CVT Controller Torque Minimization for Agricultural Vehicle Brake Wear
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Solution Overview
Problem
Existing CVT systems in agricultural vehicles fail to distinguish between gravitational resistance and braking torque, leading to unnecessary brake wear, difficult hill starts, and overheating during prolonged downhill driving, as they cannot account for applied braking torque in adjusting transmission ratios.
Innovation Solution
The controller switches between feedback strategies based on brake application, varying pump displacement to minimize transmission output torque when brakes are applied, and maintaining desired wheel or engine speed when brakes are off, using signals from brake application and engine/torque sensors to adjust hydrostatic transmission settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CVT transmission ratio is varied to counteract gravitational resistance during hill starts or downhill driving, then the vehicle can maintain desired speed, but the system cannot distinguish between gravitational resistance and braking torque, leading to unnecessary brake wear and overheating
Solution Approach 1:
The patent implements a feedback mechanism using a brake application detector that provides signal input to the controller. When brakes are detected as applied, the controller receives this feedback signal and switches to a specialized control mode that minimizes transmission torque output, thereby preventing brake overheating and unnecessary wear while maintaining system reliability
Solution Approach 2:
The control system dynamically adjusts its behavior based on brake application status. The controller switches between normal speed maintenance mode and brake-assist mode, where the transmission ratio and torque output are continuously adapted to work cooperatively with the brakes, preventing brake overload during downhill driving and hill starts
2Ease of operation
If the pump displacement is set to zero when brakes are applied, then the transmission torque is minimized, but this causes unnecessary brake wear and makes smooth hill starts difficult
Solution Approach 1:
The controller uses feedback from the brake application detector to determine when brakes are engaged. During brake application, the system gradually reduces pump displacement while monitoring brake status, allowing smooth transition and coordinated operation between engine torque and brake force, preventing abrupt stops and reducing brake wear through controlled torque minimization
Solution Approach 2:
The system dynamically changes the pump displacement parameter based on brake application status. Instead of immediately setting displacement to zero, the controller gradually adjusts the displacement parameter during brake application, enabling smooth hill starts by maintaining minimal torque while brakes are engaged and preventing excessive brake wear through controlled parameter transition
3Reliability
If the transmission ratio is open loop controlled when brakes are applied, then brake application is accounted for, but this leads to unnecessary brake wear and risks overheating during prolonged downhill driving
Solution Approach 1:
The system implements closed-loop feedback control during brake application by continuously monitoring brake status through the brake application detector. The controller receives real-time feedback signals and dynamically adjusts pump displacement to minimize transmission torque output, preventing brake overheating during prolonged downhill driving while maintaining efficient brake usage and downhill driving productivity
Solution Approach 2:
The control system automatically detects brake application status and self-adjusts the transmission torque output without requiring manual intervention. The brake application detector and controller work together to automatically minimize torque during brake engagement, allowing the system to self-regulate and prevent brake overheating while maintaining efficient operation during downhill driving
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces brake wear, improves hill start performance, and prevents overheating by accurately managing transmission torque during braking, ensuring smoother operation and reduced engine-brake conflict.
Implementation Method 1
a hydrostatic transmission which comprises a variable displacement pump connected by hydraulic lines to a hydraulic motor
Implementation Method 2
The torque applied to the wheels is set in this case by varying the displacement of the pump
Data Source
AI summary
A vehicle is described having a continuously variable transmission by means of which torque is transmitted from an engine (10) to drive wheels (24) of the vehicle, a braking system (40) for applying a braking force to the drive wheels (24) and a controller (32,34) for setting the transmission ratio of the transmission in such a manner as to maintain a desired speed of the drive wheels or of the engine. In the invention means are provided for applying to the controller (34) a signal indicative of the engine applied torque (52,54;62), and means for supplying to the controller (34) a signal to indicate application of wheel brakes. The controller (34) is operative when the brakes are applied to discontinue setting the transmission ratio in dependence upon the speed of the drive wheels (24) and to set the transmission ratio instead in such a manner as to minimise the absolute value of the engine output torque or the torque transmitted through the transmission or to follow a desired torque setpoint.