组合车辆测试

正确！解释：先略微升起挂车支腿离地；保持挂车制动锁定，挂低挡轻轻前拉以检查是否真正锁紧。 / Correct! EXPLANATION: Raise trailer landing gear slightly off ground. Pull tractor gently forward while the trailer brakes are still locked to check that the trailer is locked onto the tractor.

正确！解释：应急气路发生重大泄漏会使牵引车保护阀关闭，并触发挂车紧急制动。但只有当挂车气罐仍有压力时，制动才能保持。 / Right! EXPLANATION: A major leak in the emergency line will cause the tractor protection valve to close and the trailer emergency brakes to come on. But the brakes will hold only if there is air pressure in the trailer air tank.

对！解释：后轮抱死抓地差，会横向滑移去“追上”前轮；拖挂时，挂车会**把牵引车侧推**，造成突然折刀。 / Right! EXPLANATION: Rear wheel braking skids occur when the rear drive wheels lock. Because locked wheels have less traction than rolling wheels, the rear wheels usually slide sideways to "catch up" with the front wheels. With vehicles towing trailers, a drive-wheel skid can let the trailer push the towing vehicle sideways, causing a sudden jackknife.

正确！解释：确认**安全卡扣扣在锁柄上方**。某些五轮的卡扣需要手动放置。 / Correct! EXPLANATION: Check that the safety latch is in position over locking lever. On some fifth wheels the catch must be put in place by hand.

对！解释：若 1 分钟压降超过规范，说明漏气过大；不修复就上路，**可能失去制动**。 / Right! EXPLANATION: If the air pressure falls more than the specified psi in one minute for combination vehicles, the air loss rate is too much. Check for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving.

正确！解释：有些车辆配有“死端”假接头，未用时把手爪接头接上去，可防止**水和尘土**进入接头与气管。 / Correct! EXPLANATION: Some vehicles have "dead end" or dummy couplers to which the hoses may be attached when they are not in use. This will prevent water and dirt from getting into the coupler and the air-lines.

open, move the vehicle forward slowly, and apply trailer brakes with the hand control or trolley valve. You should feel the brakes come on. This tells you the trailer brakes are connected and working. / 正确！解释：检查气压正常，释放驻车与行车制动，确认挂车供气按入/开启，车辆低速前移，用手控阀施加挂车制动，应能感觉到制动介入——这说明挂车制动已连接且工作正常。 / Correct! EXPLANATION: Check for normal air pressure, release the parking brakes, release the service brake, make sure the trailer air supply is in

完全正确！解释：牵引车保护阀用于在挂车脱离或出现严重漏气时，**把牵引车的空气留在牵引车系统**里。它受驾驶室内的挂车供气控制阀控制；当气压过低（通常 **20–45 psi**）时会自动关闭，并释放挂车应急管路的空气，使挂车紧急制动介入。 / Exactly! EXPLANATION: The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak. The tractor protection valve is controlled by the trailer air supply control valve in the cab. The control valve allows you to open and shut the tractor protection valve. The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi). When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on, with possible loss of control.

正确！解释：一个常用规则：**40 mph 以下**，每 **10 英尺**车长至少留 **1 秒**；更高速度需再**多加 1 秒**。 / Correct! EXPLANATION: One good rule says you need at least one second for each 10 feet of vehicle length at speeds below 40 mph. At greater speeds, you must add 1 second for safety.

完全正确！解释：检查期间要先**固定车辆**：变速箱挂**空挡**，拉驻车制动，熄火并带走钥匙，防止他人移动。 / Exactly! EXPLANATION: Before inspection the trailer while coupling you need to secure the vehicle. Put transmission in neutral. Put parking brakes on. Shut off engine and take key with you so someone else won't move truck while you are under it.

正确！解释：反复踩放刹车踏板，让系统气压降至**约 20–45 psi**，这会使**弹簧制动**介入。 / Correct! EXPLANATION: – 45 psi. This will cause the spring brakes to come on.

正确！解释：测试挂车制动前应先给系统充气——按入红色挂车供气旋钮，或把牵引车保护阀拨到“**正常**”位置，待气压正常后再开始测试。 / Right! EXPLANATION: To test the trailer air brake system, first charge it with air. Push in the red trailer air supply knob or place the tractor protection valve control in the "normal" position. Wait until the air pressure reaches normal before you start your tests.

正确！解释：组合车要检查的项目**更多**：不仅有整个挂接系统（牵引销、五轮等），还有各挂车的支腿，以及更多的车轴。 / Correct! EXPLANATION: There are more things to inspect on a combination vehicle than on a bus or straight truck. First, of course, there is the entire coupling system: the kingpin, the fifth wheel, etc. Next, there is the landing gear of each trailer. Not to mention a few more axels to check.

正确！解释：挂车应略低于五轮，使牵引车倒入时能将其**轻微托起**。挂车太低可能顶伤鼻部，太高可能无法正确挂接。 / Bingo! EXPLANATION: The trailer should be low enough that it is raised slightly by the tractor when the tractor is backed under it. If the trailer is too low, the tractor may strike and damage the trailer nose; if the trailer is too high, it may not couple correctly.

正确！解释：大型组合车在空载或轻载时悬架更硬、制动更“猛”，抓地更差，车轮更容易抱死，因此反而更难刹住。 / Right! EXPLANATION: Large combination vehicles take longer to stop when they are empty than when they are fully loaded. When lightly loaded, the very stiff suspension springs and strong brakes give poor traction and make it very easy to lock up the wheels.

正确！解释：应急（供气）管路有两项作用：向挂车储气筒供气，并控制组合车辆的紧急制动。 / Right! EXPLANATION: The emergency line, also called the supply line, has two purposes. First, it supplies air to the trailer air tanks. Second, the emergency line controls the emergency brakes on combination vehicles.

正确！解释：气压充满后，熄火、释放驻车制动并计时气压下降；组合车辆在 1 分钟内的压降应**小于 3 PSI**。 / Right! EXPLANATION: With a fully-charged air system, turn off the engine, release the parking brake; and time the air pressure drop. The loss rate should be less than three psi in one minute for combination vehicles, we do not add the additional second here because the brakes are released.

答对了！解释：车辆转弯时后轮走出的轨迹与前轮不同，称为“偏轨”。**车越长偏轨越大**；若有多节挂车，最后一节的偏轨最大。 / Bingo! EXPLANATION: When a vehicle goes around a corner the rear wheels follow a different path than the front wheels, and this is called off-tracking or "cheating." Longer vehicles will off-track more. If there is more than one trailer, the rear wheels of the last trailer will off-track the most.

完全正确！解释：先用低速档开始摇起支腿，脱重后换高速档并**完全收起**；切勿让其只升到一半——可能会**挂到道口**等障碍。收好后把摇柄固定在支架上。 / Exactly! EXPLANATION: Use low gear range to begin raising the landing gear, once free of weight, switch to the high gear range. Raise the landing gear all the way up. Never drive with landing gear only part way up as it may catch on railroad tracks or other things. After raising landing gear, secure the crank handle safely.

答对了！解释：到挂车下方检查五轮，确认锁爪**抱住牵引销的颈部（shank）**。 / Bingo! EXPLANATION: Go under trailer and investigate the back of the fifth wheel. Make sure the fifth wheel jaws have closed around the shank of the kingpin.