How did Honda make its motors smaller and cheaper

Motor miniaturization is now in the face of many automotive enterprises, today we bring you the "car electric drive system thin and short" acceleration series of the second series, to introduce the technology - Honda is how to achieve smaller size and lower cost of the drive motor.

"Honda has a big weapon for electrification," says masaaki betsuka, chief researcher of the second module in the fourth R&d room of the Honda research institute's four-wheel R&d center. The big weapon here is the all-new structural drive motor used on the Honda hybrid (HEV) after 2016. Compared with conventional drive motors, the motors are approximately 23% smaller in size and 23% lighter in weight while maintaining the same output and torque (figure b-1). Therefore, the miniaturization of i-mmd drive system including inverter and reducer is possible. The 2-motor drive system (motor and motor) used in the current accord HEV has a 9.2% reduction in height and 9.7% reduction in width compared to conventional motors.

Honda technology research institute developed a new structure of the drive motor, compared with the conventional motor is smaller and lighter (a, b). As a result, high-efficiency drives (c) have been realized in the wider field. The miniaturization of the motor facilitates miniaturization of the Honda drive system, the i-mmd, resulting in a 9.7% reduction in width and a 9.2% reduction in height (d). (figures (c) and (d) are based on data from the Honda institute of industrial technology)

Because the drive system is smaller, it can be easily deployed horizontally across more models (Mr Betsuka points out). In contrast, for sedan cars, which adopt the drive system size of conventional motors and can be deployed horizontally, mainly take 2 to 3 types of cars.

Honda will use the new structural motors as the standard, and make some modifications according to the requirements of each model, so as to apply to various HEV models. Through mass production of motors with roughly the same structure, the procurement cost and manufacturing cost of parts can be reduced.

increase the deposition rate of coil

To miniaturize the motor, Honda increased the winding percentage (the proportion of copper in the space) to make the stator smaller. By using large square wires as coils, the coverage ratio reached 60% (figure b-2). In conventional motors, which use thin, circular coils, the percentage is typically only 48%.

To miniaturize the stator, the coil USES a square conductor (a) with a large cross-sectional area. Compared with a traditional round coil, a square wire increases the coverage from 48% to 60%. However, the "over current loss" in the conductor (copper) increases as the square line becomes thicker compared to the round line. Over current loss is usually reduced by increasing the slot width of the stator or decreasing the thickness of each coil (b). (figure: based on data of Honda institute of technology)

The over current loss is proportional to the square of the flux density and the thickness of the conductor, respectively. Honda reduces over current losses by reducing the density of the magnetic flux and by thinning the conductors (the coils). Reducing the flux density is mainly achieved by expanding the slot width, but the torque will decrease when the slot width is increased. Therefore, Honda aims to achieve 315Nm torque and adjust the slot width to 4.4mm. To make the conductors thinner, Honda splits the coils side by side, reducing the current flowing through a single coil. Specifically, the coil is divided into two parallel coils, each of which flows through 150A current, and the number of turns is 8. The conductor can be thinner and the loss can be reduced by about 60% compared to the case where 300A flows through a circle with 4 turns.

shorten the end of the coil

To achieve miniaturization, the Honda also shortened the coil protruding from the stator (" coil end ") (figure b-3). Honda technicians said the coil ends "did not contribute to the motor operation".

Compared with the coil end of the old structure, in the neotectonic motor, the coil part protruding from the stator (" coil end ") is shortened, effectively realizing miniaturization (a). In order to shorten the coil end, a new winding method (b) is adopted.

The traditional way of motor is to coil the round coil in advance and then pass it through the radius of the stator core, so that the end of the coil lead wire will be very long. In order to shorten the coil end, a new winding structure method is adopted. First, shape the rectangular coil into a U shape to form a "parallel split coil". Next, insert the split coil in the axial direction of the stator core. After that, the insertion side and the protruding end of the coil on the opposite side are welded together to form a coil.

In the conventional method, the pre-wound round wire coil is inserted from the radius of the stator core. In order to prevent the coil from being clamped, the winding diameter is relatively large and the end of the coil will also become longer. At the same time, after inserting the stator core, many manual processes are involved, such as tying the coil with a rope to prevent it from unraveling, flattening the end of the coil and so on.

New winding process requires investment in new manufacturing equipment. Compared with the traditional process, the new process does not need to be tied with rope, nor does it need to be compressed at the end of the coil, so it is easier to be automated. As a result, high-efficiency mass production can be achieved and the cost can be reduced. In anticipation of surging demand for electric cars in the future, Honda has adopted a process that has the advantage of mass production.

using a low-cost procurement of electromagnetic steel sheet

Another innovation is to consider the increase in the output of the drive motor, the stator USES low-cost and easy to purchase electromagnetic steel plate. In general, stators are made by stacking several layers of thin magnetic steel sheets in order to reduce iron loss. However, thin electromagnetic steel sheets are difficult and expensive to manufacture. In other words, there is a trade-off between the reduction of iron loss and the reduction of cost.

As mentioned above, the loss caused by the coil can be reduced. Although the iron loss is increased, in order to reduce the cost, the electromagnetic steel plate thicker than the conventional motor is finally used. Conventional products have a thickness of 0.25mm, but Honda USES a thickness of 0.3mm. Mr. bakzuka said the thickness of the circulation is large, not only cheap, and easy to purchase.that will be able to remove residues, scrap or scrap batteries and recycle metals," says Goad. He stressed the need to establish an infrastructure of collection points to support these waste streams before large-scale recycling could occur.

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