1. Field of the Invention
The invention relates to a fluid friction coupling for transmitting a torque from a drive shaft to a further component, more specifically a fan of an internal combustion engine of a motor vehicle, via a viscous fluid level in a working chamber in the further component, the fluid friction coupling including a supply chamber for viscous fluid with a partition having a connection opening arranged between the working chamber and the supply chamber and a valve body operatively arranged for releasing or closing the connection opening via a solenoid.
2. Description of the Related Art
A fluid friction coupling is disclosed in DE 196 45 478 A1 for transmitting torque via a viscous fluid level in a working chamber with a valve body arranged between the working chamber and a supply chamber. The valve body is operable via a solenoid for opening or closing a connection opening between the supply chamber and working chamber. In this fluid friction coupling, the valve body is mounted pivotably and bears a permanent magnet. The solenoid surrounds an input drive shaft which comprises a magnetically conducting material, and magnetic forces are conducted via the drive shaft into a housing which has the working chamber and the partition. When suitably subjected to current, the solenoid attracts the permanent magnet or repels it and thereby controls the position of the valve body. A disadvantage of this fluid friction coupling is that the solenoid is at a very great distance from the permanent magnet and therefore high magnetic losses occur. For example, in the case of high temperatures which predominate frequently at the fan of the internal combustion engine in the motor vehicle, these magnetic losses impair the controlling means of the valve body.
German reference DE 44 13 997 C2 discloses another fluid friction coupling in which a valve body is connected to a displaceable piston arranged in a housing having a working chamber and a partion arranged opposite the drive shaft. A controlling means with a stepping motor is operatively arranged for displacing the piston and has a hydraulic line which is arranged on that side of the housing which lies opposite the drive shaft. However, because of the arrangement of the controlling means on that side of the housing which is remote from the drive shaft, the fluid friction coupling requires very large dimensions.
It is an object of the present invention to provide a fluid friction coupling for transmitting a torque from a drive shaft to a further component, more specifically a fan of an internal combustion engine of a motor vehicle, via a viscous fluid level in a working chamber such that the construction is as simple and compact as possible and in which the magnetic losses are minimized.
According to the invention, this problem is met by a valve body being connected to a control element, and by the solenoid being configured for moving the control element.
In this configuration, the distance between the solenoid and the valve body is spanned via the control element. Furthermore, the magnetic field lines do not need to be conducted via the drive shaft. This minimizes magnetic losses during control of the valve body. The solenoid may be arranged in a space-saving manner close to that side of the housing which faces the drive shaft. Furthermore, since the magnetic losses of the solenoid are particularly low, the solenoid may be made with very small dimensions.
The fluid friction coupling according to the present invention is of particularly simple structural configuration when the control element has an anchor plate arranged in front of the solenoid and a control part which is connected to the anchor plate penetrates a wall of a housing in which the partition is arranged. The anchor plate may be arranged at a small distance from the solenoid and may be configured to correspond to its shape, so that magnetic losses are kept particularly low.
According to another embodiment of the present invention, the valve body comprises a particularly cost-effective configuration and may be fitted in a simple manner when it is designed as a leaf-spring.
A further reduction in the dimensions of the fluid friction coupling according to the present invention may be achieved if actuating means of the valve body are exclusively arranged in a radially outer region relative to the drive shaft. This also results in a simple structural configuration for the fluid friction coupling according to the present invention.
According to another embodiment of the present invention, the anchor plate and the valve body may be guided together axially if the control part is mounted pivotably on the anchor plate and/or on the valve body.
According to another embodiment of the present invention, the control part may be mounted via a particularly simple structural configuration if at least one of the anchor plate and the valve body has ball sockets for receiving the ends of the control part which are of spherical configuration corresponding to the ball sockets. If both side of the control part are mounted in ball sockets, the anchor plate may be mounted cardanically.
According to another embodiment of the present invention, the mounting of the control part may be further simplified if the control part penetrates the anchor plate and the valve body and if the ball sockets are arranged on mutually remote sides of the anchor plate and the valve body.
The anchor plate may, for example, be attracted and repelled by the solenoid in response to current supplied to the solenoid. If the current supply or electronic controlling means of the fluid friction coupling according to the present invention fails, a torque may be reliably transmitted if the anchor plate is prestressed by a spring element into a position in which the connection opening in the partition is released. When the fluid friction coupling is provided for the fan of a motor vehicle, the internal combustion engine is reliably cooled during a failure of the controlling means.
According to another embodiment of the present invention, the tolerances between the valve body and the anchor plate may be compensated for in a simple and particularly accurate manner after the solenoid is fitted by adjusting the length of the control part. For this purpose, the control part may be of a tappet design with length-adjustable configuration.
According to another embodiment of the present invention, a gap which is generated between the anchor plate and the solenoid when the anchor plate is moved axially may be kept particularly small if the solenoid has an edge which is arranged to fit around the radial outside of the anchor plate for conducting the magnetic field lines. This arrangement further reduces the magnetic losses of the solenoid.
According to yet another embodiment of the present invention, the solenoid is preferably fastened to a fixed component. Grinding of the rotating anchor plate against the solenoid may be avoided by arranging a contact disk connected in a rotationally fixed manner to the housing for conducting field lines of the solenoid between the anchor plate and a radially inner edge of the solenoid. The contact disk therefore conducts the magnetic field strength to the anchor plate and forms an axial stop for the anchor plate. An air gap between the fixed solenoid and the rotating anchor plate may thereby be restricted to a particularly small size.
According to a further embodiment of the present invention, a sealing element of the control part may be arranged with an edge surrounding the control part. The sealing element may be made to exhibit a particularly low damping of the movement of the control part if the sealing element arranged in the housing also comprises a casing which is manufactured from an elastic material and is spaced apart from the control part. By this means, the control part is held such that it can move in all directions.
A damping displacement restrictor may be arranged on the anchor plate to reduce wear and noise. The manufacturing costs of the fluid friction coupling according to the present invention may be further reduced if the sealing element has an axial stop for the anchor plate. Since the sealing element is in any case generally manufactured from a resilient material, the fluid friction coupling according to the invention does not require the fitting of an additional stop.
The energy consumption of the solenoid may be reduced if the solenoid is arranged in a cool region outside the housing. Since the forces of the solenoid are transmitted to the valve body via a movement of the control part, an increase in the distance between the solenoid and the valve body does not lead to an increase in the energy consumption of the solenoid. The solenoid may also be arranged in a simple manner on a fixed component. The use of sliding contacts which are prone to interference is thereby avoided.
According to another embodiment of the present invention, high energy consumption by the solenoid for long travel distances movements of the control element may be avoided in a simple manner if the spring element is arranged at a distance from the control element and by arranging the anchor plate closer to the solenoid in the region of the spring element than in the region of the control element in the currentless or deenergized state of the solenoid. In this configuration, the anchor plate is mounted cardanically. When the solenoid is in a currentless state, the anchor plate is situated opposite the solenoid in a tilted position. When current is supplied to the solenoid, the anchor plate tips into the parallel position to the solenoid.
According to yet a further embodiment of the present invention, radial play of the anchor plate may be avoided in a simple manner if the spring element is fastened nondisplaceably in each case to the housing and to the anchor plate and extends from a radially inner region toward a radially outer region. By means of this configuration, the anchor plate is guided particularly accurately and may therefore be arranged at a particularly small distance from the poles of the solenoid.
The fluid friction coupling according to the present invention is configured particularly compactly and requires particularly little current consumption if the anchor plate surrounds the drive shaft concentrically, and if the control element and the spring element are arranged eccentrically with respect to the drive shaft.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.