Hydraulic Pump

The invention relates to a hydraulic pump, in particular for the drive train of a motor vehicle.

The hydraulic pump can be used to generate a volume flow of hydraulic oil that is used to lubricate bearing points in a gearbox, for example, or to cool force transmission components such as clutch discs. The hydraulic pump can also be used to generate hydraulic pressure, which is used for the hydraulic actuation of actuators.

It is generally known that it is monitored whether the hydraulic pump is delivering hydraulic oil or whether it is running dry, for example because the pump is blocked, the inlet to the pump is blocked or no hydraulic oil can reach the hydraulic pump due to another defect. If the pump runs dry, this can lead to damage to the pump itself or to consequential damage to the components that are actually to be lubricated or cooled with the hydraulic oil. If the hydraulic oil is used as a pressure medium, the pump running dry will cause the corresponding actuator to fail.

Various approaches are known to monitor whether a pump is running dry.

One approach is to monitor the power consumption of a drive motor. When the pump runs dry, the required drive torque for the pump decreases, which also reduces the power consumption of an electric motor used to drive the pump.

It is also known to recognize the presence of lubricating oil in a lubricating oil circuit of an internal combustion engine by means of a capacitive sensor. For example, DE 198 59 337 A1 shows an oil circuit in which two capacitor plates are arranged, the space between which is filled with oil when the lubricant circuit is properly filled. Compared to the state with oil between the capacitor plates and a state without oil, the capacitance of the capacitor changes, which can be detected by a corresponding evaluation circuit.

The object of the invention is to create a hydraulic pump, in particular for a motor vehicle, which has a compact design and in which it can be detected with little effort whether it is delivering a hydraulic fluid or running dry.

To solve this problem, a hydraulic pump is provided according to the invention with a drive motor, a wet chamber, at least one printed circuit board which carries electronic or electrical components for controlling the drive motor and is located in the wet chamber, an evaluation unit and at least two electrodes which are located on the printed circuit board in the wet chamber, wherein the evaluation unit can detect a change in the capacitance of a capacitor formed by the two electrodes.

The invention is based on the basic idea of forming a capacitive sensor on the printed circuit board, which is located in the wet chamber of the hydraulic pump anyway and carries electrical or electronic components for controlling the drive motor. Two electrodes can be formed on this circuit board with little effort and without the need for additional installation space, which are then covered by hydraulic fluid when the hydraulic pump is working properly and the wet chamber is filled with hydraulic fluid. The hydraulic fluid then serves as a dielectric, which has a higher relative permittivity than air. The evaluation circuit can detect the change in the capacitance of the capacitor that occurs when the fill level in the wet chamber drops so that the electrodes are no longer covered with hydraulic fluid and, accordingly, air forms the dielectric of the capacitor.

In one embodiment of the invention, the electrodes are formed by conductor tracks on the printed circuit board. In the simplest case, these are two thin conductive tracks arranged a short distance apart, which take up virtually no space on the printed circuit board. It is also possible for the conductive tracks to be fork-shaped or meander-shaped, so that the capacitance of the capacitor is significantly higher than with two short conductive tracks arranged next to each other.

It is also possible that the electrodes are formed by larger, continuously metallized surfaces on the printed circuit board. In this case, plate-like designs are used on the printed circuit board, whereby a capacitor with the desired capacitance can be obtained.

It is also possible for the electrodes to be formed by capacitor plates that are separate from the printed circuit board and mounted on it. This results in greater freedom with regard to the material for the electrodes, as this can be selected independently of the metallization of the printed circuit board.

According to a preferred embodiment of the invention, the electrodes are arranged in such a way that they are located in the upper half of the wet chamber when the hydraulic pump is in the installation position. This makes it possible to recognize at an early stage when the fill level in the wet chamber falls below the level at which the electrodes are located. If the electrodes were located in the lower region of the wet chamber, the imminent dry running of the hydraulic pump could only be recognized when the wet chamber is already almost or even completely empty.

According to one embodiment of the invention, it is provided that the evaluation unit has a signal input with which it can receive a signal that is indicative of the current consumption of the electric motor. In this way, the evaluation unit can evaluate not only a change in the capacitance of the capacitor formed by the electrodes, but also a change in the current consumption of the electric motor, so that the detection routine for dry running is improved.

schematically shows a hydraulic pumpthat is intended to be used in a motor vehicle to deliver a hydraulic fluid to other components. The hydraulic fluid can perform lubricating or cooling functions or can be used to actuate actuators.

The hydraulic pumphas a pumpthat draws in the hydraulic fluid via a suction inletand discharges it via a pressure outlet.

The pumpis driven by a drive motor, which is embodied here as an electric motor. The electric motor is arranged in a wet chamber, i.e., an area within a housingof the hydraulic pump, which is at least substantially filled with hydraulic fluid during operation.

Arranged inside the wet chamberthere is a printed circuit board, on which various electronic or electrical componentsare arranged. These are used to control the drive motorand are connected to a control unit. One of the componentsis a Hall sensor, which can be used to detect the rotation of a drive shaft of the drive motor.

Several electrodes(see also) are arranged on the printed circuit board, which together form a capacitor. The electrodesare electrically connected to an evaluation unit, which can be separate from the control unitor integrated into it.

The capacitance of the capacitor formed by the electrodesdepends, among other things, on the relative permittivity of the dielectric located between the two electrodes. Assuming that the wet chamberis completely filled with hydraulic fluid, the permittivity is in the range of 2 to 3. If the level of the hydraulic fluid in the wet chamberdrops, air is located between an ever-increasing proportion of the electrodes of the capacitor as a dielectric, which has a permittivity of approximately 1. As soon as the fill level in the wet chamberreaches the lower end of the electrodes, only air is present as a dielectric. Of course, this only applies under the theoretical assumption that when the hydraulic fluid level drops, the printed circuit board dries completely, at least in the region of the electrodes, and that no drops of hydraulic fluid remain on the printed circuit board in the region of the electrodes.

The evaluation unitis able to determine the capacitance of the capacitor formed by the electrodesand, in particular, to detect changes. Depending on the application, different “limit values” can be stored here, which are recognized by the evaluation unit. One limit value corresponds to a capacitance of the capacitor when the electrodes are fully immersed in the hydraulic fluid. Another limit value corresponds to a state in which the hydraulic fluid is below the lowest level of the electrodes.

It is also conceivable that the evaluation electronics monitor the course of the capacitance of the capacitor and, for example, if a continuous drop in the capacitance is detected, this is interpreted as an indication that the hydraulic pumpis about to run dry. This makes it possible to react more quickly, e.g., by switching on a warning display, than by waiting until a capacitance is detected that corresponds to a fill level in the wet chamberthat is below the lowest level of the electrodes.

In principle, the electrodescan be provided at any position on the printed circuit board. They are particularly preferably arranged in the region of the printed circuit boardthat is located in the upper half of the wet chamberwhen the printed circuit board and hydraulic pump are mounted. As indicated in, the conductor trackscan run parallel to each other at a small distance. In thesimplest case, two short, straight conductor track portions are used. Large-area comb or meander patterns are also possible. It is also possible for the electrodes to be formed by a large-area metallization of the printed circuit board or by capacitor plates that are manufactured separately from the printed circuit boardand mounted on it.