An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head pivotably mounted on the main body and having a dirty air inlet, and a motor and fan unit for drawing dirty air into the dirt and dust separating apparatus via the dirty air inlet so that dirt and dust can be separated from the airflow before the clean air is expelled to the atmosphere. The dirty-air inlet or suction opening through which dirty air is sucked into the vacuum cleaner is directed downwardly so that it faces the floor to be cleaned. The dirt and dust separating apparatus can take the form of a filter, a filter bag or a cyclonic arrangement.
A brush bar may be provided in the dirty air inlet so that it protrudes to a small extent from the inlet. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core from which bristles extend along its length in a radial direction. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust and pick up debris. The suction of air causes air to flow around the brush bar and underneath it to help lift the dirt and dust from the surface to be cleaned and then carry it from the dirty air inlet or suction opening to the dirt and dust separating apparatus.
The effectiveness of an upright vacuum cleaner depends upon the amount of dirt and dust which can be picked up by the cleaner head and passed to the separation apparatus, and so it is important that the cleaner head maintains good contact with the surface being cleaned and that the bristles of the brush bar penetrate the fibres of the carpet.
It has been proposed to employ a brush bar that can move vertically with respect to the cleaner head so that the bristles of the brush bar protrude through the suction inlet to a greater or lesser degree. However, in order for this arrangement to be useful, the range of positions of the brush bar must be controllable so that the brush bar assumes an efficacious position for each type of carpet or floor surface.