GB2045866A

GB2045866A - A supercharged I.C. engine with an auxiliary compressor

Info

Publication number: GB2045866A
Application number: GB8010632A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-03-28
Filing date: 1980-03-28
Publication date: 1980-11-05
Also published as: IT8020944A0; JPS55131523A; IT1131079B; BR8002040A; SE8002430L; DE2912190A1; GB2045866B; HU181077B; FR2452594A1; DD149688A1

Abstract

An air compressor 10 for supplying vehicle accessories is connected to the engine intake pipe 7 downstream of the supercharger compressor 2. An air cooler 8 or 8a is located between the compressors 2 and 10. <IMAGE>

Description

SPECIFICATION An assembly of an air compressor and internal combustion engine having a supercharger This invention relates to an assembly comprising a multi-cylinder reciprocating internal combustion engine having at least one supercharger having an exhaust-gas driven turbine or a-drive motor and an intake-air compressor, an air compressor for auxiliary means, and means for intercooling the intake air.

Internal combustion engines supercharged in this manner have been generally known for a considerable time. Thanks to the intake-air compressor and the intercooling, a much better volumetric efficiency and, consequently, a higher output of the engine are achieved. The intake air for the air compressor for the auxiliary means, e.g. vehicle brakes, air suspension, door opening mechanisms etc., is taken from a point between the intake-air filter and the intake connection of the intake-air compressor with the advantage that the need for an additional air filter for the intake air of the air compressor and resultant maintenance work is eliminated. However, this advantage is frequently obtained at the expense of long suction pipes to the air compressor which, because of the restricted space, have to be bent with a complicated shape and are therefore expensive.The constructional costs involved are therefore often substantial.

There is a further drawback in this arrangement in that the final temperatures at the air compressor and, consequently, the thermal stressing, is high because of the intake air being heated which results in a decrease in the amounts of air delivered. The "on" cycle of the single-cylinder air compressor is therefore correspondingly high or it is necessary to provide a twin air compressor which also involves higher power requirements and more space into the bargain.

An object of the present invention is to provide an assembly of an internal combustion engine, the supercharger and an air compressor in which the above-described disadvantages may be avoided, i.e., in which the design of the suction pipes is simpler, the thermal stresses of the air compressor are reduced and the quantity of air delivered is increased.

The invention provides an assembly comprising a multi-cylinder reciprocating internal combustion engine, at least one supercharger comprising an intake-air compressor for supercharging the intake air and feeding it via an induction pipe to the engine, an intake-air cooler arranged in the induction pipe, and an air compressor for auxiliary means having an air-intake pipe connected to the induction pipe between the intake-air cooler and inlet ports of the internal combustion engine.

The invention further provides an assembly comprising a multi-cylinder reciprocating internal combustion engine, at least one supercharger comprising an intake-air compressor for supercharging the intake air and feeding it via an induction pipe to the engine, an air compressor for auxiliary means having an air-intake pipe connected to the induction pipe between the intake-air compressor and the inlet ports of the internal combustion engine, and an air inter-cooler arranged in the air-intake pipe of the air compressor for the auxiliary means.

The possibilities described provide what is practically a stage-wise compression with intercooiing for the air compressor. The first stage represents the intake-air compressor of the supercharger with adiabatic and/or isotropic compression to a relatively low pressure, the intercooling being provided by the intake-air cooler or the air intercooler. The former primarily serves the purpose of recooling the heated intake-airto a temperature level favourable for charging the engine in order to achieve a better volumetric effeciency. The second stage is then provided by the air compressor with polytropic compression to an appropriately high pressure level.

As a result of intercooling in the intake-air cooler or in the air intercooler, lower final temperatures are obtained at the air compressor than in the prior art and, as a result, thermal stressing is lower. A temperature reduction by about 60 k can be expected. As regards air delivery, the air compressor is capable of delivering up to 70% more at the same pressure, the "on" cycle being substantially reduced or, alternatively, the need for a twin air compressor is eliminated.

It should also be mentioned that the pressure conditions at the end of compression will not vary essentially for the same air compressor speeds. Consequently, there is no increase in the specific loading of the bearings.

The invention will now be described with reference to an embodiment shown by way of example in the accompanying drawings, in which: Figure 1 is a schematic view of a supercharged engine according to the invention, Figure2 is a graph showing the pressure and temperature variations of the fresh air until final compression, and Figure 3 is a graph showing the increase in the delivery volume of the air compressor obtained by the assembly according to the invention.

In Figure 1, a supercharger is shown schematically and comprises a turbine 1 operated by exhaust gas, and an intake-air compressor 2 coupled mechanically thereto. Exhaust gases from the internal combustion engine 4 flow through the turbine 1 as indicated by the arrows 3 to drive the intake-air compressor 2 which draws in air at atmospheric pressure through an intake-air filter 5 as indicated by the arrow 6 to compress it to about 2 bar and deliver it through an induction pipe 7 into an intake-air cooler 8.Assuming that the intake air has a temperature of 20 to 30"C, it will be heated as it enters the compressor 2 by heat conduction and heat radiation to about 500 to 60"C. On leaving the compressor 2, the temperature of the air is about 1200 to 130"C. In the intake-air cooler 8, the temperature of the air is reduced to about 60 C. It is at this temperature that the intake air is delivered through the induction manifold 7a to the individual cylinders of the internal combustion engine 4.

The induction manifold 7a has a branch 9 which leads to an air compressor 10 designed as a reciprocating compressor, which compresses the induction air to about 11 bar.

If intercooling is effected by means other than an intake-air cooler 8, or if there is no cooling at all, practically the same effect can be achieved by installing a separate air intercooler8a in the branch 9 as is indicated by the dashed lines in Figure 1 Figure 2 is a so-called pV graph, i.e., the volume V in units of dm3 is plotted along the ordinate 11 and the compression pressure p in bar is plotted alng the abscissa 12. If, for instance, a given volume of air is drawn in at a temperature T of about 45 C and an atmospheric pressure of 1 bar, the pressure line 13, the volume line 14 and the isothermal 15 will intersect at a point I. If the intake air is compressed to 2 bar, the lines 13', 14', 15', will intersect at point II where heating to of about 120 C has taken place. Thus a curve 16 is obtained.

Let the air compressor 10 compress the air in the traditional manner from p = 1 bar to p = 11 bar, the compression curve 17 will lead from point II as shown by the dash-dot line to point II' at which the lines 13", 14", 15" intersect. the temperature tat this point is about C.

According to the invention, compression from point I to point ll is by the intake-air compressor 2. In the air cooler 8, the air is cooled down from t r about 1200 C to T = about 60 C. Thus point Ill is attained. Now the air compteesor 10 operates to compress the air along the curve 18 to 11 bar whereby point IV results and a temperature of T of about 220 C prevails.

It follows that inte-rcooling at the end of compression results in lower temperatures whereby the thermal stress level is decreased. This line of thought can be confirmed by the following calculation: If, for instance, an intake-air volume V1 of 0X293 dm3 exists at point ill at a pressure of P111 of about 2 bar and a temperatu-re of T| of about 60 C, then, with polytropic compression, we arrive at a polytropic exponent of n = 1.3 to 11 bar n-1/n TIV = TIII . (PIV) Pm PIV = PII' = 11 bar PIII = PII = 2 bar

If this result is compared with that of an air compressor which, in the manner described initially, draws the intake air from the connecting pipe between the raw intake-air filter and the intake-air compressor, then with the same air volume, an atmospheric pressure of 1 bar and the intake air also heated by thermal conduction and radiation to about 45 C, a final temperature of about

is obtained.

Thus, there is a temperature difference of 60 K.

Thereappears to be no need for further explanation of the designations which in each case refer to the points II, II', III, IV in Figure 2.

Figure 3 shows a comparison of the air deliveries of the air compressor 10 obtained per stroke. Plotted on the ordinate 19 is the volume perstroke VHwhereasthe compression pressure p is plotted on the abscissa. If the intake air is compressed from 1 bar (P, in Figure 2) to 11 bar (p,, in Figure 2) as in the prior art by the air compressor 10, then a delivery volume Vr, is obtained with polytropic compression as indicated by the dash-dot lines 20,21.

If, however, the air compressor 10 compresses the air initially from 2 bar (pal) at 60 C 11 bar (p,v) a delivery volume Fv is obtained with the same stroke displacement VH which is about 70% greatr. This fact can also be demonstrated mathematically: VF' = VH.(PI/PII) 1/n VF = VH.(PIII/PIV) 1/n

VF=21/1.3.VF' # 1.7.VF' The delivery volume is thus increased nearly 1.7 times. In conclusion, it should be noted that the graph in Figure 3 is not to scale.

Claims

1. An assembly comprising a multi-cylinder reciprocating internal combustion engine, at least one supercharger comprising an intake-air compressor for supercharging the intake-air and feeding it via an induction pipe to the engine, an intake-air cooler arranged in the induction pipe, and an air compressor for auxiliary means having an air-intake pipe connected to the induction pipe between the intake-air cooler and inlet ports of the internal combustion engine.

2. An assembly comprising a multi-cylinder reciprocating internal combustion engine at least one supercharger comprising an intake-air compressor for supercharging the intake air and feeding it via an induction pipe to the engine, an air compressor for auxiliary means having an air-intake pipe connected to the induction pipe between the intake-air compressor and the inlet ports of the internal combustion engine, and an air inter-cooler arranged in the air-intake pipe of the air compressor for the auxiliary means.

3. An assembly substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.