Abstract: A roots type fluid machine includes a case having a side wall, a pair of rotary shafts provided in the case, a pair of rotors engaged with each other and fixed to the pair of rotary shafts so as to extend axially, respectively, a suction space formed by the case and the pair of rotors for introducing fluid, a discharge space formed by the case for discharging fluid and the pair of rotors and a transfer chamber formed by the case and the rotor. The rotor has a rotor end surface. A clearance is formed between the side wall and the rotor end surface. The transfer chamber transfers gas introduced in the suction space to the discharge space in accordance with the rotation of the pair of rotors. The case has a guide groove formed in the side wall facing the rotor end surface. Gas leaked from the discharge space into the clearance is introduced to the transfer chamber through the guide groove.

Abstract: A screw rotor is for use in a screw pump that pumps fluid by rotation of a pair of screw rotors engaged with each other in a rotor housing. The screw rotor includes a multiple-thread portion for pump suction side and a single-thread portion for pump discharge side. The screw rotor is formed so that the tooth profile of the multiple-thread portion is connected to the tooth profile of the single-thread portion through a boundary plane that is perpendicular to the rotation axis of the screw rotor. The first curved portion coincides with the third curved portion in the boundary plane.

Abstract: A housing of a Roots pump is configured by joining a lower housing member and an upper housing member that are separable from each other. With the upper and lower housing members joined together, an upper accommodating portion and a lower accommodating portion form a front bearing accommodating portion and a rear bearing accommodating portion, which accommodate whole bearings, respectively. The Roots pump further includes bearing holders attached to the bearings and fixed to the lower housing member so that the bearings are received in the lower accommodating portion in a positioned state.

Abstract: A first rotor and a second rotor have helical teeth each including a dedendum portion, an addendum portion, and an addendum tip portion. Profiles of the addendum portions of the first and second rotors are formed by cycloidal curves. Profiles of the dedendum portions of the first and second rotors are formed by trochoidal curves. A pitch circle of the second rotor is larger than that of the first rotor. The number of teeth of the second rotor is larger than that of the first rotor. A width angle of the first rotor is not less than a minimum angle at which the addendum tip portions of the first rotor are in line contact with an outer circle of the first rotor, and not more than an angle at which a discharge volume ratio is approximately equal to that at the minimum angle.

Abstract: A housing (2) of a Roots pump (1) supports a drive shaft (3) and a driven shaft (4) with radial bearings (32, 33) so as to be rotatable. The housing (2) is formed by joining an upper housing member (20) to a lower housing member (10). The lower housing member (10) has lower bearing support portions (13), and the upper housing member (20) has upper bearing support portions (23). Opening edges (13a) of each lower bearing support portion (13) are positioned above the centers (P1) of the bearings (32, 33). An opening width (T1) of each lower bearing support portion (13) is smaller than the diameter (D1) of the bearings (32, 33). This structure suppresses the bearings (32, 33) from being separated from the lower housing member (10) during an assembling operation of the fluid machine.

Abstract: A roots type fluid machine includes a case having a side wall, a pair of rotary shafts provided in the case, a pair of rotors engaged with each other and fixed to the pair of rotary shafts so as to extend axially, respectively, a suction space formed by the case and the pair of rotors for introducing fluid, a discharge space formed by the case for discharging fluid and the pair of rotors and a transfer chamber formed by the case and the rotor. The rotor has a rotor end surface. A clearance is formed between the side wall and the rotor end surface. The transfer chamber transfers gas introduced in the suction space to the discharge space in accordance with the rotation of the pair of rotors. The case has a guide groove formed in the side wall facing the rotor end surface. Gas leaked from the discharge space into the clearance is introduced to the transfer chamber through the guide groove.

Abstract: A screw rotor is for use in a screw pump that pumps fluid by rotation of a pair of screw rotors engaged with each other in a rotor housing. The screw rotor includes a multiple-thread portion for pump suction side and a single-thread portion for pump discharge side. The screw rotor is formed so that the tooth profile of the multiple-thread portion is connected to the tooth profile of the single-thread portion through a boundary plane that is perpendicular to the rotation axis of the screw rotor. The first curved portion coincides with the third curved portion in the boundary plane.

Abstract: A cross section of a tooth profile of a first screw rotor (17) perpendicular to the rotor axis includes a tooth top arc (A1B1), a tooth bottom arc (C1D1), a first curve (A1C1), and a second curve (B1D1). The first curve (A1C1) is a first trochoidal curve that connects a first end (A1) of the tooth top arc (A1B1) to a second end (C1) of the tooth bottom arc (C1D1). The second curve (B1D1) connects the second end (B1) of the tooth top arc (A1B1) to the first end (D1) of the tooth bottom arc (C1D1). The second curve (B1D1) is a composite curve formed by an involute curve (B1E1) and a second trochoidal curve (E1D1), which extend continuously from each other at a first intersection point (E1). A screw pump (11) thus suppresses leakage of fluid with improved performance.

Abstract: A vacuum pump includes rotary shafts connected to a pair of screw-type rotors, respectively, and a pair of shaft retainers extending in the housing. Each shaft retainer supports the corresponding rotary shaft by means of a proximal bearing portion and a distal bearing portion. Each pair of the proximal and distal bearing portions are fixed in the axial direction with respect to the corresponding rotary shaft and shaft retainer. Lubricant oil is stored in an oil storage space in a gear case attached to the housing. A cooling water passage through which cooling water to cool the lubricant oil passes is formed in the gear case. A controller controls the flow rate of the cooling fluid, so that the temperature of the lubricant oil in the oil storage space is kept constant. With this configuration, when the bearing portions are fixed in the axial direction with respect to the rotary shafts and the shaft retainers, it is possible to prevent load from being applied to the bearing portions in the axial direction.

Abstract: A cross section of a tooth profile of a first screw rotor (17) perpendicular to the rotor axis includes a tooth top arc (A1B1), a tooth bottom arc (C1D1), a first curve (A1C1), and a second curve (B1D1). The first curve (A1C1) is a first trochoidal curve that connects a first end (A1) of the tooth top arc (A1B1) to a second end (C1) of the tooth bottom arc (C1D1). The second curve (B1D1) connects the second end (B1) of the tooth top arc (A1B1) to the first end (D1) of the tooth bottom arc (C1D1). The second curve (B1D1) is a composite curve formed by an involute curve (B1E1) and a second trochoidal curve (E1D1), which extend continuously from each other at a first intersection point (E1). A screw pump (11) thus suppresses leakage of fluid with improved performance.

Abstract: A housing (2) of a Roots pump (1) supports a drive shaft (3) and a driven shaft (4) with radial bearings (32, 33) so as to be rotatable. The housing (2) is formed by joining an upper housing member (20) to a lower housing member (10). The lower housing member (10) has lower bearing support portions (13), and the upper housing member (20) has upper bearing support portions (23). Opening edges (13a) of each lower bearing support portion (13) are positioned above the centers (P1) of the bearings (32, 33). An opening width (T1) of each lower bearing support portion (13) is smaller than the diameter (D1) of the bearings (32, 33). This structure suppresses the bearings (32, 33) from being separated from the lower housing member (10) during an assembling operation of the fluid machine.

Abstract: A housing of a Roots pump is configured by joining a lower housing member and an upper housing member that are separable from each other. With the upper and lower housing members joined together, an upper accommodating portion and a lower accommodating portion form a front bearing accommodating portion and a rear bearing accommodating portion, which accommodate whole bearings, respectively. The Roots pump further includes bearing holders attached to the bearings and fixed to the lower housing member so that the bearings are received in the lower accommodating portion in a positioned state.

Abstract: A screw pump includes a housing and a pair of intermeshing screw rotors. An end face of the rotor adjacent to an inlet port of the housing is provided with an inlet opening. Each rotor has a first portion whose lead angle changes. The first portions and the housing cooperate to form an inlet space. During rotation of the rotors, communication between the inlet space and the inlet port is blocked by the first portions and the housing thereby to form a closed pump space adjacent to the inlet space. Volume of the pump space is set smaller than the maximum volume of the inlet space. A closure member is provided which covers at least a part of the inlet openings. The closure member closes the inlet space when the volume of the inlet space exceeds that of the pump space.

Abstract: A screw pump includes a housing and a pair of intermeshing screw rotors. The housing has an inlet port and an outlet port. Each rotor has a first portion whose lead angle decreases. The first portion and the housing form an inlet space and a pump space. Winding angle of the first portion has a first region and a second region. The first region is located in a predetermined range from the end on the first portion adjacent to the inlet port toward the outlet port. The second region is located adjacent to the first region. Reduction rate of the lead angle of the first portion in the first region is set smaller than that in the second region. The maximum lead angle of the first portion is set smaller than a lead angle which decreases at a constant rate in the first region and the second region.

Abstract: A vacuum pump includes a housing assembly having an oil-reservoir chamber in which a lubricating oil is stored; a pair of screw rotors disposed in the housing assembly and engaged with each other; a pair of rotary shafts connected to the rotors, respectively; a plurality of bearings supporting each of the rotary shafts and having an opening; an oil-feed pump for feeding the lubricating oil from the oil-reservoir chamber to the bearing; an oil-circulation passage provided for circulating the lubricating oil from the oil-feed pump to the oil-reservoir chamber through the bearing; a cover provided at the opening of the bearing to close the opening of the bearing with a clearance remained, the cover permitting the lubricating oil to enter the bearing through the clearance; and an oil-escape passage provided adjacent to the bearing for returning to the oil-reservoir chamber the lubricating oil not entering the bearing.

Abstract: A screw pump includes a housing and a pair of intermeshing screw rotors. The housing has an inlet port and an outlet port. Each rotor has a first portion whose lead angle decreases. The first portion and the housing form an inlet space and a pump space. Winding angle of the first portion has a first region and a second region. The first region is located in a predetermined range from the end on the first portion adjacent to the inlet port toward the outlet port. The second region is located adjacent to the first region. Reduction rate of the lead angle of the first portion in the first region is set smaller than that in the second region. The maximum lead angle of the first portion is set smaller than a lead angle which decreases at a constant rate in the first region and the second region.

Abstract: A screw pump includes a housing and a pair of intermeshing screw rotors. An end face of the rotor adjacent to an inlet port of the housing is provided with an inlet opening. Each rotor has a first portion whose lead angle changes. The first portions and the housing cooperate to form an inlet space. During rotation of the rotors, communication between the inlet space and the inlet port is blocked by the first portions and the housing thereby to form a closed pump space adjacent to the inlet space. Volume of the pump space is set smaller than the maximum volume of the inlet space. A closure member is provided which covers at least a part of the inlet openings. The closure member closes the inlet space when the volume of the inlet space exceeds that of the pump space.

Abstract: A vacuum pump includes a housing assembly having an oil-reservoir chamber in which a lubricating oil is stored; a pair of screw rotors disposed in the housing assembly and engaged with each other; a pair of rotary shafts connected to the rotors, respectively; a plurality of bearings supporting each of the rotary shafts and having an opening; an oil-feed pump for feeding the lubricating oil from the oil-reservoir chamber to the bearing; an oil-circulation passage provided for circulating the lubricating oil from the oil-feed pump to the oil-reservoir chamber through the bearing; a cover provided at the opening of the bearing to close the opening of the bearing with a clearance remained, the cover permitting the lubricating oil to enter the bearing through the clearance; and an oil-escape passage provided adjacent to the bearing for returning to the oil-reservoir chamber the lubricating oil not entering the bearing.