Claims: We Claim:
1. A supercharger (10) with improved volumetric efficiency, comprising:
a first rotor (105) and a second rotor (110) arranged to be rotating in a first chamber (115) and a second chamber (120) respectively;
an outlet port (125) for egress of compressed air from the first chamber (115) and the second chamber (120);
characterized in that:
a rib (130) disposed in the outlet port (125), extending along a peripheral boundary (135) of the first chamber (115) and the second chamber (120) and separating the outlet port (125) into two parts (125a, 125b).

2. The supercharger (10) as claimed in claim 1, wherein the rib (130) is integral with a casing (140) of the supercharger (10).
, Description:FIELD OF THE INVENTION
[0001] This invention relates to a supercharger with improved volumetric efficiency.

BACKGROUND OF THE INVENTION
[0002] A roots type supercharger operates by rotation of two multi-lobed rotors which transports the air from the inlet to the outlet. Pressurization of air happens by backflow compression when the chamber opens to the outlet port. The air is trapped in pockets surrounding the lobes in the rotors and is carried from the inlet to the outlet. Higher outlet pressures are always preferred in a supercharger. One benefit of higher outlet pressure is to enable raising the exhaust gas recirculation rates and bring down NOx emissions. In order to achieve the above said, higher volumetric efficiencies of a supercharger are desirable. Higher volumetric efficiencies also lead to reduced power consumption by the supercharger during engine operation, thereby reducing the fuel consumed by the engine. WO 2016/201166 discloses a supercharger wherein an outlet divider wall separates the outlet of the supercharger from the first recess.

BRIEF DESCRIPTION OF DRAWINGS
[0003] Embodiments of this disclosure is explained in principle below with reference to the drawings. The drawings are:
[0004] FIGURE 1 illustrates a cross-sectional view of a supercharger with a two-part outlet port.

DETAILED DESCRIPTION
[0005] FIGURE 1 illustrates a cross-sectional view of a supercharger 10 with a two-part outlet port. The supercharger 10 with the two-part outlet port improves a volumetric efficiency of the supercharger 10, which is explained hereinafter. The supercharger 10 comprises a first rotor 105 and a second rotor 110, wherein the first rotor 105 and the second rotor 110 are arranged to be rotating in a first chamber 115 and a second chamber 120 respectively. The supercharger 10 comprises an outlet port 125 for egress of compressed air from the first chamber 115 and the second chamber 120. The supercharger 10 further comprises a rib 130 disposed in the outlet port 125, the rib extending along a peripheral boundary 135 of the first chamber 115 and the second chamber 120 and separating the outlet port 125 into two parts 125a and 125b. In the supercharger 10, the rib 130 is integral with a casing 140 of the supercharger 10.
[0006] The rib 130 is akin to a separation or a partition, separating the outlet port 125 into two parts 125a and 125b. The rib 130 extends along the peripheral boundary 135 of the first chamber 115 and the second chamber 120. In other words, the rib 130 extends where the first chamber 115 and the second chamber 120 meet. To elaborate and visualize, there is no physical boundary as such in the supercharger 10 as the first chamber 115 and the second chamber 120 opens out into the outlet port 125. The rib 130 extends in a direction parallel to an axis of the first rotor 105 and an axis of the second rotor 110 and between two opposite sides of the outlet port 125.
[0007] The presence of the rib 130 reduces the generation of recirculation zones inside the first chamber 115 and the second chamber 120, which will be described hereinafter. In superchargers belonging to the state of the art, where the rib 130 is absent, recirculation zones of air are generated in both the chambers near the outlet port, which reduce the volumetric efficiency of the superchargers. A first reason for the formation of recirculation zones is described hereinafter. The first rotor 105 and the second rotor 110 rotate in opposite rotary directions. The rotation of the first rotor 105 pushes the air molecules from the first chamber 115 into the outlet port 125. A portion of the air molecules pushed into the outlet port 125 from the first chamber 115 is forced into the second chamber 120. The air molecules forced into the second chamber 120 from the outlet port 125 interferes with the air molecules being forced out of the second chamber 120 by the rotation of the second rotor 110. This interference leads to the generation of recirculation zones inside the second chamber 120. Similarly, recirculation zones are generated inside the first chamber 115 as well due to the effect of the air molecules forced out of the second chamber 120 into the outlet port 125 and the subsequent forcing back. The presence of the rib 130 blocks the forcing back of air molecules from the outlet port 125 into the second chamber 120 and the first chamber 115, thereby reducing the formation or generation of recirculation zones in both the chambers.
[0008] A second reason for generation of recirculation zones is described below. The air molecules in both the first chamber 115 and the second chamber 120 follow a least distance path or direct approach to the outlet port 125. For the air molecules in the second chamber 120, the least distance path is near the boundary of the first chamber 115 and the second chamber 120. Hence, the air molecules try to get into the outlet port 125 from here. But the first rotor 105, during the rotation, enters the second chamber 120 briefly, as there is an overlap between the first chamber 115 and the second chamber 120. When the first rotor 105 enters the second chamber 120, the first rotor 105 pushes down the air molecules on their way to the outlet port 125 inside the second chamber 120, thereby disturbing the flow of air molecules and forcing them to change course and generating recirculation zones inside the second chamber 120 near the peripheral boundary 135. Similarly, recirculation zones are formed or generated in the first chamber 115 also due to the corresponding effect of the second rotor 110. The presence of the rib 130 changes the physical structure of the supercharger 10 such that the least distance path is no more near the peripheral boundary 135 and therefore the rotation of the first rotor 105 and the second rotor 110 does not generate recirculation zones in the second chamber 120 and the first chamber 115 respectively. This is because the air molecules using the least distance path to exit the first chamber 115 and the second chamber 120 are not disturbed and forced to change course and recirculate by the rotation of the second rotor 110 and the first rotor 105 respectively. To elaborate, the rib 130 changes the least distance path such that the air molecules are not in the path of the rotation of the first rotor 105 and the second rotor 110.

[0009] By reducing the formation of recirculation zones, the volumetric efficiency of the supercharger 10 is increased or improved, thereby reducing the power output of the engine to run the supercharger 10. Thereby, engine efficiency can also be increased or improved.
[0010] The rib 130 is integral to the casing 140 of the supercharger 10. The advantage of this is that the supercharger 10 in accordance with the instant invention can be manufactured easily and with relatively lesser cost, which provides economical and time based benefits.
[0011] An experimental study indicated that the mass flow from the outlet port of the supercharger increased by around 2 times with a rib in the outlet port.
[0012] FIGURE 1 shows a pair of three lobed rotors. The rib 130 can also be applied for a supercharger 10 with a pair of two lobed rotors. Additionally, the rib 130 can also be applied for a supercharger 10 with rotors having any number of lobes.
[0013] It is to be understood that the foregoing description is intended to be purely illustrative of the principles of the disclosed techniques, rather than exhaustive thereof, and that changes and variations will be apparent to those skilled in the art, and that the present invention is not intended to be limited other than as expressly set forth in the following claims