Tesla Model 3 Teardown: Motor, Inverter, and Battery
Elucidation of Tesla’s Model 3 EV technology, based on Munro teardown survey data
|Tesla Model 3 teardown|
Tesla surpassed Jaguar in the global sales of luxury vehicles in 2018, coming in ninth. This report introduces the features of the electric components that were revealed in Munro's teardown survey of the Model 3, which is Tesla’s best-selling model.
According to a Nihon Keizai Shimbun (Japan Economics Newspaper) article dated February 19, 2019, the global sales volumes of the 12 luxury car brands (e.g., Mercedes-Benz, BMW, Lexus) reached a record high of 9.48 million units, up 2% y/y. The highest increase was at Tesla, whose sales increased 2.4 times y/y to 245,000 units. Of the total 220,000 unit increase for the 12 brands, 140,000 units were for the best-selling EV in the world, the Tesla Model 3.
Tesla received orders for over 300,000 units of its affordable flagship EV compact sedan, the Tesla Model 3, which was announced in 2016 and started to be delivered from 2018. Tesla managed to hit its target of producing 5,000 Model 3 vehicles at the end of June 2018, achieving stable production volumes from the third quarter of 2018. Sales volumes of the Tesla 3 model was 1,770 units in 2017, increasing to 145,610 units in 2018.
The motor used for the Model 3 has been changed from that of the conventional AC induction motors used in all Tesla products to date to an interior permanent magnet synchronous motor (IPMSM), and the cooling method has been changed from that of a water cooled system to an oil cooled system, resulting in an electric powertrain that is smaller and highly efficient. The inverter has been made smaller by adopting a new power module that is probably made of SiC (silicon carbide) steel material. For the battery, a new cell configuration has been adopted, and the battery is characterized by a number of unique connection methods and technical features to make it a highly reliable battery with a high capacity.
MarkLines is in cooperation with the Detroit-based vehicle benchmark engineering company Munro. Munro produces reports based on teardown analyses of various vehicles. The company scrutinizes detailed specifications such as the weight and dimensions of various parts, as well as costs. For detailed information, please make an inquiry through the following site.
Tesla seeking profitability with launch of lower priced Model 3s (January 2019）
The electric powertrain configuration of the Tesla Model 3 is arranged with the motor on one side of the reducer and the inverter on the other side. Although it is basically the same layout as that of the current Model S, the inside of the motor is completely different. Points that should be noted include the adoption of an interior permanent magnet synchronous motor (IPMSM) and oil cooling.
|Comparison of Model 3 and Model S specifications|
Interior permanent magnet synchronous motor
While Tesla has used induction motors* for the Roadster, Model S, and Model X, the Model 3 is the first Tesla model to adopt an interior permanent magnet synchronous motor (IPMSM)*. In terms of size, a permanent magnet synchronous motor is advantageous at lower speeds where the most torque is required, while an induction motor is advantageous at high speeds where high efficiency and high torque are considered important. The Model 3 is considered a volume production passenger car, so it adopts an interior permanent magnet synchronous motor where priority is given to efficiency (= range) over acceleration performance which requires greater torque.
*Induction motors vs magnetic synchronous motors
The stator (the stationary part) of an induction motor is basically the same as that of a magnetic synchronous motor, but the rotor (the rotating part) is different.
In the rotor of an induction motor, current flows through the rotor by the magnetic field generated from the stator to produce torque. Because there is no magnet, current is sent to the coils of the rotor itself to generate torque, which is disadvantageous in terms of efficiency, but greater torque can be obtained by increasing the voltage.
On the other hand, a magnetic synchronous motor uses a permanent magnet for the rotor, so the magnetic field of the stator and the magnetic flux of the rotor magnet interact to generate torque. In the rotor, magnetic flux is always present because of the magnet. Increasing the flow of electric current to the stator generates increased torque and high efficiency, but it cannot drive more voltage if the number of rotations is high. Therefore, in order to drive more voltage at high rotation speeds, an inverter is used to reduce the amount of power generation (referred to as field-weakening control). As a result, it becomes possible to supply voltages at high rotation speeds, but with lower efficiency in the high speed region.
Adoption of oil cooling
The rotational direction of the rotor is offset 90 degrees to the left and 90 degrees to the right of the core central portion, which is referred to as skew, a measure used to smooth out torque unevenness (ripple) during rotation.
The inside of the rotor has a 6-pole motor design in which the magnets are arranged in a V-shape. The magnet is inserted into a core made of laminated electromagnetic steel sheets.
The rotor shaft has a large number of hollow portions and holes that serve as oil passages, and the cooling oil is dispersed by rotation to simultaneously cool both the rotor core and stator.
The rotor core is made of electromagnetic steel sheets with an inner diameter of 70 mm, an outer diameter of about 150 mm, and a thickness of 0.25 mm.
A key point concerning the stator is the adoption of oil cooling. Although the Model S was water cooled, the housing of the Model 3 stator does not have a water jacket for water cooling, but instead the inside of the motor is completely oil cooled.
Only oil flows through the passages inside the motor. However, the gearbox side which has a structure that is integrated with the motor, is mounted with the heat exchanger that cools the oil with cooling water, as well as several oil cooled components such as the electric oil pump and oil filter, which play a role in circulating oil to the motor.
The stator core is also characterized by having 56 slots, an inner diameter of about 150 mm, an outer diameter of about 250 mm, and a unique shape having a large number of holes that serve as passages for the flow of oil. Also, near the center of the laminated core are passages to receive and disperse the flow of oil.
The stator winding is the same as the distributed winding of conventional induction motors, but the diameter of the wire is 0.8 mm.
The resolver for detecting the rotational position of the rotor is mounted on the opposite side of the motor gear box, and also has a distinctive structure. When the lid is removed, one can see that the layout of the resolver contains an integrated sensor unit structure that is comprised of the resolver’s stator, coil temperature sensor and connectors, which is an uncommon design among other companies.
Also, Tesla's conventional motors have been equipped with a grounding brush to prevent bearing corrosion or grinding, unlike the Model 3 where the small diameter bearing near the resolver rotor plays a role in grounding the shaft.
The inverter is mounted on the opposite side of the motor across from the powertrain gearbox.
A total of 96 power modules comprise the battery pack installed in the 2012 Model S, but the new Model 3 has 24 power modules (“bricks”, of 46 cells each), making it a much more compact inverter.
The role of the inverter is to convert the direct current (DC) of the battery into a three-phase alternating current (AC) to control the drive and regenerative energy of the motor. However, the layout of the inverter is such that the main board of the motor controller is located at the top of the inverter and the driver circuitry that sends command signals to the power module located at the bottom of the inverter.
The motor is driven by three-phase AC power generated by the inverter, but the connection terminals of the three power lines are integrated with the bus bars that connect with each power module, and pass through the gearbox where the lead wires of the motor winding are bolted.
According to Munro, when they disassembled the inverter, the connections inside the inverter were laser welded so they couldn’t just de-solder, but they had to cut the connections.
|Motor controller board||Bus bar|
Power modules and capacitors
|Power modules and capacitors|
The capacitors and power modules are located at the bottom of the inverter. The capacitor serves as a filter when the inverter turns on and off the supply of DC power supplied from the battery to the inverter, which is the portion of the power module that looks like the dark mass seen at the back on the right side of the image.
The DC power supplied to the power modules for the respective phases by the bus bars is converted to AC power by PWM (Pulse Width Modulation) control of the inverter, then drawn from the central bus bar and sent to the motor. Although DC is turned on and off at a frequency of about 5 kHz by the power module and converted to AC, much of the inverter’s performance is determined by this power module.
The power modules that are used are likely SiC power modules (the dark areas arranged in large numbers at the front of the image) that were developed by ST Microelectronics for the Model 3. The four power modules in the inverter are connected in parallel to the upper and lower arms of each phase, for a total of 24 modules in three phases.
By adopting 24 SiC MOSFET (Silicon Carbide Metal Oxide Semiconductor Field Effect Transistor) modules in each Model 3 inverter, allows reduction of conduction loss and switching losses when operated in the ON mode, and it is possible to realize an inverter that has smaller packaging and high efficiency. The heat is dissipated through the copper base plate located at the bottom of the water-cooled heat sink.
The back side of the power module mounting surface is not a plate-like protrusion, but has a radiator (pin fin heatsink) that has a shape comprised of many rods aligned in parallel, and is water-cooled by cooling water. The water channels are sealed using a slightly larger lid.
|Heatsink||Housing rear surface|
SiC material is attracting attention for applications as a new generation of power elements. There are examples of SiC being introduced for railway and infrastructure applications, but its adoption by companies is limited because of the material’s high cost and supply instability (there are few companies that can provide SiC with few crystal defects and it is difficult to source SiC in sufficient quantities). Tesla will be the first OEM to adopt SiC for the MOSFET modules used in a mass production model.
The battery equipped on the Model 3 is a 2170 format battery cells, which according to Munro is 20% larger than previous battery cells with 50% more capacity.
The battery pack has four modules, each of which has a printed circuit board. It does not have as much wiring as a standard battery pack, and it is excellent in terms of monitoring the input and output of current via ribbon cables. The battery controller in each module controls the charging status and monitors the safety and normal operating status of the battery pack.
|Battery pack||Battery controller|
The Model 3 has 4,416 battery cells. The 46 cells are called bricks at Tesla, and there are 96 bricks of 46 cells.
The cells in the bricks are connected in parallel by the current collectors, acting as one battery in total, and the nominal voltage is the same 3.6V as the individual voltages, but the capacity is 46 times greater. Connecting the bricks in series externally provides an output of 350V.
The two small wires attached to the current collector plate are for connecting the respective cells. If wires detach and one cell is lost due to vibration or aging, the loss is only 1/46 of the total capacity, so there is no need to discard the entire battery pack.
On the other hand, in the case of a short in the system, the thin wire acts as a fuse, burns, and disconnects from the system, resulting in little effect upon the performance of the vehicle. This is a highly reliable design, basically with only a slight decrease in operating performance even in the event a certain degree of failure occurs.
While other companies generally use relatively large capacity cells, Tesla's method of connecting many small capacity cells in parallel is unique. Repair doesn’t need to be considered because the battery pack is all bonded, with a construction that is viewed as non-maintenance rather than maintenance-free. According to Munro, during disassembly of the bonded battery pack they had to use a hammer and chisel to open the cover, and that it was almost as if Tesla did not want anyone seeing the contents of the battery pack.
The lithium-ion battery cells installed in the Model 3 have the same cylindrical shape as that used in other Tesla models, but the battery chemistry is different from that used for the 18650 battery cells of the battery pack in other Tesla models such as the Model S, while the Model 3 uses Tesla’s new 2170 format battery cells with a Nickel Cobalt Aluminum Oxide (NCA) chemistry. According to data by the New Energy and Industrial Technology Development Organization (NEDO), the 2170 format cells adopted for the Model 3 (2017 model) have a capacity of 4.75 Ah, an energy density of 260 Wh/kg, and 683 Wh/L. It is likely that Tesla is modularizing the cells at its Gigafatory 1 facility in Reno, Nevada, a joint venture with Panasonic.
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