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In cars, the parking brake, also called〔http://www.tekstlab.uio.no/cambridge_survey/maps/81〕 hand brake, emergency brake, or e-brake, is a latching brake usually used to keep the vehicle stationary. It is sometimes also used to prevent a vehicle from rolling when the operator needs both feet to operate the clutch and throttle pedals. Automobile hand brakes usually consist of a cable directly connected to the brake mechanism on one end and to a lever or foot pedal at the driver's position. The mechanism is often a hand-operated lever (hence the ''hand brake'' name), on the floor on either side of the driver, or a pull handle located below and near the steering wheel column, or a (foot-operated) pedal located far apart from the other pedals. Although sometimes known as an emergency brake, using it in any emergency where the footbrake is still operational is likely to badly upset the brake balance of the car and vastly increase the likelihood of loss of control of the vehicle, for example by initiating a rear-wheel skid. Additionally, the stopping force provided by using the handbrake is small and would not significantly aid in stopping the vehicle. The parking brake operates mostly on the rear wheels, which have reduced traction while braking but in some cases, parking brake operates on front wheel, as done in most Citroens manufactured since the end of World War II. The hand brake is instead intended for use in case of mechanical failure where the regular footbrake is inoperable or compromised. Modern brake systems are typically very reliable and equipped with dual-circuit hydraulics and low-brake-fluid sensor systems, meaning the handbrake is rarely used to stop a moving vehicle. The most common use for a parking brake is to keep the vehicle motionless when it is parked. Parking brakes have a ratchet locking mechanism that will keep them engaged until a release button is pressed. On vehicles with automatic transmissions, this is usually used in concert with a parking pawl in the transmission. Hand brakes are also used to assist in hill starts on vehicles with manual transmissions. Use of the handbrake frees both feet for use on the accelerator and clutch pedals, allowing the car to move off without rolling back at all. ==Types of brakes== School buses which are equipped with a hydraulic brake system will have a hand brake lever to the left of the driver (in left hand drive buses) near the floor. It is operated by pushing the lever down with one's hand to apply the brake, and pulling it upwards to release it. In cars with rear drum brakes, the parking brake cable usually actuates these drums mechanically with much less force than is available through the hydraulic system. In cars with rear disc brakes, the parking brake either actuates the disc calipers (again, with much less force) or a small drum brake housed within the hub assembly (the inner circumference of the disc is often used instead of a separate drum). Hudson automobiles used an unusual hybrid hydraulic-mechanical dual-brake system which operated the rear brakes through the otherwise conventional mechanical emergency-brake system when a failure of the hydraulic system allowed the pedal to travel beyond its normal limit. A number of production vehicles, light and medium duty trucks, and motor homes have been made with a separate drum brake on the transmission output shaft; called a driveline parking brake. This has an advantage of being completely independent of other braking systems. This is effective as long as the drive train is intact — propeller shaft, differential, and axle shafts. In many vehicles, this type of parking brake is operated by either a foot pedal or a hydraulic cylinder controlled by the transmission gear selector, or by both. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parking brake」の詳細全文を読む スポンサード リンク
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