Control circuit for transmission variable displacement pump with improved efficiency

The present disclosure relates to a control circuit for a variable displacement pump in a vehicle transmission, including: a regulator valve configured to regulate displacement control fluid to the variable displacement pump; and a response limiter in communication with the regulator valve, configured to mitigate pressure oscillations in the control circuit.

TECHNICAL FIELD

The present disclosure relates to control circuits for a vehicle transmission pump, more particularly a variable displacement transmission pump.

BACKGROUND

Most modern transmissions are equipped with pumps. Transmission pumps are generally driven by the engine crankshaft. Of the sort of pumps that are compatible with today's transmissions are fixed displacement pumps and variable displacement pumps. Fixed displacement pumps provide the same flow per revolution output regardless of engine speed. A variable displacement pump (or VDP) provides a variable flow rate output which depends on engine speed and transmission system flow requirements (which are commonly referred to as “flow demand”). While there are tradeoffs associated with using either variable displacement or fixed displacement pumps, variable displacement pumps can reduce the total power consumed by the transmission pump by delivering only the flow required by the transmission hydraulic system. For most variable displacement pumps at lower speeds pump loss is directly proportional to engine speed and then pump loss plateaus over a certain speed. In this way, variable displacement pumps offer greater powertrain efficiency.

A displacement decrease circuit can be incorporated in hydraulic circuits for variable displacement pumps in order to provide a command pressure signal to actuate the bore ring yielding a lower displacement at higher speeds. A regulator valve can be incorporated in the hydraulic circuit to selectively link a displacement decrease circuit to the bore ring. Phase lag between the regulator valve and pump bore ring can cause oscillations in both line and decrease circuits (for example as shown inFIG. 6). In the past a controlled leakage has been incorporated in the displacement decrease circuit to mitigate oscillations. However, hydraulic controlled leakages may result in significant flow losses (or hydraulic losses) up to 20% of total typical transmission hydraulic flow demand. The hydraulic loss is proportional to displacement decrease pressure and increases with engine speed when the system commands low displacement (or higher decrease pressure). This hydraulic loss results in an overall increase of engine power required to maintain hydraulic flow and leads to a reduction in fuel economy.

Therefore, it is desirable to have a more effective control circuit for a variable displacement pump that mitigates pressure oscillations in the control circuit when the pump regulator valve is regulating the pump at a displacement less than the pump maximum level. There also exists a need for a method of manufacturing a hydraulic control circuit for a vehicle transmission pump having the same utility.

SUMMARY

The present disclosure addresses one or more of the above-mentioned issues. Other features and/or advantages may become apparent from the description which follows.

One exemplary embodiment pertains to a control circuit for a variable displacement pump in a vehicle transmission, including: a regulator valve configured to regulate fluid to the variable displacement pump; and a response limiter in communication with the regulator valve, configured to mitigate pressure oscillations in the control circuit.

Another exemplary embodiment pertains to a vehicle transmission with improved power efficiency, having: a variable displacement pump; a control circuit configured to control pump displacement through a regulator valve; and a response limiter in communication with the regulator valve, configured to mitigate pressure oscillations in the control circuit.

Another exemplary embodiment pertains to a method of manufacturing a hydraulic control circuit for a vehicle transmission pump, the method including: connecting a fluid sump to a pressure line; connecting a variable displacement pump to the pressure line; incorporating a regulator valve in the pressure line, the regulator valve configured to provide a displacement decrease pressure command to the pump; and incorporating a response limiter at one end of the regulator valve thereby reducing the regulator valve positional response to noise inputs.

One advantage of the present disclosure is that it teaches a more effective control circuit for a variable displacement pump that mitigates pressure oscillations in the control circuit when the pump regulator valve is regulating the pump a at displacement less than the pump maximum level.

In the following description, certain aspects and embodiments will become evident. It should be understood that the invention, in its broadest sense, could be practiced without having one or more features of these aspects and embodiments. It should be understood that these aspects and embodiments are merely exemplary and explanatory and are not restrictive of the invention.

The invention will be explained in greater detail below by way of example with reference to the figures, in which the same reference numbers are used in the figures for identical or essentially identical elements. The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. In the figures:

Although the following detailed description makes reference to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly.

DETAILED DESCRIPTION

Referring to the drawings,FIGS. 1-5, wherein like characters represent the same or corresponding parts throughout the several views there are shown various embodiments of control circuits for a variable displacement pump in a vehicle transmission. The present control circuits improve pump efficiency by mitigating pressure oscillations in the control circuit when the pump regulator valve is regulating pressure by reducing command-pressure flow through the displacement pump—or feeding into a displacement decrease chamber for the variable displacement pump. Various response limiters are used in conjunction with a multi-stage regulator valve configured to regulate fluid to the variable displacement pump. The disclosed hydraulic circuits provide better control of the VDPs and reduce oscillation in the pump feedback circuit.

Referring now toFIG. 1, there is shown a comparative graph10of pump power loss over engine speed for several types of transmission pump systems.FIG. 1shows hydraulic power loss comparisons between VDPs and fixed displacement pumps. As shown inFIG. 1, there is a pump loss associated with fixed displacement pumps that increases with engine speed. Line A inFIG. 1represents the pump loss associated with fixed displacement pumps that increases with engine speed; pump loss is directly related to engine speed. There is also some pump loss associated with variable displacement pumps, as shown by Line B inFIG. 1. With VPDs flow output could be maintained constant when pump rotational speed increases. Change of the flow output is achieved by changing displacement of a pump or volume of fluid transported from the inlet to the outlet per revolution of a pump input shaft. As shown inFIG. 1, at lower speeds pump loss is directly proportional to engine speed however pump loss plateaus when pump output matches system requirement. Line B indicates a standard variable displacement pump not having the benefit of the present disclosure. Line C shows pump loss versus engine speed for a VDP having a control circuit according to one of the exemplary embodiments discussed hereinbelow. A change or reduction in pump loss, ΔLOSS, is indicated on the graph.

Referring now toFIG. 2, there is shown therein a vehicle transmission20having a VDP30connected to a main regulator valve40. The VDP30is a variable displacement vane pump (or VDVP). System hydraulic pressure is commanded by the electronically controlled hydraulic valve40and maintained by a hydraulic control system that is in fluid communication with a transmission sump50. Sump50is a low pressure exhaust circuit. In this embodiment the sump pressure is set to 0 psi or atmospheric pressure. In other embodiments, low pressure exhaust circuit is set to 3 psi.

As shown inFIG. 2, the control system regulates control signals to reduce displacement of the pump that exceed transmission flow requirements. A driven rotor60supports vanes70enclosed within an eccentric moveable bore ring80that enables the displacement of the pump to be reduced as the bore ring80pivots. Pivoting of the bore ring80decreases its eccentric position with respect to the driven rotor60. A spring90acts on the moveable bore and biases bore towards the maximum eccentricity. A chamber100opposes spring90, as shown inFIG. 2. Chamber100is sealed by fluid seal95. In prior arrangements a bleed circuit was necessary and occurred at or around pin55. The pressure in chamber100, which is a displacement decrease pressure, is adjusted (or selectively energized with pressurized fluid) to counteract the spring load on the moveable bore, thereby pivoting the bore and reducing the bore eccentricity. Thus pump volumetric displacement is reduced by this displacement adjustment feature.

When additional flow is required to maintain system operating pressure, flow to the sealed chamber is reduced by regulating valve40, thus reducing the force counteracting the spring90. The moveable bore ring80changes position to equalize the forces, increasing pump flow to meet the additional flow demand.

FIG. 3is a schematic depiction of an exemplary control circuit130for a variable displacement transmission pump30. Output of the pump30is directed to both main regulator valve40through feedback circuit115and a transmission system120(as shown inFIG. 3in parallel). The hydraulic control circuit130controls command pressure sent to the VDP30displacement decrease circuit110fed through sealed chamber100(as shown inFIG. 2) in the VDP.

A line pressure control solenoid170, as shown inFIG. 3, controls the command pressure which actuates the main regulator valve40. Line pressure control solenoid170is commanded electrically to output a predetermined pressure that also corresponds to a desired line pressure. The line pressure control solenoid170applies hydraulic force to the main regulator valve40in conjunction with a line pressure offset spring or driving spring180, which is opposed by pressure force from line pressure circuit230. Said opposition results in a balanced force at position or stage (3) which meters flow from line pressure feedback circuit115to decrease pressure circuit110. The decrease pressure circuit110applies hydraulic force to the displacement adjustment feature in pump (or movable bore ring80as shown inFIG. 2) when a reduction in displacement (or line pressure) is required.

Line pressure control solenoid170has two stages. Solenoid valve170is spring biased towards the first stage (or a closed position) by return spring200. Solenoid valve170is controlled by a microcontroller175. Microcontroller175, through solenoid valve170, is configured to control regulator valve40according to transmission performance (e.g., speed, gear, temperature, or pressure). When the solenoid valve170is in the closed position, stage1, line190is disconnected from the source line150. Flow through control pressure line190is at least partially limited by orifice210.

Main regulator valve40, as shown inFIG. 3, is a regulator valve. Main regulator valve40is a spool valve positioned in a valve chamber220in this embodiment. In the first stage (1) line230(which is a portion of the pump outlet circuit) is disconnected from displacement decrease circuit110and prioritized oil circuit or line120(which is a Converted feed line). Line110is connector to sump50; displacement decrease circuit110is not in direct fluid communication with the sump50. In the second stage (2), line230is connected to line120while displacement decrease circuit110is connected to sump50. In the third stage (3), both displacement decrease circuit110and prioritized oil circuit120are connected to line230

Main regulator valve40is connected to feedback circuit115which is linked to a pump outlet passage230, as shown inFIG. 3. A line pressure circuit240branches off from the outlet passage to the pump30. The flow in the circuit is variable as indicated by demarcation250. In this embodiment, the main regulator valve40metering flow gain is between 8-30 mm ^2/mm.

Noise response reduction spring260is a response limiter that acts to limit excessive main regulator valve position response due to noise input. Spring260is in communication with the regulator valve40. Spring260is a coil spring configured to apply a resistive force on the regulator valve40in proportion to regulator valve travel towards a position closing fluid communication between the pump output circuit230and a displacement decrease circuit110. No feedback circuit orifice is used in the embodiment shown inFIG. 3. Spring180is a driving spring configured to bias the regulator valve towards a position closing fluid communication between the pump output circuit230and the displacement decrease circuit110. Springs180and260effectively center main regulator valve40on the metering edge. The relative spring constant ratio is 1:1 (180,260, respectively). The springs180,260used are a factor of 10 times higher rates than commonly used in this type of control system.

As shown, coil spring260acts as a system response limiter and opposes excessive valve movement in response to noise inputs such as changes to flow load. This type of noise input to the main regulator valve40results in excursions of main regulator valve due to: (1) the speed discrepancy between main regulator valve and displacement control mechanism in the pump (30as shown inFIG. 3); and (2) the main regulator valve feedback signal which is pump output pressure230, not regulated pressure, displacement decrease110.

A method of manufacturing a hydraulic control circuit (e.g., as discussed inFIG. 3) for a vehicle transmission pump is discussed hereinbelow. This configuration provides greater efficiency and stability. The method includes: connecting a fluid sump to a pump (e.g.,50as shown inFIG. 3); connecting a variable displacement pump to the pressure line (e.g.,30as shown inFIG. 3); incorporating a regulator valve in the pressure line in parallel with the system, the regulator valve configured to provide a displacement decrease pressure command to the pump (e.g.,40as shown inFIG. 3); and incorporating a response limiter at one end of the regulator valve thereby reducing the regulator valve positional response to noise inputs (e.g.,260as shown inFIG. 3).

In one exemplary embodiment the method also includes the step of configuring the response limiter to apply a resistive force on the regulator valve in proportion to regulator valve travel towards a position closing fluid communication between a pump output circuit and a displacement decrease circuit. A centering spring260as shown inFIG. 3can be used.

In another embodiment the method of manufacturing a hydraulic control circuit for a vehicle transmission pump includes restricting direct fluid communication between the displacement decrease circuit110and a low pressure exhaust circuit (e.g., sump50ofFIG. 3), while connected to pump output230. As shown inFIG. 3, the displacement decrease circuit110and sump50(which is an exemplary low pressure exhaust circuit) are indirectly in fluid communication through regulator valve40. However, displacement decrease circuit110does not need to have a direct fluid line to sump50since bleed of the displacement decrease circuit is not needed.

In yet another embodiment, the method includes incorporating a micro-controller in the control circuit, configured to control the regulator valve according to transmission performance. E.g.,175as shown inFIG. 3. The microprocessor can be a separate module or part of the powertrain control module.

With reference now toFIGS. 4 and 5, there is shown therein two graphs of pressure over time with respect to a regulator valve for a VDP. A command pressure (as indicated by line C1inFIG. 4) is delivered from the control valve to the VDP. The actual pressure signal, Line A1, to the pump varies according to fluctuations or oscillations in the decrease pressure circuit, shown as Line D1inFIG. 4.FIG. 4shows response lag in a case of eliminated a displacement decrease pressure circuit controlled leakage (or bleed) in the present system. A pressure over time plot is also shown for a hydraulic control circuit having a response limiter incorporated in a regulator valve assembly, in accordance with the present teachings. A response limiter (as discussed inFIG. 3) eliminates oscillations in the displacement decrease pressure circuit and thus reduces oscillations in the actual pressure Line A1(as shown inFIG. 5). The decrease pressure circuit, as indicated by Line D2has less oscillation thus resulting in less fluctuation in the actual pressure signal in the command line, Line A2. The command pressure, indicated by Line C1& C2, is consistent between arrangements.

Those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.