1. Field of the Invention
The invention is based on a gear pump, in particular for pumping fuel from a fuel tank to a high-pressure fuel pump.
2. Description of the Prior Art
One such gear pump is known from German Patent Disclosure DE 101 34 622 A1. This gear pump has a housing, in which a pump chamber is formed in which a pair of gear wheels meshing with each other on their outer circumference is disposed. The gear wheels pump the medium to be pumped along pumping conduits, formed between their outer circumference and adjacent circumferential walls of the pump chamber, from a suction chamber into a pressure chamber. In operation of the gear pump, a tooth gap of one gear wheel reaches the pressure chamber, and a tooth gap of the other gear wheel reaches the pressure chamber after it, in chronological succession. The angle of rotation of the gear wheels corresponding to this spacing amounts here to 360°/2z in each case, where z is the number of teeth of the gear wheels.
Upon the entry of a tooth gap into the pressure chamber, the volume of the pressure chamber is increased, causing the pressure in the pressure chamber to drop. In operation of the gear pump, pressure pulsations thus occur in the pressure chamber, which have a period corresponding to half the tooth pitch angle of the gear wheels. For a number of teeth z=10, the period is thus 18°, relative to the respective axes of rotation of the gear wheels. In other words, after 18° of an angle of rotation of each of the gear wheels, one tooth gap enters the pressure chamber, and the pressure chamber volume is increased. The pressure pulsations lead to high mechanical stress on the gear pump, which must be taken into account by means of an expensive construction of the gear pump that has the requisite strength. Moreover, the pressure pulsations reduce the pumping capacity of the gear pump. To reduce these pulsations, it has been proposed in DE 101 34 622 A1 that grooves be provided, by which the radial spacing between the outer circumference of the gear wheels and the circumferential walls is increased. By means of this provision, it has already been possible to achieve a significant reduction in the amplitudes of the pressure pulsations.