A DEVICE FOR PROGRESSIVE GEAR CHANGE

Abstract: The present invention relates to a device for progressive gear change. The device comprises a gear wheel (2) arranged in a steering housing, and having its teeth in engagement with teeth of a gear rack (4), and which is arranged to be rotatable about its centre axis (3) by means of a rotatably arranged eccentric pivot (5), which is non-centrally fitted to the gear wheel (2). The eccentric pivot (5) is displaceable in a straight guide groove (8) provided in the steering housing (1). When the eccentric pivot rotates uniformly the gear wheel (2) will rotate non-uniformly and the gear rack (4) will move at a progressive speed.

Description: A OEVICE FOR PROGRESSIVE GEAR CHANGE The present invention refers to a device for progressive gear change, i.e. a device transforming a uniform motion introduced at the input side thereof into a non-uniform motion taken out at the output side thereof. Devices for progressive gear change are earlier known. Such earlier devices generally incorporate non-round gear wheels, or the like, by aid of which the progressive gear change may be obtained. These earlier known devices are often complex and expensive to manufacture. The device according to the invention has several advantages as compared to the known devices. For one thing, it has no non-round gear wheels, which i.a. means simpler and less expensive manufacturing methods as compared to manufacture of known devices. A suitable field of application for the device is as a part of the steering systems of a motor car. It is easy to arran¬ ge the device thus that turning of the steering wheel a cer¬ tain rotational angle results in a smaller turning motion of the front wheels of the car, whereas turning of the steering wheel another but as big rotational angle results in a bigger turning motion at the front wheels. The characterizing features of the device according to the invention are defined in the accompanying claims. The invention hereinafter will be further described by way of an exemplifying embodiment shown in the annexed drawing. Fig. 1 shows an embodiment of the device as seen from its front side. Fig. 2 is section along lines A-A in Fig. 1. The device shown in the drawing consists of a steering housing 1 in which a gear wheel 2 is rotatably supported about its non-displaceable centre axis 3. The teeth of the gear wheel engage with the teeth of a gear rack 4, which is displaceable in its longitudinal direction perpendicularly - to the centre axis 3 of " the gear wheel, when the gear wheel 2 is caused to rotate about its centre axis 3. The rotational motion of the gear wheel 2 about the centre axis is produced with aid of an eccentric pivot 5 arranged in parallel to the centre axis 3 of the gear wheel, which eccentric pivot is non-centrally attached to the gear wheel 2 and which is arranged to rotate about its longitudinal axis by means of a rotatable shaft 7, which is articulated in two positions 6. The longitudinal direction of the shaft 7 on the opposite side of the joints forming the articulated positions 6 as seen from the steering housing 1, coincides with the centre line of the centre axis 3 of the gear wheel 2. The eccentric pivot 5 is displaceably arranged in a straight guiding groove 8 provided in the steering housing 1. When the eccentric pivot rotates it will urge the gear wheel 2 to rotate about its centre axis 3 at the same time as it will be displaced in the guiding groove 8. The displacement is possible due to the joints 6, which are arranged thus that the length of "the shaft 7 is variable. The rotational speed of the gear wheel will not be uniform but it is rather small, when the eccentric pivot 5 is farthest away from or nearest to the gear rack 4 in the guiding groove 8. The rotational speed will become biggest when the eccentric pivot is situated between the end positions in the guiding grooves 8. The different circumferential speeds of the gear wheel 2, which depend on the position of the eccentric pivot 5 in the guiding groove 8, means that the gear rack will move diffe- rent distances for each rotational angle of the gear wheel, and this may be utilized e.g. for steering a motor car. The gear rack 4 then is used in such a manner, that the gear rack is in its middle portion and the eccentric pivot in its lowermost or uppermost position, if the guiding groove 8 is provided vertically, when the car wheels are pointing for driving forward. When the steering wheel is turned in the right-hand or left-hand direction, which steering wheel is provided at the free end of the shaft 7, the circumference of the gear wheel will move only a short distance for each rotational angle, when the eccentric pivot 5 is situated at an end position in the guiding groove 8. This means that the gear rack then will be displaced only a short distance, which results in a small pivoting of the front wheels of the motor car. When increasing the turning of the steering wheel the circumference of the gear wheel will move a longer distance for each rotational angle of the steering wheel, which - means that the front wheels then will pivot more rapidly. In the embodiment of the device shown, a steering round 9 is provided at each side of the gear wheel 2, which steering rounds rotate together with the gear wheel and is guided by guiding rules 10 arranged in the steering housing. The rounds may either be manufactured separately or be made in one piece with the gear wheel 2. In the rounds are provided holes for the centre axis 3 of the gear wheel and for the eccentric pivot 5. The steering housing 1 is preferably manufactured in two mainly similar halves, which are interconnected. In each half are provided guiding grooves 8 for the eccentric pivot 5 in positions opposed to each other. In order to facilitate the motion of the eccentric pivot in the guiding grooves 8, each steering groove is fitted with a guide bearing 11 about the eccentric pivot, which bearings are slidably arranged in the guiding grooves 8. The gear rack 4 is displaceably arranged in a groove 12 in the steering housing 1. For limiting the motion of the gear rack, stops 13 are provided at both ends of the gear rack. The steering housing 1 with the gear rack 4 and the shaft 7 with the joints 6, which at its free end is equipped with a steering wheel for its rotation as shown by Fig. 2, are fitted to a common frame 14. The invention hereinbefore ^ has been described as applied to a progressive steering system for a motor car, but the invention can be used for other purposes, within the scope of the appended claims, such as e.g. for feed mechanisms for a machine tool, where a rapid advance of the tool up to the work piece to be machined, is desired but where the feed during the machining procedure shall be slower. Another field of application is for bicycle tread crank mechanisms, where the progressive gear change according to the invention can be used for adapting the crank movement to the varying muscle strength of the cyclist in view of the bending of his legs about the knee-joint.

Claims: CLAIMS 1. A device for progressive gear change incorporating a gear wheel (2) provided in a steering housing (1), which gear wheel is rotatably arranged about a non-displaceable centre axis (3) and which with its teeth engages the teeth of a gear rack (4) which is displaceable in its longitudinal direction, that is perpendicular to the centre axis of the gear wheel, c h a r a c t e r i z e d t h e r e i n, that the gear wheel (2) is designed to be rotated by means of an eccentric pivot (5), which is parallel to the centre axis (3) of the gear wheel and which is non-centrally fitted to the gear wheel and arranged to be rotated about its longitudinal axis, the eccentric pivot (5) at its rotation being displaceably arranged in a straight guiding groove (8) provided in the steering housing ( 1 ) . 2. A device for progressive gear change incorporating a gear wheel (2) provided in a steering housing ( 1 ), which gear wheel is rotatably arranged about a non-displaceable centre axis (3) and which with its teeth engages the teeth of a gear rack (4) which is displaceable in its longitudinal direction, that is perpendicular to the centre axis of the gear wheel, c h a r a c t e r i z e d t h e r e i n, that the gear wheel (2) is designed to be rotated by means of an eccentric pivot (5), which is parallel to the centre axis (3) of the gear wheel and which is non-centrally fitted to the gear wheel and arranged to be rotated about its longitudinal axis by means of a rotatable shaft (7), which is articulated by joints (6) in two positions, and the centre axis of which shaft, on the opposite side of the joints (6) as seen from the steering housing (1) coincide with an imagined extension of the centre line of the centre axis (3) of the gear wheel (2), the eccentric pivot ( 5) at its rotation being displaceably arranged in a straight guiding groove (8) provided in the steering housing (1). 3. A device as claimed in claim 1 or 2, c h a r a c t e r i z e d t h e r e i , that a steering round (9) is provided at each side of the gear wheel (2), in which rounds holes are provided for receiving the centre axis (3) of the gear wheel and the eccentric pivot (5), the rounds (9) at rotation being guided together with the gear wheel (2) by guiding rules (10) provided in the steering housing (1). 4. A device as claimed in anyone of claims 1 to 3, c h a r a c t e r i z e d t h e r e i n, that a guiding groove (8) is provided in each one of the walls of the steering housing (1) being parallel to the gear wheel (2). 5. A device as claimed in claim 4, c h a r a c t e r i z e d t h e r e i n, that the eccentric pivot (5) at each side of the gear wheel (2) equipped with the steering rounds (9) is provided with a guiding bearing (11), which is movably arranged in each guiding groove (8). 6. A device as claimed in anyone of the preceeding claims, c h a r a c t e r i z e d t h e r e i n, that the gear rack (4) is displacably fitted in a groove (12) provided in the steering housing (1), and that the displacement of the gear rack is limited by stops (13) provided at the ends of the gear rack. 7. A device as claimed in claim 6, c h a r a c t e r i z e d t h e r e i n, that a set screw is arranged to act upon the gear rack (4) thus that the teeth of the gear wheel (2) and of the gear rack (4) resp. will be positioned in correct position rela¬ tive to each other. 8. A device as claimed in anyone of the preceeding claims, c h a r a c t e r i z e d t h e r e i n, that the steering housing (1) and the part of the rotatable shaft (7) facing away from the steering housing are fitted at a common frame (14), and that the free end of the shaft (7) is preferably provided with a steering wheel for rota¬ tion of the shaft. ' -

Inventors: HJERTBERG KARL-ERIK, HJERTBERG, KARL-ERIK +DI
Applicants: HJERTBERG KARL, HULTBRAND HANS & LM, HJERTBERG, KARL, HULTBRAND, HANS +LM
Application year: 1989
Main classification: F16H19
IPC codes: B62D3, F16H19