GB2031994A - Apparatus for filtering fuel for diesel engines - Google Patents

Abstract

The apparatus (10) comprises a filter (11) and a temperature controlled valve 18 which, at low temperatures, prevents a paraffin separation in the fuel and thus a blocking of the filter (11). The valve (18) controls the return of fuel from an overflow port (16) of the injection pump (15) to the filter (11). At low temperatures, a temperature sensitive element in the valve opens the valve inlet 21 to enable warm fuel from the overflow 16 to mix with the cold fuel from the tank 13 thereby warming fuel supplied to the filter and preventing blocking of the filter. <IMAGE>

Description

SPECIFICATION Apparatus for filtering fuel for diesel engines The invention originates from an apparatus for filtering fuel for diesel engines according to the type set forth in the main claim. Such an apparatus is already known from the "Buch Bosch Kraftfahrtechnisches Taschenbuch" 18th Edition, Page 289, in which the filter is connected in the supply line to the injection pump. The disadvantage with this apparatus is that, when operating below a predetermined temperature, the so-called Cloud Point, the paraffin component present in the diesel fuel crystallizes. After a time, the paraffin crystals block the pores in the strip of filter material whereby the injection pump is supplied with insufficient fuel and to an increasing extent.At temperatures which lie 1 2 C or more below the said crystallization point, the paraffin separation is so great that a flow can no longer build up in the supply line and the operation is no longer possible, even temporarily.

Furthermore, an apparatus for filtering fuel is known from United States Patent Specification 2 729 338 in which two sintered filters are arranged in parallel with one another between a low pressure pump and a high pressure pump. The sintered filters can be electrically heated and can be selectively connected in the fuel flow with the aid of valves. The disadvantage with this apparatus is that the heating is undertaken in an electrical manner and large amounts of heat require a correspondingly high outlay. In addition, due to the electrical heating, the energy source which is in any case heavily loaded is loaded still more heavily. Moreover, for this apparatus, special sintered filters are required which opposes the use of mass-produced components.

Thus, the apparatus is of relatively expensive construction and does not even serve for filtering diesel fuel. Moreover, with this apparatus, ice crystals entrained in the fuel flow are retained and melted.

As opposed to this, the apparatus for filtering fuel for diesel engines in accordance with the invention comprising the characterising features of the main claim has the advantage that with low outlay the heating of the fuel flow can be so regulated that operation of the apparatus over a considerable temperature range below the Cloud Point is possible without the filter becoming blocked. Moreover, no electrical circuits or additional pressure medium circuits are tapped. Furthermore, the apparatus may be fully constructed by using available components. In addition, it can also be fitted to already existing vehicles.

Advantageous further developments and improvements of the apparatus set forth in the main claim are made possible by the measures set forth in the sub-claims. With an arrangement according to sub-claims 2 and 3, the apparatus is of very simple construction which also leads to a more reliable mode of operation. An arrangement according to claim 4 is of special advantage because a possible intake of air through the discharge line during unsatisfactory operating conditions, can be prevented thereby.

An embodiment of the invention is illustrated in the drawing and is described in detail in the following specification. Figure 1 shows an apparatus for filtering fuel for diesel engines in a simplified representation and Figure 2 is a longitudinal section through a regulating valve according to Figure 1 in a simplified representation.

Figure 1 shows an apparatus 10forfiltering fuel for diesel engines, comprising a filter 11. The filter 11 is connected in a supply line 12 which leads from a tank 13 to a fuel delivery pump 14 which forms part of an injection pump 15. A discharge line 17 leads from an overflow port 16 in the injection pump 15 back to the tank 13. Upstream of the filter 11, a regulating valve 18 is connected in the supply line 12 and which has a tank port 19 connected to the tank 13, a filter port 20 connected to the filter 11 and a third port 21. A line 22 connects the third port 21 to the dischage line 17. Downstream of the connection between the line 22 and the discharge line 17, a non-return valve 23 is connected in the latter, which isolates the tank 13.As Figure 2 shows in more detail, the regulating valve 18 has a closure member 25 actuated by an element 24 of expansible material and which controls the connection from the third port 21 to the filter port 20. The expansible element 24 is influenced primarily by the temperature of the fuel leaving the filter port 20 and controls the closure member 25 correspondingly; moreoverthistemper- ature is equal to a mixed temperature which exists by combining the fuel flows through the tank port 19 and the third port 21. The connection from the tank port 19 to the filter port 20 is not influenced by the closure member 25.

The method of operation of the apparatus 10 is as follows, wherein its function is considered only to the extent necessary for understanding the invention.

In operation, the fuel delivery pump 14 extracts diesel fuel from the tank 13 through the supply line 12, the regulating valve 18 and the filter 11 and supplies the injection pump 15 therewith. The excess amount of fuel not used by the injection pump 15 flows through the discharge line 17 and the nonreturn valve 23 back to the tank 13. This throughflow takes place as long as the apparatus 10 is operated at temperatures above the so-called Cloud Point wherein no danger of paraffin separation exists; moreover, due to the relatively warm fuel, the expansible element 24 in the regulating valve 18 has expanded far enough for the closure member 25 to close the third port 21. If, in operation, lower temperatures occur, then paraffin can be separated out from the diesel fuel which can block the pores of the strip of filter material in the filter 11.At such temperatures of the fuel below the Cloud Point, the expansible element 24 has contracted whereby the closure member 25 opens the connection from the third port 21 to the filter port 20. A small sub-pressure normally prevails at the tank port 19 due to the flow in the supply line 12. On the other hand, there prevails in the third port 21, either atmospheric pressure or a slight over-pressure resulting from the excess flow leaving through the discharge line 17. Thus, the heated excess flow coming from the injection pump 15 arrives through the line 22 and the open third port 21 in the interior of the regulating valve 18 where it mixes with the cooler quantity of fuel drawn from the tank 13 and thereafter flows through the filter port 20 to the filter 11.The expansible element 24 is primarily influenced by the fuel leaving the filter port 20 at its mixed temperature prevailing due to the combination of the two flows and regulates the through-flow cross-section at the third port 21 with the aid of the closure member 25 so that the filter 11 is always supplied with fuel at constant temperature which lies above the Cloud Point. In this manner, the apparatus 10 can be operated over a considerable temperature range below the Cloud Point without the filter 11 becoming blocked by paraffin deposits.

The switching point of the regulating valve 18 is arranged just above the Cloud Point so that the operating time of the apparatus 10 remains as short as possible without ventilation. In order to prevent a possible intake of air through the discharge line 17, the line 22 to the fuel delivery pump 14 during unfavourable operating conditions such as, for example, a low fuel level in the tank, the non-return valve 23 isolates the tank 13.

Variations of the illustrated construction are, of course, possible without departing from the concept of the invention. Thus, the injection pump 15 can be constructed for series operation or even as a distributor. Also, additional components can be included in the fuel circuit or branch circuits can be provided, without departing from the basic concept of the invention, which provide an extremely simple, completely effective and reliable regulation of the heating of the diesel fuel.

Claims (5)

1. Apparatus for filtering fuel for diesel engines, comprising a filter which is connected in a supply line leading from the tank to the injection pump and comprising a discharge line leading from the overflow port of the injection pump to the tank characterised in that, upstream of the filter, the supply line is in communication with the overflow port of the injection pump and that a temperature-dependent controlled valve is connected in the said communication.

2. Apparatus according to claim 1 characterised in that the valve has a third port connected to the overflow port of the injection pump and a closure member actuated by an expansible element which controls the communication from the third port to a filter port in accordance with the temperature of the fuel leaving the filter port wherein the filter port is in communication with a tank port and is not influenced by the closure member.

3. Apparatus according to claim 1 or 2 characterised in that the third port is connected to the discharge line through a line.

4. Apparatus according to claim 3 characterised in that a non-return valve isolating the tank is con nected in the discharge line downstream of the junction with the line.

5. Apparatus for filtering fuel for diesel engines substantially as herein described with reference to the accompanying drawings.