US 3783301 A
The risk of damage to starter mechanism for cranking an engine is reduced by a simple and reliable lockout circuit which prevents re-energization of the starter system from inadvertent closing of the starter switch after the engine is running. The lockout circuit detects when the engine has started by sensing engine oil pressure but does not deactivate the starter system until such time as the operator releases the starter switch. Thereafter the starter system cannot be re-energized until after the engine has been shutdown. All electrical elements of the lockout circuit are de-energized during running of the engine after the starter switch is released.
Description (OCR text may contain errors)
United States Patent [191 Nieukirk [451 Jan. 1, 1974 LOCKOUT CIRCUIT FOR ENGINE STARTER SYSTEM  Inventor: Robert L. Nieukirk, Washington, 111.
 Assignee: Caterpillar Tractor Co., Peoria, ll]. 22 Filed: June 8, 1972  Appl. No.: 261,080
3,154,689 10/1964 Bubbenmoyer ..290/38 Primary ExaminerG. R. Simmons At!0rneyDonald J. McRae  ABSTRACT The risk of damage to starter mechanism for cranking an engine is reduced by a simple and reliable lockout circuit which prevents re-energization of the starter system from inadvertent closing of the starter switch after the engine is running. The lockout circuit detects when the engine has started by sensing engine oil pressure but does not deactivate the starter system until such time as the operator releases the starter switch. Thereafter the starter system cannot be re-energized until after the engine has been shutdown. All electrical elements of the lockout circuit are de-energized during running of the engine after the starter switch is released.
3 Claims, 1 Drawing Figure LOCKOUT CIRCUIT FOR ENGINE STARTER SYSTEM BACKGROUND OF THE INVENTION Starter systems for cranking an internal combustion engine or the like customarily have a pinion gear which may be shifted into engagement with a ring gear of the engine and rotated by energization of an electrical starter motor in response to actuation of a starter switch by the operator. To avoid excess wear means are provided for retracting the pinion gear out of engagement with the ring gear after start-up. Oncethe engine is running, excess wear or serious damage can occur to the ring gear, the pinion gear or other elements of the mechanism if the starter switch is inadvertently reactuated at that time.
To forestall these adverse effects, some-prior starter systems have been provided with a lookout circuit which functions to prevent reactivation of the starter system while the engine remains running. Lockout circuits of this kind have means for detecting when the engine is running and switch means for preventing operation of the starter under this condition.
In general, prior lockout circuits have been unnecessarily complex. Such circuits typically require an electrical signal, derived from the engine generator or other electromechanical transducer, to detect when the engine is running. Automatic means are provided for immediately deactivating the starter, independently of the operators actions, in response to such signal and for preventing reactivation as long as the signal remains present. in addition to circuit complexity this requires that some portion of the lockout circuit remains electrically energized throughout the period when the engine is running and the automatic action deprives the operator of the ability to control the duration of the initial starter operation.
SUMMARY OF THE INVENTION The present invention provides an extremely simple, reliable and economical lockout circuit for preventing actuation of an engine starter system while the engine is running.
In a preferred form the circuit detects the running condition of the engine by sensing a fluid pressure such as engine oil pressure rather than by requiring a continuous electrical signal input for this purpose. The lockout circuit is connected between the starter mechanism and the power source therefor through the operators starter switch and includes a switching device of the type which conducts following receipt of a gate signal and which remains conductive until current flow is stopped. Closing of the operators starter switch provides the gating signal through a normally closed fluid pressure controlled switch which is opened by engine oil pressure or the like once the engine has started. Opening of the fluid pressure controlled switch does not in itself de-energize the starting system since the switching device continues to conduct until the operator releases the starter switch. Thereafter the switching device cannot be again gated on as the gating signal path is blocked at the fluid pressure controlled switch as long as the engine continues to run.
Accordingly it is an object of this invention to provide a simplified, highly reliable and economical lockout circuit for preventing re-energization of the starter BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing diagrammatically shows an engine and electrical starting system therefor together with electrical and hydraulic circuit elements for providing a lockout function in accordance with the present invention.
DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing, an engine 1 1 to which the invention is applicable typically has a ring gear 12 coupled to a crank shaft 13 which must be turned to initiate starting of the engine. In order to crank the engine 11, a starting system 14 typically has a pinion gear 16 which is normally out of engagement with ring gear 12 but which is shifted axially into engagement therewith, as indicated by arrow 17, upon electrical energization of a pinion solenoid 18 having a movable armature 19. Solenoid 18 may be energized by manual closing of a normally open operators starter switch 21. Closing of starter switch 21 connects one side of a battery 22 to one end of the solenoid through a lockout circuit 23 which will hereinafter be described in more detail, the other end of the solenoid being coupled to the other side of the battery and being grounded to engine l l in this particular example. A protective fuse 24 and a current indicating ammeter 26 are connected in series between battery 22 and starter switch 21 and the generator 27 of engine 11 may be connected between ground and the junction between ammeter 26 and starter switch 21 to recharge the battery while the engine is in operation.
Energization of the pinion solenoid 18 to shift pinion gear 16 into engagement with ring gear 12 also closes a set of normally open switch contacts 28 which are connected across battery 22 in series with a starter motor 29 thereby causing the motor to be actuated following closing of the operators starter switch 21. Motor 29 is coupled to the pinion gear 16 through an overrunning clutch 31.
Thus closing of the starter switch 21 engages the pinion gear with ring gear 12 and rotates the pinion gear to crank the engine 11. Suitable constructional details of a starter system 14 as described to this point, with the exception of lockout circuit 23, are well known to the art and accordingly are not shown in the drawing. For example, one typical mechanical assembly for a starter motor 29, pinion solenoid and contact assembly 32, pinion gear 16 and overrunning clutch 31 is disclosed in U.S. Pat. No. 3,433,968.
Considering now the lockout circuit 23, current is transmitted between starter switch 21 and pinion solenoid 18 through a preferably solid state switching means 33 of the form which is normally nonconductive and which may be gated into conduction by a gating signal and which thereafter remains conductive, even after termination of the gating signal, until current flow therethrough is stopped, such switching means 33 being an SCR (silicon controlled rectifier) in this embodiment. To provide a gating signal to SCR 33 under conditions to be described, a normally closed fluid pressure operated switch 34 is connected between starter switch 21 and the gate terminal 36 of SCR 33 in series with a current limiting resistor 37 and a diode 38 which protects the SCR from negative voltages such as might be present if the battery 22 was inadvertently reversed. Fluid pressure operated switches 34 are known devices, apart from the context of the present invention, and may typically have contacts 39 which are normally held closed by a spring 41 acting against a piston 42 within a cylinder 43, the piston being coupled to the contacts. introduction of fluid pressure into cylinder 43 moves the piston 42 against the force of spring 41 and thereby opens the contacts 39. Engines 11 of the form to which the invention is applied typically have an oil pump 44 or other means which generates a fluid pressure when the engine is running. A conduit 46 connects the output of oil pump 44 to cylinder 43 of pressure switch 34 whereby contacts 39 are opened when the engine is running.
In operation, the operator initiates starting of engine 11 by closing starter switch 21. SCR 33 becomes conductive at this point, to energize the pinion solenoid 18, since closing of the starter switch 21 also applies a gating signal to the SCR through pressure switch 34, resistor 37 and diode 38. As previously described, energization of pinion solenoid 18 shifts pinion gear 16 into engagement with engine ring gear 12 while closing contacts 28 to energize the starter motor 29 and thereby initiates cranking of engine 11.
When engine 11 has started and is in operation, fluid pressure from oil pump 44 opens contacts 39 of pressure switch 34 removing the gating signal from SCR 33. This does not in itself stop energization of the starting system 14 since an SCR 33 remains conductive once it is gated on until current flow through the anodecathode circuit is stopped. This occurs in the present instance, when the operator releases starter switch 21. Such opening of switch 21 stops conduction through SCR 33 and de-energizes pinion solenoid 18 which then restores and shifts pinion gear 16 out of engagement with ring gear 12 while opening contacts 28 to deenergize starter motor 29. Thereafter, the pinion solenoid 18 and starter motor 29 cannot be re-energized by closing of starter switch 21 as long as engine 11 remains running. Under this condition, fluid pressure switch 34 is held open by the output of oil pump 44 thereby blocking transmission of the necessary gating signal 'to SCR 33. SCR 33 can again be gated into conduction by closing of the starter switch 21 only after engine 11 has stopped and fluid pressure is absent from pressure switch 34.
While the invention has been described with respect to a preferred embodiment it will be apparent that modifications are possible and thus it is not intended to limit the invention except as defined in the following claims.
1. In a starter system for an engine having electrically operated engine cranking means and a source of electrical power therefor and having a normally open starter switch connected between said power source and said cranking means for selectively energizing said cranking means to start said engine, a lockout circuit comprising:
a switching device connected between said power source and said engine cranking means in series relationship with said starter switch to form part of the power path through which electrical energization is supplied to said cranking means from said power source, said switching device being of the form which is normally non-conductive and which is triggered into conduction by application of an electrical gating signal to a gate terminal thereof and which then remains conductive until current flow through said switching device is interrupted, and
a gating signal switch having normally closed contacts connected between said gating terminal and said power source through said starter switch, said gating signal switch having means for opening said contacts when said enging is running.
2. The combination defined in claim 1 wherein said switching device is a silicon controlled rectifier and wherein said gating signal switch is a fluid pressure operated switch responsive to oil pressure from said engine.
3. A starter system for an engine having a ring gear which is turned to start said engine and having an oil pump, comprising,
an electrical starter motor,
a set of normally open electrical contacts connected across said battery means in series with said starter motor,
a pinion gear coupled to said motor for rotation thereby and being movable into engagement with said ring gear of said engine,
solenoid means which may be electrically energized and having means for shifting said pinion gear into engagement with said ring gear and for closing said normally open contacts to energize said motor in response to said energization,
a normally open manually operable starter switch,
a solid-state switching means connected to said battery means in series relationship with said starter switch and said solenoid means and having a gate terminal for receiving an electrical signal which initiates conduction through said switching means to provide current therethrough for energizing said solenoid means, said switching means being of the form which remains conductive until current flow therethrough is stopped, and
a normally closed fluid pressure actuated switch connected between said battery means and said gate terminal of said switching means through said starter switch and having a fluid pressure input coupled to said oil pump of said engine to be opened by fluid pressure from said oil pump.