| 摘要 |
A brake system includes a pair of brake shoes and a wheel cylinder actuating the brake shoes such that the brake shoes contact a drum to apply braking action thereto. The wheel cylinder includes a housing, a first pair of oppositely facing pistons disposed within the housing, and a second pair of oppositely facing pistons disposed within the housing between the first pair of oppositely facing pistons. When the brake is operated, hydraulic pressure causes the second pair of pistons to move outward in opposite directions. As a result, the first pair of pistons move outward in opposite directions. Since the brake shoes are connected to the first pair of oppositely facing pistons, the brake shoes are applied to the drum. The wheel cylinder further includes a member disposed between and in contact with the second pair of oppositely facing pistons. In a first position the member provides a first separation distance between the second pair of oppositely facing pistons, and in a second position the member provides a second separation distance, longer than the first separation distance, between the second pair of oppositely facing pistons. By moving the member from the first position to the second position the brake shoes will be applied to the drum. In this manner, a parking braking can be applied.
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