Abstract: A gear pair includes a first gear and a second gear that are engaged and paired with each other, wherein the arithmetic average roughness Ra of the tooth surface of the first gear is less than 0.10, and the arithmetic average roughness Ra of the tooth surface of the second gear is equal to or greater than 0.15. An improvement of the transmission efficiency is achieved due to the improved composite roughness of the gear pair. Accordingly, both of the improvement of the transmission efficiency of the gears and an improvement of the pitting fatigue life are achieved at low cost.

Abstract: A gear pair includes a first gear and a second gear that are engaged and paired with each other, wherein the arithmetic average roughness Ra of the tooth surface of the first gear is less than 0.10, and the arithmetic average roughness Ra of the tooth surface of the second gear is equal to or greater than 0.15. An improvement of the transmission efficiency is achieved due to the improved composite roughness of the gear pair. Accordingly, both of the improvement of the transmission efficiency of the gears and an improvement of the pitting fatigue life are achieved at low cost.

Abstract: A power transmission device for an electrically driven vehicle basically includes a power transmission mechanism, a sliding contact brush, a brush case cover, and a brush protective jig. The power transmission mechanism includes a case element, an axle element and a power transmission element. The sliding contact brush is mounted on an axle end of the axle element. The brush case cover is selectively mounted to the case element to enclose the axle end of the axle element in the case element. The brush protective jig is mounted to cover the brush contact when mounting the sliding contact brush to the axle end. The brush protective jig is dimensioned to contact the brush case cover and to prevent the brush case cover from being mounted to the case element while the brush protective jig is in an attached state that covers the brush contact.

Abstract: A power transmission device for an electrically driven vehicle basically includes a power transmission mechanism, a sliding contact brush, a brush case cover, and a brush protective jig. The power transmission mechanism includes a case element, an axle element and a power transmission element. The sliding contact brush is mounted on an axle end of the axle element. The brush case cover is selectively mounted to the case element to enclose the axle end of the axle element in the case element. The brush protective jig is mounted to cover the brush contact when mounting the sliding contact brush to the axle end. The brush protective jig is dimensioned to contact the brush case cover and to prevent the brush case cover from being mounted to the case element while the brush protective jig is in an attached state that covers the brush contact.

Abstract: Under control of rotation of a crankshaft 41, a friction roller 32 is pressed against a friction roller 31 in a radial direction, so as to achieve torque transmission between the rollers 31, 32. An inter-roller radial pressing reaction is canceled as an internal force in bearing supports 23, 25, with no input to a housing 11. The reaction causes a radial displacement of a bearing-fitting portion provided with inner and outer bearings 21, 42 in double layer arrangement, wherein the radial displacement is larger than that of a bearing-fitting portion provided with a bearing 18, 19, 22 in single arrangement, so as to cause unbalanced contact between rollers 31, 32. In order to prevent this, support stiffness of bearing support 23 against the inter-friction-roller radial pressing reaction is set higher than that of bearing support 25.

Abstract: Under control of rotation of a crankshaft 41, a friction roller 32 is pressed against a friction roller 31 in a radial direction, so as to achieve torque transmission between the rollers 31, 32. An inter-roller radial pressing reaction is canceled as an internal force in bearing supports 23, 25, with no input to a housing 11. The reaction causes a radial displacement of a bearing-fitting portion provided with inner and outer bearings 21, 42 in double layer arrangement, wherein the radial displacement is larger than that of a bearing-fitting portion provided with a bearing 18, 19, 22 in single arrangement, so as to cause unbalanced contact between rollers 31, 32. In order to prevent this, support stiffness of bearing support 23 against the inter-friction-roller radial pressing reaction is set higher than that of bearing support 25.