CVT Output Position Control via Indirect Shaft Sensing
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Solution Overview
Problem
Existing continuously variable transmission (CVT) systems, particularly in agricultural vehicles, face inaccuracies in slow-speed maneuvering due to limitations in hydrostatic drive control, leading to potential accidents or stalling, and high-cost, unreliable sensors are not feasible for accurate feedback.
Innovation Solution
A CVT system with two rotatable non-output shafts, Hall-effect sensors, and a processing device that calculates the desired rotational position of the output shaft based on the difference between the sensed rotational positions of the non-output shafts, allowing for precise control without the need for high-accuracy sensors on the output shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall-effect sensor with tone wheel is used to sense rotational position, then the control accuracy can be improved, but the cost increases and reliability decreases at low speeds
Solution Approach 1:
The patent introduces an intermediary computational approach by using the relationship between multiple shaft positions (θ3 = r1θ1 - r2θ2) to calculate the output shaft position indirectly. This mediator approach avoids the need for direct sensing at low speeds while maintaining accuracy through mathematical relationships between faster-rotating shafts.
Solution Approach 2:
Instead of directly measuring the output shaft position with expensive high-accuracy sensors, the patent creates a computational copy of the position information by calculating it from the positions of other shafts. This copied information achieves the same control purpose without the cost and reliability issues of direct measurement.
2Measurement precision
If high-accuracy sensors are installed on the output shaft to improve control accuracy, then the measurement precision improves, but the cost becomes prohibitive
Solution Approach 1:
The patent creates a computational copy of the output shaft position information by calculating θ3 from the positions of shafts 1 and 2 using the relationship θ3 = r1θ1 - r2θ2. This copied position information achieves the same control accuracy without requiring expensive high-precision sensors on the output shaft.
Solution Approach 2:
The patent uses inexpensive Hall-effect sensors with tone wheels on intermediate shafts instead of costly high-accuracy sensors on the output shaft. The cheap sensors provide sufficient data when processed through the computational relationship, achieving high accuracy at low cost.
3Speed
If the transmission ratio control lever is set to minimum to achieve zero speed, then the theoretical speed is zero, but control inaccuracy causes unwanted vehicle movement
Solution Approach 1:
The patent implements feedback by continuously monitoring the actual positions of shafts 1 and 2 with Hall-effect sensors and comparing the calculated output shaft position θ3 with the desired position. This feedback loop allows real-time corrections to maintain precise zero-speed control despite hydrostatic drive inaccuracies.
Solution Approach 2:
The patent replaces the mechanical control lever positioning system with an electronic control system using Hall-effect sensors and computational processing. This substitution provides more precise control by using electrical sensing and digital calculation instead of mechanical linkages and manual lever positioning.
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 solution provides highly accurate control during near-zero speed operations at a reduced cost, preventing accidents and improving maneuverability in agricultural vehicles without extensive modification to existing CVT components.
Implementation Method 1
The most suitable type of sensing device for providing a speed-related feedback signal is a Hall-effect sensor operating in conjunction with a tone wheel
Data Source
Figure 1~3
Figure 4
AI summary
A continuously variable transmission (10) comprising one or more rotatable output shafts, one or more rotatable non-output shafts, one or more continuously variable transmission elements selectively interconnecting at least one said non-output shaft and one said output shaft so as to permit variation of a transmission ratio therebetween and one or more control elements for controlling the instantaneously prevailing ratio of the transmission includes one or more sensor devices for sensing the rotational position of at least one sensed, non-output shaft, and a processing device (23) for determining the rotational position of at least one said sensed, non-output shaft at a chosen instant, the processing device (23) being operatively connected to one or more said control elements to cause variation of the transmission ratio so that a said output shaft attains a desired rotational position at a chosen instant. The transmission includes two sensed, non-output shafts and two corresponding said sensor devices located for respectively sensing the rotational positions of the non-output shafts and the outputs of which sensor devices are fed to the processing device (23) that calculates the said desired rotational position of a said output shaft based on the difference between the sensed rotational positions.