This application claims priority of German patent application no. 10 2010 015 087.8, filed Apr. 15, 2010, the entire content of which is incorporated herein by reference.
U.S. Pat. No. 7,814,888 B2 discloses a combustion engine which can serve to drive a work tool of a hand-guided work apparatus. A temperature sensor and a pressure sensor are arranged on the crankcase of the combustion engine.
U.S. Pat. No. 6,272,913 B1, for example, discloses arranging a pressure sensor and a temperature sensor in a common housing. Such sensors are typically used to measure the pressure and the temperature in the intake channel of a combustion engine.
It is an object of the invention to provide a hand-guided work apparatus which has a small size and enables safe operation.
The hand-guided work apparatus of the invention includes: a combustion engine having a crankcase defining a crankcase interior; a crankshaft rotatably mounted about a rotational axis in the crankcase; a pressure sensor and a temperature sensor; a sensor housing common to both of the sensors; the temperature sensor and the pressure sensor being arranged in the sensor housing; the work apparatus being configured to have a set-down position wherein the work apparatus is placeable on a horizontal rest surface; the pressure sensor and the temperature sensor being beneath a plane containing the rotational axis and the plane being parallel to the rest surface when the work apparatus is in the set-down position; the sensor housing defining a connecting channel for causing the pressure sensor to communicate with the crankcase interior; and, the connecting channel having a base which slopes down toward the crankcase interior when the work apparatus is in the set-down position on the rest surface.
The arrangement of pressure sensor and temperature sensor in a common sensor housing and the arrangement, for example, below the rotational axis of the crankshaft enables a space-saving arrangement. In the area lying below the rotational axis of the crankshaft, there typically is sufficient space for the arrangement of the temperature sensor and the pressure sensor. It has, however, been shown that when the pressure sensor and temperature sensor are arranged below the level of the crankshaft axis, the pressure sensor can accumulate contaminants, oil and the like, so that a safe operation cannot be ensured. This is avoided by the alignment of the base of the connecting channel of the pressure sensor relative to the crankcase interior. Oil and the like can still accumulate in the area of the pressure sensor during operation. When putting down the work tool, at which point the engine is typically still warm, it is ensured, however, that these contaminants can flow off the pressure sensor, so that any drying onto the pressure sensor is avoided. Thus, a durable operation of the pressure sensor is ensured.
Advantageously, the connecting channel widens at least partially funnel-shaped in the direction of the crankcase interior. It has been shown that a cylindrical channel configuration of the connecting channel can lead to a standing pressure wave which falsifies the measurement result. The funnel-shaped configuration also aids the gas exchange in the area of the pressure sensor and the temperature sensor, so that it is ensured that the temperature sensor measures the actual gas temperature in the crankcase. Advantageously, the temperature sensor is arranged in the connecting channel and does not project into the crankcase interior. The temperature sensor is in particular configured in an approximately rod-shaped manner and projects unobstructed into the connecting channel, so that the temperature senor is surrounded by gas in the crankcase from all sides. Thus, good measurement results are achieved.
To protect the pressure sensor from mechanical damage during assembly or during servicing, the pressure sensor is arranged at the end of the connecting channel and the temperature sensor is arranged in front of the pressure sensor. The temperature sensor thus provides simple mechanical protection for the pressure sensor's membrane delimiting the connecting channel. Advantageously, the connecting channel has a first cylindrical section and a second funnel-shaped section. The first section connects to the pressure sensor and the temperature sensor is arranged in the first section. Thus, a simple configuration is achieved.
Advantageously, the sensor housing has a connecting stub through which the connecting channel extends and which is inserted into a receptacle on the crankcase. The longitudinal center axis of the connecting stub advantageously slopes upward in direction of the crankcase interior when the work tool is put down. Thus, a space-saving arrangement results. The connecting channel can be configured comparatively short as a result of this alignment of the connecting stub and this counteracts dirt accumulating in the connecting channel.
Advantageously, the sensor housing is sealed off against the crankcase in the radial direction of the connecting stub. The contact pressure force of the seal does not need to be applied to the crankcase by the fastening elements of the sensor housing. Thus, the fastening is easier to configure, and a secure seal can be achieved independently of the holding force applied by the fastening elements. A simple configuration results when the connecting stub has a sealing ring on its outer periphery, which ring seals the sensor housing off against the crankcase. The sealing ring is advantageously configured such that the sensor housing is already held by the sealing ring in the receptacle of the crankcase. The connecting stub, in particular, has a front edge facing the crankcase interior, whose course is adapted to the roundings of the crankcase interior. Thus, a consistent course of the wall of the crankcase interior is achieved. The front edge of the connecting stub also forms, in particular, a section of the wall of the crankcase interior. In order to ensure that the sensor housing does not become removed from the receptacle during operation, for example, as a result of vibrations, the sensor housing is held on the crankcase in the axial direction with a fastening element. Because of the radial sealing, the fastening element does not need to apply the contact pressure force for the seal but must only fix the sensor housing on the crankcase. Thus, fewer fastening elements can be used than in the case of axial sealing. Thus, the space required can be reduced.
Advantageously, the pressure sensor and the temperature sensor are arranged on a common board which is held in the sensor housing. The sensors are, in particular, potted in the sensor housing with the board. Thus, protection of the sensors and the board from outside influences and a secure fixation in the housing are achieved in a simple manner.
The invention will now be described with reference to the drawings wherein:
The chain saw 1 has a housing 2 on which a rear handle 3 and a handle bar 4 to guide the chain saw 1 during operation are arranged. On the end of the housing 2 opposite the rear handle 4, there is a guide bar 5 which projects forwardly. A saw chain 6 is arranged on the periphery of the guide bar 5. The saw chain 6 is driven by a two-stroke engine 9. In
The two-stroke engine 9 draws in surrounding air through an intake channel 10 and into a crankcase 14 via an air filter 11. The crankcase 14 is connected to a combustion chamber formed in a cylinder 15 of the two-stroke engine 9 via at least one transfer channel 24. On the crankcase 14, there is arranged a fuel valve 12 which supplies fuel to the combustion air drawn into the crankcase interior. The fuel is prepared as an air/fuel mixture and passes over into the combustion chamber via at least one transfer channel 24. A sensor component 13 is arranged on the crankcase 14 and is described in more detail below.
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A board 28, on which the sensors 26 and 27 are held, is arranged in the sensor housing 31. The board 28 is contacted via four connecting lines 29 which are guided outwardly via a holder 32. Connecting lines 29 are held in the holder 32. The holder 32 is held in the housing wall of the housing 31 by a groove. An insert module 33, which will be described in more detail below, is provided on the opposite side of the holder 32.
The configuration of the sensor component 13 is shown in detail in
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It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
Number | Date | Country | Kind |
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102010015087.8 | Apr 2010 | DE | national |