Patent Application
20170191553
This application relates to a power actuators and more particularly to a power strut for lifting a pivotal lift gate closing an access opening in a motor vehicle body.
Motor vehicles of the hatchback and van configuration typically include an access opening at the rear of the vehicle body and a lift gate selectively opening and closing the access opening. The lift gate is typically manually operated and specifically requires manual effort to move the gate between open and closed positions. Various attempts have been made to provide power actuation for the lift gate. As with all automotive components, the reduction of costs, weight and spatial dimensions is a continuous concern in view of demand for increasing technology and safety features in vehicles on the one hand and for affordability and lower fuel consumption on the other hand.
In one aspect of the present invention, a power strut is described for raising and lowering a liftgate of an automotive vehicle. The power strut includes an outer housing tube having a first end carrying a first attachment element for attaching the power strut to a first vehicle part. A spindle bearing an outer thread is rotatable relative to the outer housing tube via an electric motor. The spindle defines a longitudinal axis of the power strut and is axially stationary relative to the outer housing tube. A spindle nut having an inner thread meshing with the outer thread of the spindle is displaceable along the longitudinal axis relative to the spindle. A nut tube is rigidly connected to the spindle nut and surrounds at least a portion of the spindle. A second attachment element for attaching the power strut to a second vehicle part is located opposite the first attachment element. A compression spring surrounds the nut tube and biases the first and second attachment elements apart from each other. To save machining labor and costs, the compression spring may be an open spring formed of a coiled wire with perpendicularly cut wire ends.
A profile disc in contact with a first end of the compression spring and surrounding the nut tube may have a profile complementary to the first end of the compression spring to compensate for one of the perpendicularly cut wire ends. The profile disc may be rotatable relative to the outer housing tube by torsional forces exerted by the compression spring.
A spring guide tube with a radial end collar in contact with a second end of the compression spring, the spring guide tube extending between the compression spring and the nut tube, wherein the radial collar has a profile complementary to the second end of the compression spring.
If the profile disc is rotatable, the spring guide tube may be secured against rotation relative to the outer housing tube. For example, the spring guide tube may have an internal cross-sectional shape cooperating with an anti-rotation shape formed on the spindle nut the cross-sectional shape and the anti-rotation shape allowing the spindle nut to slide axially along the spring guide tube while maintaining a relative rotational position between the spindle nut and the spring guide tube. Such an internal anti-rotation feature has the benefit that rotational forces do not need to be restrained in the locations of the upper and lower attachments to the vehicle.
The radial end collar of the spring guide tube may have a circumference with a radial annular groove and an O-ring disposed in the annular groove, wherein the O-ring preferably has an outer circumference bearing against an inner surface of the outer housing tube.
The first attachment element may have a first snap structure that is complementary to a second snap structure formed on the outer housing tube. The first and second snap structures non-rotatably secure the first attachment element to the outer housing tube.
The outer housing tube and the first attachment element, at least in the area of the first and second snap structures, may be made of plastic. One of the first and second snap structures may be formed by snap tongues and the other one of the first and second snap structures may be formed by slots so that the snap tongues are snapped into the slots.
An O-ring may be disposed between the first attachment element and the outer housing tube in a radial annular groove formed along an outer circumference of the first attachment element. The O-ring provides a seal against contamination and enhances noise reduction.
The second attachment element may include an end plug rigidly connected to the nut tube by crimping. For example, the end plug may have a cylindrical axial extension with a cylindrical surface having radial voids. The cylindrical axial extension being disposed inside the nut tube, wherein material of the nut tube is displaced radially inward into the voids.
The second attachment element may further include a joint socket with a plastic body, and the end plug may have a serrated axial extension, the serrated axial extension being disposed inside the plastic body of the joint socket and rigidly connected therewith.
The electric motor and a planetary gear box are arranged to translate a rotational output speed of the motor to a rotational drive speed of the spindle, wherein both the electric motor and the planetary gear box are disposed inside the outer housing tube.
An inner housing tube may be telescopically displaceably arranged radially inside the outer housing tube and surrounding the spindle nut, the spindle tube, and at least a portion of a compression spring.
The spring guide tube, the outer housing tube, and the inner housing tube may all be made of plastic. The nut tube is preferably made of metal.
All these features combined provide for a power strut with low manufacturing costs with respect to material and labor. Due to the strategic use of plastic parts, the power strut is lightweight yet durable.
Further details and benefits of the various aspects of the present invention will become apparent from the following description of the accompanying drawings. The drawings are provided purely for illustrative purposes and are not intended to limit the scope of the present invention.
In the drawings,
The power strut 10 of
The first joint socket 12 shown at the top of
Inside the outer housing tube 16 is a tubular drive unit housing 22 accommodating an electric motor 24 and a planetary gearbox assembly 26. A threaded drive spindle 28 extends from the drive unit housing 22 through a bearing 29 into a telescoping portion 30 of the power strut 10 and defines a longitudinal axis 32 along which the telescoping portion 30 expands and contracts.
A spindle nut 34 is molded onto an end of the nut tube 20 opposite the spring-side joint socket 14. Details of the spindle nut 34 are shown in
A cylindrical compression spring 36 is arranged around the nut tube 20 and separated therefrom by a spring guide tube 38. The compression spring 36 biases the drive unit housing 22 and the spring-side joint socket 14 apart. The spring guide tube 38 has a tubular portion 40 extending between the compression spring 36 and the nut tube 20 as well as a radial collar 42 abutted by the motor-side end of the compression spring 36. The radial collar 42 has a circumference friction-fitted against an internal circumference 44 of the outer housing tube 16 as shown in more detail in
As evident from
The opposite end 52 of the compression spring 36 rests on a ring-shaped profile disc 56 surrounding the nut tube 20. The profile disc 56 has a profile 58 complementary to the supported end 52 of the compression spring 36 to compensate for the perpendicularly cut wire end 52. The profile 58 of the profile disc 56 is shaped like or similar to the profile of the radial collar 42.
An inner housing tube 60 is friction-locked to the profile disc 56. The inner housing tube 60 protects the compression spring 36 and parts located in the telescoping portion 30 from contamination. During expansion and contraction of the power strut 10, the inner housing tube 60 glides inside the outer housing tube 16 along the longitudinal axis 32.
While the spring guide tube 38 may be non-rotatably fixed, the profile disc 56 may be rotatable relative to the outer housing tube 16 by torsional forces exerted by the compression spring 36. In general, at least one of the spring guide tube 38 and the profile disc 56 is preferably rotatable because of torsional movements of the ends 50 and 52 of the compression spring 36 during expansion and contraction of the compression spring 36.
Now referring to
With the spindle nut 34 as well as the spring guide tube 38 being formed of plastic, the interface 64 between the spindle nut 34 and the spring guide tube 38 may have a fluted design to allow the spindle nut 34 to glide inside the spring guide tube 38 along the longitudinal axis 32, while providing an anti-rotation feature that prevents the spindle nut 34 from rotating with the drive spindle 28 relative to the spring guide tube 38.
Alternatively, an anti-rotation feature may be incorporated between the outer housing tube 16 and the inner housing tube 60. In that case, the inner housing tube 60 is secured against rotation relative to the spring-side joint socket 14, for example by heat-bonding or via an adhesive or by any other suitable technique.
Now referring to
The first cylindrical extension 68 is a barb with a serrated outer surface prior to assembly as best seen in
The second cylindrical extension 70 has a smooth cylindrical outer surface with a plurality of voids 76, such as holes or indentations, that are axially and circumferentially spaced apart as best seen in
Now referring to
Adjacent to the socket portion for attaching the joint socket to the vehicle part, the motor-side joint socket 12 has a first axial portion 88 with a diameter greater than the diameter of the outer housing tube 16. The first axial portion 88 includes axial slots 84 forming the first snap structure 80 cooperating with axially protruding tongues 86 on the outer housing tube 16 that form the second snap structure 82 and that are dimensioned to be inserted into the axial slots 84 on the first axial portion 88. The first and second snap structures 80 and 82 thus secure the motor-side joint socket 12 non-rotatably to the outer housing tube 16. As shown, the first axial portion 88 may be generally circular to cover the entire cross-section of the outer housing tube 16.
A second axial portion 90 has a cross-section adapted to fit inside the internal circumference 44 of the outer housing tube 16. The second axial portion 90 is preferably circular and has a radial annular groove 94 on its circumference that carries an O-ring 96 that has an outer circumference slightly exceeding the internal circumference 44 of the outer housing tube 16. In the assembled state as shown in
The power strut 10 as described is composed mostly of plastic parts. The outer housing tube 16, the inner housing tube 60, the spring guide tube 38, the profile disc 56, and the spindle nut 34 consist of plastic. Even the drive unit housing 22, the spring-side joint socket 14 as well as the motor-side joint socket 12 may be made of plastic. The joint sockets 12 and 14 may be reinforced with metal in a few locations, for example in areas of high wear.
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise aspects disclosed. Numerous modifications or variations are possible in light of the above teachings. The aspects discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
