ELECTRIC MACHINE WITH INTEGRATED THERMAL BUFFER AND DRIVE UNIT COMPRISING SAID ELECTRIC MACHINE

Abstract

An electric machine (01), including a rotor (06), a stator (03), an electric winding (04) and a housing (02). The electric machine has an overall thermal resistance in relation to the surroundings which is dimensioned such that the continuous heat losses resulting from a continuous operating current being fed to the electric winding (04) is carried off to the surroundings so that at a predetermined ambient temperature a predetermined maximum winding temperature is not exceeded. The electric machine is characterized in that the housing (02) is filled with a dielectric liquid (11). The liquid has a heat capacity which is dimensioned such that it can absorb a peak load heat quantity which is given off by the electric winding (04), in excess to the continuous heat losses, when said winding is operated at a peak current during a peak load operating time.

Claims

1-10. (canceled)

11. An electric machine comprising: a rotor; a stator; an electric winding; and a housing, the electric machine having an overall thermal resistance with respect to surroundings, the overall thermal resistance being dimensioned such that continuous heat losses resulting during the feeding of a continuous operating current to the electric winding are dissipated to the surroundings at a predetermined ambient temperature and a predetermined maximum winding temperature, the housing being filled with a dielectric liquid having a heat capacity dimensioned to absorb a peak load heat quantity given off by the electric winding beyond the continuous heat losses when the electric winding is operated at a peak current during a peak load operating time.

12. The electric machine as recited in claim 11 wherein the dielectric liquid is an oil or an oil-containing mixture, and the housing is sealed liquid-tight.

13. The electric machine as recited in claim 11 wherein the heat capacity of the dielectric liquid is dimensioned to absorb a peak load heat quantity, the peak load heat quantity including a heat quantity given off by the electric winding beyond the continuous heat losses as well as the heat quantity, given off by other heat sources, which are immanent in the electric machine.

14. The electric machine as recited in claim 11 wherein the housing is filled with a quantity of the dielectric liquid filling 50% to 100% of free space in the housing.

15. The electric machine as recited in claim 11 wherein vane elements are mounted on the rotor, the vane elements configured for engaging with the dielectric liquid and inducing a mixing and distribution of the dielectric liquid during rotation.

16. The electric machine as recited in claim 11 wherein the housing includes a filler neck via which the dielectric liquid is fillable.

17. A drive unit including an electric motor and a drive element coupled thereto, the electric motor being the electric machine as recited in claim 11.

18. The drive unit as recited in claim 17 further comprising a control unit feeding a drive current to the electric motor in a normal operating state, the drive current not exceeding the continuous operating current of the electric machine, the control unit feeding a peak current to the electric motor in a peak load state for a peak load period of time not greater than the time required to generate the peak load heat quantity.

19. The drive unit as recited in claim 18 further comprising a temperature sensor, with the aid of which the control unit measures the instantaneous ambient temperature, the instantaneous ambient temperature being taken into account in the determination of the peak load heat quantity.

20. The drive unit as recited in claim 17 wherein the drive element is selected from the following group: a ball screw spindle, a ball planetary spindle, a hydraulic cylinder, and a cable winch.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0019] Further advantages, details and refinements of the present invention result from the following description of one preferred specific embodiment with reference to the drawing.

[0020] The FIGURE shows a greatly simplified longitudinal sectional view of the principle structure of an electric machine, which is designed as an internal rotor motor.

DETAILED DESCRIPTION

[0021] An electric motor 01 illustrated in FIG. 1 includes a housing 02, which is sealed liquid-tight. A stator 03, which carries an electric winding 04, is situated within housing 02. Electric winding 04 may include multiple coil units, which are electrically interconnected with each other, depending on the desired type of operation, and which are supplied with a driving current from an external control unit (not illustrated).

[0022] Electric motor 01 furthermore includes in this case an internal rotor 06, which is connected to a motor shaft 07. Motor shaft 07 is supported by rolling bearings 08, which are held in housing 02 and sealed via a bearing seal 09 for the purpose of preventing the escape of liquid from housing 02.

[0023] Electric winding 04 is dimensioned in such a way that the heat losses occurring during a continuous or normal operating state may be dissipated to housing 02 and, from there, to the surroundings without requiring an additional cooling system and without exceeding a maximum permissible winding temperature.

[0024] The cavities remaining between stator 03 and rotor 06 within housing 02 are filled with a dielectric liquid 11, which, in this specific embodiment, almost completely fills the cavities. In modified specific embodiments, the free space within housing 02 is filled to approximately 50% to 80% as a function of the required heat capacity provided by the dielectric liquid.

[0025] Those skilled in the art may easily determine the minimum quantity of dielectric liquid needed, in particular oil, based on the peak load heat quantity occurring in the peak load case. The difference between the heat quantity generated by the electric machine in the normal operating state and that dissipated to the surroundings by heat transfer must initially be absorbed by the dielectric liquid, which acts as a thermal buffer. In the simplest case, the required quantity for completely absorbing this peak load heat quantity may be calculated using the specific heat capacity of the dielectric liquid employed.

[0026] If a more precise dimensioning is desired, the passive heat dissipation may be taken into account, which also results in a transfer of the occurring heat losses in the peak load state. This is also dependent on the ambient temperature, which may be ascertained as needed with the aid of a temperature sensor. The resulting temperature gradient between the instantaneous operating temperature at housing 02 and the ambient temperature may be taken into account within a control unit for the purpose of generating a warning signal as needed or ending the peak load operating state when the electric winding is at risk of overheating. The control unit may also be configured in such a way that, after passing through a peak load state for a predefined period of time, only operation in the normal operating state is made possible, so that sufficient time is available to passively dissipate the additional heat quantity absorbed by the dielectric liquid to the surroundings. A peak load state may be permitted again only when this time has elapsed, or upon reaching a normal operating temperature of the dielectric liquid.

[0027] Those skilled in the art will easily recognize that the present invention may also be used in modified specific embodiments of electric machines. In particular, it may be advantageous to structurally increase in a targeted manner the cavity within the housing to be filled with the dielectric liquid to be able to provide a greater heat capacity via the liquid to be filled.

[0028] Temperature gradient profiles may be stored in the aforementioned control unit to be able to represent typical operating states and thus influence the control of the electric machine.

LIST OF REFERENCE NUMERALS

[0029] 01—electric motor [0030] 02—housing [0031] 03—stator [0032] 04—electric winding [0033] 06—rotor [0034] 07—motor shaft [0035] 08—rolling bearing [0036] 09—bearing seal [0037] 11—dielectric liquid/oil