SUSPENSION AND TRACTION SYSTEM

Abstract

A suspension and traction system is described for a vehicle equipped with a frame and a propulsive element (92) by rolling on the ground. An electric actuator (M3) is used for determining a steering angle () of the propulsive element.

Claims

1. Suspension and traction system for a vehicle equipped with a chassis and a propulsive element (92), which is propulsive by rolling on the ground and adapted to move the vehicle relative to the ground, comprising: two rotary electric motors (M1, M2), which are mounted to impart an angular torque in equal directions to the propulsive element to propel the vehicle on the ground, are independently controllable from one another and each comprises a stator (M1s, M2s) and a rotor (M1r, M2r); wherein the two rotors (M1r, M2r) are coupled to the propulsive element (92) to transfer to it rotary motion through a transmission shaft (90), and have a common rotation axis (X) which is fixed with respect to the vehicle's frame; and the stators (M1s, M2s) are controllable to rotate about the respective rotor independently of each other, and rigidly connected substantially to a same point (P), external to the motors, to exert a thrust generated by a coordinated angular displacement of theirs about the respective rotors in opposite angular directions; a mechanical transmission (26) for transmitting the thrust generated on said point (P) to the propulsive element, the thrust thereby determining the relative position of the propulsive element with respect to the frame, characterized by comprising an electric actuator (M3) mounted for determining a steering angle () of the propulsive element.

2. System according to claim 1, comprising an electronic control unit (U) for controlling said motors, wherein the electronic control unit is configured for controlling the actuator to impose a steering angle of the propulsive element according to a reference value (ST*) set by the driver of the vehicle.

3. System according to claim 2, wherein the electronic control unit is configured to calculate said steering angle as a function of said reference value (ST*) and of a value (.sub.current) indicating said relative position.

4. System according to claim 2, comprising a sensor (88) for detecting said relative position.

5. System according to claim 2, wherein the electronic control unit is configured to calculate the value indicating said relative position by processing feedback signals (M1f, M2f) coming from the first and second motor.

6. System according to claim 2, wherein the electronic control unit is configured to calculate the value indicating said relative position by processing position signals (M1f, M2f) relative to the angular position of the first and second stator.

7. System according to claim 2, wherein the control unit is configured to calculate said steering angle () as a function of said reference value (ST*) and of a value indicating said relative position (.sub.current) in order to correct the deviation with respect to said reference value caused by a vertical oscillation of the propulsive element with respect to its plane of rolling.

8. Bump steering correction method implemented within a system according to any one of the preceding claims, with the step of calculating the steering angle () to be imposed on the propulsive element as a function of a reference value (ST*) and a value (.sub.current) indicating the relative position of the propulsive element and the frame, so as to correct the deviation with respect to said reference value caused by a vertical oscillation of the propulsive element with respect to its plane of rolling.

9. Method according to claim 8, wherein from the calculated steering angle () there is produced, e.g. through a table or mathematical function, a control signal for the actuator.

10. Method according to claim 8, wherein the current steering angle (.sub.current) is detected in real time, the current steering angle (.sub.current) is compared with the nominal one (ST*), i.e. the value set by the driver and equal to the value with no road imperfection; the comparison result () is processed to generate a corrective control signal (SM3*) for an actuator (M3) acting on the propulsive element (92), in particular the said third actuator, so that the displacement of the actuator induced by the correction signal brings the steering angle () back to the value set by the driver (ST*) and equal to the value with no road imperfection.

Description

[0059] The advantages of the invention will be clearer from the following description of a preferred embodiment of a suspension and traction system, referring to the attached drawing in which

[0060] FIG. 1 shows a principle block diagram,

[0061] FIG. 2 shows a block diagram for the calculation of a correction value for a steering angle;

[0062] FIG. 3 shows a simplified mechanical scheme, with components illustrated as in use;

[0063] FIG. 4 shows a cross-section of an electric actuator.

[0064] In the figures the arrows between components indicate signal lines, wherein the arrow points towards the component that receives the signal.

[0065] The illustrated system MC is used to control the steering movement of a propulsive element, e.g. in the form of a wheel 92. The wheel 92, by rolling on a ground T (FIG. 3), moves an associated vehicle (not shown). The system MC is e.g. replicated on all the wheels of the vehicle.

[0066] The system MC comprises

[0067] two identical electric rotary motors M1, M2 which through a shaft 90 are able to rotate the wheel 92; and

[0068] a third actuator or motor M3.

[0069] The electric power supply of the motors M1, M2, M3 can be obtained, for example. through inverters or power-electronics stages of known topology.

[0070] An electronic control unit U, e.g. microprocessor-based, is programmed or configured for controlling the motors M1, M2. E.g. by controlling inverters or electronic power stages, the control unit U is able to control the wheel 92's rotation rate and the height of the point P and Q (see below). To this aim, the electronic control unit U controls the motors M1, M2 through signal lines M1L, M2L, and the third actuator or motor M3 with a signal SM3*.

[0071] The two electric motors M1, M2 are formed by a respective stator M1s, M2s and a respective rotor M1r, M2r.

[0072] The rotors M1r, M2r are coaxial and have a common rotation axis indicated with X. The axis X is fixed with respect to the vehicle frame, e.g. by mounting the rotors M1r, M2r and/or the shaft 90 on a ball bearing (not shown) having a ring integral with the frame.

[0073] Each stator M1s, M2s is connected to a respective rigid arm 22, 24, and the arms 22, 24 are connected to a common point P external to the electric motors M1, M2.

[0074] The point P belongs or is connected to the end of a lever 40 which is oscillating, approximately at its own center, about an axis Y fixed with respect to the vehicle frame. The other end of the lever 40 (point Q) is connected to a hub 94 of the wheel 92 by a rigid arm 26.

[0075] Preferably the wheel 92 is also connected to suspension arms B, e.g. spring-actuated o dumped-oscillation arms.

[0076] The rotation of the rotors M1r, M2r about the axis X causes the wheel 92 to rotate about its rotation axis W.

[0077] By controlling the power supply of the electric motors M1, M2 (i.e. by giving more or less power than that required by the wheel 92) it is possible to move the stators M1s, M2s about the axis X simultaneously with opposite angular directions, i.e. one in clockwise direction and one in counter-clockwise direction.

[0078] E.g. it is possible to cause the arms 22, 24 to raise and push the point P upwards (in this case the point P moves away from the axis X). The lever 40 then rotates about the axis Y (the angle formed by the lever 40 and a horizontal plane varies) and moves the point Q downwards. It follows that the arm 26 pushes the hub 94 downwards and towards the ground, thereby obtaining, among other things, a distance variation between the axes W and X, which are parallel in the example. In the example, the axis Y is orthogonal to an imaginary vertical plane passing through X (and/or W).

[0079] An upward movement of the hub 94 can be achieved by reversing all the motions described for the previous case (the point P approaches the axis X).

[0080] It should be noted that the rotary torque applied to the wheel 92 by the rotors M1r, M2r and the force imparted on the wheel 92 towards the ground by the stators M1s, M2s are independently-controllable variables. So it is e.g. possible, during acceleration, to push the wheel 92 further towards the ground to increase its grip.

[0081] The third motor or actuator M3 is installed on the vehicle to exert a force on the wheel 92 via a drive member 91, e.g. a rigid arm. The force generated by the third motor or actuator M3 is controlled so as to change the steering angle (see FIGS. 1 and 3), i.e. to rotate the wheel 92 about a vertical axis K passing through the ground's supporting point of the wheel 92.

[0082] The electronic control unit U also controls the third motor or actuator M3. Furthermore, the electronic control unit U is connected [0083] to a steering control member 80, such as for example a steering wheel or a cloche, which sends to the input of the electronic control unit U a reference signal ST* for steering. The signal ST* contains information or data relating to the direction desired by the driver for the vehicle; and [0084] to a vehicle speed control member 82, such as for example a pedal accelerator or a lever, which sends to the electronic control unit U a reference signal ACC* for speed or acceleration. The signal ACC* contains information or data relating to the speed or acceleration desired by the driver for the vehicle; and [0085] to a vehicle speed sensor 84, such as an optical encoder or a tachometer, which sends to the electronic control unit U a signal V* relative to the actual angular speed or acceleration of the wheel 92. The signal V* contains information or data relating to the actual angular speed or acceleration of the wheel 92, and therefore of the vehicle.

[0086] The electronic control unit U is programmed

[0087] to read the signal ST* and drive the motor M3 to obtain the desired steering (i.e. a desired angle ), and

[0088] to read the signal ACC* and the signal coming from the speed sensor 84, to then drive the motors M1, M2 in order to maintain the vehicle speed at the set reference, through e.g. known feedback control schemes.

[0089] To solve the bump steering problem, the system MC works as follows, see FIG. 2 showing a block diagram that describes calculation steps in the control unit U.

[0090] The signal ST* is processed in the electronic control unit U by a computation block W1 to generate a reference * of the steering angle, which is then processed by a computing block W2 to generate an electric reference SM3* with which to drive the motor M3 to get the desired steering angle. E.g. the electric reference SM3* is the input reference of a feedback control acting on the motor M3.

[0091] To compensate for the steering bump, the computation block W2 generates the electrical reference SM3* as a function of a second signal S, wherein S indicates the deviation of the wheel 92's level compared to its nominal value (the one without impact, hump or hole or the one related to a straight trajectory for the vehicle).

[0092] In other words, SM3*=F (S; *), where F ( ) is a two-variable mathematical function or an algorithm, executed inside the block W2.

[0093] The signal or data S may be calculated, e.g. [0094] from a signal LV of feedback M1f, M2f coming from the motors M1 M2 respectively, and then processed by a computing block W3, and/or [0095] from a signal .sub.current coming from a sensor 88 that detects the angle in real time. The electronic control unit U e.g. calculates in the block W4, which for example is a subtractor, the difference

*=*.sub.current

[0096] and uses * as a further argument of a function or algorithm for calculating the electrical signal SM3*. The angular reference * is e.g. obtained by processing the signal ST* through a computational block W5.

[0097] When the wheel 92 does not have the height it should on flat or regular ground (case e.g. of *0), by means of the block W2 the electric signal SM3* is altered to compensate for the variation of steering due to changes in the wheel 92's suspension, i.e. the bump steering. That is, the block W2 adds to the electrical signal SM3* a contribution, derived from the signal LV or *, which remains as long as the anomaly remains in the suspension, and such contribution, function of LV and/or *, translates into a corrective movement of the motor M3 on the wheel 92. Said corrective movement re-establishes the correct angle which guarantees a steering direction as set byand desired withthe signal ST*. In the illustrated example, said corrective movement consists of a displacement of the member 91.

[0098] E.g. the block W2 may be a look-up table, which has two or three input indices (e.g. *, LV and *) and an output data (i.e. SM3*). The look-up table contains a tabulated value of the electrical signal SM3* for each * and various values of LV and/or *. Or the calculation in the block W2 may be executed in real time in the digital domain, if for example the signals in FIG. 2 are digital, i.e. obtained by sampling, or analog.

[0099] The representation of FIG. 2 is only illustrative of the general logic, some computational blocks being able to be implemented or arranged in different ways or even absent. Not necessarily the system must provide for the calculation of LV or *, one of the two or another equivalent signal being sufficient.

[0100] Or the signal SM3* can be derived by exploiting other signals. E.g. some of the computational blocks as illustrated, or all, may be integrated into one another or made with just one algorithm calculated within a microprocessor.

[0101] FIG. 4 shows a diagram of the actuator M3. It is a rotary electric motor equipped with a screw 70 and a recirculating ball nut screw 72. The screw 70 is integral with the member 91 (e.g. a piston) and the nut screw 72 is integral with a rotor 74 of the motor 50. An optional but advantageous protection cap 76 is present, e.g. made of rubber, to prevent dirt from entering the screw.

[0102] The control of motor 50 allows the member 91 to move back and forth to control the angle .

[0103] The system MC is open to many variations and variables.

[0104] The electric motors M1, M2 must not necessarily be equal.

[0105] On the shaft 90 it is preferable to mount at least one joint, e.g. a Cardan joint, to allow or facilitate the offset of the axes W and X and/or a different orientation of the axis W.

[0106] Each stator M1s, M2s may be connected to the point P also by means different from the arms 22, 24, and the point P does not necessarily represent a geometric point, it can also befor mechanical needsan extended element to which the stators M1s, M2s are connected at slightly spaced points.

[0107] The lever 40 may be oscillating at a point other than its center, and the axis Y fixed with respect to the frame may be obtained e.g. by simple pivoting.

[0108] Also the arrangement of the points Q and P on the lever 40 can vary, as well as the means for transferring from the point Q to the wheel 92 the force generated by moving the stators M1s, M2s.

[0109] It is preferable to mount a mechanical (e.g. helical) spring or a gas spring in parallel to the arm 26, between the wheel 92 and the frame, to compensate for the weight of the frame.

[0110] The signals of FIGS. 1 and/or 2 may be digital, e.g. obtained by sampling of electric quantities, or analog.

[0111] The motor M3 may also be of pneumatic type.

[0112] The kinematic chain of the wheel suspension is not essential, being sufficient to be able to vary the wheel-frame distance using the electric motors.