In recent years, the global shift toward sustainable transportation has accelerated the development of electric vehicles, with China EV market leading in innovation and adoption. As a researcher focused on advancing electric vehicle technologies, I have explored the design and optimization of transmission systems to enhance performance and efficiency. This article presents a comprehensive study on the design of a two-speed transmission ratio for a pure electric vehicle, utilizing ADVISOR software for simulation and analysis. The motivation stems from the limitations of fixed-ratio transmissions commonly used in electric vehicles, which impose higher demands on motors and batteries, particularly in complex driving conditions such as climbing, acceleration, and high-speed cruising. By designing a two-speed transmission, I aim to improve the electric vehicle’s dynamic performance and energy economy, ensuring the motor operates within its high-efficiency range across various scenarios.
The electric vehicle industry, especially in China EV sector, has seen rapid growth due to government policies and technological advancements. However, most existing electric vehicles rely on fixed-ratio transmissions, which restrict the motor’s ability to adapt to varying loads and speeds. This can lead to suboptimal efficiency, reduced battery life, and compromised performance. In my work, I address this by developing a two-speed transmission that allows for better torque management and speed control. The design process involves calculating transmission ratios based on key performance indicators like maximum speed, gradability, and acceleration time. Through simulation in ADVISOR, I compare the proposed two-speed transmission with a conventional fixed-ratio system, demonstrating significant improvements in speed, battery utilization, and overall system efficiency. This approach not only aligns with the goals of China EV development but also contributes to global efforts in creating more sustainable and high-performing electric vehicles.
To begin, I established the fundamental parameters of the electric vehicle under study, which are essential for accurate transmission design and simulation. These parameters include dimensions, mass, aerodynamic properties, and motor specifications, as summarized in Table 1. The vehicle is a typical sedan model representative of China EV offerings, with a focus on urban and suburban use cases. The motor characteristics, such as peak torque and maximum speed, play a critical role in determining the transmission ratios, as they define the power delivery capabilities. Additionally, factors like rolling resistance and mechanical efficiency are considered to ensure realistic simulations. This foundational data allows me to proceed with the transmission ratio design, targeting optimal performance for the electric vehicle.
| Parameter | Value |
|---|---|
| Length × Width × Height (mm) | 4995 × 1910 × 1495 |
| Wheelbase (mm) | 2920 |
| Front/Rear Track (mm) | 1650 / 1630 |
| Curb Mass (kg) | 2100 |
| Gross Mass (kg) | 2475 |
| Drag Coefficient (CD) | 0.23 |
| Frontal Area (A, m²) | 2.2 |
| Rolling Radius (r, mm) | 400.55 |
| Rotational Mass Conversion Factor (δ) | 1.1 |
| Rolling Resistance Coefficient (f) | 0.02 |
| Mechanical Transmission Efficiency (ηT) | 0.92 |
| Rated Torque (Trated, N·m) | 130 |
| Peak Torque (Tmax, N·m) | 330 |
| Rated Speed (nrated, rpm) | 4400 |
| Maximum Speed (nmax, rpm) | 15500 |
| Maximum Vehicle Speed (vmax, km/h) | 100 |
| Maximum Gradability (%) | 30 |
Next, I delved into the design of the two-speed transmission ratios, which is central to enhancing the electric vehicle’s performance. The transmission ratios must satisfy the vehicle’s dynamic requirements, including maximum speed, gradability, and acceleration. For the first gear (I-gear), the lower limit of the ratio is determined by the maximum torque needed to climb slopes, while the upper limit ensures stable low-speed operation. The equations governing these limits are derived from fundamental mechanics and motor characteristics. Specifically, the I-gear ratio (ig1) combined with the final drive ratio (i0) must meet the following criteria based on traction and speed constraints:
$$ i_{g1} i_0 \geq \frac{r}{T_{\text{max}} \eta_T} \left( m g f \cos \alpha + m g \sin \alpha + \frac{C_D A v^2}{21.15} \right) $$
$$ i_{g1} i_0 \leq \frac{0.377 n_{\text{max}} r}{v} $$
Here, m represents the vehicle mass, g is gravitational acceleration, α is the maximum climb angle, and v is the vehicle speed. Similarly, for the second gear (II-gear), the ratios are designed to handle high-speed cruising and efficiency, with the lower limit based on aerodynamic and rolling resistances, and the upper limit constrained by the maximum motor speed:
$$ i_{g2} i_0 \geq \frac{r}{T_{\text{max}} \eta_T} \left( m g f + \frac{C_D A v_{\text{max}}^2}{21.15} \right) $$
$$ i_{g2} i_0 \leq \frac{0.377 n_{\text{max}} r}{v_{\text{max}}} $$
Additionally, the transmission ratios must prevent wheel slip by adhering to the road adhesion condition:
$$ i_g i_0 \leq \frac{m g r \phi}{T_{\text{max}} \eta_T} $$
where φ is the road adhesion coefficient, typically set to 0.7. To ensure smooth gear shifts and continuous power delivery, the ratio between I-gear and II-gear must satisfy:
$$ \frac{i_{g1}}{i_{g2}} \leq \frac{n_{\text{max}}}{n_{\text{rated}}} $$
After applying these equations with the parameters from Table 1, I selected preliminary ratios: a final drive ratio i0 = 3.9, I-gear ratio ig1 = 2.4, and II-gear ratio ig2 = 1.6. These values are optimized to balance performance and efficiency for the electric vehicle, particularly in the context of China EV applications where urban driving and occasional high-speed travel are common.
With the transmission ratios defined, I proceeded to simulate the electric vehicle using ADVISOR software, a powerful tool for analyzing vehicle performance and energy consumption. The simulation involved configuring the vehicle model with the specified parameters and running tests under standard driving cycles to evaluate both fixed-ratio and two-speed transmissions. In ADVISOR, I selected the electric vehicle (EV) model and input the components as listed in Table 2, which includes the energy storage, motor, wheel/axle, and transmission modules. The transmission was set to either a fixed ratio of 3.9 or the two-speed ratios of 2.4 and 1.6, allowing for a direct comparison. This setup mirrors real-world scenarios in China EV testing, ensuring the results are applicable to actual vehicle development.
| Component | Parameter Setting |
|---|---|
| Vehicle | VEH_SMCAR |
| Energy Storage | ESS_LI7_temp |
| Motor | MC_AC83 |
| Wheel/Axle | WH_SMCAR |
| Powertrain Control | PTC_EV |
| Transmission | TX1_sd (for fixed ratio) or custom two-speed |
The simulation was conducted under the Urban Dynamometer Driving Schedule (UDDS) cycle, which represents typical city driving conditions. This cycle is relevant for electric vehicles in China EV urban environments, characterized by frequent stops and starts. I ran the simulation for one cycle to assess key performance metrics, such as maximum speed, battery state of charge (SOC), and system efficiency. The results for the fixed-ratio transmission and two-speed transmission are summarized in Table 3, highlighting the improvements achieved with the two-speed design. These metrics are crucial for evaluating the electric vehicle’s practicality and sustainability.
| Performance Metric | Fixed-Ratio Transmission | Two-Speed Transmission | Improvement |
|---|---|---|---|
| Maximum Speed (km/h) | 97 | 99 | 2.0% |
| Battery SOC (Remaining) | 0.85 | 0.88 | 3.5% |
| Transmission Efficiency | 0.95 | 0.97 | 2.0% |
| System Efficiency | 0.424 | 0.446 | 5.0% |
Analyzing the simulation outcomes, I observed that the two-speed transmission significantly enhances the electric vehicle’s performance. The maximum speed increased from 97 km/h to 99 km/h, a 2.0% improvement, allowing for better high-speed capability. More importantly, the battery SOC rose from 0.85 to 0.88, indicating a 3.5% gain in energy retention, which translates to extended driving range—a critical factor for China EV adoption. The transmission efficiency improved from 0.95 to 0.97, meaning less energy loss in the drivetrain, and the overall system efficiency jumped from 0.424 to 0.446, a 5.0% increase. These efficiencies stem from the two-speed transmission’s ability to keep the motor operating in its optimal speed range, reducing unnecessary energy consumption and heat generation. For instance, during acceleration or climbing, the I-gear provides higher torque, while the II-gear maintains efficiency at cruising speeds. This adaptability is vital for electric vehicles facing diverse driving conditions, and it underscores the importance of transmission design in achieving superior electric vehicle performance.
To further illustrate the efficiency gains, I derived mathematical expressions for the power and energy aspects. The motor power output P can be related to torque T and speed n as follows:
$$ P = \frac{T n}{9550} $$
where P is in kilowatts, T in Newton-meters, and n in rpm. For the two-speed transmission, the power at the wheels is optimized by selecting the appropriate gear ratio to minimize losses. The overall energy consumption E over a driving cycle can be estimated by integrating the power demand:
$$ E = \int P_{\text{req}} \, dt $$
where Preq is the required power considering resistances and acceleration. With the two-speed transmission, Preq is lower due to better motor efficiency, leading to reduced E. This aligns with the simulation results, where the higher SOC and system efficiency indicate lower energy use per distance traveled. Such improvements are essential for electric vehicles, particularly in China EV market, where charging infrastructure and battery life are key concerns.
In conclusion, my design and simulation of a two-speed transmission for a pure electric vehicle demonstrate substantial benefits over fixed-ratio systems. The carefully calculated ratios, based on dynamic performance constraints, enable the electric vehicle to achieve higher speeds, better energy economy, and improved efficiency. The ADVISOR simulations validate these advantages, showing notable gains in maximum speed, battery SOC, transmission efficiency, and system efficiency. This work contributes to the advancement of electric vehicle technologies, especially in the context of China EV development, by providing a practical approach to transmission optimization. Future research could focus on refining control strategies for gear shifts, integrating regenerative braking, and exploring multi-speed transmissions for even greater performance. As the electric vehicle industry evolves, such innovations will play a pivotal role in making electric vehicles more accessible, efficient, and sustainable for global markets.
Throughout this study, I emphasized the importance of transmission design in enhancing electric vehicle capabilities. The two-speed transmission not only addresses the limitations of fixed ratios but also aligns with the growing demands of China EV consumers for longer range and better performance. By leveraging simulation tools like ADVISOR, I was able to quantitatively assess the improvements, providing a foundation for further development. As electric vehicles become more prevalent, continued research in transmission systems will be crucial for achieving the full potential of electric mobility, reducing emissions, and promoting sustainable transportation solutions worldwide.