HEATER CONTROLLER

Abstract: A controller for a heater (4) includes first and second switch circuits (l0,l2) for controlling the supply of electric power to an atomising glow plug (7) for atomising fuel and an ignition glow plug (8) for igniting the atomised fuel. The glow plugs are connected basically in parallel with each other, although a resistor (14) may be included in series with the atomising glow plug. The second switch circuit includes a series-connected resistor (11) for producing a voltage drop thereacross. During an initial period of operation of the heater as determined by a controller (16), the first switch circuit, which is free of series-connected resistance, is turned on to heat the glow plugs quickly up to respective prescribed temperatures for atomising and igniting the fuel. Upon elapse of a predetermined period of time during which the prescribed temperatures are reached, the first switch circuit is turned off and the second switch circuit with the series-connected resistor is turned on to keep the glow plugs at the prescribed temperatures whilst avoiding overheating them.

Description: This invention relates to a controller for controlling a heater which heats the interior of a vehicle passenger compartment or the like. Conventional vehicle passenger compartments are heated by introducing a coolant from the internal combustion engine, via a coolant pipe, into a heater assembly comprising a heater core and a blower, and passing air through the heater assembly so that the air heated by heat exchange from the heater core can be used for heating purposes. Such an arrangement utilising engine coolant is, however, disadvantageous for the following reasons: Since it takes more than l0 minutes for a petrol engine, or more than 20 minutes for a diesel engine, to be warmed up, the coolant is not available for heating the compartment during that time interval. Therefore, especially in colder climates, travellers in the compartment have to wear clothes designed for protecting against cold weather during such warm-up interval. The defroster for removing frost or ice from the window glass sheets does not work well until the temperature of the coolant is high enough. Another problem with the conventional heaters is that when the automobile is running down a long downward slope, the coolant temperature may fall to such an extent that the coolant is no longer effective in heating the compartment. In particular, since a diesel engine is of the type in which an air-fuel mixture is compressed in each engine cylinder and is ignited by the heat produced by the compression of the mixture under high pressure, the temperature of the exhaust gas and the coolant temperature are very apt to decrease when the vehicle is travelling down a downward slope, because only a light load is then imposed on the engine. Furthermore, a diesel engine tends to produce white smoke and odour, due to incomplete fuel combustion, under cold conditions. To eliminate the above drawbacks, the applicant has filed European Patent Application No. EP-A-0163418 in respect of an automotive heater in which a burner is provided in the air intake pipe of an engine and a heat exchanger is disposed downstream of the burner, so that heat produced by burning fuel in the burner will be recovered by the heat exchanger as a heat source. A control device therein for controlling the temperature of an atomising glow plug in a fuel atomiser of the burner and the temperature of an igniting glow plug for igniting atomised fuel has respective bridges for the glow plugs, making the control apparatus somewhat complex. It is an object of the present invention to provide a controller for controlling a heater, which has a simple control apparatus for controlling the supply of electric power to an atomising glow plug in a fuel atomiser of a burner of the heater and to an igniting glow plug for igniting atomised fuel, so that heated air can be obtained immediately after the heater is started. According to the present invention, there is provided a controller for controlling a heater including a burner having an atomising glow plug for heating and atomising fuel and an ignition glow plug for igniting the fuel which has been heated and atomised by the atomising glow plug; characterised by a first switch for supplying electric power to the atomising glow plug and the igniting glow plug which are connected in a parallel circuit; a second switch connected in series with resistance means, the series circuit being connected in parallel with the first switch; means for closing the first switch and, after a predetermined period of time, opening the first switch and closing the second switch; and means for cutting off the supply of electric power to the atomising and ignition glow plugs when the temperature in the burner has reached a predetermined value. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a cross-sectional view of a burner employed in a heater; Fig. 2 is a block schematic diagram of a control circuit for the burner; and Fig. 3 is a block diagram of a heater system embodying a controller according to the present invention. Fig. 3 of the drawings shows an internal combustion engine 1 having an air intake pipe 3 coupled to an air cleaner 2 through an air duct 31 in which a burner 4 and a heat exchanger 5 are disposed. To the air duct 31 there is connected a bypass passage 6 which bypasses the burner 4 and the heat exchanger 5. A bypass valve 61 is disposed in the inlet end of the bypass passage 6 which is coupled to the air duct 31 upstream of the burner 4. The bypass valve 61 controls the rate of flow of air into the burner 4 and the rate of flow of air into the bypass passage 6. The heat exchanger 5 takes in ambient air from an air inlet 51 and heats the air with heat from a high-temperature gas produced by burning fuel in the burner 4. The air which has been heated by the heat exchanger 5 is delivered by a blower 18 through a hot-air duct 52 and an air outlet 19 into a compartment which is to be heated. An air-conditioning unit utilising coolant of the engine 1 comprises a blower 20, an evaporator 21 and a heater core 22 which is connected to the internal combustion engine l by means of coolant pipes 23. As shown in Fig. l, the burner 4 comprises a burner assembly 40, an atomizer 7 for heating and atomizing supplied fuel, an ignition glow plug 8 for igniting the fuel which has been atomized by the atomizer 7, and a combustion sensor 9 for detecting the condition of combustion in the burner 4 and producing a signal representative of the detected condition of combustion. The burner assembly 40 is constructed of an outer cylindrical tube 44, an inner cylindrical tube 43 disposed concentrically within the outer cylindrical tube 44, and a partition 46 disposed in the inner cylindrical tube 43 and dividing the interior thereof into an ignition chamber 4l and a combustion chamber 42. The inner tube 43 is made of a heat-resistant material such as ceramics or a heat-resistant alloy. The inner tube 43 has a plurality of air inlet holes 47 defined in a peripheral wall thereof for introducing air from an air passage 45 defined between the inner and outer tubes 43, 44. The inner tube 43 also has an outlet passage 48 defined in a righthand end thereof for allowing a combusted gas to be discharged therefrom. The partition 46 is of a honeycomb structure formed of a heat-resistant material such as ceramics for introducing a mixture of atomized fuel and air and combusted gas from the ignition chamber 4l therethrough into the combustion chamber 42. The atomizer 7 has a casing 72 extending obliquely from a lower portion of the burner assembly 40 through the outer and inner tubes 44, 43 and partly exposed in the combustion chamber 42, a nozzle 73 joined to the tip end of the casing 72 and extending through the partition 46 and opening into the ignition chamber 4l, and an atomizing glow plug 7l disposed in the casing 72. The atomizer 7 is supplied with fuel from a fuel pump 240 (Fig. 3) through a fuel control valve 24 and a fuel inlet 76, and heats the supplied fuel with the atomizing glow plug 7l into atomized fuel, which is ejected from the nozzle 73 into the ignition chamber 4l. The atomizing glow plug 7l and the ignition glow plug 8 will be described in greater detail. The glow plugs 7l, 8 have heating elements 75, 82, respectively, made of a ceramics material, for example, with resistance wires 74, 8l of a positive temperature coefficient embedded respectively therein. When an electric current from a suitable power supply is passed through the resistance wires 74, 8l, the atomizing glow plug 7l is heated up to a fuel atomizing temperature such as about 500 °C, for example, and the ignition glow plug 8 is heated up to a fuel igniting temperature such as about 900 °C, for example. Since the resistance wires 74, 8l are heated to different temperatures and have different heat capacities and configurations, their resistances are also different from each other, but the resistance wires should preferably have the same rated voltage. If their rated voltages differ from each other, an adjusting resistor (described later) may be used. The combustion sensor 9 has a detector made of a ceramics material with a temperature sensor wire 9l embedded therein. The combustion sensor 9 thus serves as a means for detecting the condition of fuel combustion in the combustion chamber 42 by way of a change in the resistance of the temperature sensor wire 9l. In Fig. 2, the resistance wire 74 of the atomizing glow plug 7l and the resistance wire 8l of the ignition glow plug 8 are connected parallel to each other, and also to a circuit having an A switch l0 serving as a first switch and a B switch l2 serving as a second switch and connected in series to a resistor ll. The A switch l0 and the B switch l2 are connected parallel to each other. A voltage is applied by a battery l3 through the A and B switches l0, l2 to the resistance wires 74, 8l. The resistor ll connected in series to the B switch l2 serves to cause a voltage drop thereacross. A resistor l4 connected in series to the resistance wire 74 of the atomizing glow plug 7l serves as an adjusting resistor for matching the resistance wire 74 with the voltage supplied by the battery l3. If the rated voltage of the resistance wire 74 matches the supplied voltage, then the resistor l4 is dispensed with. A temperature detecting resistor l5 is connected in series with the temperature sensor wire 9l of the combustion sensor 9, and detects a change in the resistance of the temperature sensor wire 9l which varies with the temperature in the combustion chamber 42. The temperature detecting resistor l5 applies a signal representative of the detected temperature change to a controller l6. A voltage detecting resistor l7 detects a voltage imposed on the atomizing glow plug 7l and the ignition glow plug 8 and transmits a signal indicative of the detected voltage to the controller l6. The controller l6 is in the form of a micro-computer and has a program-implemented timer (hereinafter referred to as a "timer"). The controller l6 is energized by the battery l3 and responds to a signal from the combustion sensor 9, indicative of the temperature in the combustion chamber 42, and a voltage signal from the voltage detecting resistor l7, for opening and closing the A and B switches l0, l2 to control the supply of electric power to the atomizing glow plug 7l and the ignition glow plug 8. The controller l6 also controls the blower l8 and the fuel control valve 24 based on a signal from a coolant temperature sensor 25 which detects the temperature of the coolant in the internal combustion engine l. A power supply switch 26 in Fig. 3 supplies electric power from the battery l3 to the controller l6 and the glow plugs. Operation of the heater controller thus constructed will be described below. When the power supply switch 26 is turned on to energize the controller l6, the B switch l2 remains turned off under the control of the timer, but the A switch l0 is turned on to supply an electric current from the battery l3 to the atomizing glow plug 7l and the ignition glow plug 8 to heat the respective resistance wires 74, 8l. Upon elapse of a predetermined period of time (t seconds), the glow plugs 7l, 8 are heated up to respective prescribed temperatures. Upon energization of the controller l6, the fuel control valve 24 is opened to supply fuel from the fuel tank 240 to the atomizer 7 through the fuel inlet 76. The supplied fuel is atomized in the atomizer 7 that has been heated to the desired temperature, and the atomized fuel is then ejected by the nozzle 73 into the ignition chamber 4l. In the ignition chamber 4l, the ejected atomized fuel and air from the air inlet holes 47 are mixed into a combustible air-fuel mixture which is then brought into contact with the ignition glow plug 8 that has reached the ignition temperature. The air-fuel mixture is now combusted to produce flames and flows through the honeycomb grid-like passageways of the partition 46 into the combustion chamber 42. The combusted mixture is further mixed with air from the air inlet holes 47 into a high-temperature combustion gas, which passes through the outlet passage 48 of the combustion chamber 42 into the heat exchanger 5 located downstream of the burner 4. During this time, the temperature sensor wire 9l of the combustion sensor 9 and the outer wall surface of the casing 72 of the atomizer 7 are heated by the high-temperature combustion gas in the combustion chamber 42, for thereby heating fuel which is continuously supplied from the fuel inlet 76. Upon elapse of the prescribed time (t seconds) after the A switch l0 has been turned on, the controller l6 turns off the A switch l0 and turns on the B switch l2 to pass a current through the resistor ll to the glow plugs 7l, 8. Since the glow plugs 7l, 8 have already reached the respective temperatures by being heated by the current supplied via the A switch l0, their temperatures can well be maintained even by the current supplied via the resistor ll, preventing the heater elements 75, 82 from being overheated. When a sufficient combustion condition is reached in the combustion chamber 42, a change in the resistance of the temperature sensor wire 9l of the combustion sensor 9 is transmitted to the controller l6, which then turns off the B switch 12. Even under this condition, the atomizer 7 is kept at the fuel atomizing temperature by the high-temperature combustion gas in the combustion chamber 42. Furthermore, inasmuch as flames are continuously produced in the combustion chamber 42 on account of continued combustion, the glow plugs 7l, 8 are no longer required to be energized. If the desired combustion condition in the combustion chamber 42 fails to be accomplished for some reason, a corresponding change in the resistance of the temperature sensor wire 9l is transmitted to the controller l6. The controller l6 then turns on the A switch l0 or the B switch l2 to energize the glow plugs 7l, 8 for attaining the sufficient combustion condition in the combustion chamber 42. The controller l6 also detects the voltage across the voltage detecting resistor l7. If the voltage applied to the glow plugs 7l, 8 is too low, the controller l6 increases the timer operating time so as to be longer than the prescribed time (t seconds). Conversely, if the voltage applied to the glow plugs 7l, 8 is too high, the controller l6 reduces the timer operating time. Therefore, the controller l6 controls the time interval between the time when the A switch l0 is turned on and the time when the B switch l2 is turned on. As described above, the high-temperature combustion gas produced by the fuel combustion in the burner 4 flows through the outlet passage 48 into the heat exchanger 4. In the heat exchanger 4, ambient air introduced through the air inlet 5l is heated by the supplied high-temperature combustion gas and discharged by the blower l8 as hot air, so that the heating of the compartment can be started immediately after the power supply switch 26 is turned on. The combustion gas that has passed through the heat exchanger 5 is introduced via the air intake pipe 3 into the internal combustion engine l for assisting the engine l in getting started quickly especially in cold weather. When the temperature of the coolant is increased to the extent that the coolant can be used for heating the compartment, upon elapse of a certain time after the internal combustion engine l has started its operation, the coolant sensor 25 applies a signal to the controller l6, which now closes the fuel control valve 24 and de-energizes the blower l8 to stop the heating of the compartment by the burner 4. At the same time, the controller l6 actuates the blower 20 and the heater core 22 of the air-conditioning unit for heating the compartment with the heat of the coolant. With the arrangement of the present invention, as described above, the atomizing glow plug for atomizing fuel in the heater and the ignition glow plug for igniting the atomized fuel are connected parallel to each other, and the A switch for supplying an electric current from the power supply and the B switch to which a resistor is connected in series are connected parallel to each other. The A switch is first turned on to heat the glow plugs quickly up to respective temperatures desired for them to atomize and ignite the fuel. A timer is set to a time period which is required for the desired temperatures to be reached by the glow plugs. When the timer runs out, the A switch is turned off and the B switch is turned on to continue fuel combustion. If a sufficient combustion condition is detected by the combustion sensor, then the glow plugs are de-energized. Thus, the mechanism for energizing the glow plugs of the heater can be controlled easily, and hence the cost of components used for controlling purpose is reduced and the controlling mechanism is improved in reliability. Since the timer operating time is controlled by the magnitude of the voltage applied to the glow plugs, the temperatures of the glow plugs can appropriately be increased up to desired temperatures. The B switch l2 may be a normally-closed switch which can be turned off by a signal from the combustion sensor 9.

Claims: A controller for controlling a heater including a burner (4) having an atomising glow plug (7) for heating and atomising fuel and an ignition glow plug (8) for igniting the fuel which has been heated and atomised by the atomising glow plug (7); a first switch (10) for supplying electric power to the atomising glow plug (7) and the igniting glow plug (8) which are connected in a parallel circuit; a second switch (12) connected in series with resistance means (11), means (16) for closing the first switch (10) and means (9,16) for cutting off the supply of electric power to the atomising and ignition glow plugs (7,8) when the temperature in the burner (4) has reached a predetermined value characterised in that the series circuit is connected in parallel with the first switch (10); and in that after a predetermined period of time after closing the first switch (10), said means (17), opens the first switch (10) and closes the second switch (12). A controller according to claim 1, characterised by means (17) for detecting a voltage applied to the atomising and ignition glow plugs (7,8) to control the predetermined period of time. A controller according to claim 1 or claim 2, characterised in that the atomising glow plug (7) is connected to the first and second switches (10,12) through an adjusting resistor (14). A controller according to any preceding claim, characterised in that the atomising glow plug (7) includes a heating element (75) made of a ceramics material with a resistance wire (74) of a positive temperature coefficient embedded therein. A controller according to any preceding claim, characterised in that the ignition glow plug (8) includes a heating element (82) made of a ceramics material with a resistance wire (81) of a positive temperature coefficient embedded therein.

Inventors: KAWAMURA, HIDEO, YAMASHITA, KEIICHI, YOSHIDA, YUKIO
Applicants: ISUZU MOTORS LIMITED
Application year: 1986
Main classification: G05D23
IPC codes: F02B1, B60H1, F23N5, F23D11, G05D23