Intake system for multiple cylinder combustion engines

An intake system for internal combustion engines with multiple cylinders (10). The intake system includes a first distribution chamber (13), one separate inlet pipe (15a, 15b) for each engine cylinder, which inlet pipes extend between the first distribution chamber (13) and inlet valve/valves of the corresponding cylinders, and at least one second distribution chamber (16, 16a, 16b). This is connectable to each inlet pipe (15a, 15b) between said first chamber and the inlet valve via one corresponding passage, which can be opened by means of an operable throttle valve (19). Each second distribution chamber (16, 16a, 16b) is connected to the first distribution chamber (13) via at least one resonance pipe (14), the inlet of which to the second distribution chamber is openable by means of an additional throttle valve (17).

TECHNICAL FIELD 
Intake systems for combustion engines with multiple cylinders, including a 
first distribution chamber, one inlet pipe arranged separately for each 
engine cylinder, which inlet pipes extend between the first distribution 
chamber and the inlet valve/valves for each cylinder, and at least a 
second distribution chamber, which is connectable to each one of the inlet 
pipes between said first chamber and the inlet valve each via one passage 
each, which is openable by means of simultaneously operable throttle 
valves. 
BACKGROUND OF THE INVENTION 
It is known at internal combustion engines used within a relatively broad 
range of revolutions, that the gas volume sucked in at a certain number of 
revolutions can be increased by tuning the length and diameter of the 
inlet pipes, thereby also increasing the so-called volumetric efficiency 
of the engine. This depends on, that the gas quantity present in the 
intake system is influenced by the operating frequency of the inlet 
valves, so that the gas comes in resonance oscillation. When the 
oscillation period corresponds to the operating frequency of the valves, 
the abovementioned increase of the volumetric efficiency is obtained. 
Consequently, at certain numbers of revolution a higher volumetric 
efficiency is achieved with a long inlet pipe, whereas at other numbers of 
revolution a short inlet pipe gives a higher volumetric efficiency. 
It is also earlier known, for example from EP 0182223, to provide an extra 
air distribution chamber, which is placed between the first distribution 
chamber and the inlet valves and which is connected to each inlet pipe via 
an openable throttle. By means of this arrangement the efficient length on 
the inlet pipes can be varied, whereby opening of the throttles gives an 
increase of the volumetric efficiency within a higher range of 
revolutions. 
It is desirable to place the point for transition from the first adjustment 
stage to the second adjustment stage at such a point and with such 
overlapping of the two curves, that no marked drop in torque is 
experienced, in said transition area. Hereby the positive effect of these 
known arrangements in reality becomes rather limited. 
THE TECHNICAL PROBLEM 
The object of the present invention is to provide an intake system of the 
type initially mentioned, which permits utilization of the intake system 
resonance frequency for an advantageous volumetric efficiency within such 
a broad range of revolutions as possible. 
The solution 
This has been achieved according to the invention in that each second 
distribution chamber is connected to the first distribution chamber via a 
resonance pipe, the inlet of which to the second distribution chamber is 
openable by means of an additional throttle valve, which is operable 
simultaneously with the other throttle valves. 
By addition of the resonance pipe it has been possible to tune the 
resonance frequency for the adjustment stage with short inlet pipes in 
such a manner, that the positive effect becomes substantially higher than 
at known variable intake systems.

DESCRIPTION OF EMBODIMENTS 
FIG. 1 discloses an intake system of a four-cylinder internal combustion 
engine 10. The intake system includes an outlet spigot 11 from a non 
disclosed air filter housing. In the outlet spigot is provided a throttle 
valve 12, for adjustment of the flow volume of the cleaned intake air. 
The outlet spigot 11 opens in a first distribution chamber 13, from which 
extend one resonance pipe 14 and four inlet pipes 15a, 15b. The resonance 
pipe 14 extends to the second distribution chamber 16 situated between the 
first distribution chamber 13 and the motor 10, where the outlet of the 
pipe 14 to the chamber 16 can be opened and closed by means of a throttle 
17, which is mounted on a rotatable axis 18. 
The inlet pipes 15a, 15b extend all the way up to each inlet valve in the 
motor 10 and are each therebetween connected via a not shown manifold to 
the second distribution chamber 16. The passages via the manifolds can be 
opened and closed by means of throttles 19, which are preferably mounted 
on the same turnable shaft 18 as the throttle 17. Alternatively the 
throttles 19 can be mounted on a shaft which is operable separately 
relative to the shaft 18. 
FIG. 3 shows in diagrammatic form the function of the intake system, 
whereby the horizontal axis indicates increasing number of revolutions r/s 
and the vertical axis increasing torque Nm. 
Within a low range of revolutions, which is illustrated with the graph 20, 
an appropriate torque is obtained with closed throttles 17 and 19. Hereby 
the oscillation period of the air volume in the intake system is 
determined by the total acoustic length of the pipe parts 15a, 15b. 
Within a higher range of revolutions, which is illustrated by the graph 21, 
an appropriate torque is obtained with open throttles 17 and 19. Hereby 
the oscillation period of the air volume in the inlet system is determined 
by the acoustic length of the pipe part 15b, in combination with the 
acoustic length of the resonance pipe 14. The effect of The resonance pipe 
14 appears by the dashed part 12 of the graph 21, which discloses the 
torque at an intake system according to FIG. 1, which has no resonance 
pipe 14. 
FIG. 2 discloses an intake system of an internal combustion engine 10 
having six cylinders. The intake system is basically developed in the same 
manner as the proceeding embodiment, except for the second distribution 
chamber being divided in two partial chambers 16a, 16b. Each of these is 
connected via not shown, throttle controlled manifolds with three of the 
inlet pipes 15a, 15b. Each of the two partial chambers 16a, 16b is 
furthermore connected to the first distribution chamber via a resonance 
pipe 14, the openings of which to the partial chambers 16a, 16b can be 
opened and closed by means of throttles 17. 
The adjustment of the throttles 17, 19 occurs in both embodiments 
preferably by means of a revolution sensor. All throttles 17, 19 are 
suitably provided along a common shaft 18, so that they are opened and 
closed at the same time. 
Alternatively the throttles 19 can open when a revolution level is 
exceeded, and then throttle 17 when a further higher revolution level is 
exceeded. 
The resonance pipe 14 makes it possible to tune the resonance frequency for 
the adjustment stage with short inlet pipes by dimensioning the acoustic 
length and cross-sectional area of the pipe. 
The invention is of course not limited to the shown embodiments, but a 
number of modifications are conceivable within the scope of the following 
claims, and consequently the invention can of course also be applied to 
engines with a larger or smaller number of cylinders than the four and six 
cylinders described. Further the cylinders, which are arranged in even 
ignition sequence are grouped in the same group.