Understanding Automotive Transmission Systems
Clutches
Clutches connect and disconnect the drive shaft. If the motor and axles are at rest, the clutch is static. If the connection occurs while the axles are in motion, the clutch is dynamic. Dynamic clutches are based on static interlocking of drive shaft pieces. Connection/disconnection should be performed when both are at rest to prevent damage. Dynamic clutches allow continuous variation of power/torque to the drive shaft. Friction clutches consist of two discs: one attached to the drive shaft, the other to the axle. Power transmission occurs via friction between the discs. When not transmitting power, the discs are separated; at maximum power, they are in contact.
Gearbox
A gearbox is a train of helical gears used to vary the transmission ratio between two rotating axes. It consists of two shafts: the input shaft (connected to the motor) and the output shaft (coupled to the wheels). Gears on the input shaft rotate solidly, while gears on the output shaft rotate freely. Couplings on the output shaft with internal splines adhere to the shaft, allowing sliding. External splines fit onto the gears, fixing the output shaft. Used in automobiles for changing gears, a third pinion enables reverse gear by connecting the primary and secondary axes.
Transmission Axles
Axles can be rigid or flexible. Rigid axles are made of rigidly coupled elements, transmitting movement through fixed connections (screws, etc.). Misalignment or oscillations can cause damage in rigid axles. Flexible couplings address this by absorbing oscillations/misalignments:
- Elastic Couplings: Made of rubber or neoprene, they absorb spin irregularities and up to 15ยบ of misalignment.
- Universal Joints: Transmit movement between non-aligned shafts. Forks at each end are joined by a cross with bearings. Two joints are used per shaft due to oscillations.
- CVJs: Transmit movement between non-aligned shafts, producing oscillations. Primarily used in automotive wheel transmission.
- Oldham Couplings: Discs at each end connect to the shafts. A central disc transmits motion between parallel, closely spaced shafts.
- Spline Shaft Slide: Allows shaft length variation, also called a sliding sleeve.
Mechanical Brakes
Based on friction between two surfaces, they convert kinetic energy into heat, dissipating it into the environment. A drum rotates with the axis, while a shoe approaches the drum upon activation, slowing rotation via friction. Shoes can contact the drum internally or externally (external brakes). Disc brakes use a disc rotating with the shaft and a caliper. When activated, the caliper clamps the disc, reducing speed through friction. Both types require cooling to prevent thermal fatigue and are hydraulically actuated.
Electric Brakes
A conductive disc/rotor spins with the axis, surrounded by an electromagnet fixed to the frame. When activated, the electromagnet generates a magnetic field, inducing currents in the disc/rotor, creating an opposing electromagnetic field. The fixed magnetic field attracts the electromagnet’s field, slowing and stopping the axis. Less efficient than mechanical brakes.