WO2007003583A1

WO2007003583A1 - Method, device and system

Info

Publication number: WO2007003583A1
Application number: PCT/EP2006/063706
Authority: WO
Inventors: Christer Yngvesson
Original assignee: Haldex Traction Ab
Priority date: 2005-07-01
Filing date: 2006-06-29
Publication date: 2007-01-11
Also published as: SE0501531L

Abstract

The present invention relates to a method for inter alia monitoring and controlling a solenoid associated with a proportional valve. The solenoid comprises a coil, an armature which is movable in relation to the coil, and the proportional valve comprises a plunger that is controlled by the armature/coil system and a housing for accommodating the plunger. The method comprises the steps of supplying the coil with a nominal drive voltage having a low-level amplitude fluctuation, obtaining or alternatively determining a level of an average current in the coil and a level of the fluctuation of said coil current, determining a position corresponding to the inductance, given by the average coil current and the coil current fluctuation, by using a predetermined value, and comparing a nominal position, given by the average coil current by means of a controller, with an actual position as calculated above. The present invention also relates to a device and system utilizing the above method.

Description

Method, Device and System

Field of the Invention The present invention relates to a method for monitoring a solenoid-operated proportional valve, and more specifically a method that utilizes the position of the solenoid armature, relative to the coil, for monitoring. It also relates to a device for monitoring a solenoid-operated proportional valve using said relative position and a drive system incorporating the above device and utilizing the above method. It further relates to a monitoring device for performing the steps of said method.

Background of the Invention

A proportional valve of the present invention may generally be used for controlling a fluid flow in a fluid circuit, either pneumatic or hydraulic, e.g. within a process industry, and can also be used in automotive drive systems, where it is utilized for controlling the pressure in a hydraulic cylinder of said system. The pressure in the hydraulic cylinder forces a piston of the hydraulic cylinder against a clutch, which in turn controls said drive system. The proportional valve is an essential feature of the system and a failure of the valve will lead to an unreliable behavior of the drive system. This may in certain conditions lead to an uncontrollable vehicle and possibly to damage of the vehicle and injury to its passengers. For this reason, current drive systems are equipped with pressure transducers that monitor the pressure in the hydraulic circuit which is associated with the hydraulic cylinder. If the proportional valve fails, the pressure signal from the pressure transducer will differ from the expected value as determined by the nominal value from the controller. Other proportional valves are equipped with a position sensor that is coupled to a plunger of the valve. If the plunger moves as usual in relation to the control signal, the valve is operational. Otherwise, the control unit of the drive system indicates a failure, which is displayed to the driver.

The above solutions require additional sensors and will increase the cost of the assembled drive system.

Summary of the Invention

It is an object of the present invention to overcome the drawbacks of prior art monitoring devices by providing a method having the features as given in the first claim. Further objects and embodiments are given by its dependent claims .

It is another object of the present invention to provide an automotive drive system utilizing the method according to the first claim, and this is given in claim 9.

It is a further object of the present invention to provide a device utilizing the above method of the first claim, and this is given in claim 10. Further embodiments are given by its dependent claims .

An automotive drive system incorporating the device of claim 10 is given in claim 13. A solenoid-monitoring device for performing the steps of the first claim is given in claim 14.

Brief Description of the Drawings

The present invention will be more readily understood by reading the below description with reference to the appended drawings, wherein

Fig. 1 is a side view in section of a solenoid- operated proportional valve used with the invention,

Fig. 2 is a schematical representation of a solenoid with power supply, Fig. 3 is a graph showing the nature of the input voltage to the solenoid of Fig. 1,

Fig. 4 is an alternative representation of the power supply for the solenoid, Fig. 5 is a schematical view of a monitoring device according to the invention,

Figs. 6-10 are graphs that show how a monitored signal is processed in the monitoring device of Fig. 5,

Fig. 11 is a schematical view of a vehicle with a drive system, and

Fig. 12 is a schematical view of a hydraulic circuit for a drive system that can comprise a valve according to the invention.

Detailed Description of a Preferred Embodiment

A typical solenoid-operated proportional valve 1 is shown in section in Fig. 1. The solenoid comprises a magnetizing coil 2 and a movable, magnetisable armature 3 having a generally rod-shaped central portion, which abuts against a plunger 4 of a proportional valve 1. The plunger 4 is axially movable inside a housing 5 against a biasing compression spring 6, and holes 7, 8 in the perimeter of the housing 5 act as inlets and outlets for controlling a pressure e.g. at a hydraulic cylinder of a limited slip four-wheel drive coupling. The inlet communicates with a hydraulic power source (not shown) such as a pump, which provides high-pressure hydraulic oil to the valve 1.

The oil passes a restriction in the valve 1 between the inlet 7 and the outlet 8, and the size of the restriction is determined by the position of the plunger 4. The valve 1 is fully open when the plunger 4 is in the shown position and restricts the flow when the plunger 4 is moved to the left. The coil 2 is connected to a DC power source (see e.g. Fig. 2), and the position of the armature 3 inside the coil 2 is in a functioning valve related to an applied voltage from the DC power source. The current through the coil 2, represented by a resistance R and an inductance L in Figs. 2 and 4, is measured in a coil DC current measuring circuit comprising a DC amplifier 10 coupled over a small shunt resistor, R_sh, in the coil circuit. The signal from the DC amplifier is led to an A/D converter of a microprocessor 11, where the signal is processed and used as feedback for controlling the average DC current through the coil 2. The DC power source is electronically controlled and outputs a pulse-width modulated signal. By varying the duration of the pulses, see Fig. 3, a resulting fluctuating voltage can be obtained. The resulting superimposed fluctuation may be a dither voltage, which is used for imparting a slight oscillation to the armature and hence the plunger in the valve. The oscillation makes the plunger vibrate slightly and prevents the plunger from experiencing static friction. This removes a great deal of the hysteresis of the proportional valve. This can also be achieved with a signal generator connected in series with a DC power source, see Fig. 4. The frequency and amplitude of the voltage fluctuation should be adjusted so that no fluctuation can be detected in the hydraulic pressure that is discharged from the proportional valve. This is a standard feature of nearly all proportional valves.

A monitoring device, shown schematically in Fig. 5, for determining an inductance is electrically connected to the coil DC current measuring circuit at A and to an A/D converter of a microprocessor at B, see Fig. 2. The monitoring device comprises circuitry for signal processing, such as operational amplifiers, capacitors, and resistors, for measuring the AC current mean value. A voltage fluctuation is superimposed over the coil and a signal representing the coil current is led to the connector A, as can be seen in Fig. 2, and the signal can be seen in Fig. 6. A first capacitor Ci removes the DC level of the signal, see Fig. 7, which is supplied by the DC power source to drive the solenoid. A first operational amplifier OPi amplifies the signal about six times and also half-wave rectifies the signal, which can be seen in Fig. 8 corresponding to a position before a resistor R₄. The signal is then averaged in the following two stages comprising the resistor R₄, capacitor C₂, resistor R₅ and capacitor C₃, see Fig. 9. Some ripple may still be present in the signal. The signal is once more amplified about three times in a second operational amplifier OP2, and the signal that is fed to the A/D converter at B can be seen in Fig. 10.

These components are connected to the coil DC current measuring circuit, see Fig. 2, for detecting a current in the coil circuit, which is dependent on the inductance in the coil/armature system. The inductance of the coil/armature system is in turn dependent on the position of the armature 3 within the coil 2. Hence, if the coil current is known, the position of the armature 3 can be determined. The armature 3 in turn abuts against the plunger 4 of the proportional valve 1, as can be seen in Fig. 1. The return stroke of the plunger 4 and armature 3 is achieved by the compression spring 6. The function of the valve 1 can thus be monitored by controlling that the inductance value in the solenoid corresponds to an expected value. The superimposed voltage fluctuation over the coil may be the dither voltage or a separately provided voltage. It is thus possible to have both a dither voltage and a second superimposed voltage fluctuation, where the latter may be used for controlling and/or monitoring the position of the armature inside the solenoid.

The coil/armature system is illustrated schematically in Figs. 2 and 4. The DC power source is shown to the left and the solenoid is represented by a resistance R and an inductance L. The inductance can be calculated by measuring the voltage u and the current i using the relationship

u(t) = L— - R ^■ i(t) dt which after Fourier transformation can be written u{jω) = (jωL + R) ^■ i{jω)

The current can consequently be written

The superimposed fluctuation of the current is used for determining the inductance. The amplitude of the above expression can be written as

J_s(jω) =

where U_s and J_s are the superimposed components. If the amplitude and frequency of the voltage are kept constant, the amplitude of the current will be inversely proportional to L according to

For a superimposed sinusoidal input voltage, the amplitude of the resulting, superimposed current can easily be determined by forming the average of the half-wave rectified current signal according to

where p is the period of the fluctuation. The amplitude of the superimposed current and the DC-level of the current are then used for determining the position of the armature according to a predetermined relationship.

The inductance can thus be determined by measuring the coil current. If there is a discrepancy between the measured value and the expected value for a functional valve, the valve is probably dysfunctional to some extent.

The resistance R of the coil must also be known, in order to obtain accurate measurements of the position of the armature. The coil resistance R depends on the temperature of the coil, and should hence be determined during operation of the solenoid. This can be done in different ways. The resistance R can either be modeled using a simple expression R= R₀ + AR(T) where Ro is a predetermined parameter, T is the temperature and AR is a predetermined temperature relationship for the resistance. The resistance can also be estimated by measuring the current I and the voltage U, e.g. by using the ECU, and using the well-known relationship

U =RI

A third possibility is to perform two measurements during a relative change of position. The difference between these measurements is independent of the resistance. However, this technique requires two successive measurements and is thus slightly more time-consuming.

The functionality of the present invention can also be achieved by controlling the fluctuating component of the current running through the coil to a constant (or at least known) level. The fluctuating voltage that is required for this regulation is known, or can be measured, and can thus be used for calculating the inductance in a similar manner as given above .

The above method for monitoring a solenoid-operated proportional valve can also be used for calibration purposes. A pressure-control valve is a special type of proportional valve that counteracts the applied force from the solenoid with a hydraulic pressure between the plunger and the housing. Several positions of the plunger are determined for a valve where the applied hydraulic pressure is zero, and a corresponding series is determined for a valve that is pressurized. The position where the two curves deviate is the point at which the valve starts delivering pressure to the downstream hydraulic system. By pinpointing this position, the proportional valve will not have to be pre-calibrated from the factory, which will lower the cost of the valve.

The proportional valve is designed to move relatively slowly and does not handle transients very well. This means that no (or almost no) interfering currents are induced in the coil due to the movement of the armature. This increases the precision of the measurement and makes it possible to detect even a slightly dysfunctional valve. The development of new materials may make it possible to control the valve at much higher speeds, though. This can e.g. be done with powder metals, which are highly susceptible to a magnetic field but prevent the formation of eddy currents, since powder metals can be formed with high permeability and high resistivity. The high permeability makes them perfect materials for being magnetized and the high resistivity allows for higher measurement frequencies, without loosing the variation of the inductance with the position of the armature. The electric systems of the future may have a higher system voltage, 48 V, compared to the currently used systems, 12-13 V. If a new type of solenoid is used in such a system, as described in the previous paragraph, the dither voltage can be increased. The frequency of the dither voltage can then also be increased, since the increased dither voltage would make the armature oscillate even at this higher frequency. This is thus a suitable way of increasing the control frequency without having to introduce a separate high-frequency fluctuation. The proportional valve shown in Fig. 1 is a flow control valve, and the supply current determines the position of the plunger. The present invention also works with a pressure-reducing valve, where the control signal determines the discharge pressure.

The present invention is suitable for use in vehicles with various drive systems, and one such system can be seen in Fig. 11. A vehicle 100 is equipped with an engine 101, a transmission 102 for transferring a motive torque from the engine to a drive shaft 103, a forward 104 and a rear 105 differential and a four-wheel drive coupling 106. The differentials 104, 105 are coupled to front 107 and rear

108 wheel axles, respectively, which are coupled to front

109 and rear wheels 110, having brakes 111 mounted thereto. The engine 101, brakes 111 and four-wheel drive 106 coupling are all associated with electronic control units (ECU:s) which are not depicted in the Figure. The drive system mentioned above is not limited to just a longitudinal coupling for a four-wheel drive system. It can further comprise one or several longitudinal couplings on either side of the transmission, one or several transversal couplings at either the front or rear wheel axle or both. It may also be provided with differentials on the front and/or rear wheel axle that can have differential locks or brakes.

The drive coupling 106 comprises a clutch 200 that is activated by a hydraulic cylinder 201 being coupled to a hydraulic circuit, see Fig. 12. The hydraulic circuit is equipped with a proportional valve 202 of the type described above, for controlling the pressure in the hydraulic cylinder 201 and hence the activation and deactivation of the four-wheel drive coupling 106. The function of this valve is monitored by the method according to the invention and this lowers the cost of the hydraulic circuit, since expensive pressure or position transducers can be made redundant .

The proportional valve is supplied with pressurized hydraulic oil by a hydraulic power source 203. A reservoir 204 accommodates the hydraulic oil and collects the discharged oil from the proportional valve 201 and the hydraulic cylinder 202. The hydraulic cylinder may be double-acting or single-acting with a spring, as shown in the Figure. The proportional valve 201 is controlled by an ECU 205. The function of the valve, and hence the drive system, is monitored by utilizing the method according to the invention.

The present invention is exemplified in a hydraulic circuit of an automotive drive coupling, but can just as well be used in a general fluid circuit, where a proportional valve is used for controlling and/or driving a general process, e.g. a pneumatic or hydraulic circuit in an industrial application.

The present invention is not restricted to the valves given in the description, but can equally well be used for any solenoid operated valve that is controlled in a similar way as the present invention, e.g. a seat valve having a valve plug and a co-acting seat.

The term proportional valve is intended to refer to a valve that can control a pressure or a flow of a fluid in relation to a control signal, e.g. pressure reducing valve, pressure control valve, flow control valve etc. The configuration of the valve should be suitable for obtaining the above functionality, e.g. sliding valve, disc valve, seat valve, needle valve, ball valve, globe valve, gate valve, butterfly valve, plug valve etc.

Even though a specific embodiment has been described above it will be evident to a person skilled in the art to make modifications to the present invention without departing from the scope of the invention as defined by the appended claims .

Claims

1. A method for inter alia monitoring and controlling a solenoid associated with a proportional valve (1) , the solenoid comprising a magnetizing coil (2), a magnetizable armature (3) which is movable in relation to the coil (2), and the proportional valve (1) comprising a plunger (4) or a valve plug being controlled by the armature/coil system and a housing (5) for accommodating the plunger (4) or valve plug, where the method is characterized by comprising the steps of supplying the coil (2) with a nominal drive voltage having a low-level amplitude fluctuation, obtaining or alternatively determining a level of an average current in the coil (2) and a level of the fluctuation of said coil current, determining a position corresponding to the inductance, given by the average coil current and the coil current fluctuation, by using a predetermined value, and comparing a nominal position, given by the average coil current by means of a controller, with an actual position as calculated above.

2. A method according to claim 1, wherein the amplitude and/or frequency of the voltage fluctuation is kept constant or at a known level.

3. A method according to claim 1, wherein the amplitude and/or frequency of the resulting current is controlled to a constant or known level.

4. A method according to claim 1, where the proportional valve (1) is a pressure-control valve, which has a plunger (4) or a valve plug that during operation is substantially stationary in the operating range of the valve (1), independent of the drive current, the method comprising the steps of a) in a first measurement series determining the position of the plunger (4) or valve plug for different drive currents when the hydraulic pressure applied to the valve is zero, b) in a second measurement series determining the position of the plunger (4) or valve plug for different drive currents when full operating hydraulic pressure is applied, and c) localizing a position where the above two measurement series deviate, for calibrating a valve (1) mounted in a working environment with respect to deviations in spring force, manufacturing tolerances etc.

5. A method according to claim 4, wherein the working environment is an automotive drive system of a vehicle.

6. A method according to claim 1, wherein the method is used for a proportional valve (1) that is associated with an automotive drive system, for also monitoring the function of said drive system.

7. A method according to claim 1, wherein the method is used for controlling a proportional valve in a general fluid process for controlling and/or driving said process.

8. A method according to claim 1, wherein a dither voltage, for removing static friction from the solenoid- operated proportional valve, is used as the superimposed, fluctuating voltage.

9. An automotive drive system comprising a hydraulic power source (203), a hydraulic cylinder (202) associated with a clutch (200) of a drive coupling (106) , and a solenoid-operated proportional valve (1, 201) which controls a hydraulic pressure from the hydraulic power source (203) to the hydraulic cylinder (202) for regulating a torque that the drive system can transfer, characterized in that the proportional valve (1, 201) is monitored according to the method in claim 1.

10. A device for controlling a hydraulic pressure, comprising a proportional valve (1) having a magnetizing coil (2), a magnetizable armature (3), which is movable in relation to the coil (2) and is connected to a plunger (4) or a plug of the valve, a spring (6) for biasing the plunger (4), and hence the armature (3), to an initial quiescent position, characterized by having electronics associated therewith for determining an inductance of the coil (2) which is dependent on the position of the armature (3) and hence the plunger (4) .

11. A device according to claim 10, wherein the armature (3) is manufactured of powder metal in a way that gives the armature (3) high magnetic permeability and high electric resistivity.

12. An automotive drive system comprising a hydraulic power source (203), a hydraulic cylinder (202) associated with a clutch (200) of a drive coupling (106) , and a solenoid-operated proportional valve (1, 201) which controls a hydraulic pressure from the hydraulic power source (203) to the hydraulic cylinder (202) for regulating a torque that the drive system can transfer, characterized in that said proportional valve (201) is of the type according to claim 10.

13. A solenoid monitoring device to be used in connection with a proportional valve (1) having a magnetizing coil (2), a magnetizable armature (3), which is movable in relation to the coil and is connected to a plunger (4) or a plug of the valve, a spring (6) for biasing the plunger (4), and hence the armature (3), to an initial quiescent position, characterized in that the monitoring device comprises electronic components for isolating, rectifying and amplifying an amplitude fluctuation of a current through the coil and for comparing a resulting signal to predetermined values according to the method of claim 1.