CVT Electronic Controller Hydraulic Lag Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Torque-controlled continuously variable transmissions (CVTs) face instability and difficulty in maintaining a constant low speed ratio due to hydromechanical damping, which causes phase lag and potential positive feedback, making it challenging to rapidly adjust reaction torque and maintain stable control, especially at low vehicle speeds.
Innovation Solution
An electronic controller that measures and compares the speed ratio of a CVT, determines a transmission output torque request, converts it to a control pressure request, differentiates the pressure request to account for time lag, and outputs the compensated pressure request to the hydraulic valve arrangement to stabilize the transmission ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If hydromechanical damping is used in the hydraulic arrangement, then the variator provides stable operation, but phase lag occurs and positive feedback may arise, causing instability and difficulty in maintaining constant low speed ratio
Solution Approach 1:
The electronic controller performs preliminary differentiation of the control pressure request to anticipate the hydraulic response lag. By calculating the time derivative of the desired pressure and applying compensation in advance, the system counteracts the phase lag before it causes instability, enabling stable low-speed operation without sacrificing responsiveness
Solution Approach 2:
The controller implements closed-loop feedback by continuously measuring the actual transmission ratio, comparing it with the target ratio, and adjusting the control pressure accordingly. The feedback mechanism includes differentiation of the control pressure request to compensate for hydraulic lag, creating a self-correcting system that maintains stability while responding to load changes
2Speed
If the electronic controller rapidly adjusts reaction torque to maintain constant speed, then responsiveness to load changes improves, but hydraulic phase lag causes instability and oscillation
Solution Approach 1:
The controller applies preliminary compensation by differentiating the control pressure request before sending it to the hydraulic valve. This anticipatory action accounts for the hydraulic system's inherent time lag, allowing rapid torque adjustment without inducing oscillations or instability in the transmission ratio
Solution Approach 2:
The control system dynamically adjusts the control pressure based on the rate of change of the desired pressure. By continuously differentiating the pressure request and applying dynamic compensation, the system adapts to varying load conditions while maintaining stability, enabling rapid response without sacrificing control stability
3Speed
If the transmission operates at very low speeds to drive the vehicle slowly, then mobility in difficult terrain improves, but control of the variator becomes difficult due to phase lag and instability
Solution Approach 1:
The electronic controller implements continuous feedback control by measuring the actual transmission ratio, comparing it with the target ratio, and adjusting the control pressure accordingly. This closed-loop feedback mechanism maintains ease of operation at very low speeds by automatically compensating for phase lag and preventing instability, allowing the vehicle to operate slowly in difficult terrain without manual intervention
Solution Approach 2:
The controller applies preliminary differentiation compensation to the control pressure request before it reaches the hydraulic system. This anticipatory adjustment counteracts the phase lag that would otherwise make variator control difficult at low speeds, enabling smooth and stable operation in challenging terrain conditions
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
The electronic controller provides highly stable control of vehicle wheel speed, effectively managing rapid changes in wheel load and maintaining a constant speed over obstacles, as demonstrated in the 'beam' test, by compensating for hydraulic time lag and ensuring rapid reaction torque adjustments.
Implementation Method 1
a hydraulic arrangement for applying to the actuator(s) at least one hydraulic control pressure which determines force applied by the actuator(s) and thus determines the reaction torque
Implementation Method 2
A variator of toroidal-race rolling-traction type... rollers 20a, b running on the recessed surfaces... rollers serve to transfer drive between the input and output races
Implementation Method 3
Problems arise, however, in controlling the variator under such conditions... instability and difficulty in maintaining a constant low speed ratio due to hydromechanical damping, which causes phase lag
Data Source
AI summary
The invention concerns an electronic controller for a continuously variable transmission of the type having a variator (10) with a rotary variator input (17) coupled to a first variator race (14a) and a rotary variator output (29) coupled to a second variator race (16a). At least one roller (20) runs upon the said races to transfer drive from one to the other. The roller is movable to steplessly vary the variator ratio. The variator further comprises at least one hydraulic actuator (36), (38) which acts upon the roller and through which net torque acting on the variator races is referred via the roller to the variator's casing. A hydraulic arrangement is provided for applying to the actuator at least one hydraulic control pressure which determines force applied’ by the actuator and thus determines the reaction torque. The variator is coupled between a rotary transmission input (17) and a rotary transmission output (714) such that the transmission ratio is a function of the variator ratio. The electronic controller is adapted to cany out the following steps in a loop: measure a speed ratio of the continuously variable transmission; compare the measured speed ratio with a target speed ratio; determine a transmission output torque request on the basis of the said comparison; convert the output torque request to a control pressure request, taking account of the speed ratio; differentiate the control pressure request with respect to lime to obtain a compensation value and apply the compensation value to the control pressure request; and output the resulting compensated control pressure request to the hydraulic valve arrangement.