DE102010043137A1 - Power steering apparatus of vehicle steering system, has output stage driver that has complementary output stage with P-channel FET which is portion of primary current mirror and N-channel FET which is portion of secondary current mirror - Google Patents

Abstract

The apparatus has a three-phase drive motor and a circuit which comprises an output stage driver and an inverter for driving the three-phase drive motor. The output stage driver comprises a complementary output stage with a P-channel FET (105) and an N-channel FET (106). The P-channel FET is a portion of the primary current mirror and the N-channel FET is a portion of the secondary current mirror.

Description

FIELD OF THE INVENTION

The present invention relates to a power steering system for a steering system of a vehicle and a steering system for a vehicle.

BACKGROUND OF THE INVENTION

In the prior art drives of three-phase motors are known as drive motors of electric power steering systems having a power output stage and an output stage driver.

SUMMARY OF THE INVENTION

A power output stage can be constructed as an inverter, which consists of three half-bridges. Each half bridge consists of two circuit breakers, z. B. Performance Mosfets. To switch the power mosfet, the input capacitance of a Mosfets Ciss must be loaded. This is done with a charging current injected into the gate of the mosfet. In the prior art, a gate resistor is connected in front of the gate to limit the gate current, thus adjusting the U _DS . This gate resistance is exposed to a high pulse load during pulse width control (PWM), which can lead to its failure. From a high pulse load results in a large temperature swing on the gate resistance, which may result in mechanical stress, causing z. B. cracks at solder joints can result (aging of the solder joint).

The high pulse load can also result in an accelerated aging of the gate resistance. An aging of the gate resistance can lead to a drift of the resistance characteristics of the gate resistance, as a result of which the gate current can likewise undergo drift over time. Due to the drift of the gate current, a desired slope of the voltages over the corresponding circuit breaker over time can not be ensured. Above-mentioned drift can lead to bridge short-circuit due to insufficient dimensioning (hot branch).

If a gate resistance fails, the steering assistance may be at least partially or completely canceled. In view of the fact that at least six gate resistors must be used in the prior art final stage drivers, there is an increased risk of power steering failure in the prior art.

A factory set edge steepness should be kept as constant as possible over time in order to obtain the lowest possible power dissipation of the power MOSFETs to avoid damaging the power MOSFETs with the best possible EMC compatibility. The lowest possible power loss of the line MOSFETs can be achieved by a very fast switching, ie a high edge steepness. The lowest possible EMC load from the circuit breakers can be achieved by switching as slowly as possible, ie a low edge steepness. There is therefore a conflict of interest between low power loss of the power MOSFETs and low EMC load by the power MOSFETs. Nevertheless, in order to be able to achieve both goals as optimally as possible, a careful dimensioning of the gate resistance is necessary, which can result in an optimized edge steepness.

An aging of the gate resistance changes its resistance, which can change over time, the gate current and therefore the edge steepness. An initially optimized setting of the edge steepness, in order to obtain a high switching speed and still avoid problems due to an EMC load on the other components, can therefore be lost due to the aging of the gate resistance.

A possible constant and reliable switching behavior of an inverter for a drive motor is required in particular for the drive motor of a power steering, as a power steering is to be regarded as part of a steering system to a particular extent as a safety-relevant element of a vehicle.

One object is therefore to provide gate currents for the circuit breakers of a half-bridge for a motor phase which have the lowest possible drift due to aging.

As a first embodiment of the invention, there is provided a power steering system for a vehicle steering system, comprising: a three-phase motor as a drive motor and a circuit including an output driver and an inverter for driving the three-phase motor, the output driver having a complementary output stage with a first switch and a second switch wherein the first switch is part of a first current mirror and the second switch is part of a second current mirror.

According to the invention, an output stage driver can be embodied by a push-pull output stage or complementary output stage, one or more current mirrors and a current source which can be controllable. As a result, can be dispensed with gate resistors in the final stage driver for driving a drive motor of a power steering. By the Current mirrors can be injected with gate currents for charging or reloading the gates of circuit breakers, in particular power MOSFETs, which can result in constant gate currents for the current PWM ratio. A drift of the switching edges of the voltages across the circuit breaker by aging can thereby be largely excluded.

As a second embodiment of the invention, a steering system for a vehicle is provided, comprising a power steering system according to one of claims 1 to 8.

Exemplary embodiments are described in the dependent claims.

According to an exemplary embodiment of the invention, a power steering is provided, wherein the first switch is a field effect transistor, in particular of the p-channel type, and / or wherein the second switch is a field effect transistor, in particular of the n-channel type.

In a further embodiment of the invention, a power steering is provided, wherein an output current of a third current mirror is the input current of the first current mirror and / or wherein the input current of the second current mirror can be determined by the output current of the third current mirror.

Advantageously, the input currents of the current mirror, which can generate as output currents the resulting gate current for a circuit breaker, in turn by z. B. a further current mirror can be generated. The input current of the first and the second current mirror is impressed by the further, third current mirror. In this way, an even lower drift of the edge steepness of the voltages can be ensured via the circuit breaker to be controlled.

With the first and second current mirror z. B. by adjusting the W / L ratios of the two switches of the complementary stage of the gate current can be adjusted. Furthermore, an alternative embodiment is a parallel connection of the switches of the complementary output stage.

According to another embodiment of the present invention, a power steering is provided, wherein the input current of the third current mirror is the output current of a current source.

According to an exemplary embodiment of the invention, a power steering is provided, wherein the output current of the current source is adjustable by a resistor or by an internal reference voltage source or an external reference voltage.

In a further embodiment of the invention, a power steering is provided, which is switchable by a third switch, the output current of the third current mirror as the input current of the first current mirror and / or wherein by a fourth switch, the input current of the second current mirror by the output current of the third current mirror can be determined ,

According to another embodiment of the present invention, a power steering is provided, wherein the third switch is a field effect transistor and / or wherein the fourth switch is a field effect transistor.

According to an exemplary embodiment of the invention, a power steering is provided, wherein the output stage driver has six complementary output stages and the inverter comprises three half-bridges with two power switches each.

As an idea of the invention, it can be considered to provide an output driver for a driver that does not require gate resistors. According to the invention, instead of gate resistors, current mirrors can be used or constant current sources which are designed as complementary output stages, whereby impressed gate currents for the power switches of the power output stage of the power steering can be provided. Replacing the gate resistors with current mirrors results in less drift in the slew rate of the voltages dropped across the power switches, allowing for a factory set optimum switching behavior of the power switches over time.

Of course, the individual features can also be combined with each other, which can also be partially beneficial effects that go beyond the sum of the individual effects.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention will become apparent from the embodiments illustrated in the drawings. Show it

1 a circuit according to the invention of an output stage driver,

2 a control of a three-phase motor (inverter with three half-bridges),

3 a half bridge with two power mosfets.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

1 shows a part of a final stage driver, with a complete output stage driver switching the circuit six times 1 may include. The circuit after 1 can be used to control a single circuit breaker, z. B. a power Mosfets be used. According to the invention, a controllable current source 101 whose output current is the input current I _{e, 3} 124 can represent a multiple current mirror, wherein the individual current mirror through the components 115 and 113 . 115 and 112 . 115 and 111 can be realized. Through the current mirror 115 and 113 In the present circuit, a current I _{a, 3} 125 imprinted. If by the pulse width signal P_PWM 118 the field effect transistor 114 is turned on, the output current I _{a, 3} 125 the input current I _{e, 1} 120 the current mirror with the two field effect transistors 104 . 105 dar. By the circuit of the field effect transistors 104 and 105 as a current mirror, an impressed, constant output current I _{a, 1} 122 at the drain of the field effect transistor 105 as a gate current for charging and driving through at the point GHS 117 be made available connected circuit breaker. If not the field effect transistor 114 but the field effect transistor 109 is turned on, determines the output current I _{a, 3} 125 the input current I _{e, 2} 121 the current mirror passing through the two field effect transistors 106 . 110 is formed. This results in an impressed constant output current I _{a, 2} 123 of the current mirror, acting as a gate current at the point GHS 117 can be provided for reloading the gate of a circuit breaker to be controlled. Through a resistor Rvar 116 can be the controllable power source 101 be set. A change in the setting of the power source 101 ultimately leads to a change in the gate currents for charging or discharging the gate of the circuit breaker, which at the point GHS 117 can be made available. Due to the variable resistor Rvar 116 Therefore, the edge steepness of the voltages can be determined via a circuit breaker. By the circuit according to the invention can be dispensed with gate resistors, which may be subject to an aging process, whereby it may be that the gate currents over time can not be kept constant. Furthermore, gate resistors are also exposed to pulse width control in a pulse width control, which can lead to damage and failure. The circuit according to the invention eliminates such a power loss. Furthermore, this ensures a high temporal constancy of the gate currents.

2 shows the control of a three-phase motor with its three phase connections phase U 205 , Phase V 206 and phase W 207 , The phase U 205 can with the circuit breaker 202 against supply voltage and the circuit breaker 210 be switched against GND potential. Accordingly, the circuit breaker 203 . 209 and 204 . 208 be driven to the phases V 206 and W 207 be able to supply with an alternating DC voltage. The circuit breakers 202 . 203 . 204 . 208 . 209 . 210 can be designed as power transistors or power MOSFETs, wherein the power MOSFETs by a circuit according to the invention according to 1 can be controlled. To the circuit breaker 202 . 203 . 204 . 208 . 209 . 210 To be able to control, therefore, six circuits according to the invention after 1 needed. A capacitor 201 can be used as energy storage to buffer short power pulses.

3 shows a half-bridge with two circuit breakers 318 . 319 , where the circuit breaker 318 . 319 are designed as power mosfets. The circuit breakers 318 . 319 are controlled alternately, so that at the potential SHS 316 an alternating voltage (alternating direct voltage, alternating direct voltage) can be provided for a phase connection of a three-phase motor. For controlling the circuit breaker 318 can a circuit according to the invention after 1 be used, the potential GHS 301 of the 3 with the potential GHS 117 of the 1 can be connected and the potential SHS 316 of the 3 with the potential SHS 118 of the 1 can be connected. So that the circuit breaker 318 can be controlled and at the connection SHS 316 There must be a high potential on the connection GHS 301 the gate 307 of the circuit breaker 318 be supplied with a gate current, the capacity C _GS 317 and C _GD 302 (Miller capacity) can charge. The circuit breaker 318 can be closed by an opposite gate current, the capacity 317 . 302 can discharge. A diode 305 serves as a freewheeling diode.

It should be noted that the term "comprising" does not exclude other elements or method steps, just as the term "a" and "an" does not exclude multiple elements and steps.

The reference numerals used are for convenience of reference only and are not to be considered as limiting, the scope of the invention being indicated by the claims.

LIST OF REFERENCE NUMBERS

101

adjustable current source

102

voltage source

103

voltage source

104

Field effect transistor, p-channel

105

Field effect transistor, p-channel

106

Field effect transistor, n-channel

107

Field effect transistor, p-channel

108

Field effect transistor, p-channel

109

Field effect transistor, n-channel

110

Field effect transistor, n-channel

111

Field effect transistor, n-channel

112

Field effect transistor, n-channel

113

Field effect transistor, n-channel

114

Field effect transistor, n-channel

115

Field effect transistor, n-channel

116

resistance

117

Point GHS

118

Point SHS

119

Pulse width signal N_PWM

120

Input current of the first current mirror

121

Input current second current mirror

122

Output current of the first current mirror

123

Output current second current mirror

124

Input current third current mirror

125

Output current of third current mirror

201

Link capacitor

202

breakers

203

breakers

204

breakers

205

Phase connection three-phase motor U

206

Phase connection three-phase motor V

207

Phase connection three-phase motor W

208

breakers

209

breakers

210

breakers

301

Potential GHS

302

Miller capacity C _GD

303

Supply voltage U

304

drain

305

Freewheeling diode

306

source

307

gate

308

drain

309

Freewheeling diode

310

source

311

gate

312

Gate-source capacitance C _GS

313

Potential SLS

314

Potential GLS

315

Miller capacity C _GD

316

Potential SHS

317

Gate-source capacitance C _GS

318

breakers

319

breakers

Claims (9)

Power steering system for a steering system of a vehicle comprising a three-phase motor as a drive motor and a circuit with an output stage driver and an inverter for driving the three-phase motor, characterized in that the output stage driver has a complementary output stage with a first switch ( 105 ) and a second switch ( 106 ), wherein the first switch ( 105 ) is a part of a first current mirror and the second switch ( 106 ) is part of a second current mirror. Power steering system according to claim 1, characterized in that the first switch ( 105 ) is a field effect transistor, in particular of the p-channel type, and / or wherein the second switch ( 106 ) is a field effect transistor, in particular of the n-channel type. Power steering according to one of claims 1 or 2, characterized in that an output current I _{a, 3} ( 125 ) of a third current mirror, the input current I _{e, 1} ( 120 ) of the first current mirror and / or wherein the input current I _{e, 2} ( 121 ) of the second current mirror by the output current I _{a, 3} ( 125 ) of the third current mirror can be determined. Power steering system according to claim 3, characterized in that the input current I _{e, 3} ( 124 ) of the third current mirror is the output current of a current source. Power steering system according to claim 4, characterized in that the output current of the current source is adjustable by a resistor or by internal reference voltage source or an external reference voltage. Power steering according to one of claims 3 to 5, characterized in that by a third switch ( 114 ) the output current I _{a, 3} ( 125 ) of the third current mirror as input current I _{e, 1} ( 120 ) of the first current mirror is switchable and / or wherein by a fourth switch ( 109 ) the input current I _{e, 2} ( 121 ) of the second current mirror by the output current I _{a, 3} ( 125 ) of the third current mirror can be determined. Power steering system according to claim 6, characterized in that the third switch ( 114 ) is a field effect transistor and / or wherein the fourth switch ( 109 ) is a field effect transistor. Power steering system according to one of the preceding claims, characterized in that the output stage driver has six complementary output stages and the inverter comprises three half-bridges, each with two circuit breakers. A steering system for a vehicle comprising a power steering system according to any one of the preceding claims.

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