FORD MOTOR CO (US)
| US3267763A | 1966-08-23 | |||
| US2397356A | 1946-03-26 | |||
| US2348281A | 1944-05-09 | |||
| DE1100427B | 1961-02-23 | |||
| GB145453A | 1920-09-02 | |||
| DE747611C | 1944-10-09 | |||
| US2053597A | 1936-09-08 | |||
| DE2811616A1 | 1979-09-27 |
| 1. | _ _ _ 5 CLAIMS A method of producing the rack of variable ratio rackandpinion steering arrangements in which a uniformly toothed pinion meshes with a nonuniformly toothed rack, which rack has a central section of uniform pitch and tooth shape flanked by two outer sections having a different pitch and tooth shape so as to vary the steering ratio in dependence upon the position of the rack, the teeth in the transitional areas between the central section and the outer sections being of modified shape and pitch, the method comprising the steps of forming a rack with a central section of uniform pitch and tooth shape, forming two outer sections disposed one at a preset distance from each end of the central section and having uniform pitch and tooth shape differing from the pitch and tooth shape of the central section, and producing transitional areas by formgrinding transitional tooth spaces between the respective sections, which tooth spaces fan out from central points defined by the points of intersection (F and F^) of the helix angles of the last tooth spaces (A and AL respectively) of the central section and the first tooth spaces (D and D^) of the respective outer sections (7 and 8) A method according to Claim 1, characterised in that the tooth spaces (9 and 9' or 10 and 10' respectively) adjoining the central toothing section (7) to the right and left are machined in pairs in one operation by a grinding attachment of a formgrinding machine comprising two grinding wheels. |
The invention relates to a method of producing the rack of variable ratio rack-and-pinion steering arrangements in which a uniformly toothed pinion meshes with a non-uniformly toothed rack, which rack has a central section of uniform pitch and tooth shape flanked by two outer sections having a different pitch and tooth shape so as to vary the steering ratio in dependence upon the position of the rack, the teeth in the transitional areas between the central section and the outer sections being of modified shape and pitch.
Such a rack-and-pinion steering arrangement with a variable gear ratio is known from US Patent 3 267 763, in which the varying tooth pitch and tooth shape along the length of the rack ensures a direct steering ratio in the central position of the steering wheel (when driving straight) and an indirect steering ratio in the turned position of the steering wheel.
It is stated in column 1, paragraph 5 of the above- mentioned patent specification that a toothed rack of this type can be produced by a suitable modification of a gearwheel cutting machine, by cold hammering or another non-cutting method or by broaching. In this connection it is assumed that merely a modification of the adjacent different tooth shapes is required.
A method of producing rack-and-pinion steering arrangements with a variable gear ratio by a broaching tool is known from German Patent 28 11 616. In this case, a broaching tool carrier supporting different groups of broaching tools moves essentially transversely to the toothed rack blank and the latter is received in a workpiece carrier in such a way that it can be changed in its angular position with respect to the direction of movement of the broaching tool carrier between successive broaching steps.
This known method of producing toothed racks of this type requires considerable outlay and cost in terms of machinery.
The present invention seeks to provide an improved method by which the transitional areas in the toothed rack may be made in an inexpensive manner with little outlay in machinery.
According to the present invention, there is provided a method of producing the rack of variable ratio rack-and-pinion steering arrangements as set out above, which comprises the steps of forming a rack with a central section of uniform pitch and tooth shape, forming two outer sections disposed one at a preset distance from each end of the central section and having uniform pitch and tooth shape differing from the pitch and tooth shape of the central section, and producing transitional areas by form-grinding transitional tooth spaces between the respective sections, which tooth spaces fan out from central points defined by the points of intersection of the helix angles of the last tooth spaces of the central section and the first tooth spaces of the respective outer sections.
In the present invention, the uniform central section and the uniform outer sections on the toothed rack may be produced by any desired method and a specified distance is left between the toothing sections. Thereafter, the toothing in the transitional areas is formed by form-grinding tooth spaces in the fanned out manner described above and this can be carried out using inexpensive form-grinding machines with the tooth rack blank arranged stationary.
In form-grinding, the profile of the ground space or groove between adjacent teeth is determined by the profile of the grinding wheel and not by vertical
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movement of the grinding disc. In the case of the present invention the grinding wheel for each transitional space is not symmetrical about its own central plane, as the teeth on opposite sides of the space are not of the same shape. Furthermore, each space requires a grinding wheel which is of a different profile from the grinding wheel for the other spaces in the transitional region.
Because of the symmetry of the rack about its centre line, the axes of spaces or grooves in the transitional areas equidistant from the centre line of the rack are parallel to one another and these spaces in the transitional areas may be machined at the same time as one another in pairs using a form-grinding machine with two grinding wheels.
The uniform central toothing section and the uniform outer toothing sections are also preferably also produced by form-grinding by suitable grinding wheels with a multiple profiling in one operating procedure in each case.
The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a perspective view of a toothed rack with variable pitch toothing produced by the method of the invention.
The toothed rack 6 in the drawing comprises a central section 7 of uniform tooth pitch and tooth shape, flanked on each side by uniform outer sections 8 disposed at a specified distance from the central section 7.
The transitional areas between the central sections 7 and the respective outer sections 8 are produced by form-grinding transitional tooth spaces 9/ 10 and 9',
10'. Because of the varying pitch and shape, each last tooth space of the central section 7 is inclined relative and the first tooth space of the adjacent outer section 8 and the helix angles of these spaces, i.e. the extensions of the axes A,D and A 1 ,D 1 of these spaces, meet at the points F and F^ In the present invention, the tooth spaces in the transitional areas are ground using grinding wheels of suitable profile, such that their,axes B,C, and B 1 ,C 1 also meet at the points F,F 1 and divide the angle between the axes A,D and 1 ,D 1 into an equal number parts, in this case three parts.
By virtue of the symmetry of the rack, as the axes A and ^_ are parallel and the axes D and D-^ are also parallel, it follows that the axis B is parallel to the axis B lr and the axis C is parallel to the axis C^. For this reason, the spaces 10, 10' and 9, 9' may conveniently be machined in pairs using a grinding attachment with two wheels during the same pass of the grinding tool.
The form-grinding machines, which are required for this production method and which can perform corresponding angular and profile corrections, are at present available with CNC-controlled grinding machines.
The toothing of the uniform central section and the uniform outer sections can also be advantageously produced in one operation by form-grinding using grinding wheels of suitable width and having multiple pro iling.
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