Patent Application
20120020807
The present application relates generally to hydraulic pumps, and more particularly to pump noise control.
Conventional steering systems produce a substantial degree of noise and vibration. Although vehicle engines are being improved for quiet operation, noise from other areas, such as the steering system, is becoming increasingly apparent. Hydraulic pumps, used in power-assisted steering systems, are one of the primary noise sources in the steering system.
Typically, the vehicle hydraulic steering system uses either fixed displacement or variable displacement hydraulic pumps, which provide hydraulic pressure and serve as a source of fluid to the steering gear. The fluid flows from the pump to an actuator and motors, and then it returns to a reservoir, where it is filtered for re-use. An electric motor or the automobile engine, driven by gears, belts, or a flexible elastomeric coupling, powers the pumps. Each pump usually contains multiple vane chambers, resulting in an unsteady output flow in the form of discrete fluid pulses. The pressure pulses or “flow ripples” generate vibration, causing additional sound. Excess fluid pulses or flow ripples lead to undesirable levels of noise and vibration, particularly when the pump is installed in the vehicle steering system. The resulting vibration is perceptible to the driver, causing an uncomfortable driving experience.
With recent improvements in the vehicle systems, noise level has become a prime consideration when selecting a hydraulic steering system. As a result, there exists a need for attenuating the flow ripple and reducing the noise and vibration levels to provide a comfortable driving experience to the automotive vehicle driver.
One embodiment of the present disclosure describes a method for attenuating hydraulic pump flow pulses. The pump provides fluid to an operating device at a first hydraulic flow rate, the flow being in the form of discrete fluid pulses. Further, the method includes obtaining values of one or more parameters related to the pulses produced by the pump and modifying the first hydraulic flow rate to a second hydraulic flow rate based on the parameter values, resulting in attenuation of the pulses.
Another embodiment of the present disclosure describes a hydraulic pump flow system. The system includes a hydraulic pump for providing fluid to an operating device in the form of discrete pulses at a first hydraulic flow rate. Further, there exists a monitoring module for obtaining values of one or more parameters related to the pulses produced by the pump. An electronic control unit (ECU) modifies the first hydraulic flow rate to a second hydraulic flow rate based on the parameter values, resulting in attenuation of the pulses.
The figures described below set out and illustrate a number of exemplary embodiments of the disclosure. Throughout the drawings, like reference numerals refer to identical or functionally similar elements. The drawings are illustrative in nature and are not drawn to scale.
The following detailed description is made with reference to the figures. Exemplary embodiments are described to illustrate the subject matter of the disclosure, not to limit its scope, which is defined by the appended claims.
The following terms are used throughout the disclosure and are defined here for clarity and convenience.
Vane:
A fin shaped object attached to a rotating pumping structure.
Vane Chamber:
A volume within the pumping structure, defined by adjacent vanes.
Pump Order:
The number of pumping elements (vane chambers) within the pumping structure.
Flow Ripple:
Pressure pulse in the hydraulic fluid, produced by the pumping structure, having properties of amplitude, frequency, and phase.
The present disclosure describes systems and methods for noise control in hydraulic pumps. Usually, an electric motor or an automobile engine (or other prime mover) powers the hydraulic pumps employed in the power-assisted steering and similar systems. The fluid flow produced by the pump takes the form of discrete pulses, leading to increased noise and vibration levels. Embodiments of the present disclosure provide methods and systems for modifying the flow rate of the pump for reducing noise levels.
The system 100 may include a pump 102 having rotating vanes. The vanes rotate with a pump body, and adjacent vanes, together with the pump body, define vane chambers. The pump 102 is driven by the automotive system's engine via a belt and a pulley. The rotating vanes of the pump 102 successively draw the hydraulic fluid into the pump body and then force it out at a high pressure, providing fluid through the system 100. The system 100 may have one or more flow regulation units for adjusting the fluid flow to provide hydraulic power to the steering gear 101.
The pump 102 provides fluid to the automotive steering system at a first hydraulic flow rate. The fluid flow is continuous, but the pump vanes produce varying pressure within the fluid, seen as discrete pulses. The first hydraulic flow rate is the rate at which the flow pulses leave the pump and is a direct function of the pump order. A hydraulic fluid reservoir 104 carries the hydraulic fluid for pumping and accommodates fluid volume changes by holding the excess fluid. A primary flow control unit 106 includes a flow regulation mechanism, for bypassing extra fluid flow back to the pump 102 such that the net fluid volume flowing out of the pump 102 is constant, independent of the engine speed. Specifically, the primary flow control unit 106 functions as a main flow control device for the system 100. A secondary flow control unit 108 is a secondary hydraulic circuit for greater flow control range. The secondary flow control unit 108 includes a secondary flow bypass, in addition to the primary flow control unit 106, which routes extra fluid back to the pump 102. Additionally, the secondary flow control unit 108 includes an electronic control unit (ECU) 110 for regulating the fluid flow.
A monitoring module 112, located is located outside the pump 102, between the pump 102's outlet and the steering gear 101 on the vehicle, monitors values of multiple parameters related to the fluid pulses produced by the pump 102. In one embodiment, the monitoring module 112 includes a transducer including plurality of sensors for monitoring the parameters. Further, the transducer may be a pressure sensor, a flow rate sensor that could flow ripple directly, or any other similar sensor known in the art.
The monitored parameters can include frequency, phase, and amplitude of the fluid pulses. Pressure pulse frequency can be obtained directly, by sensing pressure pulses in the hydraulic fluid, or it can be calculated, based on engine speed and stored constants that relate engine speed to pump speed, such as the pump order or ratio of engine crankshaft pulley diameter to pump pulley diameter. Phase relationships are calculated, and the flows are adjusted to provide ripples to be out of phase, thus mutually cancelling. For best cancellation, a relationship having the second flow 180° out of phase with the first flow will provide the best results. Pressure pulse amplitude can be obtained directly from the first hydraulic flow. The amplitude for the second hydraulic flow is calculated such that it is directly proportional to the amplitude of the first hydraulic flow.
Further, the monitoring module 112 transmits the monitored values to the ECU 110. The system 100 attenuates the pulses produced by the pump by modifying the first hydraulic flow rate to a second hydraulic flow rate based on the monitored values. Attenuation of pulses leads to cancellation of flow ripple, providing a comfortable driving experience, with diminished levels of noise and vibration. Specifically, the second hydraulic flow rate is the rate at which the flow pulses are bypassed from the secondary flow control unit 108 back to the pump 102 and attenuate the pulses continuously.
Although the exemplary system 100 is part of an automotive steering system, the claimed system may be implemented in other environments and are not limited to automotive applications. Hydraulic power is employed in a variety of industries and applications, and numbers of such applications, in particular aircraft, construction, and manufacturing apparatus, would benefit from noise reduction. The claimed system could easily be adapted to such applications, well within the scope of the invention, which is defined solely by the claims appended hereto.
The hydraulic pump can be a fixed displacement pump, a variable displacement pump, or any other type of pump known in the art that produces fluid pulses. Further, the pump can have multiple pumping elements or vane chambers.
The pump provides fluid flow to an operating device at a first hydraulic flow rate at step 202. The fluid flow is continuous, but the pump vanes produce varying pressure within the fluid, seen as discrete pulses. Specifically, the first hydraulic flow rate can be a function of engine speed of the operating device and the pump order.
At step 204, the method 200 obtains values for one or more parameters related to the pulses produced by the pump. Pressure pulse frequency can be obtained directly by sensing pressure pulses in the hydraulic fluid, or it can be calculated, based on engine speed and stored constants that relate engine speed to pump speed, such as the pump order or ratio of engine crankshaft pulley diameter to pump pulley diameter. The pressure pulse frequency is directly proportional to the pump's rotational speed, which in turn is a direct function of the engine speed. Thus, by using the engine speed signal, such as RPM (revolutions per minute), the required frequency for attenuating the fluid pulses can be calculated. An exemplary equation for obtaining value for the frequency parameter is:
f=(RPM/60)*n*p (1)
The phase relationship is calculated, and the flow is adjusted such that ripples are out of phase, thus fluid flows are mutually cancelling. For complete cancellation, the second flow may be set as 180° out of phase with the first flow. Pressure pulse amplitude can be obtained directly from the first hydraulic flow. The amplitude for the second hydraulic flow is calculated such that it is directly proportional to the amplitude of the first hydraulic flow.
The method 200 monitors the flow pulses produced by the pump at step 206 and further attenuates the pulses by modifying the first hydraulic flow rate to produce a second hydraulic flow rate based on the obtained values, at step 208. Attenuation of the pulses may lead to cancellation of flow ripple, providing a comfortable driving experience, with diminished levels of noise and vibration.
In one implementation, the method 200 sets the second hydraulic flow rate as out of phase with the first hydraulic flow rate, attenuating the fluid pulses and cancelling flow ripples continuously. In another implementation, the obtained parameter values may be transmitted to an electronic control unit (ECU), which sets the second hydraulic flow rate as out of phase with the first hydraulic flow rate, cancelling flow ripples.
Modifying the flow rate, especially by producing pulses that are out of phase with the flow ripple, results in active cancellation of the flow ripple. The cancellation reduces noise and vibration in the operating device, providing a comfortable experience to the operator.
While the present disclosure is written in context with automotive hydraulic steering pumps, the embodiments of the present application apply to similar pump environments including transmission pumps, AC compressors, and fuel pumps, where unsteady flow out of the pumping device can create unacceptable levels of noise. Further, the hydraulic pumps can be fixed displacement pumps, variable displacement pumps, or any other type of pumps known in the art that produce fluid pulses.
It will be obvious to those skilled in the art that the invention can be employed in diverse operating environments for achieving the desired results, without departing from the scope and intended functions of the claimed invention.
