Belt pulley arrangement for a belt drive for driving auxiliary units of a motor vehicle and method for driving an auxiliary unit of a motor vehicle connected via a belt pulley arrangement

Abstract

A belt pulley arrangement for a belt drive to drive auxiliary units of a motor vehicle, having a belt pulley for introducing a torque that can be provided via a flexible drive means, an output shaft for driving an auxiliary unit, in particular a cooling water pump, and an electric machine for the transmission of torque between the belt pulley and the output shaft, wherein the electric machine has a rotor connected to the belt pulley and a stator connected to the output shaft. As a result of the power flow between the belt pulley and the output shaft, which can be influenced by the electric machine, it is not necessary to design the auxiliary unit that is attached via the output shaft for the least beneficial operating point, so that the auxiliary unit can be dimensioned smaller and a reduction in the installation space for motor vehicle components, in particular the installation space for auxiliary units of a motor vehicle that can be driven via the belt drive, is made possible.

Claims

1. A belt pulley arrangement for a belt drive for driving auxiliary units of a motor vehicle, said arrangement comprising a belt pulley for introducing a torque that can be provided via a flexible drive element, an output shaft for driving an auxiliary unit, an electric machine for torque transmission between the belt pulley and the output shaft, the electric machine has a rotor connected to the belt pulley and a stator connected to the output shaft; and a switching element for producing coupling of the belt pulley to the output shaft in a manner substantially fixed against relative rotation in case of a loss of power flow in the electric machine.

2. The belt pulley arrangement as claimed in claim 1, wherein the electric machine is connected to at least one of an electrical energy source for accelerating the output shaft or to an electrical energy sink for braking the output shaft.

3. The belt pulley arrangement as claimed in claim 1, wherein the electric machine has windings, and the windings are short-circuited in case of a loss of power flow in the electric machine.

4. The belt pulley arrangement as claimed in claim 1, wherein the stator has permanent magnets and the rotor has windings, or the stator has windings and the rotor has permanent magnets, and the windings are connected via a contactless or contacting electrical contacts to electric leads for at least one of introducing or withdrawing electrical energy.

5. The belt pulley arrangement as claimed in claim 4, wherein the windings are connected to a support, the support is connected to the output shaft or the belt pulley by a connecting piece extending in a radial direction, and, on a side facing away from the windings, the support has a contact element for transmitting electrical energy.

6. The belt pulley arrangement as claimed in claim 1, wherein the belt pulley has a radially outward-facing running surface for connection of the flexible drive element, and an electronic circuit for operating the electric machine is arranged radially inside of the running surface, substantially at an axial plane of the running surface.

7. The belt pulley arrangement as claimed in claim 1, wherein the belt pulley has a radially outward-facing running surface for connection of the flexible drive element, and the rotor and the stator of the electric machine are arranged radially to the inside of the running surface, substantially at an axial plane of the running surface.

8. A belt drive for driving auxiliary units of a motor vehicle, having an input belt pulley, which is connectable to an engine shaft of an internal combustion engine at least one output belt pulley, which is coupled to the input belt pulley by a common flexible drive element and is used to drive the associated auxiliary unit, and at least one output belt pulley designed as a belt pulley arrangement as claimed in claim 1.

9. A method for driving an auxiliary unit of a motor vehicle which is connected by a belt pulley arrangement as claimed in claim 1, comprising supplying electrical energy to the electric machine or withdrawing electrical energy from the electric machine, or both, depending upon a speed of the belt pulley in order to regulate a rated speed of the output shaft.

10. The belt pulley arrangement of claim 1, wherein the auxiliary units comprise at least one of an air-conditioning compressor, a generator, an oil pump, a lubricant pump, or a fuel pump.

11. The belt pulley arrangement of claim 4, wherein the electrical contact is a sliding contact connection.

12. The belt pulley arrangement of claim 5, wherein the electrical contact is a sliding contact connection, and the contact element of the support is a slip ring of the sliding contact connection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained by way of example below with reference to the attached drawings, wherein the features described below can each represent an aspect of the invention either individually or in combination. In the drawings:

(2) FIG. 1: shows a schematic sectional view of a belt pulley arrangement,

(3) FIG. 2: shows a schematic block diagram of the belt pulley arrangement from FIG. 1 in an overrunning mode,

(4) FIG. 3: shows a schematic block diagram of the belt pulley arrangement from FIG. 1 in a fail-safe mode, and

(5) FIG. 4: shows a schematic block diagram of the belt pulley arrangement from FIG. 1 in a braking mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The belt pulley arrangement 10 illustrated in FIG. 1 has a belt pulley 12 with a radially outward-facing running surface 14, via which torque supplied by a crankshaft of an internal combustion engine of a motor vehicle can be introduced by a flexible drive means, e.g. a flat belt. The belt pulley 12 is coupled via an electric machine 16 to an output shaft 18, which can be an input shaft of an auxiliary unit, e.g. a cooling water pump. The electric machine 16 has a rotor 20 firmly connected to the belt pulley 12 and a stator 22 spaced apart from the rotor 20 by means of an air gap. In the illustrative embodiment shown, the rotor 20 has permanent magnets, while the stator 22 has windings. The stator 22 is furthermore firmly connected to the output shaft 18 by means of a support 24. The support 24 is of annular design with a substantially U-shaped, axially open cross section. At the base of the U-shaped cross section, the support 24 has a connecting piece 26 extending in a radial direction, with the result that a pocket 28, in which a sliding contact connection 30 is provided, is formed between the stator 22 and the output shaft 18. On the side facing away from the stator 22, the sliding contact connection 30 has slip rings 32, against which brushes 36, which are spring-loaded by means of compression springs 34, press in order to produce an electrical contact. The compression spring 34 and the brush 36 connected to the compression spring 34 are guided in a brush guide 38. The brush guide 38 is connected to a fixed holder 40. In particular, the holder 40 can be connected to a unit housing 42 of the auxiliary unit, wherein the unit housing 42 can preferably project axially at least partially into the belt pulley 12 and/or the belt pulley arrangement 10. Electric leads 44, which can be electrically connected to the brushes 36, can be passed through the holder 40 and/or the unit housing 42. By means of an electronic circuit 46, which is arranged completely within the belt pulley 12 and, in particular, is attached to the support 24 or to the holder 40 or, in a multi-part design, to the support 24 by means of a first part and to the holder 40 by means of a second part, supply and/or withdrawal of electrical energy via the electric leads 44 can be controlled, thereby making it possible to influence the electromagnetic field between the rotor 20 and the stator 22. As a result, it is possible, in particular, for the speed of the output shaft 18 to differ from the speed of the belt pulley 12, in particular in order to regulate an intended rated speed for the output shaft 18 substantially independently of the speed of the belt pulley 12. To achieve this, the belt pulley 12 is not connected firmly to the output shaft 18 but is supported with the ability for relative rotation by means of a rolling bearing 48.

(7) If, as illustrated in FIG. 2, electrical energy E.sub.An is fed into the electric machine 16 via the electric leads 44, the output shaft 18 can be accelerated in addition to the mechanical energy An.sub.mech introduced via the belt pulley 12, enabling the stator 22 of the output shaft 18 to rotate at a speed n.sub.S which is greater than the speed n.sub.R of the rotor 20 of the belt pulley 12 by a factor s (overrunning mode). A small part of the energies supplied is lost in the form of lost energy E.sub.V and is not transmitted to the output shaft 18, as a result of which the mechanical energy Ab.sub.mech output by the output shaft 18 is somewhat lower.

(8) If, as illustrated in FIG. 3, electrical energy is neither supplied nor withdrawn via the electric leads 44, the electronic circuit 46 can, in particular, short-circuit the windings of the stator 22, allowing the output shaft 18 to rotate at a speed n.sub.S which substantially corresponds approximately to the speed n.sub.R of the rotor 20 (fail-safe mode). A small part of the energies supplied is lost in the form of lost energy E.sub.V and is not transmitted to the output shaft 18, with the result that, allowing for the lost energy E.sub.V, the speed n.sub.S of the output shaft 18 is slightly less than the speed n.sub.R of the rotor 20, as a result of which the mechanical energy Ab.sub.mech output by the output shaft 18 is somewhat lower. However, the lost energy E.sub.V is generally so small that the factor s is 1 to a good approximation.

(9) If, as illustrated in FIG. 4, electrical energy E.sub.Ab is withdrawn from the electric machine 16 via the electric leads 44, in an order, for example, to operate another electric load and/or to store electrical energy produced, the output shaft 18 can be braked in relation to the mechanical energy An.sub.mech introduced via the belt pulley 12, allowing the output shaft 18 to rotate at a speed n.sub.S which is less than the speed n.sub.R of the rotor 20 by a factor s (braking mode). A small part of the energies supplied by the belt pulley 12 is lost in the form of lost energy E.sub.V and is not transmitted to the output shaft 18 via the electric machine 16, as a result of which the electrical energy E.sub.Ab output to the energy sink by the electric machine 16 and the mechanical energy Ab.sub.mech output by the output shaft 18 are somewhat lower.

LIST OF REFERENCE SIGNS

(10) 10 belt pulley arrangement 12 belt pulley 14 running surface 16 electric machine 18 output shaft 20 rotor 22 stator 24 support 26 connecting piece 28 pocket 30 sliding contact connection 32 slip ring 34 compression spring 36 brush 38 brush guide 40 holder 42 unit housing 44 electric lead 46 electronic circuit 48 rolling bearing An.sub.mech mechanical energy supplied Ab.sub.mech mechanical energy withdrawn E.sub.An electrical energy supplied E.sub.Ab electrical energy withdrawn E.sub.V lost energy n.sub.R speed of the rotor n.sub.S speed of the stator