Friday is here, and the 'A Taste of Science for the Weekend' corner is back — number 89.
This week: some of the extraordinary engineering marvels hidden at the heart of Tesla's vehicle motors.
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Tesla has transformed from a startup that nearly went bankrupt time and again into a coveted, glittering status symbol. Beneath its sleek exterior lie numerous engineering innovations, and this week we focus on those relating to the vehicle's motor itself.
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An electric motor works on the principle of magnetic repulsion between the motor's fixed outer casing and the rotating rotor at its center. Electric drive systems fall into two types:
The first is the induction motor, in which the motor's rotor is not magnetic on its own — it becomes a magnet only through the induction of a magnetic field generated by the fixed stator surrounding it.
The second is the permanent magnet motor, in which the rotor itself is equipped with powerful magnets that help produce the torque needed for rotation.
The advantage of an induction motor is that at high speeds, the current that magnetizes the rotor can be switched off, allowing the vehicle to cruise without expending additional energy. The drawback is that at low speeds, a continuous current is required to keep the rotor magnetized and spinning.
A permanent magnet motor requires far less energy at low speeds because the rotor is itself a magnet — but when it is switched off at high speeds, it continues to interact magnetically with the surrounding stator, generating drag and energy loss.
Tesla solved this problem by combining both drive types in a dual-motor configuration.
When the vehicle accelerates and maximum power is needed, both motors operate together.
When the vehicle reaches cruising speed, the induction motor switches off and spins freely, while the permanent magnet motor continues to receive current.
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One of the greatest challenges electric vehicle manufacturers have always faced is the centrifugal force generated at high speeds, which causes the rotor to move violently inside the motor and can tear it apart.
To address this, the rotor is encased in a steel sleeve that helps hold it in place.
The drawback is that metal reacts electrically and magnetically and absorbs heat, resulting in significant energy loss and wasted electricity that could otherwise power the drivetrain.
Tesla solved this by encasing the motor's rotor in a carbon fiber sleeve. Carbon fiber does not react electrically or magnetically, heats up less than metal, and is both stronger and lighter — delivering higher overall efficiency.
One downside is that the metal rotor expands when heated more than the carbon fiber sleeve does, which can cause the sleeve to fracture under the pressure. To address this, Tesla developed a new manufacturing process in which the rotor is compressed under high pressure during production, so that the heat it generates is first absorbed in releasing that internal pressure before the rotor begins to expand.
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The current supplied by the vehicle's battery pack is direct current (DC).
To power an electric motor, it must be converted to alternating current (AC) — the rapid reversal of current direction is what drives the rotor forward through magnetic repulsion.
Earlier electric vehicles used conventional silicon-based switches for this conversion. The drawback of such switches is that the rapid switching they perform is largely dissipated as heat, causing significant energy loss and requiring cooling systems that consume additional electricity.
Tesla replaced these switches with silicon carbide (SiC) inverters.
Silicon carbide is a compound of carbon and silicon that exhibits low electrical resistance, meaning less of the current passing through it is converted to heat.
The use of silicon carbide makes it possible to greatly increase the current supplied to the motor without a significant increase in the heat generated in the process.
In the video: the new Tesla Model 3 — Tesla's mass-market electric vehicle.
Shabbat Shalom 😊
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