AWD Torque Control Under Differential Lock and Wheel Braking
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Solution Overview
Problem
In all-wheel drive vehicles, the differential limiting state can lead to reduced durability of the power transmission path to the front wheels due to excessive torque transmission, while ensuring power performance is compromised by uniformly limiting the torque of the power source, especially on rough roads or uphill conditions.
Innovation Solution
A control apparatus that executes torque limiting control by setting a smaller upper limit value for the power source torque when the wheel braking torque is large, thereby reducing the high torque transmission to the front wheels and ensuring appropriate drive torque, particularly by adjusting the engine-torque upper limit value based on the master-cylinder hydraulic pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power distribution device is placed in the differential limiting state to ensure power transmission to front wheels, then the power performance is improved, but the durability of the power transmission path to front wheels is reduced due to excessive torque
Solution Approach 1:
The control apparatus dynamically adjusts the upper limit value of power source torque based on wheel braking torque magnitude. When wheel braking torque is large, a smaller upper limit value is set to protect the power transmission path; when wheel braking torque is small, a larger upper limit value is set to maintain power performance. This parameter change strategy resolves the contradiction by adapting the torque limit to operating conditions.
2Reliability
If the torque of the power source is uniformly limited to protect the power transmission path, then the durability is improved, but the power performance is reduced especially on uphill roads
Solution Approach 1:
Instead of uniform torque limiting, the control apparatus implements dynamic torque limiting where the upper limit value of power source torque is adjusted in real-time based on the magnitude of wheel braking torque. This dynamic adjustment allows the system to maintain high power output when protection is not needed (small braking torque) while providing protection when necessary (large braking torque), thus resolving the contradiction between durability and power performance.
3Stability of the object's composition
If the wheel braking torque is applied to stop rotation of front wheels, then the slip is suppressed, but the high torque transmitted to power transmission path reduces its durability
Solution Approach 1:
The control apparatus uses feedback from the wheel braking torque magnitude to adjust the upper limit value of power source torque. When wheel braking torque is large (indicating high stress on the system), the feedback mechanism reduces the power source torque upper limit to protect the power transmission path. This feedback-based control resolves the contradiction by allowing effective wheel rotation control while adapting the torque limit to the current braking condition.
Data Source
AI summary
A control apparatus for an all-wheel drive vehicle that includes (i) a power source, (ii) a power distribution device for distributing a power from the power source to front and rear wheels, (iii) a differential limiting mechanism for placing the power distribution device in a differential limiting state in which a rotational difference between the front wheels and the rear wheels is limited, and (iv) a braking device for applying a wheel braking torque to each of the front and rear wheels. When the power distribution device is placed in the differential limiting state and the wheel braking torque is applied to each of the front wheels and the rear wheels, a torque limiting control is executed for setting an upper limit value of a torque of the power source to a smaller value when the wheel braking torque is large than when the wheel braking torque is small.