汽車慣量損失

1、.Inertia and LossesThis is a general discussion about inertia and losses in a vehicle and / or dynamometer application.Inertia is the term used to describe the resistance of a mass to changes in motion (speed). This mass can be a vehicle traveling down a road, steel drums rotating on a shaft or a mo

2、tor generating torque to simulate inertia.Inertia (total mass), torque (rotational force) and deceleration rate (change in speed over change in time) are linearly related. Torque = Inertia * Acceleration. If the deceleration doubles, the total torque must have doubled (assuming the inertia stayed th

3、e same). If the inertia suddenly drops by half, the deceleration rate will double (assuming the torque stayed the same). This simple picture gets rather muddy when all the torque (forces) working on a machine (or vehicle) is not known (or measured). The general assumption is that the only thing stop

4、ping a vehicle or dynamometer is brake torque. This is not the case; there are many other forces at work causing deceleration.Dynamometer losses:· Bearings. These usually display a linearly increasing loss with increasing speed. This loss will also change with temperature (as lubricants change

5、viscosity and bearing preload changes due to heating).· Windage. The windage losses from the inertia disks can be substantial. The more disk faces exposed to free air, the more windage losses will be experienced. These losses increase exponentially with speed.· Drive motor. DC motors have

6、a different coast torque when the field is energized than when the field is turned off. This small torque difference may be noticeable when running with a very light inertia (keep this in mind when viewing the inertia specification from the DC motor manufacturer, this inertia will be specified with

7、the motor field de-energized. During operation, the field will be energized).Vehicle losses:· Tires. This loss increases with increasing decel rates. When wheel lock-up occurs, ALL the stopping energy is absorbed by the tires. The heat buildup in tires is directly caused by frictional losses in

8、 the tires. Losses are always converted to heat. Many tire coupled, road wheel type machines use drag force (the tangential axle force) and wheel speed sensors to determine (and account for) tire losses accurately.· Bearings, seals. This loss usually displays a linearly increasing loss with inc

9、reasing speed (compared to the other losses, this one is negligible).· Windage. This loss increases exponentially with speed. This is the most significant loss at high speeds (when a vehicle is traveling at full speed (flat out), all the engine horse power is used overcoming windage, if engine

10、power is lost, the vehicle will initially decelerate at a rate equivalent to the wheel torque level the engine was supplying (but with NO measured brake torque).· Drive line. This loss is very hard to quantify. Also known as engine braking, this torque WILL appear in the drive wheel's torqu

11、e transducer and may be easily mistaken as brake torque. Wheel torque transducers DO NOT measure brake torque. They measure wheel torque. To truly measure brake torque would require an instrumented rotor, reactionary load cell on the caliper or rotating torque cell in the drive shafts. In the confin

12、es of modern vehicle wheel wells, anything other than wheel torque transducers are impractical. Also, the driveline can provide extra energy for the brakes to absorb, both at low speeds due to engine idle and in the case of driver input (two footed driving).· Grade. Stopping a vehicle on an upw

13、ard slope requires less work than stopping on a level surface. This makes the vehicle appear as if it got lighter. Grade can be a difficult thing to measure. Decel and downward grade appear to be the same physical property to a decel transducer. Inclination transducers incorporating a gyro are avail

14、able, but the calculating the total energy added or absorbed by grade changes during a braking event, using data from a multi-axis inclinometer, is not a trivial task.· Torque spread. When analyzing the vehicle data, keep in mind the overall vehicle decel observed is the result of ALL the brake

15、s on the vehicle. It is difficult to determine the amount of work a single brake has done when only total work is known. The coefficient of friction is a constantly changing value across all wheels/brakes on the vehicle. This moves the work done around to different areas. Energy spread across all wh

16、eels is also dependent on cornering, road surface changes, and general road conditions.Using the above information, the following can be deduced:· The brakes never see the total, specified mass / inertia (unless done on a machine using inertia simulation with loss compensation enabled). If the

17、brake is applied with the pressure set to zero, the machine / vehicle is going to stop anyway (with no brake torque). For example, if the brake torque is such that the machine will stop in half the time that the machine / vehicle coast down would normally take, then the brake saw only half of the te

18、st mass / inertia.· On a dynamometer, the brake sees more inertia on high decel stops than light decel stops. The faster the machine is decelerated, the less time the losses have to help the machine slow down. In a vehicle, the higher the decel, the wheel/brake sees more inertia but more and mo

19、re of the kinetic energy is transferred to the tire tread.Comparing test results (temperature profiles, stop times, stop distances, etc.) from one machine to another assumes the losses of both machines are the same.If external energy is applied (or removed) from the system during a stop (upward/down

20、ward grade, DC motor still on, transmission shifts, motor idle torque, etc.), inertia will be difficult to quantify. If there is brake torque and no change in speed over time (drag stops), this will calculate as infinite inertia.has addressed many of the issues in the above article to account for th

21、e effects of losses. These include the AIV and Inertia simulation systems.See Vehicle modeling for a general paper on brake testing.See Mathematical formulas for more information regarding the actual calculations.- -慣性和損失- -在車輛和/或測功機(jī)應(yīng)用的慣性和損失，這是一個(gè)一般性討論。轉(zhuǎn)動(dòng)慣量是一個(gè)術(shù)語，用來描述在運(yùn)動(dòng)中的變化（速度）的質(zhì)量的電阻。這種大規(guī)模的，可以在車輛行駛的道

22、路，鋼鼓的旋轉(zhuǎn)軸或電動(dòng)機(jī)產(chǎn)生的轉(zhuǎn)矩來模擬慣性。慣量（總質(zhì)量），扭矩（旋轉(zhuǎn)力）和減速率（變化的速度超過時(shí)間的變化）是線性相關(guān)的。扭矩=慣性加速度。如果減速加倍，總扭矩必須增加了一倍（假設(shè)的慣量保持不變）。如果慣性突然下降了一半，減速率將增加一倍（假設(shè)扭矩保持不變）。這個(gè)簡單的圖片變得相當(dāng)泥濘，當(dāng)所有的一臺(tái)機(jī)器上工作（或車輛）的扭矩（力）不知道（或測量）。一般的假設(shè)是，唯一停止車輛或測功機(jī)是制動(dòng)力矩。這是不是這樣，還有許多其他的工作而導(dǎo)致減速力量.測力計(jì)的損失：路軸承。這些通常顯示隨著速度的增加線性增加虧損。這種損失也將隨溫度的改變（如改變潤滑油的粘度和軸承預(yù)緊力的變化，由于加熱）。路風(fēng)阻。從慣性

23、磁盤的風(fēng)阻損失是巨大的。面接觸到自由的空氣，更多的風(fēng)阻損失將經(jīng)歷更多的磁盤。這些損失成倍增加的速度。路驅(qū)動(dòng)電機(jī)。直流電動(dòng)機(jī)有一個(gè)不同的海岸轉(zhuǎn)矩，當(dāng)該字段被激勵(lì)時(shí)，該字段是關(guān)閉的。這個(gè)小扭矩差運(yùn)行時(shí)可能會(huì)出現(xiàn)明顯在操作過程中，該字段將是一個(gè)很輕的慣量（觀看時(shí)的慣性規(guī)范直流電動(dòng)機(jī)制造商，這種慣性將指定與電機(jī)領(lǐng)域斷電，記住這一點(diǎn)。通電）。車輛損失：路輪胎。這種損失增加減速率的增加。當(dāng)車輪的鎖定發(fā)生時(shí)，所有的停止能量被吸收的輪胎。直接造成熱量積聚在輪胎在輪胎的摩擦損失。損失總是轉(zhuǎn)化為熱能。許多輪胎耦合道路輪型機(jī)使用拖曳力（切向軸力）和輪速傳感器來確定（賬戶）輪胎損失準(zhǔn)確。路軸承，密封件。這一損失通常會(huì)

24、顯示線性增加的損失隨著速度的增加（相對于其他方面的損失，這一個(gè)可以忽略不計(jì)）。路風(fēng)阻。這種損失成倍增加的速度。在高速行駛時(shí)（當(dāng)車輛行駛在全速（平出），所有的發(fā)動(dòng)機(jī)馬力用于克服風(fēng)阻，如果發(fā)動(dòng)機(jī)功率丟失，這是最顯著的損失，車輛開始減速的速率相當(dāng)于到車輪扭矩水平的發(fā)動(dòng)機(jī)供應(yīng)（但沒有測得的制動(dòng)力矩）。路車道線。這種損失是很難量化的。也被稱為發(fā)動(dòng)機(jī)制動(dòng)，扭矩將出現(xiàn)在驅(qū)動(dòng)輪的扭矩傳感器，并可以很容易誤認(rèn)為制動(dòng)轉(zhuǎn)矩。車輪扭矩傳感器，不要測量制動(dòng)轉(zhuǎn)矩。他們測量車輪扭矩。要真正衡量制動(dòng)力矩將需要檢測轉(zhuǎn)子，反動(dòng)負(fù)載上的的卡尺或傳動(dòng)軸的旋轉(zhuǎn)扭矩細(xì)胞的細(xì)胞。在現(xiàn)代化的車輪井的局限，車輪扭矩傳感器以外的任何東西是不切實(shí)際的。另外，動(dòng)力傳動(dòng)系統(tǒng)可以提供額