Axle Torque Distribution in Overrun on Low-Friction Surfaces
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Solution Overview
Problem
On low friction or loose surfaces, the delivery of overrun torque to the drive wheels can generate undesirable slip and form a wedge of material in front of the wheels, hindering vehicle motion and increasing deceleration, particularly at low speeds.
Innovation Solution
A control system that detects when a vehicle is in overrun and adjusts torque distribution between the first and second axles, reducing overrun torque on the first axle and increasing it on the second axle, using electric machines and regenerative braking to maintain consistent deceleration without significantly affecting overall vehicle deceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If overrun torque is delivered to the drive wheels on low friction surfaces, then vehicle deceleration is achieved, but wheel slip and material wedge build-up occur
Solution Approach 1:
The patent segments the drive torque delivery function across multiple axles. During overrun conditions on low friction surfaces, the control system selectively applies torque to different axles based on their traction conditions, dividing the deceleration function between front and rear axles to prevent excessive slip at any single location that would cause material wedge build-up.
Solution Approach 2:
The patent applies different torque distribution strategies to different axles based on their local traction conditions. The control system monitors wheel slip conditions at each axle and dynamically adjusts the proportion of overrun torque delivered to each axle, allowing optimal deceleration while preventing material wedge build-up at axles experiencing excessive slip.
2Object-affected harmful factors
If overrun torque is reduced on the first axle to prevent material build-up, then wheel slip is reduced, but overall deceleration capability may be affected
Solution Approach 1:
The patent merges the deceleration function across multiple axles by redistributing overrun torque from the first axle to the second axle during overrun conditions. This combination of torque application at different locations maintains overall deceleration capability while preventing material wedge build-up at the first axle where it would be most harmful.
Solution Approach 2:
The control system acts as an intermediary that redistributes torque between axles. When the first axle experiences conditions conducive to material wedge build-up, the control system mediates by reducing torque at that axle and transferring it to the second axle, thereby maintaining deceleration while preventing the harmful effect.
3Object-affected harmful factors
If torque distribution is dynamically adjusted between axles during overrun, then wheel slip is minimized, but control system complexity increases
Solution Approach 1:
The patent implements feedback control by monitoring wheel slip conditions at each axle and using this information to dynamically adjust torque distribution. The control system continuously measures actual wheel slip and compares it to desired levels, then modifies overrun torque allocation accordingly, achieving effective wheel slip control through a relatively simple feedback loop.
Data Source
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AI summary
Aspects of the present invention relate to a control system for controlling torque distribution between a first axle (110) and a second axle (120) in a vehicle (100), the control system comprising one or more controllers. The control system is configured to detect that the vehicle is in overrun and detect the vehicle speed. When the vehicle is in overrun and the vehicle speed is below a first speed threshold then the torque distribution is controlled to reduce overrun torque to the first axle and to increase overrun torque to the second axle. The vehicle may be a hybrid vehicle comprising an internal combustion engine (ICE) (201), a belt integrated starter generator (B-ISG) (205) and an electric rear axle drive (ERAD) (204).