EP0411285B1 - Device provided with a rotation inductive sensor to control particularly the ignition time of combustion engines - Google Patents

Description

The invention relates to an inductive rotary encoder for controlling the ignition timing of internal combustion engines, with a coil penetrated by a permanent magnet and a yoke wheel rotated by a shaft, over the circumference of which protruding spaced tooth segments are moved past the magnetic poles for voltage induction, according to the first part of claim 1 the invention a method for ignition of internal combustion engines, in particular in lawn mowers, chainsaws or cut-off machines using such an encoder (cf. claim 2). Finally, the invention relates to a capacitor ignition arrangement with a rotary encoder of the type mentioned (cf. claim 7).

In known capacitor ignition systems, the electronic switch is switched through either by a third-party ignition pulse generator or by an internal ignition pulse generator, which, for example, generates the required ignition signal via a voltage divider, starting from the state of charge of the capacitor. It is common to control the ignition timing in accordance with the operating state of the internal combustion engine, in particular depending on its speed. For this purpose, for example, the use of the aforementioned segment wheels coupled to the crankshaft of a gasoline engine is known; these are yoke wheels made of highly permeable, ferromagnetic material, with tooth segments projecting radially or axially evenly distributed over their circumference. The tooth segments interact with the pole pieces of a permanent magnet which is surrounded by a coil. As soon as the yoke wheel turns, due to the change in the air gap between the pole shoes and in the coil of the yoke wheel and therefore of the magnetic flux passing through the coils induces an alternating voltage. To trigger an ignition, an additional magnetic pin or the like must be attached to the known yoke wheels in order to inform the unit triggering the ignition of the angular position of the yoke wheel.

An angular position detector for internal combustion engines is known (US-A-4 797 827) which has a toothed wheel which is coupled and toothed to the crankshaft, the row of teeth running in the circumferential direction having a tooth gap. The coupling to the crankshaft is such that when this tooth gap moves past an electrical pulse-generating sensor, one of the cylinders of the internal combustion engine is at top dead center. Due to the inductive signaling, a downstream evaluation electronics can recognize its position in top dead center without additional Tregger elements on the toothed rotary encoder wheel and use it as a reference or reference point for an absolute angular position.

In contrast, the object underlying the invention is raised to facilitate the derivation of said reference point from the encoder signals, and in particular to save hardware and / or computing time for the corresponding evaluation electronics. To solve the problem it is proposed in a rotary encoder with the features mentioned in the first part of claim 1 that two separate coils are each assigned to a magnetic pole, and the spacing of the coils and / or magnetic poles corresponds to the smaller control distance, which relates to more than just two tooth segments. In this way it is achieved that the voltage induced in the coils relative to each other approximately the constant phase shift have, ie the half waves overlap each other in a phase-locked manner.

It is known (EP-A2-0 197 272) to arrange two pulse-generating inductive pickups at an angular distance from one another, which the projecting reactors of a yoke wheel, which are arranged in series with a gap, move past. However, the angular distance is dimensioned depending on the angular intervals between the top dead centers of the cylinders and the number of electronically controlled cylinders. For example, an angular distance of the two inductive transducers from one another of 128 degrees is proposed in the example given. As a result, a targeted and complete overlap of half-waves cannot be achieved, especially since the inductive pickups are not penetrated by magnetic fields of different polarities.

It is obvious that more than two tooth segments, that is to say at least three tooth segments, are expediently provided. In the course of further developments according to the invention, for example, nine tooth segments can be provided, between which there is a tangential control distance corresponding to an angle of 36 °, with one tooth segment being omitted in accordance with the above idea; as a result, there is a further spacing relating to only two tooth segments, corresponding to an angle of 72 °.

Using the rotary encoder according to the invention with a single, further distance, a method for ignition of internal combustion engines, in particular in lawn mowers, chainsaws or cut-off machines, can advantageously be designed as follows: an ignition timing control derives ignition pulses from the rotary encoder and controls them - linked to programmed ones Operating characteristics - accordingly delayed or advanced or accelerated a switching element that discharges a capacitor via the primary winding of an ignition coil; in this case, the ignition control takes place in the starting phase below a speed limit depending on the passage of the gap of the yoke wheel formed by the further spaced tooth segments on the two coils or magnetic poles. This can ensure that the ignition with respect to the (top) dead center of the internal combustion engine always takes place at the optimal time because the marking of the yoke wheel according to the invention allows the ignition timing control to always start from the absolute angular position. It is thus possible for the ignition to always take place in a specific segment wheel position in the starting speed range, irrespective of speed fluctuations or fluctuations in the angular speed, and for the ignition timing to be controlled as a function of the speed after reaching a specific speed.

In particular, it is conceivable in a development of the invention to have the ignition control take place in the starting phase with or after one of the tooth segments following the gap moves past the magnetic pole of the permanent magnet. In practice, the third tooth segment has proven itself for triggering an ignition derived from the absolute yoke wheel rotational position.

In many cases it is desirable that the triggering of the ignition with the third tooth segment or the pulse derived therefrom takes place only if the speed of the motor when the second and third tooth segments move past the gap at the magnetic poles or pole pieces is above a programmed threshold value. For this purpose, a development of the method according to the invention consists in having the ignition control take place in the starting phase depending on the angular velocity measurement by means of two adjacent tooth segments.

In continuation of these ideas, the following sequence is provided for the specific embodiment of the method according to the invention: in the starting phase, the angular velocity is counted by means of the time period between the passage of the second and then the third tooth segment after the gap, and only when the counting result exceeds a certain threshold value , the ignition is triggered when the third tooth segment moves past the pole piece. From a speed of approximately 1,500 rpm, the angular speed is counted in the interval formed by the first and second tooth segments in accordance with the specific process sequence. At the same time, the ignition control in the area triggered between the second and the third tooth segment gap. This makes it possible to adjust the ignition early. At speeds above 5,000 rpm, the advance adjustment is expanded in such a way that the ignition can be controlled before the second tooth segment has moved past a (scanned) magnetic pole. This extreme early adjustment is possible because the speed fluctuations are low in this speed range.

Known capacitor ignition arrangements (cf. previously explained method can be carried out.

In the two separate coils, induced voltage half-waves, each with the same polarity, are tapped and fed to a capacitor connected to an ignition coil for charging it. By means of a discharge switch coupled to the capacitor, which is expediently actuated by the above-mentioned ignition timing control, the capacitor can then be discharged at the desired point in time in accordance with an ignition map program. The voltage waves of different, opposite polarities induced in the two coils each become a separate pulse shaper, the outputs of which open into a pulse evaluation part, which is completed with each complete pulse from the input pulses by means of a logic switch designed for recognizing, scanning and evaluating the tooth segment gap or the corresponding pulse gap Yoke wheel revolution generates a single pulse (per revolution); this corresponds to an absolute angular position of the Yoke wheels. The pulse evaluation part can, for example, be dimensioned such that the individual pulse always occurs when the top dead center of the internal combustion engine has been reached. In any case, this single pulse can serve as an absolute reference point, from which the ignition timing can be specified by the control electronics depending on the state of the internal combustion engine and programmed operating characteristics.

In the context of the invention, the pulse evaluation part can be implemented by means of a microcomputer circuit with corresponding software or a hard-wired, digital switching mechanism. A particularly advantageous, cost-saving circuit variant goes in the last direction: the pulse evaluation part has a state-controlled or static memory element on the input side and a clock edge-controlled or dynamic memory element on the output side; the memory elements are expediently implemented as a flip-flop. They are arranged with one another in cascade or one behind the other, the input pulse signal based on the one of the two coils being used to take over control of the dynamic storage element on the output side and to reset both storage elements. The input pulse signal originating from the other coil is used to set the static storage element on the input side. This circuit variant is primarily based on the above-mentioned design of the rotary encoder, in which the distance between the coils and / or magnetic poles corresponds to the smaller (control) distance, which relates to more than just two tooth segments. Then the half-waves derived from the separate coils overlap and those on them Schmitt trigger shaped pulses. If the gap on the circumference of the yoke wheel occurs on one of the magnetic poles, only one pulse is generated by one of the two coils, which serves to set the input-side storage element in a defined state. If subsequently only one pulse occurs from the other coil, the corresponding pulse can be driven to the output-side storage element to take over the output of the input-side storage element. If the next two tooth segments move past one magnetic pole at the same time, a pulse is generated in each coil again at the same time, and the storage elements are reset.

As part of a development of the ignition arrangement according to the invention, the individual pulse is fed to a total time counter for a complete revolution, and the output signal of the total time counter influences a pulse and delay generator linked to programmed ignition maps; Its output pulses then serve to control the discharge switch and, in connection therewith, to discharge the capacitor. In this way, in particular when the internal combustion engine is no longer in the state of the starting phase, a desired, speed-dependent early adjustment of the ignition timing can be brought about if the ignition maps are encoded accordingly. With the help of a switchover part implemented by hardware or software, which switches over according to the start-up phase and the normal operating phase under load, corresponding branches or curves can be traversed within the operating map, depending on the switchover state.

In order to prevent ignition in the starting phase of the internal combustion engine when the instantaneous speed is too low, it is advantageously provided as a development of the invention that an additional switching element is interposed between the generator output and the discharge switch; This is controlled by a torque counter for speed measurement, which scans the chronological sequence of two adjacent tooth segments past the magnetic poles. The control itself takes place as a function of one or more pre-programmed threshold values that correspond to the specified minimum speeds.

Fig. 1

schematisch die Geräte- und Funktionsanordnung eines erfindungsgemäßen Kondensator-Zündsystems,

Fig. 2

ein Schaltbild des Impulsauswertungsteils und

Fig. 3

ein Impuls- und Zeitdiagramm bezüglich des Impulsauswertungsteils und

Fig. 4

ein Flußdiagramm betreffend eine Ausführung des erfindungsgemäßen Verfahrens.

Further features, details and advantages of the invention result from the following description of an embodiment of the invention and from the drawing. In it show:

Fig. 1

schematically the device and functional arrangement of a capacitor ignition system according to the invention,

Fig. 2

a circuit diagram of the pulse evaluation part and

Fig. 3

a pulse and time diagram relating to the pulse evaluation part and

Fig. 4

a flowchart relating to an implementation of the method according to the invention.

As illustrated in FIG. 1, the rotary encoder 1 according to the invention consists of a yoke wheel 2 and an ignition module 3. The yoke wheel 2 is a with a (not shown) shaft The internal combustion engine is coupled in a torsionally rigid manner and, in the example shown, has radially projecting tooth segments 41 to 49 distributed over its circumference. The tooth segments have a regular tangential distance from one another corresponding to an angle of 36 °, which would result in a total of ten tooth segments if the circumference of the yoke wheel 2 were fully utilized. However, according to the invention - in the illustration approximately in the lower left quadrant - a larger tooth segment gap 6 is formed corresponding to an angular distance of 72 ° by the tenth being omitted when the tooth segments are attached regularly. When the yoke wheel 2 is moved in the direction of rotation 5, the toothed segments 41 to 49 are successively moved past two pole pieces 7, 8. These are penetrated by the field of a permanent magnet 9 and each surrounded by a first coil L1 and a second coil L2. Upon rotation of the yoke wheel 2, which is used to produce a magnetic yoke, the air gaps between the yoke wheel 2 and the pole pieces 7 and 8 are alternately increased and decreased, which causes a change in the magnetic flux through the two coils L1, L2. As a result, a voltage is induced on the coil which corresponds approximately to the signal profiles a, b over time t according to FIG. 3. Thereafter, positive and negative half-waves tapped on each coil overlap, which is due to the fact that the distance between the pole shoes 7, 8 corresponds approximately to the (smaller) standard distance of the tooth segments 41 to 49, with the exception of the tooth segments 41 and 49 delimiting the larger gap 6 .

Rectifier diodes DL1 and DL2 are used to measure the positive half-waves tapped at coils L1, L2 fed to the capacitor CL to charge it. A free-wheeling diode DS is connected in parallel with a discharge switch Thy, in the exemplary embodiment shown a thyristor which is actuated by the output 10 of the ignition timing control 11.

The ignition timing control 11 can be implemented as a microcomputer or a customer-specific integrated circuit. It has one of the two coils L1, L2 assigned inputs 13 and 14, each of which is preceded by a rectifier diode DL3 or DL4 so that only the negative half-waves induced in the two coils L1, L2 are let through. Each of the two rectifier diodes DL3, DL4 is followed by an inverting pulse shaper IF1, IF2, which generates digitally processable pulses from the half-waves. For example, inverting Schmitt triggers (see FIG. 2) can be used for this. The negative half-waves from the coils L1, L2 which are thereby formed into positive pulses D1, D2 are then passed into a pulse evaluation part 15, which generates an individual pulse per full revolution of the yoke wheel 2. Due to the configuration of the pulse evaluation part 15 according to the invention, this corresponds to a certain absolute angular position of the yoke wheel 2, in which the gap 6 is still opposite the pole shoe which is penetrated by the north pole magnetic field.

The individual pulse D3 is first fed to a function module 16 which serves to measure the speed n for an entire revolution, the measuring output 17 of which influences a pulse and delay time generator 18. This functional module 18 is additionally with a memory module 19 with operating maps, the z. B. contain the machine speed n as parameters, functionally linked. Influenced by the speed measurement module 16 and by the operating map module 19, the pulse delay module 18 possibly generates actuation signals which are adjusted in advance and are supplied to the thyristor Thy, whereupon the latter switches on and thereby discharges the capacitor via the ignition coil LZ.

Furthermore, the ignition timing control 11 comprises a counter module 20 which determines the instantaneous speed or angular velocity on the basis of two adjacent toothed segments 41 to 49 and which, depending on the instantaneous angular velocity w, switches through the output 10 of the ignition timing control 11 or the pulse delay module 18 to the thyristor Thy by using its output 21 (shown in dashed lines) actuated a switching element 22 accordingly. 1, the counter module 20 additionally processes the individual pulse D3 at the output of the pulse evaluation module 15 and communicates with a further memory module 23 which contains threshold values sw corresponding to minimum angular velocities.

2 shows the design of the pulse evaluation module 15 as hard-wired switching logic: The negative half-waves tapped at each of the two coils L1, L2 are each fed to a Schmitt trigger ST1, ST2, which generates inverting positive pulses D1 and D2 (see the waveforms c) and d) in Fig. 3). The pulse train D1 derived from the first coil L1, which is penetrated by the south pole magnetic field according to FIG. 1, becomes the reset input R1, and that from the other coil L2 is also opposed Pulse sequence D2 derived from the polarized magnetic field is supplied to the set input S1 of an RS flip-flop FF1 known per se. An RC high-pass DG, which consists of the capacitor C and the resistor R connected to ground, is preferably connected directly upstream of the reset input R1 as a differentiating element. The complementary output Q1 of the RS flip-flop FF1 is connected directly to the data input D of a known D-flip-flop FF2 connected in cascade or series. The reset input R2 of the D flip-flop FF2 is direct, and its clock input CL, which responds to positive edges, is indirectly connected via an inverting gate I to the output of the first Schmitt trigger ST1, which detects the negative half-waves of the coil through which the magnetic south pole passes L1 forms into impulses. The output signal of the entire switching mechanism according to FIG. 2 is formed by the non-inverting output Q2 of the D flip-flop FF2, at which a single pulse is available per revolution of the yoke wheel 2 (cf. FIG. 1), as explained in more detail below .

3 shows waveforms a) to g) over time t. The signal profiles a) and b) reflect the voltages induced in the coils L1, L2, the straight-line sections 24a, 24b, which run without a slope, being formed in the yoke wheel 2 due to the tooth segment gap 6 (cf. FIG. 1). The signal curves c) - first pulse sequence D1 derived from the former coil L1 - and d) - second pulse sequence D2 derived from the second coil L2 - are derived from these induced vibrations by means of the Schmitt trigger ST1, ST2 (cf. FIG. 2) , the longer impulse-free sections 24c, 24d of the above, correspond to rectilinear sections 24a, 24b. During time I, the RS flip-flop FF1 is set and the D flip-flop FF2 is reset. Each rising, positive edge of the first pulse sequence D1 sets the clock input Cl of the D flip-flop FF2 to logic "0". The differentiator DG generates corresponding needle-shaped short pulses D1.1 from the first pulse sequence D1, the length of which is dimensioned via the dimensioning of the RC high-pass filter such that the RS flip-flop FF1 is just being safely reset. The inverting output Q1 of the RS flip-flop FF1 is then logic "1".

The subsequent rising positive edge of the second pulse sequence D2 sets the RS flip-flop FF1, which is accordingly set at time II. The then falling edge of the second pulse sequence D2 has no effect. The subsequent falling edge of the first pulse sequence D1 results in a rising edge or a positive pulse for the clock input C1 of the D flip-flop FF2 due to the interposed inverter I. This triggers the takeover of the level state at data input D of data flip-flop FF2 after its (non-inverting) output Q2. If data input D was previously at logic "0", output Q2 of data flip-flop FF2 does not change. The subsequent pulse of the second pulse sequence D2 at time III has no effect. The RS flip-flop FF1 was previously set and remains set.

At time IV, the RS flip-flop FF1 is reset by the pulse train D1.1 generated by the differentiator DG. Now that the set pulse due to the second pulse train D2 is missing, the data input D of the D flip-flop is at logic "1". With the next falling edge of the pulse sequence D1 (cf. time V), data transfer at the input D is triggered via the inverter I at the clock input C1 of the D flip-flop FF2 and the D flip-flop FF2 is therefore set. This means the output level logically "1" at the output Q2, which forms the individual pulse D3 per revolution of the yoke wheel 2 (cf. g) in FIG. 3).

From this it can be concluded that the individual pulse D3 per revolution essentially arises from the pulse gap 24d of the second pulse sequence D2, which in the example is based on the second coil L2 penetrated by the magnetic north pole field.

Finally, a possible implementation of the method according to the invention is illustrated with reference to the flow chart in FIG. 4: The function module 16 measuring the speed n for a complete revolution of the yoke wheel 2 executes a program branch 25 depending on the speed value: If the speed is below 1,500 rpm, branched into path 26, otherwise branched into path 27. Path 26 is an instantaneous speed determination, e.g. B. between the second and third toothed segment (see, for example, reference numerals 42 and 43 in FIG. 1) after the toothed segment gap 6 of the yoke wheel 2, provided by the counter module determining the instantaneous angular velocity w on the basis of the second pulse signal D2 is carried out (cf. function block 28 in FIG. 4). Then there is a query 29 as to whether the instantaneous angular velocity w determined in the memory module 23 in accordance with FIG. Fig. 1 exceeds threshold values SW corresponding to preprogrammed minimum speeds. In such a case, after the ignition 30 is rigid with the third tooth segment 43 (see waiting loop 35), otherwise the ignition or process start program ZÜND is returned without ignition.

If, on the basis of a NO decision, the program branch 25 is guided into the path 27 because the speed determined over an entire revolution of the yoke wheel 2 exceeds 1,500 rpm, a query 31 is made as to whether the resulting speed n exceeds 5000 rpm. In such a case, the ignition is permitted in the interval formed by the first and second tooth segments after the gap (cf. tooth segments 41 and 42 in FIG. 1) in accordance with function block 32 with subsequent ignition block 30. The ignition can, however, according to the stored operating map within the range of second and third tooth segment 42 and 43 defined interval are triggered. If the speed n related to a total revolution is less than 5,000 rpm, the instantaneous angular speed w is determined or monitored in the interval defined by the first and second toothed segments 41, 42 after the gap 6 - cf. Function block 33. The ignition 30 can therefore be advanced to the second tooth segment 42 within the interval defined by the second and third tooth segments 42 and 43 - cf. Function block 34. The early adjustment 32, 34 takes place in each case as specified by the operating maps BKF stored in the memory module 19 (FIG. 1).

Claims (10)

1. Inductive shaft-angle encoder (1) for controlling the ignition time of internal combustion engines, having a coil (L1, L2) penetrated by a permanent magnet (9) and a yoke wheel (2), which is rotated by a shaft and over the circumference of which are distributed projecting, spaced tooth segments (41-49), which pass over the magnetic poles (N, S) in order to induce the current, wherein toothed segments (41 to 49) which are adjacent in the circumferential direction have two different sizes of spacing (6, 39), and the larger spacing corresponds to one toothed segment gap (6) formed by the omission of a toothed segment where the toothed segments (41 to 49) are uniformly spaced apart with the smaller standard spacing (39), characterised in that two separate coils (L1, L2) are associated with each magnetic pole (N, S, 7, 8), and the distance of the coils (L1, L2) and/or magnetic poles (N, S, 7, 8) from one another corresponds to the smaller standard spacing (39) affecting more than just two toothed segments (41 to 49).
2. Method of igniting internal combustion engines, in particular lawnmowers, motor saws or abrasive cutting machines, characterised by the use of a shaft-angle encoder (1) according to claim 1 for an ignition time control (11), this control receiving ignition pulses (D2, D3) from the shaft-angle encoder (1) and therefore, by means of programmed operating characteristic fields (19, BKF), actuating a switching member (Thy) in a delayed or early manner, as is necessary, the switching member then discharging a capacitor (CL) via the primary winding of an ignition coil (LZ), wherein in the starting phase, below a speed limit (25), ignition triggering being dependent on the passing of the gap (6) in the yoke wheel (2), formed by the toothed segments (41, 49) that are further apart, over the two coils (L1, L2) or magnetic poles (N, S, 7, 8).
3. Method according to claim 2, characterised in that in the starting speed range, independently of speed fluctuations or fluctuations in the angular velocity, ignition (30) is always effected in a certain segment wheel position (35), and in that after a certain speed (31) has been reached, the ignition time (30) is controlled as a function of speed.
4. Method according to claim 2 or 3, characterised in that in the starting phase, triggering is effected during or after the passing of a toothed segment (41-49) following the gap (6), preferably of the third toothed segment (43), over the magnetic pole.
5. Method according to claim 2, 3 or 4, characterised in that in the starting phase, ignition triggering is effected as a function of an angular velocity measurement (20, 28) by means of two adjacent toothed segments (42, 43).
6. Method according to one of claims 2 to 5, characterised in that in the starting phase the angular velocity (w) is selected by means of the second and third toothed segment (42, 43) after the gap (6), and when the angular velocity exceeds a threshold value (SW), ignition triggering (30) is effected immediately with the third toothed segment (43) after the gap (6), in that upwards of a speed (n) of at least 1 500 rpm the angular velocity (w) is selected by means of the first and second toothed segments (41, 42), and ignition triggering (30) is effected as a function of the operating characteristic field (BKF) after the second and before the fourth toothed segment (42, 44), and in that at a speed (n) of more than 5000 rpm, before the second toothed segment (42) has completely passed a magnetic pole (N, S, 7, 8), ignition triggering (30) is carried out.
7. Capacitor ignition device, in particular for carrying out the method according to one of claims 2 to 6, characterised by the use of a shaft-angle encoder (1) according to claim 1, in that its two coils (L1, L2) are connected to an ignition capacitor (CL) connected to an ignition coil (LZ) via a respective rectifier element (DL1, DL2), so that the ignition capacitor can be charged up by means of the voltage half-waves of respectively the same polarity induced in the coils (L1, L2), wherein the ignition capacitor (CL) is connected to a discharge switch (Thy) controlled by an ignition characteristic field program (BKF), so that the ignition capacitor (CL) is dischargeable in accordance with an ignition characteristic field program (BKF), and the half-waves of opposite polarities of the two coils (L1, L2) of the shaft-angle encoder (1) are fed to a respective pulse generator (IF1, IF2), whose outputs lead into a pulse evaluation member (15), which is realised with a logic board (FF1, FF2) so formed for identifying, scanning and evaluating the toothed segment gap (6) of the shaft-angle encoder yoke wheel (6) or of the corresponding pulse gap (24d) that upon each complete yoke wheel revolution (5), an individual pulse (D3) based on the pulse gap (24d) is applied to the output of the pulse evaluation member (15) and corresponds to an absolute angular position of the yoke wheel (2).
8. Ignition device according to claim 7, characterised in that the circuit board of the pulse evaluating member (15) has at the input a condition-controlled store element and at the output a pulse edge-controlled store element (FF1, FF2), which are arranged in cascade, wherein the input signal (D1) based on one of the coils (L1) is used for take-over actuation (C1) of the output-side store element (FF2) and the input signal (D2) based on the other coil (L2) is for setting the input-side store element (FF1).
9. Ignition device according to claim 7 or 8, characterised in that the individual pulse (D3) per revolution of the yoke wheel (2) is fed to a total time counter (16) for a complete revolution of the yoke wheel, and the output signal (17) of the total time counter (16) modifies a pulse and delay generator (18) associated with programmed ignition characteristic fields (BKF), whose output pulses (10) actuate the discharge switch (Thy).
10. Ignition device according to claim 9, characterised in that a switching element (22) is interposed between the generator output (18, 10) and the discharge switch (Thy) and is actuated by a timer (20) for measuring the momentary angular velocity (w) by means of two adjacent toothed segments (42, 43) according to programmed threshold values (SW) and in accordance with specified minimum speeds.

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