Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed

Field of the invention
[0001] The present disclosure relates to the field of Electronic Power Steering. In particular, the present invention discloses a system for measuring asymmetric current for a motor in a motor redundant system of the Electronic Power Steering system.

Background of the invention
[0002] Electric power steering (EPS) is a key technology for highly automated driving. The EPS has an electric motor which controls the vehicle steering. With an electric motor the EPS controls and assists vehicle steering and provides an optimal and enjoying steering feel. The electric interface enables highly automated driving with maximum security till SAE-Level 4. This electrical interface is very critical for ensuring the proper functioning of the motor. In particular, this interface consists of two electric control units (ECUs) and two motors. In case one ECU or motor fails, the vehicle can be driven using the other set.

[0003] The two channels for the two batteries or powers sources causes an asymmetrical current to flow in the return path due to resistance imbalances. These negative ground return currents have to be monitored for prevention of ground Loss (Fault) or deterioration (Latent Fault Prevention) of wiring harness. The current range per channel is 40A RMS (70 peak), however there is a need to measure and safeguard the ECU for current values in each channel up to 140A peak.

[0004] US Patent Application US2013314014 AA titled “ Method and controller for an electric motor with fault detection ” discloses for each phase of a controller, semiconductor switches comprise a high side switch and a low side switch. A direct current voltage bus provides electrical energy to the semiconductor switches. A measuring circuit is adapted to measure the collector-emitter voltage or drain-source voltage for each semiconductor switch of the controller. A data processor determines that a short circuit in a particular semiconductor switch is present if the measured collector-emitter voltage or measured source-drain voltage for the particular semiconductor switch is lower than a minimum threshold and if an observed current associated with the particular semiconductor switch has an opposite polarity from a normal operational polarity. A driver simultaneously activates counterpart switches of like direct current input polarity that are coupled to other phase windings of the electric motor, other than the particular semiconductor switch, to protect the electric motor from potential damage associated with asymmetric current flow.

Brief description of the accompanying drawings
[0005] An embodiment of the invention is described with reference to the following accompanying drawings:
[0006] Figure 1 depicts an Electronic Power steering (EPS) system;
[0007] Figure 2 depicts a system (112) for measuring asymmetric current for a motor in the EPS system (100).

Detailed description of the drawings
[0008] Figure 1 depicts an automotive Electronic Power steering (EPS) system. The EPS system (100) comprises a steering wheel (104) coupled to a steering rack (114) through a steering column (106). The steering column (106) comprises an input shaft from the steering connected to an output shaft by means of a torsion bar and a gear system. The input shaft translates the rotational motion on the steering wheel (104) to a telescopic movement of the torsion bar and a gear system. A steering angles sensor is mechanically coupled to the steering column (106). The output shaft of the steering column (106) is mechanically coupled to a steering rack (114) by means of a rack and pinion arrangement.

[0009] The steering rack (114) is coupled to a motor (108) that assist the steering system. The motor (108) is coupled to the steering rack (114) by means of a worm wheel assembly and a secondary pinion. Based on the signal from a torque sensor mounted on the steering column (106), a control unit (102) calculates an optimal steering support and sends the information to the electric motor to provide the necessary assistance. The motor (108) is driven by a system and powered by two power sources i.e. a primary power source (B1) (battery) and a secondary power source (B2) (battery). At an instance only one power source and the corresponding loop is functional and hence the other is known as the motor redundant system

[0010] The control unit (102) can either be a logic circuitry or a software programs that respond to and processes logical instructions to get a meaningful result. A hardware control unit (102) may be implemented in the system as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, one or more microchips or integrated circuits interconnected using a parent board, hardwired logic, software stored by a memory device and executed by a microprocessor, firmware, an application specific integrated circuit (ASIC), and/or a field programmable gate array (FPGA), and/or any component that operates on signals based on operational instructions.

[0011] Figure 2 depicts a system (112) for measuring asymmetric current for a motor (108) in the EPS system (100). The EPS system (100) and it’s components have been elucidated in accordance with figure 1. The system (112) electrically connects the primary power source (B1) and the secondary power source (B2) to the motor. The system (112) for measuring asymmetric current comprises a primary loop and a secondary loop. The primary loop and the secondary loop are in parallel connection to each other.

[0012] The primary loop comprises the primary power source (B1), a first motor load resistance (L1) and at least a first internal resistance (Rcab1). The components of the primary loop are in series connection with each other. The secondary loop comprises the secondary power source (B2), a second motor load resistance (L2) and at least a second internal resistance (Rcab2). The components of the secondary loop are in series connection with each other.

[0013] The value of the first internal resistance (Rcab1) and the second internal resistance (Rcab2) are dependent upon the vehicle wiring harness. This internal resistance is basically dependent upon the vehicle wiring harness and is usually equal in an ideal scenario. However due to imbalances, their value become unequal. Due to unequal resistances in the loops an asymmetric current flows in system (112) for measuring asymmetric current which can destroy components of the circuit. The primary and the secondary loops further include a current sensor (A1,A2).

[0014] Table 1 below lists the value of various parameters in the proposed system (112) for measuring asymmetric current. Motor (108) is driven by two loops to enable the redundant function. The measurement circuit module employes to monitor the return path conductivity of each system individually. The system decides the drive configuration based on the measured value particularly to detect the “ground loss” and to run the motor load in the reduced functionality. B1 and B2 is taken for the 12V system and the same system can be used for the 24V system and even applicable for all the power rails.

[0015] A differential amplifier (INA) and a differential shunt resistor (Rsense) are connected in parallel connection to both the primary loop and the secondary loop. The output of the differential amplifier (INA) is supplied to the motor. The differential amplifier (INA) safeguards the primary loop and secondary during flow of an asymmetrical current in the system (112) for measuring asymmetric current.

[0016] The shunt resistance (L1,L2) is placed in both the loops and current passes through it. It therefore conducts the asymmetric current of both the loops. Magnitude of the electrical potential forms in resistor is bipolar as it conducts the current bidirectionally. A full scale mapped to the 5V full-scale ADC system with the gain of 15 is explained w.r.t. table below. The measurement for system (112) behavior w.r.t all the combinations of fault current states are given in the table. Vehicle batteries are considered in 12V and the system adapts all the standard automotive battery voltage levels including the voltage level for the E-Vehicle. Vehicle resistances are taken 1 (m ohm) as reference and this resistance varies in the actual vehicle and the measurement system adapts the actual vehicle reference and measures the asymmetric current. Rsense and INA gains are flexible to configure according to the vehicle types.

Measurement system
Parameters Measurement system states Units
Idle mode

0% Asymmetric faulty current +10% Asymmetric fault current -10% Asymmetric fault current +100% Asymmetric fault current -100% Asymmetric fault current
B1 12 12 12 12 12 V
B2 12 12 12 12 12 V

R_Cab_1 1 1 1 1 1 Ohm
R_Cab_2 1 1 1 1 1 Ohm

L1 70 70 70 70 70 A
L2 -70 -70 -70 -70 -70 A
Fault current 0 7 -7 140 -140 A

R_Sense 1 1 1 1 1 mOhm
INA_Gain 15 15 15 15 15

V_R_Sense 0 105 -105 2100 -2100 mV

[0017] It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0018] This idea to develop a system (112) for measuring asymmetric current for motor of the EPS not only safeguards the system during the flow of an abnormally asymmetrical current but with the presence of current sensors (A1,A2) in each loop also measure it’s value each time which is used for diagnostics purposes.

[0019] It must be understood that the embodiments explained in the above detailed description are only illustrative and do not limit the scope of this invention. Any modification to the system (112) for measuring asymmetric current for a motor in an Electronic Power Steering system (100) are envisaged and form part of this invention. The scope of this invention is limited only by the claims.
, Claims:We Claim:

1. A system (112) for measuring asymmetric current for a motor (108) (108) of an Electronic Power Steering system (100), said system (112) electrically connecting a primary power source (B1) and a secondary power source (B2) to the motor, said system (112) comprising:
a primary loop comprising the primary power source (B1), a first motor load resistance (L1) and at least a first internal resistance (Rcab1);
a secondary loop comprising the secondary power source (B2), a second motor load resistance (L2) and at least a second internal resistance (Rcab2), the secondary loop placed in parallel connection to the primary circuit;
a differential amplifier (INA) and a differential shunt resistor (Rsense0 in parallel connection to both the primary loop and the secondary loop, the output of the differential amplifier (INA) supplied to the motor (108).

2. The system (112) for measuring asymmetric current for a motor (108) (108) as claimed in claim 1, wherein the primary and the secondary loops further include a current sensor (A1,A2).

3. The system (112) for measuring asymmetric current for a motor (108) (108) as claimed in claim 1, wherein the components of the primary loop are in series connection with each other.

4. The system (112) for measuring asymmetric current for a motor (108) (108) as claimed in claim 1, wherein the components of the secondary loop are in series connection with each other.

5. The system (112) for measuring asymmetric current for a motor (108) (108) as claimed in claim 1, wherein the value of the first internal resistance (Rcab1) and the second internal resistance (Rcab2) are dependent upon the vehicle wiring harness.

6. The system (112) for measuring asymmetric current for a motor (108) as claimed in claim 1, wherein the first internal resistance (Rcab1) and the second internal resistance (Rcab2) are equal in an ideal scenario.

7. The system (112) for measuring asymmetric current for a motor (108) as claimed in claim 1, wherein the differential amplifier (INA) safeguards the primary loop and secondary during flow of an asymmetrical current in the system (112) for measuring asymmetric current.