Fuel Injector Drive Circuit Diagnostics Without Pre-Start Injection
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Solution Overview
Problem
Conventional load drive devices for fuel injection systems in vehicle engines face challenges in diagnosing the operation of the emergency stop mechanism, particularly when the pre-driver IC lacks an enable function, and in monitoring small injector currents, which affects the reliability of fuel injection control.
Innovation Solution
A load drive device configuration that includes first and second switching elements, a pre-driver circuit, and an arithmetic device with monitor lines and a current cut-off circuit, allowing for diagnostic control modes to monitor and diagnose the pre-driver reset mechanism without actual fuel injection, using voltage difference monitoring and control modes to ensure reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pre-driver IC with enable function is used to control injector current, then the injector can be prevented from actual fuel injection, but it is impossible to deal with cases where the pre-driver IC does not have an enable function
Solution Approach 1:
The patent introduces a current cut-off circuit as an intermediary component between the pre-driver IC and the injector. This circuit includes a cut-off transistor controlled by a reset signal from the CPU, allowing it to intercept and stop the injector drive current regardless of whether the pre-driver IC has an enable function. This mediator approach enables universal application across different pre-driver IC types while maintaining functional safety.
2Measurement precision
If the injector current is actually monitored to diagnose emergency stop mechanism, then diagnostic accuracy is improved, but it is required to monitor a minute small voltage of about 10 mV that exceeds reading accuracy of an MPU
Solution Approach 1:
The patent transforms the monitoring approach from directly measuring the small voltage across the injector to monitoring the gate signal voltage from the pre-driver IC. By shifting the measurement to another dimension (the control signal domain rather than the load current domain), the system achieves diagnostic capability without needing to measure the minute 10 mV voltage that exceeds MPU reading accuracy.
3Adaptability or versatility
If all the control currents of the injector are not necessarily about 1 A, then the control can be adapted to different injector specifications, but it is required to define a current that prevents the injector from injecting every time the injector specifications are changed
Solution Approach 1:
The current cut-off circuit is designed to work with the existing pre-driver IC control mechanism. The cut-off transistor is controlled by a reset signal that is already generated by the CPU for emergency stop functions. This self-service approach allows the system to adapt to different injector specifications without requiring additional configuration, as the cut-off circuit automatically responds to the reset signal regardless of the specific injector current requirements.
4Reliability
If a pre-driver reset mechanism is used to perform emergency stop on the injector, then the emergency stop function is achieved, but it is required to diagnose that the emergency stop mechanism is operating normally as a functional safety requirement
Solution Approach 1:
The patent implements a feedback mechanism where the CPU monitors the gate signal from the pre-driver IC to verify that the emergency stop mechanism is operating correctly. After issuing a reset signal to stop the injector, the CPU reads the gate signal to confirm that the pre-driver IC has properly responded by stopping the drive current. This feedback loop provides automatic diagnostic capability that verifies the emergency stop function without adding significant system complexity.
Data Source
AI summary
Provided is a load drive device for controlling a fuel injection device for a vehicle engine and capable of checking an operation of the fuel injection device with high reliability without actually injecting fuel before starting the engine. The load drive device includes: a first switching element that is connected to a high-side of a load; a second switching element that is connected to a low-side of the load; a pre-driver circuit that transmits a drive instruction to the first switching element and the second switching element; and an arithmetic device that transmits a control instruction to the pre-driver circuit, in which a first monitor line and the second monitor line are connected to the arithmetic device, the first monitor line monitoring the drive instruction from the pre-driver circuit to the first switching element before starting an engine, and the second monitor line monitoring the drive instruction from the pre-driver circuit to the second switching element, and the pre-driver circuit has a first control mode in which the first switching element is turned off and the drive instruction is transmitted to the second switching element, and a second control mode in which the second switching element is turned off and the drive instruction is transmitted to the first switching element.