Power valve of carburetor

For open throttle operation a richer mixture will produce more power, prevent pre-ignition detonation, and keep the engine cooler. This is usually addressed with a spring-loaded "power valve", which is held shut by engine vacuum. As the throttle opens up, the vacuum decreases and the spring opens the valve to let more fuel into the main circuit. On two stroke engines the operation of the power valve is the reverse of normal — it is normally "on" and at a set rpm it is turned "off". It is activated at high rpm to extend the engine's rev range, capitalizing on a two-stroke's tendency to rev higher momentarily when the mixture is lean.

Alternative to employing a power valve, the carburetor may utilize a metering rod or step-up rod system to enrich the fuel mixture under high-demand conditions. Such systems were originated by Carter Carburetor in the 1950s for the primary two venturis of their four barrel carburetors, and step-up rods were widely used on most 1-, 2-, and 4-barrel Carter carburetors through the end of production in the 1980s. The step-up rods are tapered at the bottom end, which extends into the main metering jets. The tops of the rods are connected to a vacuum piston and/or a mechanical linkage which lifts the rods out of the main jets when the throttle is opened (mechanical linkage) and/or when manifold vacuum drops (vacuum piston). When the step-up rod is lowered into the main jet, it restricts the fuel flow. When the step-up rod is raised out of the jet, more fuel can flow through it. In this manner, the amount of fuel delivered is tailored to the transient demands of the engine. Some 4-barrel carburetors use metering rods only on the primary two venturis, but some use them on both primary and secondary circuits, as in the Rochester Quadrajet.

Principles of carburater

The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure and the higher its dynamic pressure. The (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

When carburetors are used in aircraft with piston engines, special designs and features are needed to prevent fuel starvation during inverted flight. Later engines used an early form of fuel injection known as a pressure carburetor.

Most production carbureted  engines have a single carburetor and a matching intake manifold that divides and transports the air fuel mixture to the intake valesi, though some engines (like motorcycle engines) use multiple carburetors on split heads. Multiple carburetor engines were also common enhancements for modifying engines in the USA from the 1950s to mid-1960s, as well as during the following decade of high-performance muscle cars fueling different chambers of the engine's .intake manifold

Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top. This had the advantage of never flooding the engine as any liquid fuel droplets would fall out of the carburetor instead of into the intake manifold; it also lent itself to use of an oil bath air cleaner where a pool of oil below a mesh element below the carburetor is sucked up into the mesh and the air is drawn through the oil-covered mesh; this was an effective system in a time when paper air filters did not exist.

Beginning in the late 1930s, downdraft carburetors were the most popular type for automotive use in the united states. In Europe, the sidedraft carburetors replaced downdraft as free space in the engine bay decreased and the use of the su-type carburetor (and similar units from other manufacturers) increased. Some small propeller-driven aircraft engines still use the updraft carburetor design.

outboard moter carburetors are typically sidedraft, because they must be stacked one on top of the other in order to feed the cylinders in a vertically oriented cylinder block.

1979 Evinrude Type I marine sidedraft 

carburetorThe main disadvantage of basing a carburetor's operation on Bernoulli's principle is that, being a fluid dynamic device, the pressure reduction in a venturi tends to be proportional to the square of the intake air speed. The fuel jets are much smaller and limited mainly by viscosity, so that the fuel flow tends to be proportional to the pressure difference. So jets sized for full power tend to starve the engine at lower speed and part throttle. Most commonly this has been corrected by using multiple jets. In SU and other movable jet carburetors, it was corrected by varying the jet size. For cold starting, a different principle was used in multi-jet carburetors. A flow resisting valve called a choke, similar to the throttle valve, was placed upstream of the main jet to reduce the intake pressure and suck additional fuel out of the jets.

Brake caliper

The brake caliper is the assembly which houses the brake pads and pistons. The pistons are usually made of aluminium or chrome-plated steel.

Calipers are of two types, floating or fixed. A fixed caliper does not move relative to the disc and is thus less tolerant of disc imperfections. It uses one or more single or pairs of opposing pistons to clamp from each side of the disc, and is more complex and expensive than a floating caliper.

A floating caliper (also called a "sliding caliper") moves with respect to the disc, along a line parallel to the axis of rotation of the disc; a piston on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc. Floating caliper (single piston) designs are subject to sticking failure, caused by dirt or corrosion entering at least one mounting mechanism and stopping its normal movement. This can lead to the caliper's pad's rubbing on the disc when the brake is not engaged or engaging it at an angle. Sticking can result from infrequent vehicle use, failure of a seal or rubber protection boot allowing debris entry, dry-out of the grease in the mounting mechanism and subsequent moisture incursion leading to corrosion, or some combination of these factors. Consequences may include reduced fuel efficiency, extreme heating of the disc or excessive wear on the affected pad. A sticking front caliper may also cause steering vibration.

disc brake

A disc brake is a wheel brake which slows rotation of the wheel by the friction caused by pushing brake pades against a brake disc with a set of calipers. The brake disc (or rotor in American English) is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon-carbon or ceramic matrix composite. This is connected to the wheel and/or the axle. To stop the wheel, friction material in the form of brake pads, mounted on a device called a brake caliper, is forced mechanically, hydraulicaly, pnumatrically or elecromagnatically against both sides of the disc. friction causes the disc and attached wheel to slow or stop. Brakes convert motion to heat, and if the brakes get too hot, they become less effective, a phenomenon known as brake fade

Disc-style brakes development and use began in England in the 1890s. The first caliper-type automobile disc brake was patented by frederice william in his birmingham, UK factory in 1902 and used successfully on Lanchester cars. Compared to drum brakes, disc brakes offer better stopping performance, because the disc is more readily cooled. As a consequence discs are less prone to brake fade; and disc brakes recover more quickly from immersion (wet brakes are less effective). Most drum brake designs have at least one leading shoe, which gives a servo-effect. By contrast, a disc brake has no self-servo effect and its braking force is always proportional to the pressure placed on the brake pad by the braking system via any brake servo, braking pedal or lever, this tends to give the driver better "feel" to avoid impending lockup. Drums are also prone to "bell mouthing", and trap worn lining material within the assembly, both causes of various braking problems.

Double wishbone suspension

The double-wishbone suspension can also be referred to as "double A-arms," though the arms themselves can be A-shaped, L-shaped, or even a single bar linkage. A single wishbone or a-arm can also be used in various other suspension types, such as macpherson strut and chaman strut. The upper arm is usually shorter to induce negative camber as the suspension jounces (rises), and often this arrangement is titled an "SLA" or short long arms suspension. When the vehicle is in a turn, body roll results in positive camber gain on the lightly loaded inside wheel, while the heavily loaded outer wheel gains negative camber.

Between the outboard end of the arms is a knuckle with a spindle, hub, or upright which carries the wheel bearing and wheel.

To resist fore-aft loads such as acceleration and braking, the arms require two bushings or ball joints at the body.

At the knuckle end, single ball joints are typically used, in which case the steering loads have to be taken via a steering arm, and the wishbones look A- or L-shaped. An L-shaped arm is generally preferred on passenger vehicles because it allows a better compromise of handling and comfort to be tuned in. The bushing inline with the wheel can be kept relatively stiff to effectively handle cornering loads while the off-line joint can be softer to allow the wheel to recess under fore-aft impact loads. For a rear suspension, a pair of joints can be used at both ends of the arm, making them more H-shaped in plan view. Alternatively, a fixed-length driveshaft can perform the function of a wishbone as long as the shape of the other wishbone provides control of the upright. This arrangement has been successfully used in the jagure IRS. In elevation view, the suspension is a 4-bar link, and it is easy to work out the camber gain and other parameters for a given set of bushing or ball-joint locations. The various bushings or ball joints do not have to be on horizontal axes, parallel to the vehicle centre line. If they are set at an angle, then antidive and antisquat geometry can be dialed in.

In many racing cars, the springs and dampers are relocated inside the bodywork. The suspension uses a bellcrank to transfer the forces at the knuckle end of the suspension to the internal spring and damper. This is then known as a "push rod" if bump travel "pushes" on the rod (and subsequently the rod must be joined to the bottom of the upright and angled upward). As the wheel rises, the push rod compresses the internal spring via a pivot or pivoting system. The opposite arrangement, a "pull rod," will pull on the rod during bump travel, and the rod must be attached to the top of the upright, angled downward. Locating the spring and damber inboard increases the total mass of the suspension, but reduces the unspring mass, and also allows the designer to make the suspension more aerodynamic.

Multiple carburetor barrels

While basic carburetors have only one venturi, many carburetors have more than one venturi, or "barrel". Two barrel and four barrel configurations are commonly used to accommodate the higher air flow rate with large engine displacement. Multi-barrel carburetors can have non-identical primary and secondary barrel(s) of different sizes and calibrated to deliver different air/fuel mixtures; they can be actuated by the linkage or by engine vacuum in "progressive" fashion, so that the secondary barrels do not begin to open until the primaries are almost completely open. This is a desirable characteristic which maximizes airflow through the primary barrel(s) at most engine speeds, thereby maximizing the pressure "signal" from the venturis, but reduces the restriction in airflow at high speeds by adding cross-sectional area for greater airflow. These advantages may not be important in high-performance applications where part throttle operation is irrelevant, and the primaries and secondaries may all open at once, for simplicity and reliability; also, V-configuration engines, with two cylinder banks fed by a single carburetor, may be configured with two identical barrels, each supplying one cylinder bank. In the widely seen V8 and 4-barrel carburetor combination, there are often two primary and two secondary barrels.

The spread-bore 4-barrel carburetor, first released by Rochester in the 1965 model year as the "Quadrajet" has a much greater spreadbetween the sizes of the primary and secondary throttle bores. The primaries in such a carburetor are quite small relative to conventional 4-barrel practice, while the secondaries are quite large. The small primaries aid low-speed fuel economy and drivability, while the large secondaries permit maximum performance when it is called for. To tailor airflow through the secondary venturis, each of the secondary throats has an air valve at the top. This is configured much like a choke plate, and is lightly spring-loaded into the closed position. The air valve opens progressively in response to engine speed and throttle opening, gradually allowing more air to flow through the secondary side of the carburetor. Typically, the air valve is linked to metering rods which are raised as the air valve opens, thereby adjusting secondary fuel flow.

Multiple carburetors can be mounted on a single engine, often with progressive linkages; two four-barrel carburetors (often referred to as "dual-quads") were frequently seen on high performance American V8s, and multiple two barrel carburetors are often now seen on very high performance engines. Large numbers of small carburetors have also been used (see photo), though this configuration can limit the maximum air flow through the engine due to the lack of a common plenum; with individual intake tracts, not all cylinders are drawing air at once as the engine's crankshaft rotates.

Tyre Maintenance Tips

How much do you care for your car tyres? In fact, when was the last time you thoroughly checked the wear and tear on the tyres? In our busy life, we tend to focus merely on the outer shell of the car ignoring other essential parts. Tyres in the car are like limbs of an athlete. You don’t realise but your sprinter might be crippled thanks to your ignorance.

1 Tyre change

What’s the right time to replace the old tyre with a new one? Experts believe a tyre should not be used more than 10 years also depending on factors like total kilometres driven, driving style and climate conditions et al. Rubber compounds used Auto Bild India reveals how to avoid mavericks from ripping you off and find a reliable repair station to work on your car Tyres that will never tire Here are some tips to keep your car tyres in good shape over a long period of time in tyres contain anti-oxidising chemicals that help to slow down the natural aging process of untreated rubber. However, tyres do deteriorate with age, which increases the risk of tyre failure, and there are many ways in which this can be spotted. Cracking on the side wall of the tyre, caused by its flexing, distortion of tyre tread or deformation of the carcass of the tyre.

The tyre being used currently should be replaced with a newtyre when the tread wear indicator (1.6mm height) is exposed.

2 Wheel bolt

If wheelbolts aren’t provided by the manufacturer make sure bolts used aren’t too short, there are chances of the wheel jumping out, or too long, they can damage the suspension.

3. Rotation policy

Rotate tyre positions if any irregular wear is found on any of the tyre or after every 5,000km. The first rotation is important as it sets the stage for long and even tyre wear. Make sure that all the tyres are exposed to the road equally. Rotating tyres from time to time would ensure that all the tyres are sharing the burden equally and no tyre is under or over exposed. Some manufacturers provide uni-directional tyres which can’t be used both sides, hence can’t be rotated like regular tyres.

4 Drive smoothly

Guess who curses you the most when you apply emergency brakes? Not the cop, but your car tyres. Rough braking takes away life of your car tyre and leads to early wear and tear. It’s important to drive at a constant pace and avoid applying frequent brakes. Driving rashly and breaking regularly leads to tyre skidding resulting in tyre losing its tread much quicker.

5 Aquaplaning

During monsoons tyres become more vulnerable to wear and tear. Rainwater that lingers in the ruts of roads places demands on driving. When the ruts are deep, the risk of hydroplaning is high, but anticipatory driving and good treads can reduce the risk. New tyres are the best weapons against hydroplaning. A tread pattern that channels water out from between the tyre and the road is the most effective means of preventing hydroplaning. Make sure the tyres are keeping water at bay.

6. Careful with jack

A hydraulic car jack should be used, which guarantees easy working and proper safety of the car and the person at the time of replacing tyre. Otherwise a standard jack provided by the car manufacturer should do. The base where the punctured tyre is being replaced should be should be flat and firm.

 

7. Air-pressure

Tyre pressures should always be checked and corrected (if necessary) when they are cold. It is vital that tyre pressures are maintained at the levels recommended by the manufacturer to ensure maximum tyre life, safety, the best ride and handling characteristics. Over or under-inflating tyres is likely to seriously impair their performance and may prejudice the safe use of the vehicle. Over-inflation increases overall tyre diameter, decreases the amount of tread in contact with the road, decreases sidewall flexibility and affects road-adhesion. Under-inflation decreases overall tyre diameter, increases sidewall flexion, generates higher tyre operating temperatures and difficult vehicle handling characteristics. Running an under-inflated tyre may cause premature tyre failure. Both over and under-inflation adversely affect tyre life.

 

8. Tyre storage

First clean the tyres and mark the position. Store in cool and dry place, away from petrol, oil, grease and chemicals. Lying or standing: it depends on the correct storage. When tyres are stored they should be stored in a cool, dry place away from sources of sunlight, heat and ozone such as hot pipes and electric motors. Tyres should be stored so there is no danger of water collecting inside them. Be sure that surfaces on which tyres are stored are clean and free from grease, gasoline or other substances which could deteriorate the rubber. Tyres exposed to these materials during storage or driving may be weakened and subject to sudden failure.

 

9 Mix and match

Most passenger tyres today are radial tyres. For best performance, we recommend the same size and type of tyre be used on all four wheel positions unless the vehicle manufacturer specified different sizes, front and rear, as original equipment. Check the vehicle placard. If only two radials are mounted with two non-radials, the radials should be mounted on the rear. If tyres of different types are mixed on a vehicle in any configuration, they should not be used for long periods and speeds should be kept to a minimum. Mixing or matching of tyres on four-wheel drive vehicles requires special precautions. Always check vehicle manufacturers’ manual for their recommendations

10 Wheel-alignment

A wheel alignment is part of standard automobile maintenance that consists of adjusting the angles of the wheels so that they are set to the car maker’s specification. The purpose of these adjustments is maximum tyre life and vehicle-travel that is straight and true when driving along a straight and level road, although most machines and the technicians who use them set the alignment to adjust for crowned roads, as well as correct tracking when driving on turns. Wheel alignment should be done after every 5,000km or whenever any irregular wear on tyre is found.