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II. Brake System Terms and Characteristics
A. Lever Stroke – Lever stroke can be divided into three categories:
Dead-stroke – The initial lever stroke when the primary seal pushes fluid into the reservoir instead of toward the caliper. Once the primary seal has stroked past the porting to the reservoir, all fluid is then pushed toward the caliper. This only occurs with open hydraulic master cylinders
Pad Gap stroke – Stroke required to move the caliper pads out to contact the disc. The amount of stroke required for this stage will depend of the amount of clearance between the pads and disc as well as the brake design. Pad gap stroke begins immediately with mechanical or closed hydraulic brake systems.
Modulation – The brake pads are now clamping the rotor and by stroking the lever further, additional brake power will be generated. See below for additional information about modulation.
二、刹车系统术语和特性：
1.刹把行程——刹把行程可以分为三类：
死区行程——主油封将刹车油压入油壶而非夹器时的那段初始刹把行程。当主油封越过油壶节流孔后，全部刹车油将被压入夹器。这只在开放式主油缸上出现。
刹车片空隙行程——将夹器上的刹车片移动到接触碟盘所需的行程。这一阶段所需的行程由刹车片与碟片间的空隙大小和刹车的设计所决定。机械式或者封闭式液压刹车系统直接进入刹车片空隙行程。
调制行程——刹车片现在已经夹住碟盘了，继续掣动刹把会产生更大的制动力。关于调制的更多信息见下文。
B. Retraction – The action of the brake pads being physically pulled away from the rotor. Typically hydraulic calipers use a rubber seal (square seal) that deforms when the brake is applied, and then returns to its normal shape and pulls the pads away from the rotor when pressure is released. A few hydraulic and almost all mechanical systems use springs to pull the pads away from the rotor.
2.回弹——刹车片被拉离碟盘的动作。液压夹器一般采用一个橡胶油封（方形油封），在刹车动作发生时此油封会变形，而当液压释放后回复原形并将刹车片拉离碟盘。部分液压碟刹和几乎所有的机械碟刹系统使用弹簧将刹车片拉离碟盘。
C. Burnish – Brake power is generated by the friction material on the pads embedding into the surface of the rotor, re-bonding to the friction material still on the pads and then breaking apart or shearing. In order for this bonding/shearing to occur, the friction material must first be displaced onto the surface of the rotor. This typically happens during the first 10 – 50 stops of a brake system and is referred to as “burnishing” the rotor and pads. When a rotor is cleaned, it will need to be re-burnished again to re-deposit the friction material onto the surface.
3.磨合——制动力是这样产生的：摩擦性材料嵌入碟盘表面，又重新粘结到仍留在刹车片上的摩擦性材料上，然后断开或剪裂。为了让这种粘结/剪裂的过程发生，摩擦性材料必须首先被转移到碟盘表面。典型情况下这会在刹车系统的前10到50次制动过程中发生并被称作碟盘和刹车片的“磨合”。当碟盘被清洗后，它将需要重新磨合以使摩擦性材料重新沉积到碟盘表面。
D. Coefficient of Friction (μ - pronounced “mew”) - A number measuring the “grip” of a material used in brake pads. Coefficient of friction can vary depending on the type of material used for the brake rotor. Typically service brakes are concerned with dynamic coefficient of friction, or the coefficient of friction measured while the vehicle is moving. The coefficient of friction may change as the brake system is required to perform through different applications. Below are a few of the main characteristics. Depending on the desired performance, the characteristics can be minimized or maximized.
Speed Sensitive – Coefficient of friction typically drops as the speed of the vehicle increases.
Pressure Sensitive - Coefficient of friction typically drops as more clamp force is generated.
Temperature Sensitive - Coefficient of friction typically drops as the temperature of the brake system increases.
4.摩擦因数（μ——音“谬”）——一个衡量刹车片中使用的材料的“抓力”的数字。摩擦因数会因刹车碟盘所用摩擦性材料的种类不同而不同。典型工作条件下的刹车与动摩擦因数，即当车辆行驶时测出的摩擦因数有关。当刹车系统需要在不同应用场合下工作时摩擦因数可能会改变。以下是一些主要特性。根据所追求的性能，这些特性可以被最小化或者最大化：
速度敏感性——摩擦因数一般会随车速提高而下降
压力敏感性——摩擦因数一般会随夹力增强而下降
温度敏感性——摩擦因数一般会随刹车系统的温度升高而下降
E. Modulation – Usually incorrectly referred to as a characteristic of a brake system. Modulation actually refers to the process of a rider accurately controlling the amount of brake power required without locking the wheel. Typically modulation is best with a brake system that has a “firm” or “hard” lever. The amount of lever stroke required to increase the amount of brake power generated is minimal. Soft levers require stroke to go towards caliper and hose expansion instead of brake power. This type of soft lever is inherently more difficult to control. Levers can feel soft due to mechanical/hydraulic advantage or hose and caliper stiffness properties.
5.调制——这通常被错误地称作刹车系统的一项特性。调制实际上是指骑手精确地控制所需的制动力而避免将车轮抱死的过程。通常当刹车系统的刹把很“硬”的时候调制性能是最好的。增加制动力所需的刹把行程是最小的。软的刹把会把行程消耗在夹器和油管的扩张而非产生制动力上。这种软的刹把天生更难于控制。刹把会因为机械/液压的优点或者油管和夹器的硬度特性而使人觉得软。
（这段是Hayes在为自己生硬的刹车手感辩解，实际上显然不是那么回事，所以逻辑有些混乱）
F. Fade – Fade is generically defined as a decrease or loss of brake power and typically occurs in two ways:
Friction Material Fade – When pads reach high temperatures they can sometime “outgas” chemicals that redeposit themselves on the surface of the brake pad. This decreases the coefficient of friction and results in a decrease of brake power. The lever will remain firm however the brake will not generate the normal amount of power. This is also described as when pads “glaze” over.
Brake Fluid Fade – This type of fade occurs when the brake fluid inside a hydraulic caliper boils. An important characteristic of brake fluid is that it is incompressible. When a brake fluid boils, gas is formed within the system that is compressible and any lever stroke available goes toward compressing the gas instead of generating brake power. Interestingly enough, when a fluid is under pressure, it is very difficult for the fluid to boil. If a brake system is under pressure, the fluid temperature can rise above the boiling temperature without the fluid actually boiling. Once the pressure is released, the fluid will instantly boil and fade will occur.
6.衰减——衰减一般被定义为制动力的下降或丧失，通常会以两种方式发生：
摩擦性材料衰减——当刹车片达到高温时有时会“蒸腾”出一些化合物并再次沉积到刹车片的表面。这会使摩擦因数下降并导致制动力的下降。刹把仍会很硬，然而刹车不会产生正常的制动力。这也被叫做刹车片的“上光”。
刹车油衰减——这类衰减发生在液压夹器中的刹车油沸腾时。刹车油的一个重要特性是它不可压缩。当刹车油沸腾时，系统内会形成可压缩的气体，并且任何可能的刹把行程都消耗在压缩这些气体而非产生制动力上。有趣的是，当液体受到压迫时，它将很难沸腾。当刹车系统被压下时，刹车油的温度可以超过沸点而并不真正沸腾。一旦压力被释放，刹车油会立即沸腾而衰减将会发生。
G. Thermal Characteristics – Designing brake systems to handle high temperatures is just as important as designing them to be powerful. Below are three key elements for a system to properly handle high temperatures
Thermal Mass – A brake system must be sized appropriately to not only be able to provide enough power for a vehicle, but have enough material mass to properly handle the temperatures during braking applications. Removing material from a system to reduce size and weight also removes material that would otherwise have helped a system absorb and diffuse heat generated by braking.
Cooling Air – Keeping a brake system in the flow of air for cooling can also help reduce operating temperatures. Many calipers have open bridges that allow for air to flow through the caliper and remove heat from the braking surface.
Surface Area – The more surface area available on a brake system, the better heat dissipation will be via convection. Cooling fins are often used in systems that are attempting to reduce operating temperatures because they greatly increase the surface area.
Material Selection – Material selection is important in trying to control where the heat goes once generated. Insulators can be used to prevent heat from being conducted to the brake fluid. In the same manor, good heat conductors can be utilized to draw heat away from critical components.
7.热学特性——将刹车系统设计得可以承受高温与将其设计得强有力同样重要。下面是使刹车系统能够承受高温的三个关键因素：
吸热质量——必须恰当地选取刹车系统的尺寸以使其不仅可以为车辆产生足够的制动力，同时也具有足够的材料质量来承受刹车过程中产生的高温。从一个系统中削减材料以减小尺寸减轻重量的同时也减少了本来可以帮助系统吸收和传导刹车产生的热量的材料。
冷却风——将刹车系统置于流动的空气中以降温也可以帮助降低工作温度。许多夹器具有开放式的桥可以允许空气流过夹器并从刹车表面带走热量。
表面积——刹车系统的表面积越大，通过对流散热的效果越好。散热鳍片常被用在希望降低工作温度的系统上，因为它们能显著增加表面积。
材料选择——材料的选择在试图控制产生的热量流向何处时很重要。可以使用绝热材料来阻止热量传递给刹车油。同样的，可以利用导热材料将热量从关键部位吸走。
H. Bleeding Brakes – Bleeding brakes is the process of “bleeding” the air out of a hydraulic system and filling it with brake fluid. The Hayes Brake Bleed Process forces fluid into the caliper up through the master cylinder allowing the air within the system to flow to the top and out of the system.
8.刹车的注油——刹车的注油是将刹车油注入液压系统以将其中的空气排出的过程。Hayes刹车注油操作是迫使刹车油从上方的主油缸注入夹器以使系统内的空气流到顶部并排出系统。 |
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发表于 2008-6-7 13:36
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