Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on...
Reexamination Certificate
1999-10-29
2001-07-03
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
C474S174000, C474S188000, C029S894000
Reexamination Certificate
active
06254503
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pulley useable in power transmissions of vehicles and industrial equipments, and more specifically to a pulley useable with a V-shaped driving belt in a continuously variable transmission (CVT) of vehicles and the CVT using the pulley.
Among the conventionally proposed power transmissions of vehicles and industrial equipments, there are known two types of transmissions adapted to variably transmit revolutions through an input shaft to an output shaft. One type of transmissions is a gear train type including a plurality of meshing gears and the other type is a belt-driven CVT including a driving belt.
The belt-driven CVT conventionally proposed includes an input pulley connected with a power source such as an engine, and an output pulley drivingly connected with the input pulley through an endless driving belt that is disposed therebetween and made of metal. The pulleys each define V-shaped grooves in which the driving belt is located. The width of the V-shaped groove of each pulley is variable in a direction of a revolution axis of the pulleys. The revolution of the input pulley is continuously variably transmitted to the output pulley depending on continuous variation of the widths of the V-shaped grooves of the pulleys. The CVT of this type is disclosed in “C4 Automatic Transaxle” of New Model Car Manual titled “NISSAN Primera Primera Camino” published in September, 1997.
There has conventionally been proposed a pulley for the belt-driven CVT. The pulley is made using a workpiece made of a case hardening steel. The workpiece is subjected to carburizing-quenching and tempering, and then to grinding so as to form on the outer circumferential periphery, contact surfaces that are in contact with the belt when the belt is placed in the V-shaped groove of the pulley.
There is also known an endless driving belt for the CVT, that includes a multi-layered ring composed of a plurality of ring-shaped bands laminated on one another and a plurality of V-shaped elements continuously arranged side-by-side along the circumferential direction of the multi-layered ring. Each of the V-shaped elements has side faces that are in contact with the contact surfaces of each of the pulleys upon the driving belt being engaged with the V-shaped groove of the pulley. The V-shaped element is produced from a workpiece made of a suitable steel selected from carbon steels or alloy steels used for machines, carbon tool steels, alloy tool steels and the like. In the production of the V-shaped elements, the workpiece is subjected to a suitable heat treatment such as quenching and tempering, carburizing-quenching and tempering, carbonitriding-quenching and tempering, induction-hardening and tempering, induction-hardening and the like. U.S. Pat. No. 5,011,461 discloses a driving belt used in the belt-driven CVT. The driving belt includes an endless carrier with transverse elements disposed on the endless carrier. The transverse elements are provided with side faces mating with contact surfaces of the pulleys that define the V-shaped grooves therebetween, respectively. The side faces are formed with ridges and grooves. The ridges and grooves extend straightly or slantly relative to the longitudinal direction of the endless carrier. This arrangement is provided for discharging oil and restraining slip caused by an oil film that is formed between the contact surface of each pulley and the side face of each transverse element.
SUMMARY OF THE INVENTION
There is a demand for providing a pulley for the belt-driven continuously variable transmission (CVT) that has a reduced size and can transmit an increased torque, for the purpose of reducing weight of vehicles and improving fuel economy in view of influences on environmental circumstances in feature.
Assuming that the conventionally proposed pulley is used in the belt-driven CVT and operated by a high-power engine with high torque output, the contact surfaces of the pulley that are in friction contact with the belt tend to be adhered to the opposed surface of the belt or peeled off. This is because the contact surfaces of the pulley have less wear-resistance resulting from selection of materials for the pulley and heat treatment as conventionally proposed. The adhesion or peel-off of the contact surfaces of the pulley will cause decrease in torque transmission performance of the CVT. In the case of using the pulleys made of materials selected and subjected to the heat treatment as conventionally roposed, it, therefore, will be required to increase distance between pulley-supporting shafts or change a configuration of the belt.
It is an object of the present invention to provide a pulley having highly wear-resistive outer surfaces brought into contact with a belt of the CVT, and thus being endurable even when used in a high-torque engine operation, and to provide a belt-driven CVT using the pulley.
It is a further object of the present invention to provide a pulley having a reduced size and a belt-driven CVT using the pulley.
According to one aspect of the present invention, there is provided a pulley for use with an endless metal belt, comprising:
pulley halves rotatable about an axis and relatively moveable in a direction of the axis, the pulley halves including truncated conical portions symmetrically opposed to each other and outer surfaces disposed on the truncated conical portions so as to be engageable with the endless metal belt, the outer surfaces being axially opposed to each other and sloped relative to the axis, the outer surfaces having a centerline average roughness (Ra) of 0.1 to 0.5 &mgr;m and a Vickers hardness (Hv) of not less than 850 at a load of 200 g.
According to another aspect of the present invention, there is provided a continuously variable transmission, comprising:
an input shaft;
an output shaft;
a first pulley disposed on the input shaft, the first pulley including first truncated conical ortions symmetrically opposed to each other and a first contact surface disposed on the first truncated conical portions;
a second pulley disposed on the output shaft, the second pulley including second truncated conical portions symmetrically opposed to each other and a second contact surface disposed on the second truncated conical portions; and
an endless metal belt connecting the first pulley and the second pulley, the endless metal belt including a surface engaged with the first contact surface and the second contact surface;
at least one of the first contact surface and the second contact surface having a centerline average roughness (Ra) of 0.1 to 0.5 &mgr;m and a Vickers hardness (Hv) of not less than 850 at a load of 200 g.
According to a further aspect of the present invention, there is provided a process for making a pulley including a contact surface, comprising:
forming a preform from a workpiece made of alloy steel that contains at least manganese (Mn) and chromium (Cr);
subjecting the preform to carburizing-quenching and tempering so as to have an effective case depth of not less than 0.7 mm with respect to a reference Vickers hardness (Hv) of 550 at a load of 200 g;
grinding the preform to provide an outer surface; and
shot-peening the outer surface of the preform to provide the contact surface with a centerline average roughness (Ra) of 0.1 to 0.5 &mgr;m and a Vickers hardness (Hv) of not less than 850 at a load of 200 g.
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JIS B 0601-1994, “Surface Roughness—Definitions And Designation”,Japanese Industrial Standard, pp. 1-26, (1994).
“C4 Au
Chiba Nobutaka
Nanbu Toshikazu
Yoshida Makoto
Bucci David A.
Charles Marcus
Foley & Lardner
Nissan Motor Co,. Ltd.
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