Patent GB-798225-A (GB)
Abstract: 798,225. Change-speed control. C.A.V. Ltd. Sept. 17, 1956 [Sept. 28, 1955], No. 27591/55. Class 80 (2). A control circuit for an electromagnetically operated change-speed gear in a motor vehicle comprises three relays g, h, j, Fig. 1, each having two windings, one energized by a battery c and the other energized by a dynamo having an armature a driven at a speed proportional to the speed of rotation of the output shaft of the change-speed gear. The dynamo field winding b is energized from the battery c. The four forward speeds and reverse of the change-speed gear are established on selective energization of solenoids 1-4, r by the battery. When the vehicle is at rest, the circuit is in the condition shown. On closing a main control switch m to connect the battery c through the field winding of the dynamo, current passes to a circuit containing a signal lamp q warning the driver that the system is in condition for starting the vehicle. The current now supplied to the relays g, h, j from the battery alone is insufficient to actuate them. Slight depression of the accelerator pedal causes a switch s<SP>1</SP> to be moved to its second position, thus breaking the circuit through the warning lamp q and supplying current through closed switches d<SP>4</SP>, e<SP>5</SP> and f<SP>5</SP> to the solenoid 1 to engage the first speed. As the vehicle moves off, the speed of rotation of the dynamo armature a gradually increases until ultimately sufficient current passes through the second winding of the relay g to close a previously open switch g<SP>1</SP> and thus bring a relay d into circuit. The relay d then closes switches d<SP>1</SP>, d<SP>2</SP> and d<SP>3</SP>, which have hitherto been open, and opens switches d<SP>4</SP> and d<SP>5</SP> which have hitherto been closed. Closing the switch d<SP>1</SP> causes the solenoid 2 to be brought into circuit to engage second speed, while opening the switch d<SP>4</SP> simultaneously de-energizes the solenoid 1 and thus disengages the first speed. Closing the switch d<SP>2</SP> short-circuits the switch s<SP>1</SP> while opening the switch d<SP>5</SP> puts the signal lamp q out of circuit irrespective of the condition of the switch s<SP>1</SP>. The switch d<SP>3</SP> forms part of a throttle kickdown control circuit described below. As the speed of the vehicle increases still further, the voltage developed by the dynamo a increases until ultimately the relay h operates to close a switch h<SP>1</SP> and thereby energize a relay e which closes switches e<SP>1</SP>, e<SP>2</SP> and e<SP>3</SP> and opens switches e4 and e<SP>5</SP> to de-energize the second speed solenoid 2 and energize the third speed solenoid 3. Similarly, with still further increasing speed, the relay j is operated to close a switch j<SP>1</SP> and energize a relay f which then closes, switches f<SP>1</SP> and f<SP>2</SP> and opens switches f<SP>3</SP>, f<SP>4</SP> and f<SP>5</SP> thereby energizing the fourth speed solenoid 4 and deenergizing the third speed solenoid 3. Under the conditions described, if the vehicle speed is allowed to drop without movement of the accelerator pedal, the holding switch f<SP>2</SP> will keep the relay f, and consequentially the fourth speed solenoid 4, energized untilt he vehicle comes substantially to rest. If the driver wishes the lower speeds to be successively engaged as the vehicle slows down, he depresses the accelerator pedal further to open a switch s<SP>2</SP>. Third, second and first speeds are then engaged successively. Further depression of the accelerator pedal opens a switch s<SP>3</SP> to introduce a resistance o into the battery circuit, so that the dynamo armature a has to rotate more quickly to produce upward changes. Still further movement of the accelerator pedal opens a switch s<SP>4</SP> so that the current to the relays g, h and j is supplied wholly by the dynamo. To start the vehicle in second instead of first speed, a switch p is closed to shortcircuit the switch g<SP>1</SP>. So that the braking power of the vehicle engine may be employed, a handoperated switch t in circuit with a warning lamp u is moved from the position shown to its second position, in circuit with the warning lamp u, when the relay f is de-energized and the third speed accordingly engaged. To engage reverse, the main control switch m is moved to its second position to energize the solenoid r. In a modification, Fig. 2, the dynamo is replaced by an alternating current generator a supplying the relays g, h and through a rectifier v and a smoothing circuit. One of the windings of the relay j is in series with one of the windings of the relay h, the other winding of which is in series with two resistances o<SP>1</SP> and o<SP>2</SP> which can be short-circuited by a pair of normally closed switches s<SP>3</SP>, s<SP>4</SP>. The control switch mc is a simple master switch, a separate manually operated forward and reverse switch m<SP>2</SP> being provided. The solenoid 1 for first speed is energized by manual operation of the switch m<SP>2</SP>. To obtain automatic selection of the second, third and fourth speeds as described above, the switch m<SP>2</SP> is moved to its position 4. With the vehicle stationary and its engine idling, a switch s<SP>1</SP> is closed to energize a relay m which opens a switch m<SP>1</SP> so that current cannot be supplied to the switch m<SP>2</SP>. A relay u is energized until the accelerator is partly opened, when it closes a switch u<SP>1</SP> to supply current to the switch m<SP>2</SP>. If the accelerator pedal is depressed too far, the relay u is de-energized and the switch u<SP>1</SP> is opened to interrupt current supply to the switch m<SP>2</SP>, so that initial engagement of any of the gear speeds cannot be achieved. The switch ml is shunted by a switch d<SP>2</SP>, through which current is always supplied to the switch m<SP>2</SP> when the vehicle is running sufficiently fast for the relay d to be energized. Except when the master switch mc is open, the battery fed windings of the relays g, h and are never completely disconnected from the battery c as described with respect to Fig. 1 above. They are connected to the battery either through the resistance o<SP>1</SP>, or through both the resistances o<SP>1</SP> and o<SP>2</SP>, according to the position of the accelerator pedal. In addition, a switch e<SP>6</SP> operated by the relay e may be provided and arranged to prevent this relay from operating with increasing speed until a higher speed is attained than that at which the change occurs during deceleration. A control circuit according to the invention may be adapted to provide more or less than four speed changes, the number of relays &c. being correspondingly changed. Further, the relays g, h and j may alternatively be adapted to operate the change-speed solenoids 1-4 directly.