Heating systems – Automatic control – Heat source is a reverse cycle refrigerating system or heat...
Patent
1997-10-29
1999-12-28
Bennett, Henry
Heating systems
Automatic control
Heat source is a reverse cycle refrigerating system or heat...
237 123C, 236 78D, G05D 2300
Patent
active
06006997&
DESCRIPTION:
BRIEF SUMMARY
The present invention pertains to a heater, especially for heating the interior space of a motor vehicle, with heat transfer medium, especially water, and which is traversed by combustion gases on one side of a gas jacket and by hydraulic heat transfer medium on the other side of the gas jacket, side, is in direct heat-conducting contact with the gas jacket and generates signals reflecting the temperature, and temperature signals following each other at time intervals and stops the burner when a threshold value of the temperature gradient is exceeded.
Such a heater is the subject of an older, not previously published Patent Application No. P 44 46 829.6 (=P 1514/1). The monitoring of the temperature gradient offers the advantage that an operating state involving the risk of overheating can be recognized very early, i.e., considerably before undesirably high temperatures develop. This is based on the fact that a risk of overheating can occur essentially only when the output of the burner is too high compared with the throughput of the hydraulic medium in the heat exchanger and a high temperature gradient, i.e., a rapid increase in temperature, will correspondingly develop.
Since the burner is switched off already at the time of the onset of the risk of overheating, but before the onset of overheating, in the case of temperature gradient monitoring, other measures are unnecessary if the burner is to be switched on again later.
The object of the present invention is to detect the risk of overheating especially reliably and early.
This object is accomplished according to the present invention by the signal evaluation unit operating with different threshold values of the temperature gradient as a function of the temperature determined.
The present invention is based on the general idea that a comparatively rapid increase in temperature can be allowed to occur without the risk of overheating as long as the temperature level is low and thus it remains markedly below a dangerous temperature level.
In contrast, the increase in temperature shall be slowed down once higher temperatures have been reached, because unacceptably high temperatures could otherwise be reached in a short time, or overheating could still occur because of the residual heat present after the switching off of the heater.
The permissible temperature-dependent threshold value can be preset, in particular, as a function of the temperature present at the time of the switching on of the burner.
In addition to this or as an alternative, provisions may be made in the heater described in the introduction for the signal evaluation unit to scan the temperature at a high cycle frequency and to determine a mean value of the temperature gradient for a past time interval.
According to an advantageous embodiment of the present invention, this can happen in such a way that temperature values which are spaced from each other in time by a predetermined interval that is long compared with the cycle intervals are processed in terms of a subtraction from among the temperature values scanned at high cycle frequency.
Thus, it becomes possible as a result to determine temperature gradient values following each other at short intervals in time, according to the cycle frequency and at the same time to prevent inevitable variations in the signal or signal noise of the sensors from leading to highly incorrect values of the temperature gradients determined.
Provisions may also be made, in a basically known manner, to arrange an additional temperature sensor in heat-conducting contact with the hydraulic medium in the hydraulic medium, especially at the hydraulic outlet of the heat exchanger. The signal processing unit may operate in this case according to the present invention such that the burner will be switched off when a temperature difference exceeding a temperature-dependent threshold value appears between the sensors.
The circumstance that a comparatively great temperature difference may develop between the gas jacket and the hydraulic medium at a low temperature leve
REFERENCES:
patent: 4640262 (1987-02-01), Lucius
patent: 4685616 (1987-08-01), Stein
patent: 4700052 (1987-10-01), Wolf et al.
patent: 4726514 (1988-02-01), Adam
patent: 4984736 (1991-01-01), Reiser et al.
patent: 5037292 (1991-08-01), Steiert
Alber Andreas
Epple Jurgen
Ottenbacher Stefan
Pfister Wolfgang
Bennett Henry
Boles Derek S.
J. Eberspacher GmbH & Co.
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