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How to understanding Friction Coefficient and High-Temperature Resistance ?
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By 袁春凤 (Tiffany)
The phenomenon that two objects move relative to each other to produce motion resistance between their contact surfaces is called friction, which is called friction. The existence of friction not only increases the power consumption, but also causes the wear of parts' contact surfaces. Therefore, lubricating oil is usually used between the relative moving surfaces of automobile parts to reduce friction. Failure of automotive parts 75% is caused by friction.
Friction can be divided into dry friction, liquid friction, boundary friction and mixed friction according to the lubrication state of the parts.
(1) dry friction
The friction between the frictional surfaces without any lubricating medium is called dry friction.
When the parts are in the state of dry friction, the surface of the parts is abraded sharply, so the surface of the moving parts of the automobile should avoid the occurrence of dry friction as far as possible.
Dry friction and boundary friction are the main friction between the upper part of cylinder wall and piston ring. Dry friction will occur when the journal and bearing are subjected to impact load in the working process.
(2) liquid friction
Two the friction of the friction surface when the lubricant is completely separated is called liquid friction.
In liquid friction, the two friction surfaces are completely separated by a layer of lubricating oil film with a thickness of 1.5-2.0um, which avoids direct contact between the working surfaces of the two parts. Friction only occurs between the lubricating fluid molecules, so the friction resistance is very small, and the wear of the parts is very slight.
Most of the relative motion parts of a car are carried out under the condition of liquid friction (for example, crankshaft and bearing).
(3) boundary friction
Two friction surface separated by a very thin boundary film is called boundary friction.
The oil film thickness is usually below 0.1um. Friction only occurs between the outer molecules of the boundary film, reducing the friction and wear of the parts. But its thickness is very small, and it is easy to be destroyed by impact and high temperature, so it is not as reliable as liquid friction.
For example: between cylinder wall and piston ring; if the work crankshaft and journal between the insufficient supply of lubricant, easy to produce boundary friction.
(4) Mixed friction
The friction between two friction surfaces in the presence of dry friction, liquid friction and boundary friction is called mixed friction.
In the actual working state, the parts usually work under the mixed friction state, and the friction state varies with the working conditions.
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By Counterman
f you read automotive articles on a regular basis, you’ve no doubt read about the scientific side of brakes many times. They convert kinetic energy, which is the energy of motion, into heat energy through friction between the brake linings and the drum or rotor. Because of this, brakes get hot…real hot…and dissipating the heat is one of the most critical factors affecting brake operation.
So, would you believe that shock absorbers work off the same scientific basis of converting kinetic energy into heat energy? It’s true, and here’s how it works.
Kinetic energy is the energy of motion. The springs on a vehicle support the weight of it and allow the suspension to move. But what would happen if there were no shock absorbers? Every time you hit a bump, the springs would compress then expand, and do this over and over again until they finally settled down.
If you’ve never experienced the sensation, which is something like rocking on a boat, you’ve likely seen it on a car going down the road. The front or rear goes up and down, up and down, literally “bouncing” down the road. It happens, in this case, not due to the lack of shocks, but due to the fact that they are simply worn out, so for all practical purposes, they may as well not exist.
link hidden, please login to view The springs absorb the kinetic energy from hitting a bump, but since springs are considered elastic objects, the energy is turned into potential energy. And, in the case of a spring, or any elastic object, the potential energy is then released, and the energy output equals the energy input. The spring will return to its original shape. At that point, the momentum of the car body creates kinetic energy, which in turn acts on the spring in the opposite direction. As you can see, this is a vicious circle, and we need shock absorbers to control it.
The job of a shock absorber is therefore to control the kinetic and potential energy of a spring by dampening its movement. Shock absorbers are filled with hydraulic oil, separated between two different chambers. Between the two chambers is a piston and valve assembly. (See Figure 1). The piston is connected to a piston rod which moves in and out of the shock as the suspension moves.
Compression is when the piston rod is forced into the shock; rebound is when the piston rod is pulled back out. The key lies in the valving, which restricts the flow of oil between the two chambers. Forcing the oil through these valves creates friction, which in turn creates heat. Yes, shocks do get hot, and now the shock has turned kinetic energy into heat energy.
Changing the size of these valves changes the amount of force it takes for compression or rebound, which ultimately changes the ride characteristics of the vehicle. This is one of the main reasons there’s a difference in feel between a sports car and a luxury car.
The more restrictive the compression and rebound, the less the suspension spring will move, which provides improved handling and stability characteristics, such as those desired on a sports car, but this also results in a firmer ride. Less restrictive compression and rebound allows greater spring movement and a softer ride, but not as good handling characteristics. There’s always a tradeoff.
The comparison between the compression and rebound forces in a shock absorber is the shock ratio. Many standard shocks have a 50/50 ratio, meaning the compression and rebound forces are equal. Unequal forces one way or the other can have a drastic effect on handling, and one of the best examples to demonstrate this is with some old school drag racing tech. In drag racing, it’s important to shift the weight to the rear of the vehicle to increase traction while launching. One of the ways to attain this is by using 90/10 shock absorbers on the front.
What this means is that of the total compression and rebound forces, 90% of the force is required to compress the shock, but only 10% of the force is required to extend the shock. When launching, the front of the car wants to lift as weight shifts to the rear. With a 90/10 shock, the front will unload easily and allow the weight to shift to the rear. Then, since it takes a much greater force to compress the shock, instead of the car coming right back down and bouncing in the front after hitting the track, the shocks will remain extended with the weight shifted rearward, and slowly settle as the car goes down the track.
It often takes a while and a few different adjustments with shock ratio, both front and rear, to get a drag car suspension properly “tuned” in. By the same token, stock vehicles, either performance or luxury, are engineered to find the best of both worlds in handling versus comfort. So, the next time you talk about shocks to your customer, make it fun and talk a little science.
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By Counterman
Your customers may be using air tools in a variety of circumstances for an even wider variety of jobs. Here’s how to help them understand why they need to buy the right fitting for the application.
link hidden, please login to view There are multiple different sizes and styles, and what one shop uses may not be the same as another. The size and style affect the volume of air they can deliver, a critical point because air tools require a specific pressure and volume for proper operation, and restrictive fittings can limit their performance. Here’s a look at the most common sizes and styles found in most automotive shops, and how you can identify them.
For more ToolIntel training, visit
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By Counterman
Customers are the core of our business, and communicating with them effectively is critical to our success.
While each customer (and transaction) presents a unique set of opportunities and challenges, individual customers often can be classified into one of several broad types. Obviously, “profiling” or “stereotyping” an individual customer when you first meet them shortchanges everyone involved, but understanding the kinds of customers that make up your clientele gives us an idea of how to deal with each customer type once we actually get to know them.
Depending on which marketing firm or consulting group you choose to believe, there are between four and 10 basic customer types. No matter how many categories you prefer to use, it’s the psychology behind these differences that holds the key to connecting with as many of them as possible. You only get one chance to make a first impression, so a “new” customer is the one with the greatest potential. Even if a new customer has familiarity with your business, they may not have experienced it directly. Your advertising, reputation or a personal referral (presumably all positive) have encouraged them to visit your location for their needs. Now is the time to show them what they’ve been missing!
Consultative selling is a technique that focuses on building a relationship and determining what your products can do for your customer. By concentrating on the customer’s needs, you can further qualify them as one of the many customer types, and then offer the most appropriate solution for their individual situation. The immediate need might be for a battery or brake pads, but discovering the reason behind the intended purchase can open up the conversation in ways that make it easier for you to sell the most appropriate product for your customer. It also can minimize disappointment and build trust, by ensuring that the products and services are truly useful and meet the customer’s expectations.
Once the new customer becomes an “active” customer, you haven’t entirely sealed the deal. There’s a huge difference between gaining a customer and keeping a customer. An active customer isn’t necessarily a loyal customer, so using what you’ve already learned about their needs makes it a little easier to meet those needs each time. Neglecting or disappointing your new and active customers leaves the door open for them to become someone else’s new and active customers. Building upon each successful transaction (and learning from any less-than-successful ones) helps you turn these types of customers into the most desirable customer type: the loyal customer.
Loyal customers are at the heart of the 80/20 rule, which states that 80% of your business comes from roughly 20% of your customer base. New and active customers may come and go (sometimes through no fault of your own), but that solid core of loyal customers is what really keeps your lights turned on and your employees paid every week. As 80% of your business, these are the customers you really need to know and understand. Delivering best-in-class service and focusing on being an integral part of their success will help ensure that these customers remain loyal and even advocate for your business!
With proper care and feeding, we can reap the benefits of that natural progression from “new” to “active” to “loyal,” but along the way we may discover that we have some lapsed or unhappy customers. Timing is critical when addressing these “at-risk” customer types. An unhappy customer (even a loyal one) is likely to become a lapsed customer if we continue to fail them, especially if our competition surpasses us in service, pricing or any other metric. We need to identify and correct the core issues behind their dissatisfaction before that customer has the chance to cozy up to another vendor.
The at-risk customer tends to taper off slowly, so if you aren’t paying attention, you may not even realize it until it’s too late! If a valued customer does become lapsed, you should still attempt to salvage that relationship by determining what caused the lapse in the first place. The feedback also may prove to be useful in the future when dealing with other customers, who might have similar needs and objections.
No matter if it’s a retail or a commercial account, knowing the most effective ways to connect with each customer type helps create repeat business and build your brand.
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By Counterman
Fuel injection is as old as the internal combustion engine itself. However, many of the early systems proved to be somewhat troublesome and quirky. The carburetor, by comparison, was simple and dependable, and therefore the fuel system of choice for the majority of mass-produced vehicles through most of the 20th century.
For those who entered the automotive industry during the reign of the carburetor, fuel injection was so uncommon that as it began to make a comeback during the 1980s, it was largely misunderstood and tagged with the less-than-endearing term of “fuel infection.”
With the help of electronics and computer control, fuel-injection systems began to improve quickly and followed a course of evolution that introduced many different system designs. Suddenly, we were bombarded with unusual terms and acronyms like Jetronic, Motronic, TBI, MFI, GDI, TDI and many more. While it might have seemed confusing at first with so many different coined terms from so many different manufacturers, ultimately there are only two basic types of fuel injection.
Why Fuel Injection?
For efficient combustion to occur, fuel must be atomized first (broken up into the smallest particles possible) so it can mix with the air and vaporize. Only then will it properly burn inside the cylinder.
The job of a carburetor was simply to allow the air flowing through it to atomize the fuel as it draws it out of the various circuits. Carburetors work very well at doing this, but they also are inefficient in many ways, preventing them from remotely coming close to the efficiency required for the tightening emission regulations of the time.
This is where fuel injection proved itself a superior method of fuel metering. Fuel injection atomizes the fuel as it exits the tip of the injector. But even more importantly, with the combined advance in electronics and computer controls, it also provides precise control of the amount of fuel – a critical aspect for fuel economy and emission control.
Indirect Fuel Injection
Indirect means the fuel is injected and atomized before it enters the combustion chamber. Throttle-body injection (TBI), sometimes referred to as single-point injection, is a type of indirect injection in which the injector is located in a throttle body before the intake manifold. The throttle body looks similar to a carburetor and uses many similar components such as the intake manifold and air cleaner.
This was done by design, as it was the most efficient and quickest way for auto manufacturers to make the change to fuel injection, while utilizing many of the same components. Port, or multi-point, injection injects fuel into the intake runner just before the intake valve for each cylinder. Still a form of indirect injection because it occurs before it enters the combustion chamber, the advantage is the ability to precisely control the fuel delivery and balance the air flow into each cylinder, leading to increased power output and improved fuel economy.
Whether an engine is carbureted or fuel-injected, atomization of the fuel is critical for combustion. Many variables affect atomization, and even though a fuel injector initiates the process, the airflow and other objects around it will affect how well the atomized fuel mixes with the air and vaporizes. The location of the injector as well as the design of surrounding components are critical aspects of engine design.
TBI is at a disadvantage because the airflow is interrupted by the injector – another reason that port injection has the advantage and has made TBI obsolete on newer vehicles.
Diesel engines are fuel-injected because diesel fuel doesn’t atomize and evaporate like gasoline. It must be injected into an air stream at high pressure to atomize, and the turbulence of the air is an important factor in causing the air and fuel to mix.
Early on, due to the difficulties of creating an efficient direct-injection system, many diesel engines utilized a pre-combustion chamber that created the necessary turbulence for proper fuel atomization. The fuel was injected into this pre-combustion chamber, making these indirect fuel-injection systems as well.
Direct Fuel Injection
Direct means the fuel is injected directly into the combustion chamber. The challenge with this type of injection is the pressure inside the combustion chamber is much higher than that of the pressure in the intake manifold of an indirect-injection system.
For the fuel to be pushed out of the injector and atomized, it must overcome the high pressure in the cylinder. Indirect systems have a single fuel pump in the tank that provides adequate pressure for the system to operate, usually 40 to 65 pounds per square inch (psi). Direct systems utilize a similar pump to supply fuel to the rail but require an extra mechanically driven high-pressure pump that allows them to overcome cylinder pressure. These systems usually operate at 2,000 psi or higher.
Direct-injection systems can be identified easily by the location of the injectors going directly into the cylinder head as well as the additional lines and mechanical pump, usually visible above the valve cover.
The primary advantage of direct injection is that there is less time for the air/fuel mixture to heat up since the fuel isn’t injected in the cylinder until immediately before combustion. This reduces the chance of detonation, or the fuel igniting from the heat and pressure in the cylinder. This allows a direct-injected engine to have higher compression, which itself lends to higher performance.
Another advantage is reduced emissions and fuel consumption. With indirect injection, fuel can accumulate on the intake manifold or intake ports, whereas with direct injection, the entire amount of fuel sprayed from the injector is the exact amount that will be burned, ultimately leading to more accurate control over the combustion process.
The overall performance and efficiency of direct injection can’t be matched. However, there are still some disadvantages to it when compared with indirect injection. One of the most well-publicized is carbon buildup on the back of the intake valves. Fuel is a great cleaner, and the fuel spray from a port-injected engine keeps the back of the valves clean. Without it, excessive carbon buildup occurs, leading to interrupted airflow into the engine, reduced performance and an expensive repair.
While not an issue for typical everyday driving, indirect injection is limited at high engine rpm because there simply isn’t enough time for the injector to release the fuel and for it to properly atomize. Since port-injected engines spray fuel before or as the intake valve is opening and complete vaporization occurs and the air is pulled into the cylinder, there’s no rpm limit with indirect injection.
Low-speed pre-ignition (LSPI) is a common term you may have heard, and it’s a problem that exposes another chink in the armor of direct injection. The piston and combustion-chamber design of a direct-injected engine is very specific to create the proper air turbulence to completely vaporize the fuel for combustion. At low rpm, the piston is not able to create the proper turbulence, leaving unvaporized fuel pockets that combine with contaminants from oil vapor and carbon buildup, leading to pre-ignition.
While this problem specifically occurs on direct-injected engines, it can worsen with some engine oils depending on the additives they contain. This is why new oils are advertised to prevent LSPI.
As engine technology advanced, diesel engines saw changes in piston and combustion-chamber design that allowed them to make the switch to direct injection and realize the same performance benefits.
So, your two basic types of fuel injection are indirect and direct. There are advantages and disadvantages to both. What’s next? The simplest solution in the book: dual injection. Now manufacturers are building cars with both. Computer control utilizes both systems to eliminate the weaknesses and exploit the strong points of each type of system. It’s the best of both worlds. Wasn’t that easy?
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