Start safety ignition system

• US 7,699,039 B2
• Filed: 01/01/2008
• Issued: 04/20/2010
• Est. Priority Date: 07/01/2005
• Status: Active Grant

• Current Assignee: Husqvarna AB (HUSQVARNA)
• Original Assignee: Husqvarna AB (HUSQVARNA)
• Inventors: Andersson, Lars, Larsson, Mikael, Carlsson, Bo, Aronsson, Tore
• Primary Examiner(s): Cronin; Stephen K
• Assistant Examiner(s): HAMAOUI, DAVID E
• Application Number:
  US11/968,191
• Publication Number:
  US 20080223339A1
• Time in Patent Office: 840 Days
• Field of Search: 123/319, 123/406.54, 123/406.53, 701/110, 701/115
• US Class Current: 123/406.53
• CPC Class Codes: F02N 15/022 the starter comprising an intermediate clutch
• CPC Class Codes: F02P 1/086 for generating sparks by discharging a capacitor into a coil circuit
• CPC Class Codes: F02P 11/00 Safety means for electric spark ignition, not otherwise provided for
• CPC Class Codes: F02P 5/1506 with particular means during starting
• CPC Class Codes: F02P 5/1508 with particular means during idling
• CPC Class Codes: F02P 9/005 by weakening or suppression of sparks to limit the engine speed

Abstract

A method for controlling an ignition system of an internal combustion engine having a primary firing pulse generator for charging a capacitor. An electronic switch is included for discharging the capacitor via an ignition coil to generate an ignition voltage. A microcomputer operates the switch to control the ignition timing of the generator. The microcomputer is in communication with a speed sensor that detects the rotational speed of the engine and a speed limitation control that limits the engine speed to a limitation speed below the clutch-in speed of an included centrifugal clutch. The speed limitation control is active or activated when one of either starting the engine or an operating problem of the power tool is detected. The speed limitation control is deactivated when a low speed state of the engine is detected.

Claims

1. A method for controlling an ignition system of an internal combustion engine comprising a primary firing pulse generator for charging a capacitor and an electronic switch for discharging the capacitor via an ignition coil to generate an ignition voltage, a microcomputer operating the switch to control the ignition timing of said generator, said microcomputer in communication with a speed detection means that detects the rotational speed of the engine and a speed limitation control to limit the engine speed to a limitation speed below the clutch-in speed of a centrifugal clutch, wherein the speed limitation control is active or activated when one of (i) starting the engine and (ii) an operating problem of a power tool is detected, and the speed limitation control is deactivated when the speed detection means detects a low speed state of the engine for a defined period.

2. The method as recited in claim 1, wherein the detection of engine speed is made indirectly by detecting the time of ignition in relation to a stroke of the piston.

3. The method as recited in claim 2, wherein the detection of time of ignition is based on the microcomputer'"'"'s control to operate the engine in a preset value for its rotational speed.

4. The method as recited in claim 3, wherein the preset value is the engine'"'"'s rotational idle speed.

5. The method as recited in claim 1, wherein the low speed state of the engine corresponds to a rotational speed of the engine below the limitation speed.

6. The method as recited in claim 5, wherein the staff limitation control is deactivated when the low speed state has existed for a defined time period.

7. The method as recited in claim 6, wherein the low speed state of the engine corresponds to a throttle valve being positioned at a most closed position thereof.

8. The method as recited in claim 6, wherein the low speed state corresponds to a time of ignition which is earlier in relation to the top dead center of the piston than a preset threshold value.

9. The method as recited in claim 1, wherein the speed limitation control limits the speed through the operation of said switch via selectively activating or deactivating the ignition at different strokes of the piston.

10. The method as recited in claim 1, wherein the speed limitation control limits the speed through the operation of said switch via selecting the time of ignition in relation to a stroke of the piston.

11. The method as recited in claim 1, wherein the operating problem of the power tool is a centrifugal clutch slip problem which is detected by counting a number of revolutions during which the engine speed is within a slip speed range of the centrifugal clutch and comparing the counted number of revolutions with a compare number, and when the counted number of revolutions reach or pass the compare number, the speed limitation control is activated.

12. The method as recited in claim 11, wherein the compare number is a predetermined first number that is reduced with a predetermined second number when a second activation of the speed limitation occurs within a predetermined number of revolutions and is further reduced if a third activation occurs within the predetermined number of revolutions.

13. The method as recited in claim 1, wherein the operating problem is a centrifugal clutch slip problem and is detected by measuring a temperature in or close to the clutch.

14. The method as recited in claim 1, wherein the operating problem is an overheat problem of the engine or a component of the power tool and is detected by measuring a temperature in or close to the engine or component.

15. The method as recited in claim 1, wherein the hand held power tool is a cut off machine and the operating problem occurs above the end of clutch-in speed of the centrifugal clutch and is a slip problem of its drive belt detected by measuring a rotational speed of the working tool or its shaft and comparing it with the speed of the engine.

16. The method as recited in claim 1, wherein at least one problem indicator lamp is activated when the engine is running at the limitation speed.

17. The method as recited in claim 1, wherein the speed limitation control is also active or activated when starting the engine and being deactivated when said speed detection means detects a low speed state of the engine.

18. The method as recited in claim 16, wherein there is a separate indicator lamp each having a different a color for problems relating to the clutch, engine, and drive belt.