Electric resistance heating devices – Heating devices – Continuous flow type fluid heater
Reexamination Certificate
1999-12-13
2001-01-23
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Continuous flow type fluid heater
C392S377000, C165S175000, C165S181000
Reexamination Certificate
active
06178292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a heat exchanger of a heater in which an electric heater is disposed integrally therewith to heat air in addition to hot water heated by a vehicle engine.
2. Description of the Related Art
Conventional heat exchangers having an integrated electric heater therein are disclosed in JP-A-5-69732 and JP-A-63-203411. A heat exchanger of a heater in which hot water or engine coolant is used to heat air is provided with an integrated electric heater. When the coolant temperature is low, for example when the engine is just started, the electric heater is turned on to generate heat, thereby heating air. This structure reduces pressure loss in the heating air blow system of the heater as compared with a structure having a separate PTC heater. Because the PTC heater has a positive temperature characteristic sharply changing the resistance thereof at a set temperature, it is not necessary to provide a temperature control circuit so that the driving circuit thereof can be made simple.
The electric heater is composed of a PTC element and electrodes and is soldered to a heat exchanger core. Therefore, the PTC element is exposed to high-temperature air for soldering (e.g. 600° C. for soldering aluminum members) and, accordingly, the electric characteristic of the heater element may be damaged substantially.
In a common air conditioning system for a vehicle, a heat exchanger of a heater is disposed at a downstream side of a heat exchanger for cooling air to control reheating by the heat exchanger of the heater, thereby controlling temperature of the air blown into the passenger compartment of the vehicle. Therefore, condensed water formed on the heat exchanger for cooling air or snow coming from the air inlet may adhere the front surface of the heat exchanger of the heater. Because the electric heater is exposed to the outside from the heat exchanger core, the water or snow may cause short circuiting or electric leakage.
In the above conventional device disclosed in the publication, it is only disclosed that the set temperature of the PTC heater is 80° C. There is no explanation about how to decide the set temperature. Our experiments have revealed that the heat generated by the PTC heater may not be utilized for the heating air to be heated if the set temperature of the PTC heater is not suitable.
In a core unit of a heat exchanger, a plurality of flat tubes for conducting water or engine coolant are parallelly disposed, and each of a plurality of corrugated fins is disposed between two of the flat tubes. If a PTC heater is installed in place of one of the flat tubes, the heat of the PTC heater is conducted via the corrugated fins and the adjacent flat tubes to the water. If the PTC heater is powered when the water temperature is low, temperature of portions of the corrugated fins adjacent to the PTC heater becomes higher than the temperature of portions of the corrugated fins adjacent to the flat tubes. If the set temperature of the PTC is too high, the heat generated by the PTC heater is transmitted to the water. That is, the PTC heater can not heat the heating air to be used for the heater effectively. On the other hand, if the set temperature is too low, the PTC heater can not generate power sufficient to heat the heating air.
SUMMARY OF THE INVENTION
The present invention has been made, in view of the above problems, to provide a core unit of a heat exchanger in which an electric heater can be installed without damage.
According to a feature of the present invention, a core unit of a heat exchanger is composed of a plurality of parallel flat tubes, a plurality of corrugated fins, a support member disposed between two of the corrugated fins, and an electric heater disposed inside the support member. The support member has a pair of parallel plates bonded to the corrugated fins at the summit of corrugation, and the electric heater comprises a heating element and an insulation member inserted between the heating element and the parallel plates.
Accordingly, the support plates can be soldered to the corrugated fins before the electric heater is inserted between the two support plates. Therefore, the electric characteristic of the electric heater is not damaged during the soldering step of the core unit. Although the corrugated fins have complicated shape, the electric heater can be inserted easily without damage to the corrugated fins. Further, because the electric heater is inserted between and insulated from the two support plates, electric current can be supplied to the electric heater without passing metal portions (tubes, etc.) of the core unit, so that electric corrosion of the metal portions of the core unit can be prevented. Moreover, even if the height of the corrugations of the corrugated fins are formed uneven, solder melts and moves due to capillarity and fills gaps between the summits of the corrugation of the corrugated fins and the support plates. Thus, the summits of corrugation of the corrugated fins can be soldered to the support plates with confidence, and heat generated by the electric heater can be conducted from the support plates to the corrugated fins effectively.
It is another object of the present invention to prevent short circuiting and electric leakage caused by condensed water or the like.
According to another feature of the present invention, a core unit of a heat exchanger core having an air inlet side and an air outlet side includes a plurality of parallelly disposed flat tubes which conduct the heat carrier, a plurality of corrugated fins, a U-shaped support member having a pair of plates parallelly extending along the flat tubes, an opening end portion and a U-shaped closing end portion, and an electric heater disposed between the support plates and insulated from the support member. The support member is disposed between the summits of corrugation of adjacent two of the corrugated fins, the U-shaped closing end portion is disposed at the air inlet side, and each of the plates is bonded to one of the corrugated fins at the summits of corrugation. The opening end portion preferably projects from an end of the electric heater. The opening end portion may spread in a skirt-shape. The support member may have the same thickness as the core unit in the air flow direction, and the electric heater may have smaller thickness in the direction of core thickness than the support member.
Because the U-shaped closing portion of the support member is disposed at the air inlet side of the heat exchanger core, the closing portion prevents water from entering the inside of the support member even if water adheres to an upstream portion of the core unit. Therefore, condensed water can not adhere to the electric heater, and the short circuiting or electric leak of the electric heater due to water is prevented. Because the opening portion of the support member projects from an end of the electric heater, water can be prevented from adhering to the electric heater even if water moves along the surface of the support member to the opening portion.
It is another object of the present invention is to provide an improved core unit of a heat exchanger for heating air by hot water or engine coolant having a PTC heater which can heat the heating air at a maximum efficiency.
According to another feature of the present invention, a core unit of a heat exchanger core includes a plurality of parallelly disposed flat tubes which conduct the heat carrier, a plurality of corrugated fins having summits of corrugation disposed between two of the flat tubes, and an electric heater disposed between two of the summits of corrugation instead of one of the flat tubes. The electric heater has a positive temperature characteristic sharply changing resistance thereof at a set temperature and heats portions of the fins adjacent to the flat tubes at a temperature equal to temperature of water in the flat tubes if the water temperature is equal to or higher than 60° C. and temperature of air to be heated is equal to
Aki Yoshifumi
Fukuoka Mikio
Kamiya Sadayuki
Kuroyanagi Isao
Nakamura Mitsugu
Campbell Thor
Denso Corporation
Harness Dickey & Pierce PLC
Walberg Teresa
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