Method and apparatus for generating velocity commands for a continuously variable transmission

[0002] The present invention generally relates to continuously variable transmission, and more specifically to a method and apparatus for generating velocity commands for a continuously variable transmission.

[0003] Many work machines, particularly earth working machines, use a hydrostatic drive system to drive the traction wheels or tracks of the work machine. The hydrostatic drive system can provide a continuously variable speed output to the wheels or tracks of the work machine. In particular, the speed can be continuously varied by controlling the displacements of either a hydraulic pump or a hydraulic motor which comprise the hydrostatic drive system.

[0004] One problem with earth moving machines which use hydrostatic transmissions is that the speed output can be varied rapidly thereby producing a rapid response. This rapid response can result in high, undesirable jerk which can cause discomfort to an operator of the work machine. In addition, the high undesirable jerk can cause the operator to lose control of the machine as the rapid movement of the machine can create unwanted pedal modulations. The unwanted speed pedal modulations create control signals which cause the work machine to move in an unintended manner.

[0005] One solution to this problem is pass the control signals from the speed pedal through a low pass filter. Each low pass filter has a selected corner frequency. One corner frequency can provide optimal response during the application of oncoming jerk, i.e. jerk applied to first start accelerating the work machine, but has poor response during the application of off going jerk, i.e. the jerk applied to match the actual speed to the desired speed. On the other hand, another corner frequency will have good response during the application of off going jerk, but will have poor response during the application of oncoming jerk. A drawback of using a low pass filter is that a single filter cannot be selected which provides satisfactory response during both the oncoming jerk and the off going jerk.

[0006] Another solution to this problem is to control the oncoming jerk to provide a smooth and rapid response as the machine is accelerated. However, this solution does not control the off going jerk as the actual speed approaches the desired speed. Smoothing the off going jerk is critical for operator comfort and controllability of the work machine. A drawback to controlling only the oncoming jerk is that the response during the application of off going jerk is unsatisfactorily uncomfortable to the operator.

[0007] A third solution to this problem is to provide both oncoming and off going jerk shaping to the velocity command. This solution has been applied to work machines having a discrete number of velocity profiles, or speed targets. However, the discrete number of velocity profiles cannot provide the desired response for an infinite number of velocity values that can be commanded by the continuously variable transmission. This scheme does not allow a continuously variable adjustment of the velocity profile to match the continuously variable speed output of the transmission.

[0008] What is needed therefore is a method and apparatus for generating velocity commands for a continuously variable transmission which overcomes the above-mentioned drawbacks.

[0009] In accordance with a first aspect of the present invention, there is provided a control apparatus for a continuously variable transmission. The control apparatus includes a transmission speed sensor which generates an actual velocity signal in response measuring speed of an output shaft of the continuously variable transmission. The control apparatus further includes a first input device, or speed pedal, which is positionable in one of an infinite number of positions and generates a desired velocity signal corresponding to the position of the pedal. The control apparatus yet further includes a microprocessor controller operable to receive the desired velocity signal (from the speed pedal), receive the actual velocity signal, calculate a commanded acceleration a_c, and generate a commanded velocity V_cbased on the desired velocity signal, a jerk value j, and the commanded acceleration a_c.

[0010] In accordance with a second aspect of the present invention, there is provided a method of controlling a continuously variable transmission having a transmission speed sensor which generates an actual velocity signal in response measuring speed of an output shaft of the continuously variable transmission. The transmission further has a first input device, or speed pedal, which is positionable in one of an infinite number of positions and generates a is desired velocity signal corresponding to the position. The method includes the steps of receiving the desired velocity signal and receiving the actual speed signal. The method further includes the steps of calculating a commanded acceleration a_cand generating a velocity command signal. The velocity command signal is based on the desired velocity signal, a jerk value j, and the commanded acceleration a_c.

[0011] FIG. 1 is a schematic view of a hydro-mechanical, continuously variable transmission which incorporates the features of the present invention therein;

[0012] FIG. 2 is a schematic view of the a closed loop control which produces control signals for a displacement controllers of the continuously variable transmission of FIG. 1;

[0013] FIG. 3A is a flow chart used to set jerk values to be integrated into the commanded acceleration and the commanded velocity;

[0014] FIG. 3B is a flow chart used to calculate commanded acceleration and commanded velocity;

[0015] FIG. 4 is a graph which illustrates commanded velocity, commanded acceleration, and jerk in response to the desired velocity;

[0016] FIG. 4A is an enlarged portion of the graph of FIG. 4;

[0017] FIG. 5A is a flow chart which illustrates a first method of adjusting the commanded acceleration and commanded velocity in response to rapid changes in desired velocity;

[0018] FIG. 5B is a flow chart which illustrates a second method of adjusting the commanded acceleration and the commanded velocity in response to rapid changes in desired velocity;

[0019] FIG. 6A is a graph which illustrates velocity, acceleration, and jerk in response to the first method of adjusting the commanded acceleration and the commanded velocity in response to rapid changes in desired velocity;

[0020] FIG. 6B is a graph which illustrates velocity, acceleration, and jerk in response to the second method of adjusting the commanded acceleration and the commanded velocity in response to rapid changes in desired velocity.

[0021] While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0022] Referring now to FIG. 1 there is shown a transmission assembly 10 that incorporates the features of the present invention therein. The transmission assembly 10 is adapted for use in a work machine, such as a loader (not shown) having an engine 12. The transmission assembly 10 is of the continuously variable type and includes a mechanical transmission 14, a continuously variable transmission 16, a micro-processor based controller 18, a sensing arrangement 20 and a command input arrangement 22. Although the transmission assembly 10 is shown to be a continuously variable hydro-mechanical transmission, the invention is equally applicable to any type of continuously variable transmission including a hydro-mechanical, hydrostatic transmission system, or electromechanical transmissions. A work system 24 is connected to the transmission assembly 10 by a drive shaft 26.

[0023] The mechanical transmission 14 and an associated clutch control arrangement 28 are operatively connected to the engine 12 through a gear arrangement 30. The mechanical transmission 14 includes a summing planetary arrangement 32 operatively connected to both the engine 12 through the gear arrangement 30 and to the hydrostatic transmission 16 through a motor output shaft 34. The output of the summing planetary arrangement 32 is connected to the drive shaft 26. The mechanical transmission 14 further includes directional high speed clutches 36, 38 and a low speed clutch 40. The clutch control arrangement 28 is connected to a source of pressurized pilot fluid, such as a pilot pump 42. The controller 18 is operative to control engagement and disengagement of the respective speed clutches 36, 38 and 40 in response to electrical signals from the controller 18.

[0024] The hydrostatic transmission 16 and a displacement controller 44 are operatively connected to the engine 12 through a pump input drive shaft 46. The hydrostatic transmission 16 includes a variable displacement pump 48, a pump displacement actuator 50, a variable displacement motor 52 fluidly connected to the variable displacement pump 48 by conduits 54, 56, and a motor displacement actuator 58. The displacement controller 44 is connected to the pilot pump 42 and the controller 18. The displacement controller 44 controls movement of the respective pump and motor displacements actuators 50, 58 in response to control signals from the controller 18.

[0025] The command input arrangement 22 includes a speed input mechanism 60 having a first input device or speed pedal 62 moveable from a zero speed position to a maximum speed position for producing a desired velocity signal representative of a desired velocity V_d. The input arrangement 22 further includes a directional control mechanism 64 having a direction control lever 66 selectively moveable from a neutral position to a forward or a reverse position. The input arrangement 22 further includes a second input device or jerk input 71 which sends a jerk signal representative of the commanded jerk value j to the controller 18. The input arrangement 22 yet further includes a third input device or maximum acceleration input 73 which sends and acceleration signal representative of the maximum acceleration a_maxto the controller 18. The controller 18 includes RAM and ROM (not shown) that stores transmission control software, desired velocity V_d, the jerk value j, the commanded acceleration a_c, the commanded velocity V_c, and the maximum acceleration a_max.

[0026] The sensing arrangement 20 includes an engine speed sensor 76 operative to sense the speed of the pump input shaft 46 and direct an engine speed signal representative of the rotation speed of the output shaft of the engine 12 to the controller 18. A transmission speed sensor 78 is operative to sense the speed of the motor output shaft 34 and direct a motor output speed signal representative of the motor output speed to the controller 18. A transmission speed sensor 80 is operative to sense the speed of the output drive shaft 26 and direct an actual velocity signal representative of the actual velocity of the work machine to the controller 18.

[0027] Referring to FIG. 2, there is shown a schematic view of a closed loop control system 90 within the controller 18. The closed loop control system 90 processes the commanded velocity V_ccalculated by the controller 18 and actual velocity provided by the transmission speed sensor 80 and provides command signals to the displacement controller 44. In particular, the commanded velocity V_cis passed into a closed loop control system 90 as a command while the actual velocity is used is passed into the closed loop control system 90 as a feedback value. In a comparator 92, the actual velocity is subtracted from the commanded velocity V_cto produce an error signal which is fed into a simple proportional, integral, and derivative controller, or PID controller 94. The PID controller 94 produces a command signal based on calculations of the error signal which is directed to the displacement controller 44. The displacement controller 44 receives the command signal and responsively controls the displacement of one of the variable displacement pump 48 or the variable displacement motor 52 thereby controlling the actual velocity of the work machine to follow the commanded velocity V_c.

[0028] Referring now to FIG. 3A, there is shown the routine 100 used to generate the commanded velocity V_cand commanded acceleration a_cused by the closed loop control system 90 of FIG. 2. The routine 100 resides in the memory of the controller 18.

[0029] Advancing to step 102, the controller 18 calculates the desired velocity V_dfrom the desired velocity signal generated in response to the positioning of the speed pedal 62. The desired velocity V_dis a function of the displacement of the speed pedal 62. The desired velocity V_dis stored in the memory of the controller 18 and is used for future calculations.

[0030] Advancing now to step 104, a final velocity V_fis calculated. The final velocity V_fis the command velocity V_cthat will be generated if the subroutine 100 continues with the present commanded velocity V_c, present commanded acceleration a_c, and fixed jerk value j. In particular, the final velocity V_fis a steady state value calculated by integrating the fixed jerk value j over time until the commanded acceleration a_creaches zero.

[0031] The velocity commands generated by controller 18 are a summation of a number of discrete acceleration commands a_cadded to the current velocity command V_c. Each acceleration command a_cis separated from a subsequent acceleration command by a loop time, or time that the controller 18 takes to generate a new commanded acceleration a_cand commanded velocity V_c. During each loop of the of the controller, the commanded acceleration a_cis incremented by the jerk value j integrated over the loop time. By analogy, this is similar to the summation of a series of constants, which can be calculated using the following well known equation: $\sum _{k=1}^{n}k=1+2+3+\dots +n=\frac{n\left(n+1\right)}{2}$

[0032] In the present case, the acceleration values are incremented until the commanded acceleration a_cis obtained. Therefore, the commanded acceleration a_cis analogous to the final value n and the acceleration increment which is equal to the jerk value j integrated over the loop time is analogous to the increment between integers, or one. Thus, to calculate a future velocity V_f, it is necessary to add the summed accumulation of acceleration commands to the current commanded velocity V_c. The resulting equation is used to calculate the final velocity V_f: $V_f=V_c+\frac{a_c\left(a_c+\int j·dt\right)}{2·j}$

[0033] Referring now to FIGS. 3A and 4, the controller 18 determines the appropriate jerk value (e.g. either a negative fixed jerk or a positive fixed jerk) in steps 106, 108, 110 and 112. Starting at a time t=0 shown in FIG. 4, the commanded velocity V_c, the commanded acceleration a_c, and the jerk value j are all equal to zero. When a positive desired velocity V_dis received by the controller 18 at a time 200, the controller 18 performs the tests in steps 106, 108, 110, and 112 to determine the appropriate jerk value to apply to the commanded acceleration a_cwhich is then be applied to the commanded velocity V_c.

[0034] In step 106, if the desired velocity V_dis greater than the commanded velocity V_cand the final velocity V_f, calculated in step 104, is greater than the desired velocity V_d, then the controller 18 advances to step 114 where a negative jerk value −j is applied to the commanded acceleration a_cwhich is then applied to the commanded velocity V_c. This corresponds to an off going jerk being applied to the commanded acceleration a_cbetween a time 204 and a time 206 so as to prevent the commanded velocity V_cfrom overshooting the positive desired velocity V_d(see FIG. 4).

[0035] Similarly, in step 108, if the desired velocity V_dis less than the commanded velocity V_cand the final velocity V_f, calculated in step 104, is less than the desired velocity V_d, then the controller 18 advances to step 116 where the positive jerk value +j is applied to the commanded acceleration a_cwhich is then applied to the commanded velocity V_c. This corresponds to an offgoing jerk being applied to the acceleration a_cin the reverse direction to prevent the commanded velocity V_cfrom overshooting the negative desired velocity V_d(not shown).

[0036] In step 110, if the desired velocity V_dis greater than the commanded velocity V_c, then the controller 18 advances to step 118 where the positive jerk value +j is applied to the commanded acceleration a_cwhich is then applied to the commanded velocity V_c. This corresponds to an oncoming jerk being applied to the commanded acceleration a_cbetween the time 200 and a time 202 (see FIG. 4).

[0037] Similarly, in step 112, if desired velocity V_dis less than the commanded velocity V_cthen the controller 18 advances to step 120 where a negative jerk value −j is applied to the commanded acceleration a_cwhich is then applied to the commanded velocity V_c. This corresponds to an oncoming jerk being applied to the commanded acceleration a_cin the reverse direction (not shown). If the desired velocity V_dis equal to the commanded velocity V_c, the controller 18 advances to step 122 where the jerk value i is set to zero to prevent further changes in the commanded acceleration a_cand commanded velocity V_c. From the steps 114, 116, 118, 120, or 122 the controller 18 advances to the step 124 of FIG. 3B.

[0038] Referring now to FIGS. 3B and 4, in step 124, the controller 18 integrates the jerk value j obtained in steps 114, 116, 118, 120, or 122 over the loop time and adds the result to the commanded acceleration a_c. For example, when a positive desired velocity V_dis received by the controller 18, the positive jerk value +j is integrated and added to the commanded acceleration a_cbetween the time 200 and 202 to initiate motion in the forward direction. On the other hand the negative jerk value −j is integrated and added to the commanded acceleration a_cbetween the time 204 and the time 206 as the commanded velocity V_cconverges with the positive desired velocity V_d(see FIG. 4). After the commanded acceleration a_chas been incremented, the controller 18 advances to step 126.

[0039] In step 126, the controller 18 compares the commanded acceleration a_cto the maximum acceleration a_max. If the absolute value of the commanded acceleration a_cis greater than the maximum acceleration a_max, then the absolute value of the commanded acceleration a_cis set to the maximum acceleration a_maxthereby limiting the acceleration of the work machine. The commanded acceleration a_cis limited to the maximum acceleration a_maxbetween the time 202 and the time 204. It should be appreciated that the maximum acceleration a_maxis received by the controller 18 from the acceleration input device 73 shown in FIG. 1. For example if the maximum acceleration a_maxis 0.4 G's and the commanded acceleration a_cis equal to 0.45 G's, then the acceleration command a_cis set to the maximum acceleration a_maxof 0.4 G's. The controller 18 then advances to the step 128.

[0040] In step 128, the commanded velocity V_cis incremented by integrating the commanded acceleration a_cover the loop time. The commanded velocity V_cis incremented by an increasing commanded acceleration a_cbetween the time 200 and the time 202, incremented by the constant maximum acceleration a_maxbetween the time 202 and the time 204, and incremented by a decreasing commanded acceleration a_cbetween the time 204 and the time 206. The controller 18 then advances to the step 130.

[0041] In step 130, the controller 18 determines if the commanded velocity V_chas converged with the desired velocity V_d. In particular, the controller 18 determines if the commanded velocity V_cis within a velocity threshold V_t(shown in FIG. 4A) of the desired velocity V_d. In the exemplary embodiment, the velocity threshold V_tis less than or equal to one percent of the desired velocity V_d. If the desired velocity V_dis within the threshold V_tthen the controller 18 advances to the step 132. If the desired velocity V_dis not within the threshold V_tthen the controller 18 advances to the step 134.

[0042] In the step 132, the commanded velocity V_chas converged with the desired velocity V_d. Therefore, the commanded velocity V_cis set to the desired velocity V_d. Moreover, the commanded acceleration a_cand the jerk value j are set to zero so as to prevent changes in the commanded velocity V_c. The controller 18 then advances to step 134.

[0043] In step 134, a single loop of the routine 100 is complete. The values of commanded velocity V_c, commanded acceleration a_c, and jerk value j are stored in the memory of the controller 18 to be used in subsequent loops through the routine 100.

[0044] Referring now to FIGS. 5A and 6A, there is shown a first subroutine 300 used to generate the commanded velocity V_cand commanded acceleration a_cin response to the operator changing the desired velocity V_dprior to the commanded velocity V_cconverging with the desired velocity V_d.

[0045] In step 302, if the desired velocity V_dis less than the commanded velocity V_cand the commanded acceleration a_cis greater than zero thereby driving the commanded velocity V_cin the wrong direction, the controller 18 advances to step 306 where the jerk value is set to a negative value at least three times the jerk value j received from the jerk input 71. This condition corresponds to a time 320 where the desired velocity V_d2is lowered below the command velocity V_cprior to the command velocity V_creaching the desired velocity V_d1(see FIG. 6A). The jerk value −j can be exceeded by a factor greater than three because the operator has drastically chanced the desired velocity V_dand expects to have a quick response in order to reach the new desired velocity V_d2. In the exemplary embodiment, a jerk value of −3j is applied to the commanded velocity a_cuntil the commanded acceleration ac becomes negative at a time 321. The controller 18 then advances to step 310.

[0046] In step 304, if the desired velocity V_dis greater than the commanded velocity V_cand the commanded acceleration a_cis less than zero thereby driving the commanded velocity V_cin the wrong direction, then the controller 18 advances to step 308 where the jerk value is set to a positive value at least three times the jerk value +j received from the jerk input 71. This condition corresponds to a time 324 where the desired velocity V_d3is raised above the command velocity V_cprior to the command velocity V_creaching the desired velocity V_d2(see FIG. 6A). In the exemplary embodiment, a jerk value of +3j is applied to the commanded acceleration a_cuntil the commanded acceleration a_cbecomes positive at a time 325. The controller 18 then advances to step 310.

[0047] In step 310, the controller 18 then advances to the start of the routine 100.

[0048] Referring now to FIGS. 5B and 6B, there is shown a second subroutine 400 used to generate the commanded velocity V_cand commanded acceleration a_cin response to the operator changing the desired velocity V_dprior to the commanded velocity V_cconverging with the desired velocity V_d.

[0049] In step 402, if the desired velocity V_dis less than the commanded velocity V_cand the commanded acceleration a_cis greater than zero thereby driving the commanded velocity V_cin the wrong direction, then the controller 18 advances to step 406 where the commanded acceleration a_cis set to zero. This condition corresponds to a time 420 where the desired velocity V_d2is lowered below the command velocity V_cprior to the command velocity V_creaching the desired velocity V_d1(see FIG. 6B). Setting the commanded acceleration a_cto zero is equivalent to applying an infinite negative jerk to the commanded acceleration a_cfor an infinitesimal period of time. In a manner similar to the subroutine 300, the jerk value j can be exceeded by a great factor because the operator expects to have a quick response in order to reach the new desired velocity V_d. In addition, the actual jerk that the operator feels is limited by the maximum response of the work machine. The controller 18 then advances to step 410.

[0050] In step 404, if the desired velocity V_dis greater than the commanded velocity V_cand the commanded acceleration a_cis less than zero thereby driving the commanded velocity V_cin the wrong direction, then the controller 18 advances to step 406 where the commanded acceleration a_cis set to zero. This condition corresponds to a time 424 where the desired velocity V_d3is raised above the command velocity V_cprior to the command velocity V_creaching the desired velocity V_d2(see FIG. 6B). Setting the commanded acceleration a_cto zero is equivalent to applying an infinite positive jerk to the commanded acceleration a_cfor an infinitesimal period of time. The controller 18 then advances to step 410.

[0051] In step 410, the controller 18 advances to the start of the routine 100.

[0052] In operation, the operator first determines the desired mode of operation of the work machine. Selecting the mode of operation sets the predetermined jerk limit j with the jerk input device 71 and the maximum acceleration a_maxwith the acceleration input device 73 to match the mode of operation desired by the operator.

[0053] The operator inputs a desired velocity V_dinto the controller 18 by depressing the pedal 60. Upon receipt of the desired velocity V_d, the controller 18 executes the routine 100 and applies a predetermined jerk value j to the commanded acceleration a_c. In particular, the jerk value j is integrated over the loop time and added to the commanded acceleration a_c. The commanded acceleration a_cis then integrated over the loop time and applied the commanded velocity V_cas shown between the time 200 and the time 202 of FIG. 4. At the time 202, the commanded acceleration a_cis no longer incremented as the commanded acceleration a_chas exceeded the maximum acceleration a_max.

[0054] The commanded velocity V_cis incrementally increased until the controller 18 determines that the final velocity V_f(calculated as described above) exceeds the desired velocity V_d. This occurs at the time 204 (shown in FIG. 4) where a negative jerk value −j is subsequently integrated into the commanded acceleration a_cand commanded velocity V_c. The negative jerk value −j is integrated into the commanded acceleration a_cuntil the commanded velocity V_ccomes within the threshold velocity V_tof the desired velocity V_d(see FIG. 4A). At this point, the controller 18 determines that the commanded velocity V_chas converged with the desired velocity V_dand the commanded velocity V_cis set to the desired velocity V_d. In addition, the commanded acceleration a_cand jerk j are set to zero to prevent further changes in the commanded velocity V_c.

[0055] However, the operator may change the desired velocity V_dprior to the commanded velocity V_c10 converging with the desired velocity V_d. If the commanded acceleration a_cis positive and the desired velocity V_dis less than the commanded velocity V_c, then the commanded velocity V_cmust be rapidly changed to provide the operator with good response.

[0056] A first subroutine 300 accomplishes the required rapid change in commanded velocity V_cby integrating a negative jerk value that is greater than three times the jerk value j obtained from the jerk input 71. The resultant rapid change in the commanded acceleration a_cand the commanded velocity V_care shown between the time 320 and the time 321 of FIG. 6A.

[0057] A second subroutine 400 accomplishes the required rapid change in commanded velocity V_cby instantaneously setting the commanded acceleration a_cto zero. Setting the commanded acceleration a_cto zero is equivalent to applying an infinite jerk value to the commanded acceleration a_cfor an infinitesimal period of time. The resultant rapid change of the commanded acceleration a_cand commanded velocity V_care shown between the time 420 and the time 422 of FIG. 6B.

[0058] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.