Method and system of angle estimation

1. The method of angle estimation for use in operating a vehicle which is travelling on a surface, the vehicle comprising a vehicle body which is attached to at least two wheels, the vehicle body having a first axis, the method comprising estimating the angle of said vehicle by:

calculating θ glob1 as a first estimate of the angle θ glob between the first axis and a horizontal plane;

producing θ glob transient, an estimate of transient values of θ glob , by applying a high pass filter to θ glob1 ;

calculating θ glob steady state as an estimate of steady state values θ glob ;

calculating a further estimate of θ glob from θ glob transient and θ glob steady state; and

operating the vehicle using the further estimate of θ glob .

2. The method of angle estimation according to claim 1 , the method comprising:

providing a first height sensor for measuring h 1 , the height of the vehicle body with respect to the first wheel;

providing a second height sensor for measuring h 2 , the height of the vehicle body with respect to the second wheel;

providing a surface angle sensor for measuring θ road , the angle of the surface in relation to a horizontal plane;

providing an orientation sensor for measuring θ g{dot over (l)}ob , θ g{dot over (l)}ob being the rate of change of θ glob with respect to time;

measuring the values of h 1 , h 2 , θ road and θ g{dot over (l)}ob ;

calculating θ glob1 by integrating θ g{dot over (l)}ob with respect to time;

producing θ glob transient by applying a high pass filter to θ glob1 ;

calculating the angle θ rel of the first axis relative to the surface using the values of h 1 and h 2 ;

calculating θ glob steady state by combining θ rel and θ road and applying at least one low pass filter; and

calculating a further estimate of θ glob from θ glob transient and θ glob steady state.

3. The method of angle estimation according to claim 2 , wherein the surface angle sensor comprises an accelerometer for measuring a x , the acceleration of the vehicle with respect to the first axis.

4. A method of angle estimation for use in a vehicle which is travelling on a surface, the vehicle comprising a vehicle body which is attached to at least two wheels, the vehicle body having a first axis, the method comprising:

providing a first height sensor for measuring h 1 , the height of the vehicle body with respect to the first wheel;

providing a second height sensor for measuring h 2 , the height of the vehicle body with respect to the second wheel;

providing a surface angle sensor for measuring θ road , the angle of the surface in relation to a horizontal plane;

measuring the values of h 1 , h 2 and θ road ;

calculating the angle θ rel of the first axis relative to the surface using the values of h 1 and h 2 ; and

calculating an estimate of θ glob , the angle between the first axis and the horizontal plane, from θ road and θ rel .

5. The method of angle estimation according to claim 4 , wherein the surface angle sensor comprises an accelerometer for measuring a x , the acceleration of the vehicle with respect to the first axis.

6. The method of angle estimation according to claim 5 , wherein measuring θ road comprises calculating an estimate θ road ′, using the relationship:

θ road ′=θ glob ′−θ rel ′

wherein θ glob ′ and θ rel ′ are estimates of θ glob and θ rel .

7. The method of angle estimation according to claim 6 , the method comprising calculating θ glob ′ using the equation:

θ

glob

′

=

arcsin

⁡

(

a

x

-

u

.

+

ω

z

⁢

v

y

g

)

wherein:

ω z is the rate of yaw of the vehicle;

v y is the velocity of the vehicle along a second axis, the second axis being perpendicular to the first axis and perpendicular to the direction of acceleration due to gravity;

{dot over (u)} is the derivative with the respect to time of the speed of the vehicle along the first axis.

8. The method of angle estimation according to claim 6 , the method comprising calculating θ rel using the equation:

θ

rel

′

a

x

=

M

s

⁢

h

cg

K

pitch

+

D

pitch

⁢

s

wherein:

M s is the mass of the vehicle;

h cg is the height of the centre of gravity of the vehicle;

K pitch is the spring term associated with the vehicle suspension; and

D pitch s is the damping term associated with the vehicle suspension.

9. An angle estimation system for use in operating a vehicle which is travelling on a surface, the vehicle comprising a vehicle body which is attached to at least two wheels, the vehicle body having a first axis, the angle estimation system comprising a control unit, the control unit being arranged to:

calculate θ glob1 as a first estimate of the angle θ glob between the first axis and a horizontal plane;

apply a high pass filter to θ glob1 to produce θ glob transient, an estimate of transient values of θ glob ;

calculate θ glob steady state, an estimate of steady state values of θ glob ; and

calculate a further estimate of θ glob from θ glob transient and θ glob steady state, wherein the system is configured to operate the vehicle using the further estimate of θ glob .

10. The angle estimation system according to claim 9 , the angle estimation system further comprising:

a first height sensor for measuring h 1 , the height of the vehicle body with respect to the first wheel;

a second height sensor for measuring h 2 , the height of the vehicle body with respect to the second wheel;

a surface angle sensor for measuring θ road , the angle of the surface in relation to a horizontal plane; and

an orientation sensor for measuring θ g{dot over (l)}ob , θ g{dot over (l)}ob being the rate of change of θ glob with respect to time and θ glob being the angle between the first axis and the horizontal plane,

the control unit being arranged to:

receive signals from the sensors indicating the values of h 1 , h 2 , θ road and θ g{dot over (l)}ob ;

integrate θ g{dot over (l)}ob with respect to time to calculate θ glob1 ;

apply a high pass filter to θ glob1 to produce θ glob transient;

use the values of h 1 and h 2 to calculate θ rel , the angle of the first axis relative to the surface;

combine θ rel and θ road , and apply a low pass filter, to produce θ glob steady state; and

calculate a further estimate of θ glob from θ glob transient and θ glob steady state.

11. The angle estimation system according to claim 10 , wherein the surface angle sensor comprises an accelerometer for measuring a x , the acceleration of the vehicle with respect to the first axis.

12. A vehicle comprising an angle estimation system according to claim 9 .

13. An angle estimation system for use in a vehicle which is travelling on a surface, the vehicle comprising a vehicle body which is attached to at least two wheels, the vehicle body having a first axis, the angle estimation system comprising:

a first height sensor for measuring h 1 , the height of the vehicle body with respect to the first wheel;

a second height sensor for measuring h 2 , the height of the vehicle body with respect to the second wheel;

a surface angle sensor for measuring θ road , the angle of the surface in relation to a horizontal plane; and

a control unit, the control unit being arranged to:

receive signals from the sensors indicating the values of h 1 , h 2 and θ road ;

use the values of h 1 and h 2 to calculate θ rel , the angle of the first axis relative to the surface; and

calculate an estimate of θ glob , the angle between the first axis and the horizontal plane, from θ road and θ rel .

14. The angle estimation system according to claim 13 , wherein the surface angle sensor comprises an accelerometer for measuring a x , the acceleration of the vehicle with respect to the first axis.

15. The angle estimation system according to claim 14 , wherein measuring θ road comprises calculating an estimate θ road ′, using the relationship:

θ road ′=θ glob ′−θ rel ′,

wherein θ glob ′ and θ rel ′ are estimates of θ glob and θ rel .

16. The angle estimation system according to claim 15 , the control unit being further arranged to calculate θ glob ′ using the equation:

θ

glob

′

=

arcsin

⁡

(

a

x

-

u

.

+

ω

z

⁢

v

y

g

)

wherein:

ω z is the rate of yaw of the vehicle;

v y is the velocity of the vehicle along a second axis, the second axis being perpendicular to the first axis and perpendicular to the direction of acceleration due to gravity;

{dot over (u)} is the derivative with the respect to time of the speed of the vehicle along the first axis.

17. The angle estimation system according to claim 15 , the control unit being further arrange to calculate θ rel ′ using the equation:

θ

rel

′

a

x

=

M

s

⁢

h

cg

K

pitch

+

D

pitch

⁢

s

wherein:

M s is the mass of the vehicle;

h cg is the height of the centre of gravity of the vehicle;

K pitch is the spring term associated with the vehicle suspension; and

D pitch s is the damping term associated with the vehicle suspension.