Researchers Submit Patent Application, "Arrangement for Identifying a Switching Position of a Switch on an Internal Combustion Engine in a Handheld Work Apparatus", for Approval
The patent's assignee is Andreas Stihl AG & Co. KG.
News editors obtained the following quote from the background information supplied by the inventors: "Sensors which are intended to establish, for example, the position of the choke flap (start condition), the position of the throttle flap, the condition of the operating state of a safety braking device and the like, are arranged in portable, handheld work apparatus in order to ensure functionally reliable operation of an internal combustion engine. A short-circuiting switch is also provided, the engine being switched off when the short-circuiting switch is actuated. The sensor signals are used to control, for example, an electromagnetic fuel valve which serves to meter the quantity of fuel which is appropriate for the particular operating state.
"All of these sensors, which are configured, for example, as microswitches, can be electrically connected to a control unit which evaluates the sensor signals and accordingly controls the operation of the internal combustion engine. The electrical wiring of the sensors to the control unit is very complex."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "It is an object of the invention to provide an arrangement for identifying a switching position of a sensor, for example of an electrical switch, on an internal combustion engine in a handheld work apparatus in such a manner that the complexity for electrical wiring is reduced.
"The arrangement of the invention is for identifying a switch position of a switch on an internal combustion engine in a handheld work apparatus. The arrangement includes: a control; an inductive electrical load; an energy source configured to supply the inductive electrical load with energy; the inductive electrical load being connected to the energy source via the control so as to be switched on and off; a first voltage branch disposed parallel to the inductive load; the switch being a first switch having a first and a second switch position and being arranged in the first voltage branch; a first zener diode arranged in the first voltage branch; the first zener diode being configured to be switched to an active state and an inactive state in dependence upon the switch position of the first switch; the inductive load being configured to cause an induced switch-off voltage having an amplitude when the inductive load is switched off; and, the first zener diode being configured to limit the amplitude of the induced switch-off voltage.
"An inductive load, for example a pulse-width-controlled electromagnetic fuel valve, which is arranged on the internal combustion engine, is actuated, that is, switched on and off by an electrical controller of the internal combustion engine at controlled time intervals during operation of the internal combustion engine. According to the invention, the switch-off voltage which is induced in a system-related manner when an inductive electrical load is disconnected is used in order to identify the current switching position of a switch. To this end, the switch is arranged in a voltage branch which is connected in parallel with the inductive load. At least one zener diode is also arranged in this voltage branch, the zener diode being reverse-biased with respect to the switch-off voltage. This or these one or more zener diodes are activated or deactivated as a function of the switching position of the switch; when the zener diode is active, the amplitude of the switch-off voltage is limited to the component-specific breakdown voltage of the one or more zener diodes. Therefore, a switch-off voltage can be tapped off from the connection lines of the inductive load, the switch off voltage being limited to the breakdown voltage of the one or more zener diodes which are associated with the switch, or having another value as a function of the position of the electrical switch. Since the connection lines of the inductive load are anyway connected to the controller, wiring of the switch from its site of installation to the controller, which would otherwise be necessary, can be dispensed with; in the controller, the switch-off voltage which is applied to the connection lines of the load after the load is disconnected can be tapped off and the magnitude of its amplitude can be evaluated, as a result of which the switch position can be identified. Simple wiring of the switch to the inductive load is sufficient, for example in the form of a bus system.
"The maximum amplitude, which is tapped off from the load, of the induced switch-off voltage therefore allows a statement to be made about whether the switch which is to be monitored is open or closed in the voltage branch which is connected in parallel with the load.
"The amplitude of the induced switch-off voltage which is produced across the load as a function of the position of the switch can therefore be evaluated by an evaluation unit which is expediently integrated in the controller.
"A plurality of voltage branches which are connected in parallel are advantageously provided for the electrical load, and at least on zener diode, which is switched by a switch, is provided in each of these voltage branches. The one or more zener diodes have different breakdown voltages in this case, with the result that either the breakdown voltage of the one or another zener diode can be tapped off from the inductive load after it is disconnected. Therefore, an evaluation unit can immediately indicate, on the basis of the magnitude of the tapped-off switch-off voltage, whether the one or other switch is closed.
"In a simple embodiment of the arrangement, the switch and the zener diode are electrically connected to one another in series. If the switch is closed, the zener diode is activated; if the switch is open, the zener diode is inactive.
"As an alternative, provision can be made to arrange a plurality of switches in series with one another in a voltage branch, wherein each switch switches in each case one zener diode, the zener diodes having different breakdown voltages. In this case, the switches are connected in parallel with the zener diode, with the result that individual zener diodes which are connected in a cascade are switched by the switch position. If the switch is closed, the zener diode is short-circuited and therefore inactive; if the switch is open, the zener diode is active. In this case, provision is made to connect the zener diode to ground and to block the zener diode in the forward direction by a blocking diode. This ensures that no current can flow and no short circuit is produced in the parallel voltage branch during operation of the inductive load.
"A series circuit having a reference zener diode and a blocking diode which is connected anti-parallel is advantageously connected in parallel with the load. In this case, the sum of all the breakdown voltages of the zener diodes which can be connected via switches is smaller than the breakdown voltage of the reference zener diode.
"The voltage amplitude of the negative switch-off voltage, which voltage is induced when the inductive electrical load is disconnected and the direction of which voltage is applied against the polarity of the operating voltage, is limited by at least one respective zener diode. The inductive electrical load is preferably an electromagnetic valve, in particular an electromagnetic fuel valve, which is switched on and off when the crankshaft of the internal combustion engine rotates in accordance with a pulse width of the actuating signal, in order to meter an appropriate quantity of fuel to the internal combustion engine for operation.
"Each switch in a voltage branch is assigned a priority, wherein the priority is determined by the breakdown voltage of the associated zener diode. In this case, the switch with the highest priority is advantageously assigned a zener diode with the lowest breakdown voltage in the system.
"The arrangement according to the invention can be used to identify the switching position of a plurality of switches which are arranged on an internal combustion engine, via the connection lines of the inductive load, for example a choke switch which is arranged on a choke, a throttle flap switch which is arranged on the throttle flap, a short-circuiting switch as a stop switch for turning off the motor or an operating switch on a safety braking device.
BRIEF DESCRIPTION OF THE DRAWINGS
"The invention will now be described with reference to the drawings wherein:
"FIG. 1 is a schematic side view of a portable work apparatus;
"FIG. 2 shows a basic circuit diagram of an internal combustion engine with an arrangement for identifying the switching position of a switch;
"FIG. 3 shows a basic electrical circuit diagram of a first embodiment of an arrangement for identifying a switching position of a switch; and,
"FIG. 4 shows a basic electrical circuit diagram of a second arrangement for identifying a switching position of a switch."
For additional information on this patent application, see: Praeger, Joerg; Mandl,
Keywords for this news article include: Electronics, Electromagnet, Andreas Stihl AG & Co. KG.
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