Electrical transmission or interconnection systems – Switching systems – Plural switches
Reexamination Certificate
1999-06-16
2002-06-11
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Plural switches
C056S016700, C200S541000
Reexamination Certificate
active
06404078
ABSTRACT:
The present invention relates to lawn mowers and in particular to battery powered lawn mowers.
Commercially available types of battery powered lawn mowers usually comprise a cutting deck mounted on four wheels. A battery is mounted on the cutting deck together with an electric motor. The motor rotatingly drives a cutting blade which is located below the cutting deck. A handle is attached to the rear of the deck and which is used by an operator to maneuver the lawn mower. An electric switch is mounted on the handle near to the section gripped by an operator so that the operator can squeeze a lever which operates the switch. A cable runs from the battery to the switch, a second cable runs from the switch to the motor and a third cable runs from the motor to the battery to form an electric circuit. Activation of the switch completes the circuit and thus energizes the motor.
One problem with battery powered mowers is that run time between recharges of the mower is limited and dependent on the size of the battery.
As the size of the battery increases its weight and hence the weight of the overall mower increases, thus reducing the ease of handling and maneuverability of the mower. Therefore, the size of the battery is a compromise between the length of the run time between recharges and the maneuverability of the mower. Therefore, the amount of power which can be stored in the battery and which is available to drive the motor is limited.
It is desirable to maximize the running time of the mower between recharges of the battery.
One way of achieving this is by minimizing the amount of energy wasted through the electric circuit between the battery and motor when the motor is running. The amount of energy lost through electric cables is dependent on the length of the cables. Therefore, it is desirable to minimize the length of the cables of the circuit in order to reduce the amount of energy lost through the cables. This can be achieved by mounting the switch on the deck of the mower, thus avoiding the use of the cables which run from the deck along the length of the handle to the switch.
U.S. Pat. No. 3,564,186 discloses an electric mower having a switch mounted on the deck. The switch is operated by a bowden cable which connects at the other end to a lever mounted on the handle. In battery powered mowers the output voltage of the battery is low, often less than 20 V. Therefore, in order for the motor to generate sufficient power when it is running, it must draw a considerable current from the battery through the interconnecting cables. The amount of power lost through the interconnecting cables is dependent on the square of the value of current multiplied by the resistance of the interconnecting cable I
2
R. Therefore, a small variation in the resistance of the interconnecting cable can have a large effect on the amount of energy lost through the interconnecting cables in a battery powered mower. The problem with the design of the mower disclosed in U.S. Pat. No. 3,564,186 is that the switch is connected to the motor via wires which are require to be attached to the terminals of the switch. This introduces resistive barriers into the electric circuit and thus wastes energy. The amount of energy wasted would be considerable if the design of the mower described in U.S. Pat. No. 3,564,186 was powered by a battery.
Furthermore, due to resistance in the electric circuit there would be a voltage drop between the battery and the motor, thus reducing the voltage supply to the motor and hence the amount of power the motor is able to produce. The requirement to attach wires to the switch also increases production time and costs.
It is desirable to use regenerative breaking in an electrical lawn mower when switching the motor off. Regenerative braking can be induced in the motor when it is rotating after the electrical power to the motor has been disconnected by electrically connecting the terminals of the motor together. Regenerative braking uses the energy stored within the motor to slow the rotation of the motor. This is commonly implemented in a battery powered mower by adding a third cable which runs from the motor to a switch mounted on the handle to enable the switch to connect together the terminals of the motor when it disconnects the electricity supply to the motor. This adds extra cost in providing the additional wiring.
The energy used for the regenerative braking of the motor is lost through the regenerative braking circuit. The amounts of energy can be considerable which result in large potentials and currents being generated. This results in arcing which can damage the components of the regenerative braking circuit. It is therefore desirable to dissipate the energy generated in the regenerative circuit as efficiently as possible. Therefore, in contrast to the electric circuit which is formed whilst the motor is running, it is desirable to introduce into the regenerative electric circuit a resistance through which the energy can be dissipated. Common designs of regenerative circuits and the methods by which a resistance is incorporated are complex and thus expensive.
The object of the present invention is to provide a battery powered mower which overcomes the above problems.
According to the present invention there is provided a battery powered lawn mower which comprises a cutting deck;
an electric motor mounted on the deck;
a battery mounted on the deck and which is in electrical connection with the motor;
a switch mounted on the deck and which forms part of the electrical connection between the battery and the motor, the switch comprising terminals, with the terminals which are in electrical connection with the motor and through which electrical current passes when the motor is running extend from the switch and connect directly to the terminals on the motor.
By extending the terminals of the switch from the switch directly to the terminals of the motor the terminals of the switch act as busbars, providing a solid conductor with a large cross section between the switch and the motor which is capable of transmitting large currents efficiently and with minimal loss between the switch and the motor. Furthermore, the number of interconnections, such as solder joints, connectors etc., in the electrical circuit between the switch and motor is reduced thereby reducing the amount of energy lost through the electrical connection. This is a particularly important feature in a battery powered electric mower in which a large current is drawn through the interconnecting conductors. Any reduction of the resistance of the interconnecting conductors can make a significant reduction in energy losses and thus improve the run time of the mower. Furthermore, because the resistance of the interconnecting conductor is reduced, the voltage drop across the conductors is also reduced. Therefore, the voltage across the electric motor is increased enabling the motor to provide a higher power output due to the increased voltage supply across its terminals. It also simplifies the production process by reducing the number of electrical connections which need to be manufactured and components parts which need to be used, thus saving time and money. It also produces a more robust connection between the switch and the motor. This is an important feature for a mower as the motor and switch and their interconnections are subjected to a considerable amount of vibration when the mower is used.
Preferably, the switch comprises internal connectors which extend from within the switch to form the terminals of the switch. By having one continuous piece of conductive material forming the internal connectors, the terminals of the switch and the interconnection between the switch and the terminals of the motor, the number of interconnections in the electrical circuit between the switch and the terminals of the motor are further minimized. Furthermore, the internal connector, the terminal of the switch and the interconnection between the switch and the terminal of the motor are formed as a single component.
The terminals
Bone Daniel
Thomas Roger
Ballato Josie
Black & Decker Inc.
Harness & Dickey & Pierce P.L.C.
Rios Roberto
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