Cranking device for internal combustion engines

[0002] 1. Field of the Invention

[0003] The invention relates to a cranking device for internal combustion engines, having a starter motor whose starter pinion initially shifts into the gear ring of the engine with a starting signal via an engagement magnet, before the starter motor trips the cranking process with full force.

[0004] 2. Description of the Related Art

[0005] A cranking device of this kind is known from German Patent DE 30 02 232 C2. In this known cranking device, the engagement magnet is fully triggered upon contact of the ignition key, so that the starter pinion strikes the gear ring of the engine with full force if it cannot be shifted in directly. This leads to wear or damage to the teeth of the two colliding parts. Furthermore, the engagement magnet controls a contact bridge which turns the starter motor on. The switching process of this contact bridge is not without problems in this kind of control.

[0006] It is the object of the invention to improve a cranking device of the type referred to at the outset in such a way that the shifting of the starter pinion into the gear ring of the engine and the switching of the starter motor are improved.

[0007] This object is attained according to the invention in that the starter motor with the starting signal drives the starter pinion initially via a protective resistor with reduced torque, and the engagement magnet shifts the pinion until it is into the gear ring of the engine, and that after that, the engagement magnet presses the starter pinion all the way into the gear ring of the engine, and the starter motor turns the engine over with full torque by bypassing the protective resistor Rvor.

[0008] For the shifting in of the starter pinion, this produces a two-staged sequence. In the first stage, the starter motor is driven at low torque via the protective resistor. Rotating the starter motor makes it easier to find a gap between teeth, and with the advancement of the starter pinion, the wear upon impact of the starter pinion with the gear ring of the engine is reduced, especially whenever a gentle preshifting is done by means of supplying limited current to the relay. In the second stage, the engagement magnet receives full current, so that the starter pinion can shift all the way into the gear ring of the engine. After that, the starter motor is supplied with full current and rotates at full torque.

[0009] In one feature, it is provided that the starting signal is delivered to a logic circuit, which via a first triggered semiconductor, for instance a highside smart FET, imposes reduced current on the series circuit comprising the protective resistor and the starter motor, and that the logic circuit, via a second triggered semiconductor, for instance a highside smart FET, triggers the engagement magnet in clocked fashion, until the starter pinion shifts into the gear ring of the engine.

[0010] In this triggering, the starter contact of the ignition key is relieved, and with the triggering of the two highside smart FETs a chronological succession can moreover be initiated, so that the reduced triggering of the starter motor can be done simultaneously with the action upon the engagement magnet, or alternatively the engagement magnet can be acted upon only after the starter motor has started up.

[0011] With the clocked triggering of the engagement magnet, the current is reduced, and thus the thermal stress is reduced. Moreover, this achieves a gentle shifting of the starter pinion into the gear ring of the engine.

[0012] A chronological compulsory succession of the two shifting events can also be attained by providing that the second semiconductor is connected in series with the first semiconductor, and that after the shifting of the starter pinion, the second semiconductor is made fully conducting via the logic circuit.

[0013] The transition between the two stages of shifting in and switching of the starter motor can be done in controlled fashion in accordance with one feature, in that the shifting of the starter pinion into the gear ring of the engine is monitored by means of a travel sensor and is indicated to the logic circuit, and that the logic circuit, as a function of the response of the travel sensor, switches the second semiconductor from clocked operation to continuous operation.

[0014] The initiation of the second stage of the cranking process is effected in that after the starter pinion has been forced into the gear ring of the engine, the logic circuit triggers a third semiconductor, for instance a highside smart FET, which turns on a power relay, and that a contact of the power relay imposes full current on the starter motor, whereupon the third semiconductor is connected to the positive potential of the supply voltage and is connected in series with the power relay that is connected to ground. With the inclusion of a power relay, the contact bridge controlled by the engagement magnet can be omitted. The electrical control portion for the second stage of shifting in and switching of the starter motor can also be done, in a further feature, such that after the starter pinion has been forced into the gear ring of the engine, the logic circuit triggers an N-channel MOSFET, which turns on a power relay, and that a contact of the power relay imposes full current on the starter motor, whereupon the power relay is connected to the positive potential of the supply voltage and the N-channel MOSFET connected to ground is connected in series with the power relay (LR).

[0015] If in one feature it is provided that the logic circuit switches over, after a predetermined period of time, from clocked operation to continuous operation for the engagement magnet, then the logic takes on the function of purely sequence control without feedback. The prerequisite for this is that the starter pinion has always found a gap between teeth or in other words has shifted into place. With the cranking device of the invention, the structure can also be such that the starter motor, the engagement magnet, and optionally the travel sensor form a starter unit, which is separate from the electronic portion having the logic circuit, the protective resistor, the highside smart FETs or the N-channel MOSFET and the power relay, and which is connected to the electronic portion via three lines.

[0016] The electronic portion can be separate from the starter and can be placed directly in the vicinity of the battery. As a rule, the length of the line (Kl. 30), which as a rule is unprotected by a fuse, can be reduced to a minimum. The starter is without voltage outside the actual starting process, so that the risk of short-circuiting and fire is low. The environmental conditions (temperature stress, vibration acceleration, tightness with respect to leaks, etc.) for the electronic portion are also less critical at this mounting site then directly at the starter as in known cranking devices. The engagement magnet is simpler, because it need not control any contact bridge. This has an advantage in terms of space and expense and also offers the possibility of embodying the starter as a coaxial starter.

[0017] The cranking device also has the advantage of a simplified technique for connection to the starter, which requires only the terminals 50 and 45, as well as one connection for the travel sensor WS if it is present. No internal connections are needed at the starter, either. The control electronics take on the additional functions of the two-stage shifting in and the gentle preshifting and can take on additional functions as well, such as overload and excess it temperature protection.

[0018] The invention will be described in further detail in terms of two exemplary embodiments shown in the form of circuit diagrams in the drawing. Shown are:

[0019] FIG. 1, a first exemplary embodiment of a cranking device with a power relay, switched via a highside smart FET, and

[0020] FIG. 2, a secondary exemplary embodiment of a cranking device, with a power relay controlled via an N-channel MOSFET.

[0021] The starting signal output by the contact of the ignition key in a motor vehicle is delivered, in the cranking device of the invention, to a logic circuit L, as indicated by st at the terminal 50e. The logic circuit L, for the duration of the presence of the starting signal st, outputs a control signal to the output a1, which makes the highside smart FET T1 conducting, this highside smart FET being connected to the positive potential (terminal 30) of the supply voltage U. Thus via a series circuit comprising the protective resistor Rvor and the starter motor SM, reduced current is imposed, so that the starter motor drives the starter pinion with reduced torque. At the same time or after a time lag, the logic circuit L triggers the output a2, specifically in clocked fashion. The clock pulses, via the highside smart FET T2, act on the downstream engagement magnet EM. The prerequisite in the series circuit shown is that the highside smart FET T1 is made conducting, so that the starter motor SM is rotating. In this way, the engagement magnet EM is adjusted gently, or in other words with a reduced current demand, which leads to a gentle preshifting and shifting at reduced torque of the starter pinion into the gear ring of the engine. The shifting in can be monitored by means of a travel sensor WS, such as an end switch. Once the starter pinion has shifted into the gear ring of the engine, then the travel sensor WS outputs an indication signal to the output e1 of the logic circuit L, and this signal leads to a control signal at the output a3. The highside smart FET T3 is made conducting and turns the power relay LR on, which with its contact t connects the starter motor SM directly with the positive potential of the supply voltage U and thus bypasses the protective resistor R vor and the FET T1. The starter motor SM now, via the starter pinion, drives the gear ring of the engine with full torque.

[0022] The travel sensor WS may also be omitted, if a predetermined length of time has elapsed after the initiation of the shifting via the control signal to the output a2, and if the logic circuit L at the output a3 turns the power relay LR on. The prerequisite of this compulsory control is that the shifting and engagement process be performed successfully within this time.

[0023] As FIG. 1 shows, the starter motor SM and the engagement magnet EM can be constructed, optionally along with the travel sensor WS, as a starter ST that is separate from the electronic portion ET. Both parts are then connected to one another via two or three lines, as applicable, and make different installation sites in the motor vehicle possible, as indicated by the terminals w, 50 and 45.

[0024] The structure of the cranking device of FIG. 2 differs from that of FIG. 1 only in the current circuit for the power relay LR, which is turned on via a less-expensive N-channel MOSFET T4. This N-channel MOSFET T4 is connected to the ground potential and is connected in series with the power relay LR that is connected to the positive potential of the supply voltage U. The triggering is done with the correct triggering potential via the output a3 of the logic circuit L.

[0025] In the circuit of FIG. 1 with the third highside smart FET T3, the triggering is done via the output a3 and with the different trigger potential required for that purpose. The highside smart FET T3 is connected to the positive potential of the supply voltage U and is connected in series with the power relay LR connected to ground potential.

[0026] The control sequence of the two cranking devices of FIGS. 1 and 2 is identical, however.