Simplified inertial bank angle sensor

In order to determine the direction and degree of bank of a motorcycle, a flywheel or other weight balanced at its center of mass is mounted on the motorcycle so that it is free to rotate about an axis parallel to the longitudinal axis of the motorcycle. As the vehicle banks, the flywheel will tend to maintain its position, and the angle of bank can be ascertained by measuring the direction and degree of rotation between the plane of the motorcycle and the flywheel. Measurement of flywheel rotation is obtained by means of an electromagnetic or electro-optical scanner. This device may be used to control headlight beam rotation about the beam axis, thereby keeping the horizontal cutoff of the rectangular beam cross-section parallel to the horizon at all times. Because of friction and vibration, however, the flywheel position may drift relative to the horizon, rendering the angle measurement inaccurate. Therefore it is necessary for the operator to correct for flywheel drift periodically by stopping flywheel rotation when the vehicle is upright or normal to the road surface. This driver input also resets the headlight beam to its normal position. For daytime use, the headlight beam may be locked in its normal position.

BACKGROUND 
1. Field of Invention 
The Inertial Bank Angle Sensor can be used to determine the angle of bank 
of a tilting vehicle. Measurement of the bank angle can be useful in 
optimizing various functions on a motorcycle, such as lighting, power 
delivery, braking force, camera-mount positioning, turn signal actuation, 
etc. 
2. Discussion of Prior Art 
Prior art means for bank angle measurement have used gyroscopic sensors, 
G-force measurement, vehicle speed combined with steering angle, and 
radiation reflected from the road surface to determine the attitude of the 
vehicle. Briefly, gyro sensors are costly and complex, and G-force 
measurements are subject to gross inaccuracies due to bumps and other 
terrain variables. Speed and steering angle cannot be used to derive the 
bank angle because "countersteering", used to initiate a turn, would 
indicate a bank angle opposite to the true one. On a series of S curves, a 
bank angle thus derived could be wrong most of the time. 
Reflected radiation when used to measure distance from the road surface is 
generally reliable, but when propagated at an acute angle to the road 
surface may produce a very weak return signal. In addition, when 
propagated from the low side of a sharply banked vehicle the radiation may 
be doubly reflected, once from the road and then from some part of the 
vehicle itself. Similarly, when propagated from the high side of a banking 
vehicle, the radiation may be reflected from curbs, fences, and other 
vehicles, which would severely compromise the accuracy of the measurement. 
Another problem with sonar distance measurement is that as the speed of the 
vehicle increases, the ultrasonic pulse returns to a point behind where 
the detector would be mounted for optimum signal strength at low speeds. 
OBJECTS AND ADVANTAGES 
Accordingly, the object of the Simplified Inertial Bank Angle Sensor is to 
provide a simple, less expensive, and more reliable means of determining 
the vehicle bank angle. 
SUMMARY 
A balanced inertial mass, or flywheel, is mounted to a motorcycle, bicycle, 
or other banking vehicle so that its axis is on or parallel to the 
longitudinal axis of the vehicle. This flywheel is freewheeling within a 
housing which is mounted to the vehicle. Attached to the inside of the 
housing near the flywheel periphery is a scanning device which can measure 
the direction and degree of rotation of the flywheel relative to the 
housing, using some sort of reference marks (slots, holes, radial bars, 
reflective dots, magnetic stripes, etc). 
As the vehicle is banked in a turn, the flywheel remains stationary, thus 
the scanning device reads the bank angle of the flywheel housing relative 
to the flywheel. This bank angle data may be used to rotate the headlight 
beam about the longitudinal axis (or beam axis) of the headlight in order 
to keep the rectangular beam cross-section parallel to the horizon at all 
angles of bank. 
The headlight beam may be rotated by turning the lens, by turning an 
optical mask, or by rotating the entire headlight assembly, using a motor 
controlled by a electronic control unit, or ECU, according to the output 
of the scanning device. 
Any flywheel drift caused by friction, vibration, etc. would be minimized 
in two ways: 
(1) by shock-mounting the flywheel housing 
(2) by mounting the flywheel on bearings with the smallest possible 
diameter in order to reduce the torque on the flywheel caused by the 
ellipsoidal vibratory excursions characteristic of motorcycle engines. 
This ellipsoidal motion at the bearing journal tends to turn the shaft 
with a force proportional to shaft diameter and bearing friction. 
Although flywheel drift can be minimized, it is still necessary to provide 
a means for correcting any possible flywheel movement relative to the 
horizon. This can be done during periods when the vehicle is upright by a 
rider input which would briefly halt flywheel rotation.

DESCRIPTION 
FIG. 1 shows a flywheel (12) free to rotate within a casing or housing (10) 
which is mounted on a motorcycle with the axis of flywheel rotation 
parallel to the longitudinal axis of the motorcycle. The flywheel is 
marked with a series of reflective dots (13) at a predetermined radius. 
Two electro-optical scanners (15) are mounted to one half of the housing 
so that light from the scanner emittors reflected from the reflective dots 
will produce an electrical signal in each scanner detector. The signal 
from each detector is fed to a electronic control unit, or ECU (20), which 
may be mounted where convenient as shown in FIG. 4. 
A driver-operated switch (21) is connected to a means for stopping any 
flywheel rotation which may be caused by imbalance, friction and/or 
vibratory forces on the flywheel. In this embodiment, the stopping means 
consists of a solenoid-actuated brake pad (16) mounted to the flywheel 
housing (10) which, when actuated, can contact the flywheel periphery. 
FIG. 2 shows a bearing design using conical bearing surfaces to support a 
flywheel axle (14) with sharply pointed ends. The conical bearings (11) 
are flexibly mounted to the flywheel housing using O rings (22) in 
compression. 
OPERATION OF INVENTION 
As the vehicle banks, the flywheel will tend to maintain its position, and 
the angle of bank can be ascertained by measuring the direction and degree 
of rotation between the plane of the motorcycle and the flywheel. 
Measurement of flywheel rotation is obtained through either an 
electromagnetic or an electro-optical scanner. 
One embodiment, illustrated in FIG. 1 shows a flywheel (12) with a circular 
array of reflective dots (13) inside a housing (10) which encloses the 
flywheel and supports the flywheel axle (14). This housing is mounted to 
the motorcycle where convenient, with the flywheel axis parallel to the 
longitudinal axis of the motorcycle. 
A scanning device (15) is mounted to the flywheel housing in a position so 
that flywheel movement can be measured by the scanning device. 
Because of minute imbalance, friction, and vibration, however, the flywheel 
position will not necessarily remain constant relative to the horizon, but 
may tend to drift in one direction or the other, rendering the angle 
measurement inaccurate. Therefore it is sometimes necessary to correct the 
angle measurement when the motorcycle is upright or normal to the road 
surface. The simplest way of doing this is through a driver input. 
This can be accomplished by a thumb-switch (21) which forces a 
housing-mounted, solenoid-actuated brake pad (16) to contact the flywheel 
surface just long enough to stop any motion of the flywheel relative to 
the housing. Also, when this switch is closed, the ECU rotates the 
headlight beam to the central (level) position where the beam cross 
section is parallel to the horizon. After the flywheel is stopped, and the 
brake pad retracted, the scanner recommences bank angle measurement from 
that point. 
A second embodiment (see FIG. 3) uses a flywheel (12) with one or more 
indentations which function as cam ramps when one or more 
solenoid-operated pins or rollers (18) impinge on it, thereby forcing the 
flywheel to one of two central, or null, positions, 0 degrees or 180 
degrees. 
In this application, the range of useful rotation is considerably less than 
180 degrees, therefore the flywheel is divided into symmetrical halves in 
order to make a steeper slope for the cam ramps. The indicator marks which 
describe flywheel rotation between plus and minus 90 degrees from either 
null position are identical, so that bank angle measurements are the same 
if the flywheel is rotated 180 degrees. 
Because the flywheel always returns to one of these positions, the scanning 
method of this embodiment can measure the absolute position of the 
flywheel directly: a unique pattern of dots, barcode, perforations or 
other indicator marks will correspond to any given position on each half 
of the flywheel, so instead of counting, ascertaining direction and 
remembering, the scanning device merely reads the position of the flywheel 
at any instant. This can also be accomplished by an analog scanning method 
such as a variable area reflective strips (19) mounted near the 
circumference of the flywheel so that the amount of light reflected from 
either reflective strip to a detector indicates the position of the 
flywheel within a range of 180 degrees. 
In this passive, low speed flywheel function, it is critical to minimize 
friction. Ball or roller bearings are easily impaired by foreign particles 
(dust, sand, etc.), and the seals which are normally employed to prevent 
contamination are themselves a major source of friction. 
If bushings were used, it is clear that the least friction would obtain 
with the smallest possible axle diameter. Since the axle must be thick 
enough to resist any bending due to shock loads, there will be more 
friction than desired in normal duty in order to protect the axle against 
shock loads. 
A preferred embodiment uses a bearing design as illustrated in FIG. 2, 
where the flywheel axle (14) has sharply pointed ends which are supported 
inside conical bearings (11) which are mounted to the flywheel housing. 
Elastic O rings (22) are interposed between the bearings and the flywheel 
housing to accommodate thermal expansion of the axle or housing, and to 
serve as a shock mounting to protect the axle points from bending. If a 
radial load on the flywheel is sufficient to flex the O rings, the 
bearings will tilt until the inner edges of the bearing contact the axle 
next to the flywheel, thus transmitting the load to the strongest part of 
the axle. 
CONCLUSION, RAMIFICATION AND SCOPE OF INVENTION 
The above description should not be construed as a limitation on the scope 
of the Simplified Inertial Bank Angle Sensor, but rather as an 
exemplification of some preferred embodiments thereof. Many other 
variations are possible. Many kinds of scanning methods currently used for 
reading barcode, for scanning laserdisks, for reading computer floppy 
disks, etc., are readily adaptable and would offer extremely 
high-resolution measurement. 
The bearing system of pointed axle ends supported by conical bearings could 
be shock-mounted by allowing the axle to flex within rigidly mounted 
bearings instead of allowing the bearings to flex as in the preferred 
embodiment described above. 
The flywheel could be returned to the central position elecromagnetically. 
The thumb-switch could be combined with the turn signal switch button and 
could also have a function which locks the flywheel (and therefore the 
headlight) in the centered (or null) position where the rectangular beam 
pattern cross-section is at right angles to the plane of the motorcycle. 
This would work well in daylight when the headlight is used only to make 
the vehicle more noticeable to other traffic.