1. Field of the Invention
The present invention generally relates to a control apparatus for a braking system. More specifically, the present invention relates a braking force control apparatus that generates a braking force by pushing and separating a brake pad toward and apart from a brake rotor through a driving device.
2. Background Information
In a control apparatus for a braking system, a driving state of a motor is controlled by detecting a depressing force exerted on a brake pedal by a driver, such that the braking force that corresponds to the depressing force is generated. One of the methods of estimating the braking force is disclosed in the SAE 1990-01-0482. This braking force estimation method utilizes the rigidity of the caliper that supports pads. The braking force is estimated based on the amount of displacement of the motor from a point where the rotor and the pads initiated a contact. More specifically, since there is a certain relationship between the amount of displacement of the motor and the braking force determined by the caliper rigidity once the pads and the rotor start contacting, the braking force can be controlled by controlling the amount of motor displacement. However, the amount of motor displacement includes a portion that eliminates the clearance between the pads and the rotor. In other words, the amount of motor displacement includes the portion in which the motor moves in the pressuring direction until the pads and the rotor contact each other, and a portion in which the motor moves after the pads and the rotor start contacting. The aforementioned relationship between the braking force and the amount of motor displacement determined by the caliper rigidity exists only in the latter portion. Therefore, in order to obtain from the total amount of motor displacement, the amount of motor displacement occurring after the pads start contacting the rotor, it is necessary to eliminate precisely the portion in which the motor starts moving in the pushing direction until the pads start contacting the rotor. Therefore, it is necessary to detect the precise point at which the pads and the rotor start contacting.
One of the control apparatuses that control the braking force by detecting the position at which the pads and the rotor start contacting is disclosed in Japanese Laid-Open Patent Application H9-137841. In this control apparatus, an axial force sensor is attached to a piston that pushes and separates the pads toward and apart from each other. While the piston is moving in a direction that separates the pads apart from each other (i.e., the braking force is released), the initial contacting point of the pads and the rotor is determined as the point at which the axial force detected by the axial force sensor is zero.
In view of the above, there exists a need for a control apparatus which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that the preciseness of the axial force sensor disclosed in Japanese Laid-Open Patent Application H9-137841 would tends to be compromised under actual operating conditions. In particular, the preciseness of the detection of the axial force by the axial force sensor tends to be compromised because a change in property due to temperature changes and noise or degradation from vibration.
The present invention has been conceived in view of the aforementioned problems. More specifically, an object of the invention is to provide a control apparatus that can control braking force accurately by accurately detecting an initial contacting point of the pads (the brake friction body) and the rotor (the brake rotational body) without using an axial force sensor.
In order to achieve the aforementioned object, a braking force control apparatus is provided that includes a driving device, an operational status detector, an initial contact position detector and a brake control unit. The driving device is operatively configured to move a brake pad towards and away from a brake rotor. The operational status detector is arranged to detect an operational status of the driving device. The initial contact position detector is arranged to detect an initial contacting point between the brake pad and the brake rotor based on the operational status of the driving device detected by the operational status detector, when the driving device moves the brake pad toward the brake rotor. The brake control unit is operatively coupled to the driving device and the operational status detector to control the driving device. The brake control unit includes a brake command value setting portion that is configured to set a brake command value to control the driving device based on a pedal operation amount. The brake control unit further includes an adjustment portion configured to subsequently adjust the brake command value based on the initial contacting point between the brake pad and the brake rotor detected by the initial contact position detector.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.