Abstract:
The invention provides a cranking inhibition control system for an electric starter to an internal combustion engine. Engine rotational speed is developed from the signal produced by a cam shaft position sensor, which drives the logic of the system. Responsive to changes in engine rotation speed which result in engine speed falling below idle speed, the control logic generates a temporary cranking inhibit signal. Once engine speed falls low enough to clearly indicate cranking has ceased, a timer is triggered which resets the inhibit signal to permit cranking after a suitable delay.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to internal combustion engine control systems and in particular starting systems for diesel engines. 
     2. Background to the Invention 
     An internal combustion engine is routinely cranked for starting. Cranking of the engine continues until the cylinders of the engine begin firing and the engine begins generating sufficient power fully to compress the fuel/air mixture being injected into the cylinders for ignition. In the case of diesel engines, a starter system includes an electric motor of sufficient output to turn an engine crankshaft and to force pistons far enough into cylinders to compress the air/fuel mixture and thereby raise the mixture to its ignition temperature. The electric starter motor typically draws power from a vehicle battery, although other sources may be used. The electrical starter motor drives a pinion gear, which in turn engages a fly wheel ring gear coupled to the engine&#39;s crankshaft to crank a motor. A solenoid controls engagement of the pinion with the ring gear by moving the pinion into and out of contact with the ring gear. To prevent damage to the starter motor, excessive wear on the pinion and an unneeded load on the engine during normal operation, the solenoid operates to control positioning of the pinion relative to the ring gear. 
     Diesel engines rely on compression of the fuel/air mixture to raise the air/fuel mixture temperature to its flash point and can be difficult to start. Due to this factor, among other causes, truck drivers often make several attempts to start a diesel engine. An attempt to start an engine may end with a piston fully or partially inserted into a cylinder and a compressed air/fuel mixture in the cylinder which acts a spring forcing the piston out of the cylinder. In this situation the piston can turn the engine crankshaft in a direction counter to the cranking direction, a phenomena called rock back. If an attempt is made to reengage the pinion with the ring gear, a substantial possibility exists that the pinion will be damaged or stripped. 
     Accordingly it is preferable that rotation of an engine completely stop before a follow-up attempt to start the engine is made. One technique to achieve this, known to the art, is to force a vehicle operator to fully reset the ignition key to the off position between start attempts. The time taken to do this act is usually sufficient to allow the engine to complete any rock back. Many trucks however have a starter button, rather than, or in addition to, a start position for the ignition key. Such buttons, or ignition keys could be monitored by addition of a monitoring switch which would have to be reset. All such systems involve the additional expense of buying and incorporating such a switch into an engine starting system. 
     Engine crank inhibit circuitry has been used with trucks built by the Assignee of this Patent to block attempts to crank an engine which is already running. An electronic engine control module (EECM) provides an inhibit signal which prevents cranking by deenergizing a start relay. The EECM has no hardwire connection to either the ignition switch or to a start button and develops the inhibit signal without reference to the position of the ignition switch. 
     U.S. Pat. No. 4,916,327 to Cummins proposes a pinion block and rock-back protection circuit. Briefly, the &#39;327 circuit provides a capacitive discharge circuit, described from column 18, line 66 to column 19, line 35, which prevents reengaging the starter motor before its complete discharge. This prevents the ignition switch from engaging the starter motor after an excessively quick cycle, which is typically set at 2 seconds, but which can be adjusted. Dedicated circuit elements are used to implement this system. 
     SUMMARY OF THE INVENTION 
     The invention provides a control system for an electric starter to an internal combustion engine. Typically, the engine is mounted on a vehicle and is connected by a transmission to a drive shaft. The control system includes a starter switch which electrically connects a cranking motor to a source of electrical power. The engine has a crank shaft ring gear which is open to be engaged. A pinion rotationally driven by the cranking motor is pushed into engagement with the crank shaft ring gear while the cranking motor is turning. An indication of engine rotational speed is developed from the signal produced by a cam shaft position sensor, which functions as a tachometer. Control logic is provided which is responsive the engine rotational speed signal for developing indications of engine deceleration indicative of cessation of cranking and for generating an engine crank inhibit signal having a state reflecting cessation of cranking. 
     The control logic further comprises a delay line connected to the cam position sensor to receive the engine rotational speed signal and responsive thereto for producing a delayed engine rotational signal. A summing element connected to receive the engine rotational speed signal and the delayed engine rotational speed signal produces a difference signal corresponding to engine acceleration or deceleration. A comparator takes the difference signal and the difference threshold reference signal as inputs and responsive thereto generates a minimum speed change indication signal of one of two states, where a first state indicates a change in engine rotational velocity consistent with cessation of engine cranking and the second state indicating otherwise. 
     The control logic still further includes a source of an engine speed reference signal, a comparator taking the engine speed reference signal and the engine speed signal as inputs to produce a minimum engine speed signal of one of two states, where a first state indicates that engine speed falls below a minimum threshold and a second state which indicates that engine speed exceeds a minimum threshold. A logical AND gate taking the minimum speed signal and the minimum speed change indication signal as inputs to provide an cranking inhibit set signal when both inputs go high. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a block diagram of a starting system for an internal combustion engine. 
     FIG. 2 is a logic diagram for an engine control module used to implement the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures and in particular to FIG. 1, an engine cranking system  10  is generally depicted. Engine cranking system  10  provides for turning the crankshaft (not shown) an internal combustion engine  12  as part of starting the engine. The major features of engine cranking system  10  are well known in the art and include an engine ring gear  14  external to engine  12  which is mounted on an engine crank shaft, which, in an engine of conventional design, is connected to each of a plurality of pistons which reciprocate in cylinders. A pinion  16 , which extends on the armature shaft  20  of cranking motor  18  turns the ring gear  14  when engaged with the ring gear. 
     Pinion  16  is intended to engage ring gear  14  only when cranking of engine  12  is required for starting the engine. When the engine  12  is running, that is compression of air and fuel for ignition is sustainable by power being generated by igniting fuel, pinion  16  is withdrawn from engagement with ring gear  14 . Any number of mechanisms may be employed to controlling the positioning of pinion  16  and the illustrated system is to be taken as a general representation. A common feature to most such control systems is a solenoid. Pinion  16  is mounted on an armature shaft  20  which includes an overrunning clutch  26  and a shift collar  22 . A shift lever  24 , mounted on a pivot  28 , is connected to the shift collar to move the armature shaft back and forth to bring the pinion  16  into and out of engagement with ring gear  14 . A spring  30  is connected to shift lever  24  in a way to bias the lever to bring pinion  16  out of engagement with ring gear  14 . Extending from solenoid  38  is a solenoid link  40  which is connected to shift lever  24  at the opposite end of the lever from shaft collar  22 . Solenoid link  40  moves with solenoid plunger  42  to move shift lever  24  in response to energization of solenoid  38  from a battery  46  through a start relay  48 . 
     The solenoid  38  and cranking motor  18  energization circuitry is also conventional. Solenoid  38  has an energization coil  44  which is connectable to a battery power source  46  through a start relay  48 . Battery  46  is connected by its positive terminal to the start relay  48  by a power bus  50  and at its negative terminal to chassis ground  52 . Battery  46  also energizes cranking motor  18  in response to solenoid  38  operating to close a switch contact  36  between two terminals  32  and  34 . 
     Electronic control of start relay  48  is based in an electronic engine control module (EECM)  54 . EECM  54  has a number of functions, however, only those of interest to the implementation of the present invention are described here. EECM  54  is connected to various engine  12  monitoring systems, including an engine sensor package  58  which monitors, among other items, engine oil temperature. EECM  54  is also connected to a drive line engagement sensor  60  which generates a signal indicating whether the vehicle is in gear and to a cam position sensor  64  which tracks the angular position of the engine cam shaft (not shown). The derivative against time of the cam position signal from cam position sensor  64  indicates engine rotational speed and accordingly, the cam position sensor  64  can be used as an engine tachometer. EECM  54  is a programmable microcomputer and can be reprogrammed as indicated by a programming interface (Program. I/O)  62 . 
     Normally, the engine is started by depressing a start switch  68  which closes the start relay  48  to energize both cranking motor  18  and solenoid  38 . Both start switch  68  and EECM  54  are connected to a crank inhibit relay  66  which controls activation of the start relay  48 . On vehicles with manual transmission, a clutch switch  70  is also connected to the crank inhibit relay  66 . Before cranking is allowed all three signal sources must assume the proper state. Essentially, the clutch pedal and start button must be depressed and the EECM  54  must signal that engine conditions permit cranking. 
     FIG. 2 illustrates a logical implementation of a cranking inhibit control system  74 . Cranking inhibit control system  74  is preferably implemented in software executed in EECM  54 . Where implemented in logic, cranking inhibit control system  74  may be readily activated or deactivated as a vehicle option by option trigger module  76 . Option trigger module provides that the cranking inhibit control system  74  is always activated if the vehicle on which the system is installed is equipped with an automatic transmission. On vehicles with standard transmissions, activation of the control system is optional. Option trigger module  76  includes a programmable mode comparator  78  to implement the option selection feature. If a programmable parameter “ECI_MODE” is set a logical  1 , it signifies that the cranking inhibit logic control system  74  is to be activated regardless of the transmission type installed on the vehicle. Programmable mode comparator will pass a logical  1  to OR gate  82  which in turn passes a logical high signal to the trigger input of a triggered comparator  84  activating the device. 
     For certain transmission types, including automatic transmissions, the crank inhibit control system  74  is always active. A transmission mode (TRNS_MODE) switch set  80  is set to  1  for automatic transmissions and to 0 for standard transmission vehicles. Thus the output of OR gate  82  is high if either (or both) comparator  78  or switch set  80  provides a high logical output (ECI_MODE=1). Where the output of OR gate  82  is low then ECI_MODE=0. ECI_MODE=0 locks the output (ECI) of the bistable state circuit  84  low, while ECI_MODE=1 allows the triggered comparator  84  to assume either a high or low output state. 
     It is desirable to inhibit cranking of an engine when any of several circumstances arise. Accordingly, cranking inhibit control system  74  provides logic or inputs for the detection and evaluation of these circumstances. The logic or inputs include a run latch flag (RUN_LTCH_FLG)  86  input, disengaged driveline status (DDS_STS)  92  input, a programmable run mode timer  94  and the rock back cranking prevention logic  108  of the present invention. The outputs from each of these elements provides the input to a NAND logic array  89  comprising AND gate  90  and NOT gate  140 , which in turn generates an engine crank inhibit status flag (ECI_STS). ECI_STS must equal 0 before cranking is permitted. The occurrence of any one of the cranking inhibit conditions will prevent engine cranking since all of the inputs to NAND array  89  must be high before ECI_STS=0. ECI_STS and the output of register  142  provide the inputs to triggered comparator  84 , which generates a high engine crank inhibit signal when the input signals all match. Since the output of register  142  is locked at 0, this requires ECI_STS=0. ECI is amplified by application to an engine cranking inhibit output driver  144  which provides an engine cranking inhibit signal (ECI_SIGNAL) to the crank inhibit relay  66 . 
     The specific logical inputs relating to engine conditions which prevent engine cranking are now considered. The first three elements discussed, the run latch flag  86 , the disengaged driveline signal status  92  and the programmable run mode timer  94  are known from the prior art and are not discussed at length. The run latch flag (RUN_LTCH_FLG)  86  goes high whenever the engine has been running above a minimum threshold speed for greater than some fixed time period, e.g. 5 seconds. The run latch flag  86  is inverted by a NOT gate  88  before application to an input to NAND array  89 . Thus the input to the NAND array  89  is high only if the engine has not been running above the threshold speed, or has been running above the threshold for fewer than 5 seconds. 
     The driveline must be disengaged to prevent cranking, which is reflected by a disengaged driveline signal status (DDS_STS)  92  of 1. When the driveline is engaged DDS_STS=0. 
     The programmable run mode timer  94  applies a high input to NAND array  89  when the engine has been running (i.e. rotating at a speed exceeding a minimum threshold rotational velocity) for a period exceeding a minimum, programmable time threshold (supplied from ECI_RUN_TM register  104 ). Programmable run mode timer  94  receives an engine mode input  96  on an equality comparator gate  100 . The value of mode input  96  equals 2 if the engine is in run mode. Comparator  100  receives a static RUN value of 2 on its second input, and produces a logical high output if and only if the values for MODE and RUN are equal. 
     The output of comparator  100  is applied to a reset/run clock  102  which is set to 0 and starts running when the output of comparator  100  undergoes a low to high transition. The clock signal from clock  102  is applied to inequality comparator  106  for comparison with a static, but programmable value supplied from ECI_RUN_TM register  104 . When the clock is less than the programmable value the output from the comparator is high. Thus for cranking to be allowed after engine start the engine must be in run mode and have been in run mode for less that the programmable time limit. Where an engine is not in run mode the output of comparator  100  is zero and the clock  102  output is zero, allowing engine cranking. 
     Rock back cranking prevention logic  108  constitutes a preferred embodiment of the invention, incorporated as extended logic to cranking inhibit control system  74 . Rock back prevention logic  108  monitors engine rotational speed (N)  110  derived from cam position sensor  64  or another class of engine tachometer. Essentially, prevention logic  108  generates a delay period subsequent to the cessation of cranking following a failure to start engine  12  during which a resumption of cranking is inhibited. When realized in software, prevention logic  108  achieves this objective without the addition of physical components such as reset switches attached to the start button  68  and requires only monitoring of an existing engine tachometer signal. 
     Engine speed signal  110  is routed to each of three analytical elements, a first which derives changes in engine rotational speed, a second which compares engine speed to a minimum threshold and a third which provides for reset of the prevention logic  108 . Changes in engine speed (NDELTA) is produced by applying the engine speed signal N  110  to a delay element  112 . The delayed signal is then applied to one input of a difference summer  114 . The current engine speed signal N is applied to the remaining terminal of difference summer  114  and subtracted from delayed signal. The absolute value of this difference signal NDELTA is then applied to engine speed change comparator  118  for comparison to a threshold level NDELTA_THLD  116 . Should NDELTA equal or exceed NDELTA_THLD, a high logic level signal is provided as an input to AND gate  124 . 
     It is undesirable that AND gate  124  should pass a set signal to logical flip flop  136  prematurely, i.e. while engine speed is high. That situation is handled by the RUN_LTCH_FLG and run mode timer  94  logic. Changes in engine speed signals, NDELTA, meeting the threshold NDELTA_THLD are allowed to trigger a cranking inhibit signal only if absolute engine speed N has fallen below (or equal to) a minimum threshold NCRANK_THLD  120 . A comparator  122 , taking N  110  and NCRANK_THLD  120  is provided to determine the occurrence of this event and applies a high logic level signal to a second, and only remaining, input of AND gate  124 . When the outputs of both comparator  118  and  122  have simultaneously gone high a set signal is generated and applied to the S input of logical flip flop  136  and the Q output (NDELTA_CRNK_INHIB) goes high. This signal is inverted, i.e., set to logical 0, at NOT gate  138  to provide a low input to NAND array  89 , thereby inhibiting engine cranking. The value for NCRANK_THLD  120  may be made dynamic to reflect changing engine starting dynamics which occur at different engine temperatures. In this case NCRANK_THLD  120  may be set as a function of engine oil temperature which is obtained from the engine sensor package  58 . 
     The time delay aspect of the rock back cranking prevention logic  108  is handled by reset logic  125  for the logical flip flop  136 . Again engine speed N provides the prime input to a comparator  128 . Here engine speed N is compared to a minimum rotational speed 30 of RPM provided from register  126  to determine if the engine has substantially stopped, which is indicated by N falling to or below the reference level supplied by register  126 . Occurrence of this event results in a reset/run signal being applied to reset/run clock  130 . Once the time elapsed as tracked by clock  130  equals or exceeds a minimum threshold time delay ECI_DLY_TM  132  as determined by comparator  134 . Comparator  134  applies a reset signal in response to the clock  130  output passing ECI_DLY_TM to the reset input of flip flop  136 . The Q output NDELTA_CRNK_INHIB goes high, which in turn pulls the output of NOT gate  138  low, with the result that rock back cranking prevention logic  108  no longer inhibits cranking. 
     The invention of the present invention utilizes engine crank inhibit circuitry currently in common use on vehicles. Software modifications of an electronic engine control system are sufficient to implement the control regimen, although the system may be implemented in hardwire circuitry. Because the EECM has no hardwire connection to either the ignition switch or to a start button and develops the inhibit signal without reference to the position of the ignition switch, saving expense over prior art systems. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.