A parking mechanism in a vehicle is controlled to rotate, which engages and disengages a pawl with a spoke or gear of a wheel to selectively hold the wheel against rotation in park. A spring is connected to the parking mechanism at a first end, and is connected to the transmission housing or a stop block at a second end. The first end of the spring is a closed loop, such as a helix shape that extends over 360 degrees over a loop axis. The second end of the spring is open-ended, such as a hook. After attaching the first end of the spring to the park mechanism, but prior to attaching the second end, a valve assembly can be mounted as well as the stop block. After those components are assembled in place, the second end of the spring can simply hook into place.

TECHNICAL FIELD

This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure pertains to a spring for a park mechanism.

BACKGROUND

Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is operating at a low speed, the transmission is usually operated at a high speed ratio such that it multiples the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel-efficient cruising.

These transmissions can also incorporate a park-by-wire system. In a park-by-wire system, a controller commands movement of a parking mechanism, engaging a parking pawl with an associated toothed gear of a wheel. Mechanical components, such as springs, can be implemented to bias the parking mechanism into either an engaged or disengaged state absent any commanded force on pawl from the controller. Assembly of springs can be cumbersome and awkward during the manufacturing process, especially if the spring is surrounded by other components with tight spacing.

SUMMARY

According to one embodiment, a transmission comprising a housing, and a park brake lever in the housing, rotatable about an axis, and having first, second, and third legs extending away from the axis. A valve assembly is configured to engage the first leg. A pawl is coupled to the second arm for engaging a parking brake gear. A spring has a closed-ended first end coupled to the third leg, and an open-ended second end coupled to the housing.

The first end may be in the shape of a helix, or a helix loop. The first end may include a rod that extends and loops about a loop axis by over 360 degrees.

According to another embodiment, a park mechanism comprises a lever rotatable about an axis and coupled to a valve assembly that is configured to apply hydraulic pressure to the lever. A stop block is adjacent to the valve assembly for limiting movement of the valve assembly. A spring has first and second end portions. The first end portion defines a closed loop coupled to the lever, and the second end portion defines a hook coupled to the stop block.

According to another embodiment, a method of assembling a parking brake mechanism is provided. The method includes coupling a closed-ended first end of a spring to a parking brake lever. Then, a valve assembly is assembled to or about the lever while the spring remains coupled at one end. Then, an open-ended second end of the spring is hooked through an aperture in a flange that extends from a transmission housing.

DETAILED DESCRIPTION

FIG. 1illustrates a vehicle with a powertrain10having a transmission12that incorporates a park-by-wire system. The flow of mechanical power is illustrated by solid lines, while dashed lines indicate the flow of information signals. Power is generated by engine14and conveyed to a transmission input shaft16. A torque converter18and gearbox20modify the speed and torque at which the power is delivered to match vehicle requirements while permitting engine14to run at a suitable crankshaft speed. Other types of transmissions may utilize other types of ratio manipulation devices. Driveshaft22transfers power from transmission12to differential24. Differential24distributes the power between drive wheels26and28while allowing slight speed differences such as when turning a corner. Some transmissions, such as front wheel drive transaxles, may include the differential in the same housing with the gearbox and torque converter. In such transmissions, power transfer to the differential may utilize gears or chains as opposed to a driveshaft. In some vehicles, a transfer case may be interposed between the transmission and differential to transfer some power to additional wheels.

Torque converter18includes an impeller driven by the input shaft16which hydro-dynamically drives a turbine. Torque is transferred from the impeller to the turbine whenever the turbine is rotating slower than the impeller, including when the turbine is stationary. Torque converter18also includes a stator such that the torque exerted on the turbine may be a multiple of the torque exerted by the impeller on the input shaft. The torque converter may also include an actively controlled lock-up clutch to allow efficient transfer of torque without any speed difference between the impeller and the turbine. The gearbox may be a discrete ratio gearbox that selects is capable of establishing various power flow paths with various speed ratios by selectively engaging various combinations of clutches. Alternatively, the gearbox may include a continuously variable ratio mechanism.

Transmission controller30adjusts the state of transmission12based on various inputs, including vehicle speed measurements, driver torque demand as indicated by accelerator pedal position, and shift selector32. The driver uses the shift selector to indicate the desire to move forwards (D) or backwards (R) for example. Controller30may adjust the state of the transmission by sending signals to valve body34. In response to these signals, valve body34adjusts the pressure in hydraulic circuits to engage particular clutches, such as clutches within gearbox20and the torque converter lock-up clutch.

Park mechanism36is engaged in response to driver selection of park (P) via shift selector32in order to prevent vehicle movement when the vehicle is unoccupied. The park mechanism must be designed such that, once engaged, the system stays engaged without any vehicle power. In some vehicles, the park mechanism is mechanically linked to the shift selector32. However, in a park-by-wire system, transmission controller30engages and disengages park mechanism36in response to an electrical signal from the shift selector32. Controller30may control the park mechanism indirectly by sending electrical signals to valve body34that result in hydraulic or mechanical signals to the park mechanism36.

FIGS. 2-4show a portion of the parking mechanism36that includes a valve, a lever assembly, a spring, and a stop block. The portion of the parking mechanism36shown inFIGS. 2-4is suitable for the powertrain10ofFIG. 1. The parking mechanism36can be part of a larger braking brake system that is not shown. As known in the art, parking brake systems can include mechanisms that allows for mechanical braking on the wheels while the vehicle is parked. For example, the parking brakes can include a member of the parking mechanism36being fixedly driveably connected to the driven vehicle wheels. Two elements are driveably connected when a power flow path is established between them such that rotation of one requires rotation of the other. For example, the parking brake system may include a park gear that is fixed to an output shaft of the transmission12which is fixed to the driveshaft22. Driveshaft22is driveably connected to driven wheels26and28collectively (although it is possible for driveshaft22to rotate with one of the driven wheels being stationary due to action of the differential24). In a front wheel drive transmission, there may be multiple shafts that are driveably connected to the driven wheels and therefore could park the park gear.

The parking brake system may also include a parking pawl mounted to the transmission case that is pivotable between an engaged position and a disengaged position. In the engaged position, a tooth of the parking pawl can interlock with teeth of a parking gear to prevent rotation of the parking gear, thereby preventing movement of one or more associated wheels. The system can also include a cam, a compression spring, such as those disclosed in U.S. patent application Ser. No. 14/797,205 which is hereby incorporated by reference.

The parking mechanism36shown inFIGS. 2-4includes a lever50that is pivotable about a pivot axis. The lever50is indirectly mechanically coupled to the pawl that engages the parking gear to prevent rotation of the wheel. A spring42is also provided. The spring42is a return spring that biases the lever back to position that engages the parking gear. According to various embodiments of this disclosure, the spring42is a specially-design spring that allows the spring to be attached at one end while other components are assembled to the parking brake system, and then attached at the other end to complete the assembly.

FIGS. 2-4are shown in sequential order during an assembly process, as will be described below. InFIGS. 2A-2B, the spring42is attached at a first end44and is free or not attached at a second end46. InFIG. 3, a stop block is assembled while the spring remains attached at only one end. InFIG. 4, a valve assembly is attached, and thereafter the spring can be hooked to the stop block to complete the assembly.

FIG. 2Ashows the parking mechanism from a front view, whileFIG. 2Bshows the parking mechanism from beneath (i.e., from below the mechanism36when in its orientation inFIG. 2A). The parking mechanism includes a lever50that is pivotable about a pivot point, or rotatable about an axis. In one embodiment, the lever50includes multiple legs52,54,56for attachment to different components. The legs can be formed of the same material, or can be attached or secured to one another via bolting, welding, etc. One leg52of the lever50is located within a later-attached valve assembly, as will be described below. Another leg54of the lever50is coupled to an arm58that either directly or indirectly engages the pawl for locking with the gear of the parking brake system. A third leg56serves as an attachment point for the first end44of the spring42.

The first end44of the spring42is provided with structure to enable a secured engagement with the leg56of the lever50. The structure of the spring provides a better attachment as compared to a simple hook. For example, in embodiments shown in the Figures, the first end44of the spring42is provided with a helix loop. In this helix loop, the first end44has a helix shape. The metal of the spring may be shaped such that it spirals back into itself. This shape allows an assembly worker to attach the end of the metal through a hole62in lever50, and twist the spring around the lever in a motion that is similar to putting keys on a key chain. In other embodiments, the first end44of the spring42is provided with a clasp or other similar structure that provides a semi- or fully-permanent engagement with the lever50at the hole62. In these and other various embodiments, the first end44is rotatable coupled to the lever50through the hole62but not with a simple hook or open-ended loop such that the spring is able to fully rotate 360 degrees about the lever50at one contact region on the lever50without becoming disconnected from the lever50. This provides a more secure engagement between the spring42and the lever50than an open loop, such as the open loop of the second end46of the spring.

Referring toFIG. 3, once the first end44of the spring42is coupled to the lever50, and while the second end remains free and uncoupled, a stop block66is mounted to a transmission housing68. The stop block66is positioned in line with a path of movement of a valve assembly, which is assembled later as shown inFIG. 4. The stop block66includes a flange70extending therefrom. The flange70defines an aperture therein to serve as an attachment point for the second end46of the spring. The flange70and the stop block66can, when mounted thereto, be considered part of the transmission housing68.

Referring toFIG. 4, once the stop block66is assembled, a valve assembly74is assembled as well. The valve assembly is assembled to or about the leg52of the lever50. When a parking brake is desired, the valve assembly74can provide a force via hydraulic power to the leg52of the lever50to cause the lever50to rotate against the force of the spring42. The stop block66is positioned in-line with the path of movement of the valve assembly74to limit the movement of the valve assembly74. All throughout the assembly of the stop block66and the valve assembly74, the spring42can remain attached at only the first end44. The closed-loop nature of the first end allows the spring to rotate out of the way of any parts being assembled while still remaining attached to the lever50. After the valve assembly74is assembled, the spring42can finally be hooked to the flange70at the second end46of the spring.

In the embodiments described above, the spring42can be either an extension (i.e., tension) spring or a compression spring. In one embodiment, the spring42is an extension spring that biases the lever50counter-clockwise. As the lever50rotates or pivots clockwise in the view shown inFIG. 2Ato release the parking brake, leg52is moved by the hydraulic valve74and the arm58translates to disengage the parking brake system. The spring42, being an extension spring, biases the lever50counter-clockwise to return to park. Thus, the spring42can be referred to as a return-to-park spring. In another embodiment, the spring42is a compression spring that biases the lever50to turn counter-clockwise.

FIGS. 5A, 5B, and 5Cshow different views of one example of the spring42. The second end46of the spring42can be an open-ended hook, for example. The hook extends about a hook axis76, but not completely 360 degrees about the axis76so that the second end46takes the form of a hook. In contrast, the first end44of the spring42is a closed-ended loop in that it extends at least 360 degrees about a loop axis78. The loop axis78extends generally perpendicular to a spring axis80that extends through the central part of the main body of the spring.

A free end82of the loop at the first end44is provided. An operator can feed the free end82through the hole62in the lever50and spin the spring42about the hole62over 360 degrees to attach the spring to the lever. In one embodiment, a portion of the spring that includes the free end can have a reduced diameter than the remainder of the spring to facilitate entry of the free end82into the hole in the lever50.

The first end44of the spring can be considered closed-ended, as it defines a loop of metal that extends over 360 degrees about a loop axis78. In contrast, the second end46of the spring can be considered open-ended, as the metal does not extend 360 degrees and instead takes the shape of a hook or the like.

The spring of this disclosure increases production and improves the ease of assembly. One end of the spring can be connected, while the other end remains free until components of the parking mechanism can be installed and assembled. This allows an assembly worker to keep the spring42attached to the parking mechanism36during assembly, but not entirely attached on both ends such that it would restrict movement of the lever50during assembly of surrounding parts. Due to assembly requirements or packaging concerns, the spring42may be required to be assembled prior to other components of the parking mechanism36. Previous designs and implementations of the spring impaired work flow and throughput. For example, if the spring were attached at one end during assembly, it may have easily disconnected and fallen away from the assembly. If a worker were to assemble both ends of the spring before assembling any other components, the lever50may have been restricted in movement, making for a difficult assembly. The spring42of this disclosure combats these problems by allowing one end to be securely attached without a risk that the spring would detach entirely during assembly. The second end46can then be attached at a later time during assembly.