FIELD OF THE INVENTION

The present invention relates to pedal shaft measurement arrangement, and more particularly to a pedal shaft measurement arrangement according to preamble of claim 1. The present invention also relates to pedal shaft measurement system, and more particularly to a pedal shaft measurement system according to preamble of claim 10. The present invention further relates to a method for controlling a power unit of an electric pedal vehicle, and more particularly to a method according to preamble of claim 16.

BACKGROUND OF THE INVENTION

An electric bike comprises a drive system. The drive system comprises a power unit for providing driving assistance for driving the electric bike. The power unit is operatively connected to a pedal shaft of the electric bike. A pedal crank is further connected to the pedal shaft such that a cyclist may output torque to the pedal shaft by pedaling.

In an electric bike, pedaling torque of the user is measured by the torque sensor and transmitted to the power unit. Based on this information speed and power of the motor is controlled. The performance of the electric bike as felt by the user depends on how precisely and accurately the motor is controlled.

In order to control the power unit and the electric motor(s) thereof during riding in a way that the pedaling feels natural to the cyclist, the cyclist input torque to the pedal shaft needs to be accurately measured. By nature, the torque on the pedal shaft is a sine wave shaped curve with two peaks and valleys per one pedal shaft revolution. Highest peaks typically occur when pedal cranks are in horizontal position, hence the torque arm of the cyclist is longest. The peaks can alter in height depending on how hard the cyclist is pedaling the bike. There may also be a difference in power input between two legs of the cyclist. In order to efficiently control the power unit during riding, rider input torque readings should be measured with low delay from both pedal cranks.

The basic problem relating to the pedal shaft torque measurement is that the pedal shaft is rotating in relation to the power unit.

In prior art a torque sensor is placed on the rotating pedal shaft. The output signal is transferred to the stationary power unit through the use of mechanical slip-rings or the like which provides a mechanical contact. This provides reliability issues as well as makes maintenance necessary. Alternatively, torque is measured indirectly by placing the torque sensor on a stationary part, such as the frame, of the electric bike, and measuring other strains correlated to the torque. However, the forces become complex in the electric bike frame. Thus, the indirect measurement of torque is inaccurate and provides delay making efficient control of the motor difficult. Another way to measure torque is by using a magnetostrictive sensor. With this type of sensor, the pedal shaft is magnetized. The magnetic field of the pedal shaft changes slightly when the pedal shaft is loaded and this can be detected with the magnetostrictive sensor. However, this type of sensor can be sensitive to external magnetic fields such as one emitted by electric motors. The sensor also has to be placed directly on top of the magnetized shaft which restricts design freedom of the system.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a pedal shaft measurement arrangement, a pedal shaft measurement system and a method for controlling a power unit of an electric pedal vehicle so as to solve or at least alleviate the disadvantages of the prior art.

The objects of the invention are achieved by a pedal shaft measurement arrangement which is characterized by what is stated in claim 1. The objects of the invention are also achieved by a pedal shaft measurement system which is characterized by what is stated in claim 10. The objects of the invention are further achieved by a method which is characterized by what is stated in claim 16.

The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of providing a pedal shaft measurement arrangement arranged to measure a pedal shaft parameter of a pedal shaft of an electric pedal vehicle. The electric pedal vehicle comprising a power unit, the pedal shaft being rotatable in relation to the power unit. The pedal shaft measurement arrangement comprises a measurement unit mounted to the pedal shaft and arranged to rotate together with the pedal shaft. The measurement unit is arranged to measure the pedal shaft parameter. The measurement unit comprises a measurement circuit board and a sensor connected to the measurement circuit board. The sensor is connected to the pedal shaft. The pedal shaft measurement arrangement further comprises a transmitter unit arranged separate from the pedal shaft and connected to the power unit. The transmitter unit is arranged to transmit power to the measurement unit and receive measurement data from the measurement unit. The transmitter unit comprises a transmitter circuit board.

According to the present invention, the measurement unit comprises a first coil arranged to the pedal shaft and around the pedal shaft. The first coil is connected to the measurement circuit board and arranged to rotate together with the pedal shaft. The transmitter unit comprises a second coil separate from the pedal shaft. The second coil being arranged adjacent to the first coil such that a transmission gap is provided between the first coil and the second coil for allowing rotation of the pedal shaft and the first coil in relation to the second coil and contactless and direct transmission of the power and measurement data between the first coil and the second coil.

The first and second coil enable transmitting measurement data in contactless manner between the measurement unit rotating together with the pedal shaft and the transmitter unit arranged separate and stationary in relation to the pedal shaft. Furthermore, the first coil and second coil enable transmitting power in contactless manner from the transmitter unit to the measurement unit. Thus, no power source is needed in connection with the rotating pedal shaft and the measurement unit. As the first coil and second coil are arranged adjacent to each other, transmitting power and measurement data may be carried out during the entire revolution of the pedal shaft.

The direct contactless transmission between the first and second coils enables transmission without delay or with minimal delay between the first and second coil and between the measurement unit and the transmission unit. Further, the direct contactless transmission enables processing the measurement data in analog manner. This enables continuous analog data transmission without need for utilizing communication protocols or synchronizations.

In one embodiment, the measurement unit comprises a sensor connected to the pedal shaft for measuring the pedal shaft parameter of the pedal shaft.

The sensor is connected to the pedal shaft such that it measures the pedal shaft parameter in direct manner. As the measurement data and power are transmitted in contactless manner with the first and second coils, the sensor may be placed directly to the pedal shaft. In one embodiment, the sensor is a torque sensor arranged to measure torque inputted to the pedal shaft. Therefore, the present invention provides an arrangement for measuring torque inputted to the pedal shaft by the cyclist in direct manner and transmitting measurement data in contactless manner from the rotating pedal shaft.

In another embodiment, the sensor is a strain gauge arranged to measure torque inputted to the pedal shaft. The strain gauge measures deformation of the pedal shaft and transforms the deformation into changes in electrical resistance proportional to the deformation. The power consumption of the strain gauge is very low and therefore it may be powered efficiently by utilizing the first and second coil. Utilizing strain gauge enables the sensor, meaning the strain gauge, to be located freely in the pedal shaft.

In one embodiment, the pedal shaft comprises a first crank interface, a second crank interface and an output interface provided between the first crank interface and the second crank interface, and that the torque sensor is arranged to the pedal shaft between the first crank interface and the output interface. The torque sensor being arranged to measure torque inputted to the pedal shaft from the first crank interface.

Accordingly, the torque sensor, such as strain gauge, is arranged to measure torque inputted to the pedal shaft via the first crank interface and a first pedal, for example the left pedal and left leg of the user.

In another embodiment, the torque sensor is arranged to the pedal shaft between the second crank interface and the output interface, the torque sensor being arranged to measure torque inputted to the pedal shaft from the second crank interface.

Accordingly, the torque sensor, such as strain gauge, is arranged to measure torque inputted to the pedal shaft via the second crank interface and a second pedal, for example a right pedal and right leg of the user.

In a further embodiment, the measurement unit comprises a first torque sensor and a second torque sensor. The first torque sensor is arranged to the pedal shaft between the first crank interface and the output interface and the second torque sensor is arranged to the pedal shaft between the second crank interface and the output interface.

Accordingly, the torque sensors, such as strain gauges, are arranged to measure torque inputted to the pedal shaft separately via the first and second crank interface and the first and second pedal. Thus, the torque inputted by the right and left leg of the user via the right and left pedals may be measured separately such that the control of the power may be even more enhanced.

In one embodiment, the pedal shaft comprises a first outer shaft member and a second inner shaft member. The second inner shaft member is fitted and attached inside the first outer shaft member. A first crank interface is provided to the first outer shaft member and a second crank interface is provided to the second inner shaft member. The torque sensor being arranged to measure torque inputted to the pedal shaft from the first crank interface and from the second crank interface.

The together attached first outer shaft member and the second inner shaft member enable measuring torque inputted to the pedal shaft via both the first and second crank interfaces with only one torque sensor or strain gauge.

In one embodiment, the first outer shaft member and the second inner shaft member are attached together with an interference fit.

The interference fit enables the second inner shaft member surface be provided rotationally symmetrical such that high material stress areas in the pedal shaft may be avoided. Further, the interference fit is watertight so that there is no need to seal an inner hole of the inner shaft to avoid water ingress.

In one embodiment the pedal shaft comprises an output interface support extending from the pedal shaft, the output interface support being connected to the pedal shaft between the first crank interface and the second crank interface, he output interface being connected to the output interface support. The torque sensor is arranged to the output interface support, the torque sensor being arranged to measure torque inputted to the pedal shaft from the first and second crank interfaces.

This allows measuring the torque inputted to the pedal shaft from both the first and second crank interfaces.

In an alternative embodiment, the pedal shaft comprises an output interface support extending from the first outer shaft member of the pedal shaft, the output interface support being connected to the first outer shaft member, the output interface being connected to the output interface support, and the torque sensor is arranged to the output interface support, the torque sensor being arranged to measure torque inputted to the pedal shaft from the first and second crank interfaces. This allows measuring torque inputted from both the first outer pedal shaft and the second inner pedal shaft.

In one embodiment, the measurement unit comprises a measurement circuit board. The sensor is connected to the measurement circuit board and the measurement board is connected to the first coil.

Therefore, the measurement circuit board is provided with measurement components arranged to operate the torque sensor or the strain gauge and the first coil.

In another embodiment, the measurement unit comprises a measurement circuit board. The sensor is connected to the measurement circuit board and the measurement circuit board is connected to the first coil. The transmitter unit comprises a transmitter circuit board. The second coil is connected to the transmitter circuit board.

Therefore, the measurement circuit board is provided with measurement components arranged to operate the torque sensor or the strain gauge and the first coil. Further, the transmitter circuit board is provided with transmitter components arranged to operate the second coil.

In a further alternative embodiment, the measurement unit comprises a measurement circuit board. The sensor is connected to the measurement circuit board and the measurement circuit board is connected to the first coil. The transmitter unit comprises a transmitter circuit board. The second coil is connected to the transmitter circuit board, and the transmitter circuit board is connected to a central processing unit of the power unit.

Therefore, the measurement circuit board is provided with measurement components arranged to operate the torque sensor or the strain gauge and the first coil. Further, the transmitter circuit board is provided with transmitter components arranged to operate the second coil and to communicate with the power unit.

In one embodiment, the measurement unit comprises a first ferrite element arranged adjacent to the first coil.

The first ferrite element is arranged to direct the magnetic field of the first coil towards the second coil. There may be one or more first ferrite elements.

In another embodiment, the measurement unit comprises a second ferrite element arranged adjacent to the second coil.

The second ferrite element is arranged to direct the magnetic field of the second coil towards the first coil. There may be one or more second ferrite elements.

In an alternative embodiment, the measurement unit comprises a first ferrite element arranged adjacent the first coil, and the measurement unit comprises a second ferrite element arranged adjacent of the second coil. The first coil is arranged between the first ferrite element and the second coil. The second coil is arranged between the second ferrite element and the first coil.

The first and second ferrite elements are arranged to direct the magnetic field of the first and second coil towards and between the first and second coils. There may be one or more first and/or second ferrite elements.

The ferrite elements allow placing the first and second coil further apart from each other. Thus, the ferrite elements allow increasing the transmission gap between the first and second coil.

In some embodiments, transmission frequency of the power and measurement data between the first coil and the second coil less than 148,5 kHz or under 148,5 kHz.

In some alternative embodiments, the transmitter unit is configured to utilize transmission frequency less than 148,5 kHz between the first coil and the second coil.

In some further embodiments, the transmitter unit and the measurement unit are configured to utilize transmission frequency less than 148,5 kHz between the first coil and the second coil.

The transmission frequency less than 148,5 kHz provides low electromagnetic disturbances. Further, the mentioned frequency is below frequencies used for different kinds of radio broadcasting, meaning below broadcasting band.

The present invention is further based on the idea of providing a pedal shaft measurement system arranged to measure a pedal shaft parameter of a pedal shaft of an electric pedal vehicle. The electric pedal vehicle comprises a power unit. The pedal shaft is rotatable in relation to the power unit. The pedal shaft measurement system comprises a measurement unit mounted to the pedal shaft and arranged to rotate together with the pedal shaft. The measurement unit is comprises a sensor arranged to measure the pedal shaft parameter and generate measurement output signal based on measuring the pedal shaft parameter. The pedal shaft measurement system further comprises a transmitter unit arranged separate from the pedal shaft and connected to the power unit. The transmitter unit is arranged to transmit power to the measurement unit and receive measurement data from the measurement unit.

According to the present invention the measurement unit comprises a first coil, and the transmitter unit comprises a second coil. The second coil is arranged at a distance from the first coil such that a transmission gap is provided between the first coil and the second coil. The first coil and the second coil are arranged to provide contactless connection between the measurement unit and the transmitter unit. The second coil is configured to transmit power to the measurement unit in contactless manner, and the first coil is configured to transmit measurement data to the transmitter unit in contactless manner.

The transmitter unit is configured to supply alternating current to the second coil such that an alternating magnetic field is provided around the second coil, the alternating magnetic field provided by the second coil is arranged to induce current directly to the first coil. The measurement unit is configured to alternate impedance of the first coil at a frequency that is dependent on the measurement output signal of the sensor, the alternated impedance of the first coil is arranged to change voltage amplitude of the alternating current in the second coil.

Therefore, the first coil and the second provide direct contactless connection between the transmitter unit and the measurement unit. The transmitter unit, or a transmitter circuit board thereof, is configured to transmit power to the measurement unit in contactless manner via the second coil. The measurement unit, or a measurement circuit board thereof, is configured to transmit measurement data to the transmitter unit in contactless manner via the first coil. Thus, the pedal shaft parameter may be measured from the rotating pedal shaft in efficient manner.

In the present application, the wording separate from the pedal shaft means, that component, unit or part arranged separate from the pedal shaft is not in mechanical connection with the pedals shaft and does not rotate together with the pedal shaft.

In normal embodiments, the component, unit or part arranged separate from the pedal shaft is provided or mechanically connected to the frame of the electric pedal vehicle.

In one embodiment, the second coil is configured to induce current to the first coil such that power is transmitted to the first coil.

Accordingly, the power is transmitted to the measurement unit in contactless manner for operating the measurement unit and the measurement unit does not need any integrated power source. Power is transmitted to the first coil from the second coil.

In one embodiment, the transmitter unit, or the transmitter circuit board thereof, is configured to supply alternating current to the second coil such that an alternating magnetic field is provided around the second coil. The alternating magnetic field provided by the second coil is arranged to induce current to the first coil.

Thus, the power is supplied to the measurement unit from outside the pedal shaft in contactless manner by utilizing the alternating magnetic field generated by the second coil.

In one embodiment, the measurement unit is configured to alternate impedance of the first coil. The alternated impedance of the first coil is arranged to change voltage amplitude of the alternating current in the second coil.

The changed voltage amplitude may be utilized to interpret the pedal shaft parameter for controlling the power unit.

In one embodiment, the measurement unit comprises a sensor configured to measure the pedal shaft parameter, and that the measurement unit is configured to alternate impedance of the first coil based on the measured pedal shaft parameter.

Therefore, the voltage of the alternating current in the second coil is changed based on the sensor measurements or sensor output signal.

In one embodiment, the sensor is a torque sensor arranged to measure torque inputted to the pedal shaft, and that the measurement unit is configured to alternate impedance of the first coil based on the measured torque.

Thus, measured torque values or torque sensor output signals may be transmitted to the transmitter unit in contactless manner by utilizing the first and second coil.

In another embodiment, the sensor is strain gauge arranged to measure deformation of the pedal shaft due to torque inputted to the pedal shaft, and that the measurement unit is configured to alternate impedance of the first coil based on the measured deformation.

Thus, the output signal of the strain gauge may be transmitted to the transmitter unit in contactless manner by utilizing the first and second coil. The strain gauge provides a changed resistance values based on the torque inputted to the pedal shaft and thus the changed resistance values may be utilized to alternate the impedance of the first coil.

In one embodiment, the power unit comprises at least one motor, and that the transmitter unit is connected to the power unit for controlling the at least one motor based on the measurement data received from the measurement unit. Therefore, the measured pedal shaft parameter which is transmitted to the transmitter unit in contactless manner is utilized for controlling the power unit and motor thereof.

In some embodiments the pedal shaft measurement system comprises a pedal shaft measurement arrangement as disclosed above.

In some embodiments of the system, the measurement unit comprises a measurement circuit board, and the sensor and the first coil are connected to the measurement circuit board, and the transmitter unit comprises a transmitter circuit board and the second coil is connected to the transmitter circuit board.

Accordingly, a direct contactless connection between the measurement unit and the transmitter unit is provided via the first and second coils.

In some embodiments of the system, transmission frequency of the power and measurement data between the first coil and the second coil is less than 148,5 kHz.

In some alternative embodiments of the system, the transmitter unit is configured to utilize transmission frequency less than 148,5 kHz between the first coil and the second coil.

In some further embodiments of the system, the transmitter unit and the measurement unit are configured to utilize transmission frequency less than 148,5 kHz between the first coil and the second coil.

The present invention is further based on the idea of providing a method for controlling a power unit of an electric pedal vehicle comprising a pedal shaft arranged rotatable in relation to the power unit, the power unit comprising at least one motor. The method comprises measuring a pedal shaft parameter with a measurement unit having a sensor for providing a measurement signal. The measurement unit is mounted to the pedal shaft and arranged to rotate together with the pedal shaft. The method further comprises transmitting measurement data with a transmitter unit to the power unit, the transmitter unit is arranged separate from the pedal shaft, and controlling the at least one motor of the electric pedal vehicle based on the measurement received in the power unit.

According to the present invention measuring the pedal shaft parameter comprises transmitting power from the transmitter unit to the measurement unit in contactless manner directly between a second coil provided to the transmitter unit and first coil provided to the measurement unit, and transmitting measurement data from the measurement unit to the transmitter unit in contactless manner directly between the first coil and the second coil. The method further comprises transmitting power to the first coil comprises inducing current to the first coil by supplying alternating current to the second coil, the alternating current generates an alternating magnetic field inducing current to the first coil. The method also comprises transmitting measurement data to the transmitter unit comprises alternating impedance of the first coil with the measurement unit at a frequency that is dependent on the measurement output signal of the sensor, the alternating impedance of the first coil changes voltage amplitude of the alternating current in the second coil.

The method of the present invention enables powering the measurement unit provided to the rotating pedal shaft in contactless manner. Further, the method enables transmitting measurement data from the rotating pedal shaft in contactless manner to the transmitter unit arranged separate from the pedal shaft and stationary in relation to the pedal shaft.

In one embodiment, transmitting power to the first coil comprises inducing current to the first coil by supplying alternating current to the second coil. The alternating current generates an alternating magnetic field inducing current to the first coil.

Therefore, the power is induced to the measurement unit via the first and second coils in contactless manner by generating the alternating magnetic field with the second coil.

In one embodiment, transmitting measurement data to the transmitter unit from the measurement unit comprises alternating impedance of the first coil with the measurement unit. The alternating impedance of the first coil changes voltage amplitude of the alternating current in the second coil.

The measured pedal shaft parameter may be interpreted from the changing voltage amplitude of the alternating current by the transmitter unit or by the power unit.

In one embodiment, the method comprises alternating the impedance of the first coil with the measurement unit based on the measured values of the pedal shaft parameter.

In an alternative embodiment, the method comprises alternating voltage in the measurement unit based on the measured values of the pedal shaft parameter, and alternating the impedance of the first coil based on the altered voltage in the measurement unit.

Accordingly, the impedance of the first coil is altered such that voltage amplitude of the alternating current in the transmitter unit is changed based on the alternated impedance of the first coil and based on the measured values of the pedal shaft parameter.

In one embodiment, the method comprises measuring torque inputted to the pedal shaft with at least one torque sensor provided to the measurement unit, and alternating voltage in the measurement unit based on the measured torque or alternating the impedance of the first coil based on the measured torque.

Therefore, the torque inputted to the pedal shaft may be measured directly from the pedal shaft and the measurement data may be transmitted to the transmitter unit outside and separate from the pedal shaft in contactless manner.

In an alternative embodiment, the method comprises measuring deformation of the pedal shaft with at least strain gauge. Resistance of the strain gauge is configured to change in response to deformation of the pedal shaft. The method comprises alternating voltage in the measurement unit based on the change in resistance of the strain gauge or alternating the impedance of the first coil based on the change in resistance of the strain gauge.

Thus, a simple and standard strain gauge may be used to carry out the torque measurements.

The method may be carried out utilizing a pedal shaft measurement arrangement and/or utilizing a pedal shaft measurement as disclosed above.

An advantage of the invention is that pedal shaft parameters may be measured directly from the pedal shaft. Further, the present invention enables mounting a simple measurement unit to the rotating pedal shaft and power needed in the measurement unit is transmitted in contactless manner to the measurement unit. This also enables utilizing a simple strain gauge for measuring torque inputted to the pedal shaft by the user and thus analogue components may be used in the measurement unit. The measured pedal shaft parameters are further transmitted from the measurement unit in contactless manner. The present invention enables measuring the pedal shaft parameter during the whole revolution of the pedal shaft and also transmitting power to the measurement unit and measurement data from the measurement unit during the whole revolution of the pedal shaft. Thus, the arrangement, system and method are able to measure and transmit measurement data continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail by means of specific embodiments with reference to the enclosed drawings, in which

Figure 1 shows schematically a pedal vehicle;

Figure 2 shows schematically a pedal shaft and electric motor of a pedal vehicle;

Figure 3 shows schematically transmission of pedal vehicle;

Figures 4 to 6 show schematically one embodiment of a pedal shaft and a measurement unit according to the present invention;

Figure 7 shows one embodiment of a transmitter unit according to one embodiment of the present invention;

Figure 8 shows schematically the pedal shaft, the measurement unit and the transmitter unit together;

Figure 11 shows schematically a measurement system according to one embodiment of the present invention;

Figure 12 shows schematically another embodiment of a pedal shaft and a measurement unit according to the present invention;

Figures 14 and 15 show schematically yet another embodiment of a pedal shaft and a measurement unit according to the present invention;

Figure 16 shows schematically one kind of strain gauge;

Figures 17 to 19 show schematically different sensor assemblies with a strain gauge; and

Figures 20 to 22 shows schematically diagrams of use of strain gauge in measurement system and method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a light electric vehicle 1 which is a pedal vehicle such as an electric bike. It should be noted that the present invention is not limited to any particular pedal vehicle. However, the present invention may be the most suitable electric bike application.

The electric bike 1 comprises a drive system. The drive system comprises a power unit 2 for providing driving assistance for driving the electric bike 1. The power unit 2 is operatively connected to a pedal shaft 10 of the electric bike 1. A pedal crank 12 is further connected to the pedal shaft 10 such that the user may output torque to the pedal shaft by pedaling.

Figure 2 shows schematically the power unit 2 of the electric bike 1. The power unit 2 comprises a first motor 51 and a second motor 52. The second motor 52 is arranged to provide torque output to a pedal shaft 10 or output shaft of the electric bike 1 and thus provide assist for the user. The fist motor 51 is arranged to adjust the transmission ratio of the power unit 2. Accordingly, the first motor 51 is arranged to adjust the cadence or rotational speed of the pedal shaft 10 and the second motor 52 is arranged to adjust assistance of the power unit 2.

The power unit 2 comprises a housing 4. The first and second motor 51, 52 are both provided inside the housing 4. The housing 4 comprises a hub 6 provided around the pedal shaft 10 and an arm 8 extending from the hub 6. The first motor 51 is provided to the hub 6 of the housing 4 and the second motor 52 is provided to the arm 8. However, the first motor 51 may also be arranged to be arm 8 and the second motor 52 to the hub 6. Thus, the first and second motors 51, 52 in figure 2 are interchangeable.

The power unit 2 further comprises a main gearing (not shown). The main gearing is provided to the power unit 2 for adjusting the transmission ratio of the power unit 2. The second motor 52 and the pedal shaft 10 are connected to the main gearing and the main gearing is connected to the output interface or the chain wheel 24. The first motor 51 is connected to the main gearing and arranged to adjust the transmission ratio of the main gearing.

According to the above mentioned, the second motor 52 is an assist motor arranged to provide torque output to the pedal shaft 10 or to the output shaft of the electric bike 1. The first motor 51 is a control motor arranged to adjust the transmission ratio of the main gearing.

Figure 3 shows schematically one embodiment of the electric bike transmission in which the power unit 2 is provided in connection with the pedal shaft 10. As mentioned, the second motor 52 and the pedal shaft 10 are connected to the main gearing and the main gearing is connected to the output interface or the chain wheel 24. The first motor 51 is connected to the main gearing and arranged to adjust the transmission ratio of the main gearing.

Alternatively, the pedal shaft 10 is connected to a chainwheel 17. The chainwheel 17 is connected to a rear axle 18, or a rear wheel axle 18, with a chain 16. A pedal 13 is further connected to the pedal shaft 10 with a pedal crank 12 such that a user riding the electric bike 1 may output torque to the crankshaft 10 by pedaling. The torque outputted by the user is inputted to the pedal shaft 10 via the pedal 13 and the pedal crank 12.

Figure 4 shows schematically one embodiment of pedal shaft 10 and pedal shaft measurement arrangement according to the present invention.

The pedal shaft 10 comprises a first crank interface 20. A first pedal crank 12 of the electric bike 1 is connected to the first crank interface 20 such that the first pedal crank 12 is connected to the pedal shaft 10. The torque outputted by the user by pedaling is inputted to the pedal shaft 10 via the first crank interface 20. The first crank interface 20 is provided to a first end of the pedal shaft 10. However, the first crank interface 20 may also be provided between the first end and a second end of the pedal shaft 10.

The pedal shaft 10 further comprises a second crank interface 22. A second pedal crank 12 of the electric bike 1 is connected to the second crank interface 22 such that the second pedal crank 12 is connected to the pedal shaft 10. The torque outputted by the user by pedaling is inputted to the pedal shaft 10 via the second crank interface 22. The second crank interface 22 is provided to the second end of the pedal shaft 10. However, the second crank interface 22 may also be provided between the first end and the second end of the pedal shaft 10.

In an alternative embodiment there may also be only one crank interface 20, 22 in the pedal shaft 10.

Two crank interfaces 20, 22 is preferable such that the user may input torque to the pedal shaft 10 with both legs or with both hands.

The pedal shaft 10 further comprises an output interface 24 via which the torque is outputted from the pedal shaft 10. The output interface 24 may be the chainwheel 17. Therefore, the torque is transmitted from the pedal shaft 10 to the rear axle via the output interface 24.

The pedal shaft 10 is provided with a measurement unit arranged to measure the pedal shaft parameter. The measurement unit is mounted to the pedal shaft 10 and arranged to rotate together with the pedal shaft 10.

The measurement unit comprises sensor 32 attached or mounted to the pedal shaft 10. There may also be one more sensors 32 mounted to the pedal shaft 10. Preferably the sensor 32 is attached directly to the pedal shaft 10. The sensor 32 is arranged to rotate together with the pedal shaft 10.

The sensor 32 is for example a torque sensor arranged to measure torque inputted to the pedal shaft 10 via the first and/or second crank interfaces 20, 22. In some embodiments, the torque sensor is a strain gauge.

The measurement unit further comprises a measurement circuit board 36. The measurement circuit board 36 is provided with measurement components. The measurement components are preferably selected so that no microcontroller unit (MCU) is required to control the functionality.

The sensor 32 is connected to the measurement circuit board 36 such that current is transmitted to the sensor 32 from the measurement circuit board 36 and sensor output signal is transmitted from the sensor 32 to the measurement circuit board 36. The sensor 32 is connected to the measurement circuit board 36 with a sensor connection 31, such as sensor line(s), arranged to transmit current to the sensor 32 from the measurement circuit board 36 and sensor output signal from the sensor 32 to the measurement circuit board 36.

The resistance of the strain gauge changes as the strain gauge stretches due to the torque inputted to the pedal shaft. The changed resistance is measured and measurement value forms the output signal.

The measurement components of the measurement circuit board 36 vary depending on the type of the sensor 32.

The measurement circuit board 36 is attached or mounted to the pedal shaft 10 and rotates together with the pedal shaft 10. Preferably the measurement circuit board 36 is attached directly to the pedal shaft 10.

The measurement unit further comprises a first coil 33 wound around the pedal shaft 10. The first coil 34 surrounds the pedal shaft 10.

The pedal shaft 10 is provided with a first coil support 30 provided around the pedal shaft 10. The first coil 34 is further arranged on the first coil support 30. The first coil support 30 separates the first coil 34 electrically from the pedal shaft 10. The first coil support 30 is arranged to rotate together with the pedal shaft 10 and also together with the first coil 34.

Alternatively, the first coil 34 is wound directly on the pedal shaft 10.

The first coil 34 is connected to the measurement circuit board 36 such that current is transmitted to the measurement circuit board 36 from the first coil 34 and measurement data or measurement signal is transmitted from the measurement circuit board 36 to the first coil 34. The first coil 34 is connected to the measurement circuit board 36 with a first coil connection 33, such as coil line(s), arranged to transmit current to the measurement circuit board 36 from the first coil and measurement data or measurement signal from the measurement circuit board 36 to the first coil 34.

The measurement circuit board 34 alters the impedance of the first coil 34 by switching a capacitor with high frequency. This change in the impedance of the first coil 34 is received as voltage amplitude modulation in the second coil 44. Thus, the measurement data or measurement signal is provided as the modulated voltage amplitude in the second coil 44.

Accordingly, the pedal shaft measurement arranged may be used without any messaging protocol which further enables the measurement circuit board 36 to be provided without a microcontroller unit which would control the messaging protocol. Further, current consumption of the measurement circuit board 34 is reduced and the measurement circuit board may be powered the with the first and second coils 34, 44.

The first coil 34 is mounted around the pedal shaft 10 and stationary in relation to the pedal shaft 10. Therefore, the first coil 34 arranged to rotate together with the pedal shaft 10.

Figure 5 shows the pedal shaft 10 from the direction of the second crank interface 22 and from the second end of the pedal shaft 10. The output interface 24, or the chainwheel, is stationary in relation to the pedal shaft 10 and is arranged to rotate together with the pedal shaft 10.

The first coil 34 is arranged around pedal shaft 10 such that the first coil 34 is wound around the longitudinal axis of the pedal shaft 10.

Further, the first coil support 30 is provided on the pedal shaft 10 such that it surrounds the pedal shaft 10. The first coil 10 is supported to the first coil support 20.

Figure 6 shows the pedal shaft 10 from the direction of the first crank interface 20 and from the first end of the pedal shaft 10.

The pedal shaft 10 of the measurement unit is further provided with one or more first ferrite elements 39. The one or more first ferrite elements 39 are arranged to direct the magnetic field provided with the first coil 34 and/or second coil.

In one embodiment, the one or more first ferrite elements 39 are arranged to direct the magnetic field provided by the first coil 34 in a direction away from the pedal shaft 10 or radial direction of the pedal shaft 10.

As shown in figure 6, the one or more first ferrite elements 39 are arranged inside or adjacent the first coil 34 such that the magnetic field provided by the first coil 34 is directed away from the pedal shaft 10 or radial direction of the pedal shaft 10. The one or more first ferrite elements 39 are arranged along the entire winding(s) of the first coil 34. Thus, the one or more first ferrite elements 39 direct the magnetic field provided by the first coil 34 around the pedal shaft 10.

The one or more first ferrite elements 39 are provided between the pedal shaft 10 and the first coil 34. In one embodiment, the one or more first ferrite elements 39 are arranged to direct or restrict the magnetic field provided by the first coil 34 in the longitudinal direction of the pedal shaft 10. In this embodiment the one or more first ferrite elements 39 are arranged on opposite sides of the first coil 34 in the longitudinal direction of the pedal shaft 10.

In some embodiments, the one or more first ferrite elements 39 are arranged to direct the magnetic field provided by the first coil 34 in a direction away from the pedal shaft 10 or radial direction of the pedal shaft 10, and in the longitudinal direction of the pedal shaft 10.

In some embodiment, the one or more first ferrites are made of compounds of transition metals with oxygen. They are ferrimagnetic and nonconductive.

Figure 7 shows a transmitter unit according to the present invention. The transmitter unit is arranged separate from the pedal shaft 10 and arranged outside the pedal shaft 10. The transmitter unit is provided apart from the pedal shaft 10 such that the transmitter unit or parts thereof do not rotate together with the pedal shaft 10. Therefore, the transmitter unit is arranged stationary in relation to the pedal shaft 10.

The transmitter unit is provided with a second coil 44. The second coil 44 is provided around the pedal shaft 10 and further around the first coil 34. The second coil is arranged around the first coil 34 such that they are spaced apart from each other. Thus, the second coil 44 is separate from the pedal shaft 10 and the measurement unit. Further, the second coil 44 and the transmitter unit are provided in noncontact position in relation to the pedal shaft 10 and the measurement unit 10.

The transmitter unit comprises a second coil support 40. The second coil support 40 comprises a shaft opening 45 arranged to receive the pedal shaft 10 inside the second coil support 40. The second coil support 40 forms a sleeve member having the shaft opening 45 extending in longitudinal direction. The shaft opening 45 comprises an inner surface 43 defining the shaft opening 45. Accordingly, the shaft opening 45 is arranged to receive the pedal shaft 10 inside the shaft opening 45. Thus, the second coil support 40 is arranged to be provided around the pedal shaft 10 and to surround the pedal shaft 10.

The second coil 44 is arranged to the second coil support 40 and supported thereto. Therefore, the second coil 44 is arranged to be placed around the pedal shaft 10 such that the second coil 44 surrounds the pedal shaft 10 and is provided at a distance from the pedal shaft 10.

The transmitter unit further comprises a transmitter circuit board 42. The second coil 44 is connected to the transmitter circuit board 42 such that current is transmitted to the second coil 44 from the transmitter board 42 and measurement data or measurement signal is transmitted from the second coil 44 to the transmitter circuit board 36 to the first coil 34. The second coil 44 is connected to the transmitter circuit board 42 with a second coil connection 41, such as coil line(s), arranged to transmit current to the second coil 44 from the transmitter circuit board 42 and measurement data or measurement signal from the second coil 44 to the transmitter circuit board 42.

The transmitter circuit board 42 is supported to a circuit board base 46, which is arranged separate and stationary in relation to the rotating pedal shaft 10.

The transmitter circuit board 42 is further connected to the power unit 2 of the electric bike 1.

The transmitter unit is further provided with one or more second ferrite elements 49. The one or more second ferrite elements 49 are arranged to direct the magnetic field provided with the second coil 44.

In one embodiment, the one or more second ferrite elements 49 are arranged to direct the magnetic field provided by the second coil 44 in a direction towards the shaft opening 45 or in radial direction inwards towards the shaft opening 45 of the second coil support 40.

As shown in figure 8, the one or more second ferrite elements 49 are arranged outside the second coil 44 such that the magnetic field provided by the second coil 44 is directed in direction towards the inside of the second coil 44. The one or more second ferrite elements 49 are arranged around and adjacent the second coil 44. The one or more second ferrite elements 49 are arranged along the entire winding(s) of the second coil 34. Thus, the one or more second ferrite elements 49 direct the magnetic field provided by the second coil 34 towards the inside of the second coil 44.

The one or more second ferrite elements 49 are provided around the second coil 44 such that the one or more second ferrite elements 49 surround the second coil 49. Thus, the second coil 44 is provided between the one or more second ferrite elements 49 and the shaft opening 45.

In one embodiment, the one or more second ferrite elements 49 are arranged to direct or restrict the magnetic field provided by the second coil 44 in longitudinal direction of the shaft opening 45, or in axial direction. In this embodiment the one or more second ferrite elements 49 are arranged on opposite sides of the second coil 34 in the longitudinal direction of the shaft opening 45.

In some embodiments, the one or more second ferrite elements 49 are arranged to direct the magnetic field provided by the second coil 44 in a direction towards the inside of the second coil 44 and in the axial direction of the shaft opening 45.

In some embodiment, the one or more second ferrites are made of compounds of transition metals with oxygen. They are ferrimagnetic and nonconductive.

As shown in figures 6 and 7, the first ferrite elements) 39 are arranged to direct the magnetic field provided by the first coil 34 in a direction towards the second coil 44. Similarly, the second ferrite element(s) 49 are arranged to direct the magnetic field provided by the second coil 44 in a direction towards the first coil 34.

Figure 8 shows the pedal shaft 10, the measurement unit and the transmitter unit in assembled state. The pedal shaft 10 and is arranged inside the shaft opening 45 of the second coil support 40.

Accordingly, the first coil 34 is arranged inside the second coil 44. The first coil 34 and the second coil 44 are arranged in aligned manner such that the second coil 44 surrounds the first coil 34. Thus, the second coil 44 is arranged to surround the first coil 34.

The windings of the first coil 34 and the second coil 44 are arranged coaxially.

The first coil 34 and the second coil 44 are arranged coaxially such that the first coil 34 is inside the second coil 44. Thus, the first coil 34 and the second coil 44 are arranged aligned along the pedal shaft 10.

As shown in figure 8, the transmitter unit is arranged around the pedal shaft 10 and the measurement unit such that a rotation gap 202 is provided between the transmitter unit and the pedal shaft 10 and/or the measurement unit. Therefore, the transmitter unit is arranged to surround the pedal shaft 10 and the measurement unit such that the pedal shaft 10 and the measurement unit are arranged to rotate in relation to the transmitter unit.

The first coil support 30 is arranged inside the second coil support 40. Further, the first coil support 30 is arranged to rotate together with the pedal shaft 10 inside the second coil support 40.

The second coil 44 is arranged to surround the first coil 34 such that a transmission gap 200 is provided between the second coil 44 and the first coil 34. Accordingly, the first coil 34 and the second coil 44 are not in contact with each other. Therefore, the first coil 34 and the second coil 44 are arranged to transmit power and data in manner contactless between each other.

Accordingly, the measurement unit and the transmitter unit are connected to each other in contactless manner. Thus, there is no physical or galvanic contact between the measurement unit and the transmitter unit.

The first coil 34 is arranged to rotate together with the pedal shaft 10 inside the second coil 44. This provides continuous power and data transmission between the first and second coils 34, 44 during the revolution of the pedal shaft 10.

Figures 9 and 10 show an alternative embodiment in which the first coil 34 and the second coil 44 are arranged adjacent to each other.

Accordingly, the first and second coils 34 and 44 are arranged adjacent to each other in the direction of the pedal shaft 10 or in longitudinal direction of the pedal shaft. This provides simple structure.

As shown in figure 9, the pedal shaft 10 comprises the first coil support 30 and the first coil 34 is supported to the first coil support 30. The first coil support 30 is connected to or formed to the pedal shaft 10 and arranged to rotate together with the pedal shaft 10.

The measurement circuit board 36 is provided to the first coil support 30. Alternatively, the measurement circuit board may be provided directly to the pedal shaft 10.

The first coil 34 is arranged around the pedal shaft 10 such that it surrounds the pedal shaft 10, The first coil 34 is arranged to rotate together with the pedal shaft 10.

The second coil 44 is provided to the second coil support 40. The second coil support 40 is arranged around the pedal shaft 10 and separate from the pedal shaft 10. Accordingly, the second coil support 40 and the second coil 44 do not rotate together with the pedal shaft 10.

The second coil 44 is arranged adjacent to the first coil 34. The transmission gap 200 is provided between the first coil 34 and the second coil 44.

Accordingly, the first coil 34 and the second coil 44 are arranged adjacent to each other in the direction of the pedal shaft 10. The first coil 34 and the second coil 44 are not in contact with each other. Therefore, the first coil 34 and the second coil 44 are arranged to transmit power and data in contactless manner between each other. There is no physical or galvanic contact between the measurement unit and the transmitter unit.

The first coil 34 is arranged to rotate together with the pedal shaft 10 adjacent to the second coil 44. This provides continuous power and data transmission between the first and second coils 34, 44 during the revolution of the pedal shaft 10.

Figure 10 shows cross sectional view of the embodiment of figure 9 along the pedal shaft 10.

The first coil support 30 is provided to or connected to the pedal shaft 10 and arranged to rotate together with the pedal shaft 10. The first coil support 30 is arranged around the pedal shaft 10.

The first coil 34 is provided to the first coil support 30 and around the pedal shaft 10.

The second coil support 40 or the measurement unit is arranged around pedal shaft 10 and adjacent the first coil support 30. As shown in figure 10, the transmitter unit or the second coil support 40 is arranged around the pedal shaft 10 such that a rotation gap 202 is provided between the transmitter unit or the second coil support 40 and the pedal shaft 10. Therefore, the transmitter unit and the second coil support 40 are separate from the pedal shaft 10 and do not rotate together with the pedal shaft 10.

The second coil 44 is provided to the second coil support 40 and arranged around the pedal shaft 10.

The pedal shaft 10 is arranged to rotate relative to the transmitter unit, the second coil support 40 and the second coil 44. Thus, the first coil 34 is arranged to rotate relative to the second coil 44.

The first coil 34 and the second coil 44 are arranged adjacent to each other and the transmission gap 202 is provided between the first coil 34 and the second coil 44.

In this embodiment, the transmission gap 202 is provided in the longitudinal direction of the pedal shaft 10.

The first ferrite element(s) 39 is provided adjacent to the first coil 34. The first ferrite element(s) 39 is provided to or in connection with the measurement unit and/or the first coil support 30.

The second ferrite element(s) 49 is provided adjacent to the second coil 44. The second ferrite element(s) 49 is provided to or in connection with the measurement unit and/or the second coil support 40. As shown in figure 10, the first coil 34 is arranged between the first ferrite element(s) 39 and the second coil 44. The second coil 44 is arranged between the second ferrite element(s) 49 and the first coil 34.

Accordingly, in the embodiment of the present invention, the first coil 34 and the second coil 44 are arranged between the first ferrite element(s) 39 and the second ferrite element(s) 49.

Figure 11 shows schematically one embodiment of the pedal shaft measurement system according to the present invention.

The measurement unit 100 is provided to and mounted in connection with the pedal shaft 10. Thus, the measurement unit 100 rotates together with the pedal shaft 10.

The measurement unit 100 comprises the sensor 32, the measurement circuit board and the first coil 34.

The transmitter unit 110 is arranged separate from the pedal shaft 10 and arranged stationary in relation to the pedal shaft 10. The transmitter unit 110 comprises the second coil 44 and the transmitter circuit board 42.

The transmitter unit 110 or the transmitter circuit board 42 thereof is further connected to the power unit 2 or the central processing unit 50 of the power unit 2.

The first coil 34 and the second coil 44 are arranged spaced apart from each other with the transmission gap 200. Thus, the first coil 34 and the second are arranged to provide contactless connection between the measurement unit 100 and the transmitter unit 110 over the transmission gap 200.

Figure 12 shows schematically one embodiment of the pedal shaft measurement arrangement and system according to the present invention. In this embodiment, the pedal shaft 10 is a single piece pedal shaft. The output interface 24 is arranged to the pedal shaft 10 between the first crank interface 20 and the second crank interface 22. Further, the output interface 24 is arranged to the pedal shaft 10 between the first end and the second of the pedal shaft.

In this embodiment torque inputted to the pedal shaft 10 from the first and second crank interface 20, 22 by the user needs to be measured separately. Therefore, the measurement unit 10 is provided with two torque sensors 32, 38.

As shown in figure 12, the measurement unit 100 comprises a first sensor or a first torque sensor 32 provided or mounted to the pedal shaft 10 between the first crank interface 20 and the output interface 24. Thus, the first sensor or the first torque sensor 32 is arranged to measure torque inputted to the pedal shaft 10 via the first crank interface 20.

The measurement unit 100 comprises a second sensor or a second torque sensor 38 provided or mounted to the pedal shaft 10 between the second crank interface 22 and the output interface 24. Thus, the second sensor or the second torque sensor 38 is arranged to measure torque inputted to the pedal shaft 10 via the second crank interface 22.

In the embodiment of figure 10, both the sensors or the torque sensors 32, 38 are connected to the measurement circuit board 36. Thus, the measurement unit 100 or the measurement circuit board 36 is arranged to calculate the sum of the measured torque or the sensor output signals of the sensors 32, 38 or combine the measured torque or the sensor output signals of the sensors 32, 38. The calculated sum or combined measurement data is transmitted from the measurement unit 100 via the first coil 34 to the transmitter unit 110.

The first sensor 32 is connected to the measurement circuit board 36 such that current is transmitted to the first sensor 32 from the measurement circuit board 36 and sensor output signal or measured sensor value, for example the changed resistance value, is transmitted from the first sensor 32 to the measurement circuit board 36. The first sensor 32 is connected to the measurement circuit board 36 with a first sensor connection 31, such as sensor line(s), arranged to transmit current to the first sensor 32 from the measurement circuit board 36 and sensor output signal from the first sensor 32 to the measurement circuit board 36.

Similarly, the second sensor 38 is connected to the measurement circuit board 36 such that current is transmitted to the second sensor 38 from the measurement circuit board 36 and sensor output signal is transmitted from the second sensor 38 to the measurement circuit board 36. The second sensor 38 is connected to the measurement circuit board 36 with a second sensor connection 37, such as sensor line(s), arranged to transmit current to the second sensor 37 from the measurement circuit board 36 and sensor output signal from the second sensor 38 to the measurement circuit board 36.

The second sensor 38 may also be provided to a half bridge configuration or a full bridge configuration, as shown in figures 18 and 19.

In an alternative embodiment, the measurement unit 100 comprises two first coils 34. The first sensor 32 in operatively connected to one of the two first coils 34 and the second sensor 38 is operatively connected to the other of the two first coils 34. In this embodiment also the transmitter unit 110 comprises two second coils 44, respectively. There maybe one or two measurement circuit boards 36 and/or one or two transmitter circuit boards 42.

In a further embodiment, there may also be two separate measurement units 100 for the first and second sensors 32, 38, respectively. There may also be two separate transmitter units 110 for the two separate measurement units 100.

Utilizing two first and second coils 34, 44, two measurement circuit boards 36 and/or two transmitter circuit boards 42 is carried out in similar manner and with similar connections and operations as with only one as shown in connection with figures 1 to 11.

Figure 13 shows an embodiment in which the pedal shaft 10 comprises an output interface support 29 extending from the pedal shaft 10. The output interface support 29 is connected to the pedal shaft 10 between the first crank interface 20 and the second crank interface 22. The output interface 24 is connected to the output interface support 29. Thus, the output interface 24 in connected to the pedal shaft 10 via the output interface support 29.

As shown in figure 13, the torque sensor 32 is arranged to the output interface support 29. The torque sensor is arranged to measure torque inputted to the pedal shaft 10 from the first and second crank interfaces 20, 22.

The torque sensor 32 may also be arranged as shown in figures 4, 9, 12 or 15.

Further, the output shaft support 29 may also be provided to embodiments of figures 4, 9, 12 and 15.

Figure 14 shows an alternative embodiment, in which the pedal shaft 10 is formed from two parts which are attached to each other.

As shown in figure 14, the pedal shaft 10 comprises a first outer shaft member 26 and a second inner shaft member 28. The second inner shaft member 28 is arranged at least partly inside the first outer shaft member 26. Accordingly, the first outer shaft member 26 comprises a shaft opening extending along the longitudinal axis A of the pedal shaft 10. The second inner shaft member 28 is arranged and attached inside the shaft opening of the first outer shaft member 26. The first outer shaft member 26 and the second inner shaft member 28 are coaxial shaft members having the common pedal shaft axis A.

In the embodiment of figure 14, the first outer shaft member 26 comprises the first crank interface 20. The second inner shaft member 28 comprises the second crank interface 22. Further, the first outer shaft member 26 comprises the output interface 24. In an alternative embodiment, the first outer shaft member 26 comprises the first crank interface 20. The second inner shaft member 28 comprises the second crank interface 22. Further, the second inner shaft member 28 comprises the output interface 24 in the position outside the shaft opening.

The two shaft members 26, 28, or shaft halves, of the pedal shaft 10 are joined together with interference fit by heating the first outer shaft member 26 and cooling the second inner shaft member during assembly of the pedal shaft 10. This creates a strong joint between the first outer shaft member 26 and the second inner shaft member 28. The cooled second inner shaft member 28 is arranged inside the shaft opening of the first outer shaft member 26. Then the temperatures are let to even. Outer surface of the second inner shaft member 28 is pressed against the inner surface of the shaft opening of the first outer shaft member 26 such that the interface fit 26 is formed between the first outer shaft member 26 and the second inner shaft member 28. The interference fit 25 provides an interference fit area defining an area 27 on which the first outer shaft member 26 and the second inner shaft member 28 are pressed against each other and the interference fit is formed.

The strong interference fit 26 enables high input torques from the second crank interface 22 to be driven through the second inner shaft member 28 to the first outer shaft member 26, and further out from the pedal shaft output interface 24. The interference fit 26 enables the surface of the second inner shaft member 28 to be provided rotationally symmetrical which further enables avoiding areas of high material stress in the pedal shaft 10. Furthermore, the pedal shaft diameter can be maximized which will significantly increase load carrying capacity of the second inner shaft member 28.

As the torque inputted to the second crank interface 22 of the second inner shaft member 28 is driven to the first outer shaft member 26 and to the output interface 24 in the first outer shaft member 26, only one torque sensor 32 is able to measure the torque inputted to the pedal shaft via both the first and second crank interfaces 20, 22.

Figures 14 to 22 show a specific embodiment of the present invention. In this embodiment, the pedal shaft 10 is formed from the first outer shaft member 26 and the second inner shaft member 28 as disclosed in connection with figure 11. The measurement unit 100 comprises the first coil 34, the measurement circuit board 36 and one sensor 32. In this embodiment, the sensor 32 is a torque sensor arranged to measure torque inputted to the pedal shaft 10 from the first and second crank interfaces 20, 22. Only one torque sensor 32 is able to measure the torque inputted from both the first and second crank interfaces 20, 22 due to the two part construction and interference fit 25 of the pedal shaft 10.

In the embodiment of figures 14 and 15 output interface 24 is provided directly to the pedal shaft 10. However, the pedal shaft 10 may also comprise the output interface support 29 extending from the first outer shaft member 26 of the pedal shaft 10, as in the embodiment of figure 13. The output interface support 29 is connected to the first outer shaft member 26. The output interface 24 is connected to the output interface support 29. The torque sensor may be arranged to the output interface support 29 and arranged to measure torque inputted to the pedal shaft 10 from the first and second crank interfaces 20, 22.

The torque sensor 32 is a strain gauge. A schematic view of the strain gauge 32 is in figure 13. The strain gauge 32 is a sensor whose measured electrical resistance varies with changes in strain. Strain is the deformation or displacement of material that results from an applied stress. Stress is the force applied to a material, divided by the material’s cross-sectional area. The strain gauge 32 is arranged to convert the applied torque into an electrical signal which can be measured. Torque causes strain, which is then measured with the strain gauge 32 by way of a change in electrical resistance.

The strain gauge 32 comprises backing 60 and a resistive foil 62 provided with a strain sensitive pattern of sensor conductors 62. The strain gauge 32 is arranged to measure deformation and strain in longitudinal direction of the sensor conductors 62, as in direction S in figure 16.

The strain gauge 32 further comprises solder pads 64 connected to the resistive foil and sensor conductors thereof, and the electric leads 66 arranged to connect the strain gauge 32 to the measurement circuit board 36.

In the pedal shaft 10 the strain gauge 32 and the backing thereof is glued directly to the surface of the pedal shaft 10 or to the surface of the first outer shaft member 26. Also, other attachment means may be used.

As shown in figure 16, the strain gauge 32 may be arranged to the pedal shaft 32 such that measurement direction S of the strain gauge 32, or the longitudinal direction sensor conductors 62 is perpendicular direction of the longitudinal axis A of the pedal shaft 30. Thus, torque inputted from the first and second crank interfaces 20, 22 may be measured with the strain gauge 32.

In alternative embodiment, the longitudinal direction sensor conductors 62 is arrange in an angle of 90 to 0 degrees in relation to the direction of the longitudinal axis A of the pedal shaft 30. In a specific embodiment, the angle sensor conductors 62 in relation to the direction of the longitudinal axis A is 45 degrees.

The strain gauge 32 is connected into a Wheatstone Bridge circuit. The Wheatstone Bridge circuit is provided to the measurement circuit board 36.

In the Wheatstone bridge configuration, an excitation voltage 70 is applied across the circuit, and the output voltage 72 is measured across two points in the middle of the bridge. When there is no load acting on the load cell, the Wheatstone bridge is balanced and there is zero output voltage 72. Any small change in the material under the strain gauge 32 results in a change in the resistance of the strain gauge 32 as it deforms with the material. This causes the bridge to be thrown out of balance, resulting in a change in the output voltage.

In the measurement unit 100, either full bridge configuration, quarter bridge configuration or half bridge configuration can be used.

Figure 17 shows schematically a quarter bridge configuration, in which one strain gauge 32 is used together with three predetermined resistors 76, 73, 74. Alternatively, a half bridge configuration is used in which two strain gauges 32 are used together with two predetermined resistors 76, 73, as shown in figure 18.

Further alternatively, a full bridge configuration is used in which four strain gauges 32, as shown in figure 19.

The pedal shaft measurement system and operation thereof are further described together with figures 20 to 22.

The second coil 44 of the transmitter unit 110 is driven with alternating current (AC current) which creates an alternating magnetic field around the second coil 44. The alternating magnetic field induces current to the first coil 34 of the measurement unit 100. The current induced to the first coil 34 is used to power the measurement circuit board 36. The power transmitting frequency stays constant through-out the operation. Figure 20 shows schematically the power transmitting AC current. In figure 20 Y denotes voltage amplitude of the AC current and X denotes time.

The measurement unit 100 and the measurement circuit board 36 thereof is arranged to alternate impedance of the first coil 34 at a frequency that is dependent on the measurement output signal of the strain gauge 32. This changes the load seen by the transmitter unit 110, and second coil 44 and the transmitter circuit board 42 thereof, and affects voltage amplitude of the second coil 44. Thus, a changing amplitude modulated frequency is generated, as shown in figure 21. In figure 21 Y denotes the modulated voltage amplitude of the AC current and X denotes time. The modulated voltage amplitude has maximum amplitude points 80 and minimum amplitude points 82.

This changing amplitude modulated frequency is further and interpreted into an actual torque value. Torque value is interpreted or calculated from the frequency 84 of rising or falling edges of the amplitude modulated wave, as shown in figure 19. Y denotes amplitude and X denotes time in figure 22.

The torque value is interpreted or calculated by the transmitter unit 110 or the transmitter circuit board 42 thereof.

Accordingly, resistance changes of the strain gauge 32 is used to modulate a voltage value in the measurement unit 100 or the measurement circuit board 36. Based on the voltage value, the measurement unit 100 or the measurement circuit board 36 is arranged to alternate impedance of the first coil 34. The alternated impedance is seen as the amplitude modulated wave by the transmitter unit 110 or the transmitter circuit board 42. Finally, the transmitter unit 110 or the transmitter circuit board 42 is arranged to convert the amplitude modulated wave into analog voltage value indicating the amount of torque on the pedal axle 10.

The strain gauge 32 may also be replaced by an alternative torque sensor.

In the pedal measurement system of the present invention the first coil 34 and the second coil 44 are arranged to provide contactless connection between the measurement unit 100 and the transmitter unit 110 such that the second coil 44 is configured to transmit power to the measurement unit 100 in contactless manner, and the first coil 34 is configured to transmit measurement data to the transmitter unit 110 in contactless manner.

The power unit 2 further comprises at least one motor 51, 52, and the transmitter unit 110 is connected to the power unit 2 for controlling the at least one motor 51, 52 based on the measurement data received from the measurement unit 100 or based on the torque measurement.

The method for controlling a power unit 2 of an electric pedal vehicle 1 comprises measuring a pedal shaft parameter with the measurement unit 100 for providing measurement data, and controlling the at least one motor 51, 52 of the electric pedal vehicle 1 based on the measurement received in the power unit.

In the method the pedal shaft parameter comprises transmitting power from the transmitter unit 110 to the measurement unit 100 in contactless manner between the second coil 44 provided to the transmitter unit 110 and the first coil 34 provided to the measurement unit 100. The method further comprises transmitting measurement data from the measurement unit 100 to the transmitter unit 110 in contactless manner between the first coil 34 and the second coil 44.

The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the above examples but may vary within the scope of the claims.