Electronically controlled range valve for multi-speed planetary transmission

A shift by wire control for a multi-speed vehicle transmission is provided. The control includes a shift by wire shift valve in fluid communication with other shift valves and clutch trim valves to provide double blocking features in the neutral range and a reverse range. The shift by wire valve is configured with multiple differential areas to provide failure modes for all forward ranges.

TECHNICAL FIELD

The present invention relates generally to power transmissions for motor vehicles, and more particularly, to a shift by wire control system for a power transmission including an electronically controlled range valve.

BACKGROUND

An electro-hydraulic control system controls shifting and operation of automatic vehicle transmissions. To permit shifting by the vehicle operator, the electro-hydraulic control system typically includes either a manual valve or a shift by wire valve.

In a manual valve electro-hydraulic control system, the vehicle operator manually changes the position of the valve to accomplish certain shifts, for example, to initiate movement of the vehicle from a non-moving state to a moving state or vice versa, or to change the direction in which the vehicle is moving (i.e., shifts from neutral to a forward range, from neutral to a reverse range, from a reverse range to a forward range, from a reverse range to neutral, from a forward range to neutral, or from a forward range to a reverse range).

In a shift by wire control system, at least some of the inputs that are used to initiate shifting are in the form of electrical signals rather than hydraulic or mechanical forces. Instead of a manual shift selector, a push button range selector may be used in a shift by wire system. Activation of a push button or similar actuator by the vehicle operator sends an electrical signal to an electronic control unit. The electronic control unit executes computer logic to determine which valve(s) in the electro-hydraulic control system need to change position in order for pressurized hydraulic fluid to be directed to the appropriate clutches to accomplish the requested shift. The electronic control unit sends electrical signals to solenoid valves of the electro-hydraulic control system, which initiate the valve position changes required to accomplish the requested shift.

SUMMARY

According to one aspect of the present invention, an electro-hydraulic control for a multi-speed vehicle transmission is provided. The electro-hydraulic control includes an electrical control configured to receive shift request signals from an electronic range selector of the transmission, first, second, and third electro-hydraulic actuators each configured to receive electrical signals from the electrical control, first, second and third shift valves each being in fluid communication with the first, second, and third electro-hydraulic actuators to receive pressurized hydraulic fluid output by the electro-hydraulic actuators and being in fluid communication with each other to selectively deliver pressurized hydraulic fluid to at least one shift mechanism of the transmission, a fourth electro-hydraulic actuator configured to receive electrical signals from the electrical control, a fourth shift valve configured to selectively deliver pressurized hydraulic fluid to at least one shift mechanism of the transmission, the fourth shift valve being controllable by the fourth electro-hydraulic actuator to achieve a first position when the fourth electro-hydraulic actuator is not electrically actuated and a second position when the fourth electro-hydraulic actuator is electrically actuated, and a plurality of fluid passages selectively coupling the first, second, third, and fourth shift valves such that a neutral or reverse range can be achieved by the transmission when the fourth shift valve is in either the first position or the second position, and a forward range can be achieved by the transmission only when the fourth shift valve is in the second position.

The fourth shift valve may have a first fluid chamber fluidly coupled to a first shift mechanism and a second fluid chamber fluidly coupled to a second shift mechanism, where the first shift valve has a third fluid chamber fluidly coupled to a third shift mechanism, the third shift valve has a fourth fluid chamber fluidly coupled to a fourth shift mechanism, and the first shift valve has a fifth fluid chamber fluidly coupled to a fifth shift mechanism of the transmission. The second shift valve may be fluidly coupled to the third shift mechanism through the first and third shift valves in a first reverse range and the second shift valve may be fluidly coupled to the fifth shift mechanism through the first, third, and fourth shift valves in a second reverse range.

The electro-hydraulic control may include a torque converter clutch control valve, wherein the torque converter clutch control valve is coupled to at least one of the first, second, third and fourth shift valves.

The plurality of fluid passages may selectively couple the first, second, third, and fourth shift valves such that a first reverse range can be achieved whether the fourth shift valve is in the first position or the second position. The plurality of fluid passages may selectively couple the first, second, third, and fourth shift valves such that a neutral range can be achieved whether the fourth shift valve is in the first position or the second position. The plurality of fluid passages may selectively couple the first, second, third and fourth shift valves such that at least two of the shift valves are required to change position in order for the transmission to shift from a neutral range to a forward range.

The electro-hydraulic control may include first and second trim systems each configured to receive electrical signals from the electrical control and control the rate at which fluid pressure is delivered to the shift mechanisms of the transmission via the first, second, third, and fourth shift valves, wherein the first trim system is directly fluidly coupled to the first shift valve, the second trim system is directly fluidly coupled to the second shift valve, the second trim system is fluidly coupled to the third shift valve via the second shift valve, and the second trim system is fluidly coupled to the first shift valve via the second and third shift valves.

The fluid passages may selectively couple the first, second, third and fourth shift valves such that at least one of the trim systems and at least one of the shift valves are required to be actuated in order for the transmission to shift from a neutral range to a reverse range.

According to another aspect, an electro-hydraulic control for a multi-speed vehicle transmission is provided, including an electrical control configured to receive shift request signals from an electronic range selector of the transmission, at least one trim system actuatable by the electrical control to control the rate of delivery of pressurized hydraulic fluid to at least one shift mechanism of the transmission, first, second, and third electro-hydraulic actuators each configured to receive electrical signals from the electrical control, first, second and third shift valves each being in fluid communication with the first, second, and third electro-hydraulic actuators to receive pressurized hydraulic fluid output by the electro-hydraulic actuators and being in fluid communication with each other to selectively deliver pressurized hydraulic fluid to at least one shift mechanism of the transmission, a fourth electro-hydraulic actuator configured to receive electrical signals from the electrical control, and a fourth shift valve configured to selectively deliver pressurized hydraulic fluid to first and second shift mechanisms of the transmission, the fourth shift valve being controllable by the fourth electro-hydraulic actuator to achieve a first position when the fourth electro-hydraulic actuator is not electrically actuated and a second position when the fourth electro-hydraulic actuator is electrically actuated, the fourth shift valve being configured to maintain the first position if the fourth shift valve is in the first position when an electrical failure occurs, and the fourth shift valve being configured to maintain the second position if the fourth shift valve is in the second position and a trim system is actuated when an electrical failure occurs.

The fourth shift valve may have at least first, second and third spaced-apart lands, where the first and second lands define a second fluid chamber that is in fluid communication with the second shift mechanism and the second and third lands define a first fluid chamber that is in fluid communication with the first shift mechanism. Fluid in the first and second fluid chambers of the fourth shift valve may be at an exhaust pressure in neutral and reverse ranges during normal operation and also during an electrical failure.

The first land may have a first diameter, the second land may have a second diameter, the third land may have a third diameter, where the second diameter is larger than the first diameter, and the third diameter is larger than the second diameter. The electro-hydraulic control may apply fluid pressure to a differential area of the third land of the fourth shift valve to keep the fourth shift valve in the second position during an electrical failure occurring in a low forward range. The low forward range may be a forward range lower than a fourth forward range. The electro-hydraulic control may apply fluid pressure to a differential area of the second land of the fourth shift valve to keep the fourth shift valve in the second position during an electrical failure occurring in a high forward range. The high forward range may be a forward range higher than a third forward range.

According to another aspect, an electro-hydraulic control for a multi-speed vehicle transmission is provided, including an electrical control configured to receive shift request signals from an electronic range selector of the transmission, at least one trim system actuatable by the electrical control to control the rate of delivery of pressurized hydraulic fluid to at least one shift mechanism of the transmission, a plurality of electro-hydraulic actuators each configured to receive electrical signals from the electrical control, a plurality of shift valves each being in fluid communication with an electro-hydraulic actuator to receive pressurized hydraulic fluid output by the electro-hydraulic actuator and being in fluid communication with at least one trim system and each other to selectively deliver pressurized hydraulic fluid to at least one shift mechanism of the transmission, a shift by wire shift valve configured to selectively deliver pressurized hydraulic fluid to at least one shift mechanism of the transmission, and a plurality of fluid passages selectively coupling the first, second, third, and fourth shift valves, the at least one trim system, and the shift by wire valve to provide a neutral range in which the neutral range is maintained unless a change in position of at least one of the shift valves or shift by wire valve and actuation of at least one of the trim systems occurs.

The shift by wire valve may have a first position in which it is not electrically actuated and a second position in which it is electrically actuated. The neutral range may be achievable whether the shift by wire valve is in the first position or the second position. The at least one trim system may be in direct fluid communication with at least one of the shift valves other than the shift by wire valve.

Patentable subject matter may include one or more features or combinations of features shown or described anywhere in this disclosure including the written description, drawings, and claims.

In general, like structural elements on different figures refer to identical or functionally similar structural elements, although reference numbers may be omitted from certain views of the drawings for ease of illustration.

DETAILED DESCRIPTION

Aspects of the present invention are described with reference to certain illustrative embodiments shown in the accompanying drawings and described herein. While the present invention is described with reference to the illustrative embodiments, it should be understood that the present invention as claimed is not limited to the disclosed embodiments.

FIG. 1depicts a simplified block diagram of an electro-hydraulic transmission control20including a shift by wire valve26, in the context of an exemplary vehicle powertrain10. The lines shown as connecting blocks12,14,16,18,20,22,24,26,28of powertrain10represent connections which, in practice, may include one or more electrical, mechanical and/or fluid connections, passages, couplings or linkages, as will be understood by those skilled in the art and as described herein.

Powertrain10includes drive unit12, torque converter14, torque converter clutch16, transmission18, electro-hydraulic control20, electronic control22, range selector24, and final drive28. Drive unit12generally provides a torque output to torque converter14. Drive unit12may be an internal combustion engine of a compression-ignition type (i.e. diesel) or a spark-ignition type (i.e. gasoline), a hybrid unit, or other suitable unit for generating torque output to drive a vehicle.

Torque converter14selectively establishes a coupling between drive unit12and transmission18to convert and/or transfer the torque output from drive unit12to the vehicle transmission18. Such coupling is a fluid coupling when torque converter clutch16is not applied, and a mechanical coupling when torque converter clutch is applied. Torque converter clutches are often provided to effect unitary rotation of the torque converter pump and turbine in response to reduced hydraulic pressure within the torque converter, which may occur when “slip” (i.e., a difference in rotational speed) between the torque converter pump and turbine is not required.

Transmission18includes an input shaft, an output shaft, an assembly of gears, and a plurality of gear-shifting mechanisms that are selectively engaged and disengaged by electro-hydraulic transmission control20to cause the vehicle to assume one of a plurality of operational modes or ranges including at least six forward speed ratios, a neutral range, and at least one reverse range. As such, the shift mechanisms of transmission18are in fluid communication with hydraulic control elements of control20.

In this disclosure, the term “shift mechanism” may be used to refer to one or more clutches, brakes, or other friction elements or devices, or similar suitable mechanisms configured to cause the transmission to switch from one range or gear ratio to another, different range or gear ratio.

Control20includes a two-position shift valve26that allows for shifting into reverse and neutral ranges when in one position and allows for shifting into forward ranges when in its other position. In the illustrated embodiment, reverse and neutral ranges are achieved when shift valve26is in an off or de-actuated position and forward ranges are achievable when shift valve26is in the on or actuated position. Thus, shift valve26can control three modes of operation (reverse, neutral, and forward ranges) with only two positions. The structure and operation of shift valve26is described in more detail below.

The embodiment of control20including shift valve26shown inFIGS. 2-13relates to a six-speed vehicle transmission that includes three planetary gearsets and five shift mechanisms (e.g. two rotating shift mechanisms and three stationary shift mechanisms C1, C2, C3, C4, C5). During normal operation of transmission18, two shift mechanisms are engaged in each range except neutral. An illustrative embodiment of transmission18is disclosed in U.S. Pat. No. 4,070,927 to Polak, which is incorporated herein by this reference. Those of ordinary skill in the art will understand that such transmission is offered only as an example, and that aspects of the present invention are applicable to other multi-speed vehicle transmissions. In the illustrated embodiment, transmission18has a shift schedule as shown in Table 1 below.

While the illustrated embodiment specifies a particular shift schedule, it will be understood that in other embodiments, other combinations of shift mechanisms C1, C2, C3, C4, and C5may be applied and released to achieve particular operating ranges of the transmission.

The torque output by transmission18is applied to the final drive28. The final drive20generally includes the drive wheels and driven load mass carried by the vehicle. Characteristics of final drive20may vary considerably over the course of the vehicle's use, as may be the case particularly with commercial vehicles such as trucks, buses, emergency vehicles, and the like.

Electrical control22controls operation of transmission18based on inputs from one or more components of drive unit12, torque converter14, transmission18, range selector24; and/or other inputs. Such inputs may include electrical digital and/or analog signals received from sensors, controls or other like devices associated with the vehicle components. For instance, inputs may include signals indicative of transmission input speed, driver requested torque, engine output torque, engine speed, temperature of the hydraulic fluid, transmission output speed, turbine speed, brake position, gear ratio, torque converter slip, and/or other measurable parameters.

Electrical control22generally includes electrical circuitry configured to process, analyze or evaluate one or more of the inputs and issue electrical control signals to appropriate components of electro-hydraulic control system20, as needed, through one or more electrical lines, conductors, or other suitable connections. Such connections may include hard-wired and/or networked components in any suitable configuration including, for example, insulated wiring and/or wireless transmission as may be appropriate or desired.

Range selector24issues signals or commands indicative of a selected or desired operational mode of the vehicle, i.e., a selected or desired forward speed ratio, a desired reverse range, or neutral. In the illustrated embodiment, range selector24is an electronically-controlled or “shift-by-wire” range selecting mechanism, rather than a manual selector.

As shown inFIGS. 2-16, control20includes two-position shift valve26, three additional shift valves36,38,40, and three clutch pressure control or “trim” systems30,32, and34.

Fluid circuits, including a main pressure circuit60, a control pressure circuit62, and an exhaust circuit64, are coupled to a source of pressurized fluid (not shown). Fluid circuits60,62,64fluidly couple the hydraulic components of control20to one another as shown and described below.

During operation of a vehicle into which control20is incorporated, main pressure circuit60draws hydraulic fluid at a main pressure from a fluid supply, such as a sump or reservoir (not shown). In general, the main pressure defines a range including a minimum system pressure and a maximum system pressure for main pressure circuit60. In the illustrated embodiment, the main pressure is in the range of about 50-250 pounds per square inch (psi). In the drawings, main pressure is denoted using a backward-slash pattern.

Control pressure circuit62circulates hydraulic fluid at a control pressure, which is typically regulated by a regulator or modulator valve as will be understood. In the illustrated embodiment, the control pressure is generally in the range of about 50-110 psi. Control pressure is denoted in the drawings by a dotted pattern.

Exhaust circuit64is in fluid communication with components of control20as shown in the drawings. Exhaust pressure is in the range of about zero psi. Exhaust circuit64is operably coupled to an exhaust backfill regulator valve44. The EBF valve44provides an exhaust backfill pressure, which is configured to prevent air from entering exhausted clutches. In the illustrated embodiment, the exhaust backfill pressure is generally in the range of about 2 psi. In the drawings, exhaust pressure is denoted by a forward-slash pattern.

Also shown are restrictors or orifices80,82,84,86,88. The restrictors or orifices80,82,84,86,88are positioned in fluid passages to alter or moderate the rate of fluid flow through the passages or a portion thereof, in order to control the rate at which pressure in a fluid passage changes. These elements are typically used to provide additional control over fluid pressure in the passages. For example, series of orifices80,82,84are used to prevent actuation of pressure switches72,74,76from occurring until their corresponding shift valve38,40,26is fully stroked.

Electro-hydraulic actuators50,52,54,56, and pressure switches70,72,74,76are in fluid communication with each of the shift valves36,38,40,26, respectively. It will be understood that actuators50,52,54,56, and pressure switches70,72,74,76are electrically coupled to control22, although for ease understanding these electrical connections are not shown inFIGS. 2-16.

In general, each of the valves of control20includes a valve head, a valve spool, at least one valve land interposed between portions of the valve spool or between the valve head and a portion of the valve spool, and a return spring disposed in a spring chamber. Each valve spool is axially translatable in a valve bore in response to changes in fluid pressure or fluid flow through the various passages of control20. For ease of illustration, the valve bores have been omitted from the figures.

The valve lands each define a diameter that is greater than the diameter defined by the valve spool, such that surfaces of the lands may slidably engage interior surfaces of the valve bore when the valve spool translates within the valve bore. Spool portions between valve lands may selectively connect fluid passages to other fluid passages, or connect fluid passages to fluid chambers, depending on the position of the valve.

Each of shift valves36,38,40has more than four spaced-apart lands that define at least four fluid chambers therebetween. Shift valve26has four spaced-apart lands that define three fluid chambers therebetween.

Shift valves36and40are generally single-diameter shift valves, meaning that all of the valve's lands have substantially the same diameter or there is no pressure differential. Shift valve38is a two-diameter shift valve, with land166having a smaller diameter than land168, as best shown inFIGS. 8 and 10. The land above land166(nearest the valve head) on shift valve38has substantially the same diameter as land166, and the lands below land168(nearer to the return spring) have substantially the same diameter as land168.

Shift valve26is a three-diameter shift valve. Land172has a larger diameter than land170, and land174has a larger diameter than land172as best shown inFIGS. 11-13. Land176has substantially the same diameter as land174. The height of land174is smaller than the heights of the other lands170,172and176.

The multiple diameters on shift valves26,38allow control20to use valve latching to provide failure recovery from any range of transmission18in the event of an electrical failure. The latching features on shift valve26additionally serve to hold shift valve26in the stroked position as long as a forward range is commanded, thereby preventing an unintended shift out of a forward range in the event that shift valve26fails. These latching features of shift valves26,38are described in greater detail below.

As is well known, return springs180,182,184,186,188bias their respective valve in a destroked position. Changes in fluid pressure or fluid flow in selected fluid passages may cause the valve spool to translate within the valve bore, causing the return spring to partially or fully compress.

Responsive to the output of actuators50,52,54,56, shift valves36,38,40,26are slidable between the destroked position and a stroked position, where the stroked position is one in which the return spring is fully compressed. In the illustrated embodiment, each of actuators50,52,54,56is a solenoid valve of the on/off type. The positioning of the shift valves36,38,40,26determines which of the shift mechanisms C1, C2, C3, C4, C5receive fluid pressure and which do not, thereby controlling which shift mechanisms are applied and which are released at any given time.

The pressure control valves of clutch trim systems30,32,34are configured to assume intermediate positions between the first and second positions, in which the return spring is partially compressed, in addition to the first and second positions. As will be understood, the displacement of the pressure control valves of the clutch trim systems30,32,34is controlled by electro-hydraulic actuators that have a variable output pressure, such as variable-bleed solenoids. Because the rate of application of fluid pressure can be controlled in this way, clutch trim systems30,32,34control the rate at which a shift mechanism is applied or released. Clutch trim systems30and32control the rate of application or release of the shift mechanisms C1, C2, C3, C4, C5(depending on the positioning of the shift valves26,36,38,40), while clutch trim system34controls the rate of application or release of torque converter clutch14.

Actuators50,52,54,56and the variable-output electro-hydraulic actuators of the clutch trim systems30,32,34are operably coupled to control22to receive electrical signals (i.e. electrical current) therefrom. The electrical signals generated and sent by control22to the electro-hydraulic actuators of control20selectively actuate the valves (in response to driver input or other inputs) to accomplish shifting of transmission18.

Each of the electro-hydraulic actuators of control20is either of the normally low type or of the normally high type. A normally low (or normally off) solenoid valve provides maximum output pressure when it receives electrical input and provides zero or minimum output pressure when no electrical input is received; while a normally high (or normally on) solenoid valve provides maximum output pressure when it is not receiving any electrical input and provides zero or minimum output pressure when electrical input is provided. Thus, as used herein, when referring to an actuator or solenoid valve as being “actuated,” this means either that electrical input is supplied to the solenoid (as in the case of normally low solenoids) or that electrical input is not supplied to the solenoid (as in the case of normally high solenoids).

In the illustrated embodiment, each of actuators50,52,54,56is a normally low solenoid, the electro-hydraulic actuators of trim systems32and34are normally low solenoids, and the electro-hydraulic actuator of trim system30is a normally high solenoid.

In general, pressure switches70,72,74,76are each configured to issue an electrical output signal to control22in response to a predetermined fluid pressure being detected by the pressure switch, for diagnostic purposes or for other reasons. Such electrical signals inform control22of changes in status of components of control20. Generation of an output signal by pressure switches70,72,74can be triggered either by the presence or the absence of a predetermined level of fluid pressure, depending on the configuration of the switch. As used herein, the term “actuated” when used to describe activity of a pressure switch means simply that the switch has issued an output signal to control22, without limiting the pressure switch to a particular type or configuration.

In the illustrated embodiment, each shift valve26,36,38,40has a corresponding pressure switch76,70,72,74, in fluid communication therewith. Each of pressure switches70,72,74,76acts as a binary switch such that it is actuated when the shift valve to which it is coupled is in the stroked position. Control20may include other pressure switches in addition to those used to monitor the position of the shift valves. For example, control20may use pressure switches to detect changes in position of the trim valves30,32,34.

Table 2 shows a steady state mechanization of components of control20during normal operation. The number “1” is used to denote that a component is actuated, while the number “0” denotes that a component is not actuated. The mechanization of trim system34is omitted from Table 2 because the application of torque converter clutch34is controlled independently by trim system actuator58.

The configuration of control20during normal operation, including two possible reverse ranges, a neutral range, and multiple forward ranges, will now be described.

As shown in Table 2 andFIGS. 2-3, control20provides two alternative reverse ranges. In the reverse range ofFIG. 2, denoted as “Reverse1” in Table 2, shift valve actuators52and54are actuated, causing shift valves38and40to move to the stroked position while shift valve36remains in the destroked position due to actuator50being non-actuated. Trim system30is fluidly coupled to fluid chamber148as a result of actuation of shift valve38by actuator52. As a result, trim system30applies main pressure to shift mechanism C5through fluid chamber148and fluid passage94.

In the Reverse1range, trim system32is fluidly coupled to fluid chamber150via fluid chamber144of shift valve36, fluid passage100, fluid chamber152of shift valve40, and fluid passage98. As a result, trim system32applies main pressure to shift mechanism C3via fluid chamber150and fluid passage96.

Shift valve26is not actuated in the Reverse1range. However, even if shift valve26were actuated in the Reverse1range, control20would remain in the Reverse1range because the fluid passages104,108(which feed shift mechanisms C1, C2respectively when shift valve26is stroked) are connected to exhaust pressure. Thus, the Reverse1range can be achieved and maintained regardless of the position of shift valve26. Moreover, in order for control20to fail to a forward range, two valve malfunctions would have to occur, e.g. a failure of shift valve26and a failure of at least one of the other shift valves36,38,40, or a failure of shift valve26and a failure of one of the trim systems30,32.

In the reverse range ofFIG. 3, denoted as “Reverse2” in Table 2, the shift mechanisms fed by trim systems30,32are reversed relative to the Reverse1range. In Reverse2, trim system30supplies main pressure to shift mechanism C3via fluid chamber150of shift valve38, and trim system32supplies main pressure to shift mechanism C5via fluid chamber138of shift valve36, fluid passage114, fluid chamber156of shift valve40, fluid passage104, fluid chamber194of shift valve26, fluid passage134, fluid chamber164of trim valve34, fluid passage118, orifices87,88, fluid chamber148of shift valve38and fluid passage94. Shift mechanisms C3and C5are applied in both the Reverse1and Reverse2ranges.

A neutral range configuration of control20is shown inFIG. 4. In the neutral range, all three shift valves36,38,40are actuated by control pressure supplied by actuators50,52,54respectively. As a result, pressure switches70,72,74are actuated. Shift valve26is not actuated in the neutral range and therefore, the neutral range can be attained and maintained independently of shift valve26.

In the neutral range, trim system30supplies main pressure to shift mechanism C5via passage128, fluid chamber148, and passage94. In order to transition from the neutral range ofFIG. 4to either of the reverse ranges ofFIGS. 2 and 3, trim system32would have to be actuated and either shift valve36(for Reverse1range) or shift valve38(for Reverse2range) would have to change position. Similarly, in order to transition from the neutral range ofFIG. 4to a forward range, shift valve26and at least one other shift valve36,38,40have to change position. Thus, control20provides protection against unintentional shifting out of neutral into a moving range by requiring at least two valves to change position.

Exemplary forward range configurations of control20are shown inFIGS. 5,6, and7. Each of the forward ranges requires either shift mechanism C1or shift mechanism C2to be applied. Both shift mechanism C1and C2are in fluid communication with shift valve26. When shift valve26is not actuated (i.e. destroked), both shift mechanism C1and shift mechanism C2are in direct fluid communication with exhaust backfill circuit64and EBF valve44as shown inFIGS. 2-4. Movement of shift valve26to the on or stroked position is initiated by actuator56independently of the other valve systems of control20. Thus, shifting from a non-forward range into a forward range can only be accomplished if shift valve26is in the actuated or stroked position shown inFIGS. 5,6, and7. Thus, shift valve26is in the on or stroked position in all forward ranges, as indicated by Table 2.

Movement of shift valve26to the stroked position requires actuation of actuator56. Actuator56is actuated by electrical signals issued by control22in response to a forward range request received from range selector24in the form of an electrical signal. In this way, control20is configured so that transitions from non-forward ranges to a forward range only occur if an electrical forward range request signal has been received by control22.

FIG. 5shows a configuration of control20for a first forward range in which trim system30applies main pressure to shift mechanism C5via fluid chamber148of shift valve38. Actuation of shift valve26by actuator56places shift mechanism C1in fluid communication with main pressure via fluid chamber192of shift valve26, fluid passage104and fluid chamber156of shift valve40.

FIG. 6shows a configuration of control20for a second forward range in which trim system30applies main pressure to shift mechanism C4via fluid chamber144of shift valve36, passage100, and fluid chamber154of shift valve40. Main pressure is applied to shift mechanism C1as described above with regard toFIG. 5.

FIG. 7illustrates a configuration of control20for a fourth forward range in which main pressure is applied to shift mechanisms C1and C2. Main pressure is applied to shift mechanism C1as described above with regard toFIG. 5. Main pressure is applied to shift mechanism C2via fluid chamber190of shift valve26, fluid passage108, fluid chamber136of shift valve38, fluid passage196, and fluid chamber158of shift valve40.FIG. 7also illustrates the application of torque converter clutch14by actuator58, which by applying control pressure to the head of trim valve34, connects main pressure from passage116with the torque converter clutch14. Since main pressure flows through passage116in all of the normal modes of operation of control20, torque converter clutch14can by actuated by actuator58at any time (i.e., in any range).

Table 3 shows a steady state mechanization of components of control20in a failure mode resulting from an electrical failure. The number “1” is used to denote that a component is actuated, while the number “0” denotes that a component is not actuated. The letter “H” is used to indicate that a component is hydraulically held in position in the absence of electrical input. The mechanization of trim system34is omitted since the torque converter clutch34is not applied during an electrical failure.

FIGS. 8-13show the configuration of control20in the event of an electrical failure in the Reverse1, Reverse2, neutral, and first, second and fourth forward ranges in accordance with Table 3. Trim system30is actuated by a normally high solenoid and is therefore actuated in the event of an electrical failure. Thus, trim system30applies main pressure to either shift mechanism C5or shift mechanism C3, depending on the position of shift valve38, in the event of an electrical failure.

When shift valve38is stroked during normal operation, trim system30is fluidly coupled to shift mechanism C5. This is the case in the Reverse1, neutral, and first forward ranges as shown inFIGS. 2,4and5. If an electrical failure occurs in one of these ranges, actuator52will not deliver pressure to shift valve38because of the absence of electrical input. However, the stroked position of shift valve38is maintained because trim system30applies main pressure to the differential area d3of land168of shift valve38via fluid chamber148. This is shown inFIGS. 8(Reverse1),10(neutral), and11(1stforward range).

Since normally high trim system30controls both shift mechanisms C5and C3, and the reverse ranges require both C3and C5to be applied, in the event of an electrical failure, the reverse ranges cannot fail to reverse. Instead, both of the reverse ranges will fail to a neutral range as shown inFIGS. 8 and 9and indicated in Table 3 above.

The Reverse1range fails to a neutral state in which the C5shift mechanism is applied as shown inFIG. 8. The Reverse2range fails to a neutral state in which the C3shift mechanism is applied as shown inFIG. 9. The neutral range fails to the failure mode C5neutral state shown inFIG. 10. The failure mode C5and C3neutral states cannot be shifted out of as long as the electrical failure occurs, because shifting out of neutral to either a reverse range or forward range requires electrical input.

FIGS. 8,9, and10also show how the flow of control pressure to the head of shift valve40, via fluid chamber140of shift valve36and fluid passage108, maintains the stroked position of shift valve40in the absence of electrical input to actuator54. When shift valve40is stroked, main pressure is blocked from entering passage104, which is in fluid communication with shift valve26.

FIGS. 11,12, and13show failure mode configurations of control20for forward ranges. As shown inFIG. 11, the first forward range is maintained in the event of an electrical failure due to the latching of shift valve38by pressure applied to the differential area of land168, and the latching of shift valve26. Pressure applied to the differential area of land174maintains the stroked position of shift valve26in the absence of electrical input to actuator56.

The second and third forward ranges fail to the third forward range in the event of an electrical failure, as shown inFIG. 12. The shift valve26is latched as described above with reference toFIG. 11. During normal operation, shift valve38is destroked in the second and third forward ranges. The destroked position is maintained in the event of electrical failure because the lands below land168have the same diameter as land168. However, shift mechanism C3is applied (if the failure occurred in the second forward range) or maintained (if the failure occurred in the third forward range) because the actuator for trim system30is of the normally high type.

The fourth and higher forward ranges fail to the fifth forward range in the event of an electrical failure as shown inFIG. 13. In the electrical failure mode for these ranges, shift valve26is latched in the stroked position by pressure applied to the differential area of land172. Thus, main pressure is supplied to shift mechanism C2as described above with regard toFIG. 7. Shift valve40is hydraulically latched by control pressure via passage102as described above. Trim system30applies main pressure to shift mechanism C3because shift valve38is destroked.

In all forward ranges, the latching features on shift valve26in communication with shift mechanisms C1and C2as described above hold shift valve26in the stroked position as long as the transmission is receiving a forward range command from electrical control22or range selector24, thereby providing protection against a mechanical failure of shift valve26that might otherwise cause shift valve26to erroneously move to the destroked position.

The hydraulic latching of shift valves26,38and40in the various instances described above is maintained unless the pressure of the hydraulic fluid in the control system decreases to a point where it can no longer overcome the bias of the valve's return spring, such as is the case when the source of pressurized hydraulic fluid (e.g., the engine pump) is turned off.

The present disclosure describes patentable subject matter with reference to certain illustrative embodiments. The drawings are provided to facilitate understanding of the disclosure, and may depict a limited number of elements for ease of explanation. Except as may be otherwise noted in this disclosure, no limits on the scope of patentable subject matter are intended to be implied by the drawings. Variations, alternatives, and modifications to the illustrated embodiments may be included in the scope of protection available for the patentable subject matter.