Engine Injector Control Unit Fail-Safe Circuit Design
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Solution Overview
Problem
Conventional internal combustion engine control units face issues where a boost circuit failure prevents the injector from being actuated due to backflow of current, leading to increased heating and restricted engine speed, and existing solutions either fail to maintain stable operation or exacerbate heat build-up.
Innovation Solution
A control unit design that allows the injector solenoid coil to be excited using the power source voltage without boosted voltage, generating a first holding current for opening and a second, lower-intensity holding current for retention, with parallel current channels and a flywheel diode to prevent regenerative current and heat build-up, enabling fail-safe operation and high-precision control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the boost circuit is used to boost power source voltage to create boosted voltage for injector actuation, then the injector can be driven with higher current capability, but when the boost circuit goes out of order, current backflow occurs causing heating and restricting engine speed
Solution Approach 1:
The patent divides the current delivery path into two independent parallel channels: one for peak current (through boost circuit) and one for holding current (through holding current MOSFET). This segmentation ensures that if the boost circuit fails, the holding current channel can still deliver current to the injector solenoid coil, preventing complete system failure.
Solution Approach 2:
The patent introduces a holding current MOSFET as an intermediary component that provides an alternative current path when the boost circuit fails. This intermediary device enables the system to maintain basic injector operation without the boosted voltage, thereby preventing current backflow and heating issues.
2Reliability
If constant maximum current flows through the injector solenoid coil when boost circuit fails, then the injector can be driven, but heating increases greatly restricting upper limit of engine speed
Solution Approach 1:
The patent dynamically adjusts the current waveform by switching from constant maximum current to a two-stage current profile: first holding current (lower intensity) to open the injector, then second holding current (even lower intensity) to maintain the opened state. This dynamic adjustment reduces continuous heating while ensuring reliable injector actuation.
Solution Approach 2:
The patent applies partial action by using lower-intensity holding currents instead of continuous maximum current. The first holding current is sufficient to open the injector valve, and the second holding current maintains the opened state without requiring full power, thereby reducing thermal load on the system.
3Manufacturing precision
If Zener diode is added to perform steep fall of electric current, then current control is improved, but heat build-up increases necessitating further restriction of engine speed
Solution Approach 1:
The patent removes the Zener diode from the circuit by using a MOSFET-based current control system. The holding current MOSFET provides precise current control through gate voltage modulation, eliminating the need for Zener diodes and their associated heat generation while maintaining current control precision.
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
Ensures stable injector actuation even when the boost circuit fails, prevents heat build-up, and improves engine control by using lower-intensity holding currents and pre-charge currents, thereby maintaining engine performance and preventing further damage.
Implementation Method 1
the boost circuit is used to boost a power source voltage to create a boosted voltage
Implementation Method 2
with a flywheel diode to prevent regenerative current and heat build-up
Implementation Method 3
the injector solenoid coil is excited by making use of the power source voltage
Data Source
Figure 1
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Figure 3
AI summary
There is proposed a control unit for an internal combustion engine, which comprises a boost circuit, a switching element (21), a current detecting resistor (20) and a controller (14) and is designed to be actuated such that the boost circuit is used to boost a power source voltage (VB) to create a boosted voltage (VH), and the controller (14) is used to control the switching element (21) so as to enable the boosted voltage (VH) to flow to the injector solenoid coil (25). This control unit is designed such that, when the boost circuit goes out of order, the injector solenoid coil (25) is excited by making use of the power source voltage (VB) without using the boosted voltage (VH) and without creating a peak current to thereby generate a first holding current required for opening the injector and a second holding current required for retaining the opened state of the injector, the second holding current being lower in intensity than the first holding current.