Dual-Voltage Vehicle Heater Control via Capacitive Isolation
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Solution Overview
Problem
Conventional electric heating devices for motor vehicles with dual-voltage electrical systems face challenges in safely controlling high-voltage heating elements from a lower-voltage sub-system, particularly due to the risk of component destruction from voltage mismatch and the high costs and space requirements of galvanic isolation methods like opto-couplers.
Innovation Solution
The electric heating device incorporates a capacitive separating element and a control device integrated into the heating device, allowing for control signal transmission from a lower-voltage sub-system to a higher-voltage sub-system without the need for complex galvanic isolation. This is achieved through a capacitive connection between the control device and the switching element, enabling the use of alternating current signals to control the heating element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic isolation methods like opto-couplers are used to control high-voltage heating elements from a lower-voltage sub-system, then safety and component protection are improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the harmful high voltage from the control circuit by using a capacitive coupling arrangement. The control signal is transmitted through a capacitor that blocks DC voltage while allowing AC control signals to pass, thereby removing the risk of high voltage damaging the control electronics while maintaining a simple circuit structure without complex isolation components
Solution Approach 2:
The patent changes the voltage parameter in the control circuit by using AC coupling instead of DC coupling. The capacitive element blocks the high DC voltage from the high-voltage sub-system while allowing the lower-voltage AC control signals to pass through, effectively isolating the control electronics from high voltage exposure without requiring complex isolation hardware
2Device complexity
If direct voltage connection between lower-voltage control device and higher-voltage switching element is used, then device complexity is reduced, but reliability deteriorates due to voltage mismatch risks
Solution Approach 1:
The patent introduces a capacitive element as an intermediary between the lower-voltage control device and the higher-voltage switching element. This capacitor acts as a mediator that allows control signals to pass while blocking the harmful voltage mismatch, enabling a simple direct connection structure to remain reliable by filtering out the incompatible DC voltage component
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 solution effectively controls high-voltage heating elements from a lower-voltage sub-system, ensuring safe operation and reducing the risk of component destruction. It also eliminates the need for expensive and space-consuming galvanic isolation components, providing a cost-effective and compact heating device solution.
Implementation Method 1
a capacitive element (32) connected between an output of the control device and a control connection of the switching element, so that the control connection of the switching element is connected via the capacitive element to the control device
Implementation Method 2
an electric heating element (16) and a switching element (14) for controlling a current supply from the supply connection to the heating element
Data Source
AI summary
The present invention relates to a heating device for a motor vehicle with a dual-voltage vehicle electrical system. The heating device is operated with a power supply from the sub-system with the higher nominal voltage (for example 48 V), but actuated by a control device in the sub-system with the lower nominal voltage (for example 12 V). For this purpose, the heating device has a supply connection in the sub-system with the higher nominal voltage and a control connection in the sub-system with the lower nominal voltage. The control connection is disposed in particular on a control device which is integrated into the heating device and which is connected to a control connection of a switching element (power semiconductor) for controlling the heating device via a capacitive separating element in order to ensure potential isolation of the two sub-systems.