组合车辆测试

完全正确！解释：大型组合车在**空载**时比满载更难刹住；悬架更硬、制动更猛，抓地差、更容易抱死并导致折叠。 / Exactly! EXPLANATION: Large combination vehicles take longer to stop when they are empty than when they are fully loaded. When empty, the very stiff suspension springs and strong brakes give poor traction and make it very easy to lock up the wheels causing the tractor to jackknife.

答对了！解释：虽说车越重刹车做功越大，但重型车在**满载**时（轮胎、弹簧、减震）工作效果最好；空车抓地差，制动距离反而更长。 / Bingo! EXPLANATION: The heavier the vehicle, the more work the brakes must do to stop it, and the more heat they absorb. But the brakes, tires, springs, and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Empty trucks require greater stopping distances because an empty vehicle has less traction.

正确！解释：三挂的**后向放大**约为 3.5，也就是说，它最后一节挂车**比五轴牵引车**更容易翻车约 3.5 倍；双挂约 2。 / Right! EXPLANATION: Triples have a rearward amplification of 3.5. This means you can roll the last trailer of triples 3.5 times as easily as a five-axle tractor. While the rearward amplification of a double is around 2.

完全正确！解释：当气压降到大约 **20–45 psi** 时，红色挂车供气旋钮会**弹出**，或从“normal”切到“emergency”。 / Exactly! EXPLANATION: –45 psi, the trailer air supply control knob should pop out, or the valve control should go from the "normal" to the "emergency" position.

正确！解释：确保气管和电缆**不缠绕、不被夹、不拖地**，并留有**足够转弯余量**。 / Right! EXPLANATION: Make sure air and electrical lines are not tangled, pinched, dragging against tractor parts, and have enough slack for turns.

正确！解释：支腿刚接触地面后，先用**低速档**多摇几圈，略微卸掉牵引车上的重量，更容易解锁五轮并再次挂接。 / Correct! EXPLANATION: After the landing gear makes firm contact with the ground, turn crank in low gear a few extra turns. This will lift some weight off the tractor making it easier to unlatch fifth wheel, and to recouple to the trailer.

答对了！解释：反复踩放踏板使气压下降到 **20–45 psi**，这会使**弹簧制动介入**。 / Bingo! EXPLANATION: – 45 psi. This will cause the spring brakes to come on.

正确！解释：行车气路也称**控制线（control line）**或**信号线（signal line）**，由脚刹或挂车手控阀控制气流。 / Correct! EXPLANATION: The service line, also called the control line or signal line, carries air controlled by the foot brake or the trailer hand brake.

正确！解释：在驾驶室**按入**挂车供气旋钮，或把牵引车保护阀控制从“紧急”位切到“正常”位，即可向挂车制动系统供气。 / Right! EXPLANATION: From cab, push in air supply knob or move tractor protection valve control from the emergency to the normal position to supply air to the trailer brake system.

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：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.

完全正确！解释：车辆的**重心高度**对操控很重要；重心越高，越容易翻车。 / Exactly! EXPLANATION: The height of the vehicle's center of gravity is very important for safe handling. A high center of gravity means you are more likely to tip over.

正确！解释：应急管通常用**红色**（红色软管、红色接头等）标识，以免与**蓝色**的行车管混淆。 / Bingo! EXPLANATION: Emergency lines are often coded with red (red hose, red couplers, or other parts) to keep from getting them mixed up with the blue service line.

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

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.

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：在空气系统充满时，熄火、释放驻车制动并记录气压下降速度。组合车在 1 分钟内的压降应小于 3 psi；若踩住脚刹，则允许值再增加约 1 psi（即约 4 psi）。 / Exactly! 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, adding one second if the brakes are applied.

答对了！解释：转换拖架与 1975 年前制造的挂车**不要求**配备弹簧制动。 / Bingo! EXPLANATION: Converter dollies and trailers built before 1975 are not required to have spring brakes.

答对了！解释：等气压恢复正常后**熄火**以便听清；反复施加并释放挂车制动，应该能听到制动动作与泄气的声音。 / Bingo! EXPLANATION: Wait until the air pressure is normal, then shut engine off so you can hear the brakes. Check brake system for crossed air-lines by: applying and releasing trailer brakes and listen for sound of trailer brakes being applied and released. You should hear the brakes move when applied and air escape when the brakes are released.