Patent Publication Number: US-6983890-B2

Title: Vehicle heating appliance with a valve in the fuel supply

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a vehicle heating appliance, in particular an auxiliary or additional heating appliance, having a fuel supply for supplying a liquid fuel to a combustion device, in particular to a fuel nozzle, and having a remotely controllable valve disposed in the fuel supply. The invention further relates to a vehicle having such a heating appliance. 
   2. Description of the Related Art 
   From DE 195 45 677 A1 a fuel-operated vehicle heating appliance with atmospheric vaporizing burner is known, in which there is disposed in a fuel line a check valve, which is open during operation of the heating appliance. The check valve is a remotely controllable on-off shutoff valve. Alternatively, as a check valve, a spring-loaded pressure valve may be used, which is biased counter to the feed direction of the fuel but is not remotely controllable. The check valve is intended to prevent bubble formation and empty vaporization of the fuel line. The use of a remotely controllable on-off shutoff valve may lead to a safety-critical overpressure in the fuel line. The use of a spring-loaded pressure valve always entails a specific minimum pressure upstream of the valve if fuel is to be pumped through the latter. 
   From DE 195 26 003 A1 a heating appliance is known, in which fuel is pumped by a pressure-controlled fuel pump through a fuel line to a burner. Disposed in the fuel line is a solenoid valve, which forms a throttling point and offers the flowing fuel a resistance, which rises superproportionally as the flow volume increases. Here too, in the closed state of the solenoid valve an overpressure situation may arise in the fuel line. 
   From DE 44 15 513 A1 and DE 197 24 502 C1 heating appliances are known, in which electrically controllable valves are provided in combination with an accumulator so that, independently of the pressure supplied by a pump, a reliable delivery of fuel to the burner is guaranteed. 
   The underlying object of the invention is to provide a vehicle with a heating appliance, with which safety-critical situations are substantially avoided and, in particular, evaporative emission of fuel from an open fuel line is reduced. 
   SUMMARY OF THE INVENTION 
   According to the invention said object is achieved by an initially described heating appliance, in which an overpressure safety device is provided in the fuel supply, and by a vehicle, in which such a heating appliance according to the invention is installed. 
   The invention is based on the discovery that, whilst the arrangement, described in DE 195 45 677 A1, of an on-off check valve in a fuel line does in principle involve a safety risk, said risk may be circumvented through a clever improvement of the arrangement. To said end the invention, in addition to a remotely controllable check valve disposed in the fuel line, provides an overpressure safety device. 
   The overpressure safety device may be disposed at the fuel line at the discharge end of a fuel pump and ensures that, even in the event of malfunction of the fuel pump, no safety-critical situation may arise. At the same time, the likewise provided remotely controllable check valve prevents an evaporation of fuel at the fuel line. The check valve may be purposefully opened so that it then offers only a slight flow resistance. In contrast to a spring-loaded pressure valve known from DE 195 45 677 A1, the arrangement according to the invention of a remotely controllable check valve in combination with an overpressure safety device does not lead to an undesirably high back pressure in the fuel line. 
   In an advantageous development of the invention the overpressure safety device provided according to the invention is connected in parallel to the remotely controllable valve. With such an arrangement of check valve and overpressure safety device it is possible, in the event of the discharging of fuel at high pressure through the overpressure safety device, for said fuel to be carried away into the combustion chamber of the heating appliance. The combustion chamber may subsequently be ventilated so that the fuel volatizes. Alternatively, the fuel at the discharge end of the fuel pump may be carried away elsewhere. It is particularly advantageous when the fuel is carried back into a fuel tank, from which it was previously fetched by the fuel pump. 
   The overpressure safety device provided according to the invention is advantageously designed as a valve, the valve body of which is spring-biased counter to the direction of flow of the fuel in the fuel supply. By the term “valve body” in the present context are meant all flow bodies, which offer resistance to the flowing fuel and may simultaneously be deflected and/or displaced by the latter. Fuel may be discharged at times by means of the valve, wherein the valve body is afterwards moved back into its initial position in order to close the fuel line again. At the valve body a signalling device may be disposed, with the aid of which an opening of the valve and hence the occurrence of a safety-relevant state may be identified. 
   The overpressure safety device may be designed as a check valve, in particular as a ball valve, which changes abruptly from a closed state to an open state. The overpressure safety device may further be designed as a throttle valve, with which after opening a variable or a constant throttling effect arises. With said different types of valve variant the safety function of the overpressure safety device may be purposefully adjusted to a total or damped discharge of fuel in the event of a risk of overpressure. 
   In a particularly economical variant of the overpressure safety device provided according to the invention, said device is designed as a bursting disk. 
   In order to discharge fuel into the combustion chamber, the overpressure safety device is advantageously disposed in the vicinity of the combustion device, thereby dispensing with additional lines for carrying the fuel away. 
   The overpressure safety device may be of a particularly compact design and economical to manufacture when the overpressure safety device is constructed with the remotely controllable valve in the form of a unit. 
   In said case, a particularly compact unit may be created when the overpressure safety device is disposed in the remotely controllable valve, in particular in a piston of said valve. 
   Alternatively, the overpressure safety device may be constructed in a unit with a fuel pump, wherein the fuel may advantageously be fed back into the suction line of the fuel pump. 
   To enable purposeful adjustment of a desired overpressure threshold in a heating appliance already assembled or fitted into a vehicle, the overpressure safety device is advantageously provided with a means of adjusting a protected overpressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There now follows a detailed description of embodiments of a vehicle heating appliance according to the invention with reference to the accompanying diagrammatic drawings. Said drawings show in: 
       FIG. 1  is a partial longitudinal section of a heating appliance with a unit according to the invention comprising a remotely controllable valve and an overpressure safety device at the fuel supply. 
       FIG. 2  is an enlarged longitudinal section of the unit according to the invention comprising a remotely controllable valve and an overpressure safety device according to  FIG. 1  in a first embodiment. 
       FIG. 3  is an enlarged longitudinal section of the unit according to the invention comprising a remotely controllable valve and an overpressure safety device according to  FIG. 1  in a second embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The heating appliance partially illustrated in  FIG. 1  is an engine-independent air heating appliance having a burner  10 , to which liquid fuel is fed by a fuel supply  12  and combustion air is fed by a combustion air supply  14 . 
   The fuel supply  12  comprises a fuel tank  16 , from which the fuel is fetched through a suction light  18  by a fuel pump  20  and is then pressed into a pressure line  22 . The fuel exits at a fuel nozzle  24  in a combustion chamber  26  of the burner  10  substantially in the direction of arrows  28 . 
   As combustion air supply  14  a combustion air fan  30  is provided, which delivers combustion air through a combustion air channel  32  to the combustion chamber  26 , where it enters as primary air and secondary air i.a. through a swirl device  34  in the direction of the arrows  36 . 
   Disposed next to the fuel nozzle  24  is an ignition device  38 , by means of which the mixture of fuel and combustion air formed in the combustion chamber may be ignited. Further provided next to the fuel nozzle  24  is a flame detector  40 , by means of which the temperature of the ignited flame may be determined. 
   Disposed in the pressure line  22  immediately upstream of the fuel nozzle  24  is a unit  42 , which is illustrated in detail in FIG.  2 . 
   The flame detector  40 , the ignition device  38 , the combustion air fan  30  and the fuel pump  20  are connected by electric lines each illustrated by dashes to a control device  44 , which may process signals of the flame detector  40  and control the other described devices  20 ,  30  and  38  in dependence upon said signals. 
   During operation of the heating appliance the intention is that fuel may be made available at the combustion device  24  in as short a term as possible but, at the same time, during stoppage of the heating appliance there is no undesired exit of fuel. It moreover has to be ensured that, even in the event of a fault in a component of the heating appliance, no safety-critical state may arise. 
   In  FIG. 2  the unit  42  is illustrated in detail. It comprises a remotely controllable valve  46  in the form of a solenoid valve, which via a line  48  also illustrated by dashes in  FIG. 1  may be moved with the aid of the control device  44  into an open and a closed state. In its neutral position the valve  46  is closed. 
   Further provided in the unit  42  is an overpressure safety device  50  in the form of a spring-loaded pressure relief valve. The overpressure safety device  50  is disposed in a housing  52 , in which the valve  46  is also mounted. Extending through the housing  52  is the pressure line  22 , wherein branching off from the latter is a bypass line  54 , which bypasses the valve  46  and runs back into the pressure line  22  downstream of the valve  46 . In said bypass line  54  the overpressure safety device  50  is fashioned with a disk-shaped valve body  56 , which is pressed by a spring  58  against an annular valve seat  60 . 
   By means of the valve  46  the pressure line  22  may be purposefully opened when fuel is to exit at the combustion device  24 . The pressure line  22  may moreover be closed in order to prevent an evaporation of fuel into the combustion device  24 . 
   While the valve  46  is closed, a malfunction of the fuel pump  20  may lead to an undesirably high and possibly also safety-relevant pressure rise in the pressure line  22 . To prevent the pressure in the pressure line  22  from rising above an inadmissible value and threatening to burst the pressure line  22 , the overpressure safety device  50  is provided, by means of which fuel at high pressure may be directed through the bypass line  54  past the closed valve  46 . 
     FIG. 3  shows a second embodiment of a unit according to the invention comprising a valve  46 * and an overpressure safety device  50 *. The valve  46 * of the second embodiment is provided with a piston  62 , which for closing the pressure line  22  is mounted displaceably in the valve  46 *. The overpressure safety device  50 * in the second embodiment is disposed in the piston  62  of the valve  46 * and, when the piston  62  moves, is displaced together with the latter. 
   Like the overpressure safety valve  50 , the overpressure safety device  50 * is designed with a valve body  56 *, which is biased by a spring  58 * towards a valve seat  60 *. The valve body  56 * closes a bypass line  54 *, which penetrates the piston  62 . 
   When the valve  46 * is closed, in the event of a safety-critical pressure rise then, in the manner described above, the pressure line  22  is opened for a short time with the aid of the overpressure safety device  50 * disposed in the piston  62  and pressure is discharged through the bypass line  54 *. 
   The overpressure safety device  50  and/or  50 * may be provided at the valve body  56  and/or  56 * with a non-illustrated position pickup, by means of which the control device  44  may be informed when the overpressure safety device  50  and/or  50 * comes into operation. Alternatively, a non-illustrated pressure sensor may be provided at the pressure line  22  for identifying a safety-relevant pressure rise in the pressure line  22  and signalling said pressure rise optionally to a fault memory or a fault indicating display within the range of vision of a driver of the associated vehicle.