EP2955354A1 - Method for controlling the speed limit of a combustion engine - Google Patents

Abstract

The invention relates to a method for controlling the speed limitation of an internal combustion engine (8) in a hand-held implement (1), such as a motor chain saw. A cylinder (9) of the internal combustion engine (8) has a combustion chamber (22) delimited by a piston (10), the piston (10) driving a crankshaft via a connecting rod (11). The crankshaft drives a working tool via a clutch (33) which closes in dependence on the engine speed (n), a drive connection with the crankshaft (13) being established above an engagement speed of the clutch (33) and the drive connection being interrupted below the engagement speed. In the combustion chamber (22) a spark plug (23) is arranged, which is controlled by an ignition device (30). A speed control device (50) monitors the speed (n) of the internal combustion engine (8) and includes a speed lock circuit (51) limiting the speed (n) of the internal combustion engine to a limit speed (nG) below the engagement speed. When starting the internal combustion engine (8), the speed lock circuit (51) is turned on; it is switched off after the startup of the internal combustion engine (8) in the presence of a deactivation signal, wherein the deactivation signal is generated when an operation change signal of the internal combustion engine (8) is detected.

Description

The invention relates to a method for controlling the speed limitation of an internal combustion engine in a hand-held implement according to the preamble of claim 1.

Portable, hand-held implements such as motorized chain saws, power cutters, hedge trimmers, brush cutters, blowers or the like are usually driven by an internal combustion engine, which must be taken on site via a starting device in operation. Before pressing the starting device, the z. B. may be a recoil starter, the engine is placed in a start mode, d. h., the fuel supply and the combustion air supply adjusted accordingly. This can be z. B. done by the adjustment of a choke or throttle in the intake.

If the internal combustion engine starts after several start strokes, it must be ensured that the speed of the internal combustion engine in the starting phase does not rise above the engagement speed of the clutch via which the working tool is driven. The clutch, usually a centrifugal clutch, engages above an engagement speed and separates the work tool from the drive below the engagement speed. To ensure that in the starting phase of the engine whose speed does not rise above the engagement speed, a speed lock circuit is provided which keeps the instantaneous speed of the engine electronically below the engagement speed, preferably below a limit speed of the speed lock circuit forces.

When the speed lock circuit is activated, the speed control device will permanently try by regulating interventions to keep the speed below the predetermined limit speed of the speed lock circuit. Therefore, after the startup phase has elapsed, the speed lock circuit must be turned off so that the user can use the entire engine speed band for work.

From the EP 2 087 973 A1 is the switching on a speed lock circuit in response to the signal of a sensor of a braking device known. It should be avoided as a start of the engine with an open braking device. The manner in which an actively switched speed lockout circuit is to be deactivated is explained by way of example only, for example. Example, by a timer, a user-actuated pushbutton or by the signal of a sensor on the throttle.

After WO 2009/085006 A1 It is proposed to detect events that have to have a specific sequence in order to deactivate a speed lockout circuit. Thus, to deactivate first a "high state" of the internal combustion engine and then a "low state" of the internal combustion engine must be determined to turn off the speed lock circuit. Alternatively, the user should press a button or lever to turn off the speed lock circuit.

In the US 2010/0012084 A1 Further scenarios are proposed, after the occurrence of a deactivation of the speed lock circuit is allowed.

The invention has for its object to provide a method which causes without additional sensors with little technical effort to turn off a speed lock circuit.

The object is achieved in that a deactivation signal for switching off the speed lock circuit is generated and applied only when an operating change signal of the internal combustion engine is detected, so the operating state of the engine is changed.

According to the invention, the operation change signal is derived from the frequency of the control actions of the speed control means for maintaining the limit speed of the speed lock circuit. When the speed-lock circuit is switched on, the speed control circuit will have a control activity when the instantaneous speed approaches the limit speed. H. Make a higher number of control actions into the ignition than when the instantaneous speed is significantly below the limit speed. If the instantaneous speed exceeds the limit speed, the control activity, i. H. the number of control interventions are extremely high. Thus, from the monitoring of the control activity, an operation change signal may be derived to generate and apply the deactivation signal for the speed lock circuit.

As a result, the possibility is created without major technical effort to disable the speed lock circuit as soon as the user is full throttle.

In a simple way, the number of control interventions is monitored over time; If the number of control interventions per unit of time exceeds a predetermined value, this is an indicator that the user has given full throttle and requires the entire speed range. Thus, if the predetermined value of the control interventions per unit time is exceeded, the system outputs an operating change signal, which leads to the shutdown of the speed lock circuit.

Advantageously, the deactivation signal is generated only when a predeterminable time has elapsed after the start of the internal combustion engine. This will ensure that the internal combustion engine has reached a stable operating condition before the entire speed band is released.

It may also be expedient to generate the deactivation signal only when the operating change signal is applied for a predetermined period of time.

Fig. 1

in schematischer Seitenansicht eine Motorkettensäge mit einem Verbrennungsmotor,

Fig. 2

eine Prinzipdarstellung einer teilgeschnittenen Motoreinheit für handgetragene Arbeitsgeräte nach Fig. 1,

Fig. 3

in schematischer Darstellung ein Ablaufdiagramm zur Betriebsweise einer Drehzahlsperrschaltung.

Further features of the invention will become apparent from the other claims, the description and the drawing, in which an embodiment of the invention described in detail below is shown. Show it:

Fig. 1

in a schematic side view of a motor chain saw with an internal combustion engine,

Fig. 2

a schematic diagram of a partially cut motor unit for hand-held tools after Fig. 1 .

Fig. 3

a schematic diagram of a flowchart for the operation of a speed lock circuit.

In Fig. 1 schematically a hand-held implement 1 is shown using the example of a motor chain saw. This portable, hand-held implement 1 is exemplary of other portable, hand-held implements such. As cutters, hedge trimmers, brushcutter, pruners, blowers or the like.

The illustrated implement 1 has a housing 31, which essentially serves to receive an internal combustion engine 8. In the illustrated embodiment, the engine 8 is a one-cylinder two-stroke engine; training as a one-cylinder four-stroke engine may be appropriate.

The implement 1 has a arranged in the longitudinal direction of the housing 31 rear handle 2 and a front, bow-shaped handle 3, which extends transversely to the longitudinal direction of the housing 31 via the top thereof. The front handle 3, a hand guard 32 is assigned as a trigger of a safety brake device not shown in the illustrated embodiment, a motor chain saw.

In the longitudinal direction of the housing 31, a guide rail 34 is fixed on the side opposite the handle 2, in the circumferential groove of a saw chain 35 out is. The saw chain 35 is driven by a not shown drive pinion and a clutch 33 from a crankshaft 13 of the engine 8. The crankshaft 13 is connected via a connecting rod 11 with a piston 10 in connection, which limits a combustion chamber 22 in the cylinder 9 of the internal combustion engine 8. The necessary for the operation of the engine fuel / air mixture is sucked through an intake passage 38 into the crankcase 12 of the engine 8 and ignited in the combustion chamber 22 via a spark plug 23. The fuel / air mixture is provided by a fuel system 40 which is received in an air filter box 4 of the housing 31 and fed from a fuel tank 41.

In the rear handle 2 of the implement 1, a throttle lever 5 for controlling the rotational speed of the engine 8 is provided on the inside; on the gas lever 5 opposite longitudinal side of the handle 2, a throttle lever lock 7 is arranged. The throttle lever 5 can be operated only when the throttle lock 7 is depressed.

Further, in the area of the throttle lever 5 on the housing 31, a mode selector 39 is provided which can assume operating positions such as "stop", "operation", "start" or the like. About the mode selector 39, the engine is switched to the respective corresponding operating state.

In the illustrated embodiment according to Fig. 1 the internal combustion engine is started by a recoil starter 6, which - in a known manner - engages one end of the crankshaft 13 and rotates it to start the internal combustion engine 8.

In Fig. 2 an internal combustion engine is shown in the basic structure of the engine 8 in the hand-held implement after Fig. 1 equivalent. Instead of the fuel system 40 on the intake passage 38 is for introducing fuel in the embodiment according to Fig. 2 a fuel valve 17 is provided which opens into an overflow channel 20 of the two-stroke engine. In the illustrated position of the piston 10 near the bottom dead center, the volume of the crankcase 12 is connected via two symmetrically arranged overflow channels 20 and 21 with the combustion chamber 22. About the overflow channels 20 and 21, the combustion air sucked into the crankcase 12 via an inlet 16 is conveyed into the combustion chamber 22 and, together with the fuel introduced into the overflow channel 20, is conveyed into the combustion chamber 22. There, the mixture is ignited by the spark plug 23, wherein during the downward stroke of the piston 10, the outlet 19 opens and the combustion gases via a silencer 36 (FIGS. Fig. 1 ) dissipates. The spark plug 23 is connected to an ignition device 30, which triggers a spark on the spark plug 23 as a function of the signals of an ignition module 24 and other variables. The ignition module 24 cooperates with a rotating fan wheel 15, which is fastened on one end of the crankshaft 13 and correspondingly has circulating magnets for induction of the ignition energy in the ignition module 24.

It may be expedient to arrange on the crankshaft 13 of the internal combustion engine 8 a generator 14, which may also provide the energy required for ignition of the spark plug 23. The alternator 14 is connected to the ignition device 30 and feeds the alternating current signals into the ignition device 30. The generator 14 also provides a speed signal available, whereby the instantaneous speed n of the crankshaft 13 and the engine 8 is reported to the ignition device 30.

The adjoining an intake port 16 of the engine 8 opens into the crankcase 12 and is controlled by the reciprocating piston 10. At the throttle valve 18, a position sensor 26 is arranged, the z. B. at fully open throttle emits an operating change signal and thus indicates a change in the operating state of the engine 8.

In the same way, a position sensor 28 can be arranged on the choke flap, which, for example, emits an operating change signal when the choke is closed and thus indicates an operating change, namely the operating mode "Start". If the position sensor 28 is assigned to the open position of the choke flap, the operating change signal is emitted when the choke flap is in its inoperative position, ie the engine experiences no start enrichment, thus running in the normal operating mode. Accordingly, a sensor 29 may be arranged on the mode selector 39, which emits a respective operating change signal when the mode selector 39 is switched in its operating mode.

Operating change signals can also be generated if z. B. in the intake passage 38, a sensor, for. B. a pressure sensor 37 is attached. The prevailing in the intake negative pressure can be immediately close to the operating condition of the engine, so that when a significant pressure change occurs, for. B. falling below a predetermined pressure value, an operation change signal is issued.

Advantageously, the throttle lever 5 a position sensor 25 and the throttle lock 7 to a position sensor 27, wherein both sensors 25 and 27 respectively when operating the respective lever emit a signal which is evaluated as an operating change signal.

The ignition device 30 includes a speed control device 50, which is associated with a speed lock circuit 51. By means of the speed control device 50, unacceptable speed states of the internal combustion engine 8 are to be avoided. So z. B. via the speed control device 50, the maximum speed of the engine 8 is set as well as an idle speed of the engine. The speed lock circuit 51 specifies a limit speed n _G , over which the speed should not increase, in particular at the start of the engine 8. The predetermined limit speed n _G is below an engagement speed of the clutch 33, which is designed in particular as a centrifugal clutch. The centrifugal clutch produces a drive connection with the working tool of the implement 1 as a function of the engine speed, wherein a torque-transmitting drive connection with the crankshaft 13 is established above an engagement speed of the clutch 33. Below the Einkuppeldrehzahl the drive connection is interrupted, so that the working tool is. In particular, at the start of the internal combustion engine by means of a cable starter 6 is required that the working tool does not start uncontrollably. Here engages the speed lock circuit whose Limit speed n _G with a safety margin below the Einkuppeldrehzahl the centrifugal clutch is. This ensures that at fixed start settings, the engine 8 does not run above the limit speed.

The speed lock circuit 51 is only in the operation of the internal combustion engine, d. H. after completion of the starting phase of the internal combustion engine, switched off by generating a deactivation signal. The deactivation signal is z. B. generated by the speed control device 50 when an operating change signal of the implement is detected, so there is a change in the operating mode of the implement.

Such a permanent query that can run in the speed control device 50 is in Fig. 3 shown.

The speed lock circuit 51 is initially turned on. The speed lock circuit 51 thus provides the speed control device 50 with a limit speed n _G.

Now, the internal combustion engine 8 - via the pull starter 6 - started, the instantaneous speed n of the engine is permanently monitored. In this case, the speed control device ensures that the instantaneous speed n remains below the limit speed n _G.

After the start of the internal combustion engine is constantly monitored whether a change in operation can be detected. As described above, the sensors 25, 26, 27, 28, 37 output operation change signals indicative of a change in the operating state of the internal combustion engine. Thus, upon actuation of the throttle lever 5 and a corresponding signal from the position sensor 25, the system assumes that the user wants to accelerate the engine to do a job. The signal of the sensor 25 is processed as an operation change signal in the speed control device 50 and in the speed lock circuit 51 and in response to the speed lock circuit 51 is turned off. The user has the full speed bandwidth of the internal combustion engine available for his work.

After the speed lock circuit 51 is turned off, it is constantly checked whether the engine is still in operation. If the user turns off the machine, the speed lock circuit 51 is immediately activated, so that at a next start of the engine, the speed lock circuit 51 limits the allowable speed back to the limit speed n _G below the Einkuppeldrehzahl the clutch 33.

Similarly, the position sensor 26 will output an operation change signal when the throttle is moved from the neutral position or is in the full throttle position. The sensor 28 on the choke valve outputs an operation change signal when the choke flap is moved to its open position. Accordingly, upon return of a mode selector from the start mode to the operation mode, the sensor 29 may output an operation change signal which results in turning off the speed lock circuit.

In addition to position sensors can also be conveniently used a pressure sensor 37 which detects the Ansaugunterdruck in the intake passage 38 and emits an operating change signal in the presence of a corresponding operating pressure, which leads to a deactivation signal which is used to switch off the speed lock circuit. At idle, other pressure conditions prevail in the intake port and also in the crankcase than under full load, so that a significant pressure change is sufficient to conclude that the operating state of the internal combustion engine has changed. If the user is full throttle, the pressure conditions will change so, for. B. the negative pressure in the intake and / or sink significantly in the crankcase, indicating the change in the operating mode of the engine. This can be evaluated accordingly and generated according to an operating change signal.

Particularly noteworthy is the possibility of a sensorless detection of the change in the operating state. The speed control device 50 has a system-related control range, within which a change in the speed in a certain bandwidth is possible. So z. B. the firing angle can be changed as little as any an amount of fuel supplied via a valve. This means that even a speed control device 50 has system-related control limits above which a reasonable regulation is no longer possible.

This circumstance can be used to detect the change made by a user of the operating state. Namely, the speed lock circuit 51 is turned on, the speed control device 50 is in their starting position throttle and choke flap their task fair and keep the instantaneous speed n of the engine 8 below the limit speed n _G. If the user is full throttle when the speed lock circuit 51 is switched on, then such a high energy input into the internal combustion engine 8 occurs that its instantaneous speed n increases despite the switched-on speed lock circuit 51 and engagement of the speed control device 50 via the limit speed n _G. In full throttle position of the throttle lever 5 and the throttle valve 18, the speed control device is no longer able to keep the instantaneous speed n below the limit speed. Although the speed control circuit will continue to intervene to lower the speed; However, this will not be completely possible due to the design of the overall system. This exceeding of the instantaneous speed n of the internal combustion engine 8 over the limit speed n _{G of} the speed lock circuit 51 is detected and derived from the operating change signal, which - see. Fig. 3 - leads to a deactivation signal for the speed lock circuit 51. Thus, without a sensor, the system can recognize that the user is using the machine on the job and turning off the speed lock circuit 51. In a simple way, the operating change signal is generated when the instantaneous speed n of the internal combustion engine 8 is more than 20%, in particular more than 50%, above the limit speed of the rotational speed blocking circuit 51.

An operation change signal may also be derived from the increase in instantaneous speed n over time. If the user suddenly gives full throttle, the speed increase of the instantaneous speed n, ie the speed increase over a unit of time, will be significantly steeper than when the engine is idling. In a simple way, the slope, ie the mathematically first derivative of the course of the instantaneous speed over time, ie .DELTA.n / .DELTA.t monitored. If there is a significantly steeper speed increase, ie if the mathematical value Δn / Δt is greater than a predefined threshold value, an operating change signal is generated, which leads to the deactivation signal for the speed lock circuit 51.

Another technically simple way of deriving an operating change signal is the monitoring of the control activity of the speed control device itself. The operating state of the internal combustion engine can be derived from the frequency of the control interventions of the speed control device for maintaining the limit speed of the speed lock circuit. When the speed-lock circuit is switched on, the speed control circuit will have a control activity when the instantaneous speed of the internal combustion engine approaches the limit speed. H. Make a higher number of control actions into the ignition than when the instantaneous speed is significantly below the limit speed. If the instantaneous speed exceeds the limit speed, the control activity, i. H. the number of control interventions, extremely high. Thus, from the monitoring of the control activity, an operation change signal may be derived to generate and apply the deactivation signal for the speed lock circuit. In a simple way, the number of control interventions is monitored over time; If the number of control interventions per unit of time exceeds a predetermined value, this is an indicator that the user has given full throttle and requires the entire speed range. Thus, if the predetermined value of the control interventions per unit time is exceeded, the system outputs an operation change signal, which leads to the shutdown of the speed lock circuit 51.

It may be advantageous, in the presence of the operating change signal, to generate the deactivation signal for the rotational speed blocking circuit 51 only when a predetermined time has elapsed after the start of the internal combustion engine. In the same way, it may be expedient to generate the deactivation signal only when the operating change signal is present for a predetermined period of time. In a development of the invention, the operating change signal can also form the deactivation signal.

Claims (4)

A method for controlling the speed limitation of an internal combustion engine (8) in a hand-held implement (1), in particular a motor chain saw, a power cutter, a hedge trimmer, a brushcutter, a blower or the like., A cylinder (9) of the internal combustion engine (8) one of a piston (10) limited combustion chamber (22) and the piston (10) via a connecting rod (11) drives a crankshaft, which drives a working tool via a depending on the engine speed (n) closing clutch (33), wherein above a Einkuppeldrehzahl the coupling (33) is a drive connection with the crankshaft (13) is produced and below the engagement speed, the drive connection is interrupted, with a in the combustion chamber (22) arranged spark plug (23), which is driven by an ignition device (30), and with a Speed control device (50) for the rotational speed (n) of the internal combustion engine (8), comprising a rotational speed blocking circuit (51) which controls the D rehiring (s) of the internal combustion engine to a limiting speed (n _G ) limited below the Einkuppeldrehdrehzahl, wherein at the start of the internal combustion engine (8) the speed lock circuit (51) is turned on and the speed lock circuit (51) until the operation of the internal combustion engine (8) after generating a Deactivating signal is switched off, characterized in that the deactivation signal is generated when an operation change signal of the internal combustion engine (8) is detected, the operation change signal from the frequency of the control actions of the speed control device (50) for maintaining the limit speed (nG) of the speed lock circuit (51) is derived. Method according to claim 1,
characterized in that then an operating change signal for switching off the speed lock circuit (51) is derived when a predetermined value of the control interventions per unit time is exceeded. Method according to claim 1 or 2,
characterized in that the deactivation signal is generated only when a predetermined time has elapsed after the start. Method according to one of claims 1 to 3,
characterized in that the deactivation signal is generated only when the operation change signal is applied for a predetermined period of time.

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