DESCRIPTION

The complete specification derives priority from Indian Application No.

202211044481 dated 03/08/2022, granted on 23/05/2023 with Patent No. 432539.

TECHNICAL FIELD OF INVENTION

The present invention relates to a mini electric excavator system having two separate motors for track assemblies and moving arm respectively along with separate control mechanism, powered by a battery module. The invention essentially relates to a fully electric earth moving or construction equipment which works with zero emission.

BACKGROUND AND PRIOR ART OF THE INVENTION

Reference is taken from US10427520B2 titled “Hybrid vehicle drive system and method using split shaft power take off’ which speaks of a hybrid vehicle drive system for use with a first prime mover and a transmission driven by the first prime mover. It speaks of the Power Shift PTO located on the truck chassis between the main transmission and differential. These gearboxes are mainly used for Fire Fighting Trucks, Cleaning Combination Trucks, Sweeping Trucks and Road Maintenance Trucks. Major difference with this patent application is that in the proposed invention, wheels are controlled by a battery and an electric motor whereas the author mentioned a prime mover in his patent which is an internal combustion engine.

Reference is taken from EP2696208A1 titled, Construction machinery which speaks of a system to store energy and prevent electric shock or loss by first using an insulation resistance degradation detection device. This includes a voltage generation device and a first detection center. The purpose of the author's invention is to measure the waveform changes input from the first voltage generation device and a second insulation resistance degradation detection device to prevent loss of excess energy.

In the proposed invention there is no accommodation of an energy storage system to recoup excess energy in terms of pressure generated from the variable displacement pump. Instead, the said invention consists of a pressure relief valve which will be used to accommodate any excess pressure in the hydraulic actuator.

Reference is taken from US8639404B2 titled working machine, speaks of a hybrid type construction machine as a working machine includes: a DC bus which is connected to a rotation motor via an inverter circuit, a battery which is connected to the DC bus via a step-up/step-down converter and a switch, a controller which drives the inverter circuit and the step-up/step-down converter, a cooling liquid circulating system which includes a pump motor, and an inverter circuit which is connected to the DC bus and driving the pump motor. The working machine proposed in this patent includes an AC motor connected to the ICE to move the hydraulic pump for functions associated with boom , arm and bucket. Therefore it is evident that the authors are proposing a hybrid working machine (including both ICE and an electric motor). The said invention does not include an ICE but in fact includes a motor connected to a battery to provide motion to the variable displacement pump which will supply pressure to the actuators to carry out operations like (lifting , swinging etc.)

Reference is taken from US20180072281A1 titled, Control method for controlling a movable member of an excavator and excavator comprising a control unit implementing such a control method which speaks of s the new control method which reduces the risk of backlash when the brake is released, while minimizing the electrical power consumption controls requirement. The proposed system includes an actuator connected to the variable displacement hydraulic pump driven by an electric motor. The authors of the cited invention mention that the brake and electric motor generate an upper threshold of brake force and motor force respectively. The difference between the patent application and the proposed invention (electric excavator) is that the electric motor in the proposed control system does not have a threshold and the brake does not generate a threshold force either.

Reference is taken from JP5384476B2, titled Work machine” which speaks of have integrated the concept of a construction machine which has one ICE, 2 electric motors and 2 inverter circuits. These circuits as mentioned in the patent are controlled by 1 controller. There is one capacitor and a buck boost converter. The system proposed by this patent is similar to a hybrid integration. The major difference between the proposed invention(electric excavator) and the patent application , is that in the latter , the pump used to drive the boom receives its energy through the engine. However, in the proposed invention (electric excavator) the pump is driven through the permanent magnet synchronous motor with squirrel cage configuration. In the patent the author mentions how the first electric motor is connected to the engine and at times acts as a generator. However, in the case of the said invention there is no ICE all the functions are carried out by the electric motors.

The major difference with the existing prior art is that in almost all the prior arts either there is an Internal combustion engine, whereas in the proposed invention the IC engine is replaced by a battery and there is a use of two motors, one to drive the track assemblies and the other for the movement of the hydraulic arm.

OBJECT OF THE INVENTION

The main objective of the invention is to provide an electric excavator that works on zero emission. Another object of the proposed invention is to provide an electric excavator with dual motors.

Yet another object of the proposed invention is to provide an electric excavator system with replacing the internal combustion engine by a De motor.

Another object of the proposed invention is to provide a mini electric excavator with dual motors, wherein one motor drives the hydraulic arm and the other motor drives the track assemblies.

Another object of the proposed invention is to provide a mini electric excavator system equipped with effective control systems.

Yet another objective of the proposed invention is to provide a simple construction of earth moving equipment powered by a battery module.

Yet another objective of the proposed invention is to provide an environment friendly, low-cost construction equipment with very less operational cost.

SUMMARY OF THE INVENTION

The present invention relates to a mini electric excavator system having :

- a base frame or an undercarriage with a front-end shovel and two independently driven track assemblies;

- an upper frame or a body cage to be assembled over the undercarriage;

- a roll cage mounted over the body cage;

- an assembly of a boom, a stick and a bucket constituting a moving arm connected to the body cage by means of a swivel joint;

- two separate motors to drive the track assemblies and the moving arm;

- one or more housing for the motors, positioned below the body cage; - a main control unit and one or more control systems to control the movement of moving arm and track assemblies;

- at least one battery module with an accumulator to power the motors; and

- additional cooling mechanism for one or more motors and the battery module; wherein

- a first motor is configured to drive the moving arm; and

- a second motor is employed to drive the track assemblies;

- the motors are driven by different drivers; and are coupled to one or more controllers;

- the main control unit consists of a microcontroller; and it controls the battery module and sends one or more control action signals to motor control system, hydraulic control system and diagnostic control system; wherein, the control action signal generated by the main control unit consists of at least one of a) signal for fluid flow in directional valve; b) signal for motor torque control; c) signal for motor speed control; d) signal for regulation of current, voltage or pressure.

In an embodiment, the first motor driving the moving arm is a Permanent magnet synchronous machine, an AC motor in squirrel cage formation, selected from three phase induction motors, linear motors, direct drive motor etc.

In another embodiment the battery powers the first motor through a three-phase inverter connected to a three-phase current sensor.

In yet another embodiment, the output shaft of the first motor is connected to: - the hydraulic control system which receives control action signal from main control unit;

- a means to provides movement of the hydraulic arm such as a variable displacement pump which controls a four-way directional valve for the movement of the arm; and

- a relief valve connected to the directional valve; and it actuates the movement of the arm, according to the control action signal processed by the hydraulic control system.

In another embodiment, the second motor that drives the track assemblies is a DC motor selected from series DC motor, brushless De motor, separately excited DC motor, self-excited DC motor, permanent magnet DC motor, three phase induction motor, linear motor, servo motor, direct drive motor etc.

In yet another embodiment, the second motor is controlled by an H bridge driver and is

- connected with a Pulse Width Modulation (PWM) controller selected from robust controllers, adaptive controllers state feedback controllers, variable system controllers, controllers with modem control theories etc., at the input side;

-coupled to a planetary gearbox which is connected to a differential controller.

In another embodiment wherein one or more controllers are :

- used to control voltage supply from battery to DC motor;

-coupled to planetary gearboxes to control independent track assemblies through hub motors.

In yet another embodiment , the differential actuators control the movement of the independent track assemblies. In another embodiment, the power rating of the DC motors used in the system is in the range of 12.42KW to 24.84KW and can increase depending on the weight of the excavator under consideration.

In yet another embodiment, the weight of the mini electric excavator is in the range of 3.5 to 7 ton.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 shows an embodiment of the proposed mini electric excavator (100).

Fig 2 shows the exploded view (200) of the mini Electric excavator system(lOO).

Fig 3 shows the control system (300) of the embodiment of the proposed electric excavator(lOO).

Fig. 4 shows the block diagram (400) of the excavator control.

DETAILED DESCRIPTION OF THE INVENTION

Increasing air pollution from construction activities and rising operational costs including higher fuel prices, more spares and consumables is increasing the cost of ownership. The proposed invention promotes zero emission construction and reduction in operating costs.

The proposed invention relates to a mini electric excavator system consisting of a battery and two separate motors; one for track assemblies and the other for movement of hydraulic arm. In other words, the invention consists of dual motor technology with the integration of all electronic components for control. One motor is used to drive the tracks, the other is used to function the hydraulics responsible for the movement of the arm.

Figure 1 shows the mini electric excavator (100). The excavators are heavy construction equipment in the category of earth movers. The power of an excavator depends on its tonnage. For the purpose of elaboration, a mini electric excavator is explained through examples. The technology however is applicable on any heavy earth mover or excavator used in digging, dredging, lifting, or construction of any sort. The embodiments, examples and drawings described here must not be construed to limit the scope of the invention.

The proposed invention, relates to a mini electric excavator system comprising of an undercarriage (1) or base frame which forms the base of the machine. With a front-end shovel and provision to connect two independently driven track assemblies (12). An upper frame or a body cage (2) is assembled over the undercarriage (1) and a roll cage (3) is mounted over the body cage(2) . There is an assembly of a boom (5), a stick (6) and a bucket (11) constituting a moving arm or hydraulic arm (47) , which is connected to the body cage (2) by means of a swivel joint (4). The mini electric excavator also consists of two separate motors to drive the track assemblies (12) and the moving arm (47). The motors (50, 60) are positioned below the body cage in a single or plural housing for the motors. The electric excavator is powered by at least one battery module (40) with an accumulator to power the motors. The machine is equipped with additional cooling mechanism for one or more motors and the battery module. The battery module also includes a battery charger. Fig. 2 shows the exploded view of the mini electric excavator.

In the control part, there is a main control unit and one or more control systems to control the movement of moving arm and track assemblies in the electric excavator. Conventionally, the excavator controls or John Deeres control move the hydraulic arm or the track assemblies of the heavy machinery. An embodiment of the mini electric excavator system has a first motor is configured to drive the moving arm; and a second motor to drive the track assemblies. The two motors are driven by different drivers and are coupled to one or more controllers. The proposed construction of mini electric excavator system is not limited to excavators alone and can be implemented on backhoe loaders as well. Fig . 3 shows the control system of the mini electric excavator. The cathode of the battery is connected to a controlled pulse width modulated voltage source. The PWM is further connected to a H-bridge motor drive. This can be powered if the PWM port voltage is above the enabled threshold voltage. A current sensor is connected to the positive terminal of the H-bridge. The negative terminal is grounded. The current sensor is connected with a permanent magnet DC motor ( taken as first motor here) The mechanical output (shaft) of this motor is connected to a planetary gearbox which is further connected to the differential. The differential is connected to the track assemblies /tyres(12) . These are further connected to the vehicle body at the undercarriage (1).

The same battery is connected to a three-phase inverter. The inverter is further connected to a three-phase current sensor. This is connected to a Permanent magnet synchronous machine, an induction machine with squirrel cage formation. The output shaft of the motor is connected and is responsible for the movement of the variable-displacement pump. From here one connection is made to the hydraulic reservoir. The other end is connected to the 4-way directional valve. In the integration, a pressure relief tank is also added. The Directional valve is connected to the hydraulic cylinder, which is connected to the mass. Here the mass can vary as an excavator can carry out multiple operations through its arm.

The squirrel cage rotor induction machine requires steady state values for its initiation. It has 5 ports which can vary depending on the selection. The R port is connected with the motor to provide the mechanical rotation. C refers to the machine case therefore it is mechanically grounded. For testing purposes the model was created in MATLAB and the system was simulated for performance analysis. Port 1 is the input port where an electric command converted by simulink (from physical) is connected. Port 2 is the negative end of the motor and is connected to the ground. This machine (first motor) requires alternating current which is fed through port 1 for functioning. The result is obtained that the double acting hydraulic cylinder functions depending on the pressure difference created around the cylinder. This technology of moving the hydraulics and tracks using a separate dedicated motor in a 3.5 ton electric excavator is a novel feature of the proposed invention.

On the other hand the DC motor (second motor) does not require an inverter to function. It is ideal for the drivetrain of an EV due to it’s popularity and ease of connections amongst several gear boxes axles etc. It consists of 4 ports. One port is connected to the gearbox and differential. Two are connected to the battery and the one is a connection for the mechanical case.

Fig 4 shows the block diagram of the control of the mini electric excavator system. The battery module (40) powers both the first motor (50) and second motor (60). The battery module is connected to the first motor (50) which is a permanent magnet synchronous machine through a three phase inverter (41) and a three phase current sensor (42). The motor is connected to a variable displacement pump (43) which controls a four-way directional valve (45) for the movement of the arm (47); and a relief valve (44) connected to the directional valve (45). The hydraulic control system (46) receives control action signal from main control unit (20) which directs the movement of the hydraulic arm (47) of the excavator (100).

The battery module (40) is connected to the second motor (60) through a Pulse width modulation controller (51) connected to an H bridge (52) at the input side of the motor (50). The motor is further connected to differential controller (53) which is coupled to the planetary gearbox (54). The planetary gear boxes connected to the track assemblies (12) have individual hub motors (55).

The track assembly control system (56) receives control action signal from main control unit (20) for the control of movement of track assemblies (12) through individual hub motors (55). The motor speed control , motor torque control and track speed control signals regulate the movement of the track assemblies.

The Pulse Width Modulation (PWM)(51) controller is selected from robust controllers, adaptive controllers state feedback controllers, variable system controllers, controllers with modem control theories etc. The main control unit consists of a microcontroller and it controls the battery module. It sends one or more control action signals to motor control system, hydraulic control system and diagnostic control system depending upon the requirement. The control action signals may be a signal for fluid flow in directional valve ; a signal for motor torque control ; a signal for motor speed control; or a signal for regulation of current, voltage or pressure.

In the prior art a diesel engine is connected to the transmission which is further connected to the axles. There is a separate hydraulic tank dedicated to the functioning of the arm. The existing diesel engine is replaced by an induction machine with squirrel cage configuration and the fuel tank is replaced with a battery. An additional motor is added which is solely responsible for the functioning of the hydraulic pump. None of the above-mentioned electronic components are available or used in the manner similar to the proposed invention. The major differences with the prior art can be listed as follows :

1.The prior art consisted of a diesel tank. This had been replaced with a similar capacity battery.

2. Electric motor is used in place of an engine. An electric motor which provides the same torque as the prior engine is used for this purpose.

3. In the prior art an internal combustion engine is used to rotate the pump. This has been replaced by an electric motor

4. The prior art did not include the aforementioned equipment controller and inverter. The controller is used to monitor the current flow from the battery to the motor which is used to move the hydraulics of the system. The inverter is used to provide the consumer with a different working mode by changing the frequency of the alternating current.

5. The use of dual motor technology and the controllers provide an advantage to this equipment of being zero emission excavator that can be operated at residential areas due to their low noise pollution. From the Ease of operation and cost of operation point of view the following can be summarized. An estimate of consumption per hour of the equipment is Rs 609 in the prior art (diesel tank) while the battery-operated excavator has a consumption of about Rs 78.75.

Conventionally , the excavators used diesel engine which required more spares and consumables (engine and transmission). This leads to higher operating costs. The electric motor does not require as many spares as it has less moving parts.

The excavators described in prior art could operate at maximum load. However, any excess energy diverted to the pump would be released in the form of thermal energy. With the new electric motor, excess energy can be stored in the capacitors and reused when required. Thereby reducing the energy losses.

The electric power train with a combination of dual motor technology and a battery will produce negligible particulate emissions therefore significantly reducing air pollution and promoting zero emission construction.

The working of the components of the excavator can be further explained. The second motor is a DC motor, selected from series DC motor, brushless De motor, separately excited DC motor, self-excited DC motor, permanent magnet DC motor, three phase induction motor, linear motor, servo motor, direct drive motor etc. The motor is connected to the H bridge. The H bridge is used to control the direction and speed of the DC motor. A H-bridge switches the polarity of the voltage applied to a load. The PWM controller is responsible for regulating the flow of energy from the battery by reducing the current gradually called pulse width modulation. The speed of the electric motor depends on the modular voltage. The greater the voltage the faster the rotation of an electric motor.

In an embodiment, the electrification of the system is for an excavator which has a main pump, a variable displacement axial piston pumps and a capacity of 2*17.5 cc/rev. This pump has a maximum pressure of 230kgf/cm2 (3270psi) and a rated oil flow of 2*38.5 1/min (10.2 U.S gpm/8.5 U.K.gpm). The mentioned pump would have a rated speed of 2200 rpm. The electrification of the system includes a mini excavator which has a travel motor of variable displacement axial piston motor and relief pressure similar to that of the main pump as 230kgf/cm2 (3270psi) and a 2 stage planetary gearbox. It has an automatic spring applied braking system which is hydraulic released. The brake release pressure for the travel motor being replaced is 12kgf/cm2 (170psi). The braking torque required to stop the movement of the motor is 4.2kgf.m (3Olbf. ft).

The proposed battery life is 8 years for this configuration which is greater than any prior or mentioned art. In the future there is a possibility to use a secondary storage device including supercapacitors or an auxiliary battery.

The construction of the Mini electric excavator in terms of mounting and assembly can be described as an embodiment.

The fuel tank is replaced by the battery and the ICE is replaced by an electric motor. The battery for the proposed excavator is mounted in the body cage of the invention. The engine is replaced with the motor (DC motor) which provides the energy to the tracks and a separate motor which provides actuation energy for the hydraulic pump. The motors are placed where the existing radiator is placed and the battery is mounted on the back of the body cage (next to or behind the motor).

Special mounting may be provided to hold the batteries in place. Both the motors are placed inside the body cage with their own individual cooling systems. The motors are isolated from the environment. The battery also has its own cooling system. The undercarriage houses the gearboxes of the tracks and two individual motors (hub motors) for the forward and backward movement of the machine. The proposed invention pertains to the complete transformation of a diesel-powered excavator to a fully electric equipment. It includes controllers, inverters, motors, batteries and future scope of auxiliary storage systems including supercapacitors, capacitors and smaller batteries. The power rating of the DC motors used in the system is in the range of 12.42KW to 24.84KW and can increase depending on the weight of the excavator under consideration.

The description and drawing only illustrate embodiments of the present invention and should not be construed in limiting the scope of the invention.

ADVANTAGES

1. The proposed invention possesses Zero emission operation. The electric excavator produces no carbon emission and hence it is an environment friendly machine.

2. The excavator works in low noise levels. Hence, it can qualify to be in operation in locations with stringent laws and regulations , especially in office and residential areas .

3. There are fewer moving parts (mechanical parts) in the electric excavator. Therefore, leading to less consumables and low maintenance costs than the Internal Combustion Engine equipment.

4. The power source for working the electric excavator is one or more batteries. Hence the system has low operating costs, as cost of refuelling an Electric Vehicle is comparatively cheaper than the cost of refuelling an Internal Combustion Engine (ICE) of the same specification.