Electromagnetic Parking Brake for Electric Lawn Mower
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Solution Overview
Problem
Self-propelled electric agricultural mowers face challenges in maintaining control when the engine stops or fails, particularly on sloping ground, due to the risk of spontaneous movement, and existing parking brakes may not be effective or reliable for mowers with brushless electric motors.
Innovation Solution
An electromagnetic parking brake system using permanent magnet electric motors, which can be activated manually or automatically, including a switch to short-circuit the motor windings and generate a resistive torque to brake the mower, ensuring immobility even on slopes, and can function independently of the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional parking brake is used on electric mowers with permanent magnet motors, then the brake can be activated, but it requires additional mechanical components and may not be sufficiently reliable on slopes
Solution Approach 1:
The electric motor with permanent magnets serves dual functions: as a drive motor during operation and as an electromagnetic parking brake when stationary. By short-circuiting the motor windings, the motor generates electromagnetic braking force to prevent mower movement on slopes, eliminating the need for separate mechanical brake components.
Solution Approach 2:
The patent replaces traditional mechanical parking brake systems with an electromagnetic braking mechanism. The braking force is generated through electromagnetic induction in the motor windings rather than mechanical friction, reducing mechanical complexity while improving reliability on sloping surfaces.
2Device complexity
If the parking brake uses the electric motor with permanent magnets, then the system becomes lighter and simpler, but it requires a different braking mechanism than traditional systems
Solution Approach 1:
The existing electric motor components (stator, rotor, permanent magnets, windings) are utilized for both propulsion and braking functions. This multi-functionality approach maintains manufacturing simplicity by using standard motor components rather than requiring specialized brake parts.
Solution Approach 2:
The motor's own electromagnetic structure provides the braking function through short-circuiting its windings. The motor essentially brakes itself using its inherent electromagnetic properties, eliminating the need for external braking mechanisms and simplifying manufacturing.
3Reliability
If the switch is normally closed to provide automatic braking, then the brake activates automatically when power is lost, but it may interfere with normal motor operation
Solution Approach 1:
The switch is configured in the normally closed position, establishing the braking condition in advance. When power is supplied to the motor, the switch opens to disable braking during operation. When power is lost or the mower stops, the switch automatically closes to engage braking, providing fail-safe emergency stopping without interfering with normal operation.
Solution Approach 2:
The switch configuration creates an automatic feedback mechanism: when power is present, the motor operates normally; when power is lost or the motor stops, the switch automatically closes to engage the brake. This feedback loop ensures reliable emergency braking without manual intervention while maintaining ease of operation during normal use.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively prevents the mower from moving by dissipating mechanical energy through induced currents, providing a reliable and lightweight braking solution that maintains stationarity on slopes without the need for continuous power, acting as both a parking brake and an emergency brake.
Implementation Method 1
any rotation of the motor causes a relative displacement between permanent magnets and the windings of the motor. This displacement is then accompanied by induced currents in the windings. The induced currents in turn cause a magnetic field in each shorted winding opposing the rotation of the motor.
Implementation Method 2
The induced currents in turn cause a magnetic field in each shorted winding opposing the rotation of the motor. This results in a dissipation of the mechanical energy supplied to the motor by circulation of currents in the windings of the motor.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The invention relates to an electric mower comprising at least one battery (28) for electrically powering the mower, at least two drive wheels (22a, 22b), and at least one electric motor, with permanent magnets, (16, 20a, 20b) which is coupled to the drive wheels. In accordance with the invention the mower has an electromagnetic parking brake comprising the electric motor. The electromagnetic parking brake can comprise at least one switch (K1, K2, K3, K4, K5) with an open state and a closed state, the switch being connected to terminals (41, 42, 43, 44, 45, 46) of at least one coil (51, 52, 53, 54, 55, 56) of the electric motor, and configured to link the terminals of said coil in a short-circuit, in the closed state.