FIELD OF THE INVENTION
The present invention relates to an electric throttle grip used in two wheelers for
controlling speed. More particularly, the present invention relates to a magnetic circuit
in electric throttle grip to minimize deviation in output voltage of sensor due to
moment of rotor in thrust axis direction.
BACKGROUND OF THE INVENTION
Presently in automobiles, generally two-wheelers, an accelerator grip is rotationally
mounted on a handlebar and the accelerator is rotated with respect to the handlebar to
open and close a throttle valve of the internal combustion engine. On many
motorcycles, an electric relative position detection device is used, in which the
rotational movement of the accelerator is detected by a potentiometer and the throttle
valve is opened and closed by an actuator based upon the output voltage from the
potentiometer.
To reduce the likelihood of a malfunction in the potentiometer resulting in undesired
throttle positional control, a separate mechanical switch is also provided which is
capable of detecting a completely-closed position of the accelerator so as to close the
throttle valve if the accelerator is positioned in the closed position and the throttle
valve is not fully closed.
There also exists a system that includes a magnetic relative position detection device
in which a magnet is disposed in an accelerator and the rotational position of the
accelerator is detected via changes in the magnetic flux density.
However, in the existing systems the problem of flux leakage still persists, which
results in improper detection of magnetic flux and position of throttle.
Referring to Figure 1, the existing technology is a non-contact twist grip which
consists of magnet mounted on rotor and Hall IC mounted in housing. As rotor moves
in axial direction due to thrust play, it also causes the magnet to move in axial
direction with respect to the Hall IC. Moment of magnet in axial direction results in
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change of flux density and hence sensor output which is not desired. This change in
sensor output results in sudden acceleration of vehicle speed or increase in engine idle
rpm.
The disadvantages of the existing technology are:
1. Sensor is very sensitive to change in magnetic flux density.
2. Due to magnet movement in axial direction there is change in sensor output
characteristics.
3. As the magnetic circuit does not include any magnetic material (Flux director)
in the space formed by the magnets, very precise location of Hall IC w.r.t to
sector magnets is required to reduce detection errors.
4. Accuracy of sensor at full closed position of throttle is not achieved.
Therefore, there exists a need to develop a magnetic circuit with an additional flux
concentrator which overcomes at least one of the problems of the existing magnetic
circuits.
SUMMARY OF THE INVENTION
An accelerator position sensor (APS) system for detecting angular rotation of a
throttle pipe mounted on handlebar of a vehicle, said APS system comprising a rotor
coupled with the throttle pipe so as to rotate about a rotational axis of the throttle pipe,
a magnet being mounted on the rotor is angularly movable about the rotational axis of
the throttle pipe; a sensor case being mounted on the handlebar; wherein the sensor
case comprises: a hall sensor unit accommodated in the sensor case and configured to
provide output based on change in magnet flux due to angular movement of the
magnet; a flux concentrator being disposed on the sensor case and positioned between
the hall sensor unit and the magnet; the flux concentrator is configured to provide a
substantially constant flux density by providing minimal deviation in magnetic flux
lines during movement of the magnet in thrust direction.
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BRIEF DESCRIPTION OF FIGURES
Further aspects and advantages of the present invention will be readily understood
from the following detailed description with reference to the accompanying figures
of the drawings. The figures together with a detailed description below, are
incorporated in and form part of the specification, and serve to further illustrate the
embodiments and explain various principles and advantages but not limiting the
scope of the invention. In the accompanying drawings,
Figure 1 illustrates an existing mechanism of non-contact existing grip showing a
stator, rotor and a magnet.
Figure 2a illustrates APS magnetic circuit according to an embodiment of the present
invention.
Figure 2b illustrates sectional view of APS magnetic circuit shown in Figure 2a.
Figures 3a-3b illustrates the present invention showing front and side views of magnet,
flux concentrator and Hall IC of the APS magnetic circuit according to an embodiment
of the present invention.
Figures 4a-4b illustrates the dimensions i.e. the thickness and width of the flux
concentrator according to an embodiment of the present invention.
Figures 5a-5b illustrate the mounting of flux concentrator unit in the sensor casing
according to an embodiment of the present invention.
Figures 6a-6c illustrates the variation of flux lines in the magnetic circuit with a flux
concentrator according to an embodiment of the present invention.
Figure 7 illustrates a flux density output variation/deviation graph with and without a
flux concentrator unit in the magnetic circuit according to an embodiment of the
present invention.
Figure 8 illustrates the sensor output variation graph at full closed throttle according to
an embodiment of the present invention
Figure 9 illustrates the magnetic flux density vs. Throttle grip rotation ideal
characteristics.
Figure 10a-10c illustrates the mounting of ferromagnetic plates in the magnetic circuit
according to an alternative embodiment of the present invention.
Figure 11a-11c illustrates the variation of flux lines in the magnetic circuit with
ferromagnetic plates according to an alternative embodiment of the present invention.
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DETAILED DESCRIPTION OF THE PRESENT INVENTION
While the invention is susceptible to various modifications and alternative forms,
specific embodiment thereof has been shown by way of example in the figures and
will be described in detail below. It should be understood, however that it is not
intended to limit the invention to the particular forms disclosed, but on the contrary,
the invention is to cover all modifications, equivalents, and alternative falling with in
the spirit and the scope of the invention as defined by the appended claims.
Before describing in detail the various embodiments of the present invention it may
be observed that the novelty and inventive step that are in accordance with the present
invention resides in the construction of APS magnetic circuit and flux concentrator in
magnetic circuit. It is to be noted that a person skilled in the art can be motivated from
the present invention and modify the various construction of APS magnetic circuit
and flux concentrator in magnetic circuit. However, such modification should be
construed within the scope and spirit of the invention.
Accordingly, the drawings are showing only those specific details that are pertinent
to understanding the embodiments of the present invention so as not to obscure the
disclosure with details that will be readily apparent to those of ordinary skill in the art
having benefit of the description herein.
The terms “comprises”, “comprising”, “including” or any other variations thereof, are
intended to cover a non-exclusive inclusion, such that an assembly, mechanism,
setup, that comprises a list of components does not include only those components but
may include other components not expressly listed or inherent to such assembly,
mechanism or setup. In other words, one or more elements in an accelerator position
sensor (APS) system for detecting angular rotation of a throttle pipe mounted on
handlebar of a vehicle proceeded by “comprises” does not, without more constraints,
preclude the existence of other elements or additional elements in the assembly or
mechanism. The following paragraphs explain present invention and the same may be
deduced accordingly.
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Accordingly, it is an aim of the present invention to provide APS which overcomes at
least one of the problems associated with the prior existing APS.
Another aim of the present invention is to provide an accelerator position sensor
(APS) system for detecting angular rotation of a throttle pipe mounted on handlebar
of a vehicle with flux concentrator. Yet another object of the present invention is to
provide a flux concentrator to the existing magnetic circuit which overcomes at least
one of the problems of existing mechanism of throttle of throttle or accelerator
position sensor.
Accordingly, the present invention provides an accelerator position sensor (APS)
system for detecting angular rotation of a throttle pipe mounted on handlebar of a
vehicle, said APS system comprising;
a rotor coupled with the throttle pipe so as to rotate about a rotational axis of the
throttle pipe;
a magnet being mounted on the rotor is angularly movable about the rotational axis of
the throttle pipe;
a sensor case being mounted on the handlebar; wherein the sensor case comprises:
a hall sensor unit accommodated in the sensor case and configured to provide output
based on change in magnet flux due to angular movement of the magnet;
a flux concentrator being disposed on the sensor case and positioned between the hall
sensor unit and the magnet;
the flux concentrator is configured to provide a substantially constant flux density by
providing minimal deviation in magnetic flux lines during movement of the magnet in
thrust direction.
In an embodiment of the present invention, the flux concentrator is configured to
ensure substantially perpendicular flux lines across the Hall IC during movement of
the rotor and the magnet in the thrust direction.
In another embodiment of the present invention, the flux concentrator has a
frustoconical section and a cylindrical section.
7
In still another embodiment of the present invention, the frustoconical section has a
first end portion having a first diameter and a second end portion having a second
diameter where the first diameter is larger than the second diameter.
In yet another embodiment of the present invention, the cylindrical section has a
length and a third diameter which is equal to the second diameter of the second end
portion.
In a further embodiment of the present invention, the first diameter of the first end
portion of the frustoconical section is atleast twice the effective length of the flux
concentrator;
the second diameter of the second end portion of the frustoconical section is equal to
the effective length of the flux concentrator;
where the effective length is defined as a sum of length of cylindrical section and
length between the first end portion of the frustoconical section and second end
portion of the frustoconical section.
In a further more another embodiment of the present invention, the flux concentrator
comprises a top plate and a bottom plate located across the hall sensor unit.
In one more another embodiment of the present invention, the flux concentrator is
made of ferromagnetic material.
In another embodiment of the present invention, the flux concentrator is configured
to reduce the deviation of flux density due to throttle pipe rotation from +/- 5% to less
than 1%.
In still another embodiment of the present invention, the flux concentrator is
configured to reduce the deviation of sensor output due axial moment from 1.4% to
~0%.
The following paragraphs describe the present invention with reference to Figures 2-
11.
8
As shown in Figures 2 and 3, the accelerator position sensor (APS) magnetic system
(101) comprises of a rotor (102), a magnet (103), a sensor case (104), a hall sensor unit
(105) and a flux concentrator (106). The said system (101) is mounted on the handle
bar (not shown in Figure) of a vehicle for detecting angular rotation of a throttle pipe
(107).
In the present system, the rotor (102) is coupled with the throttle pipe (107) so as to
rotate about a rotational axis (X). The magnet (103) is mounted on the rotor (102) and
is angularly movable about the rotational axis (X). The sensor case (104) is mounted
on the handle bar.
As shown in Figure 3, the sensor case (104) comprises hall sensor unit (105) and flux
concentrator (106). The hall sensor unit (105) is accommodated in the sensor case
(104) and is configured to provide an output based on change in magnetic flux due to
angular movement of the magnet (103). The flux concentrator unit (106) is also
disposed in the sensor case (104) and is positioned between the hall sensor unit (105)
and the magnet (103). The flux concentrator unit (106) is configured to ensure that
flux lines are perpendicular while passing across the Hall sensor unit or Hall IC (105)
during axial movement of the magnet (103) due to axial movement of rotor (102) in
axial or thrust direction. The term ‘axial or thrust direction’ herein refers to a direction
along or parallel to rotational axis (X).
As shown in Figure 4a, the flux concentrator (106) is a single unit and has two sections
(106a, 106b). It has a top section (106a) which is of frustoconical shape and a bottom
section (106b) which is of cylindrical shape. The frustoconical section (106a) of the
flux concentrator (106) has two end portions, a first end portion (106c) and a second
end portion (106d). The first end portion (106c) has a first diameter (D1) and a second
end (106d) has a second diameter (D2) and the first diameter (D1) is larger than the
second diameter (D2). The cylindrical section (106b) of the flux concentrator (106b)
has a length (L) and a third diameter (D3) wherein the second diameter (D2) of the
second end portion (106d) of the frustoconical section (106a) and the third diameter
(D3) are equal.
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In an embodiment of the present invention, the first diameter (D1) of the first end
portion (106c) of the frustoconical section (106a) of the flux concentrator (106) is
atleast twice the effective length (Le) of the flux concentrator (106) and the second
diameter (D2) of the second end portion (106d) of the frustoconical section (106a) of
the flux concentrator (106) is equal to an effective length (Le) of the flux concentrator
(106). The term ‘effective length (Le)’ of the flux concentrator (106) herein is defined
as a sum of the length (L) of the cylindrical section ((106b) and length between the
first end portion (106c) of the frustoconical section (106a) and second end portion
(106d) of the frustoconical section (106a) i.e. D1 >2Le and D2~Le.
As shown in Figure 5, the flux concentrator (106) is generally made of ferromagnetic
material and is mounted in a slot (108) in the sensor case/casing (104) wherein the slot
(108) is sized to accommodate the flux concentrator (106). An adhesive may be
applied in the slot (108) for fixing the flux concentrator (106). The size of the flux
concentrator (106) can also be varied by conducting experiments and by simulation.
As can be clearly understood, the throttle pipe (107) is mounted on the handle bar (not
shown in Figures) of the vehicle and is rotatable about the rotational axis X. Since the
throttle pipe (107) is rotatably mounted on the handle bar, it is always prone to play in
the axial direction or thrust direction.
As shown Figures 3 and 6a-6c, as the throttle pipe (107) and the magnet (103) move in
the axial direction, the magnetic flux density across the Hall sensor unit (105) varies
due to deviation of the magnetic flux lines produced by the magnet (103) when they
reach the Hall sensor unit (105). The variation in the magnetic flux density results in
poor detection by the Hall sensor unit (105). The present mechanism provides an
optimized magnetic circuit that compensates for the weak signal by enhancing the
decreased magnetic flux density. The present mechanism includes a flux concentrator
(106) that provides a substantially constant flux density by providing minimal
deviation in direction of magnetic flux lines during axial movement of the magnet
(103). Due to the substantially constant flux density, the variation of magnetic flux
density due to rotation of throttle pipe (107) can be detected even during axial
movement of the magnet (103).
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As shown in Figures 6(a)-(c), at surface ‘A’ of flux concentrator flux is generally
perpendicular but at surface ‘B’ which is leaving Hall IC the flux lines tilt in x axis
and affect the flux density reaching Hall element.
Referring to Figure 7, on x axis X0’ to X7’ are different throttle pipe rotation angles in
degrees and y axis shows deviation in magnetic flux density in %. X0’ is full closed
position of throttle. Due to addition of the Flux concentrator the deviation in flux
density is reduced from ± 5% to less than 1%.
Referring to Figure 8, X0 to X5 are axial movement of magnet in milimetres (mm) and
y-axis shows the deviation in sensor output in (percent) %. Due to addition of the Flux
concentrator for axial movement of X5 the deviation is reduced from 1.4% to almost
0%.
Referring to Figure 9, 55oto 125o indicates the linear output zone. Any deviation in
sensor output at 55o will result in variation of idle RPM which is not desirable. The
target of the used flux concentrator is to reduce magnetic flux density variation at 55o
and hence sensor output deviation.
Figures 10a-10c show an alternative embodiment of the present invention wherein the
flux concentrator (1006) a pair of ferromagnetic plates (1006a, 1006b) namely a top
plate (1006a) and a bottom plate (1006b) are placed at a distance from the hall sensor
unit (105) to eliminate the change in sensor output due to movement of rotor/magnet
in thrust direction. As shown in Figures 6(a)-(c), at surface ‘A’ of flux concentrator
flux is generally perpendicular but at surface ‘B’ which is leaving Hall IC the flux
lines tilt in x axis and affect the flux density reaching Hall element, To make this flux
lines leaving surface ‘B ‘ also perpendicular ferromagnetic plates (1006a, 1006b)
configuration is used.
The top plate (1006a) and the bottom plate (1006b) are placed on opposite sides of the
hall sensor unit (105). The ferromagnetic plates ensure that magnetic flux lines always
reach hall sensor unit (105) in perpendicular direction during the movement of rotor
and magnet in thrust/axial direction. Thus, the ferromagnetic plates provide a
substantially constant flux density by providing minimal deviation in magnetic flux
lines during axial movement of the magnet. Due to the substantially constant flux
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density, the variation of magnetic flux density due to rotation of throttle pipe can be
detected even during axial movement of the magnet.
Figures 11a-11c shows the magnetic flux density variation with the use of
ferromagnetic plates (1006a, 1006b). The magnetic flux lines after originating from
the magnet (103) reach the top plate (1006a). After travelling through the top plate
(1006a), the magnetic flux density remains substantially constant when it reaches the
hall sensor unit (105). The thrust axis play limit of throttle pipe in the present
embodiment is increased to +/- 0.5mm as compared to embodiment 1.
As shown in Figures 11a-11c, at surface ‘A’ of flux concentrator (1006), flux is
generally perpendicular and also flux lines leaving surface ‘B’ are also generally
perpendicular. Hence, there is no change in flux density reaching Hall element in
thrust condition.
Some of the advantages of the present invention are as follows:
(a) Sensor is less sensitive to change in magnetic flux density due to axial moment of
rotor.
(b) Sensor output characteristics do not change due to axial moment of rotor
(c) Accuracy of sensor at full closed position of throttle is better compared to
conventional design.
(d) Manufacturing variations on positioning of Hall IC will not result in detection
errors

We Claim:
1. An accelerator position sensor (APS) system for detecting angular rotation of
a throttle pipe (107) mounted on handlebar of a vehicle, said APS system
comprising;
a rotor (102) coupled with the throttle pipe (107) so as to rotate about a
rotational axis of the throttle pipe;
a magnet (103) being mounted on the rotor (102) is angularly movable about
the rotational axis (X) of the throttle pipe;
a sensor case (104) being mounted on the handlebar; wherein the sensor case
(104) comprises:
a hall sensor unit (105) accommodated in the sensor case (104) and configured
to provide output based on change in magnet flux due to angular movement of
the magnet (103);
a flux concentrator (106) being disposed on the sensor case (104) and
positioned between the hall sensor unit (105) and the magnet (103);
the flux concentrator (106) is configured to provide a substantially constant
flux density by providing minimal deviation in magnetic flux lines during
movement of the magnet (103) in thrust direction.
2. An accelerator position sensor (APS) system as claimed in claim 1, wherein
the flux concentrator (106) is configured to ensure substantially perpendicular
flux lines across the Hall IC during movement of the rotor (102) and the
magnet (103) in the thrust direction.
3. An accelerator position sensor (APS) system as claimed in claim 1, wherein
the flux concentrator (106) has a frustoconical section (106a) and a cylindrical
section (106b).
4. An accelerator position sensor (APS) system as claimed in claim 3, wherein
the frustoconical section (106a) has a first end portion (106c) having a first
diameter (D1) and a second end portion (106d) having a second diameter (D2)
where the first diameter (D1) is larger than the second diameter (D2).
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5. An accelerator position sensor (APS) system as claimed in claim 3, wherein
the cylindrical section (106b) has a length and a third diameter (D3) which is
equal to the second diameter (D2) of the second end portion (106d).
6. An accelerator position sensor (APS) system as claimed in claim 3, wherein;
the first diameter (D1) of the first end portion (106c) of the frustoconical
section (106a) is at least twice the effective length (Le) of the flux
concentrator (106);
the second diameter (D2) of the second end portion (106d) of the frustoconical
section (106a) is equal to the effective length (Le) of the flux concentrator
(106);
where the effective length (Le) is defined as a sum of length of cylindrical
section and length between the first end portion (106c) of the frustoconical
section (106a) and second end portion (106d) of the frustoconical section
(106a).
7. An accelerator position sensor (APS) system as claimed in claim 1, wherein,
flux concentrator (1006) comprises a top plate (1006a) and a bottom plate
(1006b) located across the hall sensor unit (105).
8. An accelerator position sensor (APS) system as claimed in claim 1, wherein
the flux concentrator (106) is made of ferromagnetic material.
9. An accelerator position sensor (APS) system as claimed in claim 1, wherein
the flux concentrator (106) is configured to reduce the deviation of flux
density due to throttle pipe (107) rotation from +/- 5% to less than 1%.
10. An accelerator position sensor (APS) system as claimed in claim 1, wherein
the flux concentrator (106) is configured to reduce the deviation of sensor
output due axial moment from 1.4% to ~0%.