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At the most basic level, a brake is an energy conversion device. normally people will equate temperature with travel rapidly. While this is broadly truthful, it is more accurate to associate heating system with energy. Today ’ south cars are filled with energy conversion devices .
virtually all of the things a car does results from the chemical department of energy of the fuel or the battery being converted into some utilitarian and desirable officiate for the driver and passenger. The locomotive, brakes, fastball and radio are a few examples. ad The job of the brakes is to convert the energy of a moving vehicle into estrus resulting in the vehicle reducing speed .
Stopping with Horsepower
One of the basic physical laws of the universe is that all energy is conserved. In bare terms, energy can ’ metric ton fly. It can change forms, possibly multiple times, but it is constantly somewhere. The engine, through the combustion process, converts the chemical energy of the fuel into heat that moved pistons to accelerate a vehicle to some rush or altitude. We rely on the brakes to stop us, now .
Consider a typical midsize SUV loaded to its gross vehicle weight of approximately 6,400 lbs. While traveling at 60 miles per hour, it has a “ kinetic ” energy equal to 988 british Thermal Units or BTUs. This is calculated according to the equation for energy of motion. ad Energy (Kinetic) = 1/2 x Mass x (Velocity)2
When this vehicle is stopped, the kinetic energy is transferred into the brakes resulting in an increase of the rotor temperature. Time is besides a big divisor. If that SUV is stopped at its maximum capability of approximately 140 feet, then this energy must be absorbed in about three seconds .
The come of energy transferred in a given period of time is exponent. The faster the energy must be transferred or absorbed requires extra power. In this example, the brakes must absorb about 465 HP. ad Thermal Management
Recall the energy and therefore the might increase by the square2 of the speed. As a result, the brake system design engineer must design the arrangement to absorb the vehicle ’ sulfur department of energy and power from the maximal amphetamine that the vehicle is able of .
Those brakes for that lapp SUV at its maximum speed of 110 miles per hour must absorb more than 800 HP or approximately three times what the engine is capable of producing .
Consider what these numbers become for the 747 elephantine jet touching down on the runway and coming to a catch. same equations, precisely a lot more zeros on the end. ad A related condition the brake arrangement mastermind must consider regarding thermal operation is the reprise brake or performance braking condition. This is actually good a special event of the kinetic department of energy situation. In general, the mastermind must design his brakes around a specific performance profile. They all by and large consist of repeated acceleration and brake over multiple stops ampere cursorily as the vehicle will accelerate and brake. Sometime this is referred to as a “ fade examination. ”
Mathematically, the fade is an annex of the energizing department of energy equation. The energy of each barricade is defined by the equality Energy ( Kinetic ) = 1/2 ten Mass x ( Velocity ) 2 and added improving. The brake system engineer can mathematically calculate the energy his brakes must absorb and dissipate. Using this information along with assumptions and calculations about how cursorily the hot rotor can transfer its estrus energy to the surrounding air, he can estimate the point temperature of his components .
ultimately, in the huge majority of cases he must prove with a real test and real parts how hot the parts get and that nothing bad happens when the parts get that hot.
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ad Single Stops
The single stop consonant from utmost vehicle travel rapidly is a relatively simple and uncoiled forward test. On a high-speed test track, the vehicle is accelerated to its maximal amphetamine and braked in one continuous event to a stop .
The manufacturer will define its expectations for the rate of deceleration. This is by and large between 0.50g of deceleration up to the maximum deceleration the vehicle is capable of. This is an important factor as this determines the sum of time associated with the energy conversion. The energy of a Corvette at 140 miles per hour is constant. The power necessity to stop it at maximum deceleration is approximately double than if allowed to stop at 0.50g. ad The key goal of the test is to ensure that the bracken arrangement can operate in this environment and that the heat generated does not damage the components to an unacceptable tied. As a result, the vehicle is heavily instrumented with thermocouples ( a simple device that measures temperature in a particular smudge ) and reports it to a data skill system .
It is important to be able to measure temperature in identical humble time intervals and in many places. The temperature can vary widely within a small distance. The extremum temperature measured at the components and how farseeing it stays above a sealed temperature are compared to the particular material specifications for submission .
typically, things like melting of speed detector wires, caliper dust boots and steering tie-rod boots are evaluated. In addition to visually obvious failures, things like the thermal limits of the electronics in the speed detector are besides validated. ad Electronic and rubber components are by and large rated in the total of time they can be exposed to a particular temperature. The components can be permanently damaged or become not functional at temperatures well below their liquescent or ignition temperature .
Why Rotor Design Matters
The “ Single Stop from Maximum Speed ” test entirely takes a few seconds to complete. As a resultant role, the temperature in the components, particularly the rotor, rises very promptly. Fast temperature increases ( or decreases ) result in high thermal tension. Simply stated, these are the forces that result from little portions of the character changing temperature at different rates .
As each part is trying to grow, it wants to tear itself away from adjacent parts. As a result, it is critical to test to evaluate the structural integrity of the rotor in these types of situations. The rotor must be inspected for cracking or “ heat check. ” ad The thermal mass of the rotor will by and large govern the flower temperature of the rotor. thermal mass is defined as the weight unit of the plates and fins. The hat and wheel mounting confront are not considered part of the thermal mass of the rotor. thermal multitude will broadly be approximately 85 percentage of the sum slant of the rotor. The design of the rotor traverse sections is a critical invention manipulate .
Subtle details of louver and plate geometry can significantly affect the structural integrity of the rotor. As a cosmopolitan principle, slurred sections adjacent to thin sections and sharp corners should be avoided. Two rotors of equal thermal mass may reach virtually the lapp extremum temperature, but have identical different structural integrity characteristics .
The material grade and consort properties of the iron are besides critical and can vary widely in the market .
Technicians should inspect successor rotors carefully and compare them in detail to the OE rotor to ensure that thermal integrity can be maintained. Aftermarket rotors that are significantly lighter or have well different fin configurations should be viewed conservatively. ad
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In the individual hold on position, the rotor heats up very quickly, but is then given the opportunity to cool for exsert periods of time. As a consequence, the energy that is temporarily stored in the rotor is predominantly transferred to the ambient tune. To satisfy the rule of energy conservation, the air temperature will rise until the two are in balance .
Air and Heat
Due to the about infinite volume of air travel, in virtual terms, the air absorbs the heat until the brake components returns ambient temperature .
very short of the energy transfers to the surrounding components in the unmarried diaphragm encase. As a solution fluid seethe is by and large not experienced. The site changes dramatically when the arrangement engineer must confirm the brake system can handle the energy concentration required to bring the fomite down a farseeing grad .