Abstract: An aqueous pigment dispersion is formed of a pigment, an aqueous medium and a dispersant resin. The dispersant resin contains a hydrophobic moiety and a hydrophilic moiety in its molecule. The hydrophobic moiety is a polyester linkage chain formed of ester linkages as primary linkages. The hydrophilic moiety is a water-soluble resin containing sulfonic groups or their salts. The water-soluble resin can be produced, for example, by reacting a polyol with maleic acid and/or fumaric acid to synthesize an unsaturated polyester resin and then adding acid sulfurous acid or its salt to the unsaturated polyester resin to form groups represented by the following formula (I): ##STR1## wherein M.sup.1 represents a hydrogen atom, an alkali metal, an ammonium group or a lower aliphatic quaternary ammonium group. The aqueous pigment dispersion is useful as a water-based ink for writing or recording equipments such as writing instruments, printers, copying machines, fax machines and printing machines.

Abstract: A drive force transmission apparatus includes a housing connected to one of two shafts that are rotatable relative to each other, a rotary shaft rotatably supported by the housing and connected to the other shaft, and a multiple disc clutch composed of a plurality of outer plates engaged with the housing in the rotational direction and a plurality of inner plates engaged with the rotary shaft in the rotational direction. The multiple disc clutch transmits rotational torque between the housing and the rotary shaft through frictional engagement between the outer plates and the inner plates. The apparatus also includes a pressure generation mechanism for generating a pressure corresponding to a rotational-speed difference between the housing and the rotary shaft and for applying the generated force to the multiple disc clutch via a piston.

Abstract: A torque coupling device for use as, for example, a so-called center differential provided between front and rear road wheel axles of a four-wheeled vehicle comprises a cup-shape front housing, a rear housing closing an open end of the front housing, a rotational shaft co-axially rotatably supported by the front and rear housings therewithin, and a clutch disc assembly interposed within the front housing between an axial inner end of the front housing and an axial inner end of the rear housing. The initial clearance in axial direction between the clutch assembly and the inner ends of the front and rear housings is tuned so that when the relative rotation between the housings and said rotational shaft causes a certain temperature difference between the housing and the clutch assembly, the difference in thermal expansion between the front housing and the clutch assembly brings clutch discs of the clutch assembly into friction contact to transmit a rotational torque between the housings and the rotational shaft.