MXPA97007840A - Soleno drive circuit - Google Patents

Abstract

The present invention relates to an electrical circuit for applying an oscillating electric current to a coil of a solenoid in order to cause the solenoid to move in response to an input signal, characterized in that: the circuit supplies the coil with a current which has upper and lower peak current values and where the lower current value is essentially a fixed percentage of the peak current value above

Description

SOLENOID DRIVER CIRCUIT BACKGROUND OF THE INVENTION This invention relates to an electrical circuit for providing controlled electric current to a solenoid, such as the solenoid of a hydraulic control valve.

It is desired to use analog current controlled solenoid valves to control the hydraulic pressure applied to the clutches in a force change transmission. Accurate current control is required for a predictable and smooth modulation of the transmission elements when changing from one clutch to another. Due to the dissipation of energy, it is not practical on a vehicle to control the current to an analogous valve by controlling the voltage supplied to it. In this way to generate the desired current order, the supply voltage is pulsed intermittently at a rapid rate. The inductance in the coil stores the energy when the voltage is pulsed, and releases the energy when the voltage is turned off, thereby producing an average current.

However, current control is difficult in such an application because the primary electrical characteristics of the control valves such as resistance and inductance are not known or predictable. The resistance of the coil can change by over 100 percent through the temperature range to which it is subjected. Similarly, the inductance of the coil can change by over 100 percent due to temperature variations, voltage pulse frequency, and supply current. In addition, the amplitude of the voltage pulses can vary from 9 to 16 volts.

It is known to filter the pulse current, measure its average, and compensate the command until the desired average current is achieved. But such a technique does not work very well in a transmission control application. This is because during a change the command to a valve changes rapidly. The command is either going up or down depending on whether the transmission element is coming or going. To measure the average current of real time the command must remain constant for some time. But, during a change there is not enough time available for this to be done. Therefore, it would be desirable to have a valve driver which produces an exact average current in the coil that has an unknown resistance and an unknown inductance without a feedback perception of the average current.

SYNTHESIS OF THE INVENTION An object of the present invention is to provide a solenoid valve driver which produces an average current which is linearly related to an ordered peak current.

Another object of the present invention is to provide a valve driver wherein the coil current will have a lower peak current value which is essentially a fixed percentage of the higher peak current value.

Another object of the present invention is to provide an accurate current control of a solenoid impeller with an immediate response (minimum delay between the ordered current and the actual current).

Another object of the present invention is to provide a system for controlling the solenoid current which can be done with few components and at a low cost, and which places few demands (general load of computer program or software) on a microprocessor.

Another object of the present invention is to optimize the frequency of the solenoid impeller to a nominal operating point (rated current, resistance, inductance and supply voltage) by selecting the appropriate resistor divider network.

Another object of the present invention is to provide the maximum fault detection of the solenoid driver circuit.

Another object of the present invention is to provide a circuit in which the output current to the solenoid is zero during ignition and / or the reset mode of the microprocessor.

These and other objects are achieved by the present invention wherein an electric circuit applies an oscillating electric current to a coil of a solenoid in order to cause the solenoid to move in response to an ordered signal. The circuit includes a signal divider for generating a higher peak current signal value of the ordered signal and a lower peak current signal value which is a fixed percentage of the higher peak current signal value. A current sense resistor generates a current perception voltage representing the current through the coil. A first comparator compares the perceived current voltage with the higher current signal value. A second comparator compares the perceived current voltage with the lowest current signal value. A current driver applies a drive current to the solenoid coil as a function of the output signals generated by the first and second comparators so that the coil current has a lower peak current value which is essentially a fixed percentage of the higher peak current value. The average current follows the peak current linearly because the lower peak is always a fixed percentage of the ordered peak peak current. Since the peak-to-peak ratio is constant, the linearity between the average current and the ordered peak current is maintained even if the inductance and / or resistance of the coil changes or if the supply voltage changes. By increasing the amplitude from peak to peak with the average current, the frequency range of the solenoid impeller is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS The single Figure is a detailed circuit diagram of the solenoid driver circuit of the present invention.

DETAILED DESCRIPTION The solenoid drive circuit 10 controls the current applied to the coil Ll of a solenoid-operated transmission control valve (not shown) in response to an analog voltage command signal V-CMD generated by the PM output of a microprocessor MP. Preferably, the command signal will have a voltage range of 0 to 5 volts corresponding to a desired coil current of 0 to 1000 milliamps. The pull resistor R15 (connected to a 5 volt supply voltage regulator) and the inverter 12 convert the PWM signal from 0 percent to 100 percent of the duty cycle to 5 to 0 volts of analog voltage using a circuit 2 millisecond filter composed of resistor R14 and capacitor C5.

The filtered command signal is then applied to a voltage divider formed by the resistors Rll and RIO which supply an ordered voltage V-PU (peak peak voltage) in the common connection between them. A slight amount of additional filtering is supplied by a capacitor C4 which is connected in parallel with RIO. The voltage V-PU is supplied to the + input of a reset order comparator 14 and to a voltage divider formed by the resistors R8 and R9 connected between V-PU and ground. The common connection between R8 and R9 provides a signal V-PL (lower peak voltage) which is a certain fixed percentage of V-PU, and which is applied to the - input of an opposite command comparator 16.

The output of the reset command comparator 14 is connected to + 5 volts through the resistor R6 and is applied to an input of a put / put multivibrator 18 (with a Schmidt trigger input) formed by a pair of gates NAND cross-connected 22, 20 and capacitor C2. The output of the fixed command comparator 16 is connected to + 5 volts through resistor R7 and is applied to an input of a put / put multiviewer 18.

V-PU is also extended to the + input of comparator 24 which, with capacitance to ground C3 is part of a closing circuit 26. A voltage divider formed by the resistor R12 and R13 between + 5 volts and ground generates a closing voltage V-closing which is applied to the comparator input 24 so that the comparator 24 will generate a turn-off or close signal until the V-PU reaches a level representing a coil current of approximately 150 milliamps. A capacitor C6 is connected between ground and the common connection between R12 and R13. The output of the comparator 24 (and the closing circuit 26) is connected to the IN input of the impeller 28. The output of the impeller 28 is connected to one end of the solenoid coil Ll and ground through the "return flight" diode. GAVE.

At another end of the coil Ll is connected to ground through a current sensing resistor R2. The voltage across the resistor R2 is proportional to the current through the coil Ll, and it is filtered from the high frequency noise by the resistor R3, the capacitor Cl and the resistor R5 to generate a voltage VSENSE. The temporary suppression of voltage is carried out by diode D2. The VSENSE voltage is applied to + input of comparator 16 and to the - input of comparator 14.

A comparator 30 has a + input to which VSENSE is applied and an input to which the voltage is applied VAPAGADO. The output of the comparator 30 is connected to + 5 volts through the pull resistor R1 and the state input of the impeller 28 and pulls the ST input low after the VSENSE is down VAPAGED. The output of the comparator 30 generates a status signal which is applied to a digital input of the microprocessor MP so that the microprocessor can detect circuit faults when the ordered voltage V-PU is greater than a value corresponding to a coil current of 150 milliamps. The status signal must be ignored until the order is greater than 150 milliamps.

Preferably the impeller 28 can be a Siemens Profet device or equivalent, which has integrated features for detecting open or short circuits in the coil Ll. When the driver 28 detects a fault, it pulls the ST line of low status.

Comparator 16 pulls its output to ground when VSENSE is too low (less than V-PL). Comparator 14 pulls its output to ground when VSENSE is very high (greater than V-PU). In this example, the resistors R8 and R9 are chosen such that V-PL is 78.5 percent V-PU. When VSENSE is below V-PL, the impeller 28 is turned on and stays on until VSENSE rises above V-PU. When VSENSE reaches V-PU, the impeller 28 is turned off (put back) until VSENSE again fails below V-PL.

To ensure that the impeller 28 is turned off when the ordered voltage is very low, V-PU and a small fixed voltage VAPAGED are supplied to the comparator 24. When the ordered voltage of the microprocessor MP is less than a value corresponding to a coil current of 150 milliamps the comparator 24 pulls the input to the impeller 28 low, turns off the impeller 28 and prevents the multivibrator 18 from igniting the impeller 28.

With this circuit, the voltage current through coil Ll linearly follows the peak current because the lowest peak current is always a fixed percentage of the peak peak current. As the command increases, the amplitude from peak to peak increases, but the ratio between the upper peak and the lower peak is constant. The linearity is maintained even if the inductance and / or the resistance of the coil changes and / or if the supply voltage changes.

The circuit will run at a variable frequency. The frequency varies as a function of the ordered voltage, the resistance and the inductance of a coil and the voltage supply. But since the peak-to-peak amplitude increases with increasing average current, the frequency variation is much less than if the peak-to-peak amplitude were constant.

The ratio of resistor divider R8 and R9 can be chosen to optimize the frequency to the nominal operating point (rated current, resistance and inductance of a coil, and voltage supply).

One of these control circuits can be used with multiple impellers if the impellers are never turned on at the same time. For example, a forward and a reverse impeller must share a common low side return and current sensing circuit. The input to the impeller for forward can simply be an ANDed with the front switch, and the reverse impeller ANDed with the reverse switch. The microprocessor will drive the same command circuit regardless of which valve was actually being supplied.

Finally the circuit is simple and consists of cheap components. The overall load of the microprocessor is extremely light since it only has to generate the PWM command signal. The A / D inputs are not tied since the average current is not measured by the microprocessor. Equations or tables are not required to convert the work cycle to current since the relationship is linear. However, the PWM signal must have a fairly high frequency so that the time constant of R14, the filter C5 can be minimized, or the D / A converters can also be used. Note that the sensing resistor R2 should be chosen as large as possible and that it should preferably have a tolerance of ± 1 percent. Similarly, the resistors R8, R9, RIO, Rll and R14 should preferably have a tolerance of ± 1 percent. The path to ground between the sensing resistor R2 and the comparators 14, 16, 24 and 30 must have a very low impedance. The accuracy of the supplied voltage of the 5 volt regulator supplied to the inverter 12 is also important.

The following is a Table of components that can be used in the electronic circuits illustrated in the Figure. These components are merely exemplary and other components may be used without departing from the scope of the present invention.

Exemplary Components Resistors Rl, R6, R7, R15 10 Ohms R2 1.0 Ohms R3, R5 4.7 k R4 2.7 k R8 13 k R9 47.5 k RIO 10.2 k Rll 23.7 k R12 27.4 k R13 1.0 k 5 R14 6.04 k Capacitors Cl 47 pf C2, C3, C4, C6, C7 .047 Mf 10 C5 .33 Mf Diodes DI Gl S2G D2 BAV99 15 Integrated circuits 12 74HC14 (Trigger inverter Hex schmidt) 14, 16, 24, 30 LM2901 (Quad comparator) 20, 22 74HCI32 (Nand gates schmidt quad trigger) 28 BTS410F 25 8 Bit microprocessor (80C517A) Even though the invention has been described in conjunction with a specific embodiment it It will be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, without departing from the principle of the invention, the non-inverting energy switching device can be replaced with an inverter device with an intermediate reversing impeller phase. Therefore, this invention is intended to encompass all those alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims (7)

R E I V I ND I C A C I O N S

1. An electrical circuit for applying an oscillating electric current to a coil of a solenoid in order to cause the solenoid to move in response to an input signal, characterized in that: the circuit supplies the coil with a current which has upper and lower peak current values and where the lower current value is essentially a fixed percentage of the higher peak current value.

2. The invention as claimed in clause 1 characterized in that the circuit comprises: a signal splitter to generate a higher signal value of the input signal and a lower signal value which is a fixed percentage of a higher signal value: a current sensor for generating a perceived current signal representing a current through the coil; a first comparator for comparing the current perception signal to the higher signal value; a second comparator for comparing the perceived current signal with the lower signal value; Y an energy switching device coupled to a potential source and to the solenoid coil, the power switching device connectably connects and disconnects the potential source to the solenoid coil as a function of the output signals from the first and second comparators.

3. The circuit as claimed in clause 2 further characterized by comprises: a put / put multivibrator circuit between the comparators and the power switching device.

4. The circuit as claimed in clause 2 further characterized because it comprises: a shutdown circuit having a first input to which the upper signal value is applied, a second input to which a shutdown signal is applied and an output connected to an input of the power switching device, the shutdown circuit operates to turn off the power switching device until the upper signal value reaches a level of the shutdown signal.

5. The circuit as claimed in clause 1 further characterized because it comprises: a fault detection circuit to generate a fault signal when the input signal is greater than a certain value.

6. An electric circuit for applying an oscillating electric current to a coil of a solenoid in order to cause the solenoid to move in response to an ordered signal characterized by: a signal divider for generating a higher peak current signal value of the ordered signal and a lower peak current signal value which is a fixed percentage of the higher peak current signal value; a current sensor for generating a current perception signal representing the current through the coil; a first comparator for comparing the perceived current signal with the higher current signal value; a second comparator for comparing the perceived current signal with the lowest current signal value; a put / put multivibrator circuit connected to the comparators; Y a current driver for applying a drive current to the solenoid coil as a function of the output signals of the put / put multivibrator circuit, the current driver supplying the coil with a current which has values of upper and lower peak current variables and wherein the lower peak current value is essentially a fixed percentage of the higher peak current value.

7. The circuit as claimed in clause 6 further characterized because it comprises: a shutdown circuit having a first input to which the upper current signal value is applied, a second input to which a shutdown signal is applied and an output connected to an input of the current driver, the shutdown circuit operates to turn off the current driver until the upper current signal value reaches a level of the shutdown signal. SUMMARY An electric circuit applies an oscillating electric current to a coil of a solenoid in order to cause the solenoid to move in response to an ordered signal. The circuit includes a signal divider for generating a higher peak current signal value from the commanded signal and the lower peak current signal value which is a fixed percentage of the higher peak current signal value. A current sense resistor generates a current perception voltage representing a current through the coil. A first comparator compares the current perception voltage with the higher current signal value. A second comparator compares the current perception voltage with the higher current signal value. A second comparator compares the current perception voltage with the lower current signal value. A put / put multivibrator connects to a current driver from time to time. A current driver applies a driving current to a solenoid coil as a function of the output signals generated by the first and second comparators so that the coil current will have a lower peak current value which is essentially a fixed percentage. of the higher peak current value.