BYD Electric Motor Teardown | Full Engineering Analysis by Munro

Introduction to BYD Motor Analysis

Overview of Monroe and Associates

• Paul Turbull and Matthew Lawrence introduce Monroe Live, an engineering consulting firm focused on helping clients outperform competitors through competitive analysis and lean design principles.

• The discussion centers around BYD, a leading player in the electric vehicle (EV) and hybrid markets in China, highlighting its advancements over European and US competitors.

Examination of the Latest BYD Motor

• The motor being analyzed is identified as having 183 kilowatts of power and approximately 330 Nm of torque, weighing only 84 kg.

• This compact unit is part of a new family of motors for models like Han (performance sedan), Tang (SUV), and Tang L (seven-passenger SUV).

Insights into Design Features

Supplier Collaboration

• Borg Warner is noted as a key supplier for this BYD drive unit, indicating collaboration that enhances product quality.

Sealing Mechanism Improvements

• The motor features an advanced sealing system with both face seals and O-rings to prevent water leakage despite thermal expansion or orientation changes.

Electrical Connections and Assembly Considerations

Flexible Connections

• The use of stranded wire for motor connections allows easier assembly but raises concerns about potential electrical connection failures due to vibration.

Gear Ratio Specifications

• A high gear ratio of 12.83:1 enables fast spinning at close to 18,000 RPM, which is significant for performance metrics.

Inverter Disassembly Insights

Inverter Structure

• The inverter contains multiple components including filters for switching ripple reduction, control boards for switches, capacitors rated at 750 volts DC with 510 microfarads capacitance.

Current Sensing Mechanisms

• It appears that three current sensors are used in the inverter design to enhance fault detection capabilities compared to Tesla's two-sensor approach.

EMI Noise Reduction Strategies

Filtering Arrangements

• An interesting filtering arrangement within the inverter helps reduce electromagnetic interference (EMI), bearing currents, and losses in the motor by optimizing DC input filtering.

Electric Drive Unit Overview

Design and Components

• Water flows through the heat switching board, where most of the heat is generated before entering the motor. The design features a single large casting, which is more expensive but beneficial for overall efficiency.

• The top and bottom covers are made from stampings, significantly reducing costs at high production volumes (e.g., 150,000 units). This cost-saving approach is crucial for mass production.

• The BYD Borg Warner motor assembly resembles standard electric drive units found in mainstream electric vehicles like midsize SUVs and sedans targeted at the China market.

Motor Specifications

• The drive unit typically delivers over 200 horsepower and incorporates a two-stage gear reduction system along with a bar wound stator and an interior magnet PM machine. This integration enhances cost-effectiveness in powertrain design.

• The inverter is mounted on the rear cover of the motor, facilitating three-phase connections to the stator. A notable feature is a small resolver that determines rotor position without requiring shielding due to its placement in an aluminum pocket.

Electrical Management

• Carbon fiber brushes are utilized to dissipate static electricity generated by rotor action, preventing electrical arcs across bearings that could lead to damage.

• The rear bearing assembly includes an insert designed for thermal expansion compatibility between aluminum and steel components while isolating electrical conductivity to prevent bearing wear.

Cost Efficiency Solutions

• Special coatings on inserts reduce electrical conductivity, allowing easier paths for generated electricity away from bearings. This method proves more economical than alternatives like ceramic ball bearings or carbon brushes.

• BYD's collaboration with Borg Warner allows them to leverage extensive experience in electric drive units while customizing specifications based on regional needs (e.g., different designs for North American vs. Chinese markets).

Cooling Mechanisms

• In China, water cooling systems are favored for their cost-effectiveness; however, they primarily cool the stator while leaving the rotor susceptible to overheating—potentially leading to magnet demagnetization under extreme conditions.

Cooling Solutions for Electric Motors in Different Markets

Water Cooling vs. Oil Cooling

• In the China market, rare earth magnets can be designed to withstand high temperatures without cooling the rotor, making water cooling a viable option.

• For regions with limited access to heavy rare earth elements, oil cooling is preferred to manage rotor temperature and mitigate supply chain risks associated with permanent magnets.

Engineering Challenges and Innovations

• Multinational corporations like Borg Warner customize solutions for different applications, addressing specific market needs.

• BYD's earlier motor designs faced leak issues due to last-minute engineering changes in their water cooling systems; sealing methods were critical in preventing leaks.

Advanced Manufacturing Techniques

• BYD has implemented a unique manufacturing process using friction stir welding to create seamless inner and outer housings for their motors, eliminating potential leak points.

• This innovative approach results in a hermetically sealed design that enhances reliability compared to traditional O-ring seals.

Cost Considerations and Market Viability

• While the friction stir welding process is not the cheapest option available, it remains more cost-effective than oil cooling systems that require additional components like pumps and heat exchangers.

• The solution developed by BYD is particularly well-suited for the Chinese market but may not be recommended for Western Europe or the US due to differing requirements.

Gearbox Design Insights

• The drive unit features a standard two-stage gearbox with low friction characteristics, optimized for compactness while handling high torque from the motor.

• The gearbox design allows oil lubrication through slinging action rather than relying on dedicated pumps, which simplifies maintenance and reduces costs.

Overall Performance Evaluation

• The combined motor and drive unit represents one of the lowest-cost options available while delivering over 200 horsepower capabilities.

• Despite competitive pricing pressures faced by BYD, ongoing efforts are being made to identify further cost-saving measures without compromising performance quality.

Permanent Magnet Motor Innovations

Overview of Permanent Magnet Motor Design

• The discussion begins with the prevalent use of interior permanent magnets in motor construction, specifically highlighting single V and double V designs. This design has become standard across various manufacturers including Hyundai, GM, Ford, Toyota, and Nissan.

Unique Rotor Features

• A notable aspect is the deep groove in the outside diameter (OD) of the rotor, which is uncommon among competitors. This high-speed rotor operates at nearly 20,000 RPM.

• Typically, an unbroken OD is preferred to evenly distribute hoop stress; however, this design required extensive engineering and finite element analysis to ensure structural integrity at high speeds.

• The rotor's diameter is smaller than usual (138 mm vs. 150 mm), reducing stress on the OD and enabling the unique groove design.

Magnetic Field Optimization

• The double V magnet construction focuses magnetic fields centrally but adding a groove flattens the magnetic flux spike. This results in a more sinusoidal flux distribution that reduces losses in the motor.

• Smoothing out the flux not only minimizes torque ripple and noise but also enhances overall efficiency by decreasing energy loss.

Inverter Design Considerations

• Transitioning to inverter design, it features a thin profile akin to a pizza box for space efficiency in rear motor applications. BYD prioritized minimizing height to maximize trunk space without intruding into passenger areas.

• The inverter includes essential components like large capacitors that smooth current ripple from the motor while storing energy for switching events.

Advanced Cooling Techniques

• The inverter employs six switches (12 discrete devices), cooled on both sides through channels—a novel approach compared to other industry designs which are typically thicker.

• These switches are likely bare die mounted directly onto substrates for optimal thermal management via low-resistance cooling paths.

Electromagnetic Shielding Innovations

• Copper used as both thermal and electrical conductor provides effective shielding against electromagnetic interference generated by switching devices—critical for protecting sensitive electronics like gate drive controllers.

• Remarkably, these switches handle power equivalent to what could light up 15–20 homes during maximum acceleration; thus shielding all components from this power surge is vital for operational safety.

Cost Efficiency Through Compact Design

• Current sensors typically require steel yokes for magnetic field containment; however, this design omits them due to effective shielding from compact switch packaging—resulting in significant cost savings and reduced size/weight of components.

• Overall integration into one casting contributes further to compactness and efficiency within manufacturing processes.

Motor Design Insights

Controller Shielding and Assembly

• The controller is shielded from electromagnetic interference by both the cooling channels and the single casting design, which contrasts with other companies that use separate parts for shielding.

• A low-cost aluminum stamping is used to cover the controller instead of a heavy casting, showcasing an innovative approach to cost efficiency in design.

Concerns About Fasteners

• The reliance on numerous small screws for assembly raises concerns about potential failure modes due to vibration and thermal cycling, as screws can back out over time.

• Each screw represents a risk; if one backs out, it could lead to arcing and inverter failure, highlighting a common issue in electrical engineering designs.

Electromagnetic Design Features

• The motor features a 72-slot design with three parallel paths, similar to previous models like the Chevy Bolt, indicating a consistent approach in electromagnetic design.

• This motor family offers flexibility in power output ranging from over 350 kilowatts down to under 150 kilowatts, demonstrating versatility in application.

Winding Patterns and Connections

• The bar winding scheme minimizes special conductors while balancing inductance across all three parallel paths, contributing positively to performance.

• However, there are concerns regarding the use of flex leads for connections; they allow tolerance stack-up but compromise mechanical support integrity.

Mechanical Stress Issues

• The electrical connection also serves as mechanical support; this dual role can lead to issues when current causes thermal expansion and subsequent stress on weld joints.

• Over time, repeated flexing due to heating and vibrations may cause fatigue in copper connections leading to potential failures.

Long-term Reliability Concerns

• Copper's poor structural properties raise concerns about long-term reliability; fatigue can result in cracks that worsen over time.

• Variability in weld quality poses additional risks; maintenance lapses could lead to inconsistent joint strength compared to tested samples.

Motor Design Insights

Addressing Mechanical Load and Vibrations

• The issue of vibrations in motor design can be mitigated by adding a plastic support part underneath, which dampens these vibrations effectively.

• While it's preferable to eliminate unnecessary parts, if a component is essential for mechanical support—such as protecting an electrical joint—it must be included.

• A recommendation is made to add another plastic part on the opposite side of the joint to enhance stability and performance.

Benchmarking Electric Motor Technology

• The discussed motor sets a new standard for compact and cost-effective electrical power solutions for electric vehicles (EVs) and hybrid vehicles.

• BYD is praised for establishing this benchmark, with Borg Warner also recognized for their role in bringing this innovative technology to market.

• There is anticipation regarding how this technology will influence the broader industry moving forward.