VEHICLE

FIELD OF INVENTION

[001] The present invention relates to a sensorless hill hold assist system in a three wheeler electric vehicle. Particularly, the present invention provides a system and method for optimizing the torque and speed of the electric vehicle to provide boost at the time of starting the vehicle in an inclined position and prevents rolling back of vehicle on an inclined surface.

BACKGROUND OF THE INVENTION

[002] Electric vehicles due to their efficient and different capabilities are receiving considerable attention as a substitute for conventional vehicles. Primarily, due to almost zero atmospheric emissions obtained from all electric vehicles. Further, electric vehicles also offer other advantages including reduced dependency on non-renewable energy demands. Therefore, need for an electric vehicle is on rise in every field be it a four wheeler, three wheeler or two wheelers. Further, three wheelers in recent years have emerged as one of the major modes of transport for the local public. A need for an economic and greener solution has led to the development of electric three wheelers. As three wheelers are now available at almost every location there are various problems associated with the vehicle that have been encountered.

[003] One of the most common problems faced by the driver while driving through hills is rolling back i.e., any vehicle either having a manual gear or automatic transmission rolls back after coming to a complete stop on an inclined surface unless and until brakes are applied. The vehicle slips backward on releasing the brake pedal causing most of the accidents. Therefore, vehicle driver before starting uphill first draws and opens parking brake to maintain stationary vehicle and then presses the acceleration pedal rapidly again after releasing the brake pedal, and finally unclamps parking brake. This is a very complex method for any vehicle driver to maintain at the time of starting the vehicle at the inclined position. Sometimes when this balance between the brake pedal and acceleration pedal is not maintained the vehicle also tends to stall.

[004] Chinese patent CN103754222 relates to the implementation method of a kind of electric automobile uphill starting ancillary control function. The said function includes two steps: firstly, judging activation condition that maintains vehicle static position when driver slams brake pedal. The vehicle does not move when the driver is opening parking brake and gear at drive shift. Further, if the driver loosens the brake, rear vehicle starts to slip by slope at that time uphill starting ancillary control function is activated. Secondly, after activation of uphill starting function, the motor output torque that increases sharply, makes vehicle no longer slip by slope therefore, driving motor target torque value is revised to maintain this torque output so that vehicle is static in original place subsequently. When, the driver bends the throttle, uphill starting ancillary control function automatically ends, and vehicle starts moving gently on ramp. However, the cited prior art document discloses about the control function inbuilt in a four wheeler vehicle and not that of a three wheeler. Further, the cited prior art document discloses the use of various sensors for the implementation of uphill starting ancillary control function in a four wheeler which is not an economic solution for a three wheeler.

[005] Currently, all the uphill starting ancillary control functions are based on the manual adjustment between driving force and the brake force of each wheel to stabilize vehicle body and improve drive safety. For there is no automatic vehicle movement controlling feature to prevent rolling back of vehicle at the time of starting. During vehicle’s motion on the incline terrain vehicle have tendency to roll backwards (while going uphill) if driver is not applying constant pressure on the brake pedal. The situation gets trickier if driver has to perform a stop-and-go manoeuvre while moving uphill or a reverse while going down. The problem in both the scenarios is while driver moves from brake pedal to accelerator pedal during that instant vehicle could roll in opposite direction resulting in some unfortunate event or if not that it makes challenging to drive off smoothly. [006] Hence, with respect to the problems encountered above there is a need for a technology that provides driver assistance at the time of starting a three wheeler vehicle on an inclined plane which is economic as well.

OBJECTIVE OF THE INVENTION

[007] The primary objective of the present invention is to provide a system and method for controlling the hill hold assist system in a three-wheeler electric vehicle.

[008] Yet another objective of the present invention is to provide sensorless hill hold assist system.

[009] Yet another objective of the present invention is to optimize the torque and speed of an electric three wheeler vehicle to provide boost at the time of starting the vehicle in an inclined position and prevent rolling back of vehicle.

[0010] Yet another objective of the present invention is to provide an economic solution to detect rolling back of a three wheeler vehicle on an inclined position and prevent the same.

[0011] Other objectives and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein, by way of illustration and example, the aspects of the present invention are disclosed.

BRIEF DESCRIPTION OF DRAWINGS

[0012] The present invention will be better understood after reading the following detailed description of the presently preferred aspects thereof with reference to the appended drawings, in which the features, other aspects and advantages of certain exemplary embodiments of the invention will be more apparent from the accompanying drawing in which: [0013] Figure 1 illustrates the system diagram of an electric three-wheeler vehicle;

[0014] Figure 2 illustrates a flowchart of working of the hill hold mode in an electric three- wheeler vehicle in an incline position.

SUMMARY OF THE INVENTION

[0015] The present invention provides a system and method for controlling the hill hold assist system incorporated in an electric three-wheeler vehicle. Particularly, the present invention discloses a feature that prevents rollback of an electric three wheeler vehicle on an incline by providing a boost to the vehicle while the user switches between the brake and acceleration pedals. The hill hold mode assist in maintaining a limited torque and speed of car in the direction selected by the user for a set period of time as the user switches from the brakes to the acceleration pedal. Once the user presses the accelerator, it releases the hill hold mode. In the present invention hill hold mode only provides assistance i.e., boost in holding the car to a position and does not increase the traction, it just prevents the user from rolling backwards.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The following detailed description and embodiments set forth herein below are merely exemplary out of the wide variety and arrangement of instructions which can be employed with the present invention. The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. All the features disclosed in this specification may be replaced by similar other or alternative features performing similar or same or equivalent purposes. Thus, unless expressly stated otherwise, they all are within the scope of the present invention.

[0017] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness. [0018] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[0019] It is to be understood that the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0020] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0021] It should be understood that the present invention is specifically directed towards the implementation of the technology in three wheeler electric vehicles however, the technology can also be implemented in other types of hybrid or non -hybrid electric vehicles.

[0022] The present invention provides a system and method for controlling the hill hold assist system incorporated in an electric three-wheeler vehicle. Particularly, the present invention discloses a feature that prevents rollback of an electric three wheeler vehicle on an incline by providing a boost to the vehicle while the user switches between the brake and acceleration pedals for a set period of time. The method comprises of four modes i.e., “ Idle Mode” (100), “ Brake Release Check” (101), “Move Back Check” (102), “ Hill Hold Enable” (103).

[0023] In the present invention Figure 1 generally depicts a system for carrying out the method for preventing the roll back of an electric vehicle while moving upwards on the hill according to one embodiment described herein. The system and method prevent the rolling of the vehicle in the backward direction during ascending the hill via the automatic application of torque in forward direction thereby improving vehicle safety and reducing wear on mechanical braking components. The system for preventing the rolling of an electric vehicle comprises an electric vehicle controller incorporating an Electric Vehicle Controller and motor control unit operatively connected with an electric motor/generator, a high voltage battery pack, a direction selector switch, and motor speed encoder. In an embodiment each of these elements and the operation of the system will be described in more detail herein:

[0024] (a) Electric Motor: In an aspect, the electric motor/generator provides the ignition power for the vehicle. In the present invention a high speed torque motor is utilized, preferably a three phase air-cooled induction motor is utilized as prime mover providing the forward moving torque. In an alternate embodiment specification of the motor being utilized for ignition are:

Peak Power: 9 kW Peak Torque: 45 Nm

RPM Range: 0 to 10,000 rpm

Battery Pack Voltage: 48V.

[0025] (b) Electric Vehicle Controller : It is a main component of an Electric Vehicle

(EV) which controls the major operation in the vehicle. It is further divided into two section:

(i) Power Board: It is an array of plurality of power electronic devices which helps in generating three phase supply for the induction motor via the direct (DC) power obtained from the battery having capacity at least 48 V.

(ii) Control Board: A microcontroller based control board which performs all the control function in the vehicle from motor control to vehicle control.

[0026] (c) Battery Pack: It is a power storing device having a capacity of at least 48 volts.

It is the only power storage device fitted in the vehicle. A voltage sensor and current sensor may be electronically connected to the high voltage battery to control the charging and discharging of the high voltage battery. [0027] (d) RNFB Switch: According to an embodiment the Direction Selector Switch is also referred as RNFB Switch. The switch is operated by the user to select whether he wants to drive vehicle in forward direction (F), reverse direction (R), in boost mode (B) or want to keep in idle in neutral mode (N). The switch is interconnected with electric vehicle controller . It is a digital input knob switch which allows the driver to select the vehicle mode of operation from the following: a. Reverse: If the switch is turned to reverse, vehicle reverse mode is engaged. b. Neutral: If the switch is turned to neutral, vehicle is put into neutral mode. c. Forward: If the switch is turned to forward, vehicle moves in forward direction with a power and speed limitation (vehicle power is limited to encourage more driving range). d. Boost: If the switch is turned to boost, vehicle moves in a forward direction reaching the top speed with no limitation on power.

[0028] (e) Motor Speed Encoder: The Motor Speed Encoder is required for controlling motor. The encoder allows the calculation of the rotation speed of motor (RPMs) and the direction of rotation. The three wheeler vehicle being equipped with a simple single speed gearbox the direction of rotation of the motor determines the direction of rotation of electric vehicle wheels r. In the present invention the motor speed encoder is a bearing based encoder device that can measure the speed and direction of rotation of induction motor. The speed encoder unit produces two signals, at 90 degree phase shift each with resolution of 64 pulse per revolution. The electric vehicle controller receives these two signals via the signal harness and using the Enhanced Quadrature Encoder Pulse (eQEP) module provided in the micro-controller where the signal value is converted into the speed and the direction of the rotation. The speed of rotation is calculated in terms of RPM (Rotation per minute) while the direction is calculated in terms of CW (Clockwise) and CCW (Counter Clockwise) whenever the rotation of the motor shaft changes (technically it is calculated by measuring which of the two signal wave is leading phase wise). [0029] (g) Software Module: The EV Controller is configured with a software module for controlling the functions of the vehicle built in MATLAB Simulink environment using the generic C20x Simulink support package. The software mode is utilized for controlling the Hill Hold Mode in the three wheeler vehicle.

[0030] In an embodiment of the system for controlling vehicle speed while ascending the inclined plane or hill as depicted in figure 1 , the electric vehicle controller is programmed to selectively provide assistance to the vehicle while on incline position to prevent rolling back based on rotation signals received from the motor speed encoder. This is automatic software routine performed by EV Controller once rollback is detected and the hill hold feature was activated by the user. The vehicle needs a positive torque to move forward and a positive torque in opposite direction to move in reverse and this is provided by the induction motor.

[0031] In an exemplary embodiment of the present invention for providing the boost the EV Controller keeps a maximum torque demand of TQ_Nom. The said TQ_Nom is the value of torque that is being available during the Hill-hold mode thereby limiting the speed of the electric vehicle upto 0.5 Kmph for 5 second in the direction as defined by the user.

[0032] While the system depicted in figure 1 is specifically configured for an application of boost in speed, it should be understood that the systems and methods described herein utilizes assistance in speed of the vehicle in the direction chosen by the user to control the hill ascend speed of an electric vehicle.

[0033] Figure 2 illustrates a flow diagram of one embodiment of a method for providing assistance in starting the electric vehicle when in inclined position without rolling back. The method may provide boost during incline position of an electric vehicle through the selective control and application of torque in the direction chosen by the user through selector switch for a limited time.

[0034] The flow diagram shown in figure 2 of the Hill hold mode shows various states of the system undergoing the Hill hold routine in an electric vehicle. The method is triggered based on the following modes: (a) Idle Mode (100) : When the vehicle is running smoothly then it is always in the idle mode. Idle mode (100) is the vehicle’s internal state in which it is being piloted by the driver only and is under no automatic software routine. Idle Mode has following things features:

• The vehicle ignition is ON’,

• the vehicle may be in any RNFB mode, and

• the vehicle may be stationary or moving via driver’s inputs.

[0035] When the vehicle is switched from the “off’ position to the “on” position the constraints used in the method (e.g., brake release check, move back check, and the like) may be initialized prior to the start of the method. Accordingly, an “Idle Mode” (100) condition may exist either when the vehicle ignition was switched off and it is being switched on or when brake pedal has been applied to halt the vehicle. Every 1 millisecond the internal software module of the present invention continuously monitors to promote to next state by comparing brake position and vehicle speed. If the vehicle is stationary and brake pedal is pressed for more than 2 second, the method continues on to “Brake Release Check” (101).

[0036] (b) Brake Release Check (101): In this state the software module of the present invention checks every millisecond whether the driver is applying the brakes or not. If the software module detects that the brake pedal is not being depressed the next routine in the method cycle i.e., the move back check (102) is initiated.

[0037] The position of the vehicle brake pedal may be determined based upon a signal received from the brake pedal which is read as a digital input from the brake pedal switch sensor (Sensor is essentially a digital switch connected to brake pedal). So, when the brake pedal is not pressed the EV Controller receives high value from the brake pedal sensor and when the brake pedal is pressed the sensor get disengaged and the EV Controller receives a digital low signal indicating that the brake pedal is pressed. Similarly, the accelerator pedal incorporates an analog sensor to read the functioning of the accelerator pedal. Further, to activate the “Hill Hold Mode” the brake pedal is depressed for at least 2 sec and then released. If the brake pedal is depressed after the brake release the process is terminated and does not proceed further. If the vehicle brake pedal is not depressed, the method continues on to next step i.e., “Move back check” (102). Accordingly, the vehicle may be in a freewheel condition when the RNFB switch of the vehicle is either in drive condition and neither the accelerator pedal nor the brake pedal are depressed. Further, it should be understood that, when either the accelerator pedal or the brake pedal of the vehicle is depressed, the driver is actively controlling the speed and acceleration of the vehicle. However, when the vehicle is in inclined position as soon as the user releases the brake pedal the vehicle starts rolling rolls back as it is difficult to maintain a steady position on inclined surface. Sometimes the balance between the brake pedal and acceleration pedal is not maintained and this leads to unwanted accidents.

[0038] (c) Move Back Check (102): In this state the software module continuously monitors whether the vehicle is trying to roll back through the incline position by comparing the input signal received from RNFB switch input and the motor encoder provided direction. If the detected result ensures the backward movement of the vehicle, then the next routine in the method cycle i.e., Hill Hold mode (103) is enabled.

[0039] However, if no roll back is detected for 10 sec or as soon as the acceleration pedal is being pressed and a steady speed of the vehicle is being maintained then the “Hill Hold” condition is reset, and the software module immediately takes the vehicle to Idle mode (101) state again and the process start all over again.

[0040] In the step “Move Back Check” (102) the motor speed may be determined based on an input signal from the motor speed encoder to the EV Controller . Every millisecond the speed encoder sends signal whether the direction of rotation is clockwise (CW) or counter clock wise (CCW) of the motor and the value is updated in the EV Controller.

[0041] Further if either of the brake pedal or the accelerator pedal have been depressed since the initial assessment of the freewheel condition in step 102, the electric motor speed remains zero. If the either of the brake pedal or the accelerator pedal have not been depressed, then the method proceeds to step “Hill-Hold Enable” (103).

[0042] (d) Hill Hold Mode (103): If the software module evaluates that an unintentional roll back took place and vehicle motion needs to be corrected then EV Controller applies a torque demand of TQ_Nom for atleast 5 sec providing slight boost to the vehicle to prevent the unintentional roll back.

[0043] In step “Hill Hold Enable” (103) the speed of the motor/generator may be determined based on the signal received by the EV Controller . If the timer value is less than 5 seconds and either of the brake pedal or the accelerator pedal have not been depressed, then “Hill Hold Mode”(103) is enabled. A boost is provided to the vehicle to prevent rolling back of the vehicle and as soon as the either of the brake pedal or the accelerator pedal have been depressed the method returns to either Idle Mode (101). or Hill Hold mode (103) enable state is timed out after 5sec of torque application wherein either the driver applied pressure on accelerator or brake pedal.

[0044] In an embodiment the method for controlling the hill hold assist system in the three wheeler electric vehicle comprises of the following steps:

• starting the vehicle in “Idle Mode” (100);

• selecting the direction of movement of the vehicle through the direction selector switch by user;

• detecting the direction of the rotation of the wheels of the vehicle through motor speed encoder in the “Brake Pedal Release Mode” (101);

• comparing the direction selected by the user and the direction of movement of vehicle through EV Controller in “Move Back Check Mode” (102);

• sensing the difference in the direction selected by the user and movement of the vehicle;

• activating “Hill Hold Mode” (103) of the vehicle for a predefined time;

• enabling the vehicle to move in the direction selected by the user with the fixed torque; and

• preventing roll back of the vehicle;

• deactivating Hill Hold Mode because either Hill hold Mode is timed out after 5 sec of torque application, or the user presses the accelerator/brake pedal.

[0045] The various limitations of the system and method of the present invention for implementing the flow of the technology includes: • Avoiding an un-intended movement of the vehicle at a later time, if rollback is detected 10 seconds after brake pedal release, automatic vehicle movement will not be allowed.

• If during the automatic vehicle movement of 5 seconds, either of brake or throttle is pressed, the automatic vehicle movement would be stopped.

[0046] The advantages of the system and method of the present invention includes:

• An economic technology for providing assistance to the three wheeler electric vehicle while moving on inclined surface.

• The EV Controller includes the functionality to detect whether the vehicle is in a condition where it is about to roll backwards.

• If a rollback of the vehicle is detected, then the motor provides a slight boost for a limited time period allowing vehicle to move in intended direction.

• The hill hold system allows the user to smoothly take off if stopped on the slope without any jerks or discomfort in ride quality even while carrying heavy loads.

[0047] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.