Electrically assisted wheelchair and control method for electrically assisted wheelchair

1. An electrically assisted wheelchair comprising:

a wheelchair body including a seat on which a user sits;

a right drive that applies right auxiliary power to a right wheel by an operation of a right hand rim by the user;

a left drive that applies left auxiliary power to a left wheel by operation of a left hand rim by the user; and

a controller configured or programmed to calculate an assist value for the right wheel and the left wheel and determine the right auxiliary power and the left auxiliary power; wherein

the controller is configured or programmed to:

obtain an inclination assist value by correcting the assist value when a road surface is inclined in a left-right direction of the seat and perform a downhill turning preventing operation to cause the wheelchair body to travel straight by applying the right auxiliary power and the left auxiliary power corresponding to the inclination assist value; and

adjust the right auxiliary power and the left auxiliary power by correcting the inclination assist value based on a hand rim operation of the user to operate at least one of the right hand rim and the left hand rim in the downhill turning preventing operation.

2. The electrically assisted wheelchair according to claim 1 , wherein the controller is configured or programmed to:

estimate a disturbance value in a turning direction of the wheelchair body based on a difference between torques applied to the right hand rim and the left hand rim by the hand rim operation, estimate a difference between the left auxiliary power and the right auxiliary power and a yaw angular velocity of the wheelchair body, and obtain the inclination assist value by correcting the assist value based on the disturbance value; and

decrease the disturbance value when the hand rim operation is present.

3. The electrically assisted wheelchair according to claim 2 , wherein the controller is configured or programmed to correct the disturbance value based on a presence or an absence of the hand rim operation.

4. The electrically assisted wheelchair according to claim 3 , wherein the controller is configured or programmed to apply a low pass filter processing to the corrected disturbance value based on the difference between the torques applied to the right hand rim and the left hand rim by the hand rim operation and the yaw angular velocity of the wheelchair body.

5. The electrically assisted wheelchair according to claim 2 , wherein the controller is configured or programmed to correct the disturbance value by correcting at least one of the difference between the torques applied to the right hand rim and the left hand rim and the difference between the right auxiliary power and the left auxiliary power.

6. The electrically assisted wheelchair according to claim 5 , wherein the controller is configured or programmed to make a correction by multiplying at least one of the difference between the torques applied to the right hand rim and the left hand rim and the difference between the right auxiliary power and the left auxiliary power by a correction coefficient smaller than 1 and larger than zero.

7. The electrically assisted wheelchair according to claim 5 , wherein the controller is configured or programmed to:

calculate a correction coefficient equal to or smaller than 1 and larger than zero based on the torque applied to the right hand rim, the torque applied to the left hand rim, the right auxiliary power, and the left auxiliary power; and

make a correction by multiplying at least one of the difference between the torques applied to the right hand rim and the left hand rim and the difference between the right auxiliary power and the left auxiliary power by the correction coefficient.

8. The electrically assisted wheelchair according to claim 5 , wherein the controller is configured or programmed to apply a low pass filter processing to at least one of the difference between the torques applied to the right hand rim and the left hand rim and the difference between the right auxiliary power and the left auxiliary power based on the difference between the torques applied to the right hand rim and the left hand rim by the hand rim operation and the yaw angular velocity of the wheelchair body.

9. The electrically assisted wheelchair according to claim 1 , wherein the controller is configured or programmed to:

obtain the inclination assist value by feedback controlling the assist value using wheel speeds in a turning direction; and

correct at least one of a difference between torques applied to the right hand rim and the left hand rim, a difference between the right auxiliary power and the left auxiliary power, and the feedback controlled assist value.

10. The electrically assisted wheelchair according to claim 9 , further comprising a roll angle detector that detects a roll angle of the wheelchair body; wherein

the controller is configured or programmed to:

obtain the inclination assist value by feedforward controlling the assist value based on an inclined surface correction value corresponding to the roll angle detected by the roll angle detector; and

correct at least one of the difference between the torques applied to the right hand rim and the left hand rim, the difference between the right auxiliary power and the left auxiliary power, the feedback controlled assist value, and the inclined surface correction value.

11. The electrically assisted wheelchair according to claim 1 , further comprising a roll angle detector that detects a roll angle of the wheelchair body; wherein

the controller is configured or programmed to:

obtain the inclination assist value by feedforward controlling the assist value based on an inclined surface correction value corresponding to the roll angle detected by the roll angle detector; and

correct at least one of a difference between torques applied to the right hand rim and the left hand rim, a difference between the right auxiliary power and the left auxiliary power, and the inclined surface correction value.

12. A control method for an electrically assisted wheelchair that assists a travel of a wheelchair body by calculating an assist value based on an operation of a right hand rim and a left hand rim by a user seated on a seat and respectively applying right auxiliary power and left auxiliary power corresponding to the assist value to a right wheel and a left wheel, the method comprising:

obtaining an inclination assist value by correcting the assist value when a road surface is inclined in a left-right direction of the seat;

performing a downhill turning preventing operation to cause the wheelchair body to travel straight on the inclined road surface by applying the right auxiliary power and the left auxiliary power corresponding to the inclination assist value; and

correcting the inclination assist value based on a hand rim operation of the user to operate at least one of the right hand rim and the left hand rim in the downhill turning preventing operation.