Internal combustion engine starter motor control arrangements

Abstract

 An internal combustion engine starter motor control includes a solenoid with pull-in and holding windings (14 and 15) and a main contact (12). The pull-in winding (14) is connected in series with the starting switch (18) and the motor (10, 11) across the battery (13), the holding winding (15) being connected across the series combination of the pull-in winding (14) and the motor (10, 11). The main contact (12) connects the motor (10, 11) directly for the battery and means are provided for ensuring that, whilst sufficient current can flow through the pull-in winding (14) to index the motor (10, 11) during pull-in, the main contacts are not held closed after the starter switch (18) is opened by current flowing through the main contacts and the two windings in series. To this end, a resistor (16) and diode (17) in series are connected across the pull-in winding to pass extra current during pull-in. Alternatively, a diode may be connected in series with the pull-in winding.

Description

[0001] This invention relates to internal combustion engine starter motor control arrangements.

[0002] In a conventional starter motor control arrangement the motor is connected in series with a pull-in winding of a solenoid and a starter switch across a supply, a hold-in winding of the solenoid being connected in parallel with the series combination of the pull-in winding and the motor, and a main contact operable by the solenoid being connected across the series combination of the starter switch and the pull-in winding.

[0003] With such an arrangement when the starter switch is closed current flows through both the windings and establishes a high pull-force so that the solenoid displaces a pinion driven by the motor into engagement with an engine flywheel. Assuming tooth-to-tooth abutment does not occur the main contact is made, shorting out the pull-in winding and energising the motor, the solenoid remaining energised by virtue of current in the hold-in winding only. Should tooth-to-tooth abutment occur, the pinion is spring-loaded to allow the solenoid to travel to close the main contacts. Initial turning of the motor releases the abutment and allows the pinion to travel hone under its spring load.

[0004] This arrangement suffers greatly from damage to the gears caused by shock loads following tooth-to-tooth abutment. Although the problem could be alleviated by allowing low power indexing of the motor during pull-in conventional solenoid design makes this difficult because of the need to ensure that the solenoid is de-energised properly when the switch is opened, since current can flow through the main contacts and the two windings in series when the switch is open. To ensure that the solenoid is de-energised the two windings need approximately the same number of turns and this prevents the pull-in winding being made with a sufficiently low resistance to permit low power indexing.

[0005] It is one object of the present invention to provide a starter motor control arrangement in which this disadvantage is overcome.

[0006] According to one aspect of the invention a supplementary current path is provided in parallel with the pull-in winding, so as to provide sufficient current to the motor during pull-in to index the motor, said supplementary current path including a unidirectional current flow device.

[0007] According to another aspect of the invention, the pull-in winding is connected to the motor via a unidirectional current flow device.

[0008] In the accompanying drawings:-

Figure 1 is the circuit diagram of one example of a starter motor control arrangement in accordance with the invention, and

Figures 2 and 3 are circuit diagrams of two alternative examples of the invention.

[0009] In the system shown in Figure 1 the motor armature 10 and field winding 11 are connected in series with the main contacts 12 across the 12v battery 13. The contacts 12 are operated by a solenoid having two windings 14 and 15 with equal numbers of turns. The pull-in winding 14 is connected at one end by a starter switch 18 to the battery +ve and at the other end to the junction between the contacts 12 and the field winding 11. A resistor 16 in series with a unidirec- tion current flow device in the form of a semiconductor diode 17 provides a supplementary current path in parallel with the winding 14. The winding 15 connects the junction of the winding l4 and the switch 18 to the -ve pole of the battery.

[0010] When switch 18 is closed, sufficient total current flows through the winding 14 and the resistor 16 to cause the motor to turn slowly and avoid tooth-to-tooth abutment problems, When the contacts 12 close the motor operates at full power and winding 14 is shorted out as is conventional. On opening of switch 18, however, no reverse current can flow through the diode 17 so that the flux in windings 14 and 15 cancels out permitting immediately release of the solenoid.

[0011] Turning now to Figure 2 the arrangement differs from that shown in Figure 1 in that the diode 117 is in series with the winding 114. Thus the latter can be provided with fewer turns than usual so that its resistance is low enough to allow it to pass sufficient motor current to index the motor during pull-in. Diode 117 prevents reverse current flow through winding 114 when switch 18 opens. A resistor 116 may be connected in parallel with the winding 114, to adjust the initial motor current independently of the windings.

[0012] In the Figure 3 arrangement an additional battery 113 is connected in series with the battery 13 and the main contacts 12, the switch 18 being connected to the battery 13 as before. The arrangement is otherwise the same as that shown in Figure 2. Indexing occurs during pull-in, but 24v is applied to the motor when the contacts 12 close. The diode 117 prevents reverse current through winding 114, both when switch 18 open as before, and also when the contacts 12 close and switch 18 is still closed.

[0013] The diode 117 also serves to isolate the switch 18 and 12v solenoid windings 114,/15 from the 24v starter motor 10. Without the diode 117, it would be necessary to use 24v solenoid windings and an additional relay to control the current supply to the windings from a 12v switch.

Claims

1. An internal combustion engine starter motor control comprising compound solenoid having a pull-in winding, a holding winding and a main contact operable by said solenoid, a starter motor having a mechanical drive output member displaceable by said solenoid, a starter switch, the starter switch, the pull-in winding and the motor being connected in series across a supply and the holding winding being connected across the series combination of the pull-in winding and the motor, characterised by an auxiliary current path in parallel with the pull-in winding permitting sufficient current flow during pull-in to index the motor, but ensuring that on opening of the starter switch the main contact can open in spite of current flowing through the main contact, the pull-in winding and the holding winding in series.

2. An internal combustion engine starter motor control as claimed in claim 1 characterised in that said auxiliary current path comprises a resistor.

3. An internal combustion engine starter motor control as claimed in claim 2 further characterised by a diode in series with the resistoro

4. An internal combustion engine starter motor control comprising compound solenoid having a pull-in winding, a holding winding and a main contact operable by said solenoid, a starter motor having a mechanical drive output member displaceable by said solenoid, a starter switch, the starter switch, the pull-in winding and the motor being connected in series across a supply and the holding winding being connected across the series combination of the pull-in winding and the motor, characterised by a unidirectional current flow device in series with the pull-in winding to prevent current flow through the main contacts, the pull-in winding and the holding winding in series when the starter switch is opened.

5. An internal combustion engine starter motor control as claimed in any preceding claim in which the main contact connects the motor directly to the supply.

6. An internal combustion engine starter motor control as claimed in claim 5 in which the supply comprises two batteries in series, the junction of the two batteries being connected by the starter switch to the pull-in winding and the holding winding and the main contact connecting the motor across the series combination of the two batteries.

Drawing