Patent Application
20060156846
In actuator drive mechanisms in use today to actuate couplings or gears, electric motors are typically used. A worm, for instance, is formed onto their armature shaft. This worm cooperates with a worm wheel and optionally other gear stages provided. In some applications it is required that, if there is a power failure at the actuator-drive mechanism, that drives a worm drive, a displacement is necessary and must be performed. In these cases the worm has to be driven by the worm wheel. Therefore, the worm drive must not be self-inhibiting.
The vehicles that are driven with internal combustion engines, whether they are utility vehicles or passenger cars, exhaust gas turbochargers can be used, so that during the intake stroke of the engine better filling of the individual cylinders of the engine with gas can be achieved, whether the engine is a direct-injection type or a mixture-compressing engine with externally supplied ignition. If exhaust gas turbochargers are displaced via an electric motor, which comprises a worm drive with a worm and a worm wheel, and/or are provided with a rack and pinion assembly, then on the power takeoff side, not only a linear but a rotary motion can be generated by way of which the guide blade rings of an access gas turbocharger can be displaced and its operating behaviour and effectiveness can be varied. A power failure at the actuator drive mechanism is a major problem, since even if there is a power failure, a displacement at the exhaust gas turbocharger, to name one example, must be assured. Thus, an exhaust gas turbocharger with a variable turbine geometry, that is actuatable by means of an electric actuator drive mechanism, in the closed guide vane position, which in this state allows the passage of a flow of exhaust gas, must be capable of being opened again quickly if there is a power failure at the actuator drive mechanism associated with. Fast opening of the guide blade ring is required if, for an engine whose exhaust system contains the exhaust gas turbocharger, the driver suddenly “steps on the gas”. In this state, however, the flow of exhaust gas, which expands as it flows through the exhaust turbine, but when the guide blade ring is closed, is prevented from passing through the flow machine at the exhaust gas turbo charger, could cause considerable damage.
With actuator drive mechanisms in use today, it is extremely difficult to react to a power failure at an actuator drive mechanism.
The embodiment proposed according to the invention does not permit any transmission of force to the final control element in one control region of the actuator drive mechanism. A final control element that functions when, without current is provided, which, if there is a power failure, assures a residual displaceability. This can be achieved by making modifications in actuator drive mechanisms in present used; with the embodiment proposed according to the invention, if there is a power failure, the “open” state can be brought about quickly at the final control element to be actuated, since only short flotation paths have to be traversed. With the arrangement proposed according to the invention, a spring can be connected parallel to a drive mechanism, reinforcing the drive of the final control element; for instance, together with an electric motor, the guide blade ring of a turbo charger can be kept closed during breaking.
The disconnection of adjusting elements from final control elements, as proposed according to the invention, allows the same parts to continue to be used in driving components, since only slight modifications have to be made in known drive motors in present use, which advantageously means that retrofitting costs are saved.
The embodiment proposed according to the invention permits a disconnection of final control elements over the entire path of rotation of a final control element. The restoring effect is thus assured by the spring element, provided parallel to the actuator drive mechanism, referred to one complete revolution of the affected final control element, both before the reversal of the tension direction and after the reversal of the tension direction of the spring element, during the rotation of the final control element. This is attained by providing that the spring element is retained movably via a pin guided in a groove of the final control element and is supported by its other end at a fixed, but rotatable point. In normal operation, in which an adjusting element acted upon by the final control element is moved back and forth between two positions, the spring is always taut. Upon the revolution of the final control element, the pivot point of the spring element, which point is guided movably in the final control element, is displaced, so that after a half-revolution of the final control element a maximum tension exists in the spring element. If in this rotary position the current at the drive motor failures should fail, then the energy of the spring element stored in the spring element moves the final control element into a position in which it is disengaged from the adjusting element, for example by way of an interruption in an external toothing.
If the current at the actuator drive mechanism fails before the reversal of force of the spring element, then the adjusting element can be moved automatically into the “open” position by the spring element and the load. In that case, an overrotation of the final control element into the zone without force transmission is unnecessary.
In a further variant embodiment of the concept on which the invention is based, instead of adapted spring elements, an electromagnetic coupling and decoupling, or connection and disconnection can also be achieved.
The invention is described in further detail below in conjunction with the drawing.
Shown are:
From the view in
In this view of an actuator drive mechanism of a typical type today, with a control motor 1 and a worm gear 3, 5 and an adjusting element 11 in the form of a rack, the control motor 1 drives the worm gear 3, 5. The armature shaft 2 of the control motor 1, which coincides with the line of symmetry 4 of the control motor, is provided with a worm thread, which cooperates with an external toothing 10 on the worm wheel 5. The rotary axis 6 of the worm wheel 5 extends perpendicular to the plane of the drawing; that is, the worm wheel 5 and worm 3 are oriented at a right angle to one another. A power takeoff component 8 in the form of a pinion with external teeth is provided coaxially and rigidly relative to the worm wheel 5. Depending on the direction of rotation of the control motor 1, a motion of the worm wheel 5 in one of the directions, represented by the double arrow 7, is initiated via the established direction of rotation. The power takeoff component 8, with its external toothing 9, cooperates with a rack 11, which in the view of
With the arrangement that is schematically shown in
From the drawing cycle shown in
In the view given in
Above an adjusting element 11, such as a rack provided with an external toothing 12, a spring element 21 is suspended from a fixed bearing 23 in a stationary articulation 24. The spring element 21 may for example be embodied as a wrap spring, a spiral spring, or the like, which with its end opposite the fixed bearing 23 is supported in a movable pivot point 22, in the form of a pin 20 guided in the recess 19.
The rack functioning as an adjusting element 11 is provided with a stop 27, which in the view of
In
From
In
The residual spring force that the spring element 21, embodied for instance as a wrap spring, still has no longer suffices to rotate the worm wheel 5 or power takeoff component 8 onward counter to the detent moment of the control motor 1 and the losses that occur in the worm drive 3, 5, and so the gear stays in the position shown in
For worm gears 3, 5 like for each other gear, self-inhibition is a function of efficiency. The worm gear 3, 5 is not self-inhibiting if the efficiency is equal or greater than 50%. The efficiency of worm gears 3, 5 depends on friction factor and lead angle at the penetration of the toothing γm. The calculation of the efficiency is as follows:
ηz=tanγm/tan(γm+ρz)
with the efficiency ηz, the average lead angle at the penetration of the toothing γm and the friction angle ρz. The friction angle ρz is a finction of the tooth friction factor μz and is calculated by tan(ρz)=μz . As long as the value of the efficiency ηz is greater than 0.5 the worm gear 3, 5 is not self-inhibiting. This means, that the worm wheel 5 can be driven by the worm 3. The friction factor μz depends on the material of the worm 3 and the worm wheel 5 and—if a lubricant is used—also on the lubricant. The value of the friction factor μz is generally in the range from 0.01 to 0.2 but may even be smaller than 0.01. The friction factor can be determined as described in Maschinenelemente, Vol. III, Springer-Verlag, 2nd edition, 1986, pages 82, 83.
The following is only an example for an average lead angle at which the efficiency is bigger than 0.5 which means that the worm gear is not self-inhibiting and does not delimit the invention to the mentioned values.
If for example the angle γm is chosen as being 6°, and the friction factor μz is chosen to be 0.1 depending on the surface roughness of the material chosen, according to the equation ηz =tan γm/(tanγm−92z) an efficiency of 0.51327 is calculated, i.e. in this case the worm gear is not self-inhibiting.
Preferred materials for the worm 3 are for example CuSn-bronze, Al-bronze, or brass, but cast iron or steel is also applicable as material for the worm 3. Particularly, the worm is made of steel or bronze. Particularly for small worms 3 also plastics is suitable. Preferred materials for the worm wheel 5 are plastics, such as POM (polyoxymethylene) or PA (polyamide). However, the worm wheel 5 can also be made of CuSn-bronze, Al-bronze, brass, cast iron or steel. If the worm is made of steel, it has turned out that tempered and grinded worms 3 are more advantageous than quenched and tempered and milled worms 3. Concerning the lubricants, synthetic oils are more suitable than mineral oils, particularly regarding the running-in characteristics. Concerning the manufacturing of the thread pitch of the worm 3, big pitches are preferred. The worms can either be multiple-threaded or single-threaded. Regarding the deflection, single-threaded worms 3 having a bigger diameter d of the shaft 3.1 behave more suitable than single-threaded worms 3 having a smaller diameter d of the shaft 3.1. The length 1 of the worm 3 is selected in such a way that no or nearly no deflection occurs. If a deflection in case of the load on the worm 3 would occur, a worm 3 with a shaft 3.1 of bigger diameter d could be chosen or a supporting bearing can be used to support the worm 3. The ratio of the length 1 to the outer diameter D of the worm 3 is for example within the range from 1.5 to 3. Depending on the design of the worm gear 3, 5 also smaller or bigger ratios of length 1 to outer diameter D are suitable, as long as no or nearly no deflection occurs.
The diameter d of the shaft 3.1 of the worm 3 is chosen depending on the use of the worm gear 3, 5. Preferably, the shaft of the worm 3 has a diameter d of 4 to 8 mm. But in case of micro-drives also diameters d of the shaft being for example 1 mm or smaller are possible. In case of bigger actuators also diameters d being bigger than 8 mm are possible.
The height of the flank h of the worm 3 depends on the tooth height H of the worm wheel 5 and the purpose the worm gear 3, 5 is used for. The height of the flank h of the worm 3 can take each value up to the half diameter of the core.
The ratio of the diameter dm of the worm 3 to the diameter dm,w of the worm wheel 5 based on the reference circle is preferably within the range from 1:3 to 1:7.
In each of
As can be derived from
Just before the second extreme position 43 is reached, the pin 20 slips outward again in the recess 19 on the power takeoff component 8, and the spring prestressing of the spring element 21 acts in the opposite direction. This means that in its travel range, the control motor has to brake counter to the spring force exerted by the spring element 21. Until the second extreme position 43 is reached, the braking/motor load then decreases again somewhat, since the load increases further and the spring force decreases somewhat. When current is being supplied to the control motor 1, the system always moves between the first and second extreme positions 42 and 43, respectively.
If the power fails in the second extreme position 43, or after the reversal of the tension direction of the spring element 21, then the spring element 21 pulls the pinion with external teeth, functioning as the power takeoff component 8, into the zone labelled 31, in fact so far that the teeth of the external toothing 10 of the power takeoff component 8 and the teeth 12 of the rack functioning as the adjusting element 11 no longer mesh with one another.
Counter to the remaining worm losses 45, the pinion acting as the power takeoff component 8 rotates still some way farther until it reaches its extreme position; see
If the current at the control motor 1, conversely, fails in a rotary position of the power take-off component 8 or worm wheel S before the reversal of force of the spring element 21, then the rack acting as the adjusting element 11 automatically moves by means of the load and the spring into the first extreme position 42—an overrotation of the power takeoff component 8 into the zone 31 is not required.
From the view in
In this illustration, a spring element 53 is kept in the taut state inside an electromagnetically operating valve 50 by a coil 52 through which current flows. The spring prestressing is brought to bear by the iron core 51 that penetrates the coil 52 through which current flows; this core, by means of a rod 55 with a plate attachment 54 provided on it, acts upon the spring element 53 inside the housing of the electromagnetic valve 50. If there is a power failure, the electromagnetic field collapses abruptly, and via the iron core 51, the spring element 53 presses a peg in the horizontal direction as represented by the double arrow. As a result, the engagement position of the worm 3 and worm wheel 5, which is identified by reference numeral 56 and represents the state of the electromagnetic valve 50 with current, can be overcome, by relative displacement of the worm wheel 5. As a result, on the one hand the worm wheel 5 becomes disengaged from the worm 3, and on the other, the external toothing 9 of the power takeoff component 8 becomes disengaged from the teeth 12 of the racklike adjusting element 11. The spring element presses the coaxial assembly comprising the power takeoff component 8 and the worm wheel 5 into the position marked 57, representing the state without current. For displacement of the rack, shown shaded here in
| Number | Date | Country | Kind |
|---|---|---|---|
| 101 05 032.1 | Feb 2001 | DE | national |
This application is a Continuation-in-Part of patent application Ser. No. 10/343,364 filed on Jan. 30, 2003.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10343364 | Jan 2003 | US |
| Child | 11260603 | Oct 2005 | US |
