[adapted from Torqeedo website]
Strong core: Torqeedo torque motors
The motor is the core of a boat drive. With its torque motors, Torqeedo sets new standards in the areas of torque, efficiency and power per weight and volume. The motor which equips the Travel 1003 with the effective power of a 3 HP combustion engine only weighs around half a kg and is about the size of a packet of cigarettes.
In the case of a torque motor, the objective of the design is to use as many factors as possible to maximize the torque. Torqeedo has uncompromisingly optimized the torque motor and, with the introduction of synchronous motors, which come with permanent magnets, are electronically commutated and with external rotor, has created a true torque giant.
However, that is not all: The use of high-tech materials further improves the performance parameters of the Torqeedo torque motors: a Torqeedo motor, such as that used in the Travel 1003 model, uses rare earth magnets instead of hexaferrites.
Altogether, it exceeds a conventional internal rotor motor by 24-fold torque – although it is the same size. Combined with a 1:14 step-down gear, the 1000-watt motor can easily drive a propeller typically used by a 20 HP combustion engine.
The Torqeedo motors also take on a new dimension with regard to efficiency. They experience no excitation current and brush losses: and are equipped with additional, patented control mechanisms, reducing losses to a minimum. The efficiency not only ensures the efficient use of the available battery capacity – it also prevents thermal problems. In this way, Torqeedo can combine high performance with a small structural shape.
Clever brain – the new digital Torqeedo power electronics
The electronic commutation of electric motors described above can generally be either analog or digital. While most providers of electric motors continue to work mechanically using carbon brushes for commutation, Torqeedo has gone two steps further and uses digital power electronics in its new motor models. In contrast to analog-based electronic commutation, digital electronics has a more intelligent power control and handling. This provides more power, more stability and more comfort.
The intelligence of the power control is in its combination of propeller-speed control and control of the power intake. The propeller-speed control regulates the rpm of the propeller, i.e. the motor keeps tightly within the speed specifications and draws whatever power it requires to reach the defined propeller-speed. If, on the other hand, the power consumption is controlled then the drive processes the power made available to it as well as it can and the resultant force is then the speed of the propeller.
What is the practical value of intelligently combining these types of control logic? For example, the Torqeedo electronics functions speed-controlled within low power ranges in order to allow slow maneuvering that is absolutely precise to within a centimeter. In other cases, the electronics controls the motor via the power intake: e.g. to provide a very light boat with a higher final speed or to provide the driver with a defined power level to maximize the range.
Additionally, intelligent control logics allows the motor control to adapt itself to the use of alternative propellers, e.g. when optimizing speed or thrust by using alternative propellers.
Background information on electric motors
There are four criteria for differentiating among electric motors: the frequency response, the generation of the alternating field (commutation), the excitation of the magnetic field, and the structural shape.
Depending on the frequency response, we speak of:
Induction motors: the ratio between the engine speed and the frequency of the supply voltage is not constant: it depends on the loading condition of the machine. The higher the load, the higher the speed difference – the so-called “slip”, i.e. a specified propeller speed is not maintained at higher flow resistances. Hence, thrust is not available at the very time it is required.
Synchronous motors: with this type of motor, the ratio between the supply voltage frequency and the engine speed is constant. As a rule, synchronous engines are torque controlled. This means that they always draw as much power as they need in order
to provide the necessary torque at the desired speed. For this reason, they are the preferred motor in areas with particularly
demanding torque requirements. Should the motor require more power in order to maintain a specified propeller speed, the motor automatically draws more power.
Depending on the type of the generation of the alternating field (commutation), we divide electric motors into:
Mechanically-commutated motors: The brush-complemented motors generate the alternating field necessary for the motor to operate by means of sliding contacts. Based on their geometric organization, these “brushes” convert the power depending on the rotor position. A shortcoming in these motors is the wear-and-tear of the brushes, hence making the motors maintenance-
intensive. The contact resistance also causes so-called brush losses, impairing the degree of effectiveness of the motor.
Electronically-commutated motors: they generate the alternating field necessary for the motor to operate by means of an electronic circuit – the “frequency converter”. This prevents the occurrence of brush losses, and the motors are maintenance-free. The enormous progress that has been made in the area of electronic power components and circuit design has only made it possible in recent times for high-power motors to be manufactured at a marketable price.
Depending on the type of generation of the magnetic field, electric motors are divided into
Electromagnetic-excited motors: this type provides the necessary magnetic field by means of a second loading section. This makes this option more economical: however, it is considerably bulkier and heavier than the permanent magnet-excited motor. Further, it is also considerably less advantageous with regard to power consumption and degree of effectiveness.
Permanent magnet-excited motors: in this case, the permanent magnets generate the necessary magnetic field. Hence, there are no performance losses in the field coils.
Depending on the structural shape, we speak of:
Internal rotor motor: in this classical model of electrical motor, the rotor is surrounded by the stator. The rotor is a revolving motor component attached to the motor shaft: it is also known as a “rotor motor” or “armature”. Since the coils of the internal rotor motor are located on the outside, the motor has advantages when it comes to cooling. Compared to other structural shapes, however, it is relatively low-torque.
Disc armature motor: it generates the torque (= force times lever) by arranging the axle of the magnetic field parallel to the shaft instead of radial to the shaft. This enables the realization of geometries in which the location of the electromagnetic generation of power is a good distance from the axle. Hence, a higher torque is achieved at the same power. The disc armature geometry is disadvantageous to outboard motors with direct water cooling. Due to its extremely large diameter, it isn’t possible to build disc armature motors directly into a pylon.
External rotor motor: this is the most modern type of motor: the coils are arranged inside. The rotating magnets are located on an externally-running bell. With the same structural shape, external rotor motors hence have a significantly higher torque than internal rotor motors.