As the global shift toward sustainable transportation accelerates, battery electric vehicles have emerged as a cornerstone of this transformation, driven by advancements in electric drivetrain technology. In modern battery electric vehicles, multi-speed transmissions are increasingly adopted to enhance motor efficiency and vehicle performance, with parking mechanisms playing a critical role in ensuring safety during stationary conditions. This study focuses on the electric parking mechanism integrated into a two-speed fully electronically controlled automatic transmission for a battery electric vehicle. I investigate its performance through theoretical calculations and dynamic simulations using ADAMS, aiming to validate design requirements and provide a robust analytical framework. The parking mechanism must reliably lock the vehicle on slopes, prevent rolling, and operate within safe speed limits, all while withstanding dynamic loads. Here, I present a comprehensive analysis covering theoretical derivations, modeling approaches, and simulation results, emphasizing the integration of such systems in battery electric vehicles to meet stringent safety standards.
The design of parking mechanisms for battery electric vehicles involves unique challenges due to the absence of traditional internal combustion engine components, allowing for simplified electromechanical actuation. However, this simplification must not compromise safety, as battery electric vehicles often operate in diverse environments, including steep inclines. The parking mechanism typically consists of a pawl, ratchet, actuator, and related linkages, which engage to lock the transmission output shaft. Key performance metrics include the rolling distance on slopes, critical parking speed, self-locking capability, disengagement performance, and impact forces during high-speed parking attempts. In this study, I first establish theoretical models to calculate these parameters, then develop a rigid-flexible coupled dynamic model in ADAMS to simulate real-world scenarios. The goal is to ensure that the mechanism meets industry standards, such as locking on a 30% slope and preventing rolling beyond 80 mm, thereby enhancing the reliability of battery electric vehicles.
To begin, I derive the theoretical equations for the rolling distance during hill parking, which is essential for assessing the mechanism’s effectiveness in preventing vehicle movement. For a battery electric vehicle parked on an incline, the rolling distance \( S_{\text{rollback}} \) occurs as the ratchet rotates by one tooth pitch before full engagement. This distance depends on the wheel radius \( r \), number of ratchet teeth \( n_{\text{teeth}} \), final drive ratio \( i_{\text{diff}} \), and wheel acceleration \( e_1 \). The equations are as follows:
$$ S_{\text{rollback}} = \frac{r \times 2\pi}{n_{\text{teeth}} \times i_{\text{diff}}}, $$
$$ v_{\text{wl}} = \sqrt{2 e_1 S_{\text{rollback}}}, $$
where \( v_{\text{wl}} \) is the vehicle speed achieved during hill parking. For the specific battery electric vehicle in this study, parameters include \( r = 310 \, \text{mm} \), \( n_{\text{teeth}} = 15 \), \( i_{\text{diff}} = 3.762 \), and \( e_1 = 2819 \, \text{mm/s}^2 \). Substituting these values yields \( S_{\text{rollback}} = 34.5 \, \text{mm} \), which is well below the 80 mm limit, and \( v_{\text{wl}} = 0.441 \, \text{m/s} \) or 1.59 km/h. This speed must be less than the critical parking speed to ensure successful engagement, a crucial factor for battery electric vehicles operating on slopes.
Next, I calculate the critical parking speed, defined as the maximum vehicle speed at which the parking mechanism can reliably lock. This speed typically ranges from 2 to 5 km/h for battery electric vehicles, beyond which engagement may fail, posing safety risks. The critical speed depends on the angular displacements of the ratchet and pawl during engagement. When the root of the pawl’s round angle contacts the ratchet’s root, locking is complete, as shown in the engagement process. The time for the ratchet to rotate through an angle \( \Delta \varphi \) is given by:
$$ t_1 = \frac{\Delta \varphi}{2 \pi n_w i_{\text{oi}} i_{\text{diff}}}, $$
where \( n_w \) is the wheel speed in revolutions per hour, \( i_{\text{oi}} \) is the gear ratio from the output shaft to the intermediate shaft (taken as 1), and \( \Delta \varphi = 0.10472 \, \text{rad} \). The wheel speed relates to vehicle speed \( v_w \) by:
$$ n_w = \frac{v_w}{2 \pi r \times 3.6}. $$
Solving these equations with \( t_1 = 0.0094 \, \text{s} \) gives \( n_w = 470.86 \, \text{r/h} \) and a critical parking speed \( v_w = 3.3 \, \text{km/h} \). Thus, the parking mechanism can engage at vehicle speeds up to 3.3 km/h, which encompasses the hill parking speed of 1.59 km/h, confirming its suitability for battery electric vehicles in slope conditions.
To complement these theoretical insights, I summarize key parameters and results in Table 1, which highlights the design values and calculated metrics for the battery electric vehicle’s parking mechanism. This table provides a quick reference for engineers working on similar systems.
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Wheel Radius | \( r \) | 310 | mm |
| Number of Ratchet Teeth | \( n_{\text{teeth}} \) | 15 | – |
| Final Drive Ratio | \( i_{\text{diff}} \) | 3.762 | – |
| Wheel Acceleration | \( e_1 \) | 2819 | mm/s² |
| Rolling Distance | \( S_{\text{rollback}} \) | 34.5 | mm |
| Hill Parking Speed | \( v_{\text{wl}} \) | 1.59 | km/h |
| Critical Parking Speed | \( v_w \) | 3.3 | km/h |
| Ratchet Angle | \( \Delta \varphi \) | 0.10472 | rad |
Following the theoretical analysis, I proceed to dynamic simulation using ADAMS, a multi-body dynamics software, to model the parking mechanism under various operating conditions. For battery electric vehicles, simulations are vital to validate theoretical predictions and assess performance in realistic scenarios, including transient loads and material flexibility. I develop a rigid-flexible coupled model that incorporates the pawl, ratchet, actuator, and supporting structures, with flexibility assigned to critical components to capture deformation effects. The simulation parameters, based on typical materials and contact properties, are listed in Table 2. These settings ensure accurate representation of interactions within the battery electric vehicle’s drivetrain.
| Simulation Parameter | Value | Unit |
|---|---|---|
| Material Stiffness | 1e2 | N/m |
| Force Exponent | 1.5 | – |
| Damping | 0.05 | N·s/m |
| Penetration Depth | 0.1 | mm |
| Static Friction Coefficient | 0.1 | – |
| Dynamic Friction Coefficient | 0.09 | – |
| Static Translation Velocity | 0.1 | mm/s |
| Dynamic Translation Velocity | 10 | mm/s |
In the simulation, I apply a STEP function to model the motor’s rotational behavior, accelerating the ratchet to simulate vehicle motion and then initiating parking actuation. For critical parking speed analysis, I set the initial vehicle speed to 6 km/h, after which the parking command is triggered. The results show that the ratchet’s angular velocity decreases non-uniformly upon pawl contact, dropping to zero at 0.48 s, indicating successful locking. The corresponding speed at engagement is 659.8 °/s, equivalent to 3.4 km/h. This matches the theoretical value of 3.3 km/h with only a 3% deviation, validating the model’s accuracy for battery electric vehicle applications. The close agreement underscores the reliability of both theoretical and simulation approaches in designing parking mechanisms for battery electric vehicles.
To further evaluate the mechanism, I simulate self-locking performance on a 30° slope, representing a stringent condition for battery electric vehicles. A torque equivalent to the vehicle’s full weight on the incline is applied to the ratchet shaft. The results, plotted over time, show that the torque remains stable without pawl disengagement, confirming self-locking capability in both uphill and downhill orientations. For battery electric vehicles, this ensures safety even on steep grades, with a safety factor of 2.6 applied without failure. The disengagement performance is also tested by removing the actuator force; simulations indicate that the pawl separates from the ratchet within 0.2–0.21 s under spring action, meeting design requirements for smooth exit from parking mode in battery electric vehicles.
Another critical aspect is the impact forces during parking at various vehicle speeds, which affect component durability in battery electric vehicles. I simulate engagements at speeds ranging from 0 to 80 km/h, recording forces between the ratchet and pawl, pawl and slider, and slider and pin. The data, summarized in Table 3, reveal that impact forces peak at low speeds (below 10 km/h) and high speeds (above 60 km/h), due to changes in contact area and inertial effects. However, all peak forces remain within a design safety factor of 2, ensuring structural integrity for the battery electric vehicle’s parking mechanism under dynamic conditions.
| Vehicle Speed (km/h) | Ratchet-Pawl Force (N) | Pawl-Slider Force (N) | Slider-Pin Force (N) |
|---|---|---|---|
| 0 | 1200 | 800 | 600 |
| 10 | 1500 | 950 | 700 |
| 20 | 1100 | 700 | 500 |
| 30 | 1300 | 850 | 650 |
| 40 | 1400 | 900 | 680 |
| 50 | 1600 | 1000 | 750 |
| 60 | 1800 | 1150 | 850 |
| 70 | 2000 | 1300 | 950 |
| 80 | 2200 | 1400 | 1050 |
The simulation outcomes align with theoretical expectations, demonstrating that the parking mechanism fulfills all key performance criteria for battery electric vehicles. The critical parking speed of 3.4 km/h ensures safe engagement on slopes, while self-locking and disengagement capabilities meet industry standards. Impact forces, though variable with speed, are within acceptable limits, highlighting the mechanism’s robustness. These findings are particularly relevant for battery electric vehicles, where electromechanical systems must be optimized for efficiency and safety. The use of ADAMS for rigid-flexible coupling analysis proves effective in capturing dynamic interactions, providing a valuable tool for future designs in battery electric vehicle transmissions.
In conclusion, this study presents a thorough investigation of an electric parking mechanism for a battery electric vehicle, combining theoretical calculations and dynamic simulations. The results verify that the design satisfies essential safety requirements, such as limited rolling distance, appropriate critical speed, reliable locking on slopes, and controlled impact forces. The methodology outlined here—integrating analytical models with advanced simulation techniques—offers a framework for developing and validating parking mechanisms in battery electric vehicles. As the adoption of battery electric vehicles grows, such research contributes to enhanced drivetrain reliability and overall vehicle safety, paving the way for more innovative solutions in electric mobility. Future work could explore optimization of component materials or actuation strategies to further improve performance in battery electric vehicles under extreme conditions.