Heating device

Heating device includes: heater (2) with heating portion (6) generating heat by energization; housing (4) contains the heating portion and forms passage (18) for a heating medium between the housing and the heating portion; temperature detection means (26) detects, in the passage, temperature (T) inside the housing due to heat of the heating medium and the heating portion; and energization controlling means (40) for turning energization of the heater on/off depending on the temperature detected inside the housing. Energization of the heater is turned off to put the heater in an energization standby state if temperature detected inside the housing is equal to or greater than a first specified threshold (TS1), and is turned off to put the heater in an energization complete stop state if the temperature detected inside the housing in the energization standby state is equal to or greater than a second specified threshold (TS2).

RELATED APPLICATIONS

This is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP2013/062921 filed on May 8, 2013.

This application claims the priority of Japanese application no. 2012-108324 filed May 10, 2012, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to heating devices, and particularly to a heating device including a housing which forms a passage for a heating medium between the housing and a heating portion of a heater.

BACKGROUND ART

It is known that a heating device of this kind includes a heater having a heating portion which generates heat by energization; a housing which contains the heating portion and forms a passage for a heating medium between the housing and the heating portion; a energization controlling means for detecting the temperature of the heating medium in the passage and turning on and off the energization of the heater depending on the detected temperature of the heating medium.

Patent Document 1 discloses a protective device for protecting a water heater for electric vehicles. The protective device is provided with a heating protection means including: a temperature determination means for determining whether or not the temperature of the water heater is higher than a designated temperature based on a value detected with a temperature sensor for detecting temperature of the water heater; an off-instruction means for turning off the switch of the water heater when the temperature of the water heater is higher than the designated temperature according to a result determined by the temperature determination means; and an off-holding means for controlling the off-instruction means so as to hold the off-state of the switch when the temperature of the water heater remains higher than the designated temperature.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

When a heating medium exists in the passage, the temperature of the heating medium is controlled within a proper range by the energization controlling means for turning on/off the energization of the heater. Thus, the temperature of the heater does not abnormally rise.

On the other hand, when no or little heating medium exists in the passage due to non-supply of the heating medium to the passage, a leakage of the heating medium from the passage or other reasons, there is no or little heating medium for transferring heat from the heater. If this happens, the heating device can undergo accidental heating of an empty passage, leading to a trouble that the temperature of the heater abnormally rises.

The heating protection means of Patent Document 1 described above is disadvantageously incapable of distinguishing between a state when a heating medium exists in the passage and a state when no or little heating medium exists in the passage. For that reason, the heating protection means can be unable to detect accidental heating of an empty passage in the heating device, leading to an occurrence of smoke or fire in the heating device.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a heating device capable of detecting accidental heating of an empty passage with high accuracy and securely preventing an occurrence of smoke or fire so as to improve reliability of the heating device.

Means for Solving the Problems

In order to achieve the above-mentioned object, a heating device according to the present invention includes: a heater having a heating portion which generates heat by energization; a housing which contains the heating portion and forms a passage for a heating medium between the housing and the heating portion; a temperature detection means which detects in the passage, temperature inside the housing due to heat of the heating medium and the heating portion; and an energization controlling means for turning on and off the energization of the heater depending on the temperature inside the housing detected by the temperature detection means. The energization controlling means turns off energization of the heater to put the heater in an energization standby state if temperature inside the housing detected by the temperature detection means is equal to or greater than a first specified threshold. The energization controlling means continuously turns off energization of the heater to put the heater in an energization complete stop state if the temperature inside the housing detected in the energization standby state is equal to or greater than a second specified threshold.

Preferably, the energization controlling means should turn on energization of the heater to put the heater in an energization resuming state if the temperature inside the housing detected in the energization standby state is equal to or smaller than a third specified threshold.

Advantageous Effects of the Invention

According to the present invention, a heating device that achieves high reliability can be provided because a temperature range between the first threshold and the second threshold is designated as a range for determining heating of an empty passage, and in the standby state for energization of the heater, the energization controlling means distinguishes accidental heating of an empty passage in the heating device from normal temperature control through the heater so that the heating device promptly detects accidental heating of an empty passage with high accuracy and prevents reliably an occurrence of smoke or fire while the energization controlling means performs normal energization control of the heater.

MODE FOR CARRYING OUT THE INVENTION

A heating device in accordance with an embodiment of the present invention will now be described with reference to the attached drawings.

As shown schematically inFIG. 1, a heating device1includes a heater2and a case (housing)4which contains the heater2.

As shown schematically inFIG. 2, the heater2is an electrothermal heater which generates heat by energization. The heater2is composed of a bottomed cylindrical metal pipe6(heating portion). A coiled heating wire8such as a nichrome wire is inserted in the metal pipe6, and a heat-resistant insulating material10, such as magnesium oxide, having high electrical insulation properties and thermal conductivity is filled into the metal pipe6by pressure to seal the heating wire8.

A terminal12molded from silicon, glass and the like by casting is provided at one end opening of the metal pipe6. A lead wire14connected to the heating wire8is pulled through the terminal12. The lead wire14and an external power unit15electrically connected to the lead wire14constitute an energization circuit (not shown) for providing the heating wire8with electricity. Although only one heater2is shown inFIG. 1, two or more heaters2may be provided.

The case4is composed of one or more cast bodies. The case4contains the heater2by airtightly surrounding vicinities of both ends of the metal pipe6through O-rings16. Clearance is created between an inner surface4aof the case4and an outer circumference6aof the metal pipe6. The clearance serves as a passage18into which a heating medium as a LLC (coolant, antifreeze), such as ethylene glycol, flows. An inlet pipe20and an outlet pipe22for the heating medium are protrusively provided at appropriate positions on an outer surface4bof the case4so that the both pipes communicate with the passage.

The heating device1having such a schematic configuration, which is to be mounted, for example, in a hybrid car, an electric vehicle and the like, is used to heat a coolant or the like circulating through a refrigeration circuit in an air conditioning apparatus for a vehicle, serving as an auxiliary heat source for providing heat to make up a shortage in waste heat out of the engine in the case of a hybrid car, or as an alternative heat source for providing heat in place of the engine that does not exist in the case of an electric vehicle.

For example, in the case of a hybrid car, an LLC circulating in a cooling water circuit (not shown) for cooling an engine flows via the inlet pipe20into the passage18, and the heater2heats the LLC. Heat from the LLC which has been heated by the engine and the heating device1is used to heat a coolant circulating through a refrigeration circuit provided in an air conditioning apparatus for the vehicle. The heated coolant is used to heat and cool the air in the vehicle cabin. The LLC which has been used for heating the coolant is discharged from the passage18via the outlet pipe22and returned to the cooling water circuit. Then, the LLC is again used to cool the engine.

According to the present embodiment, a through-hole24is bored into the case4in a direction perpendicular to the longitudinal direction of the heater2. A temperature sensor26(temperature detection means) for detecting the temperature of a LLC which flows through the passage18is inserted in the through-hole24. The temperature sensor26is a roughly cylindrical shaped thermistor. An end face30of a temperature measurement end28of the sensor26comes into contact with the outer circumference6aof the metal pipe6of the heater2. This enables the temperature sensor26to detect not only the temperature of the LLC but also the surface temperature of the metal pipe6, i.e. the heating portion of the heater2.

Two annular grooves32are formed on a side26aof the temperature sensor26. An O-ring34is fitted to each annular groove32. The temperature sensor26is airtightly connected to and secured to the through-hole24through the O-ring34.

The temperature sensor26is electrically connected to an inverter40through a lead wire38pulled out of its outer end36. The inverter40controls energization (energization controlling means) by turning on and off the energization of the heater2in response to the temperature of the LLC and/or the surface temperature of the metal pipe6detected with the temperature sensor26through the power unit15and the energization circuit described above.

When an LLC exists in the passage18, the temperature of the LLC is controlled within a proper range by the use of the temperature sensor26under this energization control. Thus, the temperature of the heater2does not abnormally rise.

On the other hand, conventionally, when no or little LLC exists in the passage18due to absence of the LLC supply to the cooling water circuit, a leakage of the LLC from the cooling water circuit or other reasons, there is no or little heating medium for transferring heat from the heater2. If this happens, the heating device1can undergo accidental heating of an empty passage, leading to a trouble that the temperature of the heater2itself abnormally rises. Even when such accidental heating of an empty passage occurs, the heating device1having the temperature sensor26, which is out of contact with the metal pipe6and capable of detecting only the temperature of the LLC in the case of a conventional heating device, can undergo a deterioration in the responsiveness of the temperature sensor26due to the heat-insulation effect of the air surrounding the temperature sensor26, leading to a delay in the detection of such accidental heating. As a result, temperature in the passage18can go on to increase, causing an occurrence of smoke or fire in the heating device1.

In contrast, the present embodiment provides energization control by taking advantage of a difference in heat transfer property between the LLC as a fluid and the air as a gas, that is, the temperature of the LLC becomes dominant when the LLC exists in the passage18and the temperature of the heater2becomes dominant when no or little LLC exists in the passage18, as the temperature sensor26is brought into direct contact with the outer circumference6aof the metal pipe6, i.e. the heating portion of the heater2, while the temperature sensor26is placed in the passage18where the LLC flows.

Energization control performed by the inverter40will now be described with reference to the flowchart ofFIG. 3and the diagrams ofFIGS. 4 and 5each chronologically showing a relationship between the energization status of the heater2and a temperature T detected with the temperature sensor26.

When a control routine for the energization control starts upon energization of the heater2, it is firstly determined whether or not a temperature (temperature inside the housing) T calculated on both the temperature of the LLC in the passage18and the surface temperature of the metal pipe6detected with the temperature sensor26is equal to or greater than a first specified threshold TS1(step S1).

If the temperature T is evaluated to be true (YES) in the step S1, i.e., the expression T≧TS1holds true, the inverter40turns off the energization of the heater2to put the heater2in a standby state (a wait state) (step S2) as shown inFIGS. 4 and 5.

If the temperature T is evaluated to be false (NO) in the step S1, i.e., the expression T≧TS1does not hold true, the inverter40maintains the energization of the heater2and transitions to the step S1again as shown inFIGS. 4 and 5.

Next, when the inverter40is in the wait state of the step S2, it is determined whether or not the temperature T detected with the temperature sensor26is equal to or greater than a second specified threshold TS2(step S3).

If the temperature T is evaluated to be true (YES) in the step S3, i.e., the expression T≧TS2holds true, the inverter40determines that no LLC exists in the passage18or the quantity of the LLC is smaller than a normal level, i.e., the heater2is heating an empty passage. Then, as shown inFIG. 5, the heater2enters an energization complete stop state (a sleep state) in which the energization of the heater2is continuously turned off as a process correcting the abnormally high-temperature state of the heating device1, and it does not automatically resume a subsequent energization process (step S4).

If the temperature T is evaluated to be false (NO) in the step S3, i.e., the expression T≧TS2does not hold true, it is determined whether or not the temperature T detected with the temperature sensor26in the wait state described above is smaller equal to or than a third specified threshold TS3(step S5).

If the temperature T is evaluated to be true (YES) in the step S5, i.e., the expression T≦TS3holds true, the inverter40determines that the passage18contains a proper quantity of the LLC, and puts the heater2in an energization resuming state so as to resume normal energization control by turning on the energization of the heater2as shown inFIG. 4(step S6).

If the temperature T is evaluated to be false (NO) in the step S5, i.e., the expression T≦TS3does not hold true, the inverter40maintains the non-energization of the heater2and transitions to the step S3again as shown inFIG. 4.

In the embodiment described above, a temperature range between the first threshold TS1and the second threshold TS2is designated as a range for determining heating of an empty passage. Then, in the standby state (wait state) for energization of the heater2, the inverter40distinguishes accidental heating of an empty passage in the heating device1from normal temperature control through the heater2. If heating of an empty passage is evaluated to be true, the inverter40puts the heater2in the energization complete stop state (sleep state) in which the energization of the heater2is continuously turned off and subsequent energization cannot be automatically resumed.

Moreover, when the temperature T becomes equal to or smaller than the third threshold TS3, the inverter40is enabled to put the heater2in the energization resuming state by returning from the standby state for energization of the heater2. The energization control provides normal energization control without unnecessarily stopping the heating device1for protection when an LLC exists in the passage18while the energization control provides error processing to stop promptly the heating device1for protection when no or little LLC exists in the passage18. Thus, it is possible to provide the heating device1that achieves high reliability as it promptly detects accidental heating of an empty passage with high accuracy and prevents reliably an occurrence of smoke or fire while performing normal energization control of the heater2by the use of the temperature sensor26.

The present invention is not limited to the embodiment of the heating device1described above, but various modifications may be made.

For example, the heating device1according to the present invention is not limited to use in a car air conditioning apparatus of an hybrid car or an electric vehicle, but can be used as a heat source for other purposes.

EXPLANATION OF REFERENCE SIGNS