WO1993015926A1

WO1993015926A1 - Electric drive system for a child's ridable vehicle

Info

Publication number: WO1993015926A1
Application number: PCT/US1993/001136
Authority: WO
Inventors: Timothy S. Harris
Original assignee: Kransco
Priority date: 1992-02-10
Filing date: 1993-02-09
Publication date: 1993-08-19

Abstract

The invention provides an electric drive system (12) for a child's ridable vehicle (10) of the type which employs a battery power supply (14) and two electric drive motors (16, 18) for imparity motion to the vehicle. One of the two drive motors (16, 18) imparts rotational motion to a driven wheel on each side of the vehicle (10). A selector switch (24) allows the user to change the wiring configuration of the drive motors (16, 18) between a parallel-motor connection which results in high-speed operation and a series-motor connection which result in low-speed operation. In the low speed, series-motor configuration, the drive system (12) produces a differential effect, allowing the motors (16, 18) to operate at different speeds when the vehicle (10) turns a corner, substantially prolonging battery life.

Description

ELECTRIC DRIVE SYSTEM FOR A CHILD'S RIDABLE VEHICLE

Technical Field The invention relates generally to a power drive train for an electric child's ridable vehicle, and more particularly to an improved drive system for providing multiple speeds and a selectably engageable differential in such electric vehicles.

Background Art Toy electric vehicles designed to be ridden by children employ various drive systems, the simplest of which consists of a battery, an on-off switch and a single direct-current drive motor for turning a wheel or an axle on the vehicle. In such a simple system the vehicle operates at only a single speed. More complex drive systems offer multiple or variable speeds, plus forward-reverse. The most powerful toy cars have multiple batteries and multiple drive motors. An example of a more complex drive system for a child's ridable electric vehicle is found in U.S. Patent No. 4,639,646, invented by Harris et al. and owned by the assignee of the present application. The drive system in Patent No. 4,639,646 includes two rechargeable batteries, two drive motors, one on each rear drive wheel, an on-off switch and a forward- reverse selector. Two-speed operation is provided by selectively connecting the two batteries in either series or parallel. In series, the batteries supply "full" voltage to the drive system. In parallel, the batteries supply "half voltage to the drive system. Thus, the vehicle can be operated at either "high" speed or "low" speed. The prior art electric drive system used in Patent No. 4,639,646 is an effective way to produce multiple speeds in toy vehicles without the use of energy-wasting variable resistors or expensive pulse-width-modulation speed controllers.

One disadvantage with prior art toy electric vehicle drive systems such as the one in Patent No. 4,639,646 is the need to carry two batteries on the vehicle in order to provide two-speed operation. Another problem is that the drive motors are connected together in parallel, which wastes battery energy whenever the vehicle is driven around a corner. That is because when the vehicle turns a corner the drive wheels do not rotate at the same rate. The inside wheel turns more slowly but fights to keep up with the speed of the outside wheel, consuming additional battery current as it does so. The result is excessive current drain on the vehicle battery which shortens battery life.

It would be advantageous to have an electric drive system for a child's ridable vehicle which uses a single battery, but which allows for two- speed operation of the vehicle by selecting between alternate wiring configurations of other discreet elements in the drive system, namely, the drive motors. A single battery is less expensive to produce and replace than multiple batteries, and requires less wiring. Heretofore, multiple batteries were generally necessary to provide economical two-speed operation.

It would also be advantageous to provide a child's ridable electric vehicle which has the traction and power associated with two-motor drive trains, but which can accommodate different drive wheel speeds without drawing excessive current. Furthermore, it would be advantageous if a speed selection system was available for a child's ridable electric vehicle which allows the driver to switch between different wiring configurations of the drive motors, at least one of which provides for a differential effect.

Disclosure of Invention An electric drive system with a differential effect is provided for a child's ridable vehicle. The system is preferably used on a vehicle of the type having two direct-current drive motors for propelling the vehicle, one for imparting rotational motion to a driven wheel on each side of the vehicle. At least one pivotable nondriven wheel is also provided on the vehicle for steering. The elements of the drive system comprise a battery power supply for producing a battery voltage to energize the vehicle drive motors, a series connection between the two drive motors of the vehicle, causing current to pass through both drive motors in series, and an operative connection between the battery power supply and the series-connected drive motors. The operative connection between the battery and motors applies the battery voltage across the two series-connected drive motors, producing a voltage drop across each drive motor, when the vehicle is in motion, generally in proportion to the speed of the respective drive motor. The result is a differential effect which permits the drive motors to operate at differential speeds when the vehicle turns a corner, while each motor draws the same current.

The electric drive system for a child's ridable vehicle also provides for speed selectivity on vehicles which carry only a single battery. Speed selectivity is provided using a battery which develops a predetermined voltage at a pair of battery terminals. Two direct-current drive motors, one operatively connected to a driven wheel on each side of the vehicle, are energized by the battery. A motor interconnect selector operatively connects the drive motors in series across the battery terminals for low-speed operation, and connects the drive motors in parallel across the battery terminals for high¬ speed operation. The speed selection system for the vehicle includes the following basic elements: (1) a first wiring configuration for low-speed operation in which the drive motors are operatively connected to one another in series, (2) a second wiring configuration for high-speed operation in which the drive motors are operatively connected to one another in parallel, and (3) a selector for switching between the first and second wiring configurations to change the speed of the drive motors.

In its preferred form, the drive system employs a single solid-gel rechargeable battery with a nominal battery voltage of 18-volts. The vehicle has a maximum speed of less than 8-miles-per-hour when in the high-speed > wiring configuration and a maximum speed of less than 4-miles-per-hour when in the low-speed wiring configuration.

Brief Description of the Drawings Fig. 1 is a partial, schematic, perspective view of a child's ridable vehicle shown in phantom, with the major parts of the vehicle's wiring, incorporating the electric drive system of the present invention, shown with solid lines.

Fig. 2 is a partially schematic circuit diagram showing the major elements of the vehicle wiring of Fig. 1, including the speed selection system and the system for providing a differential effect in accordance with the present invention. Detailed Description of the Preferred Embodiment and Best Mode for Carrying Out the Invention Referring to Fig. 1, a child's ridable toy electric vehicle 10 is shown in phantom. Certain parts of vehicle 10, such as the seats, trunk lid, battery housing, and other elements unnecessary to the explanation of the present invention, have been deleted from the phantom image to more clearly show the key parts of the vehicle drive system 12. The vehicle drive system includes the electrical devices and wiring harness used to transmit power from the vehicle's battery power supply 14 to a pair of direct-current drive motors 16, 18 which impart motion to the vehicle. The other parts of the drive system include the wiring between battery 14 and motors 16, 18, a forward-reverse selector switch 20, an on-off switch 21 mounted on the floorboard in the driver's position covered by a simulated gas pedal 22, and a high-low speed selector switch 24 mounted on the dashboard or at another convenient location on the vehicle. Numerous other devices (not shown) may also be coupled to the electrical system of the vehicle, including a horn, headlights, a speed selector and other accessories. The vehicle illustrated in Fig. 1 includes only the basic elements necessary to fully describe the drive system of the present invention. Vehicle 10 is a toy electric vehicle designed to be ridden in by one or two children. It has four wheels, only two of which are shown in the phantom image of Fig. 1, which illustrates the right side of the vehicle. The left side of vehicle 10 is a mirror image of that shown in Fig. 1. Right side rear wheel 30 is a driven wheel, rotationally driven by drive motor 16. The mechanical connection between the right drive motor 16 and the right rear driven wheel 30 is shown in Fig. 1 as a connecting shaft 31 between the motor and the wheel hub. Alternatively, motor 16 can be mechanically coupled to driven wheel 30 by any other type of suitable mechanical linkage, such as a belt or chain transmission or the like. The left side wheel 33 (partially shown in Fig. 1), on the opposite side of the vehicle from wheel 30, is rotationally driven by drive motor 18 in the same manner (not shown) as wheel 30. As such, one of the motors 16, 18 imparts rotational motion to a driven wheel on each side of the vehicle.

The front wheels of vehicle 10 are not operatively coupled to drive motors and are referred to as nondriven wheels. The forward right side nondriven wheel 32 is visible in Fig. 1. An identical forward left side nondriven wheel (not shown) is provided on the left side of vehicle 10. The nondriven front wheels are pivotable for steering vehicle 10. Preferably, the front nondriven wheels are mounted on kingpins, or another suitable type of pivotable mount, and a conventional steering linkage is provided between steering wheel 34 and the front pivotable wheels. The details of the steering mechanism are not shown in Fig. 1, since such systems are well known. A suitable steering system for pivoting the front wheels of vehicle 10, including kingpins for the front wheels and linkages between the steering wheel and the wheel pivots, is shown in Figs. 2-4 of U.S. Patent No. 4,709,958, the disclosure of which is incorporated herein by reference.

Battery 14 is the power supply for vehicle 10, providing energy to operate the vehicle. The battery develops a predetermined voltage, called the battery voltage, at a pair of battery terminals 40, 42. Battery 14 is preferably a solid-gel rechargeable battery with a nominal predetermined voltage of 18-volts between terminals 40, 42. The vehicle shown in Fig. 1 is a toy version of a rear-engine car, such as a Porsche. Consequently, battery 14 is installed in the trunk of the vehicle and would typically be covered by a housing which resembles or simulates an automotive engine.

Battery 14 is coupled through a two-wire connector plug 45 to the remainder of the wiring harness of vehicle 10. Connector plug 45 is shown in Fig. 2 separated into two halves, 45a and 45b, representing the negative and positive leads of the vehicle wiring. Respective negative and positive battery connector wires 48, 49 operatively connect battery 14 to the remainder of the drive system through connectors 45a, 45b, respectively. Connector plug 45 allows quick disconnection of battery 14 from the remainder of the wiring harness and allows an external charger to be connected to the battery for recharging. A pair of wiring harness connector wires 50, 52 extend between battery connector 45 and forward-reverse switch 20, which is preferably mounted near the driver's position. A switch arm 44 which simulates a gear shift lever, operates switch 20. Forward-reverse switch 20 is a conventional double-pole double-throw switch which passes battery voltage from input wires 50, 52 to output wires 56, 58 in either standard or reverse polarity.

Battery voltage on lines 50, 52 is carried to input terminals 60, 62, respectively of switch 20. When the switch contacts are in the configuration shown in Fig. 2 (the forward position), a direct connection is made between input terminals 60, 62 and the respective output terminals 64, 66, and the polarity of switch output lines 56, 58 is the same as input lines 50, 52. If switch 20 is placed in the reverse position, input terminals 60, 62 are connected to reverse terminals 68, 70, respectively. In the reverse position, the polarity of the voltage across output lines 56, 58 is the reverse of the polarity on input lines 50, 52, respectively. Switch 20 determines the rotational direction of motors 16, 18 and the direction of vehicle operation.

Leads 56, 58 carry the output of switch 20 to motors 16, 18 through an on-off switch 21 mounted on the floorboard. Switch 21 is preferably a double-pole switch biased into the open position shown schematically in Fig. 2. The switch is operated by the driver stepping on a simulated gas pedal 22, which closes the contact between switch terminals 82, 84 to supply battery power to motors 16, 18. Stepping on pedal 22 also breaks or opens the connection between secondary switch terminals 84 and 86, the latter being connected to a dynamic brake resistor 90. When gas pedal 22 is released, the connection between terminals 82, 84 is opened and the connection between terminals 84 and 86 is closed. If vehicle 10 is in motion when the gas pedal is released, motors 16, 18 act as generates, producing a current which is dissipated in heat by dynamic brake shunt resistor 90. The result is dynamic braking which helps slow the vehicle. An important feature of the electric drive system of the present invention is the selective motor interconnection system provided by high-low switch 24. Switch 24 determines how the battery voltage available on motor input lines 58 and 92 is applied to motors 16, 18. Two motor wiring configurations are provided by switch 24, which is a double-pole double-throw switch like forward-reverse switch 20. The first wiring configuration between motors 16 and 18, for low-speed operation of the vehicle, is a series connection between the motors. When switch 24 is positioned so the right-side terminals are connected (terminals 96, 98 connected, respectively, to terminals 100, 102), motors 16, 18 are connected together in series. In that switch position, which is the opposite of the position shown in Fig. 2, motors 16, 18 operate only at low speed. Consequently, that configuration is called the "low-speed" configuration, or the first configuration. In the low-speed configuration, current passes through both drive motors in series and the voltage drop across each drive motor, when the vehicle is in motion, is divided between the motors, generally in proportion to the speed of each respective drive motor. The sum of the voltage drops across motors 16 and 18 totals the full battery voltage carried between lines 92 and 58. As illustrated schematically in Fig. 2, if the voltage between lines 92 and 58 is 18-volts, which is the preferred nominal voltage of battery 14, the voltage between the terminals 112, 114 of motor 16 will be 9-volts and the voltage between the terminals 116, 118 of motor 18 will be 9-volts, assuming the motors are operating at equal speeds with an equal load on each motor.

A second wiring configuration, for high-speed operation of motors 16, 18, is provided when switch 24 is repositioned to the position shown in Fig. 2. In the "high-speed" configuration, switch 24 connects terminal 96 with terminal 104 and connects terminal 98 with terminal 106. Simultaneously, when switch 24 is in the high-speed position, terminal 96 is disconnected from terminal 100 and terminal 98 is disconnected from terminal 102. The result is a parallel connection between motors 16, 18, in which the full battery voltage between lines 92 and 58 is applied across each drive motor. The higher motor speed resulting from this second motor wiring configuration is due to the higher voltage applied to the motors.

Selector switch 24 is a toggle or rocker switch mounted on the dashboard of the vehicle. Switch 24 could also be combined with or positioned in close proximity to forward-reverse switch 20. A vehicle wired in accordance with Fig. 2 can be operated in either the forward or reverse direction at either the high or low speed. Preferably, as a safety measure, a mechanical or electrical interlock (not shown) is provided to disable high-speed operation of the vehicle when switch 20 is in the reverse position. That would prevent a child from operating the vehicle in reverse at high speed, which could be dangerous. One suitable means for providing an interlock to prevent high¬ speed reverse operation would be to install a cut-out switch on branch line 120 (not shown) which is mechanically tied to forward-reverse switch 20 and opens whenever switch 20 is placed in the reverse position. That would automatically cut the battery connection to high-speed switch terminal 104 and disable motors 16, 18 whenever switch 20 is in the "reverse" position. Other suitable types of high-speed-reverse safety interlocks will occur to those skilled in the art. When selector switch 24 is in the low-speed position and a series connection is created between drive motors 16, 18, a differential effect is produced. By differential effect, what is meant is the effect of a mechanical differential on a car or other full-size vehicle in which the drive wheels are allowed to turn at different speeds. When motors 16, 18 are interconnected in series, the motors each receive the same current flow since the current passes through both drive motors in series. If the vehicle is turning a corner, the driven wheels 30, 33, and the motors which independently turn them, do not turn at the same rotational rate. The inside motor turns more slowly than the outside motor and each motor experiences a different load. As a result, the voltage drop across each motor automatically adjusts to balance the load requirements of that respective motor.

As an example of the differential effect, if vehicle 10 is turning to the left, in a circle, with switch 24 in the low-speed position, the driven wheel 33 on the left side of the vehicle, driven by motor 18, will turn more slowly than right side driven wheel 30, driven by motor 16. Assuming the full battery voltage of 18-volts is applied across the series-connected motors 16, 18, the voltage between lines 92 and 58 (in Fig. 2) will be 18-volts. Since inside motor 18 is turning more slowly, it will draw less power than outside motor 16. A typical division of voltage drops between motors 16 and 18 under such circumstances is a voltage drop of 7-volts across the input terminals of the inside motor 18 and a voltage drop of 11-volts across the input terminals of the outside motor 16. When vehicle 10 is turning to the right, the respective voltage drops across motors 16, 18 would be reversed. In general, when the vehicle is in motion, the voltage drop across each motor is generally in proportion to the speed of the motor. The total voltage drop across both motors always remains at full battery voltage, 18-volts. Examples of the amount of current drawn from the battery in both the high- and low-speed configurations will serve to illustrate the benefits of low-speed operation in prolonging battery life. With an 18-volt battery, the drive system at high speed draws approximately 16-amps of current, 8-amps for each drive motor. At low speed, the total current drawn from the battery is approximately 8-amps through both motors. If the vehicle is rounding a corner during high-speed operation, the inside (slower) motor sometimes will draw 11- amps or 12-amps or more, in an attempt to keep up with the outside motor, substantially increasing the total current drawn from battery 14 beyond the 16- amp norm for high-speed operation. At the low-speed setting, the total current drawn from the battery remains generally equal to 8-amps, regardless of whether the vehicle is turning a corner or going straight. By reducing the current demand on the vehicle battery power supply, both the life of the battery and the interval between recharges is extended. Consequently, use of the drive system with differential effect substantially increases battery life. The present invention provides an electric drive system with a differential effect which is usable on any child's ridable vehicle of the type which has two direct-current drive motors, one of which imparts rotational motion to a driven wheel on each side of the vehicle. The low-speed series- connected motor configuration helps prolong battery life and increases the recharging interval by reducing current demand from the battery, particularly when the vehicle is frequently driven around corners. It may even be desirable to eliminate the optional high-speed configuration and provide a child's ridable vehicle with only series-connected drive motors. For example, in some vehicles sold by the assignee of the present invention, a protective device accessible only with tools not generally usable by children, can be installed to disable the high-speed operation of the vehicle until a child is familiar enough with its operation to operate it at high speed. As an alternative embodiment of the present invention, switch 24 can be omitted entirely from the circuitry of the drive system. Instead, motors 16, 18 could be permanently joined together in series by connecting a wire 122 between terminal 114 of motor 16 and terminal 116 of motor 18 (as shown with dashed lines in Fig. 2). Such an alternative vehicle drive system would always operate with a differential effect.

Other alternative embodiments of the present invention will occur to those skilled in the art. For example, reference has been made to a single 18-volt battery for use with the present invention. While the inventor prefers using such a relatively high-voltage battery, the drive system of the present invention will function well with a battery having a voltage generally in the range of 16-volts to 20-volts. Higher-voltage batteries, should they become available at reasonable cost for use on toy ridable vehicles, would also be suitable for use of the present invention. The drive system may also be used on vehicles having only a single nondriven wheel which is pivotable for steering the vehicle. Other alternative embodiments are possible within the scope of the present invention.

Industrial Applicability The invention provides an electric drive system for a child's ridable vehicle of the type which employs a battery power supply and two electric drive motors for imparting motion to the vehicle. The invention allows for two-speed operation of the vehicle through selective connection of the motors to the battery power supply in either a series or parallel configuration. The electric drive system and speed selection system is suitable for use on children's electric vehicles which operate at a maximum speed of 8-miles-per- hour in the high-speed configuration and at a maximum speed of 4-miles-per- hour in the low-speed configuration. The actual speed of operation for vehicle 10 is preferably 6-miles-per-hour at high-speed and 3-miles-per-hour at low- speed. The system also provides a differential effect on any child's ridable vehicle which has two drive motors, one of which imparts rotational motion to a driven wheel on each side of the vehicle, the differential effect resulting when the drive motors are wired in series. The invention is particularly applicable to toy ride-on vehicles with simple controls which allow for two- speed operation.

The present invention provides a drive system for a child's ridable vehicle which can provide two-speed operation without the need for two batteries on the vehicle. Instead, two-speed operation is provided by switching between series and parallel motor connections. Moreover, the drive system provides a differential effect when the motors are connected in series, which prolongs battery life and lengthens each charging cycle by reducing the current demands on the battery.

Claims

WHAT IS CLAIMED IS:

1. An electric drive system with differential effect for a child's ridable vehicle of the type having two direct-current drive motors for propelling the vehicle, one of the motors imparting rotational motion to a driven wheel on each side of the vehicle, and the vehicle having at least one nondriven wheel which is pivotable for steering, the drive system comprising: a battery power supply for producing a battery voltage to energize the vehicle drive motors, a series connection between the two drive motors of the vehicle wherein current passes through both drive motors in series, and an operative connection between the battery power supply and the series-connected drive motors which applies the battery voltage across the two series-connected drive motors producing a voltage drop across each drive motor, when the vehicle is in motion, generally in proportion to the speed of the respective drive motor, whereby the drive motors can operate at different speeds while drawing the same current, resulting in a differential effect when the vehicle turns a corner.

2. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the battery power supply produces a battery voltage generally in the range of 16-volts to 20-volts.

3. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the battery power supply is a single battery carried on the vehicle producing a single battery voltage. 4. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the electric differential is part of an electric drive system for a child's ridable vehicle which has a maximum speed of less than 8-miles-per-hour, and in which the battery voltage applied across the two series-connected drive motors is nonadjustable and is generally in the range of 16-volts to 20-volts.

5. A drive system including an electric differential for a child's ridable vehicle as in claim 4 including means for disconnecting the series connection between the two drive motors and for selectively making a parallel connection between the two drive motors in which the full battery voltage is applied across each drive motor, whereby the differential effect resulting from the series connection between the drive motors is lost and the drive motors operate at a higher speed than when connected in series, including means for selectively reconnecting the series connection and for disconnecting the parallel connection between the drive motors to provide for selective two-speed operation of the vehicle.

6. A drive system including an electric differential for a child's ridable vehicle as in claim 1 in which the battery power supply is a single battery with a fixed output battery voltage generally in the range 16-volts to 20-volts, and the speed of the vehicle when propelled by the two series- connected drive motors, is less than 5-miles-per-hour.

7. A drive system including an electric differential for a child's ridable vehicle as in claim 6 in which the battery which forms the battery power supply is a solid-gel rechargeable battery with a nominal battery voltage of 18-volts. 8. An electric drive system for a child's ridable vehicle, comprising: a battery for providing energy to operate the vehicle, the battery developing a predetermined voltage at a pair of battery terminals, two direct-current drive motors, one drive motor being operatively connected to a driven wheel on each side of the vehicle, and a motor interconnect selector for operatively connecting the drive motors in series across the battery terminals for low-speed operation of the vehicle and for operatively connecting the drive motors in parallel across the battery terminals for high-speed operation of the vehicle.

9. An electric drive system for a child's ridable vehicle as in claim 8 including a single battery on the vehicle for providing energy to operate the vehicle, and in which the battery produces a predetermined voltage generally in the range of 16-volts to 20-volts.

10. An electric drive system for a child's ridable vehicle as in claim 8 in which the vehicle has two rear wheels and each of the two drive motors is operatively connected to one of the rear wheels of the vehicle.

11. A electric drive system for a child's ridable vehicle as in claim 8 in which the battery has one pair of battery terminals and the predetermined voltage across the terminals is generally in the range of 16-volts to 20-volts, and the drive system produces a maximum vehicle speed of 4- miles-per-hour during low-speed operation and a maximum vehicle speed of 8- miles-per-hour during high-speed operation. 12. An electric drive system for a child's ridable vehicle as in claim 8 including a single battery for providing the energy to operate the vehicle, the battery being a solid-gel rechargeable battery with a nominal predetermined voltage of 18-volts.

13. A speed selection system for a child's ridable electric vehicle of the type having a battery power supply which develops a predetermined battery voltage and having at least two drive motors for imparting motion to the vehicle, the speed selection system comprising: a first wiring configuration for low speed operation of the drive motors in which the drive motors are operatively connected to one another in series and the battery voltage is applied across all the series-connected drive motors, whereby the battery voltage is divided between the drive motors, a second wiring configuration for high speed operation of the drive motors in which the drive motors are operatively connected to one another in parallel and the full battery voltage is applied across each drive motor, and a selector for switching between the first and second wiring configurations to change the speed of the drive motors.

14. A speed selection system for a child's ridable vehicle as in claim 13 in which the vehicle has two drive motors, one of the motors being operatively connected to a driven wheel on each side of the vehicle.

15. A speed selection system for a child's ridable vehicle as in claim 14 in which the vehicle has two rear wheels and each of the two drive motors is operatively connected to one of the rear wheels of the vehicle. AMENDED CLAIMS

[received by the International Bureau on 12 July 1993 (12.07.93); original claims 1, 4-9 amended; other claims unchanged (4 pages)]

1. An electric drive system with differential effect for a child's ridable vehicle of the type having two direct-current drive motors for propelling the vehicle, one of the motors imparting rotational motion to a driven wheel on each side of the vehicle, and the vehicle having at least one nondriven wheel which is pivotable for steering, the drive system comprising: a battery power supply for producing a low-voltage battery voltage to energize the vehicle drive motors, a series connection between the two drive motors of the vehicle wherein current passes through both drive motors in series, and an operative connection between the battery power supply and the series-connected drive motors which applies the battery voltage across the two series-connected drive motors producing a voltage drop across each drive motor, when the vehicle is in motion, generally in proportion to the speed of the respective drive motor, whereby the drive motors can operate at different speeds while drawing the same current, resulting in a differential effect when the vehicle turns a corner.

3. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the battery power supply is a single battery carried on the vehicle producing a single battery voltage.

4. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the electric drive system produces a maximum speed of less than 8-miles-per-hour, and in which the battery voltage applied across the two series-connected drive motors is nonadjustable and is generally in the range of 16-volts to 20-volts.

5. An electric drive system with differential effect for a child's ridable vehicle as in claim 4 including means for disconnecting the series connection between the two drive motors and for selectively making a parallel connection between the two drive motors in which the full battery voltage is applied across each drive motor, whereby the differential effect resulting from the series connection between the drive motors is lost and the drive motors operate at a higher speed than when connected in series, including means for selectively reconnecting the series connection and for disconnecting the parallel connection between the drive motors to provide for selective two-speed operation of the vehicle.

6. An electric drive system with differential effect for a child's ridable vehicle as in claim 1 in which the battery power supply is a single battery with a fixed output battery voltage generally in the range 16-volts to 20-volts, and the speed of the vehicle when propelled by the two series- connected drive motors, is less than 5-miles-per-hour.

7. An electric drive system with differential effect for a child's ridable vehicle as in claim 6 in which the battery which forms the battery power supply is a solid-gel rechargeable battery with a nominal battery voltage of 18-volts.

8. An electric drive system for a child's ridable vehicle, comprising: a battery power supply for providing energy to operate the vehicle, the battery power supply developing a predetermined low-level voltage at a pair of battery power supply terminals, two direct-current drive motors, one drive motor being operatively connected to a driven wheel on each side of the vehicle, and a motor interconnect selector for operatively connecting the drive motors in series across the battery power supply terminals with the full battery voltage being divided between the two drive motors for low-speed operation of the vehicle, and for operatively connecting the drive motors in parallel across the battery power supply terminals with the full battery voltage being supplied across each of the two direct-current drive motors for high-speed operation of the vehicle.

9. An electric drive system for a child's ridable vehicle as in claim 8 wherein the battery power supply is a single battery on the vehicle for. providing energy to operate the vehicle, and in which the battery produces a predetermined voltage generally in the range of 16-volts to 20-volts.

11. A electric drive system for a child's ridable vehicle as in claim 8 in which the battery power supply has one pair of battery power supply terminals producing a predetermined voltage across the terminals generally in the range of 16-volts to 20-volts, the drive system producing a maximum vehicle speed of 4-miles-per-hour during low-speed operation and a maximum vehicle speed of 8-miles-per-hour during high-speed operation.

12. An electric drive system for a child's ridable vehicle as in claim 8 wherein the battery power supply is a single battery for providing the energy to operate the vehicle, the battery being a solid-gel rechargeable battery with a nominal predetermined voltage of 18-volts.

13. A speed selection system for a child's ridable electric vehicle of the type having a battery power supply which develops a predetermined battery voltage and having at least two drive motors for imparting motion to the vehicle, the speed selection system comprising: a first wiring configuration for low speed operation of the drive motors in which the drive motors are operatively connected to one another in series and the battery voltage is applied across all the series-connected drive motors, whereby the full battery voltage is divided between the drive motors, a second wiring configuration for high speed operation of the drive motors in which the drive motors are operatively connected to one another in parallel and the full battery voltage is applied across each drive motor, and a selector for switching between the first and second wiring configurations to change the speed of the drive motors.

15. A speed selection system for a child's ridable vehicle as in claim 14 in which the vehicle has two rear wheels and each of the two drive motors is operatively connected to one of the rear wheels of the vehicle.