FIG. 2, behavior
of the statically-steerable number determination unit 33 of
5 embodiment 1 will be described.
The statically-steerable number determination unit
33 estimates a target steering amount for each turnabout,
from the target steering angle 26a and the target vehicle
speed 26b inputted from the calculation command means 24 of
10 the parking assistance device 2 and needed from an own
vehicle position to a target parking position (step S1).
Here, the target steering angle 26a to be inputted need not
be all time-series data until the completion of parking
assistance, and may be data only at each timing of performing
15 turnabout with great change to the target steering angle.
[0024] On the basis of the target vehicle speed 26b,
whether or not operation is static steering can be determined,
and thus, the current amount necessary for turnabout can be
estimated from the target steering amount, which is a
20 variation amount of the target steering angle 26a (step S2).
A predetermined estimated motor current amount per turnabout
is corrected by using the estimated current amount (step S3).
An overheat protection current limit value X to be used until
the completion of parking assistance is calculated, from the
25 corrected estimated motor current amount and the above
12
overheat protection current limit value Y (step S4). This
calculation is the same as that for the overheat protection
current limit value Y to be calculated from the motor current
amount in the overheat protection current limit unit 32, but
5 is performed using the corrected estimated motor current
amount instead of the motor current amount. That is, the
overheat protection current limit value X to be used until
the completion of parking assistance is a maximum current
value of current that can flow through the motor, calculated
10 from the estimated current amount until the completion of
parking. Since the motor is overheated when the current
flows, the overheat protection current limit value X is a
value that basically decreases depending on the corrected
estimated motor current amount.
15 [0025] When the overheat protection current limit value X
until the completion of parking assistance exceeds a
predetermined steerable determination current limit threshold
(a minimum motor current value needed until parking has been
completed) (step S5), a fact that steering can be performed
20 at the inputted target steering angle 26a is outputted as a
determination result of a parking possibility determination
35b (step S6).
[0026] On the other hand, when the overheat protection
current limit value X is not greater than the steerable
25 determination current limit threshold, a fact that steering
13
cannot be performed at the inputted target steering angle is
outputted as a result of the parking possibility
determination 35b (step S7). Then, a statically-steerable
upper limit number 35a is calculated, from the overheat
5 protection current limit value Y and a predetermined
estimated overheat protection current limit value variation
amount per turnabout with static steering (step S8). Here,
the statically-steerable upper limit number 35a is the number
of times of turnabouts with static steering allowable until a
10 predetermined statically-steerable determination current
limit threshold is reached. The statically-steerable upper
limit number 35a is outputted to the route generation means
23 of the parking assistance device 2 (step S9).
[0027] In this case, the statically-steerable upper limit
15 number 35a may be obtained through a map generated from a
relationship between the overheat protection current limit
value Y, the predetermined statically-steerable determination
current limit threshold, and the estimated overheat
protection current limit value variation amount per turnabout
20 with static steering.
[0028] Alternatively, a gain depending on the target
steering angle variation amount inputted in advance is added
to the predetermined estimated overheat protection current
limit value variation amount per turnabout with static
25 steering, and the obtained value may be used for the
14
calculation as well.
[0029] In this case, whether or not a load of the electric
power steering (EPS) 3 in the route generated by the route
generation means 23 is within an acceptable range can be
5 checked, thereby preventing automatic parking control from
being interrupted during automatic parking control due to the
electric power steering (EPS) 3 being in a high-load
condition. Furthermore, even if it is determined that
steering cannot be performed, the statically-steerable upper
10 limit number 35a is outputted to the route generation means
23, and thus the route generation means 23 can add the
statically-steerable upper limit number 35a as a condition to
regenerate a more feasible route.
[0030] According to the present embodiment, as described
15 above, whether or not the electric power steering (EPS) 3 is
in an overheat condition and whether or not the scheduled
parking assistance can be performed are determined. Even
when the electric power steering (EPS) 3 is in an overheat
condition, the statically-steerable number is determined in
20 consideration of a load of the electric power steering (EPS)
3, and thus the parking assistance device can be notified of
information necessary for calculation of a feasible parking
route. Therefore, a shorter route in which parking is
performed than a parking route in which static steering is
25 not performed can be calculated, even when the motor is in an
15
overheat condition.
[0031] Embodiment 2.
A configuration of an electric power steering
device according to embodiment 2 is basically not different
5 from that of embodiment 1, but input and output signals for
the parking assistance device 2 and the electric power
steering (EPS) 3 are different. FIG. 3 is a schematic
configuration diagram of the electric power steering device
according to embodiment 2. That is, in embodiment 1, control
10 is performed in a state in which steering to be performed has
been recognized in advance, whereas in embodiment 2, control
is performed in a state in which steering to be performed has
not been recognized in advance.
[0032] With such difference between the states to be a
15 precondition for control, the target steering angle 26a and
the target vehicle speed 26b needed from an own vehicle
position to a target parking position, which are outputted
from the calculation command means 24 to the staticallysteerable number determination unit 33 in embodiment 1, need
20 not be outputted in embodiment 2. Furthermore, the parking
possibility determination 35b which is outputted from the
statically-steerable number determination unit 33 in
embodiment 1 need not be outputted in embodiment 2.
[0033] In embodiment 2, route generation means 23 detects,
25 for example, a distance to a vehicle located to the front,
16
rear, or side, lanes, a parking frame line, an obstacle, and
the like, on the basis of information from a camera of a
surrounding environment sensor group 1. From among the
information, map information in a parking lot, GPS
5 information, and the like, the route generation means 23
selects information necessary for performing parking control.
[0034] Furthermore, on the basis of the selected
information, the route generation means 23 calculates own
vehicle position information 21 and target parking position
10 information 22. A statically-steerable upper limit number
35a, which is outputted from the electric power steering
(EPS) 3, is added as a condition, and as a route from an own
vehicle position to a target parking position, a parking
route in which static steering is performed within the
15 statically-steerable upper limit number 35a is generated. In
this case, turnabout in which static steering is not
performed may be included.
[0035] Calculation command means 24 calculates a target
steering angle command 25 needed from the own vehicle
20 position to the target parking position, according to
information, generated by the route generation means 23, on a
parking route in which static steering is performed, and
outputs the target steering angle command 25 to the electric
power steering (EPS) 3. In addition, the calculation command
25 means 24 calculates and outputs an acceleration and
17
deceleration command to a driving device 6 and a braking
command to a braking device 5. For example, the calculation
command means 24 issues commands, such as accelerating so as
to travel along a route, steering to cause the vehicle to
5 park between parking vehicles, braking wheels to cause the
vehicle to stop at a vehicle stop position according to a
route, and the like.
[0036] As shown in a flowchart illustrated in FIG. 4, a
statically-steerable number determination unit 33 calculates
10 a statically-steerable upper limit number 35a, from an
overheat protection current limit value Y calculated from a
motor current amount of the electric power steering (EPS) 3
in an overheat protection current limit unit 32, and a
predetermined estimated overheat protection current limit
15 value variation amount per turnabout with static steering
(step S10). Here, the statically-steerable upper limit
number 35a is the number of times of turnabout with static
steering allowable until a predetermined statically-steerable
determination current limit threshold is reached. The
20 statically-steerable upper limit number 35a is outputted to
the route generation means 23 of a parking assistance device
2 (step S11).
[0037] In this case, the statically-steerable upper limit
number 35a may be obtained through a map generated from a
25 relationship between the overheat protection current limit
18
value Y, the predetermined statically-steerable determination
current limit threshold, and the estimated overheat
protection current limit value variation amount per turnabout
with static steering.
5 [0038] In embodiment 2, a load condition of the electric
power steering (EPS) 3 using a motor is not used at the time
of generation of a route or calculation of commands, such as
a target steering angle command, an acceleration and
deceleration command, a braking command, and the like, each
10 of which is processing of the parking assistance device 2.
That is, since steering to be performed has not been
recognized in advance, a load condition cannot be considered.
Therefore, if the electric power steering (EPS) 3 falls into
a steering disabled state during parking assistance due to
15 overheat protection, it is necessary for a driver to take
over the steering halfway through parking control. However,
being in a high-load condition, the electric power steering
(EPS) 3 cannot sufficiently perform steering assistance, that
is, assistance to a driver’s steering to be usually performed.
20 [0039] In this case, the statically-steerable upper limit
number 35a is sent from the electric power steering (EPS) 3
to the route generation means 23, whereby feasibility of
driving assistance can be ensured. The electric power
steering (EPS) 3 outputs, from the statically-steerable
25 number determination unit 33, information on the number of
19
times that the vehicle can perform turnabout with static
steering during which the electric power steering (EPS) 3 may
fall into a high-load condition, to the route generation
means 23.
5 [0040] In this case, since the electric power steering
(EPS) 3 notifies the route generation means 23 of the
statically-steerable upper limit number 35a and a route is
calculated before the start of parking operation, a route
with a shorter vehicle movement distance can be generated,
10 compared to a case where turnabout without static steering is
performed after the electric power steering (EPS) 3 is
detected to be in a high-load condition. For example, during
parallel parking control in which a vehicle can perform
static steering only twice due to the electric power steering
15 (EPS) 3 being in a high load condition, steering without
static steering is performed first, and then turning back
with static steering is performed when a vehicle is driven
between a front vehicle and a rear vehicle in parallel
parking and when final turnabout is performed so as to align
20 a parking direction between the vehicles within a limited
vehicle-movable space. Thus, a route with a consequently
shorter vehicle movement distance can be generated.
[0041] Embodiment 3.
Embodiment 3 will be described with reference to
25 FIG. 5 or FIG. 6. An electric power steering (EPS) 3 in
20
embodiment 3 is different from embodiment 1 or embodiment 2
in that the electric power steering (EPS) 3 in embodiment 3
includes EPS temperature detection means, and a method for
calculating an overheat protection current limit value in an
5 overheat protection current limit unit 32 is also different
as below.
[0042] In embodiment 1 or embodiment 2, the overheat
protection current limit value is calculated solely from the
motor current amount. However, the overheat protection
10 current limit unit 32 of the electric power steering (EPS) 3
according to embodiment 3 calculates the overheat protection
current limit value from an EPS temperature from an EPS
temperature detection means 36, and a motor current amount.
This EPS temperature may indicate any of temperatures of heat
15 generation components, such as a motor of the electric power
steering (EPS) 3, a Field Effect Transistor (FET) mounted in
an Electric Control Unit (ECU) of the electric power steering
(EPS) 3, and the like, constituting the electric power
steering (EPS) 3.
20 The EPS temperature detection means 36 enables more
accurate calculation of the overheat protection current limit
value according to temperature characteristics for each EPS
component.
[0043] In FIG. 7, an example of a hardware configuration
25 mounted in a parking assistance device 2 and the electric
21
power steering (EPS) 3 is shown. The parking assistance
device 2 and the electric power steering (EPS) 3 include a
processor 100 and a storage device 200. Although not shown,
the storage device includes a volatile storage device such as
5 a random access memory and a non-volatile auxiliary storage
device such as a flash memory. The storage device 200 may
also include an auxiliary storage device of a hard disk
instead of the flash memory. The processor 100 executes a
program inputted from the storage device 200 to perform
10 processing of, for example, the route generation means 23,
the calculation command means 24, the automatic steering
control unit 31, the statically-steerable number
determination unit 33, or the like. In this case, the
program is inputted into the processor 100 from the auxiliary
15 storage device via the volatile storage device. The
processor 100 may also output data such as a calculation
result to the volatile storage device of the storage device
200, or may store data into the auxiliary storage device via
the volatile storage device. A plurality of the processors
20 100 and the storage devices 200 may be provided.
[0044] Although the disclosure is described above in terms
of various exemplary embodiments and implementations, it
should be understood that the various features, aspects and
functionality described in one or more of the individual
25 embodiments are not limited in their applicability to the
22
particular embodiment with which they are described, but
instead can be applied, alone or in various combinations to
one or more of the embodiments of the disclosure. It is
therefore understood that numerous modifications which have
5 not been exemplified can be devised without departing from
the scope of the present disclosure. For example, at least
one of the constituent components may be modified, added, or
eliminated. At least one of the constituent components
mentioned in at least one of the preferred embodiments may be
10 selected and combined with the constituent components
mentioned in another preferred embodiment.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0045] 1 surrounding environment sensor group
15 2 parking assistance device
3 electric power steering (EPS)
4 steering angle sensor
23 route generation means
24 calculation command means
20 25 target steering angle command
26a target steering angle
26b target vehicle speed
31 automatic steering control unit
32 overheat protection current limit unit
25 33 statically-steerable number determination unit
23
34 motor control unit
35a statically-steerable upper limit number
35b parking possibility determination
36 EPS temperature detection means
5 41 steering angle information
24
WE CLAIM:
[1] An electric power steering device comprising:
route generation means for generating a route for
driving from an own vehicle position to a target parking
5 position;
calculation command means for calculating a target
steering angle command for performing traveling along the
route generated by the route generation means;
an automatic steering control unit for calculating
10 motor current for causing a steering angle to follow the
target steering angle command;
an overheat protection current limit unit for
calculating an overheat protection current limit value from
the motor current; and
15 a statically-steerable number determination unit
for calculating a statically-steerable upper limit number on
the basis of the overheat protection current limit value.
[2] The electric power steering device according to
20 claim 1, wherein
the statically-steerable number determination unit
calculates the statically-steerable upper limit number
allowable until a predetermined statically-steerable
determination current limit threshold is reached, from the
25 overheat protection current limit value and a predetermined
25
estimated overheat protection current limit value variation
amount per turnabout with static steering.
[3] The electric power steering device according to
5 claim 1, wherein
the calculation command means calculates a target
steering angle and a target vehicle speed from the own
vehicle position to the target parking position, and
the statically-steerable number determination unit
10 calculates a current amount in turnabout from a
variation amount of the target steering angle,
corrects a predetermined estimated motor
current amount per turnabout, on the basis of the current
amount,
15 calculates the overheat protection current
limit value until completion of parking assistance, from the
corrected estimated motor current amount and the overheat
protection current limit value, and
when the overheat protection current limit
20 value until the completion of the parking assistance is not
greater than a predetermined steerable determination current
limit threshold, calculates the statically-steerable upper
limit number allowable until a predetermined staticallysteerable determination current limit threshold is reached,
25 from the overheat protection current limit value and a
26
predetermined estimated overheat protection current limit
value variation amount per turnabout with static steering.
[4] The electric power steering device according to
5 claim 3, wherein
when the overheat protection current limit value
until the completion of the parking assistance exceeds the
predetermined steerable determination current limit threshold,
a determination result that steering is possible is outputted,
10 and
when the overheat protection current limit value is
not greater than the predetermined steerable determination
current limit threshold, a determination result that steering
is impossible is outputted.
15
[5] The electric power steering device according to
claim 2 or 3, wherein
the statically-steerable upper limit number is
obtained through a map generated from a relationship between
20 the overheat protection current limit value and the
predetermined estimated overheat protection current limit
value variation amount per turnabout with static steering.
[6] The electric power steering device according to any
25 one of claims 1 to 5, wherein

an EPS temperature detected by EPS temperature
detection means is used in calculation of the overheat
protection current limit value.