Wide ratio coverage continuously variable transmission

Provided with a wide ratio coverage CVT which has a driving power source, a first coupling axis, a clutch section, a second coupling axis, and a forward and rearward driving section, the CVT comprising: an input axis; an output axis located on the same axis with the input axis; a continuously variable unit section having a first continuously variable axis rotatably mounted on the output axis, a continuously variable driving part mounted on the first continuously variable axis, a continuously variable driven part mounted on a second continuously variable axis, and a continuously variable coupler for transmitting rotational power from the continuously variable driving part to the driven part; a coupling section having a first coupler integrally formed with the second continuously variable axis, a second coupler integrally formed with the output axis, and a third coupler for transmitting rotational power from the first coupler to the second coupler; and a gear section provided in the form of a gear set located between the input axis and the continuously variable unit section, the respective components of the gear section being operatively coupled to the input axis, the output axis, and the first continuously variable axis. It is possible to prevent a rapid decrease in the transmission efficiency at high and low speeds, reducing fuel consumption and exhaust gas and enhancing acceleration performance with a wider ratio coverage.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a continuously variable transmission (CVT)
 and, more particularly, to a wide ratio coverage CVT which is adapted to
 enhance the transmission efficiency over the conventional CVT at low and
 high speeds and improve its application by providing a high torque driving
 force.
 2. Description of the Related Art
 In the prior art, a CVT uses a continuously variable unit section only
 resulting in the disadvantage of a rapid reduction in transmission
 efficiency at high and low speeds due to the characteristics of the
 continuously variable unit section.
 Therefore, some problems arise in that the fuel efficiency is not good at
 high and low speeds, which adversely effects the exhaust emissions, and
 the transmission efficiency is decreased more at high and low speeds when
 used in large-sized vehicles (large automobile, truck, etc.), and as a
 result, the application of the CVT is limited.
 SUMMARY OF THE INVENTION
 Accordingly, an object of the present invention is to provide a wide ratio
 coverage CVT to prevent rapid transmission efficiency deterioration at
 high and low speeds where only a continuously variable unit section is
 used.
 Another object of the present invention is to provide a wide ratio coverage
 CVT with a fuel efficiency mode for providing optimized fuel efficiency, a
 power mode for dynamic driving, and a low speed mode for attaining an
 engine breaking effect.
 Still another object of the present invention is to provide a wide ratio
 coverage CVT which has a wide ratio coverage and high efficiency at high
 and low speeds to prevent the deterioration of transmission efficiency at
 a high torque, thereby being applicable to large-sized automobiles and
 other devices requiring high torque, and which can be readily installed in
 any a front wheel, rear wheel or multi-wheel drive cars since it has input
 and output axes which are coaxially located.
 To attain the objects of the present invention, there is provided a wide
 ratio coverage CVT which includes a driving power source, a first coupling
 axis, a clutch section, a second coupling axis, and a forward and rearward
 driving section, the CVT comprising: an input axis; an output axis located
 on the same axis with the input axis; a continuously variable unit section
 having a first continuously variable axis rotatably mounted on the output
 axis, a continuously variable driving part mounted on the first
 continuously variable axis, a continuously variable driven part mounted on
 a second continuously variable axis, and a continuously variable coupler
 for conveying the power from the continuously variable driving part to the
 continuously variable driven part; a coupling section having a first
 coupler integrally formed with the second continuously variable axis, a
 second coupler integrally formed with the output axis, and a third coupler
 for transmitting rotational power from the first coupler to the second
 coupler; and a gear section provided in the form of a gear set located
 between the input axis and the continuously variable unit section, the
 respective components of the gear section being operatively coupled to the
 input axis, the output axis, and the first continuously variable axis.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention can be arranged in various configurations including
 the gear section, the continuously variable unit section and the coupling
 section. The first preferred embodiment of the present invention will be
 described with reference to FIG. 1.
 As illustrated in FIG. 1, there is provided a general driving system in
 front of an input axis 2 in terms of the power transmission path. A
 driving power source 4 is an engine or motor which generates torque. This
 driving power source 4 transmits the torque to a clutch section 8 through
 a first coupling axis 6 such as crank shaft. The clutch section 8,
 comprising a torque converter or a magnetic clutch, transmits the torque
 to a forward and rearward driving section 14 through a second coupling
 axis 12. A one-way clutch 16 is provided on the second coupling axis 12 to
 prevent the second coupling axis 12 from rotating in a reverse rotational
 direction to that of the driving power source 4. This prevents a vehicle
 from spontaneously being powered backward as, for example, when the
 vehicle goes up a hill, stops and rolls backward. The forward and rearward
 driving section 14 may be installed at the back of an output axis 18 but
 is preferably located as illustrated in FIG. 1 where the variation of the
 torque is constant and the torque is low. However, it can be disposed at
 other operable positions due to space limitations. If the forward and
 rearward driving section 14 is installed at the back of the output axis
 18, the second coupling axis 12 and the input axis 2 are same axies.
 Referring to FIG. 1, the forward and rearward driving section 14 transmits
 the torque to the input axis 2.
 The input axis 2 is directly connected to a ring gear 28 of a gear section
 20 and transmits the torque to the ring gear 28. Further, a clutch 30 is
 positioned between the input and output axes 2 and 18 so that it is
 operatively coupled to each when the input and output axes are rotating at
 the same rotational speed in order to enhance efficiency of the
 transmission. Clutch 30 can be attached at an appropriate position in
 order to realize a simultaneous rotation of the input and output axes 2
 and 18.
 The gear section 20 is in the form of a planetary gear set, comprising a
 sun gear 22, a planet gear 24, a carrier 26 for supporting the planet gear
 24, and the ring gear 28. The gear section 20 may be provided as a
 differential gear set, as illustrated in FIG. 5, comprising a first gear
 23, an idle gear 25, a housing 27 for supporting the idle gear 25, and a
 second gear 29.
 When a vehicle or an object stops and thus the sun gear 22 coupled to the
 output axis 18 is stopped, the carrier 26 coupled to a first continuously
 variable axis 42 of a continuously variable unit section 40 (hereinafter
 described) is subjected to decreased rotation with respect to the ring
 gear 28, transmitting an increased torque relative to that of the ring
 gear 28 to the carrier 26. This torque is then transmitted from the
 carrier 26 to a continuously variable driving part 43 (hereinafter
 described) installed on the first continuously variable axis 42 of the
 continuously variable unit section 40.
 The continuously variable unit section 40 is well known in the related art
 examples of which are a pulley type, a traction type, etc. This
 continuously variable unit section 40 comprises the first continuously
 variable axis 42 rotatably mounted on the output shaft 18, a continuously
 variable driving part 43 mounted on the first continuously variable axis
 42, a continuously variable driven part 45 mounted on a second
 continuously variable axis 52 parallel to the input and the output axis,
 and a continuously variable coupler 47 for conveying power from the
 continuously variable driving part 43 to the driven part 45.
 The pulley type is described. That is, the driving pulley 44 corresponds to
 the continuously variable driving part 43, the driven pulley 46
 corresponds to the continuously variable driven part 45, and the belt (or
 chain) 48 corresponds to the continuously variable coupler 47. The driving
 pulley 44 transmits the torque to the driven pulley 46 via the belt 48.
 The mutual separation adjustment between the driving and driven pulleys 44
 and 46 enables a stepless speed change. The torque is transmitted from the
 driven pulley 46 to a first coupler 54 of a coupling section 50 (hereafter
 described) through the second continuously variable axis 52. The driven
 pulley 46 and the first coupler 54 are integrally installed on the second
 continuously variable axis 52, so that the second continuously variable
 axis 52, the driven pulley 46 and the first coupler 54 are integrally
 rotated always at the same rotational speed and in the same rotational
 direction.
 The coupling section 50 comprises the first coupler 54, a second coupler 56
 and a third coupler 58 and causes an increase or decrease in the fixed
 ratio to facilitate a control of speed change. In the aspect of power
 transmission, the first, second and third couplers 54, 56 and 58,
 respectively, are constructed with components that correspond or cooperate
 with one another, for example, when the first and second couplers 54 and
 56 are pulleys, the third coupler 58 is a belt, or when the first and
 second couplers 54 and 56 are sprockets, the third coupler 58 is a chain,
 or when the first and second couplers 54 and 56 are gears, the third
 coupler 58 is also a gear. The torque is transmitted from the first
 coupler 54 to the second coupler 56 via the third coupler 58, then the
 rotational speed is decreased or increased. This rotational speed is
 determined by the transmission characteristic of the system. Mostly, the
 type in which the rotational speed of the second coupler 56 is decreased
 relative to that of the first coupler 54 is used. The torque from the
 second coupler 56 is transmitted to the output axis 18.
 On the output axis 18, the sun gear 22, the second coupler 56, and the
 clutch 30 are installed. The clutch 30 is to provide simultaneous rotation
 of the input and output axes 2 and 18, maximizing the transmission
 efficiency operatively in when the input and output axes 2 and 18 have the
 same rotational speed.
 Hereinafter, the operation of the present invention will be described with
 reference to FIG. 1.
 When torque is generated by the driving power source 4, it is transmitted
 to the clutch section 8 through the first coupling axis 6 and then
 transferred to the forward and rearward driving section 14 via the second
 coupling axis 12. The torque at the forward and rearward driving section
 14 is transmitted to the input axis 2.
 The torque is transmitted to the ring gear 28 from the input axis 2. As the
 vehicle or driving body is stopped at the initial stage, the output axis
 18 and the sun gear 22 installed on the output axis 18 are stopped.
 Therefore, the carrier 26 coupled to the first pulley axis 42 is subjected
 to a decreased rotation with respected to the ring gear 28, and the torque
 increased relative to the ring gear 28 is transmitted to the carrier 26.
 This increased torque is transmitted to the first continuously variable
 axis 42.
 The torque is transmitted from the first continuously variable axis 42 to
 the driving pulley 44 installed on the first continuously variable axis
 42, and then to the driven pulley 46 through the belt 48. The process for
 transmitting the torque of the driving pulley 44 to the driven pulley 46
 via the belt 48 is known in the art. Here, a stepless speed change is
 achieved through a mutual adjustment of the separation between the driving
 and driven pulleys 44 and 46. The torque is transmitted from the driven
 pulley 46 to the first coupler 54 through the second continuously variable
 axis 52.
 The torque of the first coupler 54 is transmitted to the second coupler 56
 through the third coupler 58, then the rotational speed is decreased or
 increased (generally in the decreased form). The torque is then
 transmitted to the output axis 18 from the second coupler 56.
 The torque at the output axis 18 is used to balance the torque of the gear
 section 20 including the sun gear 22 coupled to the output axis 18, and
 the rest of the torque is used to accelerate the vehicle or driving body,
 thereby rotating the output axis 18.
 When the rotational speed of the output axis 18 is gradually raised and
 reaches the rotational speed of the input axis 2, the clutch 30, installed
 for a simultaneous rotation of the input and output axes 2 and 18, is
 operated to achieve the same rotational speed of the input and output axis
 2 and 18. In this aspect, there is no need to adjust the speed change by
 the continuously variable unit section 40 and no deterioration of the
 speed change efficiency in the continuously variable unit section 40.
 Consequently, the entire transmission efficiency can be enhanced.
 If the output axis 18 is needed to rotate at higher speed than the input
 axis 2, clutch 30, installed on the input and output axes 2 and 18, does
 not operate and the output axis 18 is rotated at a higher rotational speed
 than the input axis 2 according to the speed change by the continuously
 variable unit section 40.
 Next, second to fifth preferred embodiments of the present invention will
 be described. The present invention may be constructed to various
 embodiments according to the type of the gear section 20 and coupling of
 the respective components of the gear section 20. Here, the operational
 procedures of driving power source 4, first coupling axis 6, clutch
 section 8, second coupling axis 12, one-way clutch 16 and forward and
 rearward driving section 14, continuously variable unit section 40 and
 coupling section 50 are analogously given to the above description and
 will not be described here. The clutch 30 is provided to achieve a
 simultaneous rotation of the input and output axes 2 and 18. For example,
 the clutch 30 is installed between the input and output axes 2 and 18 in
 the first to third embodiments, while it is installed between the input
 axis 2 and the carrier 26 in the fourth embodiment (see FIG. 4), or
 between the input axis 2 and the housing 27 in the fifth embodiment (see
 FIG. 5). However, the operational procedures are the same as previously
 described.
 Basically, the gear section 20 uses a planet gear set or a differential
 gear set. The planet gear set and the differential gear set are different
 from each other in the coupling to the input axis 2, the output axis 18
 and the first continuously variable axis 42. However, both the planet gear
 set and the differential gear set are similar in the operational procedure
 using the coupling section 50 and the speed change procedure, which is set
 forth in the following table.
 TABLE 1
 Coupling to
 Coupling First
 Em- to Continuously
 bodi- Draw- Gear Input Coupling to Variable
 ment ing Type Axis 2 Output Axis 18 Axis 42
 1 FIG. 1 Planet Ring Sun Gear 22 Carrier 26
 gear Gear 28
 2 FIG. 2 Planet Sun Ring Gear 28 Carrier 26
 gear Gear 22
 3 FIG. 3 Planet Carrier Sun Gear 22 Ring Gear 28
 gear 26
 4 FIG. 4 Planet Sun Carrier 26 Ring Gear 28
 gear Gear 22
 5 FIG. 5 Differ- First Second Gear 29 Housing 27
 ential Gear 21
 gear
 The present invention is not limited to the exemplary embodiments herein
 and may be applicable to all devices using a driving force based on the
 gist of the present invention.
 Such as in the present invention described above, using the continuously
 variable unit section having the ratio of the rotational speed of the
 continuously variable driving part to that of the continuously variable
 driven part, for example 2:1 to 0.5:1 (that is, a ratio coverage of 4.0)
 enables a change to the CVT having a 5.0 to 7.0 ratio coverage according
 to the required performance.
 In addition, the present invention can dramatically prevent deterioration
 of transmission efficiency at high and low speeds and also can enhance the
 efficiency by minimizing the sliding area of the clutch at the starting
 stage due to a wide ratio coverage.
 The present invention can realize a fuel efficiency mode for providing an
 optimized fuel ratio, a power mode for dynamic driving, and a low speed
 mode for attaining an engine break effect. Furthermore, the present
 invention has a wide ratio coverage and high efficiency at high and low
 speeds to prevent transmission efficiency from being deteriorating at high
 torque, thereby being applicable to a large-sized automobile and a driver
 apparatus using a high torque, and can be readily installed in front
 wheel, rear wheel or multi-wheel drive cars since it has input and output
 axes which are coaxially located.