DE19955863A1 - Electrically-assisted bicycle uses biomechanical movement direction sensor for activating and de-activating different operating regions of electric motor characteristic field - Google Patents

Abstract

The electrically-assisted bicycle has an electric motor (2) coupled to an electronic control (1) dependent on the signal from a bicycle velocity indicator (11) and a signal from a biomechanical movement direction sensor (8). The electronic control defines limits for the mechanical motor parameters, e.g. the revs, output and torque, detected from the motor electrical parameters, with the motor characteristic field divided into motor operating regions which are activated and de-activated via the biomechanical movement direction sensor.

Description

The invention relates to a vehicle with an auxiliary electric drive, especially electric bike with an electric motor, a Driving speed sensor (setpoint device) for an electronic Control for controlling the motor and with a biomechanical Direction of movement sensor.

In order to obtain the freedom of registration of a vehicle, it is important to comply with the relevant provisions of the STVZO. The two following vehicle classes exist among others:

• a) Vehicles with a design-related maximum speed below 6 km / h, which are not subject to approval (according to the currently valid STVZO).
• b) Bicycles with electric auxiliary drive that are approval-free are when the power of the electronic auxiliary drive Does not exceed 250 watts, the engine power is only available, when pedaling forward and support at the same time the engine is reduced from 20 km / h so that at high speed speeds greater than or equal to 24 km / h no more motor support is available (according to the currently valid STVZO or according to the practitioner approval).

The crucial criterion for distinguishing these Vehicle classes is forward pedaling. This is done not, the vehicle can be classified in category a), when the engine characteristic ends at 6 km / h, i.e. from this speed excess power is no longer delivered.

If there is forward pedaling, the Motor characteristic of a bicycle with auxiliary drive by category b) correspond. According to current practice, the engine is allowed deliver a maximum power of 250 W and its idling speed must not exceed 24 km / h.

So while a vehicle of category a) also an assistant drive with a power greater than 250 W, this is the case not in the second category in the entire speed range allowed. For the switchover, it is therefore also necessary for Category a) the engine power to max. Limit 250 W.

A vehicle with is a complex implementation of this concept two motors, each with one of the two characteristics. Becomes forward pedaling is detected, so the motor Category b) switched on, otherwise category a). In both cases, a separate setpoint generator controls the speed of the engines.

The engine is controlled according to the current state of the art via a pulse width modulated voltage signal (PWM). In that case the maps are realized by limiting this PWM signals to the minimum of the setpoint generator and a limit value signal. The limit value signal itself is derived from a regulation of the Engine torque and engine power depending on the Engine speed won. In the case of a wheel hub motor, these are Parameters without additional electromechanical sensors on the motor accessible because it consists of motor voltage, motor current and possibly Have the engine temperature derived.  

The object of the present invention is to belong to a To obtain vehicle in two different vehicle classes. This should be possible with little effort.

To solve this problem it is proposed that the controller defined limits for certain mechanical motor parameters such as speed, power and possibly torque, which without additional, electromechanical transducers from the electrical state variables of the motor are derived with their Help the engine map in approval-free engine operating areas is divided by means of the biomechanical direction of movement sensors are activated or deactivated.

By skillful use of the vehicle's electronic controls the use of a second motor can thus be avoided. By the control can vary the characteristic so that the second Engine is simulated by the controller. This is a map the corresponding engine map in the control. By Using a microcontroller can make this tamper-proof happen.

By detecting the pedaling movement, two different ones can be used Operating modes of the vehicle can be distinguished. This classify two different types of vehicles, based on their engine different requirements are set in the STVZO. By evaluating the engine map and switching the Limiting function depending on the pedaling movement can, for. B. the design-related maximum speed are specified, and the maximum engine power can be adjusted. This ensures you optimal driving pleasure with regard to an with an electric Auxiliary engine equipped bike without the freedom of registration to give up. There is no for the evaluation of the map additional sensor effort is necessary, since the process involves a measurement of the motor current alone can be realized. In particular, there is no measurement of the vehicle speed or the engine speed is necessary.  

Regardless of the vehicle category, the driver has one Setpoint adjuster (accelerator pedal, twist grip, etc.) influence the Engine power. The switching of the maps can be done by ramps this setpoint into a steady important for driving comfort Transition. In addition, limits can be set by technical point of view are necessary, e.g. B. as protection against overload of the engine or its components, integrated in the map become. It offers z. B. on, the torque of the engine too limit.

A map can be calculated from the engines, so that at given motor voltage and given motor current is determined how the engine turns quickly and the power it delivers. Through a Control algorithm, e.g. B. a PID method, a specific Approach the point in the motor diagram. In particular, it is possible to define special curves in the motor diagram as limit values and to ensure via the control loop that these are not exceeded become. A wheel hub motor is also preferably used to a direct assignment of engine speed to vehicle speed to have. It should be noted that an engine freewheel this assignment not significantly affected because whenever the engine Outputs power or torque to the vehicle, including the assignment of speed and speed is given.

A setpoint generator is available to the driver as the operating device Available, e.g. B. a twist grip. In the further this signal also referred to as setpoint request. There is also a sensor that forward pedaling senses.

It is also assumed that a map for the Engine power is available. The engine torque is always limited to a maximum value determined by the mechanics, it a complex map is therefore not necessary. For the map there is a PID controller that has an upper control variable Limiting value for the PWM control of the motor provides. The actual control is then the minimum of the time  ramped setpoint request and the limits.

The following categories, which have nothing to do with the previous STVZO, are to be distinguished as categories for the approval:

• a) Vehicles with a design-related maximum speed below 10 km / h, which are not subject to approval.
• b) Bicycles with electric auxiliary drive that are approval-free are when the power of the electric auxiliary drive is 300 W. does not exceed, the engine power is only present if pedaling forward and support at the same time the engine from 25 km / h is reduced so that at speed speeds greater than or equal to 28 km / h no more motor support is present.

However, the decision for admission is the transition between the two vehicle categories.

1) Operating behavior of the vehicle according to category a)

The power is allowed for low speeds up to a maximum value of 300 W can be freely selected. For engine speeds that one Vehicle speed above 10 km / h, it must Be zero. The map needs for smooth driving still a transition range from z. B. 7 km / h to 10 km / h, where the Values e.g. B. linearly reduced.

2) Operating behavior of the vehicle according to category b)

The max. Performance is up to a speed of 25 km / h 300 W. Between 25 km / h and 28 km / h it is reduced to zero, this can e.g. B. linear.

3) Change from category a) to category b) by inserting the forward pedaling

The switch to category b) is done by the second map for torque and power is activated. Because in this case possibly more power is released than in the map of the Category a), it is necessary the driver's setpoint request temporarily set to the currently output PWM ratio and then slowly ramp up again to the current desired value. This ensures a smooth, therefore smell-free transition between the Driving characteristics of the two vehicle categories created.

4) Change from category b) to category a) by suspending the forward pedaling

In this case it can be assumed that the driver is traveling at high speed strives for reduction. Therefore the control of the motor in this case also discontinuous to lower powers and torques be changed. So it simply becomes the map for category a) activated. One can assume that this map does not can specify higher limit values, but only lower ones. Therefore the drive is temporarily switched off in certain cases become.

In summary, there are innovations:

• - The control algorithm for engine control is independent of the approval category.
• - The vehicle speed has no influence on the assignment of the vehicle in one of the registration categories. The speed speed therefore does not change the control strategy or has none Influence on the selection of the map and thus on the Driving behavior of the vehicle.
• - The signal from the pedal sensor is solely responsible for which category the vehicle is classified.
• - To ensure a transition between the two categories In category a) there must also be a power limitation as in category b) be guaranteed.
• - There are no external components for speed sensing needed because a wheel hub drive is preferably used.
• - When using wheel hub motors, the system is independent of  the selected translation of the muscle drive train. this applies in particular because only one direction of travel sensor is used shall be.

Embodiments of the invention are listed in the subclaims. The following is the invention with its essential details explained in more detail with reference to the drawings. It shows:

Fig. 1 is a stationary control diagram of a bicycle engine and

Fig. 2 is a functional diagram in the form of a block diagram.

Fig. 1 shows the stationary control diagram of a bicycle engine for a battery voltage of U _B = 36 volts.

The control diagram includes:

• 1. The characteristic field of the motor speed n over the motor torque M of a mechanically or electronically commutated direct current motor, preferably with permanent excitation by high-energy permanent magnets for different ratios of the pulse width modulation PWM of the motor voltage between 100% and 25% (indices 1 to 9).
  The advantageous design of the bicycle motor as a wheel hub motor provides a direct assignment of motor speed and driving speed V for a given wheel diameter, here 26 ", taking into account the tire flattening (D _wheel = 0.65).
• 2. The characteristic field of the mechanical engine power in dependence speed of the motor torque for different PWM ratios,
• 3. a torque- _independent horizontal straight line P _{limit, 1} for limiting the engine power to 0.25 KW,
• 4. a torque- _independent straight line n _{limit, 1} or V _{limit, 1} for the engine speed or the speed _limitation to 50 min ^-1 or 6 km / h,
• 5. a speed, torque limit characteristic n _gP1 (M, P = 250 W) for an engine power of 250 W,
• 6. a speed-torque limit characteristic curve n _gP2 (M, P = 400 W) for an engine power of 400 W,
• 7. A speed- _independent (vertical) straight line M _limit for limiting the engine torque to 50 Nm.

The characteristic fields points 1 and 2 are based on simple relationships

V = π * D _RAD * n (2)

M = K _M * (I _M - I _MO ) (3)

P = 2π * M * n (4)

with the engine parameters (for an average engine temperature)
K _E - (speed) voltage constant
K _M - K _E / 2π - (current) torque constant
R - connection resistance
I _MO - engine idling current
and the operating parameters
U _B - battery voltage
PWM - pulse width modulation ratio
filed in the microprocessor controller, using equation (3) for greater accuracy through the relationship

M = K _M * I _M - (M _R + K _d * n) (3a)

with M _R - friction torque
K _d - damping constant
can be replaced.

Accuracy can be further increased by storing the motor parameters k _E and R depending on the motor temperature.

With the help of equations (1) to (4) anyone can Operating point of the motor depending on the motor current by choice a corresponding PWM ratio can be set.

In particular, the motor characteristic field according to FIG. 1 can be divided into sub-ranges for the torque, the speed and thus the speed and the power by selecting desired limits and activated or deactivated simply by simply measuring the motor current and one or more additional conditions without any additional speed or speed measuring device become.

In Fig. 1, for example, the torque to protect the mechanical components of the motor against overload is limited to 50 Nm by a corresponding motor current limitation.

The motor current limitation is usually also against electrical, magnetic and / or thermal overload used.

For example, for a motor torque measured with the aid of the motor current of M _L2 = 26 Nm according to FIG. 1, the driving speed should not exceed 6 km / h. Then the PWM ratio according to characteristic curve n ₈ (M) must not exceed the value of 32%. If the motor power should not exceed 250 watts for M _L2 = 26 Nm, the PWM ratio must be max. Be limited to 50%.

On the other hand, the torque- _dependent speed _limitation n _limit2 (M) according to FIG. 1 for M _L1 = 10 Nm is only maintained if the PWM ratio does not exceed 75%.

Finally, with M _L3 = 47 Nm, the PWM ratio must be limited to 43% if the engine speed should not exceed 50 min ^-1 , i.e. the driving speed 6 km / h, in which case a maximum of 250 watts of engine power is output.

If the task is only to limit the motor power P _M to P _Mg , then this can be done very simply by means of a motor current-dependent PWM limitation with an average motor efficiency η _M according to the relationship

take place, this type of limitation for a simple Microprocessor control is suitable.

For analog controls in which divisions or multiplications of variable sizes cannot be carried out in a simple manner, the motor power is limited by the battery current I _B ≦ I _Bg according to the relationship

with the overall efficiency η _g of the motor and the control, which can typically be set as a first approximation when operating at the power limitation P _M = 250 W, η _g ≈ 0.5, which results in a battery current limitation for U _B = 24 V, for example I _Bg ≈ 20 A.

A functional example is described below with reference to FIG. 1.

Given the engine diagram shown in FIG. 1. Depending on the driving situation, such as incline or acceleration, the respective motor current is set according to the necessary torque. This current is detected by the control. Let us assume, for example, that the curve n _gP1, which stands for a constant motor power of 250 W, would be chosen as the limitation. Then there is an intersection between the vertical straight line at the corresponding current torque with this limiting curve. Exactly one of the straight lines marked by the PWM passes through this intersection (n ₁ -n ₉ ). The corresponding PWM ratio of this straight line is then the limit for the PWM associated with the current driving state.

The limit value of the PWM can be determined in the same way for another limitation curve in the motor diagram. From these limitations, one is activated by the pedal sensor by means of a switch according to FIG. 2, depending on whether the pedaling is forward, backward or not. The minimum PWM is then output to the output stage, which results from the travel sensor, ie the driver's request, and the limit signal.

If the battery voltage is not constant, this effect can eliminated by an additional measurement of the battery voltage become. Likewise, by measuring the battery current and the known PWM ratio can be concluded on the motor current, so that the motor current measurement can be replaced. However, this is usually available to protect the motor from overload anyway.  

The process described is unregulated, i.e. the limit for the PWM is always determined for the stationary limit case. It is conceivable that a regulation is a faster approximation allows corresponding curves. A control strategy usually becomes depend on a distance definition in the engine map and can therefore make it necessary to evaluate additional motor data. However, the regulation is not for the basic idea of limitation necessary.

The function of the engine control according to the invention is described below with reference to the block diagram of FIG. 2. The engine controller 1 includes a motor 2-addressing End stage 3. With the help of a current meter 4, a current measurement is carried out either in the motor line or in the battery line. This current signal is used to generate two limit values Limit1 and Limit2 for the PWM signal to be output by a pulse width modulator 7 with the aid of two limit transmitters 5 , 6 . It may also be necessary to evaluate the current PWM signal that is forwarded to the output stage. The signal of the pedal sensor 8 is used to activate a changeover switch 9 , which selects one of these two limit value signals as the active one. From the signal from the travel sensor 11 and this active limit value signal, the minimum is then formed by a minimum generator 10 , which is passed on to the output stage 3 as the new PWM signal to be output.

In the block diagram is not specified that z. B. for a limitation of the motor current, which is required to protect against a mechanical overload, other limit values can be generated, which must also be continuously processed in the minimum generator 10 . It is also conceivable to select one from more than two limit values. For example, you can select the limit value zero, i.e. switch off the engine when pedaling backwards.

Claims (8)

1. Vehicle with auxiliary electric drive, in particular electric bike with an electric motor ( 2 ), a Fahrgeschwindig keitsgeber ( 11 ) (setpoint generator) for electronic control ( 1 ) for controlling the motor and with a biomechanical direction sensor ( 8 ), characterized in that the Control ( 1 ) contains defined limits for certain mechanical engine parameters such as speed, power and possibly torque, which are derived without additional, electromechanical transducers from the electrical state variables of the engine alone, with the help of which the engine map is divided into approval-free engine operating ranges, which by means of of the biomechanical movement direction sensor can be activated or deactivated. 2. Vehicle according to claim 1, characterized in that the Drive control below a defined speed limit a preferably constant torque limit and thus a speed-variable power limitation and upper half of this speed limit a constant in particular Has power limitation. 3. Vehicle according to claim 1 or 2, characterized in that that performance in an upper engine speed range between a lower and an upper speed limit monotone is preferably linearly reduced to zero. 4. Vehicle according to claim 1, characterized in that the Speed and power limits through motor current evaluated pulse width modulation limitation and control input current (battery current) limitation is effected.   5. Vehicle according to the preamble of claim 1, characterized in that a measuring device ( 4 ) for measuring the motor and / or battery current is provided that, if appropriate, an additional evaluation device for evaluating the pulse width modulation control signal and / or the Battery voltage and / or the motor voltage is provided so that at least two limit values ( 5 , 6 ) are formed for the pulse width modulation signal to be output, that one of the limit values is selected as the active pulse width modulation signal by a selection device ( 9 ) by means of a directional sensor ( 8 ) is and that the output pulse width modulation signal represents the mini mum between this limit signal and the driver signal of the driver, so that a delimitation of individual areas of the engine map takes place. 6. Vehicle according to claim 5, characterized in that a Control is provided with a control strategy that the Control signal regulated to the limit value. 7. Vehicle according to claim 5 or 6, characterized in that that the controller for one or more additional loading Limitations of the pulse width modulation signal formed is to limit the permissible motor current, the un work depending on the other limitations. 8. Vehicle according to the preamble of claim 1, characterized ge indicates that it has two engines with different Has characteristic curves that depend on the selected Operating mode or approval category can be switched on or it has a controller that has two different motors Characteristic curves depending on the selected operating mode  or approval category, or, if it is from the STVZO is approved, a transient behavior of the tax is possible, which provides a higher performance supply than is permitted in the inpatient case.