Patent Application
20080058148
The invention relates to a friction wheel drive for the frictionally engaged driving of units of an internal combustion engine. For this purpose, the friction wheel drive is provided with an adjustable friction wheel, which can be pressed with a non-positive fit against at least one contact disk of a drive and driven element.
Alternatively, a friction wheel drive with an adjustable friction wheel is presented, which can be pressed against the contact disk of a drive element and which has a self-propulsion unit.
From DE 196 35 808 A1, a friction wheel drive of the type noted above is known. This publication relates to a friction wheel drive designed for a vehicle. It is used to assist the conventional drive of the vehicle when needed through an auxiliary drive for the vehicle wheels that are normally not driven.
The friction wheel drive includes an electric motor, which, via a transmission, drives a friction wheel that is adjustable in the direction of the wheel rim when needed. The wheels driven electrically by means of the friction wheel drive assist the conventionally driven wheels when there is too little static friction, which can occur, for example, when there is clear ice or when the conventional drive supplies too little power, e.g., on inclines that are too steep.
A disadvantage in the friction wheel drive described above is that a large number of auxiliary components are necessary due to its standalone drive, which increases the likelihood of faults and also the necessary installation space and the weight of the system.
The invention is based on the objective of providing a friction wheel drive, which enables minimal axial installation space and reliable driving of an auxiliary unit of the internal combustion engine depending on needs.
The objective is met according to the invention by the features of the independent claims 1 and 7. Other advantageous configurations of the invention are the subject matter of the dependent claims 2 to 6 and 8 to 12.
The invention according to claim 1 provides that the friction wheel is in sustained, frictionally engaged connection with the contact disks of a respective drive and driven element, at least when the internal combustion engine is running, by means of which the operation of an auxiliary unit is guaranteed during the operating period of the internal combustion engine.
The switchable coupling is used for separating the driven and drive elements of the auxiliary unit depending on need. If the auxiliary unit is a coolant pump, then this can be turned off, for example, in the startup phase of the internal combustion engine and thus can realize quicker heating. Reaching the operating temperature more quickly decisively influences the wear and the pollutant emissions of the internal combustion engine. Simultaneously, the drive power required when the internal combustion engine starts is reduced by the magnitude of the drive power of the coolant pump. Therefore, in this phase of the internal combustion engine, its fuel consumption decreases.
An advantageous improvement of the invention according to claim 1 provides that the switchable coupling is constructed as a friction-disk coupling. A friction-disk coupling is distinguished by simple construction, reliable function, and oil-free operation. Therefore, it is an economical component, which is suitable for a non-enclosed friction wheel drive.
In addition, the friction-disk coupling has the advantage of being able to be integrated into the installation space of the contact disk of the auxiliary unit, so that no additional spatial requirements are produced.
An actuator is advantageous, which is used for applying a contact pressure force to the friction wheel that is required for frictionally engaged transfer of the necessary power from the driven element to the drive element. For a friction wheel that has a rubber lining with an increased coefficient of friction, the smallest possible contact pressure force that can be achieved in this way reduces its wear and its flexing work.
A fixed measure of the slippage between the driven and the drive element is used as a measure for the required contact pressure force. This fixed measure can be determined, e.g., by comparing the rotational speed between the driven and drive elements.
The contact pressure force of the friction wheel can be generated in various ways. Mechanical means, e.g., in the shape of a compression or tension spring are distinguished by low construction expense and high reliability, but are less suited for precise and rapid setting of the contact pressure force.
This disadvantage is avoided in hydraulic and pneumatic systems. They can be used when an existing on-board hydraulic or pneumatic system in the vehicle can be used, in order to achieve loading of the friction wheel depending on needs through the use of a corresponding controller. The on-board pneumatic system can operate using of high or low air pressure. A low-pressure capsule, whose membrane that is connected to a low-pressure source of the internal combustion engine guarantees an exact adjustment of the actuator, is suitable for the low-pressure controller.
An electromagnet that can be excited, for example, in a time-delayed way after the start of the internal combustion engine, in order to activate the friction wheel drive, offers another possibility for adjusting the actuator.
An electric motor offers another way for adjusting the actuator. Here, a combination of the electric motor with a threaded spindle in the form of a ball screw or a roller screw can also be used. The electric motor permits, in an especially simple way, control using an electronic regulator, which is regulated under consideration of the slippage between the driven and drive elements.
The objective of the invention is also met by the independent claim 7. This describes a need-dependent friction wheel drive, which, together with a traction-mechanism drive, forms a drive for auxiliary units of an internal combustion engine. Because the friction wheel, the traction-mechanism drive, and its common driven element are arranged in a plane and have the same width, its axial spatial requirements are limited to their width. The space-saving arrangement of the friction wheel, traction-mechanism drive, and driven element in one plane requires the drive of the friction wheel indirectly via the traction mechanism and not directly via a correspondingly wide contact disk of the crankshaft, on which the traction mechanism and the friction wheel must be arranged one next to the other.
Because the friction wheel is in indirect contact with the contact disk of the crankshaft via the traction mechanism, the contact pressure force of the traction mechanism on the contact disk of the crankshaft is increased by the contact pressure force of the friction wheel and therefore the slippage of the traction mechanism on the contact disk is reduced.
The need-dependent friction wheel drive of the coolant pump allows it to be stopped, which leads to rapid heating of the internal combustion engine during the startup phase of the engine. In contrast to the coolant pump, it is useful that the generator takes in power over the entire operating range of the internal combustion engine.
When the power-steering pump is driven electrically, an elastic belt is sufficient for the sole drive of the generator. This is economical, because it requires no tensioning device. Variants with air-conditioner compressors and/or starter generators require a conventional belt drive with known tensioning systems.
It is advantageous when the friction wheel is in pressure contact both with the contact disk of the coolant pump and also with the loose section of a normal belt, which is used, for example, for driving at least one generator and one air-conditioner compressor. In this case, the friction wheel replaces a belt tensioner for the traction-mechanism drive and is used as a vibration damper for this mechanism.
To achieve the necessary contact pressure force of the friction wheel on the contact disk of the coolant pump and on the loose section of the normal belt, its tensioning motion must be directed against the direction of movement of the loose section.
Additional features of the invention emerge from the following description and from the drawings, in which an embodiment of the invention is shown schematically. Shown are:
In
The friction wheel drive 1 has a friction wheel 3 with a friction lining 17 for promoting static friction. The friction wheel 3 is in frictionally engaged pressure contact with a contact disk 4 of a drive element 5 of a coolant pump of the internal combustion engine and with a contact disk 6 of a driven element 7 of the crankshaft during the operating period of the engine. The contact pressure force of the friction wheel 3 is directed outwards from an actuator 8. This is constructed as an electrically operated threaded drive, which has a threaded spindle 12 that is continuously adjustable by an electric motor 13. At the free end of the threaded spindle 12 there is a friction wheel bearing 14 for supporting the friction wheel 3 and for the transfer of the contact pressure force to this wheel.
At the free end of the actuator 8 there is a housing-fixed support bearing 15 for supporting the contact pressure force.
The electric motor 13 is conductively connected to a regulator 16. With the help of not-shown sensors, this regulator evaluates the circumferential speed of the contact disks 4 and 6 and calculates from this speed the slippage between the driven element 7 and the drive element 5. The regulator 16 regulates the required minimum contact pressure force of the actuator 8 as a function of the power to be transferred, such that a certain minimum slippage is maintained during the entire operation of the internal combustion engine. Maintaining this minimum contact pressure force for the power to be transferred offers the advantage that the wear and the flexing work of the friction lining 17 are minimized.
The need-based dependency of the friction wheel drive is achieved through a friction-disk coupling 18, which is integrated into the contact disk 4 of the coolant pump. The friction-disk coupling 18 is automatically disengaged at the start of the internal combustion engine and automatically engaged again when a certain coolant and/or lubricant temperature has been reached. In this way, a rapid heating profile of the internal combustion engine is achieved with simultaneously reduced power loss.
The traction-mechanism drive 2 is used for driving auxiliary units of the internal combustion engine, for example, a generator 9 and an air-conditioner compressor 20. For this purpose, a traction mechanism 10 connects all of the associated contact disks or belt disks with the contact disk 6, which is locked in rotation with the crankshaft and which simultaneously forms the driven element 7. In addition, the traction-mechanism drive 2 has a deflection roller 11.
The contact disk 6 wrapped by the traction mechanism 10 and constructed as a belt disk is in only indirect contact with the friction wheel 3 via the traction mechanism 10, while the contact disk 4 of the drive element 5 of the coolant pump is in direct contact with the friction wheel 3 or its friction lining 17.
In
At the position of the indirect, frictionally engaged pressure contact of the friction roller 3 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004025542.3 | May 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/04345 | 4/22/2005 | WO | 2/7/2007 |
