The invention relates to a starting method for internal combustion engines in motor vehicles, with a start-stop system and to a starting device for carrying out the method.
Internal combustion engines of motor vehicles are customarily turned on by means of a starter motor, wherein first of all a pinion of the starting device meshes in a ring gear of the internal combustion engine before the starter motor is switched on. In addition, with a start-stop system in motor vehicles, if the motor vehicle has stopped for a relatively long time, the internal combustion engine is automatically switched off and, at the end of the stop phase, the engine is then started again automatically in order to be able to continue the journey.
It is known from EP 08 48 159 A1 to bring starter pinions into the meshed position right at the beginning of a stop state of the engine in order subsequently, at the beginning of the starting operation, to immediately switch on the starter motor at full power. This significantly reduces the time for the starting operation. However, this solution still has the disadvantage that, for the meshing of the starter pinion at the beginning of the stop phase, it is necessary to wait first until the engine is at a standstill, this meaning, if the stop phases are very short, a delay which may be critical, for example in a traffic jam because of vehicles following too closely.
In order to shorten the meshing operation at the beginning of a stop phase, it has already been proposed using electronic activation of the starter motor to synchronize the rotational speed of the pinion with the rotational speed of the ring gear of the engine, in order thereby for the starter pinion to already be meshed in the still rotating ring gear of the engine. A disadvantage here is that, in order to synchronize the circumferential speed of the ring gear and of the starter pinion, a considerable electronic outlay on control has to be expended, since the circumferential speed of the ring gear changes greatly due to compressions in the engine cylinders when the switched-off internal combustion engine comes to a stop.
It is endeavored with the present invention to ensure that, at the beginning of a stop operation, the starter pinion meshes in a simple manner in the still rotating ring gear using simple mechanical means after the internal combustion engine is switched off.
In start-stop systems for an internal combustion engine for carrying out the method according to the invention and in a starting device according to the invention, a temporarily shortened starting operation is obtained using simple mechanical means by the starter pinion meshing in the engine ring gear as it comes to a stop. The electronic control of the start-stop system is substantially simplified as a result. Furthermore, this has the effect that, in comparison to an uncushioned meshing of the starter pinion in a still rotating ring gear, no damage occurs due to recoils occurring in the process at the free wheel or planetary gearing of the starter.
Since, in the event of an axial pressure spring system of the starter pinion, meshing in the revolving ring gear takes place only at slow rotations of the ring gear and with the best tooth-to-gap position, in an advantageous development of the invention the effect achieved by a selected spring characteristic of the pressure spring is that the pinion is first of all engaged by a small amount in the ring gear and, in the process, is first of all carried along only via correspondingly small contact surfaces of the teeth of the pinion and ring gear. At low circumferential speeds, the pinion can be meshed completely in the ring gear by the force of the pressure spring. By contrast, the teeth of the starter pinion are pushed out of the ring gear again if the circumferential speed of the ring gear is too great. The starter pinion which now rotates slowly is then optionally repeatedly engaged again to a greater extent into the next gap until the starter pinion is finally completely meshed in the ring gear as the rotational speed increases.
An advantageous development of the invention consists in that, even before the engine is at a standstill, the crankshaft can be rotated by means of the engine control unit from the starter motor into the optimum starting position in order thereby to shorten the time of the subsequent restart.
In a first particularly simple and expedient embodiment for carrying out the starting method, with a starter pinion which can be displaced axially on a pinion shaft, the pressure spring in the form of a helical compression spring is clamped between a shoulder of the pinion shaft and the annular shoulder formed rear side of the pinion, wherein the pinion is accommodated as a slip-on pinion in an axially displaceable manner on the pinion shaft by means of a sliding toothing. In the event of an additional arrangement of a meshing spring which is known per se, the pressure spring advantageously has a smaller spring constant than the meshing spring.
In order to facilitate the meshing of the pinion, the teeth of the pinion and/or of the ring gear are advantageously provided on the front end sides thereof with a beveled portion of the tooth flanks and with a beveled portion on the tooth tip. In this case, the beveled portions are advantageously provided in particular on those tooth flanks of the ring gear which are in front in the direction of rotation of the ring gear and on the rear tooth flanks of the pinion. In addition, the pinion shaft can advantageously be displaced axially by a drive shaft of the starting device, preferably by means of a free wheel via a sliding toothing without a quick-acting screw thread.
In a further embodiment, adjacent teeth of the pinion and of the ring gear, in a development of the invention, each have an axial length which differs by the same amount in the region of the front end sides which are opposite in the demeshed state. In this embodiment, the meshing of the pinion in the ring gear can be shortened even at high rotational speeds by the protruding teeth of the pinion and ring gear now being spaced apart from one another by double the tooth pitch such that, even at high speeds of rotation of the ring gear, the pinion teeth can still penetrate to an adequate depth in the tooth gaps by means of the axial pressure spring in order to be carried along. In the simplest embodiment, every second tooth of the pinion and ring gear is shortened in relation to the pinion width and ring gear width. Expediently, the non-shortened teeth are also provided here on the front end sides thereof with a beveled portion on the tooth tip, which beveled portion is preferably shorter than the tooth projection. In order, even here, to provide the possibility of allowing the starting pinion to first of all slide off the teeth of the ring gear, it is proposed, in a refinement of the invention, to provide beveled portions on those tooth flanks of the projecting teeth of the ring gear which are in front in the direction of rotation of the ring gear and on the rear tooth flanks of the projecting teeth of the pinion.
Details of the invention are explained in more detail below by way of example with reference to the figures, in which:
During cold starting of the engine 15, first of all the starter relay 12 is activated via the engine control unit 19 by a starting signal triggered by the motor vehicle driver, the starter motor 11 being activated and rotated slightly directly by the engine control unit 19 via a further connection. By means of the relay winding 16, the pinion 13 is also advanced via the tappet 17 and the engagement lever 20 as far as the ring gear 14 of the engine. In a tooth-to-tooth position, an engagement spring 24 which is inserted between the free wheel 23 and engagement lever 20 is tensioned in a known manner such that, by means of slight rotation of the starter motor 11, the teeth of the pinion 13 can engage in the next tooth gap of the ring gear 14 as far as a stop on the drive shaft 22.
The start-stop system of the motor vehicle is then activated during the driving mode, and, at the beginning of each stop phase of the vehicle, the internal combustion engine is switched off, for example, by the speed of rotation at the front wheels of the vehicle being detected. At the same time, in a first stage for preparing a subsequent restart of the engine, a meshing operation of the pinion 13 in the still moving ring gear 14 of the engine 15 is triggered by a metered excitation current being passed via the engine control unit 19 to the starter relay 12. The pinion 13 is now advanced axially by the engagement lever 20 via the tappet 17 to mesh in the ring gear 14. In order to make the internal combustion engine 15 ready to start again as rapidly as possible after being switched off, the pinion 13 now has to be meshed by means of an axial pressure spring 25 in the still rotating ring gear 14 even before the internal combustion engine 15 is at a standstill and with the starter motor 11 not in use. The axial pressure spring 25 is arranged and axially prestressed here between the pinion 13 and the pinion shaft 26.
In a development of the invention, before the engine 15 is at a standstill, the crank shaft is now rotated by means of the engine control unit 19 from the starter motor via the ring gear 14 into an optimum starting position for the subsequent restart.
In this exemplary embodiment, likewise at the beginning of a stop cycle of the internal combustion engine 15, the pinion 13 is first all moved forward to the ring gear 14 by the starter relay 12 via the engagement lever 20 after the internal combustion engine is switched off and before it is at a standstill and with the starter motor 11 not in use. Upon reaching a tooth-to-gap position, the pinion 13 is first of all engaged by a small amount in the ring gear 14 by means of the pressure spring 25. In the process, first of all two non-shortened teeth 13a and 14a of the pinion 13 and ring gear 14 come into contact by means of the beveled tooth flanks 13b and 14b thereof. The pinion 13 is first of all carried along only via a correspondingly small contact surface of the beveled portions 35a of the pinion tooth flanks 13b with the beveled portions 35b of the ring gear tooth flanks 14b. During slow rotation of the ring gear 14, the prestressing of the pressure spring 25 and the force of the engagement spring 24 of the starting device 10 are sufficient in order to carry along the low-mass pinion 13 and then to mesh the latter completely in the ring gear 14. In the process, the starting motor 11 and the gearing 21 of the starting device 10 are decoupled by the free wheel 23. By contrast, at a greater speed of rotation of the ring gear 14 and with pinions of larger mass, the pinion 13 is not immediately completely carried along by the ring gear 14 but rather slides in an axially resilient manner off via the beveled portion 35a, 35b of the unshortened teeth 13a and 14a, which are in contact with each other, by the pinion 13 being pressed axially out of the ring gear 14 again counter to the force of the pressure spring 25. Since the next non-shortened tooth 14b of the ring gear 14 is spaced apart by twice the tooth pitch from the preceding unshortened tooth, the pinion 13 now has available twice as much distance along the teeth in order to be able to engage to a greater extent in the ring gear 14 by means of the force of the pressure spring 25. In this position, the pinion is now completely carried along and is completely meshed in the ring gear 14 by means of the force of the engagement spring 24. It can therefore be ensured that, even with small advancing forces on the pinion 13, a toothing penetration depth sufficient for a long service life is achieved. When relatively low-mass slip-on pinions are used, the shortened teeth 13a1 and 14a1 and the advancing force of the engagement spring 24 cause the pinion 13 to be engaged in the ring gear 14 to a sufficient extent so as to be carried along immediately by the ring gear 14 without sliding off and springing back. Therefore, the pinion 13 slides off from and springs back axially onto the ring gear 14 only if there is a great difference in speed of rotation between the ring gear 14 and pinion 13.
The invention is not restricted to the embodiments illustrated and described but rather also comprises alternative solutions which can be adapted depending on the design of the starting device 10 from
Number | Date | Country | Kind |
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10 2008 054 979 | Dec 2008 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/063763 | 10/21/2009 | WO | 00 | 9/7/2011 |
Publishing Document | Publishing Date | Country | Kind |
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WO2010/069646 | 6/24/2010 | WO | A |
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