The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission; the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission.

The main components that make up an automatic transmission include:

• Planetary Gear Sets that are the mechanical systems that provides the various forward gear ratios as well as reverse.
• The Hydraulic System that uses a special transmission fluid sent under pressure by an Oil Pump through the Valve Body to control the Clutches and the Bands in order to control the planetary gear sets.
• Seals and Gaskets are used to keep the oil where it is supposed to be and prevent it from leaking out.
• The Torque Converter, which acts like a clutch to allow the vehicle to come to a stop in gear while the engine, is still running.
• The Governor and the Modulator or Throttle Cable that monitor speed and throttle position in order to determine when to shift.
• On newer vehicles, shift points are controlled by Computer, which directs electrical solenoids to shift oil flow to the appropriate component at the right instant.

Planetary Gear sets:
The main parts of a planetary gear set are:

• An ingenious planetary gear set
• A set of bands to lock parts of a gear set
• A set of three wet-plate clutches to lock other parts of the gear set
• An incredibly odd hydraulic system that controls the clutches and bands
• A large gear pump to move transmission fluid around

The basic planetary gear set consists of a sun gear, a ring gear and two or more planet gears, all remaining in constant mesh. The planet gears are connected to each other through a common carrier, which allows the gears to spine on shafts called “pinions” which are attached to the carrier.

One example of a way that this system can be used is by connecting the ring gear to the input shaft coming from the engine, connecting the planet carrier to the output shaft, and locking the sun gear so that it can’t move.  In this scenario, when we turn the ring gear, the planets will “walk” along the sun gear (which is held stationary) causing the planet carrier to turn the output shaft in the same direction as the input shaft but at a slower speed causing gear reduction (similar to a car in first gear)

If we unlock the sun gear and lock any two elements together, this will cause all three elements to turn at the same speed so that the output shaft will turn at the same rate of speed as the input shaft. This is like a car that is in third or high gear. Another way that we can use a Planetary gear set is by locking the planet carrier from moving, then plying power to the ring gear which will cause the sun gear to turn in the opposite direction giving us reverse gear.

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The illustration on the right shows how the simple system described above would look in an actual transmission. The input shaft is connected to the ring gear (Blue). The Output shaft is connected to the planet carrier (Green), which is also connected to a “Multi-disk” clutch pack. The sun gear is connected to a drum (Yellow), which is also connected to the other half of the clutch pack.  Surrounding the outside of the drum is a band (Red) that can be tightened around the drum when required to prevent the drum with the attached sun gear from turning.

The clutch pack is used, in this instance, to lock the planet carrier with the sun gear forcing both to turn at the same speed. If both the clutch pack and the band were released, the system would be in neutral.  Turning the input shaft would turn the planet gears against the sun gear, but since nothing is holding the sun gear, it will just spin free and have no effect on the output shaft. To place the unit in first gear, the band is applied to hold the sun gear from moving.  To shift from first to high gear, the band is released and the clutch is applied causing the output shaft to turn at the same speed as the input shaft.

Let’s take a look at a single planetary gear set. One of the planetary gear sets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gear set.

Clutch Packs:

A clutch pack consists of alternating disks that fit inside a clutch drum. Half of the disks are steel and have splines that fit into groves on the inside of the drum.  The other half have a friction material bonded to their surface and have splines on the inside edge that fit groves on the outer surface of the adjoining hub.  There is a piston inside the drum that is activated by oil pressure at the appropriate time to squeeze the clutch pack together so that the two components become locked and turn as one.

One-Way Clutch:

A one-way clutch (also known as a “sprag” clutch) is a device that will allow a component such as ring gear to turn freely in one direction but not in the other. This effect is just like that of a bicycle, where the pedals will turn the wheel when pedaling forward, but will spin free when pedaling backward. A common place where a one-way clutch is used is in first gear when the shifter is in the drive position.

Bands:

A band is a steel strap with friction material bonded to the inside surface.  One end of the band is anchored against the transmission case while the other end is connected to a servo.  At the appropriate time hydraulic oil is sent to the servo under pressure to tighten the band around the drum to stop it from turning the servo under pressure to tighten the band around the drum to stop it from turning.

Torque Converter:

On automatic transmissions, the torque converter takes the place of the clutch found on standard shift vehicles.  It is there to allow the engine to continue running when the vehicle comes to a stop.  The principle behind a torque converter is like taking a fan that is plugged into the wall and blowing air into another fan, which is unplugged.  If you grab the blade on the unplugged fan, you are able to hold it from turning but as soon as you let go, it will begin to speed up until it comes close to the speed of the powered fan.  The difference with a torque converter is that instead of using air, it uses oil or transmission fluid, to be more precise.

A torque converter is a large doughnut shaped device (10″ to 15″ in diameter) that is mounted between the engine and the transmission.  It consists of three internal elements that work together to transmit power to the transmission.  The three elements of the torque converter are the Pump, the Turbine, and the Stator.  The pump is mounted directly to the converter housing, which in turn is bolted directly to the engine’s crankshaft and turns at engine speed.  The turbine is inside the housing and is connected directly to the input shaft of the transmission providing power to move the vehicle.  The stator is mounted to a one-way clutch so that it can spin freely in one direction but not in the other. Each of the three elements has fins mounted in them to precisely direct the flow of oil through the converter

Hydraulic System:

The automatic transmission in a car has to do numerous tasks.  For instance, here are some of the features of an automatic transmission:

• If the car is in overdrive (on a four-speed transmission), the transmission will automatically select the gear based on vehicle speed and throttle pedal position.
• If you accelerate gently, shifts will occur at lower speeds than if you accelerate at full throttle.
• If you floor the gas pedal, the transmission will downshift to the next lower gear.
• If you move the shift selector to a lower gear, the transmission will downshift unless the car is going too fast for that gear. If the car is going too fast, it will wait until the car slows down and then downshift.
• If you put the transmission in second gear, it will never downshift or up shift out of second, even from a complete stop, unless you move the shift lever.

It is really the brain of the automatic transmission, managing all of these functions and more. The passageways you can see route fluid to all the different components in the transmission. Passageways molded into the metal are an efficient way to route fluid; without them, many hoses would be needed to connect the various parts of the transmission. First, the key components of the hydraulic system and their functions be discussed.

The Pump:

Automatic transmissions have a neat pump, called a gear pump. The pump is usually located in the cover of the transmission. It draws fluid from a sump in the bottom of the transmission and feeds it to the hydraulic system. It also feeds the transmission cooler and the torque converter.

The inner gear of the pump hooks up to the housing of the torque converter, so it spins at the same speed as the engine. The inner gear turns the outer gear, and as the gears rotate, fluid is drawn up from the sump on one side of the crescent and forced out into the hydraulic system on the other side.

The Governor:

The governor is a clever valve that tells the transmission how fast the car is going. It is connected to the output, so the faster the car moves, the faster the governor spins. Inside the governor is a spring-loaded valve that opens in proportion to how fast the governor is spinning — the faster the governor spins, the more the valve opens. Fluid from the pump is fed to the governor through the output shaft. The faster the car goes, the more the governor valve opens and the higher the pressure of the fluid it lets through. The faster the car goes, the more the governor valve opens and the higher the pressure of the fluid it lets through.

Throttle Valve or Modulator:

To shift properly, the automatic transmission has to know how hard the engine is working. There are two different ways that this is done. Some cars have a simple cable linkage connected to a throttle valve in the transmission. The further the gas pedal is pressed, the more pressure is put on the throttle valve. Other cars use a vacuum modulator to apply pressure to the throttle valve. The modulator senses the manifold pressure, which drops when the engine is under a greater load.

Manual Valve:

The manual valve is what the shift lever hooks up to. Depending on which gear is selected, the manual valve feeds hydraulic circuits that inhibit certain gears. For instance, if the shift lever is in third gear, it feeds a circuit that prevents overdrive from engaging.

Shift Valves

Shift valves supply hydraulic pressure to the clutches and bands to engage each gear. The valve body of the transmission contains several shift valves. The shift valve determines when to shift from one gear to the next. For instance, the 1 to 2-shift valve determines when to shift from first to second gear. The shift valve is pressurized with fluid from the governor on one side, and the throttle valve on the other. They are supplied with fluid by the pump, and they route that fluid to one of two circuits to control, which gear the car, runs in.

The shift valve will delay a shift if the car is accelerating quickly. If the car accelerates gently, the shift will occur at a lower speed. Let’s discuss what happens when the car accelerates gently.

As car speed increases, the pressure from the governor builds. This forces the shift valve over until the first gear circuit is closed, and the second gear circuit opens. Since the car is accelerating at light throttle, the throttle valve does not apply much pressure against the shift valve.

When the car accelerates quickly, the throttle valve applies more pressure against the shift valve. This means that the pressure from the governor has to be higher (and therefore the vehicle speed has to be faster) before the shift valve moves over far enough to engage second gear.

Each shift valve responds to a particular pressure range; so when the car is going faster, the 2-to-3-shift valve will take over, because the pressure from the governor is high enough to trigger that valve.

Computer Controls:

The computer uses sensors on the engine and transmission to detect such things as throttle position, vehicle speed, engine speed, engine load, stop light switch position, etc. to control exact shift points as well as how soft or firm the shift should be.  Some computerized transmissions even learn your driving style and constantly adapt to it so that every shift is timed precisely when you would need it.

Because of computer controls, sports models are coming out with the ability to take manual control of the transmission as though it were a stick shift, allowing the driver to select gears manually.  This is accomplished on some cars by passing the shift lever through a special gate, then tapping it in one direction or the other in order to up-shift or downshift at will.  The computer monitors this activity to make sure that the driver does not select a gear that could over speed the engine and damage it.

Another advantage to these “smart” transmissions is that they have a self-diagnostic mode, which can detect a problem early on and warn you with an indicator light on the dash.  A technician can then plug test equipment in and retrieve a list of trouble codes that will help pinpoint where the problem is.

CVT CONTINUOUSLY VARIABLE TRANSMISSION

CVT is a system that makes it possible to vary progressively the transmission ratio. So it allows selection of a infinite number of ratios (between a minimum and a maximum value).

CVT is a user and environmentally friendly automatic type transmission. While the concept of a CVT transmission is as old as the motor car itself, it has taken Honda to re-engineer the idea to suit the demands of the 21st Century, including full grade logic electronic control with drive and sport modes.

Why CVT? ‘Conventional’ automatic transmissions have a series of fixed gear ratios. The transmission automatically selects a gear which is nearest to the current road speed and throttle position, however, ideal gear matching is not often accomplished. In addition most automatic transmissions use a ‘torque converter’ to connect to the engine. Even if this is fitted with a ‘lock up clutch’ only an average of 90% engine power efficiency is achieved. There are no fixed gear ratios with the CVT technology. Nor does it have a power robbing torque converter. As its name suggests, it is stepless in operation, ranging from rest to full speed on one smooth jet-like operation. By continuously matching the ideal ratio to engine performance, the engine can be operated in a highly-efficient manner in D range or take advantage of S range for brisker performance.

Technically, in a CVT conventional gears are replaced by two variable size drums and a steel drive belt. The flexible steel belt runs in a groove formed between the sides of each drum. The diameter of each drum is controlled by the transmission computer, applying or reducing oil pressure to the movable part of each drum. The drive pulley has low oil applied, and has expanded to allow the belt to run in a small diameter. In turn, the driven pulley has high oil pressure applied, forcing the belt outward around a larger diameter. This condition results in the driving pulley turning over four resolutions to the driven pulleys once. This is a low ratio (1st gear). In its highest ratio (‘top gear’), high oil pressure is applied to the drive pulley and removed from the driven pulley. The drum diameters are now reversed so the driven pulley is turning faster than the driving pulley. In between these two positions, lowest to highest ratios, the transmission computer provides the right balance of oil pressure to each drum. This achieves the correct ratio to suit the prevailing road conditions and accelerator position. Drive mode selected etc.

ANDERSON CONTINUOUSLY VARIABLE TRANSMISSION

The A+CVT is a breakthrough variation on a well-known principal of two parallel cones positioned with the larger end of each one alongside the smaller end of the other. What’s different about the A+CVT is an innovative component called floating sprocket bars (FSBs.).

The FSBs are mounted in channels in the surface of each cone. A specially-designed chain winds around the cones, moving longitudinally as needed to maintain the desired gear ratio. The sprocket bars pivot slightly, compensating for the change in distance between them at different positions along the cones. This allows them to accommodate the uniformly-spaced chain segments.

The result is a transmission that is capable of adjusting its gear ratio by as much, or as little, as necessary to enable a vehicle to operate at the optimum level of efficiency under any driving conditions.

Why the A+CVT is better

• It uses uniquely designed floating sprocket bars (FSBs) mated with a specially-adapted chain. The FSBs, along with the unique chain, compensate for the differences in distance between the sprocket bars. The “float” of the sprocket bars permits them to accommodate the chain segments at any position along the cone surface.
• It uses multi-tapered cones, making possible the use of a constant length drive chain. Constant chain tension is maintained.

The A+CVT is superior to two transmission designs that are now being used in some small automobiles, namely the variable diameter pulley belt-driven type, and the newer toroidal system. Some advantages of the A+CVT are:

• Significant fuel savings
• Simpler design requiring fewer components
• Compact and light-weight
• Lower production cost than other designs currently in use
• Easily adaptable to any type of motor or vehicle, including bicycles

The New A+CVT Chain   :
Better, Stronger, Scalable

The n ew A+CVT Steel Block Chain was designed specifically for use with the dual-cone A+CVT. This chain consists of steel block links connected with steel pins and side plate links. Each block link has a drive lug protruding from the inner side, which meshes with the floating sprocket bars. The drive lug is designed so that there is a single vertical line of contact with the floating sprocket bars. This allows for a single speed ratio at each point. This would be impossible with a belt, since a belt has multiple speed ratios across its width, and a CVT cannot function with multiple speed ratios simultaneously.