U.S. patent application number 10/755689 was filed with the patent office on 2005-07-14 for distance tolerant leadless current sensor.
Invention is credited to Beutel, Kris C., Howard, Charles E..
Application Number | 20050151533 10/755689 |
Document ID | / |
Family ID | 34711809 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050151533 |
Kind Code |
A1 |
Howard, Charles E. ; et
al. |
July 14, 2005 |
DISTANCE TOLERANT LEADLESS CURRENT SENSOR
Abstract
A leadless current sensing device utilizes a pair of radially
aligned Hall Effect Sensors to generate a current measurement for a
conductor without knowledge of the distance between the probe and
the conductor. The device has particular application to the
automotive and truck assembly industry where current measurements
at fixed points in an electrical system are required, but close
tolerances on spacing of probes expensive.
Inventors: |
Howard, Charles E.; (Silver
Lake, IN) ; Beutel, Kris C.; (Fort Wayne,
IN) |
Correspondence
Address: |
INTERNATIONAL TRUCK INTELLECTUAL PROPERTY COMPANY,
4201 WINFIELD ROAD
P.O. BOX 1488
WARRENVILLE
IL
60555
US
|
Family ID: |
34711809 |
Appl. No.: |
10/755689 |
Filed: |
January 12, 2004 |
Current U.S.
Class: |
324/117H |
Current CPC
Class: |
G01R 15/202
20130101 |
Class at
Publication: |
324/117.00H |
International
Class: |
G01R 019/00 |
Claims
What is claimed is:
1. A leadless current sensing system for a conductor, comprising: a
framework for capturing a section of a conductor; first and second
Hall Effect sensors positioned with respect to the framework at
different radial distances from the captured section of the
conductor and to be perpendicular to lines of equal flux density as
occur around the captured section of the conductor; and data
processing means for determining current in the conductor from the
magnitudes of first and second signals generated by the first and
second Hall Effect sensors, respectively, treating the distance
between the sensors as known and disregarding the values for
distances between either sensor and the conductor.
2. The leadless current sensing system as set forth in claim 1,
further comprising: third and fourth Hall Effect sensors positioned
with respect to the framework at different radial distances from
the captured section of the conductor and to be perpendicular to
lines of equal flux density as occur around the captured section of
the conductor for providing measurements of magnetic flux densities
over a different useful range of currents in the conductor than the
first and second Hall Effect sensors provide.
3. The leadless current sensing system as set forth in claim 2, the
framework further comprising: a opening through the framework for
fitting around the conductor.
4. A current sensing system for conductors installed on a motor
vehicle including a controller area network and an onboard computer
coupled to the controller area network and programmable to operate
on data received over the controller area network, the current
sensing system comprising: a framework for capturing a section of a
conductor; first and second Hall Effect sensors mounted on the
framework at a known distance from one another and at different
radial distances from the captured section of the conductor, the
first and second Hall Effect sensors being mounted to be
perpendicular to lines of equal flux density around the captured
section of the conductor; a data link interface from the first and
second Hall Effect sensors to the controller area network for
transmitting sensor data relating to magnetic flux density from the
first and second Hall Effect sensors over the controller area
network; and a program executable by the onboard computer, the
program operating on the sensor data relating to magnetic flux
density for determining current in the conductor.
5. The current sensing system of claim 4, further comprising: third
and fourth Hall Effect sensors mounted on the framework at a known
distance from one another and at different radial distances from
the captured section of the conductor, the third and fourth Hall
Effect sensors being mounted to be perpendicular to lines of equal
flux density around the captured section of the conductor; and the
data link interface being further coupled to format and transmit
data from the third and fourth Hall Effect sensors to the
controller area network for transmitting sensor data relating to
magnetic flux density over the controller area network.
6. The current sensing system of claim 5, further comprising: the
conductor being a vehicle battery cable; and the framework being
adapted to depend from a motor vehicle frame rail.
7. A motor vehicle comprising: a controller area network; an
onboard computer coupled to the controller area network and
programmable to operate on data received over the controller area
network; a plurality of electrical conductors installed on the
vehicle; a framework for capturing a section of a conductor; first
and second Hall Effect sensors mounted on the framework at a known
distance from one another and at different radial distances from
the captured section of the conductor, the first and second Hall
Effect sensors being mounted to be perpendicular to lines of equal
flux density around the captured section of the conductor; a data
link interface from the first and second Hall Effect sensors to the
controller area network for transmitting sensor data relating to
magnetic flux density from the first and second Hall Effect sensors
over the controller area network; and a program executable by the
onboard computer, the program operating on the sensor data relating
to magnetic flux density for determining current in the
conductor;
8. The motor vehicle as set forth in claim 7, further comprising:
third and fourth Hall Effect sensors mounted on the framework at a
known distance from one another and at different radial distances
from the captured section of the conductor, the third and fourth
Hall Effect sensors being mounted to be perpendicular to lines of
equal flux density around the captured section of the conductor;
and the data link interface being further coupled to format and
transmit data from the third and fourth Hall Effect sensors to the
controller area network for transmitting sensor data relating to
magnetic flux density over the controller area network.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The invention relates to current sensing devices and more
particularly to a leadless current sensor using Hall Effect
detectors.
[0003] 2. Description of the Prior Art and Problem
[0004] U.S. Pat. No. 4,887,027 to Strasser describes a leadless
current sensing probe which, when placed near a current carrying
conductor, generates signals from which the probe's angle of
orientation and distance from the conductor can be determined.
Strasser teaches a probe for direct current (D.C.) electrical
systems constructed using two Hall Effect plates, one placed
forward of the other in a probe. It is anticipated that in use the
end of the probe where the forward Hall Effect plate is located is
directed toward the current carrying conductor. The Hall Effect
plates have a common center axis, with the rearward plate rotated
on the axis relative to the forward plate. The distance between the
plates is treated as a known.
[0005] Hall Effect devices measure magnetic flux density by
exhibiting a voltage across the devices proportional to the local
magnetic flux density or by exhibiting changes in resistance as a
function of magnetic field flux density (magneto resistive
devices). It is well known that a wire carrying a current has a
magnetic field associated therewith. If the wire can be treated as
being linear and infinite in length the relationship between the
current carried by the wire and the magnetic field flux density B
at a distance r to the wire is:
B=.mu.I/2.pi.r (Strasser equation (18)) (1)
[0006] where:
[0007] .mu. is the permeability of the medium surrounding the
conductor, with the permeability for vacuum after being the default
valve,
[0008] I is the current in the conductor, and
[0009] r is the minimum perpendicular distance to the wire.
[0010] Strasser rearranges equation (1) to derive the
relationship:
I=B2.pi.r/.mu. (Strasser equation (32)) (2)
[0011] From this relationship Strasser concludes that once "r" or
distance is determined "I" or current can be solved for using
measured magnetic flux. Strasser is able to determine distance by
comparison of two voltage measurements taken across each of the
pair of Hall Effect plates, a total of four measurements.
[0012] Current sensors are essential components in contemporary
control systems for motor vehicles. Such sensors are preferably
inexpensive and should not require leads connected to the wire in
which current is to be measured. The Strasser device and other Hall
Effect based current measuring devices provide leadless current
measurement. However, many of the devices, other than Strasser,
have required careful control, and prior knowledge of, the distance
separating the Hall Effect based probe and the conductor. The
Strasser device, though tolerant of changes is spacing between the
probe and wire, still treats determination of the distance between
wire and probe as a necessary step before determining the conductor
current.
SUMMARY OF THE INVENTION
[0013] According to the invention there is provided a leadless
current sensing system for a conductor. The sensing system includes
a framework for capturing a section of a conductor. First and
second Hall Effect sensors are mounted on the framework at
different radial distances from the captured section of the
conductor. The sensors are also mounted to be perpendicular to
lines of equal flux density as occur around the captured section of
the conductor when carrying a current. The sensing system is
intended for installation on a motor vehicle having an on board
computer and a controller area network. A data link interface
between the sensors and the controller area network formats sensor
data relating to magnetic flux density for transmission over the
controller area network, which, upon receipt by the onboard
computer, is used by the computer for determining current in the
conductor. The calculation treats the distance between the sensors
as known and disregards values for distances between the sensors
and the conductor.
[0014] Additional effects, features and advantages will be apparent
in the written description that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself however,
as well as a preferred mode of use, further objects and advantages
thereof, will best be understood by reference to the following
detailed description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
[0016] FIG. 1 is a perspective view in partial cutaway of a vehicle
truck and an electrical system for the truck.
[0017] FIG. 2 is a perspective view of a vehicle chassis
illustrating a possible mounting position for batteries on the
vehicle's frame and cables used to attach the batteries to the
charging and engine starting systems.
[0018] FIG. 3 is a block diagram of a vehicle electronic control
network.
[0019] FIG. 4 is a front elevation view of a leadless current
sensor in accordance with one embodiment of the present
invention.
[0020] FIG. 5 is a cross sectional view of the leadless current
sensor of FIG. 4 taken along lines 5--5.
DETAILED DESCRIPTION OF THE INVENTION
[0021] FIG. 1 is a perspective view of a vehicle 11 and of a
vehicle electrical control system 10 installed on the vehicle.
Vehicle electrical control system 10 comprises a network which may,
in one embodiment, comprise a twisted pair (either shielded or
unshielded) cable operating as a serial data bus/data link 18. One
node of bus 18 is an electrical system controller (ESC) 24, which
is a major component of a vehicle electronic control system. ESC 24
manages a number of vocational controllers connected to serial data
bus 18 as nodes. ESC 24 also monitors some of the sensors used on
vehicle 11 including, in a preferred embodiment of the present
invention, the current sensing arrangement of the present invention
and is programmed to determine current from detected magnetic
fields. Collectively, serial data bus 18 and the various nodes
attached thereto form a controller area network (CAN).
[0022] Active vehicle components are typically controlled by one of
a group of autonomous, vocational controllers, which include an
instrument and switch bank 12, a gauge cluster 14, an engine
controller 20, a transmission controller 16, and an antilock brake
system (ABS) controller 22, all of which are connected to ESC 24
over a serial data bus 18 and all of which are connected to the
serial data bus as nodes. The autonomous controllers include local
data processing and programming and are typically supplied by the
manufacturer of the controlled component. For each autonomous
controller there is a defined set of variables used for
communications among the autonomous controller and the other data
processing components on the network or attached to the network.
Gauge cluster 14, transmission controller 16 and engine controller
20 all communicate with ESC 24, which also monitors inputs received
from the auxiliary instrument and switch bank 12 over the serial
communication link in harness 18. Detected current may be of
interest to any one of a number of the controllers depending upon
the application of the sensor. High overall current demand may
necessitate an increase in engine output, involving the engine
controller 20. Or a current sensor could be applied to monitor
operations of a component, such as a light bulb, where the absence
of a current can indicate failure.
[0023] Auxiliary power for vehicle 11, particularly used for
cranking and starting an engine, is supplied by one or more lead
acid batteries 21, shown installed toward the rear of the vehicle
from a vehicle frame rail 13. Electrical power from batteries 21
may be supplied upon moving a key switch from an off position to an
on position, without cranking the vehicle engine. Battery current
monitoring is among the more important applications of current
monitoring sensors.
[0024] FIG. 2 illustrates an array of batteries 21 and the manner
of connection of the batteries to a starter system 30 for an engine
46 installed on vehicle 11. Batteries 21 are connected in parallel
to supply a high amp/hour capacity to vehicle starter system 30
during cranking. A negative terminal battery cable 26 is connected
from a negative terminal of one of batteries 21 to a terminal of a
starter motor 31, both of which are connected to the vehicle
chassis, which serves as a floating ground in a conventional
manner. A positive terminal battery cable 28 is connected between a
positive terminal from the same one of batteries 21 to an input
terminal on a starter system component 33 through a leadless
current sensor 37. Negative terminal battery cable 26 is routed
around and preferably magnetically shielded from leadless current
sensor 37. Terminal cables 26 and 28 are usually 0000AWG cables. A
framework 32 may be used to hold a section of positive terminal
battery cable 28 straight adjacent where leadless current sensor 37
is positioned.
[0025] FIG. 3 illustrates electronic control of a vehicle 11
schematically, based on a network and an overall electrical system
controller 24 as adapted to incorporate a leadless current sensor.
As already described, ESC 24 communicates with several autonomous
controllers over a SAE J1939 data link 18, including a gauge
cluster 14, a transmission controller 16, an antilock brake system
controller 22 and an engine controller 20. Each of these local
autonomous controllers may in turn receive data directly from
switches and sensors, as ESC 24 does from a switch bank 48 and
discrete input section 50. Discrete inputs may include ignition key
switch position and start button position. Engine controller 20 is
commonly used to monitor a number of operational sensors on a
vehicle 11 because of the immediate need of the engine controller
for such measurements in controlling fuel flow and air/fuel mixture
control to engine 46. Each local controller may provide control or
informational signals to local discretely controllable components,
as ESC 24 does with discrete output section 52. A sensor module bus
interface 42 receives analog signals from current sensor 37,
digitizes the signals, and formats the digital for transmission
over data link 18.
[0026] Current measurement is illustrated as being made with
respect to a battery cable 26 using a Hall Effect leadless current
sensor 37 disposed alongside the battery cable. However, current
measurement may be made with respect to any cable of interest on a
vehicle.
[0027] Leadless current sensor 37 is positioned relative to a cable
where magnetic field density around the cable can be approximated
treating the cable as a narrow gauge linear conductor of infinite
length. Leadless current sensor 37 provides measurements of
magnetic flux density around a conductor of interest at two
differentially spaced points on a radial from the cable. Magnetic
flux density around the cable for direct current for two
differentially spaced points on a single radial from the conductor
can be found by applying Equation (1) to the two points as
follows:
B.sub.1=.mu.I/2.pi.r.sub.1 (3)
[0028] for a point a distance r.sub.1 from the conductor and
B.sub.2=.mu.I/2.pi.r.sub.2 (4)
[0029] for a point a distance r.sub.2 from the conductor where
r.sub.1 is greater than r.sub.2. The distance r.sub.1 can be
expressed in terms of r.sub.2 and a known distance .DELTA.r
separating the two points.
r.sub.1=r.sub.2+.DELTA.r. (5)
[0030] Substituting for r.sub.1 from equation (5) into equation (3)
yields the relationship:
B.sub.1=.mu.I/2.pi.(r.sub.2+.DELTA.r) (6)
[0031] From this it can be derived that:
r.sub.2=.mu.I/2.pi.B.sub.1-.DELTA.r (7)
[0032] Substituting the result of equation (7) back into equation
(4) allows r.sub.2 to be eliminated:
B.sub.2=.mu.I/2.pi.(.mu.I/2.pi.B.sub.1-.DELTA.r) (8)
[0033] Now solving for I (current), the only unknown, may be done.
Simplifying equation (8) provides:
B.sub.2=.mu.IB.sub.1/(.mu.I-2.pi.B.sub.1.DELTA.r) (9)
[0034] Multiplying both sides of equation (8) by the denominator of
the right side yields:
.mu.B.sub.2I-2.pi.B.sub.1B.sub.2.DELTA.r=.mu.IB.sub.1 (10)
[0035] Grouping all terms containing I on the left side results
in:
I(.mu.B.sub.2-.mu.B.sub.1)=2.pi.B.sub.1B.sub.2.DELTA.r (11)
[0036] And finally:
I=2.pi.B.sub.1B.sub.2.DELTA.r/(.mu.B.sub.2-B.sub.1) (12)
[0037] Thus current can be accurately approximated knowing only the
distance between the points where the flux density measurements are
taken, provided the conductor can be treated as a linear conductor
of infinite length at both points and permeability considerations
adjacent the sensors are controlled. Electrical system controller
(ESC) 24 is readily programmed to determine current from
measurements of magnetic flux density supplied by leadless current
probe 37 and passed to the ESC over data link 18.
[0038] In a preferred embodiment, leadless current sensor 37 is
implemented by capturing a conductor for electrical current and
positioning two sets of Hall Effect sensors 64-67 relative to the
conductor for measuring magnetic flux density as illustrated in
FIGS. 4 and 5. The distance of the Hall Effect sensors 64-67 from
and orientation with respect to cable 28 is fixed in a given
application, however, the distance of the sensors from the cable
may vary from vehicle to vehicle and need not be known. Cable 28 is
held in a housing 52 comprising upper and lower halves 56 and 58. A
conduit 54 is defined between adjacent faces of the upper and lower
halves 56 and 58 which is perpendicular to the direction of
alignment (and spacing) of pairs of Hall Effect Sensors. The first
pair of sensors includes sensors 64 and 65. The second pair of
sensors includes sensors 66 and 67. Housing halves 56 and 58 are
held to one another using a plurality of plastic screws 60. Housing
56 is preferably fabricated from a material having a permeability
close to that of vacuum, which includes a wide variety of
diamagnetic and paramagnetic materials.
[0039] Extending upwardly from a base in housing 56 is a circuit
board 62 which is preferably disposed almost directly above
conductor 28, paralleling the plane of the conductor. Circuit board
62 positions each of two sets of Hall Effect Sensors 64-67 in a
plane with the center axis of cable 28 and perpendicular to the
lines of equal magnetic flux B. Each pair of sensors, including
sensors 64 and 65 as one pair, and sensors 66 and 67 as a second
pair, is located with one sensor aligned on the other on a radial
extending from cable 28. The distance .DELTA.r between sensors of a
pair is known and fixed. Each of Hall Effect sensors 64-67 modifies
an electrical signal applied to the sensor in a way dependent upon
the intensity of the magnetic flux through the sensor. For
application to a battery cable the pair of sensors comprising
sensors 64 and 65 are preferably selected for measuring currents in
from -300 to +300 amperes and the anticipated distance. The second
set of sensors 66 and 67 are used for currents from 0 to 2000
amperes. The first current range corresponds to normal vehicle
operation while the second range corresponds to surge currents
occurring during engine cranking. Two sets are used for a vehicle
battery cable because of range limits exhibited by contemporary
Hall Effect sensors. Other applications may not require two sets of
sensors.
[0040] The invention provides a leadless current sensor and
implements a current determination algorithm which works regardless
of the distance of the probe from the conductor, as long as the
probe is at a distance where both sensors in a pair are spaced from
the conductor in a way that allows the conductor to be treated as
an infinite, linear current path.
[0041] While the invention is shown in only one of its forms, it is
not thus limited but is susceptible to various changes and
modifications without departing from the spirit and scope of the
invention.
* * * * *