Some recreational vehicles include extendable slide-out rooms to increase the size of the living quarters while also providing an appropriate size for highway travel. Such slide-out rooms are driven by various types of mechanisms, such as hydraulic cylinders, electric drive screws, or rack-and-pinion gear drives. Rack-and-pinion drive mechanisms sometimes connect to a recreational vehicle within the aperture in which the slide-out room moves. These slide-out mechanisms are considered aesthetically pleasing because the components, except for the gear racks mounted to the side walls of the slide-out room, are relatively inconspicuous.
Nevertheless, wall mounted rack-and-pinion drive mechanisms have several drawbacks. For example, the side walls that mount the gear racks are typically skewed (that is, not parallel) relative to the direction in which the room moves or each other due to manufacturing tolerances. As such, the gear racks are typically skewed relative to the drive direction, which in turn may cause several problems. First, the gear racks may simply move away from and disengage the pinions as the slide-out room moves. Second, if the drive mechanism includes some type of feature that attempts to hold the gear rack in engagement with the pinion (for example, a pinion support bracket that engages the gear rack), the slide-out room wall may bend or deform because the rack urges it away from its manufactured position.
Some designs have attempted to address the above problems. These designs typically include a pinion mounting bracket that is movably mounted to the vehicle in a transverse direction (that is, a direction perpendicular to the drive direction). As such, the pinion moves relative to the vehicle and remains in engagement with the gear rack even if the gear rack is skewed relative to the drive direction.
However, these designs introduce yet another problem. To permit the mounting bracket and pinion to move in the transverse direction, a small clearance space (about 0.5 inch) is provided in the transverse direction between the bracket and a channel that houses the bracket. As such, the pinion mounting bracket, the gear racks, and the slide-out room may shift in the transverse direction as the vehicle moves. In particular, when the vehicle comes to a stop, the large mass of the room may cause the room to shift over the clearance space, and the pinion mounting bracket may abruptly strike the support channel. Such an action could damage the drive mechanism and could be relatively loud for the vehicle's occupants.
This problem is difficult to address because of the pinion mounting bracket's position within the support channel. Furthermore, even if the mounting bracket can be accessed, fixing the bracket in the transverse direction again causes the original problem of the gear rack disengaging the pinion.
As another example of the limitations of rack-and-pinion drive mechanisms, the components that support the weight of the slide-out room are also disposed within the aperture and are typically relatively small due to the limited space. These small supports can only carry a relatively small load, which essentially limits wall mounted rack-and-pinion mechanisms to use with relatively small and light slide-out rooms. Similarly, the weight of the slide-out room is transmitted to the supports from the rack, which is in turn supported by one of the slide-out room walls. The slide-out room walls typically comprise a light-weight (and low-strength) material such as wood and, as such, the slide-out room walls can only carry a relatively small load. This again limits wall mounted rack-and-pinion mechanisms to use with relatively small and light slide-out rooms.
Another drawback of wall mounted rack-and-pinion mechanisms is that the slide-out room typically only moves horizontally between the retracted position and the extended position and vice versa. As such, the slide-out room cannot act as a so-called “flush floor” room in which the floor of the slide-out room moves downwardly and is level with the floor of the vehicle in the extended position to eliminate the step between the vehicle and slide-out room.
As yet another example of the limitations of rack-and-pinion drive mechanisms, a speed reducer (for example, a gearbox) connecting a drive motor to the pinion is not sufficient for inhibiting unintentional movement of the slide-out room while the vehicle travels, or to maintain the seals in compression over extended periods of time when the vehicle is parked. That is, the speed reducer provides a relatively large reduction ratio and is difficult to back-drive. Nevertheless, the speed reducer may be back-driven by the large forces imparted by the slide-out room when the vehicle accelerates or turns, or wind or other lateral forces applied to the vehicle over time even if stationary. As such, the slide-out room may unintentionally move out or in.
Therefore, what is needed is a slide-out room drive mechanism that addresses one or more of the drawbacks described above.