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How to bleed break ?what's break system?
08-12-2019, 02:06 AM
Post: #1
How to bleed break ?what's break system?
We all know that pushing down on the brake pedal slows a car to a stop. But how does this happen? How does your car transmit the force from your leg to its wheels? How does it multiply the force so that it is enough to stop something as big as a car?

When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot. It does this in two ways:
  • Mechanical advantage (leverage)
  • Hydraulic force multiplication
[Image: main-qimg-327b8e723146b11f0fcd81c962f4a0b6]
The layout of a typical brake system.
The brakes transmit the force to the tires using friction, and the tires transmit that force to the road using friction also. Before we begin our discussion on the components of the brake system, we'll cover these three principles:
  • Leverage
  • Hydraulics
  • Friction
Leverage and Hydraulics

In the fi­gure below, a force F is being applied to the left end of the lever. The left end of the lever is twice as long (2X) as the right end (X). Therefore, on the right end of the lever a force of 2F is available, but it acts through half of the distance (Y) that the left end moves (2Y). Changing the relative lengths of the left and right ends of the lever changes the multipliers.
[Image: main-qimg-9cfcb50a34d723686ef20c0b3722d518]
The pedal is designed in such a way that it can multiply the force from your leg several times before any force is even transmitted to the brake fluid.
The basic idea behind any hydraulic system is very simple: Force applied at one point is transmitted to another point using an incompressible fluid, almost always an oil of some sort. Most brake systems also multiply the force in the process. Here you can see the simplest possible hydraulic system:
[Image: main-qimg-6d0c1e91193f0833741b2f58a4801519]


Simple hydraulic system
In the figure above, two pistons (shown in red) are fit into two glass cylinders filled with oil (shown in light blue) and connected to one another with an oil-filled pipe. If you apply a downward force to one piston (the left one, in this drawing), then the force is transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very good -- almost all of the applied force appears at the second piston. The great thing about hydraulic systems is that the pipe connecting the two cylinders can be any length and shape, allowing it to snake through all sorts of things separating the two pistons. The pipe can also fork, so that one master cylinder can drive more than one slave cylinder if desired, as shown in here:


[Image: main-qimg-eeac081dde8f2dc57c2ecf7a48a9d08f]

The other neat thing about a hydraulic system is that it makes force multiplication (or division) fairly easy. you know that trading force for distance is very common in mechanical systems. In a hydraulic system, all you have to do is change the size of one piston and cylinder relative to the other, as shown here:


[Image: main-qimg-41ba33a51f2bb031e39a3ded497d781f]


Hydraulic multiplication
To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches (5.08 cm) in diameter (1-inch / 2.54 cm radius), while the piston on the right is 6 inches (15.24 cm) in diameter (3-inch / 7.62 cm radius). The area of the two pistons is Pi * r2. The area of the left piston is therefore 3.14, while the area of the piston on the right is 28.26. The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will come out nine times greater on the right-hand piston. So, if you apply a 100-pound downward force to the left piston, a 900-pound upward force will appear on the right. The only catch is that you will have to depress the left piston 9 inches (22.86 cm) to raise the right piston 1 inch (2.54 cm).

Friction


[Image: main-qimg-1d9f3ab46b9edcef983ae431d417a8ac]
Friction force versus weightFriction is a measure of how hard it is to slide one object over another. Take a look at the figure below. Both of the blocks are made from the same material, but one is heavier. I think we all know which one will be harder for the bulldozer to push.

To understand why this is, let's take a close look at one of the blocks and the table:


[Image: main-qimg-3cb3e145c497ea541ee948fc4dfe97a4]
Because friction exists at the microscopic level, the amount of force it takes to move a given block is proportional to that block's weight.

Even though the blocks look smooth to the naked eye, they are actually quite rough at the microscopic level. When you set the block down on the table, the little peaks and valleys get squished together, and some of them may actually weld together. The weight of the heavier block causes it to squish together more, so it is even harder to slide.

Different materials have different microscopic structures; for instance, it is harder to slide rubber against rubber than it is to slide steel against steel. The type of material determines the coefficient of friction, the ratio of the force required to slide the block to the block's weight. If the coefficient were 1.0 in our example, then it would take 100 pounds of force to slide the 100-pound (45 kg) block, or 400 pounds (180 kg) of force to slide the 400-pound block. If the coefficient were 0.1, then it would take 10 pounds of force to slide to the 100-pound block or 40 pounds of force to slide the 400-pound block.

So the amount of force it takes to move a given block is proportional to that block's weight. The more weight, the more force required. This concept applies for devices like brakes and clutches, where a pad is pressed against a spinning disc. The more force that presses on the pad, the greater the stopping force.

Coefficients

An interesting thing about friction is that it usually takes more force to break an object loose than to keep it sliding. There is a coefficient of static friction, where the two surfaces in contact are not sliding relative to each other. If the two surfaces are sliding relative to each other, the amount of force is determined by the coefficient of dynamic friction, which is usually less than the coefficient of static friction.

For a car tire, the coefficient of dynamic friction is much less than the coefficient of static friction. The car tire provides the greatest traction when the contact patch is not sliding relative to the road. When it is sliding (like during a skid or a burnout), traction is greatly reduced.

A Simple Brake System
Before we get into all the parts of an actual car brake system, let's look at a simplified system:


[Image: main-qimg-e878cd9f10091afe12e14d44a69a6bb5]You can also see that the diameter of the brake cylinder is three times the diameter of the pedal cylinder. This further multiplies the force by nine. All together, this system increases the force of your foot by a factor of 36. If you put 10 pounds of force on the pedal, 360 pounds (162 kg) will be generated at the wheel squeezing the brake pads.
There are a couple of problems with this simple system. What if we have a leak? If it is a slow leak, eventually there will not be enough fluid left to fill the brake cylinder, and the brakes will not function. If it is a major leak, then the first time you apply the brakes all of the fluid will squirt out the leak and you will have complete brake failure.
How to Maintenance Braking systems
  1. Brakes need to be Bled
All hydraulic brakes are bled or purged for one of two reasons:
  • To remove air bubbles from the brake system, or
  • To replace the brake fluid with new
Removing Air
For hydraulic systems to work efficiently they must rely on an incompressible fluid as a means of transferring forces.
In hydraulic braking systems the input forces you create by operating the brake lever travel via the brake fluid to operate the calliper pistons, which in turn, move the brake pads to contact the rotor. This is only possible because the brake fluid is incompressible.
Think of brake fluid then as a means of communication. The brake fluid transmits the message given at the master cylinder (lever) to the slave cylinder (calliper) with minimal loss in quality.
Air in the system causes a breakdown in this communication. Input forces created by operating the brake lever can no longer be transmitted effectively as these forces are wasted as the air inside the system is compressed.
Replacing the Brake Fluid
Part of the general maintenance and upkeep of your hydraulic brake is to periodically change the brake fluid. Over time your brake fluid will become old and discoloured as it takes on contaminates from the environment. Dirt, air and water can and will find their way in eventually.
Replacing the brake fluid occasionally will keep these to a minimum and extend the life of your brake and keep it performing like new.
  1. Best Braking systems Maintenance Tool
Autel Maxicheck pro

used the Autel several times since receiving it, it works as advertised. I have used it once or twice in bleeding ABS brakes. It has the step by step procedure, it's user-friendly. You won't be disappointed when you order it.


[Image: main-qimg-f2c0e92a6edd834d6ae20652c32b3691]
Autel ScannerMaxicheck Pro Best For Break System

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