Transmission Gear Preselection for Deceleration Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional transmission control systems struggle to accurately preselect gear ratios, often downshifting too aggressively or not enough, especially when descending hills or coasting at negative engine torque, failing to consider the operator's intention and varying vehicle configurations such as axle size, tire size, and engine type.
Innovation Solution
A method for controlling a transmission in a motor vehicle that includes determining an autobrake preselect state based on throttle position, engine brake status, cruise control, and road grade, calculating the required tractive braking effort, and adjusting gear ratios to match the operator's intended deceleration rate, using a transmission control circuit that communicates with an engine control circuit and sensors to optimize gear shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional transmission control systems use fixed gear ratio preselection logic, then the control system is simple to implement, but the system cannot accurately match operator intention and varying vehicle configurations
Solution Approach 1:
The system preselects gear ratios by calculating predicted vehicle acceleration based on road grade and estimated vehicle mass before actual shifting occurs. This preliminary calculation allows the transmission control to anticipate the needed gear ratio rather than reacting after the operator inputs brake pressure, improving accuracy while maintaining manageable complexity through proactive control.
Solution Approach 2:
The system continuously compares predicted vehicle acceleration with measured vehicle acceleration to calculate an error value. This feedback loop allows the transmission control to adjust gear ratio preselection dynamically based on actual vehicle behavior, significantly improving accuracy. The feedback mechanism adapts to varying vehicle configurations and operator intentions without requiring complex manual programming for each scenario.
2Speed
If the transmission downshifts aggressively to maximize braking effort, then vehicle deceleration performance is improved, but brake wear increases and drivability deteriorates
Solution Approach 1:
The system preselects the optimal gear ratio before the operator applies service brakes by predicting the vehicle acceleration based on road grade and estimated mass. This preliminary gear selection positions the transmission in the correct gear beforehand, allowing the engine brake to provide deceleration assistance without requiring excessive service brake application, thereby reducing brake wear while maintaining deceleration performance.
Solution Approach 2:
The system converts the potential harm of insufficient braking effort into a benefit by using the predicted acceleration error to select gear ratios that optimize engine brake contribution. By calculating the difference between predicted and measured acceleration, the system identifies opportunities to use engine braking to supplement service brakes, reducing overall brake wear while achieving the desired deceleration rate.
3Productivity
If the transmission uses fixed gear ratios without considering road grade, then the control logic is simple, but the system fails to optimize deceleration on hills
Solution Approach 1:
The system receives road grade measurements from a sensing device and uses this information in advance to calculate predicted vehicle acceleration. By incorporating road grade into the prediction calculation before gear selection, the system proactively adjusts gear ratio preselection for hill conditions. This preliminary consideration of road grade enables optimized deceleration efficiency without requiring complex real-time adjustments during braking.
Solution Approach 2:
The system changes the parameter used for gear ratio selection from fixed thresholds to dynamic calculations that incorporate road grade and estimated vehicle mass. By modifying the selection criteria to include these varying parameters, the system adapts to different driving conditions (flat roads vs. hills, loaded vs. empty vehicle) and achieves optimized deceleration efficiency across diverse scenarios while maintaining a unified control approach.
4Adaptability or versatility
If the transmission control calculates predicted acceleration based on estimated vehicle mass, then the system adapts to varying vehicle configurations, but the calculation complexity increases
Solution Approach 1:
The system uses the existing vehicle mass estimation data (already available for other transmission control functions) to calculate predicted acceleration. Rather than requiring separate sensors or complex measurement systems for mass, the transmission control leverages the mass estimation that the powertrain system already maintains for fuel management and performance optimization. This self-service approach enables adaptability to varying vehicle configurations without significantly increasing system complexity.
Solution Approach 2:
The vehicle mass estimation serves multiple functions simultaneously: it is used for fuel injection calculations, emission control, and now gear ratio preselection. By making the mass estimation data universal across different control systems, the patent enables the transmission control to adapt to varying vehicle configurations (passenger count, cargo weight) without adding dedicated sensors or complex measurement infrastructure. The same mass data supports multiple control objectives, reducing overall system complexity.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present disclosure provides a method of selecting a gear ratio of a transmission. The method includes measuring a current road grade with a sensing device and communicating the current road grade measurement to the controller. The controller receives a signal corresponding to a service brake input and determines a desired maximum acceleration limit of the vehicle. The method also includes calculating a predicted vehicle acceleration, measuring a current vehicle acceleration, and calculating an error value as a function of the predicted vehicle acceleration and measured vehicle acceleration. The method also computes an estimated required tractive braking effort and estimated tractive braking effort for at least one of N automatically selectable gear ratios of the transmission and selects one gear ratio of the N automatically selectable gear ratios for the operation of the transmission based on a comparison of the estimated required tractive braking effort and estimated tractive braking effort.