Common Rail Pressure Control Using Dynamic PWM Frequency Switching
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Solution Overview
Problem
The dynamic response of closed-loop pressure control in common rail systems is challenging during load reductions due to lag times and pressure oscillations, as existing methods struggle to synchronize PWM signals with pressure control, leading to rail pressure overshoot.
Innovation Solution
Implementing a dual-filter system to detect load reductions more swiftly, switching from a standard PWM frequency of 50 Hz to 500 Hz when the second actual rail pressure exceeds a limit, and reverting when it falls below a hysteresis value, allowing for temporary open-loop control to reduce lag time and rail pressure overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If closed-loop pressure control is used with standard PWM frequency (50 Hz), then system stability is maintained, but dynamic response during load reduction is too slow causing rail pressure overshoot
Solution Approach 1:
The PWM frequency is made dynamic rather than fixed. The system switches between 50 Hz and 500 Hz based on operating conditions. During load reduction, the frequency increases to 500 Hz to improve dynamic response, then returns to 50 Hz during normal operation to maintain stability and reduce heat generation.
Solution Approach 2:
The PWM frequency parameter is changed from a constant 50 Hz to a variable parameter that can be 50 Hz or 500 Hz. This parameter change allows the system to adapt its response characteristics to match the transient requirements during load reduction while maintaining normal operating stability.
2Loss of time
If PWM frequency is increased to 500 Hz during load reduction, then lag time is reduced, but heat generation in semiconductors increases
Solution Approach 1:
The high PWM frequency of 500 Hz is applied periodically only during transient load reduction events rather than continuously. The system monitors pressure gradients and activates the high frequency mode only when needed, then returns to 50 Hz for normal operation, minimizing energy consumption and heat generation.
Solution Approach 2:
The system detects the load reduction event early using pressure gradient monitoring and switches to high PWM frequency in advance of the full pressure transient. This preliminary action at higher frequency reduces the lag time more effectively, allowing the system to correct the pressure deviation before it becomes severe.
3Measurement precision
If closed-loop control is used, then pressure regulation is accurate, but synchronization between PWM signal and pressure control is difficult during load reduction
Solution Approach 1:
The system performs preliminary detection of load reduction events by monitoring pressure gradients before the full pressure transient occurs. This early detection allows the control system to prepare and switch to high PWM frequency in advance, reducing the synchronization lag between pressure measurement and control response.
Data Source
AI summary
The invention relates to a control and regulation method for an internal combustion engine having a common rail system, wherein a rail pressure is regulated in normal operation in that a first actual rail pressure is determined via a first filter from the rail pressure, an offset is calculated from a target rail pressure and the first actual rail pressure, a variable is calculated via a pressure regulator from the offset and a PWM signal having a first PWM frequency (f1) for activation of a control process is determined in dependence on the variable. A second actual rail pressure (pCR2(IST) is determined via a second filter, a load rejection is recognized if the second actual rail pressure (pCR2(IST)) exceeds a first threshold value (GW1), upon exceeding the first threshold value (GW1) the PWM signal switches over from the first PWM frequency (f1) to a second PWM frequency (f2) and the rail pressure is controlled upon exceeding a second threshold value in that the PWM signal is temporarily set to a PWM value that is higher than that of normal operation.