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How an automatic gearbox works: the ZF 8HP — Transcript · YTtoTranscript

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How an automatic gearbox works: the ZF 8HP

autodoc.co.uk · 1,167 words · 6 min read · EN-ORIG

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Below is the complete, readable transcript of How an automatic gearbox works: the ZF 8HP by autodoc.co.uk on YouTube. Read the full text, copy any part you need, or generate a transcript for any video with our free tool.

How an automatic gearbox works, the ZF 8HP. An automatic gearbox consists of a metal casing containing up to a thousand individual parts. The main components of a modern automatic gearbox. Transmission casing. Oil sump. Torque converter. Mechatronic unit or valve body in older models. Oil pump. Clutch packs and planetary gear sets. Input and output shafts.

Torque converter. This is a hydraulic coupling [snorts] between the engine and the automatic gearbox, which transmits torque from the engine to the transmission. Main components of the torque converter. The pump wheel is integrated into the torque converter housing. The pump wheel is bolted directly to the engine, [music] much like a clutch cover

is bolted to the flywheel on a manual gearbox. It spins the automatic transmission fluid, ATF, forcing it through [music] the system and transferring energy to the turbine wheel. In this way, the engine's mechanical energy is converted [music] into the kinetic energy of the flowing fluid.

The turbine wheel receives energy from the oil flow and rotates the automatic gearbox input shaft.

The operating principle of the pump wheel and turbine wheel can be demonstrated using two fans. The air flow from the first fan causes the second one to rotate. >> [music] [music]

>> The turbine wheel is connected to the input shaft via a splined connection. At [music] the same time, the turbine wheel has no direct mechanical connection to the torque converter housing. Stator. This is a stationary wheel located between the pump and turbine that accelerates the fluid.

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It increases torque at low revs, allowing the car to pull away without needing to increase the engine speed. Lock-up clutch. [music] It firmly connects the pump wheel of the torque converter to the turbine wheel, allowing the engine to drive the gearbox input shaft directly. The lock-up clutch consists of the following: a damper system that absorbs

shock loads when lock-up is engaged. A friction clutch pack with a hydraulic piston that converts oil pressure into mechanical force to lock the torque converter. How can I support this channel? Like this video. Subscribe to the channel. Clutch packs and planetary gear sets. The ZF 8HP uses five clutch packs and four planetary gear sets.

The planetary sets are arranged sequentially along the axis of the gearbox. Clutch packs are positioned around or adjacent to each planetary set. The clutches determine which elements of each gear set rotate and which are held stationary. This is how the required gear ratios and output torque are formed at the output shaft.

Planetary gear set components. Ring gear. Sun gear. Planet gears housed within the planet carrier. To increase the service life and reduce noise, helical gears with an increased contact area are used.

The gear ratio and rotation direction depend on which element is stationary and which is rotating. In this example, the ring gear is held and the carrier rotates via the sun gear with a ratio of approximately 1:3.

By holding the carrier in place, the ring gear rotates in the opposite direction. This engages reverse gear. Fixing both the carrier and the ring gear in place simultaneously creates a direct drive.

>> The elements of the planetary gear set are stopped by the friction packs.

Friction packs. These are the clutches inside the gearbox that connect the shafts or gears to transmit torque and engage different gears.

Each pack consists of alternating friction plates and steel discs.

The friction plates are coated with a friction material on both sides, ensuring smooth synchronization with the steel discs.

The steel discs feature notches to increase grip with the friction material. Both the steel discs and friction plates have lugs pointing in different directions. These lugs lock the discs in place, preventing them from rotating freely. When the pack is disengaged, the friction plates do not contact the stationary steel discs, allowing them to

spin freely.

Engaging and disengaging these packs enables control of the gear shifts. An example of the ZF 8HP shift logic table, where X indicates an engaged pack. The arrangement of all the friction packs within this specific gearbox. For instance, packs A, B, and C engage the first gear, while [music] A, C, and D engage the seventh.

Gear shifting is controlled by the mechatronic unit. Mechatronic unit. This is the control center of the gearbox. It manages gear shifts by delivering the required oil pressure to engage the friction packs. It consists of both hydraulic and electronic components. The electronic part includes the control unit and solenoids. It also incorporates sensors for the

temperature, pressure, and rotational speed, as well as the parking mechanism actuator.

The hydraulic part consists of a valve body with various channels, valves, and springs. The valve body directs pressurized transmission fluid to the relevant sections of the gearbox.

The shape and cross-section of the channels ensure smooth fluid supply to the necessary clutches without sudden pressure spikes. The connection between hydraulics and electronics is provided [music] by the solenoids. Solenoids are electromagnetic valves that regulate fluid pressure by opening [music] or closing based on signals from the ECU.

The oil pressure is managed by the mechatronic unit and generated by the oil pump.

Oil pump. The pump is directly connected to the torque converter via a chain drive and a gear.

The ZF 8HP utilizes a vane type rotary pump, which generates pressure throughout [music] the entire system. Fluid is fed into the pump through a filter located in the oil sump. Oil sump. This is the reservoir at the bottom of the gearbox, where the ATF is collected and stored. Filters, and in some cases,

sensors are also housed here. Metal shavings are [music] captured by magnets.

When servicing the gearbox, check the amount of metal shavings, as this indicates the level of wear. Any remaining wear debris is caught by the filter made of either mesh or paper.

Summary. Knowing the basic components of an automatic gearbox makes it easier to grasp how it works. When the engine starts, the torque converter housing begins to rotate, engaging the oil pump via the chain drive. The pump wheel of the torque converter generates fluid pressure and transfers torque to the turbine wheel. The turbine wheel rotates the input

shaft, which is not yet connected to the output shaft. Filtered fluid from the sump is delivered to the oil pump [music] maintaining system pressure.

The mechatronic unit waits for the D mode to be selected. Once activated, it commands the solenoids to open the hydraulic channels. The fluid exerts pressure acts on the pistons [music] and the pistons engage the friction packs that control the planetary gear sets. The circuit is complete. Engine torque is transmitted from the input shaft to

the output shaft and then to the wheels. Let us know in the comments which car mechanisms you'd like to learn more about. If you have any questions about the ZF 8HP, leave them below. We'll be happy to [music] answer them.