GB2175656A

GB2175656A - Change-speed gearing

Info

Publication number: GB2175656A
Application number: GB08612926A
Authority: GB
Inventors: Kiyoshi Kumazawa
Original assignee: Unix Co Ltd
Current assignee: Unix Co Ltd
Priority date: 1985-05-29
Filing date: 1986-05-28
Publication date: 1986-12-03
Also published as: GB8612926D0; DE3617688A1

Abstract

A speed change device comprises two electric motors 1,2 which can be individually actuated by an electric control means adapted to receive a radio signal from a remote place, and a differential gear mechanism 3 or a planetary gear mechanism which transmits the revolving force to a drive means, one motor only being actuated to provide a first speed and both motors together to provide a second speed. Further, this speed change device comprises a revolution preventing means for preventing an idling revolution of the non-actuated motor by the revolving force owing to the actuated motor. The gearing may be used in a ratio-controlled toy vehicle. <IMAGE>

Description

SPECIFICATION Speed change device BACKGROUND OF THE INVENTION 1) Field of the Invention The present invention generally relates to a speed change device. More particularly, the present invention relates to a speed change device which is adapted for a remote controlled automotive vehicle.

2) Description of the Prior Art Conventionally, a moving object equipped with a driving force generating means, such as an automotive vehicle comprises means for changing speed. Such speed change means has been selected from several types such as a gear shift system, a torque converter system, and an electrically controlled system. The gear shift system can change the speed by changing the gear ratio of an output gear meshingly engaged with an input gear connected to the driving force generating means in accordance with a shifting operation of a gear shift lever. The torque converter system can change the speed on account of the function between a pair of blade wheels arranged oppositely each other through fluid.The elec tricaily controlled speed change system has been used for the case that the vehicle contains electric motors as the driving force generating means. The driving speed can be changed in response to the change of voltage for DC motor, and the change of frequency for AC motor.

In order to control a toy vehicle from the remote place through a radio control system, such conventional speed change systems may possibly cause several problems. The gear shift system further requires an electromagnetic actuating device for actuating the shift lever in accordance with a command signal.

This gear shifting operation generates a harsh sound and makes the gear abrade. Further, it is extremely difficult to use the torque converter system and the AC motor for such radio controllable toy vehicle. Almost conventional toy vehicles employ DC battery and DC motor, so that their speed control is carried out by changing the voltage applied to the DC motor.

According to this speed control system, its torque depends on the change of voltage.

This may cause a trouble that the vehicle can not go up a slope when the vehicle moves slowly with a low voltage. Further, this change of voltage makes the battery life shorten since current energy is quickly consumed in response to the change of voltage.

SUMMARY OF THE INVENTION With these problems in mind, it is an object of the present invention to provide an improved speed change device which can reduce energy consumption.

Another object of the present invention is to provide an improved speed change device which can generate a torque even when its driving speed is decreased.

Further object of the present invention is to provide an improved speed change device which is adapted to a remote control system.

To accomplish the above described objects, the speed change device according to the first aspect of the present invention comprises a plurality of revolving force generating means each of which can be individually actuated by an electric control means adapted to receive a radio single from a remote place, and a differential gear mechanism or a planetary gear mechanism which transmits the revolving force form the revolving force generating means to a drive means.

According to the second aspect of the present invention, the speed change device comprises a plurality of revolving force generating means each of which is independently actuated by an electric control means adapted to receive a radio signal from a remote place, a differential gear mechanism or a planetary gear mechanism which transmits the revolving force from the revolving force generating means to a drive means, and a revolution preventing means for preventing an idling revolution of the non-actuated revolving force generating means by the revolving force owing to the actuated revolving force generating means.

According to the above described first aspect, one of the revolving force generating means is actuated so that the revolution at a first speed is transmitted to the drive means such as drive wheels. When a plurality of the revolving force generating means are simultaneously actuated, the high speed, multiplied by the actuated numbers, of the first speed is transmitted owing to the dirrerential gear mechanism or the planetary gear mechanism.

This speed change does not depend on the change of the voltage applied to the revolving force generating means, so that the revolving torque is kept at a constant level.

According to the above described second aspect, the revolution preventing means can lock the drive axle of the revolving force generating means, not actuated, when one revolving generating means is actuated. So that the revolving force generated from the actuated generating means is not transmitted to the non-actuated generating means. This can improve the revolving torque at a low speed and eliminate energy loss which may be consumed for an idling movement in the non-actuated revolving force generating means.

Other objects, features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a fragmentary sectional plan view showing a first embodiment of speed change device according to the present ivention; Fig. 2 is a circuit diagram showing a system for supplying an electric energy to revolving force generating means; Fig. 3 is a fragmentary sectional plan view showing an essentiai elements of a second embodiment; Fig. 4 is a fragmentary sectional plan view showing an essential elements of a third embodiment; Fig. 5 is a fragmentary sectional plan view showing a speed change device of a fourth embodiment equipped with a revolution preventing means; Fig. 6 is a circuit diagram showing a system for supplying an electric energy to revolving force generating means of Fig. 5; Fig. 7(A) and Fig. 7(B) are side views showing a revolution preventing means in Fig. 5;; Fig.8(A) and Fig. 8(B) are a sectional plan view and an elevational view showing another example instead of the revolution preventing means in Fig. 5; Fig. 9 is a fragmentary sectional plan view showing a speed change device of a fifth embodiment of the present invention; and Fig. 10 is a fragmentary sectional plan view showing a speed change device of a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, there is shown a first preferred embodiment of speed change device according to the present invention. This first embodiment is particulary adapted for a drive mechanism of a radio controllable automotive vehicle. In Fig. 1, the reference numeral 1 denotes a first revolving force generator for a first speed. Also the reference numeral 2 denotes a second revolving force generator for a second speed. These generators 1 and 2 are arranged that their drive axes are substantially aligned with a some space therebetween. For these generators, the same DC motors are used. The reference numeral 3 denotes a defferential gear unit connected to both generators 1 and 2. The first generator 1 has a first output gear 4 which is meshingly engaged with a first spur gear 5 of the differential gear unit 3.Also, the second generator 2 has a second output gear 6 which is meshingly engaged with a second spur gear 7 of the differential gear unit 3. The first and second spur gears 5 and 7 are respectively formed with a first bevel gear 8 and a second bevel gear 9 so that both bevel gears 8 and 9 face each other. Between bothe bevel gears 8 and 9, third and fourth bevel gears 10 and 11 are arranged so as to form a meshing-engagement between them. Axes 1 0a and 11 a of the third and fourth bevel gears 10 and 11 are fixed to an output shaft 12 in its radial direction. The output shaft 12 is loosely assembled within a center opening of the first spur gear 5. The top end of the output shaft 12 is formed with a gear section 12a.This gear section 12a is meshingly engaged with a third spur gear 13 fixedly connected to a drive axle 15 for drive wheels 14. The reference numeral 16 denotes an annular housing to coveringly support the axes 10a and 11a.

The gear number of each pair of the first and second output gears 4 and 6, the first and second spur gears 5 and 7, and the first and second bevel gears is respectively equivalent.

Referring to Fig. 2, there is shown a circuit diagram for supplying DC current to the above described revolving force generators 1 and 2.

The refernce numeral 17 denotes a DC power source. The positive terminal of this DC power source 17 is connected to each positive terminal of the first and second revolving force generators 1 and 2 through a leading wire 18 and branch wires 19 and 20. Also the negative terminal of the DC power source 17 is connected to each negative terminal of the first and second generators 1 and 2 through a leading wire 20 and branch wires 21 and 22.

A first switch 24 is interposed in the branch wire 19 before the first generator 1 and also a second switch 23 is interposed in the branch wire 20 before the second generator 2. Further, a resistor 26 is bridgedly connected between the branch wires 19 and 20.

Both switches 24 and 25 are connected to a radio controlled unit 27 through wires 28a and 28b, respectively. This radio controlled unit 27 contains a micro computer which outputs a turn-on or turn-off signal to the first and second switches 24 and 25 in response to a control signal transmitted from a remote place.

Nextly, an operation of the speed chane device according to the first embodiment will be explained in detail.

In order to start this vehicle at a first speed, an user transmits a signal to the radio controlled unit 27 from a remote place. The radio controlled unit 27 receives a start signal and thus outputs a turn-on signal to the first switch 24. The first switch 24 is closed in response to the turn-on signal, so that electric current is supplied to the first revolving force generator 1. The revolving force is transmitted to the first spur gear 5 through the output gear 4. This revolving force is further transmitted to the third andfourth bevel gears 10 and 11 through the first bevel gear 8. On the other hand, an electric current with an extremely small quantity is also supplied to the second generator 2 through the resistor 26. The second generator 2 generates a weak revolving force in the reverse direction to the revolving direction of the second bevel gear 7 which is forcibly revoluted by the third and fourth bevel gears 10 and 11. Thus the second spur gear 7 is prevented from revolving.

The output shaft 12 is revoluted by the revolving force of the third and fourth bevel gears 10 and 11, and then the third spur gear 13 is revolved through the gear section 12a of the output shaft 12. Accordingly, the drive axle 15 is revolved by the third spur gear 13.

Finally, the drive wheels 14 are revolvingly drived.

Nextly, in order to accelerate the vehicle speed; i.e., to shift up to the second speed level, the second switch 25 is turned on in the same manner as the above. The second revolving force generator 2 revolves as the switch 25 is closed. At the same occasion the first generator 1 continues to generate the revolving force. Thus the first spur gear 5 and the second spur gear 7 are revolved by the same revolving force, so that the third and fourth bevel gears 10 and 11 are revolved in the same direction. The output shaft 12 makes the third spur gear 13 revolve at the twice of the first speed. As a result, the drive wheels 14 can revolve at the twice speed.

Fig. 3 and Fig. 4 show second and third embodiments of the speed change device according to the present invention. These second and third embodied devices employ respective planetary gear units 3a and 3b instead of the differential gear unit 3 of the first embodied device, so that the other components and parts are the same as the first embodied device. In Fig. 3 and Fig. 4, the same reference numerals denote the same or corresponding elements shown in Fig. 1, thus the same explanation is not repeated.

In Fig. 3, the reference numeral 3a denotes a planetary gear unit employed in the second embodied speed change device of the present invention. Output gears 4 and 6 of first and second revolving force generators 1 and 2 are respectively meshingly engaged with a first spur gear 5 and a second spur gear 7 independent of the first spur gear 5. The first spur gear 5 is provided with a pair of axes 5a and 5a which are fixed on the one side surface of the gear 5 at redially symmetric positions about a center of the gear 5. A planetary gear 29 is pivotably mounted on each the axis 5a.

This planetary gear 29 is formed with a stepped gear sections consisting of a large diameter gear section 29a and a small diameter gear section 29b. The large diameter gear section 29a is meshingly engaged with a gear section 7a integrally formed with the second spur gear 7. The small diameter gear section 29b is also meshingly engaged with a gear section 12b of an output shaft 12. The output shaft 12 is so assembled as to penetrate a center opening of the first spur gear 5.

The output shaft 12 is meshingly engaged with a third spur gear 13 through a gear section 12a in the same manner as the first embodied device. This output shaft 12 can revolve independent of the first and second spur gears 5 and 7.

The gear number of each pair of the output gears 4 and 5, the first and second spur gears 5 and 7, and the planetary gears 29 and 29 is resectively equivalent.

This second embodied device is also actuated by the same circuit shown in Fig. 2. As the first revolving force generator 1 is actuated, the first spur gear 5 is also revolved.

But the second spur gear 7 is not revolved.

The planetary gears 29, 29 are forcibly revolved by the revolving force of the first spur gear 5. The output shaft 12 is also revolved since the small diameter gear section 29a of the planetary gear 29 meshingly engages with the gear section 12b of the output shaft 12.

As a result, the drive sheels are revolvingly driven in the same manner as the first embodiment.

When the second revolving force generator 2 is actuated, the first and second spur gears 5 and 7 are simultaneously revolved in the same direction. The planetary gears 29, 29 revolve at a twice speed than the first speed revolution caused by only the first generator 1. The output shaft 12 is also revolved at the twice speed. Accordingly, the vehicle can be accelerated to the twice speed.

In Fig. 4, the reference numeral 3b denotes another configuration of planetary gear unit.

An output shaft 12 is integrally formed with a wheel containing an inner gear section 12b.

The inner gear section 1 2b is meshingly engaged with a pair of planetary gears 30, 30.

The planetary gears 30, 30 are pivotably mounted on respective axes 5a, 5a formed on the side surface of a first spur gear 5 at the radially symmetrical two portions about the center of the gear 5. The first spur gear 5 is meshingly engaged with a first output gear 4 of a first revolving force generator 1 through a gear section 5b formed in its circumference. A second spur gear 7 is loosely assembled within a center opening of the first spur gear 5 and meshingly engaged with the planetary gears 30, 30 through a gear section 7b. On the other hand, the second spur gear 7 is meshingly engaged with a second output gear 6 of a second revolving force generator 2 through a gear section 7c.

The output shafts of the first and second revolving force generators 1 and 2 are arranged in parallel each other. The gear number of each pairs of the first and second output gears 4 and 6, and the planetary gears 30 and 30 is equivalent each other.

This third embodied speed change device is actuated by the same circuit shown in Fig. 2.

As the first revolving force generator 1 is actuated, the first spur gear 5 is revolved. Since the second spur gear 7 is not revolved, the output shaft 12 is forcibly revolved through the planetary gears 30, 30 which engage with the inner gear 12b of the output shaft 12.

Further, when the second revolving force generator 2 is actuated, the first and second spur gears 5 and 7 are simultaneously revolved in the same direction. The planetary gears 30, 30 are forcibly revolved at the twice speed as the first speed in the same manner as the second embodiment.

Referring to Fig. 5, there is shown a fourth embodiment which is essentially same as the first embodiment except for a revolution preventing means. Thus the same numerals denote the same or corresponding components or elements of the first embodiment shown in Fig. 1, and the same explanation on the components and the structure of the speed change device is not repeated.

In Fig. 5, the reference numeral 31 denotes a revolution preventing means which comprises a metal ring 31 a made of iron and the like, mounted on a drive shaft 2a of a second revolving force generator 2, and an electromagnetic coil 31b containing an electromagnetic core 31 c. The electromagentic coil 31b is fixed on a base member, not shown, on which this speed change device per se is fixed. One end of the electromagnetic core 31c is extremely close to the metal ring 31a.

This metal ring 31 a is not only limited to the position between the second output gear 6 and the second generator 2, but can be also arranged at the outside of the output gear 6.

Fig. 6 shows an example of circuit diagram for supplying DC energy to the first and second revolving force generators 1 and 2 and the electromagnetic solenoid 31b of the revolution preventing means 31. The numerals 32, 33, 32a, 33a and 34 denote transistors which execute switching operation according to command signal transmitted from a control unit 35 through respective signal communicating wires 36, 37 and 38. The transistors 32 and 32a execute a regular revolving operation of the first generator 1 and the transistors 33 and 33a execute a reverse revolving operation.

The transistor 34 executes a regular revolving operation of the second generator 2 in order to accelerate the vehicle speed to the second speed. The electromagnetic coil 31b is energized when the first generator 1 is only actuated. On the other hand, the electromagnetic coil 31b is not egergized when the first and second revolving force generators 1 and 2 are revolved in their regular direction since both terminals of the electromagnetic coil 31b are kept at the equivalent voltage.

Fig. 7(A) and Fig. 7(B) are side views showing examples of configuration among the electromagnetic solenoid 31 b, the electromagnetic core 31c and the metal ring 31a mounted on the drive shaft 2a. In Fig. 7(A), the electromagnetic core 31 c is formed in a substantially channel section which has a pair of ends parallel to the longitudinal axis of the drive shaft 2a. In Fig. 7(B), the electromagnetic core 31c has a pair of ends formed with an arc section having the same curvature as the metal ring 31a.

An operation of this fourth embodied speed change device will be explained. In order to actuate this vehicle at a first speed, an user transmits a command signal to the control unit 35 from a remote place by means of a radio control system. The control unit 35 outputs signals representing turning-on operation to the transistors 32 and 32a through the signal communicating wire 37. As the transistors 32 and 32a has been truned on, the first revolving force generator is actuated and the electromagnetic coil 31b is energized. The revolving force generated by the first generator 1 is transmitted to the drive axle 15 through the differential gear unit 3 in the same manner as the first embodied speed change device, so that the same explanation on the revolving force transmitted mechanism is not repeated.

On the other hand, the energized coil 31b allows the core 31 c to be attracted to the metal ring 31 a. The output shaft 2a of the second revolving force generator 2 is electromagnetically attracted to the core 31 c; i.e., the generator 2 is locked by the revolution preventing means 31. The revolving force generated by the first generator is not subjected to the counter revolution generated by the second generator 2, so that the torque caused by the first generator 1 is not reduced.

In order to accelarate the vehicle speed, the control unit 35 outputs additionally a signal to the transistor 34 through the communicating wire 38. As the transistor 34 is turned on, the second revolving force generator 2 is actuated. On this occasion, the electromagnetic coil 31b is not energized since its both terminals are applied with the same voltage, so that the drive shaft 2a of the second generator 2 is free from the locked state by the revolution preventing means 31. The first and second generators 1 and 2 are simultaneously revolved and output their revolving force to the differential gear unit 3. The drive axle 15 can be revolved at the second speed, twice as the first speed, in the same manner as the first embodiment as shown in Fig. 1.

In order to move the vehicle in the reverse direction, the control unit 35 outputs a turn-on signal to the transisors 33 and 33a through the wire 36. As the transistors 33 and 33a have turned on, the first revolving force generator 1 is revolved in the reverse direction. At the same occasion, the electromagnetic coil 31b is energized and thus the drive shaft 2a of the second generator 2 is locked by this revolution preventing means 31. Thus, the revolving force in the reverse direction is transmitted to the drive axle 15 in the same manner as the first embodiment.

Fig. 8(A) and Fig. 8(B) show another example of a revolution preventing means instead of the revolution preventing means 31 shown in Fig. 5. In Fig. 8(A), the second spur gear 7 is further integrally formed with or as sembled with a ratchet gear 40, and a pawl 41 adapted to engage with the ratchet gear 40 is pivotably mounted on the base member on which the second generator 2 is fixed. The pawl 41 is always urged by a coil spring 42 so as to engage with the ratchet gear 40.

According to this arrangement, the pawl 41 lockingly engages with the ratchet gear 40 when the first generator 1 revolves in the regular derection, so that the second spur gear 7 is prevented from revolving.

Needless to say, this arrangement can eliminate the electromagnetic coil 31b and core 31c from the circuit diagram shown in Fig. 6.

Further, a cam clutch may be used instead of this revolution preventing means consisting of the ratchet gear 40 and the pawl 41. For example in Fig. 5, this cam clutch may be interposed between the frive shaft 2a and the output gear 6 so that the cam clutch transmits the revolving force generated from the second generator 2 to the second spur gear 7 but does not transmit the revolving force of the second spur gear 7 to the second generator 2. This cam clutch may be used for one-way transmitting means.

Fig. 9 shows a fifth embodiment of the speed change device according to the present invention, which comprises a revolution preventing means in addition to a planetary gear unit identical with the second embodiment shown in Fig. 3. This revolution preventing means is also indentical with the means 31 shown in Fig. 5. The fifth embodied speed change device is actuated by the circuit diagram shown in Fig. 6. The revolving force transmitting mechanism and the revolution preventing mechanism are essentially same as the second and fourth embodiments, so that the same explanation is not repeated.

Fig. 10 shows a sixth embodiment of the speed change device according to the present invention, which comprises a revolution preventing means in addition to the planetary gear unit identical with the third embodiment shown in Fig. 4. This revolution preventing means is also identical with the means 31 shown in fig. 5. The sixth embodied speed change device is actuated by the circuit shown in Fig. 6. The revolving force transmitting mechanism and the revolution preventing mechanism are essentially same as the third and fourth embodiments, so that the same explanation is not repeated.

The revolution preventing means is not only limited to the above described means, but the other means may be also used. For example, the output gear 6 may be a worm gear and the second spur gear 7 may be a worm wheel engaged with the worm gear 6.

In the above described first to sixth embodied devices, the first and second revolving force generators 1 and 2 are actuated by the same power source. This arrangement can eliminate the disadvantage that one power source will be consumed if each power source is provided for each generator and can decrease the energy consumption owing to the change of voltage.

The first, second and third embodiments use the resistor 26 in their control circuit shown in Fig. 2 for preventing the second spur gear 7 from idling since the conter-revolution of the second generator 2 is generated owing to a small quantity current through the resistor 26. This counter-revolution of the second generator 2 and the resistor 26 consume the electric energy in addition to the energy consumed for the first generator 1. Further, if the load is extremely great such as rising along a slope during the first generator is only actuated, the first generator requires a high voltage. Thus the current may not be supplied to the second generator at all and it may be idled. As a result, the required torque may not be transmitted to the drive wheels. However, this system can satisfy the revolution preventing function under the normal load. On the other hand, the fourth, fifth, and sixth embodied devices equipped with the electromagnetic or mechanical revolution preventing means can reduce their energy consumption and can certainly lock the second drive shaft or the second spur gear under any condition.

Thus the required torque can be transmitted to the drive wheels even when the vehicle is driven at a low speed.

It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made in the invention without departing from the spirit and scope as set out in the accompanying claims.

Claims

1. A speed change device comprising; a plurality of revolving force generating means each of which can be independently actuated; a differential gear unit or a planetary gear unit for transmitting the revolving force from said revolving force generating means to a drive means; and an electric control means for actuating said plurality of revolving force generating means individually.

2. The speed change device as set forth in Claim 1, wherein said plurality of revolving force generating means comprises a first electric motor which is actuated at a first speed and a second speed, and a second electric motor which is not actuated at the first speed and actuated at only a second speed.

3. The speed change device as set forth in Claim 1 further comprising a revolution preventing means for preventing an idling revolution of the non-actuated second motor by the revolving force owing to the actuated first motor.

4. The speed change device as set forth in Claim 1, wherein said differential gear unit comprises a first spur gear (5) connected to a first drive shaft of said first motor (1); a first bevel gear (8) integrally formed on the side surface of said first spur gear (5); a second spur gear (7) connected to a second drive shaft of said second motor (2) which is substantially aligned with said first drive shaft of said first motor (1); a second bevel gear (9) integrally formed on the side surface of said second spur gear (7); a pair of third and fourth bevel gears (10) and (11) meshingly engaged with the first and second bevel gears (8) and (9); and an output shaft (12) fixed with the pair of third and fourth bevel gears (10) and (11) which are symmetrically arranged with respect to the longitudinal axis of said output shaft (12), said output shaft being loosely assembled on a center opening of said first spur gear (5) and formed with a gear (12a) meshingly engaged with a third spur gear (13) connected to drive wheels (14).

5. The speed change device as set forth in Claim 1, wherein said planetary gear unit comprises a first spur gear (5) connected to a first drive shaft of the first motor (1), said first spur gear (5) being fixed with a pair of axes (5a) arranged at raidally symmetric position about a center of said first spur gear (5); a second spur gear (7) connected to a second drive shaft of said second motor (2) which is substantially aligned with the first drive shaft of said first motor (1), said second spur gear (7) being integrally formed with a gear section (7a); a pair of planetary gears (29) pivotably mounted on said axes (5a) on said first spur gear (5), said planetary gear (29) being formed with a large diameter gear section (29a) meshingly engaged with said gear section (7a) of said second spur gear (7) and a small diameter gear section (29b); and an output shaft (12) loosely assembled in a center opening of said first spur gear (5), said output shaft (12) being formed with a large gear section (12b) meshingly engaged with said small gear section (29b) of said planetary gears (29) and a small gear section (12a) meshingly engaged with a third spur gear (13) connected to drive wheels (14).

6. The speed change device as set forth in Claim 1, wherein said planetary gear unit comprises a first spur gear (5) connected to a first drive shaft of said first motor (1) and provided with a pair of axes (5a) integrally formed on the side surface of said first spur gear (5) at the radially symmetrical two portions about the center of said gear (5); a pair of planetary gears (30) pivotably mounted on said axes (5a); a second spur gear (7) connected to a second drive shaft of said second motor (2) which is arranged in parallel to said drive shaft of said first motor (1), said second spur gear (7) being loosely assembled within a center opening of said first spur gear (5) and meshingly engaged with a pair of said planetary gears (30); and an output shaft (12) formed with an output gear section (12a) and integrally formed with a wheel containing an inner gear section (12b) which is meshingly engaged with said planetary gears (30), said output gear section (12a) being meshingly engaged with a third spur gear (13) connected to drive wheels.

7. The speed change device as set forth in Claim 1, wherein said electric control means is a circuit containing switches for respective revolving force generating means each of which is alternatively turned on or off in response to a command signal from a remote place by a radio control system.

8. The speed change device as set forth in Claim 7, wherein said circuit further comprises a resistor between the wires connected to the positive terminals of the first and second revolving force generating means so that a small quantity current can be flowed to the second generating means when the first generating means is only actuated.

9. The speed change device as set forth in Claim 3, wherein said revolution preventing means comprises a metal ring (31a) mounted on a drive shaft (2a) of said second motor (2); an electromagnetic coil (31b) electrically connected to a control means for actuating said first and second motors (1) and (2) so that said coil (31b) is energized when said first motor is not actuated; and an electromagnetic core (31c) arranged in said coil (31b) and its top end being extremely close to said metal ring (31a).

10. The speed change device as set forth in Claim 3, wherein said revolution preventing.

means comprises a ratchet gear (40) integrally formed on said second spur gear (7) connected to said second motor (2) and a pawl (41) adapted to engage with said ratchet gear (40) owing to a bias force of a spring (42) when said second motor (2) is not actuated.

11. The speed change device as set forth in Claim 3, wherein said revolution preventing means comprises a cam clutch interposed between the drive shaft of said second motor (2) and an output gear (6) meshingly engaged with said second spur gear (7) so that said cam clutch acts as one-way transmitting means.

12. The speed change device as set forth in Claim 3, wherein said revolution preventing means comprises a worm gear connected to the drive shaft of said second motor (2) and a worm wheel arranged instead of said second spur gear (7) to engage with said worm gear.

13. A drive mechanism comprising a plurality of motors, an output drive shaft, and means for coupling each said motor to the shaft so that the respective motor can rotate the shaft, whereby the speed at which the shaft rotates can be controlled in dependence upon which of the motors is actuated.

14. A toy vehicle comprising a speed change device as claimed in any one of claims 1 to 12 or a drive mechanism as claimed in claim 13.

15. A toy vehicle as claimed in claim 14, including control means whereby the vehicle can be remotely controlled.

16. A speed change device substantially as herein described with reference to any of the accompanying drawings.