Two motors in electric vehicles - what tricks do manufacturers use to increase range? [DESCRIPTION]

Electric vehicles have one, two, three, and sometimes four motors. From an economic point of view, one engine is the best option, but some people feel more confident when they have all-wheel drive. But how do you balance the confidence offered by AWD with low power consumption? Manufacturers have several ways to do this.

Multi-motor drives in electrics. How do cars reduce energy consumption?

Table of contents

• Multi-motor drives in electrics. How do cars reduce energy consumption?
  • Method # 1: use the clutch (eg Hyundai E-GMP platform: Hyundai Ioniq 5, Kia EV6)
  • Method # 2: Use an induction motor on at least one axis (eg Tesle Model S / X Raven, Volkswagen MEB)
  • Method # 3: increase the battery discreetly

Let's start from the starting point - a single-axis drive. Depending on the decision of the manufacturer, the engine is located on the front (FWD) or rear axle (RWD). Front-wheel drive In a way, this is a departure from combustion-engine cars: decades ago, it was thought to provide better safety, which is why most early electricians had front-wheel drive. To this day, it is the basic solution in Nissan and Renault (Leaf, Zoe, CMF-EV platform) and models that are conversions of internal combustion vehicles (for example, VW e-Golf, Mercedes EQA).

Tesla abandoned the front-wheel-drive approach from the very beginning, and BMW with the i3 and Volkswagen with the MEB platform, where the basic solution is the engine is located on the rear axle... This is somewhat of a concern for many drivers because front-wheel drive internal combustion vehicles are actually safer in situations close to the gate, but with electric motors, there really isn't much to worry about. Electronics and electrical systems are much faster than mechanical systems in inertial combustion engines.

Simply put, one motor is one set of high-voltage cables, one inverter, one control system. The fewer elements in the system, the less will be the total loss. Because Single-engine electric vehicles will, in principle, be more economical than vehicles with two or more engines.which we wrote about at the beginning.

Besides drivers, he loves all-wheel drive. Some people buy it for better performance, others because they feel safer with it, and still others because they regularly drive in difficult off-road conditions. The electric motors here spoil the engineers: instead of a big, hot, shaking tubular body, we have a sleek, compact design that can be added to a second axle. What to do in such a situation in order not to overdo it with energy consumption and guarantee the owner a reasonable range? Obviously: you must turn off as many engines as possible.

But how to do that?

Method # 1: use the clutch (eg Hyundai E-GMP platform: Hyundai Ioniq 5, Kia EV6)

There are two types of motors used in electric vehicles: an induction motor (asynchronous motor, ASM) or a permanent magnet motor (PSM). Permanent magnet motors are more economical, so their use makes sense wherever maximum range is important. But they also have a significant drawback: permanent magnets cannot be turned off, they create a magnetic field, whether we like it or not.

Since the wheels are rigidly connected to the engine by axles and gears, each ride will result in a flow of electricity: from battery to engine (vehicle movement) or from engine to battery (recuperation). So, if we use one permanent magnet motor on each axle, a situation may arise where one will drive the wheels and the other will brake the car, because it converts mechanical energy into electricity. This is an extremely undesirable situation.

Hyundai has solved this problem by means of a mechanical clutch on the front axle... Its operation is fully automatic, like the Haldex system in combustion cars: when the driver needs more power, the clutch is locked and both engines accelerate (or brake?) The car. When the driver is driving quietly, the clutch decouples the front engine from the wheels, so there is no problem with braking.

The main advantage of the clutch is the possibility of using more economical PSM engines on both axles. The disadvantage is the introduction of another mechanical element into the system, which must withstand high torques and respond quickly to changes. This way the part will gradually wear out - and while it looks fairly simple in design, the level of attachment it has to the drive system makes replacement unlikely.

Method # 2: Use an induction motor on at least one axis (eg Tesle Model S / X Raven, Volkswagen MEB)

Method number 2 has been used longer and more often, from the very beginning it appeared in the Tesla Model S and X, now we can also find it among other Volkswagen MEB platforms, including the VW ID.4 GTX. It lies in the fact that asynchronous motors with electromagnets are installed either on both axles (old Tesla model), or at least on the front axle (MEB AWD, Tesle S / X from the Raven version).... We all know the principle of operation of an electromagnet since elementary school: a magnetic field is created only when a voltage is applied. When the current is turned off, the electromagnet turns into an ordinary bundle of wires.

Therefore, in the case of an asynchronous motor, it is sufficient to disconnect the winding from the power source.that he would stop resisting. The undoubted advantage of this solution is the simplicity of the design, because everything is done using electronics. However, the disadvantage is the lower efficiency of induction motors and the fact that some resistance is created by the rigidly meshed gearbox and the motor itself.

As we already mentioned, induction motors are most often used on the front axle, so their main role is to add power when you need it and not bother when the rider is moving slowly.

Method # 3: increase the battery discreetly

It is worth remembering that the efficiency of electric motors is very high (95, and sometimes 99+ percent). Hence, even with AWD drive with two permanent magnet motors, which always wheel drive (not counting recuperation), the losses in relation to the configuration with a single engine will be relatively small. But they will, and the energy stored in the battery is a scarce commodity - the more we use it for driving, the worse the range will be.

Thus, the third method of increasing the range of electric four-wheel drive vehicles with two PSM motors is to increase the usable battery capacity in a subtle way. Overall capacity may stay the same, usable capacity may vary, so people choosing between RWD/FWD and AWD won't necessarily notice the difference unless the manufacturer says so directly.

We do not know if the method we described is being used by anyone. Tesla in the new 3 performance models gives the buyer access to slightly more usable battery capacity, but here it may turn out that the performance option (Twin motor) in terms of range did not differ from the Long Range (Dual Motor) variant.

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