Brushless AC Starter Motor Hybrid Sensor Control
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Solution Overview
Problem
Existing starter motor systems for internal combustion engines face challenges in accurately controlling torque, especially at low speeds, due to the reliance on position sensors which can be costly and less effective above a certain speed threshold, limiting power level and flux-weakening control.
Innovation Solution
A hybrid sensor/sensorless control methodology is implemented, where the controller uses measured angular position signals from position sensors below 1000 RPM to calibrate sensorless logic, and transitions to exclusive sensorless logic above this speed, enabling precise torque control and improved flux-weakening without the need for expensive absolute position sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position sensors are used for torque control at low speeds, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The control system is segmented into two distinct modes: sensor-based control for low speeds (0-1000 RPM) and sensorless control for high speeds (above 1000 RPM). This segmentation allows each mode to operate in its optimal performance range, using sensors only when their measurement precision is most valuable at low speeds, and transitioning to sensorless operation at higher speeds to reduce complexity and cost.
Solution Approach 2:
The system dynamically changes the control parameter basis based on speed threshold. Below 1000 RPM, the controller uses measured angular position signals from position sensors; above 1000 RPM, it transitions to using estimated angular position from sensorless logic. This parameter change resolves the contradiction by adapting the measurement approach to the operating conditions.
2Measurement precision
If position sensors are used above threshold speed, then control accuracy is maintained, but cost increases due to expensive absolute position sensors
Solution Approach 1:
The position sensors are extracted from the system for high-speed operation. The controller is designed to use sensor-based control only when needed (below 1000 RPM) and transitions to sensorless control above this threshold, effectively removing the expensive sensing requirement for high-speed operation while maintaining control accuracy through the sensorless estimation algorithm.
Solution Approach 2:
The control system dynamically adapts its operation mode based on the speed threshold. The controller automatically switches between sensor-based and sensorless control modes, making the system flexible and cost-effective by using expensive sensors only when necessary for low-speed precision control.
3Device complexity
If sensorless logic is used exclusively, then device complexity is reduced, but measurement precision deteriorates at low speeds
Solution Approach 1:
The position sensors provide preliminary accurate measurement data during the low-speed cranking phase (below 1000 RPM), which is critical for engine starting. This preliminary sensor-based operation ensures precise torque control when the engine is most vulnerable during startup, before transitioning to sensorless control at higher speeds.
Solution Approach 2:
The system dynamically selects the appropriate control mode based on operating speed. At low speeds where precision is critical, sensor-based control is used. At high speeds where sensorless control is sufficient, the system transitions to the simpler sensorless mode, optimizing both precision and complexity across the full operating range.
4Power
If hybrid sensor/sensorless control is implemented, then power level and flux-weakening control are improved, but control complexity increases
Solution Approach 1:
The controller changes the control parameter basis based on the speed threshold (1000 RPM). Below this threshold, measured angular position signals are used for optimal low-speed torque control and flux-weakening. Above the threshold, estimated angular position from sensorless logic is used, maintaining power level control while simplifying the system architecture.
Solution Approach 2:
The system uses feedback from the speed threshold condition to automatically switch between control modes. The controller monitors starter motor speed and uses this feedback to determine whether to engage sensor-based or sensorless control, enabling the hybrid approach to improve power and flux-weakening control while managing complexity through automated mode selection.
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 achieves enhanced power level and improved flux-weakening control of the starter motor across varying speeds, reducing the reliance on costly sensors and ensuring accurate torque delivery, thereby improving the overall efficiency and cost-effectiveness of the starter motor system.
Implementation Method 1
the position sensors may be optionally embodied as multiplying rotary encoders, digital or analog Hall-effect sensors
Implementation Method 2
the sensorless logic possibly such techniques as back-electromotive force (BEMF), inductance, or high-frequency signal injection
Data Source
AI summary
An electric starter system includes a brushless alternating current (AC) starter motor selectively coupled to an engine and having a rotor with a rotor position. A position sensor generates measured position signals indicative of rotor position. A controller is in communication with the sensor. The controller has sensorless logic, e.g., a BEMF, inductance, or high-frequency signal injection method, for generating an estimated rotor position. The controller executes a method in which, below a threshold speed of the starter motor, the controller calibrates the sensorless logic using the measured position signals and controls a torque operation of the starter motor using the measured position signals. Above the threshold speed, the torque operation is controlled solely using the estimated rotor position. A powertrain includes the engine, a transmission, a drive shaft, and a load, along with the electric starter system.