Air Starter

Abstract

A pneumatically operated starter having a combination piston-valve, located in a first chamber downstream of the usual on-off valve, that throttles the starter to a low speed initially in its closed position and as air is supplied opens in response to the air pressure and simultaneously engages the starter pinion with the engine ring gear and upon further engagement of the starter pinion allows air to freely pass and accelerate the starter. Upon the starting of the engine, the piston-valve is automatically returned to its initial position by a combination of mechanical helical pinion throwout, spring return and latching pressurization of a second chamber behind the piston-valve. Latching pressurization is accomplished by a second valve admitting air pressure behind the piston-valve in response to a pressure signal developed in the starting cycle. The air supply may then be shut off manually to stop the throttled rotation of the starter and to reset the second valve controlling the latching pressurization of the chamber behind the piston-valve to ready the starter for the next starting cycle.

Description

BACKGROUND OF THE INVENTION

This invention relates to a pneumatically operated "air" starter for driving internal combustion engines to start them and more particularly to a new type of starter that combines the best features of both of the two general classes of starters known as the "pre-engaged" starter and the "inertial- engaged" starter.

The pre-engaged starter has a mechanism for moving the pinion into engagement with an engine ring gear prior to the rotation of the starter motor while the inertial-engaged starter screws its pinion axially into engagement with the engine ring gear as the starter motor rotates. Pre-engaged starters were developed because of the high shock loads created by the inertial-engaged starters. These high shock loads tend to excessively wear the teeth on the pinion and ring gear and can cause breakage of parts of the starter and engine.

On the other hand, pre-engaged starters are more complicated and expensive than inertial-engaged starters. Pre-engaged starters need a separate mechanism for moving the pinion axially, usually a piston in an air starter, and an overrunning clutch to protect the starter motor against being driven by the engine after the engine is started. Pre-engaged air starters also need additional air circuits for acting on the pinion engaging piston prior to opening the main air supply valve of the starter.

SUMMARY OF INVENTION

The principal object of this invention is to provide an air starter that combines the good features of both the pre-engaged and inertial-engaged starters while minimizing or overcoming the undesirable characteristics of both types of starters.

Other important objects of this invention are: to provide a pre-engaged starter that eliminates the use of an overrunning clutch in this type of starter; to provide a pre-engaged starter that automatically disengages and reduces its air supply with the starting of the engine, to provide a pre-engaged starter having internal piping and a motor throttling valve mechanically connected to the pinion engagement mechanism, and to provide an air starter that automatically opens the throttling valve to accelerate the starter motor with the engagement of the pinion or starter clutch member and automatically disengages its pinion or clutch member and slows the starter motor to a safe rotation speed with the starting of the engine .

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in connection with the accompanying drawings wherein:

FIG. 1 is an axial section of a starter embodying the invention;

FIGS. 2 and 3 are sections taken respectively on lines 2--2 and 3--3 in FIG. 1; and

FIGS. 4 to 6 are enlarged fragmentary sections of the rear end of FIG. 1 showing the starter piston-valve and associated elements in different positions during an operation cycle of the starter.

FIGS. 7 to 10 are fragmentary sections similar to FIGS. 4 to 6 of a second embodiment, showing the combination piston-valve in various positions sequentially during an operating cycle.

DESCRIPTION OF PREFERRED EMBODIMENTS

The air-operated starter 1 shown in FIG. 1 includes a casing 2 comprising a cylinder 3 with a backhead 4 and nose 5 attached at its opposite ends. The cylinder 3 forms part of an air motor that includes a rotor 6 fixed to a drive shaft 7 and a pair of end plates 8 and 9 located at the ends of the cylinder 3. The rotor 6 carries several sliding vanes 10 spaced around its periphery. The drive shaft 7 includes a rear portion 11 extending into the backhead 4 and rotating in a roller bearing 12. A forward portion 14 of the drive shaft 7 extends into the nose 5 and carries a helical spline 15 on its periphery.

A pinion 18 having a rearwardly opening socket 19 fits over the forward portion 14 of the drive shaft 7 and carries internal splines cooperating with the helical splines 15 to form a screw joint therebetween. In a typical starter, the splines 15 are arranged to screw the pinion 18 to the right as shown in FIG. 1 when the motor turns in a counter-clockwise direction looking at the starter from the left as shown in FIG. 1. The pinion 18 supports the forward portion 14 of the drive shaft 7 and is in turn supported in a pair of roller bearings 20 mounted in the nose 5. The bearings 20 allow the pinion 18 to slide axially without interference from such bearings. The end of the socket 19 in the pinion 18 carries a hollow nut 21 that encircles and slides axially on an annular portion of the drive shaft 7 to limit the distance that the pinion 18 can be extended from and retracted into the nose 5.

The nose 5 also serves as a means for muffling the exhaust from the air motor. The front end plate 9 cooperates with the rear end of the nose 5 to form a first chamber 23 receiving exhaust from the motor through several ports 24. The first chamber communicates through several ports 26 to a second chamber 27 formed by a perforated sleeve 28 surrounding the nose 5. Exhaust in the second chamber 27 is exhausted to atmosphere through the perforations in the sleeve 28 which are sized and located to provide the best muffling characteristics. The nose 5 also includes a flange 30 for mounting the starter 1 on a flywheel housing of an engine in a conventional manner.

The backhead 4 contains an air supply port 32 and a plenum chamber 33 separated by a sliding piston-valve 34. The plenum chamber 33 supplies air to the motor through ports (16) provided in the rear end plate 8 (see FIG. 7 for approximate location).

The piston-valve 34 is threaded to a rod 35 extending through the hollow drive shaft 7 and attached to the pinion 18. The piston-valve 34 slides in an arcuate valve seat 38 to serve as a valve between the supply port 32 and the mouth 39 of the plenum chamber 33, as shown in FIG. 2. As the piston-valve 34 moves axially forward, it uncovers the mouth 39 of the plenum chamber 33, as can be seen in FIG. 4. FIG. 3 shows the chamber 33 as a substantially annular space separated at the top by a top radial web 36.

The arcuate valve seat 38 contains a groove 31 that allows a controlled leakage of the air from the supply port 32 to the plenum chamber 33 while the piston-valve 34 is in its fully closed position, as shown in FIG. 1. This allows the starter motor to begin turning slowly as soon as air pressure is admitted to the supply port 32.

The hollow drive shaft 7 contains a spring 40 engaged between the end of the piston-valve 34 and a shoulder 41 formed in the drive shaft 7 urging the piston-valve 34 and rod 35 rearwardly. The annular space in the drive shaft 7 containing the spring 40 is designated spring chamber 43.

When air pressure is supplied to the inlet port 32, it acts on the exposed ends of the piston-valve 34 and rod 35 to begin moving the rod 35 and pinion 18 to the right as shown in FIG. 1. This is normally accomplished by means of the operator opening a conventional valve (not shown) to supply air pressure to the port 32. Simultaneously, the controlled leakage of the air by the piston-valve 34 via the grooves 31 will start the motor to rotating slowly. The motor has the ability to be driven at slow speeds by small amounts of air. As the motor rotates and the pinion 18 moves axially, the pinion 18 will engage the ring gear (not shown) of the engine. As soon as the teeth of the pinion 18 mesh with the ring gear, the driving torque of the motor will cause the helical splines 15 to force the pinion 18 into full mesh with the ring gear. In case the teeth of the pinion and ring gear abut end to end, the slow rotation of the motor will continue to rotate the pinion 18 until it meshes with the ring gear. As the splines 15 force the pinion 18 into fully meshed engagement with the ring gear, the piston rod 35 opens the piston-valve 34 to full open position, shown in FIG. 5, wherein the starter motor is supplied with full air pressure and it drives the pinion with full power.

Means is provided to reduce the thrust force on the pinion 18 after the starter motor pinion 18 is engaged with the engine ring gear. Such means allow air pressure to enter the spring chamber 43 to balance the air pressure on the rear end of the piston-valve 34, thereby reducing the effective area of the piston-valve 34 to the cross section of the rod 35. Reduction of the piston area to the rod cross section results in reducing the force on the piston-valve 34 caused by the air to a magnitude of less than the retracting force applied to the piston-valve 34 by the spring 40. However, the pinion 18 remains in meshed engagement with the ring gear as the result of the motor torque transmitted through the splines 15. The reduction or cancellation of the engaging force on the pinion 18 can be accomplished immediately after the pinion 18 engages the ring gear or can be delayed until the pinion 18 is fully meshed with the ring gear. We prefer to do it immediately after the pinion 18 begins to mesh with the ring gear and prior to being fully meshed with the ring gear.

As long as the starter motor is driving the engine, the camming force of the helical splines 15 on the pinion 18 will overcome the retracting force applied to the pinion 18 by the spring 40, resulting in the pinion remaining in its engaged position. When the engine starts, it will rapidly gain speed until the torque supplied by the starter motor through the splines 15 drops to a small enough value or magnitude for the spring 40 to retract the pinion 18. In case the pinion 18 is not retracted before the engine attempts to drive the starter, the driving of the starter will cause the splines 15 to automatically cam the pinion 18 to a disengaged position, thereby preventing the starter from being damaged by being driven by the engine.

The backhead 4 includes a lateral passage 45 communicating with the spring chamber 43 by an opening 46 provided in the drive shaft portion 11. The lateral passage 45 is connected to a longitudinal passage 47 extending to the air supply port 32 and normally closed by a sliding valve 48. The valve 48 slides in a bore 49 and is urged to the closing position of the passage 47 by a spring 50 located in the bore 49. A second passage 52 communicates between the plenum chamber 33 and the valve bore 49, and the valve 38 contains an internal conduit 53 extending between the passage 52 and the end face 54 of the valve 48. The end face 54 is located on the valve end remote from the spring 50 and is arranged whereby pressure applied to it will urge the valve 48 toward its open position.

Once the valve 48 opens, as shown in FIG. 5, the supply pressure in the passage 47 holds it open. The strength of the spring 50 is selected so that the valve 48 will remain closed, as shown in FIGS. 1 and 4, until the pressure in the plenum chamber rises to near the supply air pressure, and this will not occur until after the pinion 18 is meshed at least partly with the engine ring gear and the starter motor is operating under full power conditions.

The opening of the valve 48 admits the supply air pressure from the supply port 32 to the spring chamber 43 to balance the pressure on the rear end of the piston-valve 34, as previously explained.

As earlier explained, with the pressure on the piston-valve 34 being less than the retracting force of the spring 40, the pinion 18 will be retracted after the engine starts and gains sufficient speed for the force of the spring 40 to overcome the force of the helical splines 15 holding the pinion 18 engaged. With the retraction of the pinion, the piston-valve 34 is also retracted simultaneously to close the mouth 38 of the plenum chamber 33 and thereby throttle the air to the starter causing it to rotate slowly. The air supply may then be shut off normally by means of a conventional valve (not shown) to stop the slow throttled rotation of the starter and to reset sliding valve 48 for the next starting cycle. Sliding valve 48 acts as a latching valve preventing a reengagement of the starter until it is reset by shutting off the air pressure to the starter.

SECOND EMBODIMENT

A second starter embodiment 60 is shown in FIGS. 7 to 10, wherein parts or elements similar to the first embodiment are identified with the same reference numbers. The only change in this second embodiment 60 is in the mechanism for reducing or cancelling the effect of the air pressure on the combined piston-valve 34' after the pinion 18 begins to mesh with the engine spring gear. In this second embodiment, the longitudinal position of the piston-valve 34' in the valve seat 38 determines when the balancing air pressure is allowed to enter the spring chamber 43.

The piston-valve 34' contains an internal bore 61 containing a small spool valve 62 urged forwardly by a light spring 63. The rod 35' contains a central passage 65 extending from its rear end, wherein it opens into the bore 61, to a port 66 opening into the spring chamber 43. In the at-rest position of the starter shown in FIG. 7, the spool valve 62 is urged forwardly to close the central passage 65 and thereby prevent air pressure from entering the spring chamber 43.

As the piston-valve 34' moves forward to the position shown in FIG. 8, it contains a front port 68 that passes an opening 69 provided in the rear portion 11 of the drive shaft 7. The opening 69 communicates with a passage 70 that extends to the supply port 32. As the front port 68 crosses the opening 69, the air pressure from the supply port 32 enters the bore 61, acts on the shoulder 72 on the spool valve 62 moving that valve rearwardly to uncover the central passage 65 in the rod 35'. At this point the air pressure in the supply port 32 is free to flow into the valve chamber 43. As the spool valve 62 is moved rearwardly by the air pressure, it uncovers a rear port 74 provided in the piston-valve 34' that opens into a longitudinal groove 75 extending from the port 74 to the rear of the piston-valve 34', thereby allowing the air pressure from the supply port 32 to flow into the bore 61 to latch and hold the spool valve 62 in its open, rear position, as shown in FIGS. 9 and 10, throughout the remainder of the cycle of the starter, until the air pressure is removed from the supply port 32. As the air pressure is exhausted from the supply port 32 after the end of the starting cycle, the spool valve 62 returns to its beginning position shown in FIG. 1.

We have chosen to allow the piston-valve to throttle air to the starter motor in the preferred embodiments shown for reasons of manufacturing economy and because of the limited usefulness of a complete shut off valve in view of the upstream main shut off valve. However, if desired, it should be obvious to one skilled in the art that piston-valve 34 and mating surface 38 may be suitably machined and properly guided to effect positive shut off without effecting the operation described above.

Although we have described our invention in connection with a starter-engine clutch including a pinion and ring gear, it should be understood that our invention is not limited thereby and could be used with other types of axially engaging clutches such as a pair of axially engaging jaws or splines, these alternate clutches being commonly used on gas turbines wherein the axis of the starter clutch member is aligned with the turbine clutch member.

While several embodiments of the invention are shown and described in detail, this invention is not limited simply to the specifically described embodiments but contemplates other embodiments and variations utilizing the concepts and teachings of this invention.

Claims

We claim:

1. A fluid-operated starter comprising;

a casing containing a fluid-operated motor driving a shaft;

a starter clutch member slidable axially and rotatably mounted in said casing;

means interconnecting said starter clutch member and motor shaft for driving said starter clutch member and operative, in response to the driving rotation of said motor, to cause said clutch member to remain in engagement with an engine clutch member;

a piston located in a first fluid chamber in said casing and connected to said starter clutch member to move with it in engaging and disengaging directions;

means for applying a large fluid force to said piston to cause it to move said starter clutch member in an engaging direction; and

fluid-pressure counter-biasing means for automatically reducing the large fluid force applied to said piston to a smaller fluid force by reducing the fluid pressure differential across the piston immediately after the starter clutch member is engaged and prior to the starting of the engine whereby said starter clutch member can be disengaged by the engine driving the starter motor after the engine starts.

2. The starter of claim 1 wherein:

said starter clutch member is threadably engaged to said motor shaft whereby the driving of said starter clutch member by said motor urges the starter clutch memeber toward engagement with the engine clutch member and the driving of the starter clutch member by the engine urges the starter clutch member toward its disengaged position.

3. The starter of claim 2 wherein:

said piston is connected to a first valve that moves with the piston between closed and open positions supplying fluid to the starter motor and corresponds respectively to disengaged and engaged positions of said starter clutch member.

4. The starter of claim 1 including:

a spring urging said piston toward the disengaged position of said starter clutch member with a force that exceeds the force applied to said piston by said smaller fluid force and is less than the force applied to said piston by said large fluid force.

5. The starter of claim 4 including:

means for bypassing a small amount of pressure fluid around said first valve in its closed position to drive said starter motor slowly.

6. The starter of claim 5 wherein:

said means for reducing said large fluid force includes a second valve that opens to admit fluid pressure to a second chamber located on the opposite face of said piston from said first chamber.

7. The starter of claim 6 wherein:

said second valve opens to admit fluid to said second chamber while said starter clutch member is completing its engagement movement with the engine clutch member.

8. The starter of claim 7 wherein:

said second valve opens in response to the location of said piston in its movement in the starter clutch member engaging direction.

9. The starter of claim 7 wherein:

said second valve opens in response to the pressure of fluid supplied to said motor.

10. A fluid-operated starter comprising:

a casing containing a fluid-operated motor driving a shaft;

a starter clutch member slidable axially and rotatably mounted in said casing;

helical spline means interconnecting said starter clutch member and motor shaft for driving said starter clutch member and operative to cause said starter clutch member to be screwed into engagement with an engine clutch member by the driving rotation of said motor;

a piston located in a first fluid chamber in said casing and connected to said starter clutch member to move with it in engaging and disengaging directions; and

a means for admitting fluid pressure to said first chamber to apply a large fluid force to said piston to cause it to move said starter clutch member in an engaging direction; and

fluid-pressure counter-biasing means for automatically reducing the force applied to said piston by reducing the fluid pressure differential across the piston immediately after said starter clutch member is engaged with said engine clutch member and while the starter is driving the engine.

11. The starter of claim 10 wherein:

said means for reducing said force includes valve means for applying a second fluid force to said piston acting in said disengaging direction to at least partially counter-balance said large fluid force.

12. The starter of claim 11 including:

a spring urging said piston in the starter clutch member disengaging direction and being weaker than said large force but stronger than the effective fluid force on said piston after said large fluid force is counterbalanced by said second fluid force.

13. The starter of claim 12 wherein:

said valve means admits fluid pressure into a second chamber located on the opposite face of said piston from said first fluid chamber.

14. The starter of claim 13 wherein:

said valve means opens in response to the location of said piston in its movement in the engaging direction.

15. The starter of claim 13 wherein:

said valve means opens in response to the pressure of fluid supplied to said motor.