1. An on-board device comprising an on-board communication device that communicates with a ground communication device and a speed detection device that detects a vehicle speed, wherein, when the vehicle speed detected by the speed detection device is equal to or lower than a predetermined value, the on-board communication device determines that the on-board communication device is present within a communication range of the ground communication device when a signal magnetic field intensity of a signal from the ground communication device received by the on-board communication device is higher than a first threshold, and when the vehicle speed detected by the speed detection device is higher than the predetermined value, the on-board communication device determines that the onboard communication device is present within the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the onboard communication device is higher than a third threshold smaller than the first threshold.

2. The on-board device according to claim 1, wherein, when the vehicle speed detected by the speed detection device is equal to or lower than the predetermined value, the on-board communication device determines that the onboard communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the onboard communication device is lower than a second threshold smaller than the third threshold, and when the vehicle speed detected by the speed detection device is higher than the predetermined value, the on-board communication device determines that the onboard communication device is present outside the communication range of the ground communication device 0 4 1'93~4 1 4 FEB 2011 b - 13 - ORIGINAL when the signal magnetic field intensity of the signal from the ground communication device received by the onboard communication device is lower than the third threshold.

3. The on-board device according to claim 2, wherein the magnetic field intensity received by the on-board communication device from the ground communication device is used as the third threshold when a distance between the on-board communication device and the ground communication device is equal to a prescribed value.

4. The on-board device according to claim 2 or claim 3, wherein the magnetic field intensity received by the onboard communication device from the ground communication device is used as the second threshold when the distance between the on-board communication device and the ground communication device is equal to the prescribed value plus a difference between a height of the vehicle measured when the vehicle is empty and a height of the vehicle measured when the vehicle is full.

5. The on-board device according to any one of claims 2 to 4, wherein the magnetic field intensity received by the on-board communication device from the ground communication device is used as the first threshold when the distance between the on-board communication device and the ground communication device is equal to the difference between the height of the vehicle measured when the vehicle is empty and the height of the vehicle measured when the vehicle is full, minus the prescribed value.

6. The on-board device according to claim 1, wherein information on the vehicle speed detected by the speed detection device is reliable information duplicated by -an automatic vehicle control device. ORIGINAL 7 . The on-board device according to claims 1 to 6, wherein the predetermined value is equal to or lower than 45 km/h.

8. The on-board device according to claims 1 to 6, wherein the predetermined value is a speed close to zero.

9. An on-board device comprising an on-board communication device that communicates with a ground communication device and a door open and close detection device for a vehicle, wherein, when door open and close information detected by the door open and close detection device is indicative of door close, the on-board communication device determines that the on-board communication device is present within a communication range of the ground communication device when a signal magnetic field intensity of a signal from the ground communication device received by the on-board communication device is higher than a first threshold, and when the door open and close information detected by the door open and close detection device is indicative of door open, the on-board communication device determines that the on-board communication device is present within the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is higher than a third threshold smaller than the first threshold.

10. The on-board device according to claim 9, wherein, when the door open and close information detected by the door open and close detection device is indicative of door close, the on-board communication device determines that the on-board communication device is present outside a communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on board communication device is lower than a second threshold smaller than the third threshold, and when the door open and close information detected by the door open and close detection device is indicative of door open, the on-board communication device determines that the on-board communication device is present outside the communication range of the ground communication device when the signal magnetic field intensity of the signal from the ground communication device received by the on-board communication device is lower than the third threshold.

11. An on-board device, substantially as herein described with reference to accompanying drawings.

SPOT COMMUNICATION EQUIPMENT FOR VEHICLE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an on-board
communication device that detects a ground communication
device in a system that transmits and receives, for
example, position information used for moving vehicle
control between the ground and the vehicle, and more
particularly to prevention of possible misdetection of
the ground communication device.
Description of the Related Art
According to a conventional technique, information
is transmitted from the ground to a vehicle via a ground
communication device installed on the ground and an onboard
communication device installed on the vehicle. The
ground communication device is wirelessly supplied with
power by the on-board communication device using a
driving power wave. After the power supply, the ground
communication device transmits information to the onboard
communication device by electromagnetic coupling
using a frequency different from the frequency of the
driving power wave.
A magnetic field intensity received from the ground
communication device is utilized to determine that the
on-board communication device has entered and exited the
communication range of the ground communication device
(hereinafter expressed as "the ground communication
device has been detected"). The magnetic field intensity
is maximized when an electrically central position of the
on-board communication device aligns with an electrically
central position of the ground communication device. The
magnetic field intensity decreases with increasing
distance between the electrically central position of the
on-board communication device and the electrically
central position of the ground communication device.
This characteristic is used to set an appropriate
threshold of one or more and to determine that the ground
communication device has been detected when the magnetic
field intensity exceeds the threshold. Refer to Japanese
Patent Laid-Open No. 2005-8103 (Patent Document 1) and
Japanese Patent Laid-Open No. 2010-70021 (Patent Document
2).
For example, possible shaking of a moving vehicle
varies vertical and lateral positional relations between
the on-board communication device and the ground
communication device. In particular, when vibration
occurs while the moving vehicle is stopped, the signal
level of the received magnetic field intensity and the
like may fluctuate across the threshold. When such a
phenomenon occurs, the on-board communication device
detects one ground communication device a plurality of
times, thus hindering normal moving vehicle control.
SUMMARY OF THE INVENTION
With the above-described problem in view, the
present invention provides an on-board communication
device that has a first threshold and a second threshold
for low speed traveling in connection with a threshold
for determining that a ground communication device has
been detected based on a magnetic field intensity
received from the ground communication device, the first
threshold being a ground communication device entry side
threshold and the second threshold being a ground
communication device exit side threshold. The thresholds
have a hysteresis property that resists noise. This
prevents possible misdetection of the ground
communication device during low speed traveling.
Moreover, an on-board device is provided which has a
third threshold for traveling and in which the on-board
communication device switches among the first threshold,
the second threshold, and the third threshold depending
on an operating condition of a moving vehicle determined
based on, for example, speed information on the moving
vehicle to prevent a possible shift in the communication
range between the on-board communication device and the
ground communication device during traveling.
The present invention can provide an on-board device
that prevents possible misdetection of the ground
communication device during low speed traveling including
vehicle stop.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating relations between
the speed of a moving vehicle and a magnetic field
intensity threshold for detection of a ground
communication device;
FIG. 2 is a diagram showing Embodiment 1 according
to the present invention;
FIG. 3 is a diagram showing Embodiment 2 according
to the present invention;
FIG. 4 is a flowchart of an operation of detecting
the ground communication device according to the present
invention;
FIG. 5 is a diagram defining a third threshold;
FIG. 6 is a diagram illustrating a moving vehicle
and the height of an antenna of an on-board communication
device in a case where passengers are present and in a
case where no passengers are present;
FIG. 7 is a diagram showing a slide distance for a
communication range slide used when the value of the
threshold is not changed depending on the speed of the
moving vehicle;
FIG. 8 is a diagram illustrating a first threshold,
a second threshold, and the third threshold;
FIG. 9 is a diagram of Example 1 of relations
between time and the magnetic field intensity received by
the antenna of the on-board communication device when the
moving vehicle is stopped; and
FIG. 10 is a diagram of Example 2 of relations
between time and the magnetic field intensity received by
the antenna of the on-board communication device when the
moving vehicle is stopped.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be
described with reference to the drawings below. FIG. 2
shows a general configuration of the present invention.
An on-board communication device including a computing
section 2-2 and an antenna 2-3 is mounted on a moving
vehicle 2-1. Furthermore, a speed detector 2-6 mounted
to a wheel 2-5 detects a vehicle speed. The speed
detected by the speed detector 2-6 is transmitted to an
on-board control section 2-4 that ensures safety of a
vehicle. Speed information utilized by the on-board
control section 2-4 is transmitted to an on-board
communication device 2-2. Each of the on-board control
section 2-4 and the speed detector 2-6 are duplicated,
and thus, the speed information used by the on-board
control section 2-4 is very secure. Based on the speed
information provided by the on-board control section 2-4,
the on-board communication device 2-2 switches between a
threshold beyond which the on-board communication device
2-2 determines that a ground communication device 2-7 has
been detected during low speed traveling when the moving
vehicle 2-1 is near a stop position such as a bus stop
and a threshold beyond which the on-board communication
device 2-2 determines that the ground communication
device 2-7 has been detected during high speed traveling.
For the threshold used during low speed traveling,
different thresholds are used for a ground communication
device entry side and for a ground communication device
exit side. The ground communication device entry side
threshold is hereinafter referred to as a first threshold.
The ground communication device exit side threshold is
hereinafter referred to as a second threshold.
Furthermore, a threshold used for high speed traveling is
a third threshold.
The first threshold increases a determination level
compared to the third threshold. The second threshold
reduces the determination level compared to the third
threshold. This provides the thresholds with a
hysteresis property, offering resistance to noise caused
by shaking and the like of the moving vehicle during low
speed traveling including vehicle stop.
A flowchart in FIG. 4 shows an operation flow of
detection of the ground communication device according to
the present invention.
For limitation of a communication range between the
ground communication device and an antenna, the third
threshold is defined as a magnetic field intensity
received by the on-board communication device when the
distance between the ground communication device and the
antenna of the on-board communication device is equal to
L.
FIG. 5 shows relations between the magnetic field
intensity and the distance between the antenna and the
ground communication device.
Now, it is assumed that the moving vehicle is
traveling from a left side to a right side in FIG. 5.
The magnetic field intensity received by the antenna
increases consistently as the antenna mounted on the
moving vehicle approaches the ground communication device
as shown at 5-1. At a point A shown at 5-2 (the distance
between the ground communication device and the antenna
is equal to L), the antenna receives a magnetic field
intensity higher than the third threshold. This allows
the on-board communication device to determine that the
ground communication device has been detected (determine
that the antenna has entered the communication range).
That is, the on-board communication device determines
that the antenna is present within the communication
range of the ground communication device.
Subsequently, the moving vehicle passes over the
center of the ground communication device. At a point B
shown at 5-3 (the distance between the ground
communication device and the antenna is equal to L), the
on-board communication device receives a magnetic field
intensity lower than the third threshold. Then the onboard
communication device determines that the antenna
has exited the communication range of the ground
communication device. That is, the on-board
communication device determines that the antenna is
present outside the communication range of the ground
communication device.
In general, a carrier frequency used for
communication from the ground communication device to the
on-board communication device is equal to or lower than
10 MHz, and the maximum communication range L is equal to
or smaller than about 2 m. In this case, the magnetic
field intensity received by the on-board communication
device attenuates in proportion to the cube of the
distance between the ground communication device and the
on-board communication device in accordance with a
neighborhood solution. Thus, the third threshold for the
magnetic field intensity is expressed by:
[Equation 11
Third threshold = C/(LI3
In this expression, a coefficient dependent on the
construction of the ground communication device and the
antenna is denoted by C, which is a constant herein.
While the moving vehicle is stopped at a bus stop or
the like, passengers get on and off the moving vehicle,
and thus, the antenna mounted on the moving vehicle
shakes in the vertical direction along with the moving
vehicle. When the range of the shake is denoted by Ah,
the maximum value Ah,,, of the range of the shake can be
approximated to the difference in the height of the
moving vehicle between when the moving vehicle is full of
passengers (full vehicle) as shown at 6-1 in FIG. 6 and
when the moving vehicle has no passenger (empty vehicle)
as shown at 6-2.
If the empty moving vehicle is stopped when the
distance between the ground communication device and the
antenna is equal to L and passengers get on the moving
vehicle until the moving vehicle is full, then a magnetic
field intensity H2 received by the antenna of the onboard
communication device is expressed by:
[Equation 21
A change AH2 from the magnetic field intensity obtained
when the moving vehicle is empty is expressed by:
[Equation 31
Furthermore, if the full moving vehicle is stopped
when the distance between the ground communication device
and the antenna is equal to L and all the passengers get
off the moving vehicle, a magnetic field intensity H3
received by the antenna of the on-board communication
device is expressed by:
[Equation 41
A change AH3 from the magnetic field intensity obtained
when the moving vehicle is full is expressed by:
[Equation 51
AH3 = CIQ3 - C/(L+dh ma33
The third threshold is changed to the first
threshold and the second threshold when the moving
vehicle is stopped so as to prevent the change in
magnetic field intensity from causing the on-board
communication device to detect entry into and exit from
the range of communication with the ground communication
device.
The on-board communication device can determine that
the moving vehicle is stopped based on speed information
provided by the on-board control section.
In this case, the first threshold and the second
threshold are set as follows so as to prevent the
Expressions (3) and (4) from being affected by the
maximum range of fluctuation of the magnetic field
intensity occurring when passengers get on and off the
moving vehicle.
[Equation 61
For entry determination : First threshold = Hz = CI(L-Ah ma33
[Equation 71
For exit determination : Second threshold = H3 = C/(L+dh mad3
The on-board communication device determines that
the moving vehicle has left and that loading and
unloading of passengers has ended, based on the speed
information provided by the on-board control section.
Subsequently, the on-board communication device returns
the threshold for the magnetic field intensity to the
third threshold in order to limit the communication range
between the antenna and the ground communication device
to L. If the on-board communication device uses the
first threshold and the second threshold for all the
speed regions of the moving vehicle instead of switching
the threshold depending on the speed, the communication
range shifts by Ahmax in a direction in which the moving
vehicle travels as shown in FIG. 7.
FIG. 1 shows relations between the vehicle speed of
the antenna with respect to the ground communication
device and each of the first threshold, the second
threshold, and the third threshold. FIG. 8 shows
relations among the distance, the magnetic field
intensity, the first threshold, the second threshold, and
the third threshold.
Furthermore, a case will be described in which the
moving vehicle is stopped near the boundary of the
communication range between the antenna and the ground
communication device and in which passengers get on and
off the moving vehicle.
FIG. 9 is a diagram showing relations between the
time and the magnetic field intensity received at the
antenna which are observed when the moving vehicle full
of passengers is stopped inside the boundary of the
communication range (and closer to the ground
communication device) between the antenna of the on-board
communication device and the ground communication device
and when passengers then get off the moving vehicle. The
magnetic field intensity received by the antenna of the
on-board communication device while the moving vehicle is
stopped as shown at 9-2 slightly exceeds the third
threshold. Thus, the on-board communication device
determines that the ground communication device has been
detected (determines that the antenna has entered the
communication range). Upon determining that the moving
vehicle is stopped based on the speed information, the
on-board communication device changes the third threshold
to the first threshold beyond which the on-board
communication device determines that the ground
communication device has been detected (determines that
the antenna has entered the communication range) and the
second threshold beyond which the on-board communication
device determines that the antenna has exited the
communication range. At 9-3, a door of the moving
vehicle is opened, and the passengers get off the moving
vehicle. At this time, the moving vehicle vibrates up
and down and moves away from the ground communication
device. Thus, the received magnetic field intensity
behaves as shown at 9-4. However, since the threshold
beyond which the on-board communication device determines
that the antenna has exited the communication range has
been changed to the second threshold, the on-board
communication device does not determine that the antenna
has exited the communication range. At this time, if the
present invention is not used and only one type of
threshold is provided, then the on-board communication
device repeatedly determines, at a point 9-4, that the
antenna has exited the communication range and that the
ground communication device has been detected (that the
antenna has entered the communication range).
FIG. 10 is a diagram showing a case where an empty
moving vehicle is stopped slightly outside the boundary
of the communication range of the antenna of the on-board
communication device and where passengers get on the
moving vehicle until the moving vehicle is full. The
magnetic field intensity received by the antenna of the
on-board communication device while the moving vehicle is
stopped as shown at 10-2 is slightly lower than the third
threshold. Thus, the on-board communication device does
not determine that the ground communication device has
been detected (not determine that the antenna has entered
- 10 -
the communication range). When the on-board
communication device determines that the moving vehicle
is stopped based on the speed information, the third
threshold changes to the first threshold beyond which the
on-board communication device determines that the ground
communication device has been detected (determines that
the antenna has entered the communication range) and the
second threshold beyond which the on-board communication
device determines that the antenna has exited the
communication range. At 10-3, the door of the moving
vehicle is opened, and passengers get on the moving
vehicle. At this time, the moving vehicle vibrates up
and down and approaches the ground communication device.
Thus, the received magnetic field intensity behaves as
shown at 10-4. However, since the threshold beyond which
the on-board communication device determines that the
ground communication device has been detected (determines
that the antenna has entered the communication range) has
been changed to the first threshold, the on-board
communication device does not determine that the ground
communication device has been detected. At this time, if
the present invention is not used and only one type of
threshold is provided, then the on-board communication
device repeatedly determines, at a point 10-4, that the
ground communication device has been detected (that the
antenna has exited the communication range) and that the
antenna has entered the communication range. Thus, one
ground communication device is detected a plurality of
times.
Other embodiments will be described belo-w..
Furthermore, the speed information is transmitted to the
on-board communication device via the on-board control
section in order to allow the use of reliable speed
information. However, as shown in FIG. 3, the speed
information may be transmitted from the speed detectors
directly to the on-board communication device. In this
case, since the speed information relates to safety,
speed detection needs a high safety arrangement such as
duplication. The speed information may be reliable
information resulting from a duplication process carried
out by an automatic vehicle control device mounted in the
vehicle.
Furthermore, in the above-described embodiment, the
on-board communication device determines whether the
moving vehicle is traveling at high speed (the moving
vehicle is traveling) or at low speed (the moving vehicle
is stopped). However, another device such as the onboard
control section may make this determination and
report to the on-board communication device by
communication.
A speed beyond which the moving vehicle is
determined to be traveling at high speed (the moving
vehicle is traveling) or at low speed (the moving vehicle
is stopped), that is, a vehicle speed at which the
threshold is switched, may be equal to or lower than a
speed limit for the vicinity of a stop position (for
example, 45 km/h). Alternatively, the speed may be a
speed close to zero.
Additionally, the above-described embodiment
determines whether the moving vehicle is traveling or
stopped based on the speed information. However, a
device that can detect whether the door is open or closed
may be provided to allow determination of whether the
moving vehicle is traveling or stopped based on door open
and close information from the device, in turn allowing a
change of the threshold for the magnetic field intensity.
That is, when the door is closed, the on-board
communication device determines that the moving vehicle
is traveling and then determines the positional relation
between the on-board communication device and the ground
communication device using the third threshold as
described above. When the door is open, the on-board
communication device determines that the moving vehicle
is stopped and then determines the positional relation
between the on-board communication device and the ground
communication device using the first and second
thresholds as described above.

Claims:
~ ~ ~ G I N A L
1. An on-board device comprising an on-board
communication device that communicates with a ground
communication device and a speed detection device that
detects a vehicle speed,
wherein, when the vehicle speed detected by the
speed detection device is equal to or lower than a
predetermined value, the on-board communication device
determines that the on-board communication device is
present within a communication range of the ground
communication device when a signal magnetic field
intensity of a signal from the ground communication
device received by the on-board communication device is
higher than a first threshold, and
when the vehicle speed detected by the speed
detection device is higher than the predetermined value,
the on-board communication device determines that the onboard
communication device is present within the
communication range of the ground communication device
when the signal magnetic field intensity of the signal
from the ground communication device received by the onboard
communication device is higher than a third
threshold smaller than the first threshold.
2. The on-board device according to claim 1, wherein,
when the vehicle speed detected by the speed detection
device is equal to or lower than the predetermined value,
the on-board communication device determines that the onboard
communication device is present outside the
communication range of the ground communication device
when the signal magnetic field intensity of the signal
from the ground communication device received by the onboard
communication device is lower than a second
threshold smaller than the third threshold, and
when the vehicle speed detected by the speed
detection device is higher than the predetermined value,
the on-board communication device determines that the onboard
communication device is present outside the
communication range of the ground communication device
0 4 1'93~4
1 4 FEB 2011
b - 13 -
ORIGINAL
when the signal magnetic field intensity of the signal
from the ground communication device received by the onboard
communication device is lower than the third
threshold.
3. The on-board device according to claim 2, wherein
the magnetic field intensity received by the on-board
communication device from the ground communication device
is used as the third threshold when a distance between
the on-board communication device and the ground
communication device is equal to a prescribed value.
4. The on-board device according to claim 2 or claim 3,
wherein the magnetic field intensity received by the onboard
communication device from the ground communication
device is used as the second threshold when the distance
between the on-board communication device and the ground
communication device is equal to the prescribed value
plus a difference between a height of the vehicle
measured when the vehicle is empty and a height of the
vehicle measured when the vehicle is full.
5. The on-board device according to any one of claims 2
to 4, wherein the magnetic field intensity received by
the on-board communication device from the ground
communication device is used as the first threshold when
the distance between the on-board communication device
and the ground communication device is equal to the
difference between the height of the vehicle measured
when the vehicle is empty and the height of the vehicle
measured when the vehicle is full, minus the prescribed
value.
6. The on-board device according to claim 1, wherein
information on the vehicle speed detected by the speed
detection device is reliable information duplicated by -an
automatic vehicle control device.
ORIGINAL
7 . The on-board device according to claims 1 to 6,
wherein the predetermined value is equal to or lower than
45 km/h.
8. The on-board device according to claims 1 to 6,
wherein the predetermined value is a speed close to zero.
9. An on-board device comprising an on-board
communication device that communicates with a ground
communication device and a door open and close detection
device for a vehicle,
wherein, when door open and close information
detected by the door open and close detection device is
indicative of door close, the on-board communication
device determines that the on-board communication device
is present within a communication range of the ground
communication device when a signal magnetic field
intensity of a signal from the ground communication
device received by the on-board communication device is
higher than a first threshold, and
when the door open and close information detected by
the door open and close detection device is indicative of
door open, the on-board communication device determines
that the on-board communication device is present within
the communication range of the ground communication
device when the signal magnetic field intensity of the
signal from the ground communication device received by
the on-board communication device is higher than a third
threshold smaller than the first threshold.
10. The on-board device according to claim 9, wherein,
when the door open and close information detected by the
door open and close detection device is indicative of
door close, the on-board communication device determines
that the on-board communication device is present outside
a communication range of the ground communication device
when the signal magnetic field intensity of the signal
from the ground communication device received by the on board communication device is lower than a second
threshold smaller than the third threshold, and
when the door open and close information detected by
the door open and close detection device is indicative of
door open, the on-board communication device determines
that the on-board communication device is present outside
the communication range of the ground communication
device when the signal magnetic field intensity of the
signal from the ground communication device received by
the on-board communication device is lower than the third
threshold.
11. An on-board device, substantially as herein described with reference to accompanying drawings.