Compensation of the Thermal Effect in a Vehicle Suspension System

Abstract

A method for controlling the damping characteristic of a shock absorber of a vehicle, particularly for compensating the variation of the operating temperature of the shock absorber, in an active or semi-active suspension system. The compensation of the variation of the operating temperature of the shock absorber takes place by: estimating a mechanical power dissipated in heat by the shock absorber; estimating a thermal power exchanged by the shock absorber with the environment; evaluating the current operating temperature of the shock absorber as a function of the dissipated mechanical power and of the thermal power exchanged with the environment; and controlling the driving current of the control valve of the shock absorber according to a shock absorber reference model indicating a relationship between the damping force of the shock absorber, the operating temperature of the shock absorber and the driving current of the control valve.

Claims

1. A method for controlling the damping characteristics of a shock absorber of a vehicle for compensating the variation of the operating temperature of the shock absorber, in an active or semi-active suspension system comprising: a plurality of adjustable damping shock absorbers, each including a pressure chamber containing a damping fluid, inside which a piston is slidable, the position of which defines a lower pressure chamber and an upper pressure chamber, a by-pass chamber in communication with the upper pressure chamber, and a control valve, arranged to control the passage of the damping fluid between the pressure chamber and the by-pass chamber; sensors that detect the relative vertical acceleration or the relative vertical movement between the body of the vehicle and each wheel with which a shock absorber is associated; and an electronic processing and control unit that receives signals indicative of said relative acceleration or said relative movement, and arranged to emit driving signals for the control valves of the shock absorbers to achieve predetermined damping characteristics of the shock absorbers, the method includes the steps of: estimating a mechanical power dissipated in heat by the shock absorber as a function of the relative vertical translation speed between the wheel with which the shock absorber is associated and the body of the vehicle and of the quantity representative of the driving signal of the control valve of the shock absorber in a current operating condition of the shock absorber, according to a first predetermined reference response model of the shock absorber indicative of a nominal relation between the relative vertical speed of the shock absorber, said quantity representing the driving signal of the control valve and the damping force of the shock absorber; estimating a thermal power exchanged by the shock absorber with the environment according to at least one current operating condition of the vehicle; evaluating the current operating temperature of the shock absorber as a function of said estimated mechanical power dissipated in heat and of said estimated thermal power exchanged with the environment; and controlling the driving signal of the control valve of the shock absorber according to a second predetermined shock absorber reference model indicating a relationship between the damping force of the shock absorber, the operating temperature of the shock absorber and said quantity representative of the driving signal of the control valve, varying the magnitude of the quantity representative of the driving signal of the control valve to reach a working point of said model corresponding to a predetermined nominal damping force of the shock absorber.

2. The method as set forth in claim 1, wherein the step of estimating the thermal power exchanged by the shock absorber with the environment as a function of at least one current operating condition of the vehicle includes estimating the heat exchange of the shock absorber with the surrounding environment as a function of the ambient temperature.

3. The method as set forth in claim 1, wherein the step of estimating the heat output exchanged by the shock absorber with the environment according to at least one current operating condition of the vehicle includes estimating the heat exchange of the shock absorber with the surrounding environment as a function of the vehicle's travel speed.

4. The method as set forth in claim 1, wherein the step of estimating the heat output exchanged by the shock absorber with the environment as a function of at least one current operating condition of the vehicle includes estimating the heat exchange of the shock absorber with the surrounding environment as a function of the use of the vehicle's braking system.

5. The method as set forth in claim 1, wherein the step of estimating the heat output exchanged by the shock absorber with the environment as a function of at least one current operating condition of the vehicle includes estimating the heat exchange of the shock absorber with the surrounding environment as a function of the operating temperature of the vehicle propulsion unit.

6. The method as set forth in claim 1, wherein the operating temperature of the shock absorber is estimated as a function of the shock absorber's thermal capacity.

7. The method as set forth in claim 1, wherein said first predetermined reference response model and said second predetermined reference model are integrated into an overall reference model indicative of a plurality of nominal relationships between the relative vertical translation speed of the shock absorber, of said quantity representing the driving signal of the control valve and the damping force of the shock absorber for different operating temperatures of the damping fluid.

8. The method as set forth in claim 1, wherein said first reference model is an analytical relationship between, or a map of numerical values in a objective correspondence with, relative vertical speed of the shock absorber, said quantity representative of the driving signal of the control valve and damping force of the shock absorber determined at an operating temperature of the shock absorber comprised between −40° C. and 120° C.

9. The method as set forth in claim 1, wherein said quantity representative of the driving signal of the control valve of the shock absorber is a quantity representative of the driving current of said valve.

10. The method as set forth in claim 1, wherein the relative vertical translation speed between the wheel with which the shock absorber is associated and the vehicle body is determined by integration of signals indicative of a relative vertical acceleration.

11. The method as set forth in claim 10, wherein said sensors include at least three accelerometers coupled to the body of the vehicle and at least one accelerometer coupled to a wheel hub of the vehicle with which the shock absorber is associated.

12. The method according as set forth in claim 1, wherein the relative vertical translation speed between the wheel with which the shock absorber is associated and the vehicle body is determined by derivative of signals indicative of a stroke of the shock absorber associated with said wheel.

13. A control system of the damping characteristic of a shock absorber of a vehicle for the compensation of the variation of the operating temperature of the shock absorber, in an active or semi-active suspension system comprising: a plurality of adjustable damping shock absorbers, each including a pressure chamber containing a damping fluid, inside which a piston is slidable, the position of which defines a lower pressure chamber and an upper pressure chamber, a by-pass chamber in communication with the upper pressure chamber, and a control valve, arranged to control the passage of the damping fluid between the pressure chamber and the by-pass chamber; sensors that detect the relative vertical acceleration or the relative vertical movement between the body of the vehicle and each wheel with which a shock absorber is associated; and an electronic processing and control unit that receives signals indicative of said relative acceleration or said relative movement, and arranged to emit driving signals for the control valves of the shock absorbers to achieve predetermined damping characteristics of the shock absorbers; said electronic processing and control unit including a processing module for estimating and compensating the variation of the operating temperature of the shock absorber, said processing module including: a first estimator module arranged for estimating a mechanical power dissipated in heat by the shock absorber as a function of the relative vertical translation speed between the wheel with which the shock absorber is associated and the body of the vehicle and of the representative quantity size of the driving signal of the control valve of the shock absorber in a current operating condition of the shock absorber, according to a first predetermined reference response model of the shock absorber indicating a nominal relation between the relative vertical translation speed of the shock absorber, said quantity representative of the driving signal of the control valve of the shock absorber and the damping force of the shock absorber; a second estimator module arranged for estimating a heat power exchanged by the shock absorber with the environment as a function of at least one current operating condition of the vehicle; an evaluator module that evaluates the current operating temperature of the shock absorber as a function of said estimated mechanical power dissipated in heat and of said estimated thermal power exchanged with the environment; and a controller module that controls the driving signal of the control valve of the shock absorber according to a second predetermined shock absorber reference model indicative of a relationship between the damping force of the shock absorber, the operating temperature of the shock absorber and said quantity representing the driving signal of the control valve, by varying the intensity of the quantity representative of the driving signal of the control valve to reach a working point of said model corresponding to a predetermined nominal damping force of the shock absorber, said processing module for estimating and compensating for the variation in operating temperature of the shock absorber being configured to implement the steps of the method as set forth in claim 1.

14. An active or semi-active suspension system for a vehicle, comprising a control system of the dampening characteristic of a shock absorber of a vehicle for compensating the variation of the operating temperature of the shock absorber as set forth in claim 13.

15. A computer program or group of programs executable by a processing system, comprising one or more code modules for implementing a control method of the damping characteristic of a shock absorber of a vehicle for compensating the variation of the operating temperature of the shock absorber in a semi-active suspension system as set forth in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Further features and advantages of the invention will appear more clearly from the following detailed description of an embodiment thereof, given by way of non-limiting example with reference to the accompanying drawing, in which:

[0021] FIG. 1 is a schematic representation of the control architecture of an active or semi-active suspension system, arranged for compensation of the variation of the operating temperature of the shock absorber;

[0022] FIG. 2 is another representation of the block diagram of the control architecture of an active or semi-active suspension system of FIG. 1, including a detailed representation of a processing module for an estimation and compensation of the variation of the operating temperature of the shock absorber;

[0023] FIG. 3 is an exemplary diagram of the pattern of the damping force curves as a function of the relative vertical translation speed for a shock absorber, depending on the driving current of the control valve of the shock absorber;

[0024] FIGS. 4A-4D are exemplary diagrams of the pattern of the mechanical power dissipated in a shock absorber according to different thermal exchange parameters; and

[0025] FIG. 5 is an exemplary diagram of the pattern of the damping force curves as a function of the relative vertical translation speed for a shock absorber, depending on the operating temperature of the shock absorber.

DETAILED DESCRIPTION OF THE INVENTION

[0026] With reference to the block diagram of FIG. 1, the control architecture of an active or semi-active suspension system according to the invention is schematically shown.

[0027] A control unit 10 of the system comprises a processing module 12 of a control strategy, arranged to select one of a plurality of predefined control strategies according to the detected conditions of the road surface, the lateral and longitudinal dynamics of the vehicle, the damping characteristic model set and/or desired by the user, according to predetermined priority rules in view of keeping the vehicle running in a safe condition.

[0028] The control module 12 is coupled to sensor assemblies 20, 22 (generally including accelerometers), respectively coupled to the vehicle body and to the wheel hubs, adapted to detect the relative acceleration (i.e., relative vertical acceleration) or the relative movement (i.e. relative vertical movement) between the vehicle body and the wheel hub. In one embodiment, the sensor assembly 20 comprises three sensors coupled to the vehicle body in order to be able to evaluate the body motions, for example two sensors positioned on the front axle at the suspension domes, and one positioned on the rear axle, and the sensor assembly 22 comprises at least one pair of sensors arranged on the front wheel hubs and preferably a number of sensors corresponding to the number of wheels of the vehicle, arranged on the hubs of the front and rear wheels.

[0029] It is also coupled to an on-board CAN bus on which other on-board control units are communicatively connected, typically a motor control unit, a transmission control unit, a longitudinal vehicle dynamic control unit arranged for management of the ABS, EBD, ASR functions during braking or acceleration maneuvers, a lateral vehicle dynamic control unit arranged for steering maneuvering management, and a control unit for the interior and bodywork devices, commonly referred to as “body computer”.

[0030] In one embodiment, a user interface is also provided (not shown) for acquiring commands to set the desired behavior of the suspension system as a whole (comfort, sports) and/or the representation of operating status information of the system, for example by use of a warning light of a detected anomaly condition.

[0031] Finally, reference numeral 30 generally indicates the adjustment valves for the damping characteristics of the shock absorbers, individually controlled by the control module 12.

[0032] Reference numeral 14 indicates a processing module for estimating and compensating the variation of the operating temperature of the shock absorber, integrated in the control unit 10, and coupled to the control module 12, from which it receives in input signals or data indicative of the relative vertical translation speed between each wheel to which a respective shock absorber is associated and the vehicle body, generally indicated V.sub.amm, and signals or data indicative of the driving signals of the shock absorber control valves, generally indicated I.sub.amm, in particular of the values of a quantity representative of driving signals, preferably a driving current. The module 14 is further arranged to supply the control module 12 with a control signal of the driving signal of the shock absorber control valve, preferably an offset signal ±ΔI.sub.amm of the driving current.

[0033] The processing module 14 will be described in greater detail in the remainder of the present discussion, with reference to the block diagram of FIG. 2.

[0034] The processing module 14 is furthermore coupled in reading and writing with a memory module M adapted to store a predetermined plurality of reference models of the shock absorbers (or of each individual shock absorber or pair of shock absorbers), for example a first reference response model which is indicative of a nominal relationship between the relative vertical translation speed of the shock absorber, the quantity representative of the driving signal of the control valve and the damping force of the shock absorber and a second reference model which is indicative of a relationship between the damping force of the shock absorber, the operating temperature of the shock absorber and the quantity representative of the driving signal of the control valve.

[0035] The first reference model can be an analytical relationship between, or a map of numerical values in a one-to-one correspondence of, relative vertical translation speed supported by the hub of the wheel with which the shock absorber is associated, which is representative of the driving signal of the control valve of the shock absorber and damping force of the shock absorber, generally represented as F=F(I, V), at an operating temperature of the shock absorber preferably between −40° C. and 120° C.

[0036] The second reference model can be an analytical relationship between, or a map of numerical values in a one-to-one correspondence of the shock absorber damping force, the operating temperature of the shock absorber and the quantity representative of the driving signal of the shock absorber control valve.

[0037] For example, each model can be generated starting from experimental measurements of the aforementioned parameters during bench tests of the shock absorber or in a calibration step at the time of vehicle tuning.

[0038] The first reference response model and the second reference model can be integrated into a single overall reference model indicative of a plurality of nominal relationships between the relative vertical translation speed of the shock absorber, the quantity representing the driving signal of the control valve of the shock absorber and the damping force of the shock absorber for different operating temperatures of the damping fluid.

[0039] With reference to the block diagram of FIG. 2, the processing module 14 for estimating and compensating the variation of the operating temperature of at least one shock absorber and preferably of all the shock absorbers of the vehicle is described below.

[0040] The processing module 14 includes a first estimator module 50 adapted to receive in input signals or data indicative of the driving signals of the shock absorber control valves, generally indicated I.sub.amm, in particular of the values of a quantity representative of driving signals, preferably a driving current.

[0041] The processing module 14 also includes a second estimator module 52 adapted to receive in input signals or data from the CAN network of the vehicle or from ad hoc sensors, indicative of at least one of the following parameters: the ambient temperature, the vehicle speed, the use of the vehicle's braking system in the proximity of the shock absorber and the operating temperature of the vehicle's engine in the proximity of the shock absorber.

[0042] The first estimator module 50 arranged for estimating a mechanical power P.sub.in dissipated in heat by the shock absorber as a function of the relative vertical translation speed between the wheel with which the shock absorber is associated and the body of the vehicle and of the quantity representative of the driving signal of the control valve of the shock absorber in a current operating condition of the shock absorber, according to the first reference response model of the shock absorber stored in the memory M and indicating a nominal relation between the relative vertical translation speed of the shock absorber, the quantity representative of the driving signal of the control valve of the shock absorber and the damping force of the shock absorber, at a standard environmental temperature of 25° C.

[0043] A graphical representation of the relationship between the relative vertical translation speed of the shock absorber and the damping force of the shock absorber as a function of the intensity of the driving current of the control valve is shown in FIG. 3.

[0044] The second estimator module 52 is arranged to estimate a thermal power P.sub.out exchanged by the shock absorber with the environment according to at least one current operating condition of the vehicle, preferably as a priority starting from the temperature of the environment T.sub.amb and possibly—in improved embodiments—from other quantities including the vehicle speed v, the heat exchange between the engine and the shock absorber, i.e. as a function of the operating temperature of the engine T.sub.engine and the heat exchange between brake discs and shock absorber, i.e. depending on the use and consequent overheating of the braking system of the vehicle which causes a temperature T.sub.brake in the adjacent environment in which the shock absorber is located.

[0045] An illustrative graphic representation of the relation between the thermal power exchanged with the environment P.sub.out and respectively (a) the longitudinal traveling speed v of the vehicle, (b) the temperature of the environment T.sub.ammb, (c) the temperature T.sub.brake of the vehicle brakes, (d) operating temperature T.sub.engine of the vehicle engine shown in the diagrams in FIGS. 4A-4D. These figures show how the thermal power exchanged with the environment P.sub.out increases, for example linearly, with the vehicle's longitudinal travel speed v, decreases, for example linearly, with increasing ambient temperature T.sub.amb and temperature T.sub.brake of the brakes of the vehicle, initially decreases and then remains constant with increasing of the operating temperature of the vehicle engine T.sub.engine (which does not exceed an operating temperature T.sub.e).

[0046] An evaluator module 54 is coupled to the outputs of the estimator module 50 and of the estimator module 52 and arranged to evaluate the current operating temperature T.sub.amm(t) of the shock absorber as a function of the mechanical power dissipated in heat P.sub.in estimated by the first estimator module 50 and of the thermal power exchanged with the environment P.sub.out estimated by the second estimator module 52.

[0047] The evaluator module 54 evaluates the current operating temperature T.sub.amm(t) of the shock absorber according to a general relationship

T.sub.amm=f (C, P.sub.in, P.sub.out, t)

therefore as a function of the thermal capacity of the shock absorber (complete in its parts, the thermal capacity being estimated with experimental bench and vehicle measurements), of the mechanical power input to the shock absorber and of the thermal power dissipated, over time.

[0048] The evaluator module 54 emits a signal or data indicative of the current operating temperature T.sub.amm (t) of the shock absorber, which is supplied in feedback to the second estimator module 52 so that it is possible to estimate the thermal power dissipated as a function of the current temperature of the shock absorber, and is supplied in input to a controller module 56 in communication with the second reference model of the shock absorber stored in the memory M. The evaluator module 54 is arranged to control the driving signal of the shock absorber control valve, preferably for determining an offset signal ±ΔI.sub.amm of the intensity of the driving current according to a reference model of the shock absorber indicative of a relationship between the damping force of the shock absorber, the operating temperature of the shock absorber and the intensity of the driving current of the control valve.

[0049] A graphical representation of the relationship between the relative vertical translation speed of the shock absorber and the damping force of the shock absorber as a function of the operating temperature of the shock absorber is shown in FIG. 5.

[0050] The offset signal or data ±ΔI.sub.amm of the driving current intensity is provided by the evaluator module 54 at the input of the control module 12 so that it can consequently vary the intensity of the driving current of the control valve to reach a working point corresponding to a predetermined nominal damping force of the shock absorber.

[0051] The processing module 14 is arranged to execute a program or group of computer programs, for example stored locally, adapted to carry out the process (algorithm) for controlling the damping characteristic of a shock absorber of a vehicle, particularly for compensating the variation of the operating temperature of the shock absorber.

[0052] Advantageously, the entire process described above is repeated at regular time intervals or continuously, so as to periodically or continuously update the driving current of the shock absorbers to maintain the damping characteristic of the shock absorbers unaltered. In this way it is possible to adapt the behavior of the suspension system to the variation (as long as sustainable) of the temperature of the shock absorbers, i.e. the viscosity of the operating fluid, so as not to make an alteration of the absolute driving comfort, of the comfort settings desired by the driver and the dynamic performance of the vehicle perceivable to the passengers.

[0053] If the thermal effect on the shock absorbers is not fully recoverable, since it is objectively excessive with respect to the predetermined control dynamics, the system is designed to warn the driver of reaching a critical temperature (for example 100° C.), still within a safe limit for component reliability, signaling the opportunity to let the damper cool down to avoid damage to the suspension system.

[0054] Of course, the principle of the invention being understood, the manufacturing details and the embodiments may widely vary compared to what described and illustrated by way of a non-limiting example only, without departing from the scope of the present invention as defined in the appended claims.