Engine Starter Circuit With Shared Solenoid and Braking Switches
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Solution Overview
Problem
Existing engine starter circuits in the aerospace industry suffer from unnecessary duplication of common circuits, leading to increased component count and board area, due to separate solenoid and braking circuits with high side and low side switches, necessitating a need for improvement.
Innovation Solution
A combined solenoid and braking circuit design using a common switch, inductor coil, freewheeling diodes, and insulated-gate bipolar transistors (IGBTs) with built-in-test (BIT) circuits to monitor switch states and control current flow, reducing components and board space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate solenoid and braking circuits with high side and low side switches are used, then functional reliability is improved, but device complexity and board area increase
Solution Approach 1:
The patent combines the solenoid circuit and braking circuit into a single integrated circuit board. The solenoid circuit includes a high side switch and low side switch, while the braking circuit includes a high side switch and low side switch, all mounted on the same board with shared power and ground connections. This merging reduces overall system complexity while maintaining the functional reliability of separate circuits through proper isolation and control.
Solution Approach 2:
The integrated circuit board serves multiple functions simultaneously: it houses both the solenoid control circuitry and the braking control circuitry, provides power distribution to both circuits, and enables independent control of solenoid engagement/disengagement and braking activation. This multi-functionality reduces the need for separate dedicated circuits while maintaining operational reliability.
2Adaptability or versatility
If separate solenoid and braking circuits are used, then functional independence is improved, but area occupied by circuits on circuit board increases
Solution Approach 1:
Both the solenoid circuit and braking circuit are merged onto a single circuit board with shared power rails and ground connections. The solenoid circuit uses switches S1 and S2 while the braking circuit uses switches S3 and S4, all controlled by the same microcontroller unit. This consolidation significantly reduces the board area required compared to having completely separate circuits while maintaining functional independence through independent control logic.
Solution Approach 2:
The patent utilizes the vertical dimension of the circuit board by implementing multi-layer PCB design with power and ground planes. This allows dense routing of traces and placement of components in three-dimensional space rather than just two dimensions, effectively reducing the footprint of the circuit board while maintaining all necessary functional connections and isolation.
3Device complexity
If duplication of common circuits is avoided, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The circuit board is segmented into distinct functional zones: the solenoid control section with switches S1 and S2, the braking control section with switches S3 and S4, and shared power distribution areas. Each segment has dedicated trace routing and component placement areas, which simplifies the manufacturing process by reducing the complexity of any single routing path while maintaining overall system integration.
Solution Approach 2:
The patent uses different trace widths and copper weights in different areas of the circuit board to optimize current carrying capacity and reduce heating. Power traces have higher current ratings with wider widths, while control signal traces use standard dimensions. This parameter variation allows the use of standard manufacturing tolerances while achieving precise electrical performance without requiring ultra-precise fabrication across the entire board.
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 design reduces the number of IGBTs and sense resistors, saving space and cost while maintaining functionality, and enhances fault detection through integrated BIT circuits.
Implementation Method 1
an inductor coil configured to provide current to the electric machine
Implementation Method 2
a freewheeling diode configured to provide a path for decay of current through the inductor coil
Implementation Method 3
a brake resistor circuit works by monitoring the DC bus voltage and activating the brake resistor circuit if it senses the DC link voltage above a set voltage, to absorb the excess voltage
Data Source
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AI summary
In accordance with at least one aspect of this disclosure, an engine (10) (e.g., an aircraft turbine engine) can include a turbine (12) mounted to a turbine shaft (14) to rotate the turbine. A starter system (100) can include a starter circuit (102), for example for powering the starter system to start the engine. More specifically, the starter circuit can be configured to provide power to an electric machine (e.g., an electric motor capable of also acting as a generator) coupled to the turbine shaft to drive the engine.