Vehicle HVAC Ram Pressure Control via Independent Air Doors
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Solution Overview
Problem
Vehicle HVAC systems face a decrease in fuel economy efficiency due to increased ram air pressure at higher vehicle speeds, which alters the ratio of fresh air to recirculation air, leading to higher humidity and increased compressor load.
Innovation Solution
A blower unit with a controllable ram air valve and circulating air valve, supported for independent pivotal movement, maintains a predetermined airflow ratio between fresh and recirculation air by controlling ram pressure as vehicle speed increases, using a partition in the suction passage and sensors to adjust door positions based on vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the vehicle travels at higher speeds, then the ram air pressure increases, but the ratio of fresh air to recirculation air changes unfavorably
Solution Approach 1:
The ram air valve is made dynamically controllable to adjust the exterior air intake aperture area based on vehicle speed. As speed increases and ram pressure rises, the valve dynamically reduces the aperture area to compensate, maintaining a stable fresh air to recirculation air ratio despite changing operating conditions.
Solution Approach 2:
The system changes the physical parameter of the exterior air intake aperture area through the ram air valve. By adjusting this geometric parameter in response to vehicle speed changes, the system compensates for ram pressure variations and maintains the desired airflow ratio.
2Object-affected harmful factors
If fresh air intake increases due to high ram pressure, then passenger comfort is improved, but fuel economy efficiency decreases
Solution Approach 1:
The system uses sensors to detect vehicle speed and ram pressure conditions, then feeds this information back to the controller which adjusts the ram air valve position. This closed-loop feedback mechanism ensures that fresh air intake is optimized to balance passenger comfort requirements with fuel economy efficiency.
Solution Approach 2:
The ram air valve proactively counteracts the harmful effect of excessive fresh air intake by reducing the exterior air intake aperture area before the compressor load becomes excessive. This preliminary anti-action prevents the harmful effect of increased fuel consumption while maintaining adequate fresh air supply.
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 maintains a consistent airflow ratio between fresh and recirculation air, reducing the impact of increased ram pressure on fuel economy efficiency and ensuring passenger comfort by controlling ram air pressure and preventing excessive fresh air intake at higher speeds.
Implementation Method 1
the pressure of the exterior air entering the exterior air intake of the HVAC system (i.e., the 'ram air' or 'ram pressure') is relatively high
Data Source
AI summary
A blower unit for a vehicle HVAC system, which is operable in one of a fresh air mode, a recirculation air mode and a mixture mode, comprises a housing defining an exterior fresh air intake aperture and an interior recirculation air intake aperture. A suction passage is in communication with both the exterior and interior air intake apertures. A first door is operably associated with the exterior air intake aperture for selectively opening and closing the exterior air intake aperture. A second door operably associated with the interior air intake aperture for selectively opening and closing the interior air intake aperture. The first and second doors are movable independent of each other. A partition is located in the suction passage for at least partially dividing the suction passage. The partition is selectively engaged by at least one of the first and second doors depending on the mode of the HVAC system. In the mixture mode, the first door is configured to control ram pressure as vehicle speed increases to maintain a predetermined airflow ratio between fresh air flowing into the housing via the exterior air intake aperture and recirculation air flowing into the housing via the interior air intake aperture.