Electric brake system

1. An electric brake system comprising a plurality of electric brake devices,

each electric brake device including:

a brake rotor;

a friction member configured to operatively contact the brake rotor;

a friction member actuator configured to cause the friction member to contact the brake rotor;

an electric motor configured to drive the friction member actuator;

a braking force estimation device configured to determine an estimate of a braking force generated by the friction member being pressed against the brake rotor, the estimated braking force being greater than zero; and

a control device configured to perform follow-up control of the generated braking force by controlling the electric motor so that the generated braking force matches a braking force target value,

the electric brake system further comprising:

a controlled variable error estimation module configured to estimate, for each electric brake device, a controlled variable error that is a difference between the estimate of the braking force determined by the braking force estimation device and a braking force produced by the brake device having no functional degradation; and

a controlled variable compensating module configured to, when the controlled variable error estimation module estimates the existence of the controlled variable error, distribute a braking force corresponding to the controlled variable error among the electric brake devices other than the electric brake device in which the existence of the controlled variable error is estimated so as to be added to the braking force target values of the respective electric brake devices to perform the follow-up control of the generated braking forces of the electric brake devices other than the electric brake device in which the existence of the controlled variable error is estimated, while continuing to perform the follow-up control of the generated braking force of the electric brake device in which the existence of the controlled variable error is estimated.

2. The electric brake system as claimed in claim 1 , further comprising a plurality of diagnosis modules configured to detect functional degradations of the respective electric brake devices, wherein

the controlled variable error estimation module is configured to estimate a difference between an estimate of a braking force determined by the braking force estimation device of an electric brake device in which functional degradation is detected by the diagnosis module, and an estimate of a braking force determined by the braking force estimation device of an electric brake device in which no functional degradation is detected by the diagnosis module.

3. The electric brake system as claimed in claim 1 , wherein

in order to determine the braking force in the case where no functional degradation occurs, the controlled variable error estimation module uses a state transition formula expressing relationships among:

a state variable including a motor rotation angle of the electric motor;

a manipulated variable including voltage or current of the electric motor;

a state transition matrix including electric actuator inertia of an electric actuator that includes the electric motor and the friction member actuator; and

a controlled variable including a braking force.

4. The electric brake system as claimed in claim 2 , further comprising:

a main power supply device configured to supply power to each of the control devices of the plurality of electric brake devices and to each of the electric motors of the plurality of electric brake devices; and

a backup power supply device used when the main power supply device is in an abnormal state, wherein

the diagnosis module includes a power supply diagnosis section configured to determine whether or not supply of power from the main power supply device is abnormal, and

the electric brake system further comprises a power supply switching mechanism configured to perform switching of power supply to the backup power supply device when the power supply diagnosis section has determined that supply of power from the main power supply device is abnormal.

5. The electric brake system as claimed in claim 4 , further comprising a power limitation unit configured to limit the power supplied to the electric motor, when the power supply switching mechanism performs switching of power supply from the main power supply device to the backup power supply device, wherein

the estimated controlled variable error is a difference between an estimate of a braking force determined by the braking force estimation device of an electric brake device subjected to power limitation by the power limitation unit and an estimate of a braking force determined by the braking force estimation device of an electric brake device not subjected to power limitation by the power limitation unit.

6. The electric brake system as claimed in claim 1 , further comprising a yaw moment calculation module configured to determine a yaw moment that occurs in a vehicle equipped with the electric brake system, wherein

when the controlled variable compensating module adds the distributed braking force corresponding to the controlled variable error to the braking force target value, the controlled variable compensating module determines the braking force to be added so that a yaw moment detected by the yaw moment calculation module becomes smaller than or equal to a predetermined value.