Powertrain and Brake Coordination for Downhill Coasting Speed Control
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Solution Overview
Problem
Existing vehicle control systems struggle to maintain constant speed on downhill slopes without excessive brake load, leading to brake fade and discomfort due to gear-shift shock and vibration.
Innovation Solution
A driving force control device that cooperatively controls the gear ratio of the power train and brake to achieve desired driving force by adjusting the gear ratio of the power train and compensating with brake force, using a requested driving force calculation unit, power train control unit, braking force calculation unit, and brake control unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If braking force is generated by using the brake without downshifting during coasting on a downhill road, then the requested braking force can be achieved, but the load on the brake becomes excessively great causing brake fade
Solution Approach 1:
The braking function is segmented between two systems: the engine brake (power train) and the service brake. The engine brake handles the primary braking through downshifting, while the service brake provides only supplementary braking force. This segmentation allows the service brake to operate within its effective range without excessive load, preventing brake fade while still achieving the required total braking force.
Solution Approach 2:
The system changes the gear ratio parameter of the power train through downshifting to generate engine braking force. By adjusting this parameter, the engine brake can provide variable braking force that supplements the service brake, allowing the service brake to maintain optimal operating conditions without excessive load.
2Reliability
If downshifting is performed to generate braking force during coasting on a downhill road, then the load on the brake is reduced, but gear-shift shock and vibration occur causing discomfort
Solution Approach 1:
Instead of relying solely on downshifting for braking, the system applies partial braking action through the service brake in addition to the engine brake. This combined approach allows for more gradual and controlled deceleration, reducing the shock and vibration associated with aggressive downshifting while still achieving the required braking force.
Solution Approach 2:
The service brake acts as an intermediary that smooths out the transition during braking. By providing supplementary braking force, it allows for more gradual gear ratio changes and reduces the abruptness of downshifting, thereby minimizing gear-shift shock and vibration while maintaining effective braking.
3Speed
If the brake is used to compensate for insufficient braking force, then constant speed running control is achieved, but the brake load increases excessively
Solution Approach 1:
The braking function is segmented between the engine brake and service brake, with the engine brake providing the primary braking force through downshifting. This segmentation ensures that the service brake does not bear excessive load while maintaining the required braking force for constant speed control.
Solution Approach 2:
The system utilizes gear ratio parameter changes in the power train to generate engine braking force, which supplements the service brake. This parameter change allows the service brake to operate within optimal load ranges while achieving the desired vehicle speed control.
Data Source
AI summary
The driving force control device includes: a requested driving force calculation unit configured to calculate requested driving force requested to the vehicle, in a coasting state where neither an accelerator operation nor a brake operation is performed by a driver; a power train control unit configured to control a gear ratio of the power train on the basis of the requested driving force and driving force that is achieved by the power train in the coasting state; a braking force calculation unit configured to calculate braking force required for achieving the requested driving force, when the requested driving force is smaller than driving force that is achieved by the power train at a gear ratio set by the power train control unit; and a brake control unit configured to cause the brake to generate the braking force calculated by the braking force calculation unit.