Motorbikes are inherently unstable vehicles. In particular, when a motorcyclist suddenly applies a large acceleration the front wheel can lift off from the ground. If the motorcyclist continues to accelerate, the motorbike may flip backwards over its rear wheel, potentially resulting in a serious injury to the motorcyclist or to bystanders. Other vehicles such as tractors or JCBs are also prone to tipping over backwards, especially if the driver applies too much acceleration when the vehicle is already on a slope.

Experienced motorcyclists will often attempt to perform stunts such as"wheelies", where the front wheel of the motorbike is purposefully lifted off the ground for extended periods by carefully controlling the motorbike's acceleration. However, while performing a"wheelie"it can be difficult for the motorcyclist to determine the angle of the motorbike relative to the ground. As a result, people practising "wheelies"may become frustrated if they are unable to sense that they are making progress in developing their skill.

Accordingly, there is a need for a means of sensing the pitch of a vehicle, and in particular a motorbike, relative to the horizontal or to some other reference position. There is also a need for a safety device which stops excessive rearward pitching or rotation of a vehicle and for a device which informs a

rider or driver of the angle of their vehicle relative to the horizontal.

According to a first aspect of the present invention there is provided a sensor device mountable on a vehicle of the type having a front wheel, a rear wheel and means for providing motive power to the rear wheel, the device comprising: sensor means for sensing the pitch of the vehicle relative to a reference position ; and processing means connected to the sensor means and connectable to the motive power means for determining if, when the vehicle is under power, the pitch of the vehicle has reached a preselected angle relative to the reference position and for providing an output indicative of the pitch of the vehicle. The preselected angle may be a threshold"safe"angle, above which the vehicle is at risk of tipping over.

Alternatively, the preselected angle may be a mark that the rider of a motorbike is aiming for when performing a"wheelie". Embodiments of the present invention therefore provide useful information about the pitch of the vehicle.

Preferably, the device further comprises display means coupleable to the processing means for receiving the output from the processing means and for displaying an output representative of the pitch of the vehicle. In this embodiment, a driver or rider, or other interested parties are provided with visual information indicating the rearward pitch of the vehicle.

In another preferred embodiment, the processing means comprises control means coupleable between the motive power means and the vehicle for at least reducing acceleration of the vehicle effected by the motive power means when the pitch of the vehicle reaches or exceeds a threshold value. In this way, over-pitching of the vehicle can be prevented by

limiting the acceleration of the vehicle when the sensed rearward pitch exceeds a predetermined threshold or"safe"angle.

In one preferred embodiment, the control means is coupleable to the motive power means in order to directly control the amount of acceleration effected by the motive power means. Alternatively, or in addition, the control means is coupleable to an ignition system of the vehicle in order to control the ignition signals passed to the engine of the vehicle.

In yet a further preferred embodiment, the control means is coupleable to a spark plug of the vehicle such that the spark plug can be prevented from firing in order to limit the amount of motive power which can be generated by the engine.

Preferably, the acceleration of the vehicle effected by the motive power means is reduced in relation to the amount by which the pitch of the vehicle exceeds the threshold value. Advantageously, this allows in fine control of the maximum acceleration of the vehicle such that motive power to the vehicle is not lost completely when the rearward pitch exceeds the threshold value, but is reduced gradually or in stages if the pitch continues to rise above the predetermined"safe"angle.

Preferably, the sensing means comprises a rotation rate sensor for sensing a rate of change of pitch of the vehicle. In one preferred embodiment, the acceleration of the vehicle effected by the motive power means is reduced in relation to the rate of change of pitch of the vehicle. Advantageously, this results in additional fine control of the maximum acceleration such that motive power can be reduced rapidly if the rate of change of pitch is large, indicating that the rider or driver is in danger of losing control of the vehicle.

Preferably, the device further comprises means

for re-calibrating the processing means such that the pitch of the vehicle is measured relative to a re- calibrated reference position. Advantageously, this allows the processing means to be manually or automatically re-calibrated to the horizontal, or to another reference position, to correct for errors in sensing the pitch of the vehicle.

According to a second aspect of the present invention there is provided a method of controlling a vehicle, the vehicle having a front wheel, a rear wheel, and means for providing motive power to the rear wheel, the method comprising the steps of: sensing the pitch of the vehicle relative to a reference position; comparing the sensed pitch of the vehicle with a threshold value ; and at least reducing motion of the vehicle effected by the motive power means when the sensed pitch of the vehicle reaches or exceeds the threshold value.

A preferred embodiment of the present invention will now be described by way of an example and with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of the components forming a device according to a preferred embodiment of the present invention; Figure 2a illustrates a device embodying the present invention connected to a vehicle ignition system which operates on a normally grounded signal ; Figure 2b illustrates a device embodying the present invention connected to a vehicle ignition system which operates on a normally not grounded signal; Figure 2c illustrates a device embodying the present invention connected to a vehicle ignition system and arranged to interrupt a control signal to a spark plug; Figure 3 illustrates a visual display and control

panel of one embodiment of the present invention.

Figure 1 shows a schematic representation of a device 10 embodying the present invention. The device 10 is attachable to a double-axled vehicle 12 such as a motorbike, moped, car, tractor or other motorised vehicle. Alternatively, the vehicle 12 may be a bicycle or other double-axled vehicle propelled by the rider.

A device 10 embodying the present invention is adapted to sense a rearward pitching of the vehicle 12 about a lateral axis through the vehicle, or an axis running substantially parallel to an axis of rotation of the wheels of the vehicle, in order to determine the pitch of the vehicle relative to the horizontal or to some other predetermined zero-point. To sense this pitching or rotation, the device 10 is provided with a rotation sensing means such as a rotation rate sensor 14 or similar device.

Rotation rate sensors 14, also known (inter-alia) as rate-gyros or angular rate sensors, are well known devices which often employ a sensing device which resembles a tuning-fork. The tines of the fork undergo a forced oscillation and a capacitance between the tines is measured. When the fork is rotated, the vibrating tines experience a Coriolis force and the measured capacitance varies in a predictable way depending on the rate of rotation. Accordingly, the rate of rotation can be determined from measurements of the change in capacitance of the tines of the fork.

This is only one device for sensing a rotation and other types of rate-gyro or other devices are well known in the relevant arts.

In a device embodying the present invention, the output 15 from the rotation rate sensor 14 feeds into a processor means 16 which may be a printed circuit board or similar, or a preprogrammed microprocessor.

The processor means 16 includes an integrator 18 which integrates the output 15 from the rotation rate sensor 14 with respect to time to obtain an absolute value for the amount of rotation of the vehicle 12, and hence to determine the pitch of the vehicle relative to a predetermined zero-point.

In a preferred embodiment, the processor means 16 further includes a comparator 24 for comparing the rearward pitch of the vehicle with a predetermined threshold value. When the sensed pitch of the vehicle 12 is greater than the threshold value, the processor means 16 provides an output 26 to a control means 28 which is coupleable to the vehicle 12. The control means is adapted to act on the vehicle 12 to at least reduce acceleration of the vehicle. By limiting the forward acceleration of the vehicle, the force of gravity can overcome the tendency of a front wheel of the vehicle to lift off from the ground when the vehicle is under acceleration such that the vehicle is prevented from rotating further. Limiting the acceleration of the vehicle may be achieved, for example, by coupling the control means 28 to a braking system on a rear wheel of the vehicle 12. When the sensed pitch is greater than the threshold value, the control means 28 acts to apply the brakes, slowing or stopping the rear wheel or wheels from moving such that the forward momentum of the vehicle 12 forces the front wheel or wheels of the vehicle back towards the ground. Preferably, however, the control means is coupled to the ignition system of the vehicle, as illustrated in Figures 2a, 2b, and 2c, and is arranged to limit or cut power provided by the engine to prevent over-pitching of the vehicle 12. In this embodiment, engine braking causes deceleration of the vehicle 12 such that the forward momentum of the vehicle acts to bring the front wheel or wheels of the vehicle back towards the ground.

Figure 2c shows a device 10 embodying the present invention connected to an ignition system including an ignition control system 30, transformer coils 32, and a spark plug 34. In one embodiment, the control system 28 of the device 10 comprises a relay depicted as an on/off switch 28 in Figure 2c. The switch 28 is normally in the on position, such that the ignition control system 30 can supply power to the spark plug 34 via the transformer coils 32. In the event that the sensed pitch of the vehicle 12 is greater than the threshold value, the processor 16 causes the switch 28 to open, interrupting the supply of power to the spark plug 34, cutting power provided by the engine and preventing further acceleration of the vehicle. In this way, the possibility of further pitching of the vehicle 12 due to over-accleration is prevented. With no power going to the engine, the front wheel or wheels of the vehicle 12 will fall back towards the ground under the force of gravity and due to the effects of engine braking as described above such that the sensed pitch of the vehicle 12 will fall below the threshold value. At this point, the processor 16 causes the switch 28 to close again so that power is again supplied to the spark plug.

Figures 2a and 2b show alternative arrangements where the control system switch/relay 28 interrupts a control signal 36 to the ignition control system 30, instead of interrupting the power supply to a spark plug 34 directly.

Figure 2a shows an ignition system which operates via a normally grounded signal. In normal operation, an ignition switch 38 is in the closed position so that the ignition control system 30 is connected to ground. The ignition switch 38 may, for example, be a side stand lock-out switch on a motorbike. Such safety switches open, breaking the connection between the ignition control system 30 and ground, in the event

that the side stand on the motorbike falls loose from its mounting. When the connection to ground is broken, the ignition control system 30 cuts power to the engine as a safety measure. In the embodiment shown in Figure 2a, a normally closed control system switch 28 is placed in series with the ignition switch 38. In the event that the sensed pitch of the vehicle 12 is greater than the threshold value, the processor 16 causes the control system switch 28 to open, breaking the connection between the ignition control system 30 and ground. When the connection to ground is broken, the ignition control system 30 cuts power to the engine preventing further acceleration of the vehicle.

In this way, the possibility of further pitching of the vehicle 12 due to over-acceleration is prevented.

As the front wheel or wheels of the vehicle 12 falls back towards the ground, the sensed pitch falls below the threshold value and the processor 16 causes the control system switch 28 to close, such that the ignition control system 30 can again supply power to the engine.

Another type of ignition system is shown in Figure 2b. In normal operation, the ignition switch 38 is in the open position so that the ignition control system 30 is not connected to ground. The ignition switch 38 in this arrangement may, for example, be a "kill"switch on a motorbike or similar control operated by the rider or driver to stop the engine in an emergency. If the ignition switch 38 is closed and the ignition control system 30 connected to ground, then the ignition control system 30 cuts power to the engine. In the embodiment shown in Figure 2b, a normally open control system switch 28 is connected in parallel with the ignition switch 38. In the event that the sensed pitch of the vehicle 12 is greater than the threshold value, the processor 16 causes the control system switch 28 to close, connecting the

ignition control system 30 to ground. When connected to ground, the ignition control system 30 cuts power to the engine preventing further acceleration of the vehicle 12. In this way, the possibility of further pitching of the vehicle 12 due to over-acceleration is prevented. As with the previous embodiments, the front wheel or wheels of the vehicle 12 falls back towards the ground, the sensed pitch falls below the threshold value and the processor 16 causes the control system switch 28 to open, such that the ignition control system 30 can again supply power to the engine.

Many vehicles have more than one spark plug, and may have more than one ignition control system to activate the spark plugs. Devices embodying the present invention may be arranged to interrupt the power to one, several or all of the spark plugs of the vehicle. When power is cut to only some of the spark plugs, then power will not be cut to the engine entirely, but the amount of acceleration which can be applied to the vehicle is severely limited and over- acceleration becomes impossible.

As an example, embodiments of the device 10 may includes a plurality of relays 28, each of which is arranged to control the power supplied to one or more spark plugs 34 of the vehicle 12. If the pitch of the vehicle 12 reaches the threshold value, at least one of the plurality of relays is activated cutting power to at least some of the spark plugs, thereby reducing the amount of power which the engine can provide and limiting the maximum acceleration of the vehicle 12.

If the pitch of the vehicle 12 nevertheless continues to increase, the processor activates more of the plurality of relays 28 in relation to the amount by which the pitch exceeds the threshold value.

Alternatively, the processor 16 may be programmed with a plurality of threshold values. When the sensed pitch of the vehicle 12 passes any of these threshold

values, a relay 28 is activated, cutting power to the associated spark plugs 34. If the vehicle 12 continues to rotate backwards, such that the sensed pitch reaches or exceeds the next highest threshold value, a further relay 28 will be activated, cutting power to more of the spark plugs 34. In either of the two arrangements described above, as the pitch of the vehicle 12 increases, the maximum acceleration that can be effected by the engine is reduced in stages.

Preferably, the processor means 16 provides an output 40 to a display means 42. The display means 42 provides a visual, audio or tactile output indicative of the pitch of the vehicle 12. For example, the display means can provide a noise to indicate that the pitch is greater than the threshold value. Preferably, however, the display means 42 is located on the dashboard of the vehicle 12 and provides a visual output for example on an LCD screen or by lighting one or more LEDs.

Figure 3 illustrates a display means 42 embodying the present invention. The display panel 43 includes a plurality of attitude LED's 44 arranged in an arc, a control LED 46 and a button or switch 48. Preferably, each of the LED's 44,46 is a dual colour LED which can produce either red or green light. As the pitch of the vehicle 12 increases, the attitude LED's 44 light progressively around the arc to give a direct visual indication of the angle of the vehicle 12. For example, when the processor 16 determines that the pitch of the vehicle 12 has reached 45°, the first six of the attitude LED's 44 shown in Figure 3 are lit.

Preferably, when the pitch of the vehicle 12 is less than the threshold value, each of the attitude LED's 44 is green. However, when the pitch reaches or exceeds the threshold value, some or all of the attitude LED's 44 may light up in red as a clear warning to the rider or driver. The control LED 46 may

also light up or flash to warn the rider or driver that the vehicle 12 is at an angle greater than the threshold value. As another alternative, the attitude LED 44 at a position on the arc representative of the threshold value may be constantly lit in red to provide a direct visual indication of how close the vehicle 12 is to the threshold angle.

A button 48 on the display panel 43 is provided to control the processor 16. By pressing the button 48, the threshold angle is increased by a predetermined amount and the LED at the position on the arc representative of the new threshold value lights up in red. Further presses of the button 48 increase the threshold value in steps up to 90°, at which point the next press of the button 48 cycles the threshold value back to 0°.

The button 48 may also be used to calibrate the device 10 to set the zero-point from which the pitch of the vehicle 12 is measured. When the vehicle 12 is horizontal, or at any other desired angle, the rider or driver can press and hold the button 48, re- calibrating the processor 16 such that the pitch is measured from the new zero-point. Re-calibration of the device 10 may be required at regular intervals or when the device 10 is first turned on because the position of the zero-point may drift with time due to small errors in the pitch sensed by the rate gyro 14.

For example, sudden pitching or slight vibrations of the vehicle 12 may result in the rate gyro 14 providing an erroneous signal to the processor 16, or else the processor may not update rapidly enough to maintain an accurate value for the pitch. In either case, it would then be necessary for the rider or driver to re-calibrate the device 10.

Embodiments of the invention also provide an automatic re-calibration system comprising an accelerometer 50, tilt switch or similar device,

coupled to the processor 16. The accelerometer 50 is arranged to be in equilibrium, with the measured force on it being zero, when the vehicle 12 is horizontal and is either stationary or moving at a constant velocity. When the vehicle 12 is accelerating, or is at an angle other than the horizontal, then the accelerometer 50 records a net force acting upon it.

An output 52 from the accelerometer 50 passes to and is interpreted by the processor 16. If the sensed force on the accelerometer 50 is zero or is less than a preselected value for a quarter of a second, or some other predetermined length of time, then the processor 16 re-calibrates such that the measured pitch is set to zero.

Embodiments of the present invention therefore allow drivers, or especially motorcyclists, to safely accelerate their vehicle without the fear that the vehicle might flip over backwards. A visual output enables the motorcyclist to immediately determine the angle of the motorbike when practising"wheelies"and other stunts.