APPARATUS FOR VARYING THE DAMPING CHARACTERISTICS OF A SHOCK ABSORBER

Abstract: This invention relates to an apparatus for varying the damping characteristics of a shock absorber of the kind comprising a piston rod and an adjusting shaft mounted coaxially within the piston rod for rotation relative to the piston rod. Upon a change in its angular position relative to the piston rod, the adjusting shaft effects a change in an oil passage in the shock absorber, and thus varies its damping characteristics. The adjusting shaft has a free end located at the end of the piston rod. According to the invention, the apparatus comprises a housing (4, 18, 19, 50) arranged to be attached to the end of the piston rod. The housing accommodates, in succession: - an electric motor (1) adapted to be driven and positioned in two directions; - a speed reductor (2) coupled to an output shaft (26) thereof; and - a cardanic joint (3) disposed between an output member (33) of the speed reductor (2) and the free end (15) of the shock absorber adjusting shaft (16).

Description: This invention relates to apparatus for varying the damping characteristics of a shock absorber, said shock absorber comprising a piston rod and an adjusting shaft mounted coaxially within the piston rod for rotation relative to said rod and, upon a change in its angular position relative to the piston rod, effecting a change in an oil passage in the shock absorber, the adjusting shaft having a free end located at the end of the piston rod. Shock absorbers of this type are known from practice. A change in their damping characteristics is brought about in a garage by means of hand tools, with which the rotatable adjusting shaft can be turned. In principle, this adaptation of the damping characteristics is effected once and intended to adapt the damping behaviour of the shock absorber to the spring characteristics of the vehicle on which the shock absorber is mounted. A "hard" shock absorber adjustment generally improves the road stability of the vehicle at high velocities, while a "soft" shock absorption is used to enhance travelling comfort. It is an object of the present invention to provide an apparatus or adjusting instrument, by means of which the damping characteristics of the shock absorber can be continuously adapted to the road behaviour of the vehicle. For example, at low velocities, it will be possible for the damping characteristics of the shock absorber to be so adjusted that travelling comfort, while yet still justified, is as great as possible, while at high velocities there is automatic adaptation in the direction of a greater stiffness of the shock absorber to improve road stability. The adjusting instrument must permit being accommodated in a very small compass, and therefore be of extremely compact construction. For this purpose, the apparatus according to the present invention is characterized by comprising a housing arranged to be attached to the end of the piston rod, said housing accommodating, in succession, - an electric motor adapted to be driven and positioned in two directions; - a speed reductor coupled to an output shaft thereof; and - a cardanic like joint disposed between an output member of the speed reductor and the free end of the shock absorber adjusting shaft. The compact construction is obtained by placing main parts of very small height, such as the speed reductor and a cardanic joint, one after the other. On the ground of its small rotary clearance and low structural height, a preferred speed reductor is a planetary transmission capable of effecting a sufficient reduction to produce the desired, proportional increase of the adjusting torque. The cardanic joint between the speed reductor and the free end of the adjusting shaft provides a possibility of compensation in cases in which the axis of the instrument is out of alignment with the axis of the adjusting shaft. In order to obtain a remote position indication, the electric motor is preferably coupled to a rotation position detector of the inductive type. Preferably, a Hall sensor is used for this purpose. The combination of electric motor and position detector may be replaced by an stepping motor capable of rotating the adjusting shaft in a number of discrete steps. An angular displacement of the adjusting shaft through 160° is sufficient to give the shock absorber a sufficiently large series of different damping character­ istics. As the adjusting instrument is accommodated in corrosive surroundings in the engine compartment of a vehicle, it is necessary that the instrument be of dustproof and waterproof construction. For this purpose the housing is made of sections that snap together to vertically confine the various parts of the adjusting instruments as laid down in the subclaims. The electric motor of the adjusting instrument is controllable through signal and supply lines connected through an electronic control unit to tranducers arranged within a vehicle to determine the vehicle speed, the vehicle load, the inclination of the vehicle related to its cross and longitudinal axis respectively and the viscosity of the oil within the shock absorber. One embodiment of the adjusting instrument according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 shows a vertical cross-sectional view of the adjusting instrument; Fig. 2 shows a diagrammatic bottom view of the cardanic joint, used in the instrument shown in Fig. 1; and Fig. 3 shows a top plan view of the adjusting instrument with the top cover being removed. The piston rod 11 of a shock absorber is secured to a seat 10 by means of a nut 12, which seat is to be supported on a vehicle chassis through the medium of rubber blocks. Extending within piston rod 11 and coaxially therewith is an adjusting shaft 16, the upper end 15 of which is located within piston rod 11, but extends beyond nut 12 to be accessible from the outside. The end 15 of adjusting shaft 16 is formed, for example, as a spline shaft. An open-ended, cylindrical cap 4 is placed around nut 12 and is pressed firmly into contact with seat 10 by means of nut 12. Cap 4 is provided at the top with an outward, toothed flange 17 arranged to mesh with an internally toothed edge 20 of the housing top section 18. The meshing toothed edges 17, 20 provide for the connection in circumferential direction of housing section 18 relative to cap 4. The axial confinement of housing 18 in cap 4 takes place through the medium of the housing bottom section 19. This is provided at the top with at least three click fingers 21, regularly spaced about its circumference and arranged to catch behind a click edge 22 provided in the housing top section 18. At the bottom the housing bottom section 19 is provided with a click edge 23, which can be axially confined behind a click spring 24, housed in a horizontal slot 25 in cap 4. Coaxially confined in the housing top section 18 is a D.C. motor 1 adapted to be driven and positioned in two directions. At the top, the rotor of motor 1 is provided with an impeller 44, which rotates in the permanent magnetic field of a rotation detector 5, to be described in more detail hereinafter, to provide a position indication of the angular position of the rotor of the electric motor 1. The output shaft 26 of motor 1 is connected to the input shaft of speed reductor 2. Speed reductor 2 is comprised by a planatory transmission system which is free from clearance and capable of supplying a high speed reduction and a proportionate increase of the torque generated by motor 1. Mounted on motor shaft 26 is a sun wheel 27, which meshes with three planet wheels 28. Sun wheel 27 is axially confined by a ring 29. Planet wheels 28 are provided with double gears 30, 31, the upper 30 of which meshes with sun wheel 27 and with a toothed inner ring of housing 18. The lower teeth 31 of each planet wheel 28 mesh with an internally toothed ring 32 of an output disk 33, mounted for rotation within housing 18. The output disk 33 is axially confined in housing 18 by means of the upper edge of the housing bottom section 19. The reduction between motor shaft 26 and output disk 33 is, for example 1 to 45 or more. In order to permit a certain eccentricity and also an oblique position of the axis of the adjusting mechanism relative to the axis of the shock absorber, output disk is coupled by means of a cardanic joint 3 to the end 15 of the shock absorber adjusting shaft 16. This cardanic joint 3 is shown diagrammatically in bottom view in Fig. 2. Secured to the bottom of output disk 33 are four catches 34, placed in juxtaposition to each other in pairs. Between each pair of catches 34, an arm 35 of a cross piece 36 can be received for transverse sliding movement. Extending at right angles to the arms 35, 35 of the cross piece are arms 37, 37 of cross piece 36, each consisting of juxtaposed, parallel wings. Between each pair of wings of an arm 37, an arm 38 of a connector 39 can be received for sliding movement transverse to the axis. The diametrically opposed arms 38 of connector 39 are connected to a hollow cylindrical member 40, which is provided with keyways on the inside, by virtue of which member 14 can be pushed onto the end 15 of the shock absorber adjusting shaft 16, which end 15 is provided with corresponding keyways. When motor 1 is rotating, the end 15 of adjusting shaft 16 is circumferentially adjusted, with a reduction, through the medium of speed reductor 2 and cardanic joint 3, which results in an increase or decrease of the oil passage in the shock absorber, depending on the direction of rotation of shaft 16. The cross piece 36 of joint 3 is axially confined by a partition 41 of the housing bottom section 19. This partition 41 is provided with a central orifice to permit the passage of the cylindrical part 40 of connector 39. Confined within partition 41 is a gasket 42, which is in contact with an edge of piston rod 11 projecting beyond nut 12, and surrounding the end 15 of the shock absorber adjusting shaft 16. In this way all of the parts of the adjusting instrument accommodated in housing 18, 19 are protected from moisture and dust. The rotation detector (see Figs. 1 and 3) comprises a four-bladed impeller 44 mounted on the motor shaft. The blades of impeller 44 can move between a permanent magnet 45 and a juxtaposed Hall sensor 46 capable of detecting a change in the magnetic field by impeller 44 and converting it into a signal which is a measure for the number of revolutions of motor 1. The permanent magnet 45 is attached to motor 1, for example, by means of an adhesive. Hall sensor 46 is housed in a cap 47, also attached to motor 1. Housed further in cap 47 is a printed-circuit panel 48 comprising three terminals for the Hall sensor 46 and further terminals for the supply lines of motor 1. Rotation detector 5 is confined within the housing top section 18 by means of a snap cover 50. Extending from the housing top section 18 are a series of signal and supply lines to the control electronics of the system. Through the medium of these signal lines, the position of adjusting shaft 16 is indicated to the control electronics by means of position detector 5, and adjusting signals from the control electronics are supplied to motor 1. When the vehicle is started, care is taken that a signal is given to motor 1 through the signal and supply lines so that adjusting shaft 16 comes to be in a zero or starting position, in which the oil passage in the shock absorber is largest or smallest, so that the shock absorber has the softest or hardest damping characteristics. Depending on a number of parameters, such as road condition, travelling speed, load, etc., which parameters are converted by various detectors in the vehicle into control signals which are passed to the control electronics, the damping characteristics of the shock absorber can be automatically varied and optimally adjusted in response to measured values of the various parameters.

Claims: 1. Apparatus for varying the damping characteristics of a shock absorber, said shock absorber comprising a piston rod and an adjusting shaft mounted coaxially within the piston rod for rotation relative to said rod and, upon a change in its angular position relative to the piston rod, effecting a change in an oil passage in the shock absorber, the adjusting shaft having a free end located at the end of the piston rod, characterized in that the apparatus comprises a housing (4, 18, 19, 50) arranged to be attached to the end of the piston rod, said housing accommodating, in succession, - an electric motor (1) adapted to be driven and positioned in two directions; - a speed reductor (2) coupled to an output shaft (26) thereof; and - a cardanic joint (3) disposed between an output member (33) of the speed reductor (2) and the free end (15) of the shock absorber adjusting shaft (16). 2. Apparatus as claimed in claim 1, characterized in that said electric motor (1) is connected to a rotation position transducer (5) of the inductive type (Hall sensor). 3. Apparatus as claimed in claim 1 or 2, characterized in that said electric motor (1) is an incremental motor. 4. Apparatus as claimed in any one of claims 1-3, characterized in that the housing comprises a housing top section (18) accommodating the electric motor (1) and the speed reductor (2), and a housing bottom section (19) connected thereto through a snapping connection (21, 22) and housing the cardanic joint (3), said housing bottom section including a partition (41) supporting the universal joint (3) in axial direction. 5. Apparatus as claimed in claim 4, characterized in that the housing bottom section (19) is provided at its bottom with a click edge (23) adapted to engage behind a click spring (24) provided in a mount (4) securable to the piston rod (11), the arrangement being such that an axial coupling is formed between the housing top section (18) and said mount (4), said mount (4) having a toothed outward flange (17) adapted to mesh with a correspondingly toothed internal edge (20) of the housing top section (18) for circumferentially coupling said mount (4) and said housing top section (18). 6. Apparatus as claimed in any one of claims 1-5, characterized in that the speed reductor (2) is a planet gear mechanism comprising a sun wheel (27) in operative association with three planet wheels (28) having double rings of teeth (30, 31), one ring of teeth (30) being arranged to roll over the stationary toothed inner ring of the housing top section (18), the other ring of teeth (31) being arranged to drive an output disk (33), forming the driven member, by way of an internally toothed ring (32) provided thereon. 7. Apparatus as claimed in any one of claims 1-6, characterized in that the cardanic joint (3) includes a four-armed cross piece (36) having its one pair of arms (35-35) mounted for transverse sliding movement between catches (34) provided on said output disk (33), and by way of the other pair of arms (37-37) is connected for transverse sliding movement to a connector (38, 39, 40) adapted to be placed on the free end (15) of the adjusting shaft (16), the pivot axes of the cardanic joint extending through the two pairs of arms (35-35; 37-37). 8. Apparatus as claimed in any one of claims 1-7, characterized in that the connector (39) is connected to the free end (15) of the adjusting shaft (16) by means of a spline-shaft joint. 9. Apparatus as claimed in any one of claims 1-8, characterized in that the electric motor (1) is arranged to be controlled via signal and supply lines which via an electronic control unit are connected to detectors arranged within a vehicle to determine the vehicle speed, the vehicle load, the inclination of the vehicle related to its cross and longitudinal axis respectively and the viscosity of the oil within the shock absorber.

Inventors: COLLEE, RONALD, DE BAAN, JOHANNES J., KINZL, MARWIN, Collée, Ronald
Applicants: AUGUST BILSTEIN GMBH & CO KG, IKU HOLDING MONTFOORT B.V., LEOPOLD KOSTAL GMBH & CO. KG
Application year: 1986
Main classification: F16F9
IPC codes: F16F9