ENGINE WITH REVOLUTION COUNTER

Abstract: An electronic revolution counter comprises a ferro-magnetic metal disc 20, with teeth 26, attached to the main shaft 12 of the engine and a fixed electromagnetic pick-up coil 28 past which the teeth sweep. In order to permit retrofitting to various engines, the coil is carried by a mounting structure comprising a sheet metal L-shaped bracket 34, 36 welded to a flat plate 42. This plate is fixed to the engine block 18 by bolts 46 and spacing sleeves 48 on the bolts have lengths adapted to the profile to which the plate is fixed. The bolts 46 pass through slotted holes in the plate 42, enabling the clearance between the coil 28 and the teeth 26 to be adjusted precisely.

Description: ENGINE WITH REVOLUTION COUNTER The present invention relates to an internal combustion engine with an electromagnetic revolution counter, comprising a disc with ferromagnetic teeth on a shaft of the engine and an electromagnetic pick-up coil mounted closely adjacent the path of the teeth. Engines with such revolution counters (or tachometers) are well known and operate on the principle that the ferromagnetic teeth moving past the pick-up coil induce voltage pulses therein. These pulses are processed in ways well known in themselves and forming no part of the present invention, in order to provide an indication of engine speed. In order to ensure reliable operation, it is necessary that the pulses shall always have sufficient amplitude and this in turn requires the pick-up coil to be mounted precisely and sufficiently close to the path of the teeth. Nevertheless adequate clearance must be maintained to avoid the coil fouling the teeth. Accordingly, in designing engines with such revolution counters, it is known to incorporate suitable mounting means which ensure that the pick-up coil is correctly positioned. However a need arises to be able to fit such revolution counters to engines originally designated without them. In particular it is found desirable to be able to add electromagnetic revolution counters to the engines of tractors and other agricultural vehicles. In such a situation, where the engine has not been designed to locate a pick-up coil correctly, there is the problem of conveniently, cheaply and yet accurately mounting the pick-up coil so that it is sufficiently close to the path of the teeth while preserving the necessary clearance therefrom. This problem is solved according to the invention as defined in claim 1. Advantageous developments are defined in the further claims. The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a fragmentary end elevation of a diesel engine with a revolution counter embodying the invention, Fig 2 is a partially sectioned side elevation taken from the right in Fig 1, and Fig 3 is a partial plan view corresponding to Fig 1. The diesel engine of a tractor is represented by a bolt drive pulley 10 which is keyed on to the main shaft 12 of the engine and held in position by a retaining plate 14 and bolts 16. The engine block is indicated in a purely schematic and fragmentary manner at 18 in Fig 2. The pulley wheel 10 has a disc 20 bolted to it by means of bolts 22 and spacers 24. The disc 20 is made of mild steel or other magnetically soft material and is shaped so as to have a plurality of peripheral teeth 26, ten teeth in the illustrated embodiment. When the engine is running, the teeth 26 sweep closely past a pole face of an electromagnetic pick-up coil encapsulated in a coil unit 28 having terminal posts 30 connected to the two ends of the coil. Wires 32 running from the terminal posts lead to the instrumentation whereat the voltage pulses induced in the coil are processed to provide a measurement of the engine speed (RPM). The coil unit 28 is mounted above the disc 20 through a horizontal part 34 of an Shaped sheet metal bracket having a vertical part 36. The coil unit is held in place and'protected by a cover 38 attached to the bracket part 34 by nuts and bolts 40. The Shaped bracket 34, 36 is welded to a flat mounting plate 42 which is perpendicular to both parts of the bracket so that the resulting structure is very rigid. The mounting plate 42 has three slots 44 through which pass bolts 46, the bolts being screwed into threaded holes in the engine block 18. Behind the mounting plate 42, spacer sleeves 48 are employed on the bolts 46 and the length of each spacer sleeve can be chosen appropriately in accordance with the existing profile of the engine block 18. In the illustrated embodiment (Fig 2) the bolts 46 are also used to clamp a timing gear cover schematically represented at 19 on to the engine block 18. Thus the cover 19 is interposed between the engine block 18 and the spacers 48 and the profile to which the lengths of the spacers are adapted is actually the timing gear cover profile. In any event, no major changes whatsoever are required in adding the revolution counter. Apart from attaching the disc 20 in some convenient manner to the engine shaft, it is merely necessary to provide tapped holes in the engine block for the bolts 46 to fix the mounting plate 42 to the engine block. Moreover, because the bolt holes through the plate 42 are in the form of slots 44, it is possible to adjust the clearance between the coil unit 28 and the teeth 26 to the precise desired value. This attachment does not require precise location of the bolt holes in the engine block or over precise dimensioning of the mounting structure for the coil unit comprising the plate 42 and the bracket 34, 36. Although other forms of spacer structure could be employed, it is particularly advantageous to employ a flat mounting plate 42 in conjunction with spacing sleeves 48 since adaptation of the mounting to different engines merely requires selection of the appropriate bolt and spacer lengths. The coil unit 28 can be positioned accurately by slackening off the bolts 46, positioning a tooth 26 immediately beneath the coil unit and introducing a thickness gauge establishing the desired clearance between the teeth and the coil unit. The bolts 46 are then retightened.

Claims: CLAIMS 1. An internal combustion engine with an electromagnetic revolution counter, comprising a disc with ferromagnetic teeth on a shaft of the engine and an electromagnetic pick-up coil mounted closely adjacent the path of the teeth, at the coil (28) is monitored on a mounting structure (35, 36, 42) including a plate (42) which is fixed to the block (18) of the engine by a plurality of bolts (46) passing through holes (44) in the plate into the engine block, with spacing means (48) between the plate and the engine block adapted to the profile of the engine block. 2. An engine with d revolution counter according to claim 1, characterised in that the said holes (44) are slots permitting the clearance between the coil (28) and the teeth (26) to be adjusted. 3. An engine with a revolution counter according to claim 1 or 2, characterised in that the spacing means comprise spacing sleeves (48) on the bolts (46), the lengths of the bolts and sleeves being adapted to the profile of the engine block (18). 4. An engine with a revolution counter according to claim 1, 2 or 3, characterised in that the mounting structure comprises an Shaped sheet metal bracket (34, 36) welded to the plate (42). CLAIMS 1. An internal combustion engine with an electromagnetic revolution counter,comprisingadisc with ferromagnetic teeth on a shaft of the engine and an electromagnetic pick-up coil mounted closely adjacent the path of the teeth, characterised in that the coil (28) is mounted on a mounting structure (35, 36, 42) including a plate (42) which is fixed to the block (18) of the engine by a plurality of bolts (46) passing through holes (44) in the plate into the enigne block, with spacing means i48) between the plate and the engine block adapted to the profile of the engine block. 2. An engine with a revolution counter according to claim 1, characterised in that the said holes (44) are slots permitting the clearance between the coil (28) and the teeth (26) to be adjusted. 3. An engine with a revolution counter according to claim 1 or 2, characterised in that the spacing means comprise spacing sleeves (48) on the bolts (46), the length of the bolts and sleeves being adapted to the profile of the engine block (18). 4. An engine with a revolution counter according to claim 1, 2 or 3, characterised in that the mounting structure comprises an L-shaped sheet metal bracket (34, 36) welded to the plate (42).

Inventors: KARCH, RUDI, KRYSCYK, ROBERT
Applicants: DEERE & COMPANY
Application year: 1981
Main classification: G01P3
IPC codes: G01P3