METHOD AND DEVICE FOR SENSING THE DIRECTION OF CRANKSHAFT ROTATION IN A DIESEL ENGINE

Abstract: A method and device for sensing the direction of crankshaft rotation in a diesel engine relies on measuring the angular difference ( alpha ) between a reference mark (BM) dependent on crankshaft rotation and commencement of fuel injection (FB). Since the normally trailing flank of the cam of the fuel injection pump, effectively becomes the leading flank on reverse rotation, this angular difference becomes substantially larger or substantially smaller than a reference ( alpha r) in the event of the reverse rotation. The signal produced upon reverse rotation can be used to stop the engine immediately.

Description: Method and device for sensing 'the direction of crankshaft rotation in a diesel engine The invention relates to a method and device for sensing the direction of crankshaft rotation of a diesel engine during starting, whereby the engine can be immediately stopped, should it have commenced rotating in the wrong direction. During the starting of an internal combustion engine, there is the possibility of it commencing to rotate in the wrong direction after 'kickback. Apart from the possible dangerous consequences of rotation in the wrong direction, there is also the possibility of mechanical damage to the engine. It is an object of the invention to detect rotation in the wrong direction by monitoring the commencement of fuel injection in relation to the top dead centre (TDC) in one cylinder of the engine. In DE-A-2653046 there is described a method of controlling injection advance (instant of commencement of injection in relation to TDC), in which the actual igniton advance is determined and is compared with a desired injection advance. The actual injection advance is determined by measuring the crank-angle relationship between a reference mark, produced by a pulse generator disc on the crankshaft, and commencement of injection, detected by a sensor in the vicinity of an injection nozzle. Advantages of the invention The invention provides a method and device for sensing the direction of crankshaft rotation in a diesel engine during starting, in accordance with claims 1 and 2, respectively. This has the advantage that the signal indicating "wrong direction" can be used to stop the engine immediately, e.g. by feeding it to the engine governor so that the latter sets the injection pump at zero delivery. Since actual fuel injection might not be readily detectable at an injection valve at very low engine speeds, below starting speed, e.g. at speeds below 400 r.p.m. it is preferable to detect the commencement of the injection stroke at the injection pump. The slight delay between the commencement of the injection stroke and the actual commencement of injection, which in any case is not sharply defined at very low engine speeds, is of no consequence. Since the commencement of the injection stroke is directly related to the angular position of the camshaft of the injection pump, the commencement of the injection stroke can be determined by measuring the angular position of the camshaft. Di-awings . The invention is further described, by way of example, with reference to the accompanying drawings, in which:- Fig.l is a block circuit diagram of a device for sensing the direction of crankshaft rotation in a diesel engine in accordance with the invention; Fig.2 is a side view of one embodiment of cam of the fuel injection pump of the engine; Fig.3 is a cam lift and pulse diagram relating to the fuel injection pump, to which Fig.2 refers, for a 6-cylinder diesel engine; Fig. is a similar cam lift and pulse diagram but relating to an 8-cylinder engine; Fig.5 is a side view of another* embodiment of cam; Fig.6 is a pulse diagram relating to the cam of Fig.5; and Fig.6a refers to a modification to the pulse diagram of Fig.6. escription of the exemplary embodiments. A pulse generator 10 is fitted to the crankshaft of a diesel engine and produces one or more reference pulses BM in precisely timed relation to crankshaft rotation. These reference pulses may be used for operation of an electronic governor and/or for operation of an electronic ignition advance control as described.in DE-A-2653046 or in DE-A-3202614. According to the invention, the reference pulses BM are used as references from which a signal designating or denoting commencement of fuel injection is measured. The commencement of injection signal may be the actual commencement of injection SB or the commencement of actual fuel delivery FBA by the injection pump but is preferably the commencement of the injection stroke FB, which can be a signal obtained from an inductive transducer 11 responsive to reciprocating movement of the pump piston. The slight differences between SB, FBA and FB due to fuel compressibility and the running time are of no consequence, particularly at the very low engine speeds at which the invention is relevant. The reference mark BM and the injection commencement signal FB are applied respectively to the start and stop inputs of a counter 12 to which is fed a counting pulse train n representative of rotation of the crankshaft, i.e. indicative of engine speed. The speed signal n can be a pulse train obtained from another pulse generator on the crankshaft and adapted to produce, for example, one pulse per degree rotation as described in DE-A-2653046. Alternatively the speed signal n can be derived from the reference marks BM, using for example a frequency multiplier. The output count of the counter 12 represents the actual injection angle ~- and is applied to a comparator 14 which checks whether the angle exceeds a threshold dr provided by a reference store 16. Fig.2 shows a symmetrical cam 18 of the camshaft. The point on the cam corresponding to commencement of the pumping stroke when the cam is rotated in the normal direction denoted by the arrow 20 is marked FB. The corresponding point at which the pumping stroke commences .upon rotation in the wrong direction is denoted by FB'. The working angle of the cam 18 in Fig.2 is 60°. That is to say, the angular range between the commencement of the pumping stroke and the completion of the suction stroke is 60° and this applies whichever the direction of rotation. This angle is equivalent to 120° crankshaft angle for a four stroke engine. The bottom part of Fig.2 shows the production of the reference pulses BM and the top part of Fig.2 shows the cam lift in relation to the crankshaft angle and the reference pulses BM, in the case of a six cylinder, four stroke engine. The TDC of a given engine cylinder is 20° crankshaft angle after a corresponding reference mark BM. The engine is fitted with the usual provision for injection advance, i.e. adjustment of the instant of actual commencement of injection at the injection valves in relation to TDC of the respective cylinders. However, Fig.3 shows the crankshaft angle to which the signal FB is related. Upon starting of the engine, the injection advance is zero (20° after BM) as shown by the chain dotted line 24, but injection is advanced to lO 1 ' before TDC (10° after BM) at idling speed, as shown by the full line 26, and is advanced further as speed increases, as shown by the dotted line 28. When a reference mark BM is produced 20° in advance of TDC of the associated engine cylinder, the counter 12 starts counting the engine speed-dependent pulses n. As soon as the transducer 11 associated with the cam 18, and thereby with the associated engine cylinder, detects that the respective injection pump piston has commenced its lifting stroke, the counter 12 stops counting. During normal engine starting the count of. stored in the counter 12 can correspond to no more than 20°, as shown at the left-hand side of Fig.3. However, should the engine crankshaft start to turn in the wrong direction, ' the count ol in the counter 12 reaches a value corresponding to not less than 40° as can be seen from the right-hand side of Fig.3. A reference angle o r between 20° and 40° is applied by the store 16 to the reference input of the comparator 14 to set a threshold for response of the comparator. Upon rotation of the crankshaft in the wrong direction, therefore, the comparator 14 responds to deliver an engine stop signal which can, for example, set the injection pump to zero fuel delivery. A holding circuit (not shown) is provided to prevent re-commencement of fuel injection until after the engine has come completely to rest. Fig.4 is similar to Fig.3, except that it relates to an eight cylinder, four stroke diesel engine. Again the maximum possible value for c-t is 20° during starting in the correct direction and its minimum possible value is 40° should the crankshaft rotate in the wrong direction, whereby there is an ample distinction which is easy to detect as the value ofo r is not critical. Fig.5 shows a cam 22 in which the working range between FB and FB' is only 36°, corresponding to a crankshaft angle of about 72°. Fig.6 shows that the maximum value for o for rotation in the correct direction is no more than 20° and that the minimum value ofoCfor incorrect rotation is not less than 28° . There is thus only a narrow range of choice between 20° and 28° for^ r - To avoid having to work to such accuracy, the reference mark BM can be increased from 20° in advance of TDC to 40°, as shown in Fig.6a. The value of -~L can then be as little as 30° for speeds up to idling speed for rotation in the correct direction 20 or as much as 18° with incorrect rotation. The reference value ~_ τ thus becomes less critical but the counter 12 must be arranged to count down rather than count up and a controlled gate must be provided between the counter and the comparator to prevent the counter output from reaching the comparator until counting is stopped. Another possibility for widening the difference in oL between correct and incorrect direction of rotation in the case of an in-line injection pump is to modify the trailing flank of the cam. This is possible because the shape of the trailing flank does not affect the injection operation. The injection pump to which the device of the invention is fitted can be provided with injection timing which is servo-controlled by an injection angle governor whose feedback signal is derived from a separate sensor disposed adjacent an injection nozzle for sensing the actual commencement of injection (SB control), as described in DE-A-3202614. Since the method and device of the invention are not needed once the engine has started in the correct direction, provision can be made for the stop engine signal to be blocked when the starting process has been completed. This prevents the device from -7- interferring with the normal running in the event of a failure of the sensor 11 or with running under the control of a stand-by system in the event of failure of the SB or FB control of injection timing. The sensor 11 could also be used for FB control or, in the case of SP control, the sensor for sensing the actual commencement of injection could be used in the device and method of the invention.

Claims: CLAIMS 1. Method for sensing the direction of crankshaft rotation in a diesel engine in which the angular difference between a signal denoting or representing the commencement of injection and a reference mark associated with a specific angular position of the engine crankshaft is measured and is compared with a reference value, the direction of rotation being indicated by whether the actual value is greater or less than the reference value. 2. Device for sensing the direction of crankshaft rotation in a diesel engine, comprising a pulse generator (10) for producing reference marks (BM) in timed relation to rotation of the engine crankshaft, a sensor (11) for producing a signal (FB, FBA or SB) representing or denoting commencement of fuel injection, an element (12) for producing a signal (*-O representing the angular difference between the reference mark and the commencement of injection signal, and a comparator (14) for producing an output signal when the difference signal (^) is greater or less than a reference signal (_ ~ κ τ ) . 3. Device according to claim 2, in which the element (12) for producing the difference signal (< . ) is a counter* (12) to which counting pulses (n) repres¬ entative of engine speed are fed. 4. Device according to claim 2 or 3, in which the sensor (11) is responsive to commencement (FB) of the pumping stroke of the associated injection pump piston, 5. Device according to any of claims 2 to 4, in which the trailing flank of a cam (18) of the injection pump is modified to increase the difference between the values of the signal ( ) for correct and incorrect rotation of the crankshaft. 6. Device according to any of claims 2 to 5, which is used for producing an engine stop signal in the event of starting of the engine in the wrong direction of rotation.

Inventors: SAUTTER WILFRIED, STUMPP GERHARD, SAUTTER, WILFRIED, STUMPP, GERHARD
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02D41
IPC codes: F02B3, F02D41, F02D45