SYSTEM FOR CALIBRATION OF ELECTROHYDRAULIC PUMP START CURRENT BASED ON ENGINE'S OUTPUT TORQUE SIGNAL

Abstract

A system for calibrating an electrohydraulic pump for a vehicle having a propel system that includes an engine connected to the electrohydraulic pump. A micro-controller having software and an input device is connected to a plurality of sensors mounted about the vehicle. The software uses a plurality of parameters to convert internal analog drive signals into analog output signals to control the electrohydraulic pump and motion of the machine where the parameters include a forward start current value and a reverse start current value.

Claims

1. A system for calibrating an electrohydraulic pump, comprising: a vehicle having a propel system that includes an engine connected to an electrohydraulic pump; a micro-controller having software and an input device that is connected to sensors; wherein the software uses a plurality of parameters to convert internal analog drive signals into analog output signals to control the electrohydraulic pump and motion of the machine where the parameters include a forward start current value and a reverse start current value.

2. The system of claim 1 wherein the sensors are load sensors.

3. The system of claim 1 wherein the electrohydraulic pump is a non-feedback proportional electric controlled pump.

4. The system of claim 1 wherein the start current value brings the electrohydraulic pump into stroke as the input device is controlled by an operator.

5. The system of claim 1 having a button on a service tool for initiating a calibration process.

6. The system of claim 1 wherein the software commands a hydraulic motor to a displacement between 0% and 25%.

7. The system of claim 6 wherein the software commands the hydraulic motor to a displacement between 20% and 25%.

8. The system of claim 6 wherein flow is pumped into a dead volume and is not consumed by a working device.

9. The system of claim 1 wherein the software commands the engine to a constant speed and un-commands the electrohydraulic pump to measure a baseline engine load.

10. The system of claim 1 wherein the software ramps up the electrohydraulic pump to determine a configurable minimum value at a configurable rate.

11. The system of claim 1 wherein the software determines and stores a start current based on an increase in a torque signal by a configurable amount over a baseline electrohydraulic pump value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a schematic view of an environment for a system for calibrating an electrohydraulic pump; and

[0016] FIG. 2 is a flow diagram for a system for calibrating an electrohydraulic pump.

DETAILED DESCRIPTION

[0017] Referring to the Figures, the system 10 for calibrating an electrohydraulic pump start current based upon an engine's output torque signal includes a vehicle or machine 12 having a propel system 14. The propel system 14 includes an engine 16 connected to an electrohydraulic pump 18. While any number of applications of pump control types and vehicle applications can be used, preferred is that the system is used with Non-Feedback Proportional Electric (NFPE) controlled pumps used in automotive control systems commonly implemented on construction vehicles such as wheel loaders, telehandlers, dumpers, and the like.

[0018] The system 10 further includes a micro-controller 20 with software 22, an input device 24 such as a drive pedal, and sensors 26. While any type of sensor 26 is used, preferably load sensors that are present on modern vehicles with electronically-controlled engines are desired. In some examples there is no physical load or torque sensor, and instead the signal is calculated or estimated internally by the engine control unit 20 (ECU). The software uses a plurality of parameters to convert internal analog drive signals into analog output signals to control the pump 18 and the motion of the machine 12. Included in these parameters are a forward start current value and a reverse start current value. The start current value is an especially important parameter as it is used to bring the pump into stroke and the vehicle into motion as the input device 24 is controlled by an operator.

[0019] In operation, in case of a failure where the vehicle 12 could unexpectedly go into motion, even though most likely at a relatively low ground speed, initial safety precautions are taken. As examples, the vehicle is restrained to the ground with safety chains, placed directly in front of an immovable wall or other object, or lifted with the wheels in the air. The vehicle 12 is then started and will remain in a stationary position throughout the process. With the operator seated in the cab, the calibration process is initiated by pressing a button 28 on a service tool 30 or a special display screen in the cab. For accuracy, the engine crankcase oil temperature and hydraulic oil temperature must begin within configurable ranges before the process can continue, otherwise the process will abort. This prevents the process from being conducted in extreme conditions that could affect the accuracy of the measurements.

[0020] The traction drive is automatically placed in a low-torque condition by the software 22. To achieve this the software 22 commands a hydraulic motor 32 to its minimum displacement which typically is 20-25% or as low as 0% displacement, shifts a multi-speed gearbox (if present) to the highest gear, automatically applies or requires manual application of a park brake, and requires the operator to press and hold the service brake pedal at all times. The process involves running a blocked port procedure on the vehicle 12 in which the vehicle's traction drive output is held stationary by its onboard braking system and the pump command current is increased from a lower starting value until the pump increases in displacement. In the process any flow is being pumped into a dead volume and is not being consumed by any connected working device like the hydraulic motor 32.

[0021] The accuracy of the process relies on all torque loads on the engine, except for the torque from the propel pump being calibrated, remaining relatively constant. To avoid inaccuracies, any variable loads coming from other sources such as AC compressors, open-circuit pumps, or other auxiliary loads should be disabled or remain deactivated until the process is completed. If an auxiliary load activity is detected, such as joystick or steering wheel movement, or if the engine load measurement ever changes at an unacceptable rate or an unacceptable amount, the process will be aborted.

[0022] With the safety considerations observed and the starting conditions met, the engine 16 is commanded by the software to a constant speed value while the pump is un-commanded, to produce a baseline engine load that can be measured. In Automotive Control systems, the commanded speed value reflects the engine speed at which motion is first desired on low-resistance terrain and is referred to as the start speed. The baseline load value represents the load required to overcome the internal drag torque of the engine and any constant auxiliary loads. Modern engines with electronic control units (ECUs) normally output two signals indicating the engine load. For example, according to a J1939 CAN standard engine, the two signals are called “Actual Engine-Percent Torque” and “Engine Percent Load at Speed.” These signals are an instantaneous estimation of the actual torque output by the engine and are present for nearly all modern vehicles with diesel engines. Either one of these signals can be used reliably as the reference torque signal for this process.

[0023] Next, the pump current is ramped up by the software 22 a configurable minimum value (mA) at a configurable rate (mA/s). The minimum value typically should be set somewhat below the normal start current range of the pump and could optionally take into account the pump control orientation and/or oil temperature, both of which have an effect. As the pump current increases, the pump will at some point go into stroke and begin building system pressure as it pumps against a stationary motor. The simultaneous displacement and pressure increases on the load torque of the pump and on the engine will be represented as an increase in the engine load signals. An increase in the load torque signal by a configurable amount over the baseline value the pump current value is stored as the start current in the micro-controller 20. The increase of the engine torque by a specified amount is then considered to indicate that the starting current for that direction of the pump has been reached. The process is then repeated for the other direction of the pump, and the overall process is then considered to be complete. More specifically, as the pump current to the Non-Feedback Proportional Electric (NFPE) control is ramped up from a minimum value, it reaches a value that actuates a valve and increases the pressure of the servo system. The servo pressure in the pump eventually increases to a value that causes the pump swashplate to swivel and bring the pump into stroke, thus increasing its displacement. As the pump increases in displacement and generates flow against a stationary motor, the system pressure increases. The simultaneous increases in system pressure and pump displacement require an increased driving torque from the prime mover, which is an engine in this example.

[0024] If desired, the process could automatically repeat a configurable number of times to ensure that there is agreement among the calibrated values on each side and to establish a final parameter value based on the average of multiple runs. Alternatively the oil temperature measured during the process could be used to automatically compensate or adjust the final start current value up or down based on the known impact of temperature on oil viscosity.

[0025] Additional safety measures can be implemented if certain conditions are detected during the process. For example, if during the process motor speed is detected, the brake pedal is released, the park brake is released, the operator leaves the seat, the motor feedback or other motor position sensor indicates a commanded position other than minimum displacement, and/or the gearbox switches indicate a gear position other than the highest gear, the process will abort automatically.

[0026] From the above discussion and accompanying figures and claims it will be appreciated that the system 10 offers many advantages over the prior art. It will be appreciated further by those skilled in the art that other various modifications could be made to the device without parting from the spirit and scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in the light thereof will be suggested to persons skilled in the art and are to be included in the spirit and purview of this application.