Drum brake
A drum brake with the drum removed as used on the rear wheel of a car or truck. Note that in this installation, a cable-operated parking brake uses the service shoes.
A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum.
The term "drum brake" usually means a brake in which shoes press on the inner surface of the drum. When shoes press on the outside of the drum, it is usually called a clasp brake. Where the drum is pinched between two shoes, similar to a conventional disk brake, it is sometimes called a "pinch drum brake", although such brakes are relatively rare. A related type of brake uses a flexible belt or "band" wrapping around the outside of a drum, called a band brake.
History
A drum brake at the rear wheel of a motorbike
Kawasaki W800
The modern automobile drum brake was invented in 1902 by Louis Renault, though a less-sophisticated drum brake had been used by Maybach a year earlier. In the first drum brakes, the shoes were mechanically operated with levers and rods or cables. From the mid-1930s the shoes were operated with oil pressure in a small wheel cylinder and pistons (as in the picture), though some vehicles continued with purely-mechanical systems for decades. Some designs have two wheel cylinders.
The shoes in drum brakes are subject to wear and the brakes needed to be adjusted regularly until the introduction of self-adjusting drum brakes in the 1950s. In the 1960s and 1970s brake drums on the front wheels of cars were gradually replaced with disc brakes and now practically all cars use disc brakes on the front wheels, with many offering disc brakes on all wheels. However, drum brakes are still often used for handbrakes as it has proven very difficult to design a disc brake suitable for holding a car when it is not in use. Moreover, it is very easy to fit a drum handbrake inside a disc brake so that one unit serves as both service brake and handbrake.
Early type brake shoes contained asbestos. When working on brake systems of older cars, care must be taken not to inhale any dust present in the brake assembly. The United States Federal Government began to regulate asbestos production, and brake manufacturers had to switch to non-asbestos linings. Owners initially complained of poor braking with the replacements; however, technology eventually advanced to compensate. A majority of daily-driven older vehicles have been fitted with asbestos-free linings. Many other countries also limit the use of asbestos in brakes. Early automotive brake systems, after the era of hand levers of course, used a drum design at all four wheels. They were called drum brakes because the components were housed in a round drum that rotated along with the wheel. Inside was a set of shoes that, when the brake pedal was pressed, would force the shoes against the drum and slow the wheel. Fluid was used to transfer the movement of the brake pedal into the movement of the brake shoes, while the shoes themselves were made of a heat-resistant friction material similar to that used on clutch plates. This basic design proved capable under most circumstances, but it had one major flaw. Under high braking conditions, like descending a steep hill with a heavy load or repeated high-speed slow downs, drum brakes would often fade and lose effectiveness. Usually this fading was the result of too much heat build-up within the drum. Remember that the principle of braking involves turning kinetic energy (wheel movement) into thermal energy (heat). For this reason, drum brakes can only operate as long as they can absorb the heat generated by slowing a vehicle's wheels. Once the brake components themselves become saturated with heat, they lose the ability to halt a vehicle, which can be somewhat disconcerting to the vehicle's operator.
Self-applying characteristic
Drum brakes have a natural "self-applying" characteristic.[1] The rotation of the drum can drag either or both of the shoes into the friction surface, causing the brakes to bite harder, which increases the force holding them together. This increases the stopping power without any additional effort being expended by the driver, but it does make it harder for the driver to modulate the brake's sensitivity. It also makes the brake more sensitive to brake fade, as a decrease in brake friction also reduces the amount of brake assist.
Disc brakes exhibit no self-applying effect because the hydraulic pressure acting on the pads is perpendicular to the direction of rotation of the disc. Disc brake systems usually have servo assistance ("Brake Booster") to lessen the driver's pedal effort, but some disc braked cars (notably race cars) and smaller brakes for motorcycles, etc., do not need to use servos.
Note: In most designs, the "self applying" effect only occurs on one shoe. While this shoe is further forced into the drum surface by a moment due to friction, the opposite effect is happening on the other shoe. The friction force is trying to rotate it away from the drum. The forces are different on each brake shoe resulting in one shoe wearing faster. It is possible to design a two-shoe drum brake where both shoes are self-applying (having separate actuators and pivoted at opposite ends), but these are very uncommon in practice.
Drum brake designs
Rendering of a drum brake
Drum brakes are typically described as either leading/trailing or twin leading.[1]
Rear drum brakes are typically of a leading/trailing design(For Non Servo Systems), or [Primary/Secondary] (For Duo Servo Systems) the shoes being moved by a single double-acting hydraulic cylinder and hinged at the same point.[1] In this design, one of the brake shoes will always experience the self-applying effect, irrespective of whether the vehicle is moving forwards or backwards.[1] This is particularly useful on the rear brakes, where the footbrake (handbrake or parking brake) must exert enough force to stop the vehicle from travelling backwards and hold it on a slope. Provided the contact area of the brake shoes is large enough, which isn't always the case, the self-applying effect can securely hold a vehicle when the weight is transferred to the rear brakes due to the incline of a slope or the reverse direction of motion. A further advantage of using a single hydraulic cylinder on the rear is that the opposite pivot may be made in the form of a double lobed cam that is rotated by the action of the parking brake system.
Front drum brakes may be of either design in practice, but the twin leading design is more effective.[1] This design uses two actuating cylinders arranged so that both shoes will utilize the self-applying characteristic when the vehicle is moving forwards.[1] The brake shoes pivot at opposite points to each other.[1] This gives the maximum possible braking when moving forwards, but is not so effective when the vehicle is traveling in reverse.[1]
The optimum arrangement of twin leading front brakes with leading/trailing brakes on the rear allows for more braking force to be deployed at the front of the vehicle when it is moving forwards, with less at the rear. This helps to prevent the rear wheels locking up, but still provides adequate braking at the rear when it is needed.[1]
The brake drum itself is frequently made of cast iron, although some vehicles have used aluminum drums, particularly for front-wheel applications. Aluminum conducts heat better than cast iron, which improves heat dissipation and reduces fade. Aluminum drums are also lighter than iron drums, which reduces unsprung weight. Because aluminum wears more easily than iron, aluminum drums will frequently have an iron or steel liner on the inner surface of the drum, bonded or riveted to the aluminum outer shell.
Advantages
Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake. Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. In this situation, a small drum is usually fitted within or as part of the brake disk also known as a banksia brake.
In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.
Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.
Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.
Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often times the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).
Brake technology, just like suspension technology and fuel-system technology, has come a long way in recent years. What began in the '60s as a serious attempt to provide adequate braking for performance cars has ended in an industry where brakes range from supremely adequate to downright phenomenal. The introduction of components like carbon fiber, sintered metal and lightweight steel, along with the adoption of ABS, have all contributed to reduced stopping distances and generally safer vehicles (though ABS continues to provide controversy).
Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increase their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.
Disadvantages
Drum brakes, like most other types, are designed to convert kinetic energy into heat by friction.[1] This heat is intended to be further transferred to atmosphere, but can just as easily transfer into other components of the braking system.
Brake drums have to be large to cope with the massive forces that are involved, and they must be able to absorb and dissipate a lot of heat. Heat transfer to atmosphere can be aided by incorporating cooling fins onto the drum. However, excessive heating can occur due to heavy or repeated braking, which can cause the drum to distort, leading to vibration under braking.
The other consequence of overheating is brake fade.[1] This is due to one of several processes or more usually an accumulation of all of them.
1. When the drums are heated by hard braking, the diameter of the drum increases slightly due to thermal expansion, this means the brakes shoes have to move farther and the brake pedal has to be depressed further.
2. The properties of the friction material can change if heated, resulting in less friction. This is usually only temporary and the material regains its efficiency when cooled,[1] but if the surface overheats to the point where it becomes glazed the reduction in braking efficiency is more permanent. Surface glazing can be worn away with further use of the brakes, but that takes time.
3. Excessive heating of the brake drums can cause the brake fluid to vapourise, which reduces the hydraulic pressure being applied to the brake shoes.[1] Therefore less retardation is achieved for a given amount of pressure on the pedal. The effect is worsened by poor maintenance. If the brake fluid is old and has absorbed moisture it thus has a lower boiling point and brake fade occurs sooner.[1]
Brake fade is not always due to the effects of overheating. If water gets between the friction surfaces and the drum, it acts as a lubricant and reduces braking efficiency.[1] The water tends to stay there until it is heated sufficiently to vapourise, at which point braking efficiency is fully restored. All friction braking systems have a maximum theoretical rate of energy conversion. Once that rate has been reached, applying greater pedal pressure will not result in a change of this rate, and indeed the effects mentioned can substantially reduce it. Ultimately this is what brake fade is, regardless of the mechanism of its causes.
Disc brakes are not immune to any of these processes, but they deal with heat and water more effectively than drums.
Drum brakes can be grabby if the drum surface gets light rust or if the brake is cold and damp, giving the pad material greater friction. Grabbing can be so severe that the tires skid and continue to skid even when the pedal is released. Grabbiness is the opposite of fade: when the pad friction goes up, the self-assisting nature of the brakes causes application force to go up. If the pad friction and self-amplification are high enough, the brake will stay on due to self-application even when the external application force is released.
Another disadvantage of drum brakes is their complexity. A person must have a general understanding of how drum brakes work and take simple steps to ensure the brakes are reassembled correctly when doing work on drum brakes. Incompetent mechanics should not attempt working on drum brakes.
Re-arcing
Before 1984, it was common to re-arc brake shoes to match the arc within brake drums. This practice, however, was controversial as it removed friction material from the brakes and caused a reduction in the life of the shoes as well as created hazardous asbestos dust. Current design theory is to use shoes for the proper diameter drum, and to simply replace the brake drum when necessary, rather than perform the re-arcing procedure. Before you can appreciate the difference between drum and disc brakes, you have to understand the common principles that both systems use when stopping a car: friction and heat. By applying resistance, or friction, to a turning wheel, a vehicle's brakes cause the wheel to slow down and eventually stop, creating heat as a byproduct. The rate at which a wheel can be slowed depends on several factors including vehicle weight, braking force and total braking surface area. It also depends heavily on how well a brake system converts wheel movement into heat (by way of friction) and, subsequently, how quickly this heat is removed from the brake components. This is where the difference between drum brakes and disc brakes becomes pronounced.
Adjustment
Early drum brakes (before about 1955) required periodic adjustment to compensate for drum and shoe wear. If not done sufficiently often long brake pedal travel ("low pedal") resulted. Low pedal can be a severe hazard when combined with brake fade as the brakes can become ineffective when the pedal bottoms out.
Self adjusting brakes may use a mechanism that engages only when the vehicle is being stopped from reverse motion. This is a traditional method suitable for use where all wheels use drum brakes (most vehicles now use disc brakes on the front wheels). By operating only in reverse it is less likely that the brakes will be adjusted while hot (when the drums are expanded), which could cause dragging brakes that would accelerate wear and increase fuel consumption.
Self adjusting brakes may also operate by a ratchet mechanism engaged as the hand brake is applied, a means suitable for use where only rear drum brakes are used. If the travel of the parking brake actuator lever exceeds a certain amount, the ratchet turns an adjuster screw that moves the brake shoes toward the drum.
There are different Self Adjusting Brake Systems. Basically can be divided in to RAI and RAD. RAI systems are much more efficient than RAD systems and have built in systems that avoids the systems to recover when the brake is over heating. The most famous RAI are developed by Lucas, Bendix, Bosch, AP. For RAD systems the most famous are Bendix, AP, VAG ( Volkswagen ) and FORD recovery systems.
The manual adjustment knob is usually at the bottom of the drum and is adjusted via a hole on the opposite side of the wheel. This requires getting underneath the car and moving the clickwheel with a flathead screwdriver. It is important and tedious to adjust each wheel evenly so as to not have the car pull to one side during heavy braking, especially if on the front wheels. Either give each one the same amount of clicks and then perform a road test, or raise each wheel off the ground and spin it by hand measuring how much force it takes and feeling whether or not the shoes are dragging.
Use in music
A brake drum can be very effective in modern concert and film music to provide a non-pitched metal sound similar to an anvil. Some have more resonance than others, and the best method of producing the clearest sound is to hang the drum with nylon cord or to place it on foam. Other methods include mounting the brake drum on a snare drum stand. Either way, the brake drum is struck with hammers or sticks of various weight.
It is also commonly used in steelpan ensembles, where it is called "the iron."
鼓式制动器
鼓式制动器是由一组摩擦蹄片挤压一个叫做制动鼓的旋转鼓状部分实现摩擦动。
术语“鼓式制动器”意味着制动蹄片压紧在制动鼓的内表面。当制动蹄片压在制动的外表面时通常叫做一扣刹。制动鼓夹在两制动蹄片间,类似盘式制动器时,通常叫做捏鼓式制动器,这样的刹车很少见。还有一中类似形式的制动器,它采用一个活动的或者固定的带披在鼓的外表面,叫做带式制动器。
历史
在摩托车的后轮鼓式制动器川崎W800
现代汽车鼓式制动器由路易斯雷诺发明于1902年,尽管一年前迈巴赫已经使用了,一种有欠成熟的鼓式制动器。在早期的鼓式制动器里,那些蹄片由杆和电缆机械的组合在一起。从30年代中期开始,蹄片以一个小轮缸与活塞的油压运作,尽管车辆仍然以纯粹的机械系统持续了几十年,有些设计有两个轮缸。
在鼓式制动器里蹄片很容易磨损同时刹车还需要定时调节,知道20世纪50年代才引进鼓式制动器自动调节系统。在60和70年代前轮逐渐以盘式制动器取代了鼓式制动器,现在几乎所有的前轮都是盘式制动器,同时提供所有轮子的盘式制动器。然而,鼓式制动器仍然经常用于手刹,因为事实证明很难设计一个盘式制动器去保持一辆不在使用时的汽车。此外,它很容易适合一个盘式制动器里面的鼓内手刹,这样一个部件就既能实现刹车跟手刹。
早期型制动蹄含有石棉。当旧汽车制动系统工作时,必须注意不要吸入任何灰尘在制动器总成存在。美国联邦政府开始管制石棉生产,刹车制造商不得不转向非石棉垫。业主最初的抱怨更换刹车,但最终由于先进的技术得以补偿。大量的日常使用的旧车辆大部分无石棉衬片。许多其他国家也限制使用石棉刹车。早期的汽车制动系统,在经过了手拉式杠杆制动的时代后,在所有的4个轮子上设计一个鼓用来制动。它之所以被称作鼓式制动器是因为它的工作组件被装在一个随着车轮转动的鼓里。里面有一双制动蹄片,当刹车踏板踩下时,蹄片被迫使摩擦鼓以减慢轮子的速度。液压用于传递制动踏板的运动到制动蹄片的运动,而制动蹄片本身由类似做离合器的耐热摩擦材料制成。
这样设计的鼓式制动器被证明在大多数情况是可实现制动的,但是同时它也有一个重大缺陷。在高难度制动条件下,像在一个陡峭的山坡上高负荷,或者反复高速制动,鼓式制动器就会制动力就会衰退而失去效力。通常产生这种衰退的原因是制动过热。我们要知道鼓式制动器的原理是将车轮的动能转换为热能。出于这个原因,鼓式制动器只有在能吸收减慢汽车车轮速度产生的热量时才能实现制动。一旦制动器的制动元件本身以热饱和,他们就会失去停止车辆的能力,这可能会宁一些车辆的运营商感到不安。
自应用特点
鼓式制动有个天然的“自应用”特性。旋转的鼓可以拖动一片的一边或两边进入摩擦表面,引起刹车咬负荷加重,这样增加了压力把它们压在一起。这增加停止阻力,不需要司机额外的动作,但这却又使得司机调整刹车的灵敏性更加困难。这也使得刹车衰退更加敏感,由于制动摩擦的减少同时也降低了制动辅助系统的效果。
盘式制动器没有展现自应用效果,是因为液压压力作用在垂直制动盘的旋转方向,盘式制动器通常带有伺服援助(“制动助力器”)来减轻驾驶员对踏板的努力,但是一些装了盘式制动器的汽车(特别是三车)和小型盘式刹车的摩托车,等等,并不需要伺服援助系统。
注:在大多数设计中,“自应用”效果只发生在一只蹄片上。当一只蹄片压入制动鼓产生摩擦的一刻,作用效果却是发生在相对的另一只蹄片上。摩擦力试图远离旋转鼓。产生的效果在两只蹄片上不同,导致一只蹄片磨损的更快。虽然可能设计一个双蹄鼓式制动器,且两只蹄片都能自应用效果(具有独立的执行器和两端),但这在实践中是非常罕见的。
鼓式制动器设计
鼓式制动器通常称为领从蹄式尾从蹄式或双领蹄式。
后鼓式制动器通常设计为领从蹄式(非伺服系统),(对于双伺服系统)(主/副)制动蹄片通过一个单一的双液压缸和铰链连接在同一点而运动。这种设计中,一个制动蹄会一直产生自应用效果,不管车辆是在前进或后退。当制动器(手刹或者驻车制动)需要施加足够大的力量阻止汽车后退或者使汽车停在斜坡上时,这个特点对后制动器是非常有用的。提供制动器足够大的接触面积不是自应用效应能安全的停稳汽车的唯一的原因,还因为当汽车后退或者斜坡上时车辆的重量转移到后制动器上。用一个独立的液压缸在后的另一个优点是,相对的支撑点在一个双瓣形式的凸轮上,由驻车制动系统的运动带动其旋转。
前鼓式制动器在实践和设计中都是存在的,但是双领蹄式的设计更有效。本设计采用两个驱动汽缸排列,以便两个蹄片在车辆前进中都能利用其自应用特点。两制动蹄片相对,这在前进时给出了最大的制动可能,但当车辆后退时就不那么有效。前轮采用双领蹄式制动器配合后轮采用领从蹄式制动器,这样最佳的安排能在汽车前进是提供更大的制动力。这有助于防止后轮锁死,却仍然能在需要时提供后轮足够的制动力。
制动鼓本身通常由铸铁制成,虽然一些在使用车辆,特别是前轮应用铝鼓。铝合金比铸铁导热,提高散热性能更好,减少褪色。铝桶,也轻于铁桶,从而降低了簧下重量。因为铝比铁更容易磨损,铝鼓会经常对的内表面衬铁或钢鼓,保税或铆接到铝外壳。
优点
鼓式制动器用于多数重型卡车,部分中、轻型卡车,还有一些汽车、轻型摩托车和沙滩车。由于车辆的制动力大部分由前轮产生,因此鼓式刹车常用于后轮,使其产生的热量显著减少。鼓式制动器可以简单结合手停车制动。即使后轮主要使用的是蝶式刹车器,鼓式制动器也偶尔适用于制动和紧急停车。通常被安装在刹车盘内部或作为其一部分的小鼓,在这种情况下被称为班克西亚刹车。
在混合驱动汽车的应用中,能源再生马达发电机(见再生制动)使制动系统的磨损大大减少,因此,一些诸如GMC育空和丰田普瑞斯(除第三代)的混合制动汽车使用鼓式制动器。
蝶式刹车器依靠卡钳密封的柔韧性和轻微的跳动来释放衬垫,导致阻力、燃油的里程损失和阀瓣而得分。而复位弹簧鼓式制动器则有更积极的举动来进行恰当的调整,使其在释放时往往产生更小的阻力。
当限定了轮缸压力时,某些负荷更重的鼓式制动系统就会补偿负荷,而用盘式制动器则无这一特点。吉普科曼奇就是一辆这样的车。科曼奇可以根据负荷的大小来自动给后方鼓更大的压力,然而这对盘式制动器来说是不可能的。
基于摩擦接触面积在于刹车的周长这一事实,鼓式制动器可以提供比同等直径的盘式制动器更多的制动力。鼓式制动器刹车片增加的摩擦接触面积使其在相似规格和制动力的制动系统中比盘式刹车片在鼓上持续更长的时间。鼓式制动器保持热量且比盘式制动器复杂,但很多时候,由于后轮刹车产生的低热量,自适应性,大的摩擦接触面积,磨损寿命长等特点使其在后轴制动器的应用中显得更经济,更强大。
虽然在几乎所有的高性能的刹车装置中,对于后刹车装置,鼓式制动器是一个很好的选择,但是还是越来越多的人在汽车后轮上安装盘式刹车系统。这是由于前面通风盘式制动器引进后,盘式制动器的大量流行。前面通风盘式制动器比他们取代的鼓式制动器展现出更好的性能。前面通风盘式制动器与鼓式制动器性能的区别将会影响汽车买主对车的购买,同时也会影响后轮盘式制动器。另外,后轮盘式制动器通常与那些能够在马路上增加他们的知名度的赛车是相关的。后轮盘式制动器在大多数的装置中是不通风的,与鼓式制动器相比通常是没有性能优势的。即使后轮盘式制动器能够通风,后轮制动可能还是从这个通风设备中得不到任何益处,除非在高性能要求的赛车过程中。
缺点
鼓式制动器像大多数其他类型,旨在通过摩擦转化为热能的动能。[1]这种热是为了进一步转移到大气中,但也可以很容易地转移到制动系统的其他组件中去。
制动鼓要大,以应付所涉及的巨大力量,他们必须能够吸收和浪费的大量热量。传递到大气中的热量可以被纳入到制动鼓的散热片中。然而,过度的热会发生频繁反复制动,这会导致鼓变形,制动时振动。
过热的其它后果是导致刹车衰退。这是由于几个进程中的一个过于频繁运动积累导致的。
1.当制动鼓经过强制动时,制动鼓的直径由于热膨胀略微增加,这意味着制动蹄片必须运动更远同时刹车踏板的行程也增大。
2.如果过热摩擦材料的特性也会改变,造成摩擦不够。只通常是短暂的,当冷却后材料就会回复其效率,但如果材料表面过热到极点而变得光滑制动效率就会大大的降低。光滑的表面经过长久的使用会磨掉,但需要太多时间。
3.刹车鼓的过热会导致制动液的蒸发,从而降低了应用到制动蹄上的液压。因此给定一个一定的制动踏板的额定值。如果保养不善其结果会更加恶化。如果制动液过旧,吸收了水分,就会具有较低的沸点导致制动迟早会衰退。
制动衰退也不总是由于过热引起的。如果有水在制动鼓和摩擦表面之间,水起到润滑的作用也会降低制动效能。水会一直待在那里,知道被加热到蒸发,此时制动效能才会恢复。所有的摩擦制动系统都有一个最大能量转换理论率。一旦这比率达到,在制动踏板加更大的力也不会产生变化,而事实上,上述提到的不良影响可以大大的减少。不论其他机制,这才是刹车衰退的根本原因。
盘式制动器也不能幸免于这些过程中的任何一个,但是它们能比鼓式制动器更好的处理水跟热的影响。
鼓式制动器会产生多余的制动当制动鼓的表面有轻微的锈迹或者制动鼓潮湿和过冷,这时会给予摩擦衬片更大的摩擦。使得轮胎打滑,有时甚至在制动踏板松开时,轮胎还会打滑。这是一种相对的刹车衰退:当摩擦垫上升,刹车的自我协调性能迫使制动效能因素也上升。如果摩擦垫和自我放大足够高,制动会由于自我申请始终停留,即使外部应用程序力量被释放。
鼓式制动器的另一缺点是其复杂性。一个从事鼓式制动器工作的人,必须具备对鼓式制动器如何工作有一定的了解以确保鼓式制动器正确的组装。不称职的技工不适合从事鼓式制动器的工作。
再弧制
在1984年之前,为了与鼓式制动器内的弧度相匹配,对刹车片进行二次弯曲是很常见的。然而这种做法备受争议,因为这样就会使刹车的摩擦材料脱落从而减少刹车片的寿命,同时也会产生有危害的石棉灰。当今的设计理论认为刹车片应该使用在适当直径的鼓上从而能在必要的时候代替刹车鼓,而不应该对刹车片进行二次弯曲。
校准
早期的鼓式制动器(1995年)需要进行定期的调整来对鼓和摩擦板进行补偿。如果没有进行这样的定期补偿那么会造成制动器踏板行程变长(低踏板)。而低踏板有时是十分危险的,特别是在刹车踩到底而失灵的时候。制动系统只可能在汽车的反向运动停止时使用自我调节的机制,这是一种传统方的应用(现在大部分车辆都是用的是前轮盘式制动器)。只有当反向操作时,它才不太可能在制动器发热的时候被调整(当鼓扩大),这可能造成刹车刹车拖拉,加速摩擦板以及燃油的消耗。如果进行手刹的话,自我调节的制动系统还可能作为棘轮机制使用,这也只有在后轮鼓刹使用时才适合。如果车载制动杆超过了一定的行程,棘轮就会变成一个调节螺钉来使刹车板向鼓移动。存在着不同的自我调节制动系统,基本上可以划分为RAI和RAD.RAI系统比RAD系统更加有效,并且已经设立了避免刹车过热而能自动停止运行的机制。最著名的RAI系统是由LUCAS,BENDIX,BOSCH,AP研发。而RAD系统最著名的是为BENDIX,AP,VAG以及FORD公司研制的恢复系统。
手动调节旋钮通常是在鼓的底部并且是通过一个在轮子里面的小孔来行调节。这需要到车辆的底部并且要用平头螺丝刀来把轮子取下。最重要也是最繁琐的是为了不至于在进行急刹时车会倾斜,我们必须等量的调节每个轮子,特别是在装置处于前轮的时候。要么给每个相同的旋量,然后进行道路试验,或将每个车轮提升使离开地面,并用手工测量有多紧并且感觉刹车板是否在拖动。
在音乐中的应用
鼓式制动器能提供一种类似于乐砧的非尖锐的金属声音,它在当今音乐会和电影音乐中的应用效果很好。部分鼓式制动器能比其他的产生更多的共振,而制造最纯净声音的最好方法就是用尼龙绳来悬挂鼓或者把鼓放在泡沫上,还有的方法是把鼓式制动器安装在小军鼓的机座上。这两种方法中都要用不同重量的锤子或者木棒来敲打鼓式制动器。
鼓式制动器同样被广泛应用于被称为“钢铁”乐队的合奏表演中。