Vehicle Control Apparatus Neutral Range Drag Prevention
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Solution Overview
Problem
When a vehicle with a fluid-type automatic transmission is set in the neutral range, the existing braking force retaining apparatus fails to retain brake fluid pressure, leading to potential vehicle dragging due to remaining clutch torque and engine torque upon engine restart, especially on flat roads.
Innovation Solution
A vehicle control apparatus that includes a prime mover stopping unit and a braking force retaining unit, which retains braking force for a predetermined time even when the transmission is in the neutral range, allowing the braking force to gradually decrease and ensuring the prime mover restarts after a separate predetermined time, thereby preventing vehicle dragging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the braking force retaining apparatus releases brake fluid pressure when the transmission is in the neutral range, then the driver can operate the vehicle smoothly without brake interference, but the vehicle may experience dragging due to remaining clutch torque and engine torque upon engine restart
Solution Approach 1:
The braking force retaining apparatus performs preliminary action by maintaining brake fluid pressure for a predetermined time period after the brake operation member is disengaged, even when the transmission is in the neutral range. This preliminary retention of braking force occurs before the engine restarts and before the clutch torque fully dissipates, preventing the vehicle dragging that would otherwise occur when engine torque and residual clutch torque act on the stationary vehicle.
2Object-generated harmful factors
If the braking force is retained for a long period, then vehicle dragging is prevented, but the hill holder function may be compromised and fuel consumption increases
Solution Approach 1:
The braking force retention system employs dynamics by setting a predetermined time period that is optimized to balance two opposing requirements: it is long enough to prevent vehicle dragging during engine restart in neutral range, but short enough to allow the hill holder function to operate effectively and to minimize fuel consumption. The system dynamically adjusts the retention duration based on operational conditions, releasing the brake fluid pressure after the predetermined time period elapses.
3Reliability
If the brake fluid pressure is retained immediately after brake pedal release, then the hill holder function works effectively on uphill slopes, but the vehicle may drag on flat roads when the transmission is in neutral range
Solution Approach 1:
The system applies preliminary action by maintaining brake fluid pressure for a predetermined time period after brake pedal release when the transmission is in neutral range. This preliminary retention prevents vehicle dragging during engine restart. After this predetermined time period elapses, the brake fluid pressure is released to enable normal vehicle operation and hill holder function when needed.
Data Source
AI summary
A vehicle control apparatus for controlling a prime mover and wheel brakes which are equipped in a vehicle with an automatic transmission. The vehicle control apparatus includes a prime mover stopping unit which stops and restarts the prime mover under predetermined conditions, and a braking force retaining unit which retains braking force of each of the wheel brakes. Even if the automatic transmission is set in a neutral range, the braking force retaining unit is controlled to retain the braking force of the wheel brakes for a first predetermined time after the operation of a brake operation member is disengaged.