This document describes a device for rapidly braking two-stroke internal combustion engines that can operate in reversible directions. The device uses two contact breakers associated with different rotational directions. When the ignition switch is changed to the opposite direction, one contact breaker will open shortly before top dead center to provide an ignition spark, braking the engine. This allows the starting motor to be reversed without heavy loading before the engine fully stops.

1. * GB780055 (A)
Description: GB780055 (A) ? 1957-07-31
Improvements in or relating to devices for rapidly braking reversible
internal combustion engines
Description of GB780055 (A)
PATENT SPECIFICATION
Date of Application and filing Complete Specification: Oct. 18, 1955.
Application made in Germany on Oct. 23, 1954.
Complete Specification Published: July 31, 1957.
Index at acceptance:-Classes 7(4), B2D(10:11B); 7(5), B2F11G;
International Classification:-FO2d, f, H02j.
780,055 No. 29642/55.
and 38(4), A15B1.
COMPLETE SPECIFICATION
Improvements in or relating to Devices for Rapidly Braking Reversible
Internal Combustion Engines We, ROBERT BoscHGMBH, a German i Company
of 4, Breitscheidstrasse, StuttgartW, Germany, do hereby declare the
invention, for which we pray that a patent may be granted to us, and
the method by which it is to be performed, to be particularly
described in and by the following statement: -
The present invention relates to engine braking and more particularly
to a device for rapidly braking two-stroke internal combustion engines
which are adapted to be optionally started and to run in either
direction of rotation, under reversible spark ignition.
The term "reversible ignition" as used herein and in the appended
claims refers to ignition which may be changed over or reversed" when
it is desired _to change the direction of running of the engine; this
enables the ignition system to have a similar operative connection
with the engine, relatively to the engine piston displacement, when
running in either direction.
In known systems including two-stroke internal combustion engines
which are fitted with spark ignition and started by means of a
reversible starting motor, it may happen when changing over from one
direction of rotation to the other that the starting motor is already

2. reversed in said other direction before the engine has stopped. In
this case the starting motor is extremely heavily loaded, having to
oppose and neutralize the kinetic energy still remaining in the engine
when the motor is reversed.
According to the present invention a device for rapidly braking by
means of an ignition pulse an engine adapted to be started in either
direction and then to run in that direction under reversible spark
ignition, includes two contact-breakers which are respectively
associated with one or other of the two directions of rotation and are
also associated with the ignition, either of said contact-breakers
being optionally connectable by means of a change-over switch to a
source of ignition [Price 316] current, and a control member driven by
the engine and adapted to actuate the contactbreakers is so formed and
disposed relatively to the contact-breakers that when the engine is
running in a particular direction the contact-breaker associated with
that direction will open at the most 35 before but not later than top
dead centre, whilst the other contact-breaker will open at least 1600
before said top dead centre. 55 The present invention will now be
further described by way of example with reference to the accompanying
drawings, in which:Fig. 1 is a diagrammatic view of a twostroke
internal combustion engine having a 60 separate reversible ignition
system and a reversible starting motor; Figs. 2 and 3 diagrammatically
illustrate the ignition system contact-breaker on an enlarged scale,
in different positions; and 65 Fig. 4 shows a wiring diagram of a
further development of the system.
The two-stroke internal combustion engine shown in Fig. 1 is equipped
with a sparking plug 11 which is supplied by the high 70 tension
winding 12 of an ignition coil 13.
One end of the primary winding 14 of the coil is connected by an
ignition switch 15 with one terminal of an accumulator 16 whose other
terminal is earthed. The other end of 75 the primary winding 14 is
connected to one or other of two stationary contacts 19 and 20 by the
switch member 17 of a change-over switch 18. A contact breaker lever
21 is connected to the contact 19; a second interrupter lever 22 is
connected to the contact 20.
These contact-breaker levers are respectively pivotally mounted on
spindles 23 and 24, and respectively carry moving contacts 25 and 26.
These moving contacts are operatively associated with fixed contacts
27 and 28 respectively; these fixed contacts are both earthed.
Springs 29 and 30 respectively engage said contact-breaker levers and
bias them towards a cam 32 fixed on the engine crank-shaft 31. 90
780,055 As may be seen more clearly in Fig. 2, the cam disc has a
flattened section 33 with an included angle of about 1705, the
so-called closure angle of the cam. The lever 21 is so arranged that

3. the section 33 leaves it about 300 before top dead centre upon
rotation of the cam disc of the engine in the direction of the arrow
A. At this point, the contacts 25, 27 will thus be opened. The other
lever 22 is offset relative to the lever 21 by about 1300 in the
opposite angular direction to the arrow A. Preferably the closure
angle lies within the range of 1500 to 175 and the angular separation
of the contact-breakers is at least 1200.
To start the engine in the required direction of rotation a reversible
electric starting motor 34 is used. The motor 34 can be connected to
the battery 16 through a two-way switch 35. When this switch is in the
position I the motor is connected for running clockwise and in the
position II for running anticlockwise.
The system operates in the following manner: Assuming that the engine
is turning over in the direction of the arrow A (running
anticlockwise), the switch member 17 of the change-over switch 18 is
on contact 19 so that the lever 21 is connected to the ignition coil.
The contact-breaker is opened as usual 300 before top dead centre,
whereby the machine receives an ignition spark.
When the driver wishes to drive the internal combustion engine in the
opposite direc-35 tion, he places the switch member 17 on the contact
20. The contact lever 21 is thus replaced by the contact-lever 22 in
the ignition circuit. If the internal combustion engine has not
stopped at this time and, for example, makes another turning movement
in the direction of the arrow A through top dead centre past the
position shown in Fig. 2, the contact lever 22 moves on to the section
33 of the cam after about 600 engine rotation past the position of
Fig. 2, i.e., 30 after top dead centre. The contacts 26, 28 are thus
closed so that current flows from the battery through the primary
winding 14 of the ignition coil. After a further rotation of 170 in
the same direction, the contacts 26, 28 are opened and an ignition
spark is produced.
At this moment the engine piston is 1600 before top dead centre. The
impulse produced by the combustion due to the ignition spark
immediately brakes the engine and stops it. The driver now operates
the twoway switch 35, moving it to the position I for clockwise
running of the starting motor which starts the engine in the desired
direction.
In order to prevent reversing of the starting motor before the
ignition change-over, it is expedient to control the two-way switch
through the ignition change-over switch lever 17. Fig. 4 shows a
wiring arrangement suitable for such an arrangement. The twoway switch
35 is actuated into one position or the other by the eneraisation of
electromagnet 40 or 41 respectively.
The energising windings of these electromagnets are respectively

4. connected to contacts 42 and 43. their other ends being earthed.
Between the contacts 42, 43 is disposed a contact 44 which can be
connected to the battery 16 through a press button 75 switch 45 used
for actuating the starting motor. A switch bridge 46 connects the
contact 44 with either contact 42 or with contact 43 according to
which of its two operative positions the lever 17 is displaced, thus
serving to reverse change-over switch 35 to reverse the engine
ignition. The switch bridge 46 is secured on but insulated from the
switch lever 17.
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