1. Field of the Invention
This invention relates generally to a parking mechanism that provides both stable Park and non-Park positions without external power being applied. This is primarily useful for Shift-by-Wire systems that lack a driver actuated mechanical linkage to the parking pawl.
2. Description of the Prior Art
Parking mechanisms or assemblies are used in automotive vehicles to allow the vehicle to enter into and maintain a “parked” condition or state. Parking assemblies typically include a park rod, which selectively actuates a parking pawl, which operatively engages the vehicle's park gear, thereby maintaining the vehicle in a “parked” position or state.
The park rod is typically mechanically linked to the vehicle's shifter and moves in response to shifter movement. When the shifter is moved to the “park” position, the park rod engages the parking pawl, which pivots or rotates into a position where it is disposed between a pair of teeth on the park gear, thereby substantially preventing the park gear and the output shaft from further rotating.
A need exists in a shift-by-wire park mechanism, to remain in Park, thereby securing the vehicle when power is off, to remain in Neutral when power is off to support towing the vehicle, and to provide a mechanical override to enter and exit Park.
A park mechanism includes a cam pivotal between Park and not-Park ranges, including a radial outer surface formed with angularly spaced lobes, a roller urged by a spring into contact with the outer surface, a park spring urging the cam toward the Park-range, a power source for pivoting the cam, and a pawl actuated by cam movement into a Park state and a not-Park state.
Using a modification of a standard rooster comb, this mechanism is capable of maintaining both Park and non-Park positions without external power being provided.
Unless a specific control action is taken to stay out of Park, the mechanism will secure the vehicle into Park if power is removed from the mechanism.
The mechanism is mechanically stable in either a Park or non-Park state without additional energy input.
The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
The park mechanism 10 of
The cam is divided into a Park range 22 and a not-Park range 28. The crests of lobes 17, 18 define a range 29 within the not-Park range 28, wherein the mechanism holds the park mechanism of
A source of power 30, such as an electric motor or hydraulic pressure, applies alternately both clockwise and counterclockwise torque to cam 12. Torque produced by the power source 30 is able to overcome both the torque applied to the cam by the park spring 20 and resistance to rotation of the cam produced by roller 24 and the spring that urges the roller into contact with the cam.
A lever arm 32, secured to cam 12, is secured also to a parking pawl 34, shown in
Park gear 36 includes several peripherally disposed and substantially identical teeth or projections 38. Each tooth 38 is separated by a recess 40. When the angular position of cam 12 is as shown in
To exit the Park range 22, the power source 30 must rotate shaft 14 clockwise with sufficient torque to overcome the torque of spring 20, which urges the cam 12 toward the Park range 22. If cam 12 rotates clockwise such that roller 24 passes crest 50 and enters the region between lobes 17, 18, the mechanism 10 will be maintained in the non-Park state without additional force or torque being applied.
The necessary input rotation of cam 12 produced by power source 30 can be accomplished by using hydraulic pressure to oppose spring 20, which urges cam 12 toward the Park range 22, and, if necessary, the force applied by spring 25 applied to roller 24 as it moves over the crest 50 of lobe 17.
When the power source 30 is hydraulic pressure, the mechanism 10 is insensitive to a temporary loss of electrical power as long as hydraulic pressure is maintained. A disadvantage is that the mechanism cannot exit park if the engine (or other hydraulic pressure generating system) is off.
As an alternative to hydraulic actuation, shaft 14 can be rotated using an electrical motor. The advantage of this is that the mechanism can enter or exit Park range 22 even with the vehicle's engine being off.
The mechanism's output transmitted on lever arm 32 is connected to a standard parking pawl mechanism, as described with reference to
If shaft 14 is extended outside the transmission case, the Park mechanism can be manually actuated to enter or exit Park range 22.
The mechanism 10 can easily be modified to stay in Neutral, i.e., to default to neutral instead of defaulting to Park upon loss of torque from the power source 30, provided crest 50 of lobe 17 is located at the boundary 52 between Park range 22 and not-Park rage 28, instead of at the location shown in
In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.