Hydraulic Motor Speed Estimation Without Wheel Hub Sensors
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Solution Overview
Problem
Existing hydrostatic drive systems in mobile working machines face challenges in accurately measuring output speed due to the high cost and complexity of speed encoders, efficiency losses from oil immersion, and structural constraints in wheel hub motors, making traditional speed sensors impractical.
Innovation Solution
A method to determine hydraulic motor velocity using operating variables such as the angle of inclination, hydraulic pump and motor displacement, and fluid leakage functions, eliminating the need for speed sensors by calculating motor speed through formulas and adapting a leakage model to vehicle-specific conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a speed encoder wheel is used to measure output speed, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical speed encoder wheel with a calculation-based approach using operating variables (pump discharge flow, motor displacement, leakage functions) to determine motor velocity. This substitution eliminates the need for physical speed sensors while maintaining measurement accuracy through mathematical relationships inherent in the hydrostatic drive system.
Solution Approach 2:
The system uses its own operating variables (discharge flow from pump, displacement of motor, leakage characteristics) to self-determine the motor velocity without external measurement devices. The hydrostatic drive system's inherent parameters serve the dual purpose of operation and self-measurement.
2Measurement precision
If a speed encoder wheel is used to measure output speed, then measurement precision is improved, but loss of energy increases due to oil immersion friction
Solution Approach 1:
The patent eliminates the mechanical encoder wheel that operates in oil by using a calculation method based on hydraulic parameters. This substitution removes the source of frictional energy loss while maintaining the ability to measure output speed through mathematical relationships between pump flow, motor displacement, and leakage.
3Measurement precision
If multiple speed sensors are used in machines with multiple motors, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies the same calculation method to all motors in the system, using each motor's specific operating variables (discharge flow, displacement, leakage functions) to determine velocity. This universal approach eliminates the need for multiple different sensor systems while maintaining measurement capability across all motors.
4Measurement precision
If speed sensors are integrated in wheel hub motors, then measurement precision is improved, but ease of manufacture decreases due to structural constraints
Solution Approach 1:
The patent replaces physical speed sensors with a calculation approach that uses operating variables obtainable from the motor's normal operation. This substitution eliminates the need for additional components that would be difficult to integrate into the compact wheel hub motor structure, thereby improving ease of manufacture while maintaining measurement capability.
Data Source
Figure 1
AI summary
The present invention relates to a Method for determining a velocity of at least one hydraulic motor (3) in a hydrostatic drive system of a mobile working machine, wherein said hydrostatic drive system comprises a drive motor and a hydraulic pump (12), the rotation of which is ensured by said drive motor, and said at least one hydraulic motor (3) connected in a closed circuit to said hydraulic pump (12), wherein said hydraulic pump (12) has an adjustment unit (16) for adjusting the displacement of said hydraulic pump (12), wherein said displacement is adjustable by adjusting an angle of inclination (αpmp) of an inclined element (2), said method comprises the following steps: a. Detecting a first operating variable, which corresponds to an actual angle of inclination (αpmp) of said inclined element (2) or a quantity dependent thereon; b. Detecting a second operating variable, which corresponds to an actual revolution speed of said hydraulic pump (12) or a quantity dependent thereon; c. Detecting a third operating variable, which corresponds to a displacement of said at least one hydraulic motor or a quantity dependent thereon; d. Determining said velocity of said at least one hydraulic motor (3) based on said first, said second and said third operating variable.