Ride control system

A ride control system and method where the system includes first hydraulics for equalizing pressure between ride control accumulators and boom cylinder head side, and second hydraulics for providing low pressure drop connection between ride control accumulators and boom cylinder head side. When ride control is engaged, the first hydraulics equalizes pressure between ride control accumulators and boom cylinder head side to within a pressure threshold, then the second hydraulics provides the low pressure drop connection between ride control accumulators and boom cylinder head side. Ride control system can include third hydraulics for providing fluid connection between boom cylinder rod side and tank; where after first hydraulics equalizes pressure to within pressure threshold, then third hydraulics provides connection between boom cylinder rod side and tank. The ride control system can also monitor the condition of the ride control accumulators.

FIELD OF THE INVENTION

The present invention generally relates to the field of hydraulic vehicle control and more specifically to activation and control of a ride control system.

BACKGROUND OF THE INVENTION

Some machines have a ride control system that is hydraulically coupled with other hydraulic systems, for example a loader or boom system. In these and similar machines, it is desirable to have pressure equalization between the ride control system and the coupled hydraulic systems prior to ride control activation. By matching the pressure between the ride control accumulators and the pressure in, for example, the boom cylinders any unintended raising or lowering motion in the boom can be avoided or reduced when ride control is engaged.

It would be desirable to have the ride control system designed to perform one or more of the following functions: (1) to equalize the pressure between the head side of the loader cylinder and the ride control cylinders, (2) to provide a low pressure drop connection between the head side of the loader boom cylinder and the cushioning volume in the ride control accumulators, and (3) to provide a low pressure drop connection between the rod side of the loader boom cylinder and tank. It would also be desirable to have the ride control system perform some auxiliary functions, which could include: (1) to provide a mechanism for dead engine lower, (2) to provide a mechanism for safely discharging the pressure in the ride control accumulators, and (3) to provide condition monitoring of the ride control accumulators.

SUMMARY

A ride control system is disclosed for a machine having a main hydraulic system, a ride control accumulator, a tank, and a boom cylinder, where the boom cylinder has a head side and a rod side. The ride control system includes a first hydraulic system for equalizing pressure between the ride control accumulator and the head side of the boom cylinder, and a second hydraulic system for providing a low pressure drop connection between the ride control accumulator and the head side of the boom cylinder. When the ride control system is engaged, first the first hydraulic system equalizes pressure between the ride control accumulator and the head side of the boom cylinder to within a pressure difference threshold, and then the second hydraulic system provides the low pressure drop connection between the ride control accumulator and the head side of the boom cylinder. The ride control system can also include a third hydraulic system for providing a hydraulic connection between the rod side of the boom cylinder and the tank; where after the first hydraulic system equalizes pressure between the ride control accumulator and the head side of the boom cylinder to within the pressure difference threshold, then the third hydraulic system provides the hydraulic connection between the rod side of the boom cylinder and the tank. The ride control system can also include an accumulator pressure sensor that monitors the pressure of the ride control accumulator, where readings from the accumulator pressure sensor are used for equalizing pressure between the ride control accumulator and the head side of the boom cylinder.

The first hydraulic system can include a ride control valve providing fluid connection between the main hydraulic system and the ride control system, and a fourth control valve providing fluid connection between the ride control system and the tank. The ride control system can also include a check valve that prevents fluid flow from the ride control system to the main hydraulic system. The first hydraulic system can also include a tank valve in pressure balance between the pressure in the ride control accumulator and the pressure in the head side of the boom cylinder. When the pressure in the ride control accumulator is greater than the pressure in the head side of the boom cylinder, the tank valve vents pressure from the ride control accumulator to the tank, and when the pressure in the ride control accumulator is less than the pressure in the head side of the boom cylinder, the tank valve prevents the release of pressure from the ride control accumulator to the tank.

The second hydraulic system can include a logic valve for providing a fluid connection between the ride control accumulator and the head side of the boom cylinder, the logic valve including an internal pilot and an external pilot, a first control valve for providing a fluid connection between the ride control system and the external pilot of the logic valve, and a second control valve for providing fluid connection between the external pilot of the logic valve and the tank. Activating the first control valve blocks hydraulic flow from the ride control system to the external pilot of the logic valve, activating the second control valve vents the external pilot of the logic valve to the tank, and activating both the first and second control valves simultaneously vents the external pilot of the logic valve to the tank and enables the logic valve to open and close through the internal pilot.

A method is disclosed for controlling a ride control system of a machine having a main hydraulic system, a ride control accumulator, a tank, and a boom cylinder, the boom cylinder having a head side and a rod side. The method includes waiting until a ride control selector of the machine is enabled and boom controls of the machine are idle; equalizing pressures of the ride control accumulator and the head side of the boom cylinder; after equalizing pressures of the ride control accumulator and the head side of the boom cylinder, providing a low pressure drop connection between the ride control accumulator and the head side of the boom cylinder; and disabling ride control when the ride control selector is disabled. Ride control can also be disabled if the boom controls are activated. The method can also include, after equalizing pressures of the ride control accumulator and the head side of the boom cylinder, providing a hydraulic connection between the rod side of the boom cylinder and the tank.

The method can also include determining whether automatic or manual ride control mode is selected; and disabling ride control when ride control mode is switched from automatic mode to manual mode, or from manual mode to automatic mode. The method in automatic ride control mode can also include, after equalizing pressures of the ride control accumulator and the head side of the boom cylinder, determining if machine speed is greater than a speed threshold; waiting until machine speed is greater than the speed threshold before providing the low pressure drop connection between the ride control accumulator and the head side of the boom cylinder, and before providing the hydraulic connection between the rod side of the boom cylinder and the tank; and disabling ride control when machine speed goes below the speed threshold after machine speed was above the speed threshold.

Equalizing pressures of the ride control accumulator and the head side of the boom cylinder can include determining the pressure difference between the ride control accumulator and the head side of the boom cylinder; comparing the determined pressure difference to a threshold pressure difference; and when the determined pressure difference is greater than the threshold pressure difference, adjusting the pressure of the ride control accumulator to make the determined pressure difference less than the threshold pressure difference. Adjusting the pressure of the ride control accumulator can include, when the pressure of the ride control accumulator is less than the pressure of the head side of the boom cylinder, using the main hydraulic system to increase pressure in the ride control accumulator; and when the pressure of the ride control accumulator is greater than the pressure of the head side of the boom cylinder, venting excess fluid from the ride control accumulator to the tank. Decreasing the pressure of the ride control accumulator can include using a tank valve to pressure balance between the ride control accumulator pressure and the head side boom cylinder pressure, such that when the pressure in the ride control accumulator is greater than the pressure in the head side of the boom cylinder, fluid is vented from the ride control accumulator through the tank valve to the tank, and when the pressure in the ride control accumulator is not greater than the pressure in the head side of the boom cylinder, fluid is blocked from venting from the ride control accumulator through the tank valve to the tank.

Providing a low pressure drop connection between the ride control accumulator and the head side of the boom cylinder can include enabling a logic valve to open through an internal pilot of the logic valve. Providing a low pressure drop connection between the ride control accumulator and the head side of the boom cylinder can also include blocking fluid connection between the ride control system and an external pilot of the logic valve; and providing fluid connection between the external pilot of the logic valve and the tank.

The method can also include monitoring the condition of the ride control accumulator. Monitoring the condition of the ride control accumulator can include increasing the pressure of the ride control accumulator to a high threshold pressure; discharging the fluid of the ride control accumulator over a known hydraulic restriction; recording a decay time it takes for the ride control accumulator pressure to go from the high threshold pressure to a low threshold pressure, the low threshold pressure being less than the high threshold pressure; and using the decay time to determine the condition of the ride control accumulator.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the novel invention, reference will now be made to the embodiments described herein and illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel invention is thereby intended, such alterations and further modifications in the illustrated devices and methods, and such further applications of the principles of the novel invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel invention relates.

The ride control system can perform one or more of the following functions: (1) equalize the pressure between the head side of the boom cylinder and the ride control cylinders, (2) provide a low pressure drop connection between the head side of the boom cylinder and the cushioning volume in the ride control accumulators, and (3) provide a low pressure drop connection between the rod side of the boom cylinder and tank. The ride control system can also be designed to perform auxiliary functions, including for example: (1) to provide a mechanism for dead engine lower, (2) to provide a mechanism for safely discharging the pressure in the ride control accumulators, and (3) to provide condition monitoring of the ride control accumulators.

FIG. 1shows a schematic diagram of the hydraulics for an exemplary embodiment of a ride control system100that includes a ride control valve HSV1, a tank valve EP1, four control valves SF1-SF4, two logic valves HEP1and HEP2, a check valve120and an orifice122. The ride control system100is hydraulically coupled to a main hydraulic system102, ride control accumulators104,106, a ride control accumulator pressure sensor108, tank110, the head side of a boom cylinder112and the rod side of the boom cylinder114.

The ride control valve HSV1provides a fluid connection between the ride control system100and the main hydraulic system102. In an electronic pump control system, it may be necessary to stroke the pump of the main hydraulic system102to ensure oil is supplied through the ride control valve HSV1to the ride control accumulators104,106. The check valve120can be used to prevent backflow from the ride control system100to the main hydraulic system102. The amount of flow can be determined by field testing. In a load sense controlled system, the accumulator pressure sensor108can be used to monitor the pressure to the ride control accumulators104,106in order to control pump flow. By activating ride control valve HSV1and activating the main hydraulic system102, the pressure in the ride control accumulators104,106can be increased.

The fourth control valve SF4provides a fluid connection to the tank110via the tank valve EP1and the orifice122. The head side of the boom cylinder112and the rod side of the boom cylinder114are also fluidly connected to the ride control system100. When the fourth control valve SF4is active, the tank valve EP1is in a pressure balance between the accumulator pressure and the boom cylinder head pressure. As shown inFIG. 1, when the valve SF4is active, the accumulator pressure exerts pressure on one side of the tank valve EP1and the boom cylinder head pressure exerts pressure on the opposite side of the tank valve EP1. The tank valve EP1is forced open when the accumulator pressure is greater than the boom cylinder head pressure by an amount sufficient to overcome the spring bias of the valve EP1(which is typically small). By activating the fourth control valve SF4, the pressure in the ride control accumulators104,106can be reduced.

Activating the first control valve SF1, blocks the supply passage of external pilot oil to the logic valves HEP1and HEP2. Activating the second control valve SF2, vents the supply passage of external pilot oil to tank110. Simultaneous activation of the first and second control valves SF1, SF2reduces the external pilot pressure to tank and allows the logic valves HEP1, HEP2to open through their internal pilot. This opens a low pressure drop passage between the boom cylinder head side112and the ride control accumulators104,106. A sufficiently large direct acting valve could be used to alleviate the need for the valves to be piloted.

Activating the third control valve SF3connects the boom cylinder rod side114to tank110.

FIG. 2is an exemplary flow chart for a ride control system. At block202the system waits until ride control is enabled by the operator. When ride control is enabled control passes to block204to determine if automatic or manual mode is selected. If automatic mode is selected control passes to block226, otherwise control passes to block206for manual mode.

In manual mode, at block206the system checks whether the boom controls are idle. The system waits at block206until the boom controls are idle. When the boom controls are idle, control passes to block208.

At block208, the system equalizes the pressures in the ride control accumulators104,106with the pressure in the boom cylinder head side112. Pressure equalization happens prior to ride control activation to match the pressure in the ride control accumulators104,106with the head pressure in the boom cylinders112so that there is no unintended raise or lower motion in the boom when ride control is engaged. During equalization the valves HSV1and SF4are activated. At block210, the system checks if the pressures are equalized. If the pressures are not sufficiently equalized, control remains with the pressure equalization routine of block208. When the pressures are sufficiently equalized control passes to block212.

The following steps provide an exemplary pressure equalization routine. First, the system can test whether pressure equalization is complete by comparing the difference between the ride accumulator pressure and the boom cylinder head pressure with a threshold pressure difference. If the pressure difference exceeds the threshold, then the system can determine if the ride control accumulator pressure needs be raised or lowered. If the ride control accumulator pressure needs to be raised, then valves HSV1and SF4can be activated and the pump of the main hydraulic system102can be stroked until the pressure of the ride control accumulators104,106and the pressure of the boom cylinder head side112agree within some tunable accuracy. If the ride control accumulator pressure needs to be lowered, then valves HSV1and SF4can be activated to vent the pressure of the ride control accumulators104,106to the tank110until the pressure of the ride control accumulators104,106and the pressure of the boom cylinder head side112agree within some tunable accuracy. When sufficient pressure agreement is reached or if the boom controls become active or if the ride control status becomes inactive, the valves HSV1and SF4are closed and the pump of the main hydraulic system102can be destroked if necessary. In another system, a load sensing system for example, this could be done by closing a communication valve between the accumulator pressure and the pump.

At block212, after pressure equalization is complete then ride control is engaged. When ride control is engaged valves SF1, SF2and SF3are activated. Activating valves SF1and SF2opens the low pressure drop passage between the boom cylinder head side112and the ride control accumulators104,106. Activating valve SF3connects the boom cylinder rod side114to the tank110. At block214, the system checks for various triggering events to disengage manual ride control, including for example: (a) if ride control is disabled by the operator, or (b) if ride control is switched to automatic mode. Ride control can also be disabled if the boom controls are activated. The system remains at block214with manual ride control engaged until one of the triggering events occurs. When one of the triggering events occurs, control passes to block216where ride control is disengaged and valves SF1, SF2and SF3are deactivated; then control passes back to block202.

The control flow for automatic mode is very similar to the flow for manual control, but they are explained separately for clarity. In automatic mode, at block226the system checks that the boom controls are idle. The system waits at block226until the boom controls are idle. When the boom controls are idle, control passes to block228.

At block228, the system equalizes the pressures in the ride control accumulators104,106with the pressure in the boom cylinder head side112. Pressure equalization happens prior to ride control activation to match the pressure in the ride control accumulators104,106with the head pressure in the boom cylinders112so that there is no unintended raise or lower motion in the boom when ride control is engaged. During equalization the valves HSV1and SF4can be activated in the equalization routine described above. At block230, the system checks if the pressures are equalized. If the pressures are not sufficiently equalized, control remains with the pressure equalization routine of block228. When the pressures are sufficiently equalized control passes to block232.

At block232, the system checks if the vehicle speed is greater than a speed threshold. If the vehicle speed is not greater than the speed threshold, the control returns to block228, otherwise control passes to block234.

At block234, after pressure equalization is complete and the speed exceeds the speed threshold then ride control is engaged. At block236, the system checks for various triggering events to disengage automatic ride control, including for example: (a) if ride control is disabled by the operator, or (b) if ride control is switched to manual mode, or (c) if vehicle speed goes below the speed threshold. Ride control can also be disabled if the boom controls are activated. The system remains at block236with automatic ride control engaged until one of the triggering events occurs. When one of the triggering events occurs, control passes to block238where ride control is disengaged and valves SF1, SF2and SF3are deactivated; then control passes back to block202.

The ride control valve can be used as a diagnostic tool for monitoring the precharge condition of the gas in the ride control accumulators. The stored energy in the accumulator is related to the precharge pressure. This energy may be quantified by measuring how long the accumulator takes to discharge from a high pressure state to a low pressure state by flowing oil over a known hydraulic restriction. The restriction in the exemplary embodiment ofFIG. 1is the orifice122. Through proper sequencing, the ride control accumulators104,106can be forced to discharge over the orifice122and the condition of the ride control accumulators104,106can be determined from the time it takes to move from a first pressure state to a second pressure state.

The ride control accumulator condition monitoring test can be performed using the exemplary control flow shown inFIG. 3. This description will refer to the elements of the exemplary embodiment of a ride control system shown inFIG. 1, but those of skill in the art will readily understand how it can be applied to other ride control system embodiments.

At step302, the pressure in the boom cylinder head side112is reduced. This can be done by performing an unpowered lower to ground. Then at step304, the pressure in the ride control accumulators104,106is brought to a first threshold pressure. This can be done by activating valve HSV1and stroking the pumps of the hydraulic system102. This can vary by application and can be determined on a case by case basis. At step306, the system waits until the ride control accumulator pressure has reached an equilibrium second pressure. This can be done by destroking the pumps of the hydraulic system102and closing the valve HSV1. Then at step308, the elapsed time is recorded to move from the second pressure to a third threshold pressure. Both the second and third pressures can be determined on a case by case basis. This can be done by activating the valve SF4and recording the elapsed time of the pressure change. Then at step310, the charge state of the ride control accumulators can be determined from this decay time. This can be done using the most appropriate form of the thermodynamic gas laws.

One exemplary method to determine the charge state of the ride control accumulators is to solve for the decay time produced by the accumulator at the bottom end of its specification, and compare the test result to this value in a pass/fail test. An alternative method is to solve the gas law directly for the precharge pressure given the resulting change in the control volume as quantified by the flow out of the accumulator, which would allow for a “percent life” value to be computed and possibly displayed to the operator.