The invention relates to a drive unit for electrically powered vehicles, especially for electrically driven cycles, for driving at least one wheel.
A motor-wheel drive unit, which comprises a disk-like housing having a rotating section and a fixed section, the rotating section being coupled to the wheel, was disclosed by European patent EP 0 561 268 B1. The fixed section is connected to the cycle frame and serves as carrier for a wheel drive motor, which is powered by a battery, together with a speed reduction gear, which connects the motor on the fixed section to the rotating section. The fixed section finally also has a control circuit component of a control unit, which controls the motor torque according to the torque introduced by way of the pedal drive.
The electrical power is provided by a battery, which is subjected to maximum loading especially on starting of the vehicle, since the electric motor is capable of developing high torques particularly at lower speeds. In the meantime developments in the manufacture of high-voltage current batteries have progressed so that it is now possible, for example with NiCa batteries, to provide high current strengths, at least for brief periods. The disadvantage to this is that such batteries are not only expensive, but also have a limited life. Furthermore, the capacity for recharging is governed by certain rules, in which users of motor-powered cycles are not always prepared to acquiesce. Thus, for example, the recharging of partially discharged batteries presents problems, since the full capacity can no longer be utilized owing to the memory effect. Moreover, comparing a NiCa battery with a lead battery having the same storage capability the purchase costs of the lead battery amount to approximately one fifth of the purchase costs of a NiCa battery. The advantages of lead batteries also lie in their universally regulated disposal and in the fact that toxic cadmium is not used.
The proposed drive unit for electrically powered vehicles relates to a drive solution, the object of which is to act in association primarily with conventional lead storage batteries as battery. Because the battery may be damaged by an excess of current strength through the drive, it is proposed to provide two motors to drive one wheel, the said motors either being electrically connected in series or in parallel by an electronic control unit, or by means of pulse-width modulated actuation in the case of a parallel connection only being loaded in a certain phase. For starting the vehicle it is proposed that the two motors be connected in series and that the electric motors be switched to parallel operation on reaching a certain number of revolutions which corresponds to a slower speed of the vehicle.
Dividing the power between two motors halves the feed cable-related power loss and also halves the voltage drop and peak current, which leads to the following advantages:
The battery is no longer loaded with high peak currents, which means that low-cost lead storage batteries can be used instead of expensive NiCa storage batteries.
By halving the voltage drop it is possible to operate with a lower battery voltage, so that standard batteries can be used.
The lower power consumption means that the battery capacity and hence the weight can be reduced.
A further advantage lies in the fact that the structural design of a drive unit for electrically powered vehicles with two electric motors is more easily manageable than a similar unit with only one motor. A further objective of the proposed design was to keep the costs of providing the electric motors low, an objective which has been impressively achieved by the use of small motors, which are widely available on the market for other purposes.
Finally, another advantage to have emerged is that the power transistors for the modulated current supply of the individual motors are available at low cost and can be better controlled in their thermal reactions than a single power transistor for a large electric motor.
The pulse-width modulated actuation of the two electric motors is used for moderate cycle speeds up to a pulse duty factor of 50%, the current supply phase of one electric motor coinciding with the open-circuit phase of the other electric motor and vice-versa. To spare the battery, the pulse duty factor does not exceed the 50% mark. Only at higher speeds, when the electric motors are running with reduced current strength, is the pulse duty factor between 50% and 100% utilized, 100% corresponding to the top speed of the vehicle.
Another advantage results from the fact that all the control adjustments of the electronic control unit can be performed as a function of the speed. For this purpose it is necessary to continuously compare the number of pedal revolutions with the number of revolutions of the wheel, electrical power being released only at a number of pedal revolutions proportional to the speed in the case of the proposed embodiment of a drive unit. In this way it is ensured by simple means that muscle power is being used to drive the cycle at all times.
Both of the above-mentioned speeds can be scanned in the drive unit. A plurality of magnets is fitted on the circumference of the hub and these are scanned by means of a reed switch in order to sense the speed of the wheel.
A multipole ring magnet is fitted on the planet carrier of the integrated multi-speed hub for sensing the number of pedal revolutions. Two Hall sensors at offset angles of rotation detect the speed and the direction of rotation of the ring magnet through the aluminum housing. Only the changes between the north and south poles of the magnets are used for control purposes. These represent defined angles on the circumference and permit precise control.
For control purposes the angular velocities of wheel and planet carrier are compared. If the difference exceeds a predetermined factor, the drive unit is switched off. By using a factor rather than a fixed value as the default it is possible to switch off substantially faster at higher speeds, which improves safety.
The object of the invention, therefore, is to create a drive unit for electrically powered vehicles, which can be operated with ordinary lead storage batteries and which, integrating the muscle power involved in pedaling, has a measured current supply, which is associated with improved utilization of the battery in order to achieve the maximum possible range for the lowest possible battery weight.
In order to achieve this object a circuit for adjustment of the muscle power, at least two separately actuatable electric motors together with control electronics and a lockup clutch for the freewheel clutch are provided in a common hub body.