Abstract
A method to operate a fuel-operated vehicle heater comprising the lowering of a combustion air ratio λ between supplied combustion air and supplied fuel to a combustion chamber of the fuel-operated vehicle heater from a starting value λ.sub.start>1 to a range λ<λ.sub.start for a time period Δt.
Claims
1. A method to operate a fuel-operated vehicle heater comprising the lowering of a combustion air ratio λ between supplied combustion air and supplied fuel to a combustion chamber of the fuel-operated vehicle heater from a starting value λ.sub.start>1 to a range λ<λ.sub.start start for a time period Δt, wherein the lowering of the combustion air ratio λ starts during stable steady-state operation of the fuel-operated vehicle heater, wherein the combustion air ratio λ is returned to a final value range of the combustion air ratio with λ>1 subsequent to the time interval Δt, and wherein the lowering of the combustion air ratio λ to the range λ<λ.sub.start is initiated based on an operating time of the vehicle heater since the last lowering and/or is terminated based on an air pressure detected by a sensor.
2. The method according to claim 1, wherein the combustion air ratio λ is maintained in a constant value range in the range λ<λ.sub.start during the time interval Δt.
3. The method according to claim 1, wherein the combustion air ratio λ is returned to a final value range of the combustion air ratio with λ>1 subsequent to the time interval Δt.
4. The method according to claim 1, wherein the length of the time interval Δt is between 2 minutes and 5 minutes.
5. The method according to claim 1, wherein an amount of combustion air supplied to the combustion air chamber is reduced and/or an amount of fuel supplied to the combustion air chamber is increased.
6. The method according to claim 5, wherein the amount of combustion air supplied to the combustion chamber and/or the amount of fuel supplied to the combustion chamber being determined depending on an air pressure detected by a sensor.
7. The method according to claim 1, wherein the lowering of the combustion air ratio λ to the range λ<λ.sub.start is initiated based on an operating time of the vehicle heater since the last lowering and/or terminated based on an air pressure detected by the sensor.
8. A fuel-operated vehicle heater having a control unit configured to perform the method according to claim 1.
Description
(1) FIG. 1 a flow diagram of a method for operating a fuel-operated vehicle heater; and
(2) FIG. 2 a schematic representation of a fuel-operated vehicle heater.
(3) FIG. 1 shows a flow diagram of a method for operating a fuel-operated vehicle heater. The described method 100 starts at start 110. Starting from the start 110, the system checks whether a condition is met, step 120. For example, the operating time of the vehicle heater since the last lowering can be used as a condition. Furthermore, the time totally elapsed since the last lowering can also be used as a condition. The possible operating time between two lowering phases can, for example, be between 8 and 30 hours. The operating time can preferably be between 8 and 12 hours, with 10 hours being the preferred operating time until the next lowering. The maximum time period between two lowerings can, for example, be 1 year. If the condition is not met, step 120-no, it is resumed at start 110. If the condition is met, step 120-yes, it is continued with a lowering at step 130. In addition to the conditions explicitly mentioned in connection with FIG. 1, i.e., the operating time of the vehicle heater since the last lowering and the maximum time period since the last lowering, other conditions mentioned elsewhere in this description can also be used to initiate the lowering. At step 130, the combustion air ratio λ is lowered from a starting value of λ.sub.start>1 to a value range of 1<λ<λ.sub.start. The starting value λ.sub.start can, for example, be 1,7 or 1,8. The value range 1<λ<λ.sub.start, to which the value is lowered, can be, for example, the range from 1,1 to 1,5. Preferably, the lowering can be carried out to a constant value λ.sub.target. λ.sub.target can, for example, be 1,2. The lowering of the combustion air ratio π can, for example, be achieved by reducing the supplied combustion air. This can, for example, be achieved by throttling the air supply or reducing a fan speed, whereby the fan supplies combustion air to the combustion chamber. It is also possible to change the amount of supplied fuel, for example, by increasing the delivery rate of a fuel pump. In this way, the combustion air ratio can also be shifted to the desired range. The reduction of the supplied combustion air has the advantage over an increase in the amount of fuel supplied that the heating power of the fuel-operated vehicle heater remains almost constant during the lowering phase, as the amount of supplied fuel remains essentially unchanged. The lowering can essentially be achieved almost stepwise by directly switching the appropriate suppliers for combustion air and/or fuel to the desired values. Subsequent to the lowering, it can be checked at step 140, whether the initiated lowering phase shall be terminated. A corresponding criterion is, for example, the expiry of a time interval Δt, which can start with the beginning of the lowering at step 130. The length of the time interval Δt can be between 2 and 5 minutes, preferably 4 minutes. A further criterion for terminating the lowering phase can be the air pressure in the vicinity of the vehicle heater, since a lower air mass is supplied to the combustion chamber when the air pressure drops with otherwise constant operation of the combustion air supplier. If the lowering phase is not yet to be terminated, step 140-no, essentially only the previous operating state is maintained, i.e., the regeneration is continued, in a subsequent step 160. From this point, it is checked again whether the lowering phase should be terminated, step 140. If there is a condition for ending the lowering phase, step 140-yes, the vehicle heater is returned to its original operating state in a subsequent step 150. This can be done, for example, by increasing the amount of supplied combustion air and/or reducing the amount of supplied fuel to the original initial values, depending on how the lowering was previously carried out. The method 100 can then be restarted or continued at step 110.
(4) FIG. 2 schematically shows a fuel-operated vehicle heater 10. The fuel-operated vehicle heater 10 has a fuel line 12 and a combustion air line 14 via which fuel and combustion air are supplied to the fuel-operated vehicle heater respectively. The supplied fuel can be dosed by a fuel pump 20 and supplied to a combustion chamber 32. A nozzle 30 is arranged in the combustion chamber 32 and serves to spray the supplied fuel. The combustion air supplied to the fuel-operated vehicle heater 10 can also be supplied to the combustion chamber 32 via an air control device 18, for example a blower and/or a throttle device. Within the combustion chamber, the sprayed fuel and the supplied combustion air form a fuel/combustion air mixture with a combustion air ratio λ depending on the fuel and air mass supplied per time unit. The combustion air ratio λ can be adjusted via a control unit 16 which controls the air control device 18 via a control line 22 and the fuel pump 20 via a further control line 24. An exhaust gas discharge of the fuel-operated vehicle heater is not explicitly shown in FIG. 2, but is undoubtedly present. In the exhaust gas discharge likewise not shown sensors can be present, which can supervise for example exhaust gas emission values of the fuel-operated vehicle heater, for example the soot number and the carbon monoxide load. FIG. 2 shows a sensor 28 that can, for example, detect an ambient pressure in the vicinity of the fuel-operated vehicle heater 10. The control unit 16 can in particular be configured to carry out the method described above.
(5) The features disclosed in the above description, in the drawings and in the claims may be essential for the realization of an invention, either individually or in any combination.
REFERENCE NUMERALS
(6) 10 vehicle heater
(7) 12 fuel line
(8) 14 combustion air line
(9) 16 control unit
(10) 18 air control device
(11) 20 fuel pump
(12) 22 control line
(13) 24 further control line
(14) 28 sensor
(15) 30 nozzle
(16) 32 combustion chamber
(17) 100 method
(18) 110 start
(19) 120 condition met?
(20) 130 lowering
(21) 140 finishing?
(22) 150 return
(23) 160 hold
