STEPLESS SPEED CHANGE APPARATUS

Abstract: A stepless speed change apparatus includes first and second parallel shafts (12, 14), each carrying a plurality of discs (20) disposed in succession along the shaft. The discs on the first shaft have progressively increasing diameters along one axial direction and the discs on the second shaft have progressively decreasing diameters in that direction. There is also an intermediate shaft (48) which is disposed at an angle to the plane containing the axes of the first and second shafts. The intermediate shaft carries intermediate discs (50) each of which is aligned radially with one of the discs on the first shaft and one of the discs on the second shaft. The intermediate shaft can be shifted in a direction perpendicular to the plane containing the axes of the first and second shafts, so that as the intermediate shaft is moved the intermediate discs are, in turn, brought into engagement with respective pairs of discs on the first and second shafts at the peripheries of the discs.

Description: The present invention relates to a stepless speed change apparatus for use in automobiles and various machines. Various types of mechanical stepless speed change apparatuses have been provided. Automobiles, which are a typical machine requiring frequent speed change, have been provided with a so-called "Van Doorne type stepless speed change apparatus", which combines steel belts and segment pieces to transmit rotary force between variable-gap V-pulleys, and another type stepless speed change apparatus, which uses a stepless speed change device in the bypass circuit of a differential gear mechanism. Automobiles are often driven under severe conditions such as quick start and quick acceleration. As a result, the life of the power transmission system tends to be reduced. In the case of the Van Doorne type apparatus, the steel belts tend to have a short life. Furthermore, when a compact design is required, the highest output of the apparatus is generally said to be limited to about 100 horsepowers (1 hp ≙ 0,7457 kW). In the case of the other type apparatus, if the conventional stepless speed change device with friction wheels is used, it is also difficult to obtain large horsepowers because the area of frictional engagement is small. DE-A-1650674 describes a stepless speed change apparatus comprising two parallel shafts each of which carries a plurality of discs, and each disc on the one shaft is constantly engaged between two discs on the other shaft by means of intermediary members which are radially moveable in relation to the two sets of discs thereby to change the transmission ratio between the two shafts in a continuous manner. FR-A-524154 describes in accordance with the features of the preamble of claim 1 a speed change apparatus comprising two parallel shafts each of which carries a plurality of discs, the discs on one of the shafts increasing in diameter along the shaft, and the discs on the other shaft decreasing in diameter. Intermediate discs are carried on respective shafts, and each can be brought into engagement with a corresponding disc on each of the two shafts so as to engage the shafts at a desired transmission ratio; each intermediate shaft, by engaging a corresponding pair of discs on the two shafts, causes the two shafts to be linked with a different transmission ratio. However, such an arrangement provides a stepped speed change apparatus. It would therefore be desirable to provide a stepless speed change apparatus which is robust, simple and compact in structure, quick in speed change, and excellent in power transmission efficiency. In accordance with the present invention there is provided a speed change apparatus as defined in claim 1. A preferred embodiment of this invention is shown below with reference to the accompanying drawings, wherein: Fig. 1 is a side view partially in section of a speed change apparatus according to the invention; Fig. 2 is a sectional plan view taken along line A-A of Fig. 1; Fig. 3 is an enlarged view of portion B circled by a chain line in Fig. 1; Figs. 4a-c are diagrams illustrating changes of engagement between disc assemblies as shown in Figs. 1-3; Fig. 5 is a diagram illustrating an arrangement wherein the apparatus of this invention is combined with a differential gear; Fig. 6 is a diagram illustrating an example of numbers of revolutions of various parts of the differential gear shown in Fig. 5. With reference to Fig. 1, the apparatus includes a casing 10. On the casing are journalled an input shaft 12 and an output shaft 14, which extend horizontally in parallel to each other. The shafts 12 and 14 are formed with splines 16 and 18. On each shaft 12, 14 are mounted the same number of disc assemblies 20, 22. Each disc assembly 20 on the input shaft 12 includes two outer discs 24 and four, for example, inner discs 26 between the outer discs. The outer and inner discs 24 and 26 of each assembly 20 have the same diameter. The diameters of assemblies 20 increase slightly and stepwise to the right in Fig. 1. The splines 16 of the input shaft engage with the outer and inner discs 24 and 26, and with spacer rings 28 interposed between adjacent disc assemblies 20. On the input shaft 12 are mounted belleville springs 30 adjacent its left end to urge all discs 24 and 26 to the right. The disc assemblies 22 on the output shaft 14 are substantially the same as the assemblies 20 on the input shaft, but have diameters decreasing slightly and stepwise to the right. The assemblies 22 similarly engage with the splines 18 of the output shaft, and are urged to the right by belleville springs 32 mounted on the output shaft. With reference to Figs. 1-2, two horizontal and parallel screw shafts 34 are journalled on the casing 10 and extend between the input and output shafts 12 and 14 perpendicularly to the vertical plane containing the axes of these shafts 12 and 14. The screw shafts 34 have chain sprockets 36, which can be driven through a chain 38 by power transmission means (not shown) to rotate the screw shafts 34 in the same direction. Each screw shaft 34 engages with a threaded portion 40 of a coupling member 42, 44. The coupling members 42 and 44 are bridged by a connecting rod 46, and support an intermediate shaft 48 fixed thereto at an angle to that vertical plane as shown in Fig. 2, and a slight angle to a horizontal plane as shown in Fig. 1. Thus, the rotation of screw shafts 34 shifts the intermediate shaft 48 at the constant angles and perpendicularly to the vertical plane. The intermediate shaft 48 carries the same number of disc assemblies 50 as the assemblies 20 or 22. The assemblies 50 all have the same diameter, and each include five discs 52 of the same diameter supported rotatably around a hub 54 and axially slightly loosely. The hubs 54 are fixed to the shaft 48 with their axes in parallel to the input and output shafts 12 and 14, so that all disc assemblies 20, 22 and 50 are parallel to each other, and each assembly 50 is substantially aligned radially with one assembly 20 and one assembly 22. As best shown in Fig. 3, each inner disc 26 on the input and output shafts has a thinned outer periphery 56 with a tapered edge. Peripheral grooves 58 are formed between each outer disc 24 and adjacent inner disc 26 and between adjacent inner discs, when they contact together. Similarly, each disc 52 on the intermediate shaft 48 has a thinned outer periphery 60 with a tapered edge. Peripheral grooves 62 are formed between adjacent discs 52 when they contact together. The discs 26 and 52 may have the same thickness, with their peripheries 56 and 60 having a thickness slightly larger than half the thickness of discs 26 and 52. When each disc assembly 50 comes between the associated assemblies 20 and 22, the peripheries 60 and 56 engage together compressively by the springs 30 and 32. The operation is explained below with reference to Figs. 4a-c as viewed in the axial direction of all disc assemblies. In Fig. 4a, one disc assembly 50a on the intermediate shaft 48 (Fig. 2) is diametrically aligned with both associated assemblies 20a and 22a on the input and output shafts, with their maximum area of engagement, while no other disc assemblies engage. In Fig. 4b, as the intermediate shaft shifts to the right, the engagement area between the disc assemblies 20a, 22a and 50a gradually decreases, while the succeeding assembly 50b starts to engage with the associated assemblies 20b and 22b, which differ in diameter from the assemblies 20a and 22b, respectively. In Fig. 4c, as the intermediate shaft further shifts to the right, the engagement area between the disc assemblies 20a, 22a and 50a further decreases, while that between the assemblies 20b, 22b and 50b increases. Thus, the rotation of the input shaft is transmitted through the intermediate shaft to the output shaft at an increased or reduced speed depending on which disc assemblies engage. This apparatus can effect substantially stepless speed change, because of a continuous change between two modes of engagement, which are the maximum engagement between one set of radially aligned disc assemblies and partial engagement between an adjacent set. Fig. 5 shows a differential gear in combination with a stepless speed change apparatus 64 according to this invention. In Fig. 5, a portion of rotary torque of an input shaft 66 is transmitted through a ring gear 68, planetary gears 70 and a sun gear 72 to an output shaft 74. The other portion of torque is transmitted via a gear 78, the apparatus 64, a claw clutch 80 with synchronizing mechanism and a plurality of gears 82, which bypass the differential gear, to a carrier 76 by which the planetary gears 70 are journalled. Fig. 6 shows an example of the numbers of revolutions of various parts of the differential gear of Fig. 5. The P.C.D. (pitch diameter) of each gear is proportional to the number of teeth. In Fig. 6, d1 and d2 represent the ratio of P.C.Ds. of sun gear 72 and ring gear 68 when the sun gear has 26 teeth and the ring gear has 134 teeth. The number of revolutions is also proportional to the pitch diameter (number of teeth), and straight lines L1, L2 and L3 indicate the numbers of revolutions (RPM) of the input shaft, carrier and output shaft, respectively. If the number of revolutions of the input shaft is 6,000 RPM, the number of revolutions of the output shaft at overdrive is 7,000 RPM, the number of revolutions at the start and low speed is reduced to one quarter (1,500 RPM), and the number of revolutions in reverse gear is also reduced to one quarter (1,500 RPM), the corresponding range of number of revolutions of the carrier will be determined by the crossing points of the line L2 and the lines connecting the point at 6,000 on the line L1 and the points at 7,000 and -1,500 on the line L3; from 4,780 to 6,162 RPM. Furthermore, the line connecting the point at 1,500 on the line L3 and the point at 6,000 on the line L1 and the line L2 cross with each other to give 5,270 RPM. As a result, the range of number of revolutions of the carrier from the start and low speed up to the overdrive is from 5,270 to 6,162 RPM. As the speed change apparatus of this invention operates within this range, a wide range of stepless speed change will be achieved. If a high-performance torque sensor 84 is used in combination, because the torque will be highest when the brake is actuated, no clutch will be needed by arranging the speed change apparatus to quickly come to a stop by a signal from the torque sensor. The engagement area is an important factor for determining the magnitude of the transmittable torque. As the present invention uses a system wherein flanges of discs are pressed to engage each other to transmit rotating torque, the engagement area may be increased with ease by simply increasing the number of discs. The input and output shafts are provided with belleville springs, which generate force of compressive engagement, and the simple construction can reliably transmit rotary torque. As the outer diameters of the disc assemblies on the input and output shafts vary slightly, the engagement areas hardly generate heat or wear due to slippage. As the rotating force is transmitted with the engagement areas being variable continuously, smooth stepless speed change is accomplished without using a clutch.

Claims: A speed change apparatus comprising: first and second shafts (12,14) disposed substantially within a common plane; a plurality of first disc means (20) carried by said first shaft to rotate therewith; a plurality of second disc means (22) carried by said second shaft to rotate therewith; and a plurality of intermediate disc means (50) being arranged rotatably with respect to said first and second disc means and with their axes in parallel with the axes of said first and second disc means; each of said intermediate disc means being movable in a direction transverse to said plane so as fully to engage simultaneously a respective one of the first disc means and a respective one of the second disc means; wherein at least one of said plurality of first disc means (20), said plurality of second disc means (22) and said plurality of intermediate disc means (50) comprises disc means having differing diameters, whereby the engagement of each intermediate disc means gives rise to a different respective transmission ratio between said first and second shafts; characterised in that said apparatus further comprises: an intermediate shaft (48) disposed at an angle to said common plane, said plurality of intermediate disc means (50) being carried by said intermediate shaft, whereby said intermediate shaft can be moved to cause the movement of the intermediate disc means (50) in said transverse direction and thus to cause an alteration of the transmission ratio between said first and second shafts (12,14), the arrangement being such that, as one of said intermediate disc means starts to disengage its respective first and second disc means, another one of said intermediate disc means starts to engage its respective first and second disc means, so as to provide a continuous change of transmission ratio upon said movement of said intermediate shaft; each of said first and second disc means (20,22) comprising at least two discs (24,26) of the same diameter, which are mounted slidably on said first or second shaft (12,14), respectively, said apparatus further comprising spring means (30,32) mounted on one end of each of said first and second shafts (12,14) to urge said two discs axially toward the other end. The apparatus of claim 1, wherein each of said intermediate disc means (50) comprises at least one intermediate disc (52), said intermediate disc having a thinned outer periphery (60) with a tapered edge, the periphery (60) of said intermediate disc cooperating with peripheral grooves (58) formed by the discs of said first and second disc means, which are axially slightly narrower than the thickness of said periphery of said intermediate disc, when said two discs contact together, said periphery of said intermediate disc being adapted to compressively engage with said groove. A speed change apparatus as claimed in claim 1 or claim 2, wherein: said first and second shafts (12,14) are parallel; said first and second disc means (20,22) have diameters increasing axially in the opposite directions to each other, said plurality of intermediate disc means (50) have the same diameter and are mounted on said intermediate shaft (48) with their axes in parallel to said first and second shafts. The apparatus of claim 3, further comprising: a plurality of hubs (54) fixed to said intermediate shaft (48), each of said hubs having an axis in parallel to said first and second shafts (12,14) and supporting one of said intermediate disc means (50), a pair of parallel screw shafts (34) extending perpendicularly to the plane containing the axes of said first and second shafts, drive means connected to said screw shafts to rotate them, and a pair of coupling means (42,44), each fixed to one end of said intermediate shaft, and each engaging with one of said screw shafts so as to shift said intermediate shaft when said screw shafts rotate. The apparatus of any preceding claim, wherein the intermediate shaft (48) is adapted to move in a direction perpendicular to said common plane and in such a manner as to maintain said angle to said common plane constant.

Inventors: KUME, TAKESHI
Applicants: TKM ENG KK
Application year: 1989
Main classification: F16H15
IPC codes: F16H37, F16H15