DESCRIPTION

Field of the invention

The present invention relates to a force sensor comprising a guide provided with a detection medium, which detection medium is movable between a first and a second stop position in said guide for measuring a resulting force on the detection medium, further comprising means for providing an activation signal in dependence on a current position of the detection medium in the guide.

The invention further relates to a motion stabilization system provided with such a force sensor and to a vehicle provided with a motion stabilization system or with a force sensor as described above.

Background of the invention

Motion stabilization systems for stabilising, for example, the road behaviour of a vehicle, frequently make use of force sensors or accelerometers for measuring force or acceleration components in various directions relative to, for example, the direction of movement of the vehicle. More complex versions of such stabilization systems are based inter alia on force sensors capable of measuring the magnitude of the force in various gradations of precision, which parameter can be used in calculations on the basis of which feedback to the vehicle's driving mechanism can be provided. Simple motion stabilization systems may for example comprise a force sensor which determines whether the force in a specific direction exceeds a limiting value. When a limiting value is being exceeded, such systems will interfere with the vehicle's driving mechanism, for example.

Also in the case of simple motions stabilization systems it may be useful to base the decision whether or not to interfere with the driving mechanism on more factors than just the force in a given direction. This is for example the case with a motion stabilization system for stabilising the motion of, for example, an electrically driven vehicle. An electrically driven vehicle is generally used by persons who have difficulty walking, for example, or by elderly people whose physical condition does not allow them to cover large distances on foot. An important function of the motion stabilization system of such a vehicle is that it protects the person driving the vehicle against the vehicle getting off balance, which may lead to serious accidents. In some embodiments thereof (such as a mobility scooter), an electrically driven vehicle is configured as a three-wheeled vehicle, which does not have a positive effect on the stability of the vehicle.

In order to be able to adequately assess the risk of destabilization, it is important to take into account not only the force component in a given direction but also the position of the steering wheel of the vehicle before interfering with the driving mechanism of the vehicle. In addition to that, other parameters may also play a role in determining whether interference by the system is required.

Taking other parameters besides the force component into account renders the motion stabilization system significantly more complex than making a determination solely on the basis of the force component in a given direction. In order to be able to compare the two parameters with each other, a microprocessor unit is generally required, which unit makes the necessary computations on the basis of the measured parameters. This complexity of the motion stabilization system will have an adverse effect on factors such as speed and cost price.

Summary of the invention

It is an object of the present invention to obviate the above drawbacks of the prior art and to provide a device which makes it possible in a simple manner to take other parameters besides the measured force component into account in stabilizing a vehicle's motion.

In order to accomplish that object, the invention provides a force sensor comprising a guide provided with a detection medium, which detection medium is movable between a first and a second stop position in the guide for measuring a resulting force on the detection medium, further comprising means for providing an activation signal in dependence on a current position of the detection medium in the guide, wherein the detection medium is made of a magnetizable material and the force sensor is further provided with means for providing a magnetic field for exerting a magnetic force on the detection medium, which magnetic field is adjustable so as to make it possible to adjust the sensitivity of the force sensor in dependence on the magnetic field.

The force sensor according to the present invention is a simple force sensor by means of which it is possible to determine on the basis of the position of the detection medium between two stop positions in the guide whether the resulting force on the detection medium in a particular direction exceeds a limiting value. In addition to that, however, the force sensor according to the present invention makes it possible to adjust said limiting value, and thus the sensitivity of the force sensor, at will in that the detection medium in the guide is made of a magnetizable material and in that the force sensor is capable of applying an adjustable magnetic field across the guide. The strength of the magnetic field can be used to influence the equilibrium of forces on the detection medium. In the case of a stronger magnetic field, the limiting value of the resulting force on the detection medium required for activating the force sensor is higher than in the case of a magnetic field having a relatively low field strength. Such a force sensor can be used to advantage in a motion stabilization system in which, in addition to the force components, also another parameter is to be taken into account before interfering with the driving mechanism.

According to a preferred embodiment, the force sensor comprises at least two guides, wherein each of said at least two guides is provided with a detection medium, and wherein the force sensor comprises means for providing the activation signal in dependence on a current position of at least one of the detection media in said at least two guides, and wherein each of said at least two guides is disposed so that a longitudinal direction of each of said guides is suitable for measuring the resulting force on the detection medium in a respective direction, wherein the means for providing the magnetic field are designed to provide an adjustable magnetic field near each of the guides for the purpose of making it possible to adjust the sensitivity of the force sensor in each respective direction. In said force sensor, the resulting force on the detection medium can be measured in two directions. The sensitivity can be adjusted by means of a magnetic field.

According to another embodiment, the invention provides a force sensor in which the or each guide is disposed at an angle to the force of gravity for the purpose of providing a starting position of the detection medium in the guide under the influence of the force of gravity. If the guides are disposed at an angle to the force of gravity, the detection medium will be located at one of the stop positions in the guide under the influence of the force of gravity when the vehicle is stationary or accelerates slightly. If, on the other hand, the guide is not the disposed at an angle, the starting position can be reached in an alternative manner, for example by applying a small magnetic field across the guides even when the vehicle is stationary. The skilled person will appreciate that the use of the force of gravity is to be preferred at all times over the application of a magnetic field. Such an embodiment is more energy-efficient.

According to another embodiment, the means for providing the magnetic field comprise a coil, wherein the strength of the magnetic field can be adjusted by adjusting the intensity of the current through the coil. This embodiment has the advantage that the sensitivity of the force sensor can be adjusted by means of a simple electronic circuit.

According to a preferred embodiment of the present invention, a motion stabilization system for a vehicle is provided wherein the vehicle has at least three wheels, and wherein the motion stabilization system is provided with a force sensor as described above.

The invention in particular provides a motion stabilization system according to this embodiment, which further comprises a sensor for determining the position of the steering wheel of the vehicle and means for providing an adjusting signal in dependence on the position of the steering wheel to the means for providing the magnetic field for the purpose of adjusting the strength of the magnetic field.

In this embodiment, the output signal provided by the force sensor (the resulting force on the detection medium does or does not exceed a limiting value) depends on the position of the steering wheel. A change in the position of the steering wheel will result in a change in the strength of the magnetic field, so that also the limiting value will change and the force sensor will provide an output signal. This makes it possible in a relatively simple manner to obtain a motion stabilization system which takes into account both the position of the steering wheel of the vehicle and force components in the directions detected by the force sensor. A complicated calculation for composing said value will not be needed in that case. A simple electronic circuit for controlling the magnetic field on the basis of the signal from the sensor for determining the position of the steering wheel will suffice for achieving a good result.

In a preferred embodiment, the adjusting signal is provided in such a manner that the strength of the magnetic field is inversely dependent on the position of the steering wheel in relation to a reference position, which reference position corresponds to a steering wheel position in which the vehicle moves in a straight line. When the vehicle is moving straight ahead, it is reasonably stable, with no centrifugal forces acting on the vehicle. The vehicle may get off-balance, however, when moving up too steep a lateral slope with the attendant risk of the vehicle turning over. The limiting value at which the force sensor will deliver a signal may be fairly high, considering the vehicle's reasonably stable driving condition. When the vehicle makes a sharp bend, however, a relatively large centrifugal force will act on the vehicle. A minor imbalance or undesirable force component in the direction of the centrifugal force, but also the centrifugal force itself, may result in the vehicle running into difficulty. In the case of a relatively major deviation of the steering wheel position from the starting position, the limiting value at which the force sensor responds will have to be relatively low, therefore. A large steering wheel deflection will correspond to a low-strength magnetic field, and thus to a low limiting value of the force sensor.

According to another embodiment, the motion stabilization system comprises processing means for receiving the activation signal and, in response thereto, reducing the power to be supplied to the vehicle by a driving mechanism. By directly interfering with the power of the vehicle, the risk of an imbalance can be strongly reduced in a quick and simple manner in an emergency situation. As soon as the vehicle is threatens to get off-balance, the power (and thus the speed) will be reduced, so that the vehicle will remain in balance.

A very simple embodiment is, for example, a motion stabilization system built into a vehicle provided with an electric motor, such as a mobility scooter as mentioned above. The processing means can in that case directly interfere with the power supplied to the vehicle by the electric motor. Since the vehicle is electrically driven, the design can remain simple and no mechanical parts need to be operated for reducing the power.

According to another embodiment, the force sensor is suitably placed for determining a resulting force in the direction transversely to the direction of movement of the vehicle. Resulting forces and force components in a direction transversely to the direction of movement constitute a major risk to the stability of the vehicle while driving. The skilled person will appreciate that also other resulting force components can be measured and be taken into account, and that the invention is not limited to measuring only force components transversely to the direction of movement.

According to another embodiment, the invention provides a vehicle provided with motion stabilization systems as described above or with a force sensor according to the invention.

The embodiments described in the foregoing can make use of any desired detection medium that is compatible with the specific design or the application for which the invention is used. The detection medium may be an element from a group comprising a ball, a wheel, a cylinder, a magnetizable, electrically conductive fluid or a suitably shaped object.

Brief description of the drawings

The invention will be explained in more detail hereinafter by means of a description of non-limitative, specific examples thereof, in which reference is made to the appended drawings, in which:

Figure 1 shows a motion stabilization system according to the present invention;

Figure 2 shows a force sensor according to the invention;

Figure 3 shows a force balance on a ball in a force sensor according to the present invention.

Detailed description of the drawings

Figure 1 shows a motion stabilization system 1 according to the present invention. In the system 1 , the power supplied to a vehicle by a motor 5 is controlled by means of a power control element 3. Connected to said power control element 3 are, for example, a power regulation unit 6 (equivalent to an accelerator pedal used with a combustion engine), a gear switch 7 (for switching the motor to one or more fast and slow positions), and (directly or indirectly) the battery of the vehicle.

The power control unit 3 also comprises a number of inputs and outputs 30 for receiving signals by means of which the operation of the power control unit can be influenced or set, for example. In the present embodiment, the inputs and outputs 30 are connected to a motion stabilization system 10. The motion stabilization system 10 is connected to sensors 17, 27, by means of which parameters that affect the road behaviour and stability of the vehicle can be sensed. An input/output port 14 provides a (digitized) signal to the inputs and outputs 30 of the power control unit 3. The motion stabilization system 10 is connected to a power sensor 17, which is capable of determining on the basis of a power balance whether interference by the motion stabilization system 10 with the motion of the vehicle is required. The force sensor 17 consists of two guides 19 and 20, in which balls 22 and 23 are present. The guides 19 and 20 are disposed at an angle to the gravity vector on the balls 22 and 23 (when the vehicle is stationary), which angle does not equal 90°. By disposing the guides at a slight angle relative to a plane perpendicular to the force of gravity in this manner, it is achieved that the balls 22 and 23 will have a preferred starting position in one of the ends of each of the guides 19 and 20. The guides consist of a pair of tubes, for example, whose ends form of first and a second stop position for the balls. When the vehicle is stationary or moving in such a manner that it is not necessary to interfere with the motion of the vehicle, the balls 22 and 23 will be in a starting position, for example in one of the two stop positions. When the forces on one of the balls 22 or 23 are off-balance, however, the ball will experience a resulting force which causes the ball to move to the second stop position (this will be explained in more detail yet with reference to figure 3). In the second stop position, the ball 23 provides an electric contact, in response to which the force sensor 17 will supply a signal to the motion stabilization system 10. When the motion stabilization system 10 receives a signal from the force sensor, the latter will send a digital signal to the power control unit 3. Said power control unit 3 causes the power supply to the vehicle by the motor 5 to be reduced (or even cut off altogether), as a result of which the vehicle will no longer be driven with sufficient force, if at all. Calamities such as the vehicle turning over or crashing as a consequence of dangerous driving can thus be prevented.

The need to interfere with the power control by the motion stabilization system 10 depends not only on the force balance as determined by the force sensor 17, but also on the position of the vehicle's steering wheel. When the vehicle makes a sharp bend, for example, and the position of the steering wheel 29 of the vehicle deviates strongly from the position of equilibrium (which position of equilibrium is defined as the position of the steering wheel in which the vehicle is moving ahead in a straight line), a minor imbalance of the forces can easily result in the vehicle becoming unstable. If the vehicle is moving straight ahead and the position of the steering wheel 29 does not deviate from the position of equilibrium, not every imbalance will constitute a risk to the vehicle's stability.

The influence of the position of the steering wheel 29 on the interference of the motion stabilization system 10 with the vehicle motion is taken into account in the motion stabilization system shown in figure 1 by providing the steering shaft of the steering wheel 29 with a steering wheel position sensor 27, which measures the extent to which the position of the steering wheel 29 deviates from the position of equilibrium. The signal provided by the steering wheel position sensor 27 is made dependent on the speed or the thrust of the motor and, amplified by means of difference amplifier 28, is supplied to drive electronics 25 for energizing an electromagnet 26 formed by an inductor. A feedback signal from the power control unit 3, provided via the connection 31 , is used for making the signal from the steering wheel position sensor 27 dependent on the speed/thrust. The skilled person will appreciate that the various connections between the system's components and elements may differ from those shown in figure 1. In the case of a deviation which is very small or zero, a relatively strong current will be supplied to the coil 26. The coil 26 generates a magnetic field near the guides. The balls 22 and 23 are made of a magnetizable material and experience a magnetic force which is commensurate with the strength and direction of the magnetic field generated by the coil 26. The skilled person will appreciate that the direction of the magnetic field near the guide 19 is opposite to the direction of the magnetic field near the guide 20 so as to ensure that the balls 22 and 23, respectively, will both experience a force that draws the balls towards the first position. The result of the magnetic field applied by means of the coil 26 is that a much greater imbalance is required for causing the balls 22 and 23 to move to the second stop position. When the user of the vehicle makes a sharp bend, this will be detected by the sensor 27 on account of the relatively large deviation of the steering wheel position from the position of equilibrium. The current through the coil will be reduced, so that the strength of the magnetic field will decrease. A small imbalance in the forces can in that case easily result in one of the balls 22 or 23 moving to the second stop position, so that the force sensor 17 will deliver a signal to the motion stabilization system 10. Said signal is digitized by means of a timer and suitable electronics and subsequently presented to the inputs and outputs of the power control unit 3. Said power control unit will adjust (reduce) the power delivered to the vehicle by the motor 3.

Figure 2 shows a force sensor 35 according to the present invention. The force sensor 35 consists of two guides 36 and 37. Each of said guides 36 and 37 comprises a ball 38, 39, respectively. The balls 38 and 39 are movable between two stop positions in their respective guides 36 and 37. The ball 38 is movable between a first stop position 44 and a second stop position 45 in the guide 36. The ball 39 is movable between a first stop position 46 and a second stop position 47 in the guide 37. In the first stop position 44, the ball 38 will make contact with electrodes 40 and 41 in the guide 36. In the second stop position 45, the ball 38 will make contact with the electrodes 43 and 40. At positions between the first and the second stop position, the ball 30 only makes contact with the electrode 40 but not with the electrode 41 , because the diameter of the guide 36 is larger than the diameter of the ball 38. In the first stop position, the electrodes 41 and 40 are positioned closer together, so that the ball 38 will make contact with the electrodes 40 and 41 in the first stop position. The electrodes 48, 49 and 50 in the guide 37 are arranged in a similar manner, so that the ball 38 will make contact with the electrodes 48 and 49 in the first stop position 46. In the second stop position, the ball 38 will make contact with the electrodes 49 and 50.

The force sensor 35 also comprises means 52 for generating a magnetic field near each of the guides 36 and 37. The direction of the magnetic field provided by said means 52 near the guide 36 is opposite to the direction of the magnetic field near the guide 37.

The force sensor 35 is also provided with a connector 53, so that said connector can be connected to control means which are capable of determining on the basis of contact between the electrodes 40, 41 , 43, 48, 49 and 50 whether one of the two balls 38 or 39, or both balls, are in the second stop positions 45 and 47, respectively, so that an activation signal needs to be transmitted for activating the motion stabilization system.

Figure 3 shows a force balance on a ball 55 in a guide 60 of a force sensor according to the present invention. The guide 60 is disposed at an angle φ to the force of gravity. Said angle φ does not equal 90°, so that the ball 65 has a preferred starting position in one of the ends of the guide 60. Said ball 65 is subject to the force of gravity F _e . Said force of gravity can be resolved into components F _g// and F _gx parallel and perpendicular, respectively, to the longitudinal axis of the guide 60.

When the vehicle moves through a bend (a bend to the left, seen from the guide shown in figure 3), the bail 65 is subject to a centrifugal force F _c perpendicular to the direction of movement in the plane of the curve described by the vehicle on the road. Said centrifugal force F _c is indicated by the arrow 70 in figure 3 and can again be resolved into a component F^, parallel to the longitudinal axis of the guide 60, indicated at 73, and a component F _Cl perpendicular to the longitudinal axis of the guide. The components F _9i and Fc _± are hardly, if at all, relevant to the movement of the ball 65 through the guide 60. The components of the forces parallel to the longitudinal axis of the guide, the gravity component 72 and the centrifugal force F ₉ „ 73 determine whether the centrifugal force is sufficiently large for setting the ball 65 in motion in the direction of the second stop position, where the electrodes 61 and 62 are located. In the case of a gentle curve, the centrifugal force F _c 70 will be small and the ball 65 will remain in the first stop position under the influence of the force of gravity F _g . If the centrifugal force F _c 70 becomes larger than the force of gravity F ₈ 60, the ball 65 will move in the direction of the electrodes 61 and 62.

The operation of the force sensor can be influenced by means of the magnetic field 68 that is generated by means of the coil 67. The magnetic field B 68 produces a magnetic force F _b 75 as shown in figure 3. Under the influence of said magnetic force F„ 75, the ball 65 is drawn to the first stop position and the centrifugal force F _c 70 will have to be sufficiently large to overcome both the gravity component F _g „ 72 and the magnetic force F _b 75 so as to set the ball 65 in motion.

A motion stabilization system according to the present invention is suitable for use in vehicles which are electrically driven at a relatively low speed, such as a mobility scooter, for example. The invention is not limited to the use thereof in electrically driven vehicles, however, but when suitably modified in a manner that will be obvious to those skilled in the art, it can also be used in vehicles which are driven by means of combustion engines or other driving means. In addition to that, a motion stabilization system according to the present invention can be used in vehicles provided with two or more wheels. The vehicle is furthermore suitable for use in vehicles capable of moving at higher speeds. In the above- described embodiments, the magnetic field used for influencing the sensitivity of the force sensor is controlled on the basis of the position of the vehicle's steering wheel in relation to a position of equilibrium. The skilled person will appreciate that it is also possible to use other parameters for influencing a magnetic field. It is furthermore possible to make the magnetic field dependent on several parameters at the same time, in which case the control electronics for the current through the coil for providing the magnetic field will be more complex.

The invention can be used as a combination sensor (inclination / G- force sensor), for example in a vehicle for stabilising undesirable motion forces. The sensor responds not only to resulting forces on the detection medium, but the present sensor also responds to (or in any case is influenced by) the orientation of the sensor relative to the surface on which the vehicle is driving. Using the activation signals from the centre, the vehicle can be decelerated at the right moment, so that the limits within which the vehicle can be safely driven are significantly and advantageously extended. In a simple embodiment, a sensor is a mass provided at the end of a spring; in this way the motion of the mass caused by changing forces is detected.

The term G-force is related to the source of calibration of the sensor, being the force of gravity (G-value or acceleration due to gravity 9.81 m/sec ² ). In the present sensor, the spring has been substituted for a magnetic field, this makes it possible to change the response value at desired moments. Since the mass in the sensors is disposed at a particular angle relative to the (level) ground surface, they also provide information on the position and orientation on the road or the ground surface. The sensor will be more sensitive in the case of a laterally sloping ground surface and respond sooner to an impending imbalance. The bandwidth within which the sensor must respond can be adjusted by means of the strength of the magnetic field.

The inductive resistance of the coil that is used for generating the magnetic field will change in case of a change in the position of the magnetic dynamic bodies in the sensor. Thus, when the detection medium is in motion, this can in principle be detected as a disturbance of the inductive resistance of the coil by means of which the magnetic field is generated, even before an activation signal is produced. By measuring this parameter, for example by means of an AC signal on the DC component through the coil (to generate the magnetic field), it is possible to obtain information on the motion of the detection medium. Said parameter can be readily measured, for example by means of a 5 kHz AC signal having a small, suitably selected amplitude, on top of a DC signal for the magnetic field. Thus it is possible to detect, for example, that the vehicle is driving over a hump or an object, whilst an activation signal is not produced. This information can be used to advantage in the stabilization system.

It is possible to use a ball, for example, for the dynamic bodies. The invention is not limited thereto, however. In an alternative embodiment, the detection medium is a small cylinder or wheel that moves within a guide. Furthermore, a magnetizable, electrically conductive liquid material may be used.

The invention is not limited by the above specific embodiments, but it is only limited by the scope of the appended claims in the light of the description and the drawings of the present application. It is in particular noted that the invention is suitable for and can be used to advantage in electric vehicles of any desired type. The example of a mobilized scooter that has been cited a few times in the foregoing merely serves by way of illustration of the principles of the invention and should not be interpreted as being limitative to the invention. Although stabilization is also important in the case of four-wheeled (or multi-wheeled) vehicles, the use thereof in vehicles having less than four wheels is very advantageous in connection with the lower initial stability of such vehicles.