EP0715704B1

EP0715704B1 - Pump arrangement for an oil burner

Info

Publication number: EP0715704B1
Application number: EP94926110A
Authority: EP
Inventors: Poul Kirkelund
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1993-09-04
Filing date: 1994-08-29
Publication date: 1999-06-23
Anticipated expiration: 2014-08-29
Also published as: EP0715704A1; DE4329955A1; DE69419256T2; DE69419256D1; WO1995007439A1; DE4329955C2

Description

The invention relates to a pump arrangement for an oil burner according to the preamble of claim 1, and to a method for regulating the capacity of an oil burner according to the preamble of claim 14.

Known oil burners, as commercially available for heating purposes, operate with a predetermined power level at which the pump arrangement delivers the oil at a constant, generally adjustable, pressure to the atomiser unit, in particular a nozzle. Matching the pump output to the required heat output of the boiler or similar vessel is effected by switching the oil burner on and off. Incomplete combustion resulting from this switching on and off pollutes the environment, however, and causes deposits to form on the nozzle and in the combustion chamber and so on.

A pump arrangement within the same genus is already known (US 4,391,580 A), which, further to a pressure-side outlet, has a modulation outlet, which is alternately connected with the outlet of the pressure side and the suction or return side, respectively, of the oil pump. For this purpose a pitch circle shaped groove in the pump housing is provided with two valve openings, which co-operate with several valve openings in the toothed ring serving as rotary slide in a gear wheel pump. This leads to very short pressure impulses, during which the pressure build up and pressure reduction phases last relatively long. The result of this is an undesirable environment pollution.

From DE 41 13 067 A1 it is known to supply the in pulses to the atomiser unit and to adjust the desired output by influencing the pulses, for example, by the pulse frequency. For that purpose, the pressure-side output of the continuously operating supply pump is connected by way of a non-return valve, which opens only when the oil pressure is above 2 bars, to the atomiser unit and is connected by way of a rhythmically controllable electromagnetic valve to the oil reservoir. When the electromagnetic valve is closed, a pressure builds up at the pressure-side output of the pump which leads to the non-return valve opening and which can be, for example, 10 bars. If the electromagnetic valve opens, this pressure collapses, the non-return valve closes and atomisation is interrupted. At a pulse frequency of 3 Hz and a pulse duration of 0.03 sec., the oil throughput can be reduced to about 20% of the amount that is delivered with a permanently closed electromagnetic valve. The service life of the electromagnetic valve is limited, however, because of the high frequency with which it opens and closes. In addition, there is a high noise level.

It is the aim of the invention to specify new ways of matching the amount of oil that is supplied to the atomiser unit of an oil burner to requirements.

This aim is achieved in practically by the features of claim 1. The pump arrangement has two operational states, in which, with the pump running, different amounts of oil are delivered. Demand can be matched by use of a conventional thermostat which, by operating the change-over device, alternately causes the first or the second operational state to be effective at the connection leading to the atomiser unit. Since the intervals during oil feed with modulated pressure are so brief that the flame in the combustion chamber is not extinguished, a continuous operation with proper power regulation can be achieved, without the disadvantages mentioned in the introduction as a result of the pump switching on and off occurring.

In the construction the change-over device is constituted by the on-off valve which, on account of its low operating frequency, has a long service life even when in the form of an electromagnetic valve. The modulation valve requires no special regulation, since the change-over device already exists for that purpose. The modulation valve can therefore be of simple construction, operate at a constant switching rate, and for example, be mechanically driven.

In the invention two outputs are provided with constant or modulated pressure. The mode of operation of the second output can be achieved most simply with a modulation valve which connects the second output alternately with the output side and the intake or return side of the pump. Here too, the modulation valve does not need to be regulated. It is sufficient for modulation to be effected at a constant frequency and pulse shape.

A very simple solution is obtained which provides a rotary pump with rotary slide valve which takes on the function of the modulation valve.

The gear pump according to claim 2 is particularly advantageous for the construction of the rotary slide valve. It is also an advantage that such a gear pump as a heating oil pump has proved a millionfold success.

The embodiments of claims 3 to 5 show that conventional pumps can be provided with a modulation valve with very little modification, and therefore correspondingly cheaply.

By means of a pressure regulating valve according to claim 6, the pressure at the first output can be kept strictly constant. Using a second output, which is temporarily connected to the output side and therefore to the first output, the maximum amplitude of the modulated pressure is also limited to the set value. The pump arrangement can be operated at two different pressure levels. The normally operative higher-pressure regulating valve loses its function when the second lower-pressure regulating valve is rendered operative by the on-off valve. In this manner, four power levels are achieved, because the two pressure levels have an influence on the conditions both at the first output and at the second output. By controlling the said on-off valve and the change-over device, power can therefore be influenced over a large operating range.

If the change-over device according to claim 7 consists of two on-off valves, no additional on-off valve is required to disconnect completely the line leading to the atomiser unit.

A non-return valve ensures in a manner known per se that the atomiser unit is supplied with oil only when the oil has reached a sufficiently high atomisation pressure.

The invention is explained in detail hereinafter with reference to preferred embodiments illustrated in the drawings, in which

Fig. 1: shows diagrammatically the circuit diagram of a pump arrangement according to the invention,
Fig. 2: shows a second embodiment of a pump arrangement according to the invention,
Fig. 3: is a graph of pressure plotted against time,
Fig. 4: is a longitudinal section through a gear pump with a built-in modulation valve,
Fig. 5: is a plan view of the gear pump of Fig. 4, assuming the cover plate to be transparent,
Fig. 6: shows a modified embodiment in a view similar to that of Fig. 4,
Fig. 7: is a plan view of the embodiment of Fig. 6, assuming the cover plate to be transparent,
Fig. 8: shows a further embodiment of the pump arrangement and
Fig. 9: shows a section through the drive shaft of that embodiment.

Fig. 1 shows a pump arrangement 1 for an oil burner having, in addition to a blower, not illustrated, an atomiser unit 2 with an atomising nozzle 3, and a non-return valve 4, which opens only when an adequate atomisation pressure is present. An associated nozzle line 5 is connected to a connection 6 of the pump arrangement 1.

The pump arrangement has a rotary pump 7 which draws oil from a reservoir 8 by way of an intake line 9 and a filter 10 and then feeds it from the intake side 11 to the output side 12. This output side 12 is connected by way of a throttle 13 to a return line 14 leading to the reservoir 8. Parallel therewith there is arranged a pressure-regulating valve 15, which keeps the pressure of the output side 12 constant at an adjustable value. Between the intake side 11 and the return line 14 there is moreover a non-return valve 16 which becomes effective whenever the system operates in single-line mode. The output side 12 forms a first output 17.

A modulation valve 18, the rotary slide valve of which is rotated by the shaft 19 of the rotary pump 7, connects a second output 20 alternately to the output side 12 and the intake side 11 of the rotary pump 7. At the first output 17 there is therefore a constant oil pressure available, and at the second output 20 a modulated oil pressure.

A change-over device 21 consists of a first on-off valve 22 and a second on-off valve 23, both of which are in the form of electromagnetic valves. The first on-off valve 22 is arranged between the first output 17 and the connection 6, the second on-off valve 23 is arranged between the second output 20 and the connection 6. When the on-off valve 22 is open, the oil burner is therefore supplied with a first power level, and when the on-off valve 23 is open, the oil burner is supplied with a second power level of reduced heating capacity.

A temperature sensor 24 relays the boiler temperature, that is, the temperature of the water warmed by the heated boiler, to a regulator 25, which is pre-set at a desired temperature 26. The regulator controls the on-off

valves

22 and 23 by way of the

signal lines

27 and 28. When the temperature is too low, the first output 17 becomes effective, and at too high a temperature the second output 20 becomes effective. The individual pulses of modulated pressure follow each other so quickly that the flame in the combustion chamber is not extinguished but ignites the freshly supplied oil immediately. In this manner the burner can be operated as it were continuously, so that the problems (environmental pollution and the like) associated with switching the system on and off are avoided.

In the embodiment of Fig. 2, the same reference numerals as in Fig. 1 are used for corresponding parts. A new feature is that the modulation valve is built into the rotary pump 29. Furthermore, in a branch parallel to the first pressure regulator 15, a second pressure regulator 30, which is set to a lower pressure than the first pressure regulator 15, is arranged in series with an on-off valve 31. The latter is illustrated as a normally open electromagnetic valve and is operated by way of a signal line 32 by the regulator 25. If the on-off valve 31 is closed, there is a higher pressure on the output side 12, but if the on-off valve 31 is open, there is a lower pressure. With the on-off valve 31 closed, the operating conditions are the same as in Fig. 1. With the on-off valve 31 open, conditions are similar but at a lower pressure or power level.

Fig. 3 illustrates four power levels A, B, C and D, the power levels A and B applying to both embodiments. The largest feed rate, and thus the greatest power, is obtained at power level A, at which the feed pressure P1 is constant. In that case the on-off valve 22 is open, while the on-off

valves

23 and 31 are closed. A lower power is achieved at stage B, when a modulated pressure with a maximum amplitude P1 is present. In that case the on-off valve 23 is open, while the on-off

valves

22 and 31 are closed. Next is power level C, where the lower pressure P2 is maintained constant. This happens when the on-off

valves

22 and 31 are open and the on-off valve 23 is closed. Last is power level D, which provides a modulated pressure with a maximum amplitude P2. For that purpose the on-off

valves

23 and 31 must be open, while the on-off valve 22 is closed.

It is obvious that the regulator 25, which controls all three on-off

valves

23, 23, 31, allows power to be modified over a very wide range.

Figs 4 and 5 show a gear pump with a built-in modulation valve. A housing 33 has a cylindrical recess 34 which is covered over by a cover plate 35 and receives a rotatable gear ring 36 with internal teeth. The gear ring forms pockets 37 with an externally toothed gearwheel 38 which is arranged eccentrically with respect to the gear ring 36 and is driven by way of a shaft 39 by a motor. In the cover plate 35 there is a pressure groove 40, which is connected by way of a channel 41 to the output side 12, and an intake groove 42, which is connected by way of a channel 43 to the intake side 11. Such a pump is known as a gerotor gear pump.

On the outer circumference of the gear ring 36 there is an annular groove 44. Leading from that is a radial channel which forms a valve opening 45. During rotation of the gear ring 36, the valve opening communicates alternately with the region below the pressure groove 40 and with the region below the intake groove 42. In addition, the annular groove 44 is connected to a channel 46 which leads to the second output 20. This second output is consequently alternately pressurised with high pressure and with intake or return pressure, that is, with modulated pressure.

In the embodiment of Fig. 6 and 7, the gear pump is of the same construction as in Figs 4 and 5. Reference numbers increased by 100 have therefore been used for corresponding parts. The essential difference is that in the cover plate 135 there is formed an annular groove 144 which extends along the front face of the gear wheel 138 and is connected to a line 146 leading to the second output 20. A recess in the front face of the gear wheel 138 serves as the valve opening 145. This recess extends radially into the region of the pressure groove 140 and the intake groove 142. On rotation of the gear wheel 138, this valve opening 145 communicates alternately with the output side and the intake side. Here too, a modulated pressure consequently forms at the second output 20.

In the embodiment according to Figs 8 and 9, in which reference numbers increased by 200 have been used for corresponding parts, the drive shaft 239 of the rotary pump 7, which has a valve opening 245 in the form of part of an annular groove, forms the modulation valve 218. In the associated housing 233 there is a valve opening 240 in the form of a bore which is connected to the output side 12 of the pump, and a valve opening 242 in the form of a bore which is connected to the intake side 11 of the pump. The modulation valve 218 is in series with an on-off valve 221 arranged between the output side and the return line 14 and serving as the change-over device. If the on-off valve 221 is opened, there is modulated pressure present at the connection 6, if it is closed, there is a constant pressure.

Claims

Pump arrangement with an oil burner operable in at least two output steps, with an oil pump (7, 29) which is connected with a connection for an oil atomisation unit (2) via a pressure pipe (5), and with a pressure controller (15) for maintaining a constant pressure in the pressure pipe and with a three-way valve arrangement (21) which optionally connects the connection of the oil atomisation unit with the pressure side of the oil pump or with the outlet of a control valve (18), which valve has a rotary slide (36) connected with a rotary part of the pump and which valve alternately creates a connection to the pressure side and to the suction or return side, respectively, of the oil pump with the purpose of producing a modulated pressure, characterised in that the rotary slide has one single valve opening (45; 145; 245) which, on each rotation, co-operates alternately with one single pressure side valve opening (240; 40, 140) and one single suction side valve opening (242; 42, 142) and that a non-return valve (4) is provided in the atomisation unit (2), which valve only opens when a sufficiently high atomisation pressure is available..
A pump arrangement according to claim 1, characterized in that the rotary pump (7, 29) is a gear pump with a rotating inner gear wheel (38; 138) and, meshing therewith, an outer gear ring (36; 136) mounted eccentrically with respect to the gear wheel.
A pump arrangement according to claim 1 or 2, characterized in that associated with the rotary slide valve there is an annular groove (44; 144) which is connected on the one hand to a valve opening (45; 145), which valve opening is moved in succession past output side and intake side, and on the other hand to the second output (20).
A pump arrangement according to claim 3, characterized in that the annular groove (44) runs along the circumference of the gear ring (36) and the valve opening (45) is formed by a radial channel in the gear ring.
A pump arrangement according to claim 3, characterized in that the annular groove (144) runs radially within the pressure groove (140) and intake groove (142) of the rotary pump along the front face of the gear wheel (138) and the valve opening (145) is formed by a recess in the front face passing over the pressure groove and intake groove.
A pump arrangement according to one of claims 1 to 5, characterized in that the output side of the pump (7, 29) is connected by way of a pressure-regulating valve (15) to the return side and that parallel with the first higher-pressure regulating valve (15) there is arranged the series connection of a second lower-pressure regulating valve (30) and an on-off valve (31).
A pump arrangement according to one of claims 1 to 6, characterized in that the three-way valve arrangement (21) consists of two on-off valves (22, 23) which are arranged in the line between the first (17) and second output (20) respectively and the connection (6).