Heater device for a motor vehicle

Abstract: A heater device for a motor vehicle comprises a fuel burner (4) supplied with combustion air by a blower (2), and a heat exchanger (5) for transferring heat from the combustion gas from the burner (4) to heating air which is drawn through the heat exchanger by a blower (13) and is then introduced into the passenger compartment of the vehicle. To prevent the heater device overheating when the engine of the vehicle is switched off thus stopping the blowers (2,13), sensors (32,34) detect the temperature within the heat exchanger and the burner and a sensor (33) detects the temperature of the air from the heat exchanger. Also a flame sensor (31) detects whether the burner is alight or not. These sensors send signals to a main control unit (9), and, if the temperatures sensed reach a prescribed limit, the controller switches the blowers on again by means of a switch (194) to introduce cooling air to the burner and the heat exchanger and thereby prevent the burner and the heat exchanger from being overheated.

Description: The present invention relates to a heater device for heating the passenger compartment of a motor vehicle. The passenger compartment or cabin of a motor vehicle is generally heated by a heat source employing the cooling water of the internal combustion engine of the motor vehicle. However, in cold weather, it takes time to increase the temperature of the cooling water, and hence the compartment cannot be heated quickly. Japanese Laid-Open Patent Publication No. 61-157422 discloses a proposed vehicle heater device in which fuel is combusted by a burner separate from the internal combustion engine and heat generated by the fuel combustion is recovered by a heat exchanger to supply heating air into the compartment. In the event that a heating blower is turned off by stopping the operation of the vehicle and thus turning off a main power supply, or for some other reasons while the heater device is in operation, the fuel combustion in the burner ceases, but the temperature of the heat exchanger and other components is not quickly lowered because of a heat build-up around the combustion chamber of the burner. The instant that the blower is stopped, the temperature may tend to be increased into a dangerous range. It is an object of the present invention to provide a heater device for a motor vehicle of the kind comprising a burner for combusting fuel and a heat exchanger for transferring heat between the combustion gas from the burner and heating air to be introduced into the passenger compartment of the motor vehicle, wherein the burner thereof is prevented from being subjected to an abnormal temperature increase and hence prevents the heater device itself from being brought into a dangerous condition even when the operation of the heater device is abruptly interrupted. US-A-3301248 describes a system for maintaining operation of a blower by means of a thermostatic switch which is integrally formed with a switch control unit, the thermostatic switch being operable at all times, by means of a bimetallic strip, to sense overheating of part of the heating device. WEBASTO Einbauanweisung HL 6511/6512, HL9511/9512, January 1983, over which the present invention is characterised, discloses a heater device for a motor vehicle, with heat exchanger and heater device stop detection. According to the present invention there is provided a heater device for a motor vehicle as defined in claim 1. An example of a heater device in accordance with the invention, and its mode of operation will now be described with reference to the accompanying drawings in which: Fig. 1 is a block diagram of the heater device; Fig. 2 is a graph showing how the temperature of the heater device varies with time; Fig. 3 is a flowchart of a general control sequence of the heater device; and Fig. 4 is a flowchart of a detailed control sequence of the heater device. As shown in Fig. 1, an internal combustion engine 1 such as a diesel engine or a gasoline engine has an intake pipe 3 connected to an air cleaner 40 through an air duct 30. In the air duct 30, there are disposed a combusting blower 2, a burner 4 positioned downstream of the blower 2, and a heat exchanger 5 positioned downstream of the burner 4. The air duct 30 is bypassed by a bypass pipe 51 which directly introduces air from the air cleaner 40 via the intake pipe 3 to the internal combustion engine 1. The bypass pipe 51 has a control valve 52 controlled by controller 19 (described later). The burner 4 has a combustion chamber 41, a fuel atomizer 7 inclined such that it extends from the bottom of the combustion chamber 41 near an outlet thereof toward the center of the combustion chamber 41, and an igniting glow plug 6 disposed in the combustion chamber 41 for igniting fuel as atomized by the fuel atomizer 7. The fuel atomizer 7 houses therein an atomising glow plug 71 in the form of a pipe or a rod made of a ceramic material such as silicon nitride (Si₂No₄) for heating and atomizing fuel. The atomizing glow plug 71 has a resistance wire of a positive temperature coefficient which is embedded centrally therein. The igniting glow plug 6 is in the form of a rod made of a ceramic material such as silicon nitride (Si₂No₄) and has a centrally embedded resistance wire. The igniting glow plug 6 can be heated by energizing the resistance wire. A fuel supply device 8 supplies fuel fed from a fuel pump 9 via a suction valve 35 to the fuel atomizer 7. The combustible air-fuel mixture in the combustion chamber 41 is ignited by the energized igniting glow plug 6 to produce flames and high-temperature gases which are delivered to the downstream heat exchanger 5. The combustion gases that have passed through the heat exchanger 5 are then delivered via the intake pipe 3 to the internal combustion engine 1 or via a discharge pipe 60 to an exhaust pipe (not shown) of the internal combustion engine 1, dependent on the position of a directional control valve 27 controlled by the controller 19. The heat exchanger 5 draws fresh air from an air inlet 11 communicating with the passenger compartment to be heated of the motor vehicle and transfers heat from the combustion gases to the fresh air. The hot air heated by the heat exchanger 5 is discharged through an outlet 12 into the passenger compartment by a heating air blower 13. The outlet 12 is open at the exit of a cooling water heater core 14 which is separately provided for heating the passenger compartment. A hot air temperature sensor 15 is disposed in the exit of the heater core 14 for detecting the temperature of the hot air discharged from the exit. An air blower 16, an air conditioning evaporator 17, and a hot water passage 18 are components of an air conditioning unit which utilizes the engine cooling water. While the heating blower 13 is located downstream of the heat exchanger 5 in the illustrated embodiment, the heating blower 13 may be positioned upstream, i.e., at the air inlet 11. The controller 19 comprises a main control unit 191 which is supplied with a rotation signal GT from a generator 20 driven by the engine 1, an ON/OFF signal FS from an actuating switch 21, a water temperature signal WS from a water temperature switch 22 which detects the temperature of the cooling water for the engine 1, a start position signal ST, an accelerator opening signal AS, a load signal EL from an engine load sensor 24 which detects the load condition of the engine 1, a hot air temperature signal WA from the hot air temperature sensor 15 at the outlet 12, a heating signal WP from a heating position switch 25 operated by the driver, and a plug temperature signal PS from an igniting plug sensor 26 which detects the temperature of the igniting glow plug 6. The controller 19 also includes a bridge circuit 192 for controlling the atomizing glow plug 71 of the fuel atomizer 7 so that it is heated to the temperature for atomizing the fuel, a bridge circuit 193 for controlling the igniting glow plug 6 so that it is heated to the temperature for igniting the mixture of the atomized fuel and air, and a switch assembly 194. The main control unit 191 is in the form of a computer having a processor, memories, and an input/output interface. The bridge circuit 192 comprises a Wheatstone bridge having the resistance wire for heating the atomizing glow plug 71 as one branch and three other resistance wires as other branches, a comparator for detecting the balanced condition of the Wheatstone bridge, and a relay actuatable by an output from the comparator. The relay turns on and off the resistance wire to heat the atomizing glow plug 71 to the fuel atomizing temperature, e.g., about 500° C. The bridge circuit 193 comprises a Wheatstone bridge having the resistance wire for heating the igniting glow plug 6 as one branch and three other resistance wires as other branches, a comparator for detecting the balanced condition of the Wheatstone bridge, and a relay actuatable by an output from the comparator. The relay turns on and off the resistance wire to heat the igniting glow plug 6 to the temperature for igniting the mixture of the atomized fuel and air. The switch assembly 194 has a switch 194a for turning on and off the heating blower 13, a switch 194b for controlling the supply of electric power to the bridge circuit 192, a switch 194c for controlling the supply of electric power to the bridge circuit 193, a switch 194d for controlling a bypass valve 10 in the air duct 30, and a switch 194e for turning on and off the combusting blower 2. Denoted at 28 is a power supply battery, and 29 a key switch. A flame sensor 31 detects the temperature in the combustion chamber 41 of the burner 4 to ascertain whether flames are produced in the combustion chamber 41 or not. An overheat sensor 34 is provided for preventing the burner 4 from being overheated. Another overheat sensor 32 is provided for preventing the heat exchanger 5 from being overheated. An overheat sensor 33 serves to detect the temperature of the discharged hot air heated by the heat exchanger 5. Signals from these sensors are applied to the main control unit 191 through respective signal lines which are omitted from illustration for the sake of brevity. Fig. 2 illustrates how the temperature of the burner and the heat exchanger of the heater device varies with time. As shown in Fig. 2, if the heating blower 13 is stopped after the heater device is shut off, the temperature will rise up to a dangerous temperature. However, by continuously operating the heating blower 13 after the heater device is stopped in operation, the heat can be discharged and dangerous conditions can be avoided. A general control sequence of the heater device of the invention will be described with reference to Fig. 3. First, the engine is shut off in a step S1, and then the heater device is shut off in a step S2, which is followed by turning off the main power supply in a step S3. After the heater device power supply is turned off for some reason in a step S4' or the ignition key is pulled out in a step S4, a step S5 ascertains whether or not the temperature of the heater device is equal to or lower than a prescribed temperature level. If the temperature of the heater device is equal or or lower than the prescribed temperature level, then the heating blower 13 is turned off in a step S6, and the heater device power supply is turned off in a step S7. If the temperature of the heater device is higher than the prescribed temperature level, then the heater device power supply such as a backup power supply is turned on in a step S8, and the heating blower 13 is turned on in a step S9. Therefore, the heat of the heater device is discharged, and the heater device temperature does not reach a dangerous temperature. A detailed control sequence of the heater device will be described below with reference to Fig. 4. As described above with reference to Fig. 3, when the key is pulled and a stop command is issused, the fuel pump 9 is stoped in operation in a step S11, and the suction valve 35 is operated in a step S12. The flame sensor 35 ascertains whether flames are generated or not in a step S13. Upon elapse of a preset time in a step S14, a step S15 detects whether a signal from the overheat sensor 34 in the burner 4 is below a preset value, and then a step S16 detects whether a signal from the overheat sensor 32 in the heat exchanger 5 is below a preset value. Then, a step S17 detects whether a signal from the overheat sensor 33 is below a preset value. If the signals from these sensors are higher the respective preset values in the steps S15, S16, S17, then it is determined that the heater device is backed up and remained actuated. If the signals from these sensors are below the respective preset values in the steps S15, S16, S17, then the heating blower 13 is shut off in a step S18, and, after the signal from the overheat sensor 34 reaches the preset value in a step S19, the combusting blower 2 is shut off in a step S20. Then, after the heating blower 13 and the combusting blower 2 are turned off, steps S21, S22 ascertain whether the signals from the overheat sensors 34, 32 are below the respective preset values. If not, i.e., if the temperature in the burner 4 is high and the temperature in the heat exchanger 5 is high, the combusting blower 2 is operated in a step S23. If the signals are still not below the respective preset values upon elapse of a preset time in a step S24, a warning buzzer (not shown) is turned on in a step S25, and the heating blower 13 is actuated in a step S26. If the signals are below the preset values and a preset interval of time has elapsed in a step S27, all of the device components are shut off in a step S28. With the present invention, as described above, the temperature sensors are provided in the heater device, and when the temperatures detected by the temperature sensors are higher than respective preset levels at the time the heater device is shut off, the heating blower is actuated to prevent the heater device from being overheated and hence from being brought into dangerous conditions.

Claims: A heater device for a motor vehicle, comprising a burner (4) for combusting fuel; a heat exchanger (5) for transferring heat between the combustion gas from the burner (4) and heating air to be introduced into the passenger compartment of the motor vehicle; means (31) for detecting when the burner stops its operation; means (191,194a) for actuating blower means (2,13) to introduce air into the heater device; and a temperature detecting means (32,33,34) which includes an overheat burner temperature sensor (34) for detecting the temperature of the burner (4), for preventing the burner from being overheated, an overheat temperature sensor (32) for detecting the temperature of the heat exchanger (5), for preventing the heat exchanger from being overheated, and an overheat temperature sensor (33) for detecting the temperature of the discharged hot air heated by the heat exchanger (5), characterised in that the means (191,194a) for actuating the blower means (2,13) is actuated when the respective temperature sensed by all of the temperature sensors (32,33,34) is above a prescribed respective temperature and the device stop detection means (31) has detected that the burner has stopped its operation. A heater device according to claim 1, wherein the blower means comprises a combusting blower (2) for supplying combusting air to the burner. A heater device according to claim 1 or claim 2, wherein the blower means comprises a heating blower (13) for supplying heating air from or to the heat exchanger into the passenger compartment. A device according to any of claims 1 to 3, wherein the blower (2,13) comprises a combusting blower (2) and a heating blower (13) which are separately actuated. A device according to claim 4, wherein the combusting blower (2) is shut off after the heating blower (13).

Inventors: OKADA MASAKI, OKADA, MASAKI
Applicants: ISUZU MOTORS LTD, ISUZU MOTORS LIMITED
Application year: 1987
Main classification: B60H1
IPC codes: B60H1